Feeds | Nanoprobe Network

AFM-IR Webinar: nanoscale IR Spectroscopy where AFM meets IR on Wed, May 23 at 11AM EST

rshetty — Fri, 18 May 2012 16:40:03 +0000

The ability to identify material under an AFM tip has been identified as one of the “Holy Grails” of probe microscopy. IR spectroscopy can characterize and identify materials via vibrational resonances of chemical bonds and is a very widely used analytical technique. We have successfully integrated AFM with IR spectroscopy (AFM-IR) to obtain high quality infrared absorption spectra at arbitrary points in an AFM image, thus providing chemical characterization on the sub-100 nm length scale. The webinar will discuss:

How the AFM-IR technique works to provide simultaneous chemical and mechanical property information
NEW: polarization control that enables nanoscale molecular orientation studies. Data will be presented on molecular orientation of individual electrospun PVDF fibers
Applications ranging from reverse engineering to characterization of polymer blends, multilayer films, organic photovoltaics, life sciences etc

You can register at www.anasysinstruments.com

AFM Webinar -Introduction and Innovations in High Speed, Quantitative Nanomechanical Imaging, May 23

tmehr — Wed, 16 May 2012 14:56:37 +0000

Asylum Research’s Dr. Roger Proksch will present the webinar “Introduction and Innovations in High Speed Quantitative Nanomechanical Imaging” on May 23 at 8:00am and 5:00pm PDT. This presentation, the first in a three-part series, will begin with a survey of the mechanical properties that can be investigated with the wide array of both old and new nanoscale property mapping techniques available to materials scientists. We will then introduce two new techniques for nanomechanical studies that allow unambiguous interpretation of material properties: AM-FM and Loss Tangent. These techniques allow high speed, low force imaging in tapping mode – a proven, reliable, and gentle imaging technique- while providing quantitative Stiffness and Loss Tangent images. Free registration for either time slot can be found on the link below:

8:00am (PDT), May 23

5:00pm (PDT), May 23

http://www.asylumresearch.com/Webinars/

International Scanning Probe Microscopy Meeting, Toronto, Canada, June 15-18 2012

Leonenko — Sun, 29 Apr 2012 18:38:34 +0000

14th Annual International Scanning Probe Microscopy Meeting, Toronto June 15-18 2012,

Abstract deadline is extended to May 10, 2012,

One day tutorial on Scanning Probe Microscopy on June 15th,

Venue: Westin Harbour Castle Hotel, Toronto, Canada

http://ispm2012.uwaterloo.ca/index.html

Early Registration deadline is May 15th

ISPM 2012 committee

2012 Annual Nanoprobes Workshop at Stanford University

mariaw — Mon, 16 Apr 2012 19:49:16 +0000

You are cordially invited to attend the Center for Probing the Nanoscale’s 8th Annual Workshop, a one-day workshop on nanoscale probing and imaging. Meet CPN investigators and the broader Bay Area community interested in nanoscale imaging and metrology.

Location:
Jen-Hsun Huang Engineering Center, McKenzie Room 300
475 Via Ortega, Stanford, California 94305-4200

Hours:
8:30-6, with continental breakfast and lunch included. There will be a poster session from 4-6, with hors d’oeuvres served. Prizes will be awarded for the top 3 posters

Speakers so far:

Stuart Lindsay, Arizona State University
“Recognition Tunneling – An Interface Between Chemistry and Electronics”

Sarah Tolbert, University of California, Los Angeles
“Self-Organized Nanostructured Materials for Energy: Supercapacitors, Batteries, and Solar Cells“

Felice Frankel, Harvard University
“More Than Pretty Pictures”

Katherine Aidala, Mount Holyoke College
“Manipulating Magnetic States with a Local Circular Magnetic Field”

Carlos Arguello, Columbia University
“Fundamental Role of Disorder in Phase Transitions of Strongly-Interacting Materials”

H. Kumar Wickramasinghe, University of California, Irvine
“Raman Probe Force Microscope”

Ania Bleszynski Jayich, University of California, Santa Barbara
“Coherent Detection of Mechanical Motion with a Single Spin Qubit”

Michael Flatté, University of Iowa
“Nanoscale Manipulation and Control of a Solitary Dopant within a Semiconductor“

James Hone, Columbia University
“Graphene NEMS Resonators in the Quantum Hall Regime“

Fee Information and Registration Link

Questions:
Laraine Lietz-Lucas, lietz@stanford.edu

Postdoctoral Fellow in SPM/Nanomechanics at ExxonMobil

dgyablon — Wed, 11 Apr 2012 17:25:31 +0000

Member of the Technical Staff Post doc Position – Nanomechanical Characterization,

Advanced Sensing and Analytics

ExxonMobil Research and Engineering Company has an immediate opening for a Postdoctoral Fellow at its Corporate Strategic Research laboratory, located in Clinton, NJ, 50 miles from New York City in scenic western New Jersey.

Candidates are sought to fill a research position in the area of nanomechanical characterization with scanning probe microscopy (SPM) based methods. The candidate will conduct research with state of the art SPM instrumentation (including nanoindentation) to develop novel methods in quantitative and semi-quantitative characterization of elastic and viscoelastic materials. The position is primarily experimental-based but will also include simulations of tip-sample interactions and incorporate use of contact mechanics modeling to improve data interpretation.

A Ph.D. in materials science/applied physics/physical chemistry/materials or mechanical engineering and a demonstrated ability to perform independent research is required. A strong background in scanning probe microscopy with a proven track record in research is essential. Experience in advanced scanning probe methods and theory including multifrequency, dynamic methods, nanoindentation, advanced image analysis, nano-thermal analysis methods, tip-sample interaction simulations and contact mechanics is strongly desired. Excellent collaboration and communication skills are required.

ExxonMobil offers a competitive compensation and benefits package and a broad range of opportunities.

Please submit your application letter and resume to our website at www.exxonmobil.com/ex and apply for the Post Doc – Nanomechanical Characterization position.

ExxonMobil is an Equal Opportunity Employer

Stanford Summer Institute for Middle School Teachers Nanotechnology

mariaw — Thu, 05 Apr 2012 21:05:32 +0000

The Center for Probing the Nanoscale at Stanford University is accepting applications for its annual Summer Institute for Middle School Teachers on July 23-27, 2012. At the Institute, teachers learn about the physical concepts underlying nanotechnology and nanoscience in simple terms. Daily sessions focus on content lectures by Stanford scientists and on inquiry-based modules that explicitly address California’s 5-8th grade physical science content standards. Teachers receive a hands-on activity kit with many fun activities that bring nanoscience into the classroom. Teachers also have the opportunity to tour research labs and to receive a $650 stipend and professional development units. For more information and to apply by May 7, visit http://simst.stanford.edu

Normal force calibration

dave11420 — Tue, 03 Apr 2012 20:51:56 +0000

If I have a silicon substrate and I want to measure normal forces, I take the change in setpoint x the cantilever stiffness x the sensitivity from the force displacement (fd) curves. However, if I am scanning in a liquid (fluid cell) do I use the sensitivity from the fd curves from the liquid or the fd curves from the silicon substrate in air?

Normal force calculation

dave11420 — Mon, 02 Apr 2012 16:59:09 +0000

Lateral force calibration using the "test probe method"

M. Tekaat — Thu, 29 Mar 2012 07:58:48 -0400

I read the paper: RSI 77, 053701 (2006) for the lateral calibration in atomic force microscopy. But I would like to use the test cantilever with the colloidal probe for the friction measurements. In this case, am I right if I leave out the last step where the changes in the torsional moment arm length and the total signal on the PSD between the test and the target probes are taken into account? Then I would just use the equation a=k' lat / S lat.

Associate Research Fellow (Postdoctoral Fellow)

bharish — Tue, 27 Mar 2012 14:16:44 +0000

There are immediate openings for postdoctoral researchers (Associate Research Fellow grades) at the University of Exeter’s Advanced Nanoscale Engineering Laboratory in Devon, United Kingdom. Projects include advanced NEMS devices using novel phase change materials, as well nanomanufacturing. Our lab is excellently linked to several industrial and academic labs around the world. The University has invested heavily in world-class experimental infrastructure, and the successful candidate will be part of our growing team. The fellow would have the freedom to pursue creative ideas, leadership opportunities as well as an excellent support infrastructure.

Exeter is among the most desirable locations in the UK, and is minutes away from dramatic coastlines or if you prefer, just 2.5 hours away from London (or a couple of hours by flight to the beaches of Southern France and Italy).

The most important qualification is the ability to hit the ground running, and extraordinary motivation. A PhD in a related field and evidence of high quality experimental scientific work during the PhD would be required.

Please contact Harish Bhaskaran http://people.exeter.ac.uk/hb306 (e-mail on website) or by phone at +44 – 1392 725 820 for more information.

Monday submission deadline SPM Polymer symposium at ACS

dgyablon — Fri, 16 Mar 2012 18:29:16 +0000

Call for Abstracts – ACS Fall Meeting, 8/19-8/23 2012, Philadelphia PA

“Advances in Methods and Applications of Scanning Probe Microscopy to Polymer Materials”

This symposium will focus on recent research progress to understand mechanical, rheological, thermal, electrical, and self-assembly behavior of polymers on the nanoscale and to establish composition-processing-morphology-performance relationship. Experimental and theoretical aspects of all SPM based methods will be considered, including traditional mechanical, thermal, and electrical based methods as well as more recent multifrequency measurements and high speed AFM. Application of SPM to a wide variety of polymer materials is to be covered including amorphous and semicrystalline polymers, nanocomposites, block copolymers, elastomers, impact copolymers or toughened polymers, conductive polymers, single polymer chains, etc.

Invited speakers include:

Robert Carpick (University of Pennsylvania), Steve Minne (Bruker), Yifu Ding (University of Colorado), Sergei Magonov (NT-MDT), Liang Fang (Arkema), Ken Nakajima (Tohoku University), Greg Haugstad (University of Minnesota), Rene Overney (University of Washington), Jamie Hobbs (University of Sheffield), Roger Proksch (Asylum Research), Donna Hurley (NIST), Arvind Raman (Purdue University)

Kevin Kjoller (Anasys), Vladimir Tsukruk (Georgia Inst. of Tec)h, Mark Van Landingham (Army Research Lab), Gil Walker (University of Toronto), Robert Magerle (Technical University of Chemnitz), Julius Vancos (Univ. of Twente)

To submit abstract, go to http://abstracts.acs.org, POLY division, this symposium. Abstract and preprint submission deadline on March 19^th, 2012.

Single Molecule Unfolding Experiments

bigkahunaburger — Wed, 14 Mar 2012 23:47:17 -0400

I'm a novice in unfolding measurements of single molecules. I've been trying to unfold a commercially available modular protein I270 protein, which contains 8 identical modules of the I27 domain of human fibronectin.

I can see the sawtooth pattern, but I'm unsure why the force doesn't return to zero after each sawtooth ruptures. At the end of each sawtooth rupture there is still >80pN force exerted on the cantilever.

I was wondering whether anyone had an explanation for why the force doesn't return 0 after each sawtooth.

Any help would be appreciated.

An unknown source of damping in tapping mode probes

vnahid54 — Tue, 31 Jan 2012 19:57:08 -0500

While acquiring f-d curves in tapping mode, recently, I have been seeing a continuous reduction in the oscillation amplitude while approaching to and retracting from the sample over a range of 5 micron distance. This reduction in amplitude happens before the tip and sample begin interaction with each other; where we see a sharp drop in amplitude. These probes that I'm using have kind of low aspect ration tips than the regular silicon probes. It seems that there is an unknown source of damping for these probes that doesn't exist for the regular silicon probes. I'm sure the AFM itself has no problem as the regular silicon probes f-d curves show a constant amplitude before the initiation of the tip-sample interaction. I can't figure out what could be the source of this energy dissipation. I have tuned these probes far from and at distances close to the sample and realized that the closer the probe gets to the sample, the lower is the quality factor, and the higher is the drive amplitude required to achieve a certain oscillation amplitude. I am wondering if anybody has seen this before or there is a publication that deals with this problem.

Thanks
Vahid

test

nn admin — Wed, 21 Dec 2011 16:21:58 -0500

test

Sapphire Surface Roughness Measurements

grindstone — Wed, 21 Dec 2011 16:00:19 -0500

This question conerns interpretation of surface roughness data on very smooth surfaces. It is my understanding that in measuring surface roughness only height data (either contact or tapping mode) should be used. Is there a point however, when a surface is smooth enough that deflection data (contact mode) should give you the same value or is maybe even more accurate? The source of this question is that the data we collect on highly polished (CMP) sapphire wafers may give a surface roughness of 1nm in height mode and 2A in deflection mode and published data does not normally say what mode it was collected in. Is it a well known standard operating procedure to only use height data? If the roughness of the surface is physically lower than the average cantilever deflection shouldn't deflection data be just as relevant? Any opinions on this would be highly regarded. Thanks. (Mike Kamrath, Nalco Co., Naperville, IL)

Trouble Scanning Tungsten Tips, Any Ideas?

montanez82 — Wed, 10 Aug 2011 13:42:59 -0400

Response from: carpick

Hi - we use two techniques in our group: 1. TEM. This gives you a transverse image (i.e., a 2-d projected profile) of the tip along one axis (transverse to the long axis of the lever). You can tilt a bit to get profiles from somewhat different angles, but this is rather limited in most TEMs. It required adapting a standard TEM holder in which you mount the cantilever, but once that is done, one can have pretty decent throughput. In our group, we machined a new TEM holder that holds 3 cantilevers and a calibration grid all at once, for better throughput. We are happy to share the info on this device. Advantages: works for tips down to even 10 nm or less, if you have a good TEM; you can do analytical work (diffraction, EELS, EDX) on the tip to determine the structure and composition, and can even get atomic lattice resolution if desired. Disadvantages: Requires dismounting the cantilever from your AFM each time you want to image it, which can be risky; exposes tip to possible e-beam induced damage or contamination buildup in TEM (TEM must have good vacuum, and/or use short imaging times and not-to-high beam intensity); a bit time-consuming (mounting the cantilever in the holder, TEM wand has to pump down each time, etc.). 2. Blind tip reconstruction - scan the tip over samples with sharp features and reconstruct the tip shape. Commercial samples like TipCheck and NioProbe from Aurora Nanodevices, or the TGT-01 from NT-MDT, are good for this. Advantages: no TEM needed, it's in-situ and relatively fast. Disadvantages: you need software (you can buy SPIP which is expensive; I believe the free softwares like Gwyddion and WSXM can do it too but I'm not sure; we are working on a free MatLab version but its not ready yet); software is sensitive to algorithm parameters so you need to be careful; tip can be accidentally damaged during the imaging process, but a good AFM person can avoid this. Method #2 is much easier to start with, especially if you are not trained on using a TEM! This paper discusses details on both methods, with references to further background on them: Preventing nanoscale wear of atomic force microscopy tips through the use of monolithic ultrananocrystalline diamond probes. J. Liu, D. S. Grierson, N. Moldovan, J. Notbohm, S. Li, P. Jaroenapibal, S. D. O’Connor, A. V. Sumant, N. Neelakantan, J. A. Carlisle, K. T. Turner, R. W. Carpick. Small, 6, 1140-9 (2010). Good luck! Please let us know here how it works out.

single electron transistor

saranya — Sun, 26 Jun 2011 14:41:42 -0400

Designing of quantum dot transistor.(single electron transistor).the source is connected to the drain via quantum dot, which acts as an island. The quantum dot is controlled by gate electrode.my doubt is how to fabricate all this components?what should be used as source ,drain and gate electrode if the island is made up of indium arsenide quantum dot?

Calibration of Lateral sensitivity of AFM cantilever (mV/nm)

mminary2 — Fri, 25 Mar 2011 22:58:39 -0400

Response from: rcannara

Depending on the type of probe you are using, the lateral deflection sensitivity can be obtained in a way that is analogous to vertical force-displacement curves. Instead, the probe is pressed laterally against a vertical sidewall of, for example, a cleaved cubic crystal (NaCl, KBr...) or GaAs, as in the paper: RSI 77, 053701 (2006). This works well for spherical probe tips. If you can't use those in your experiment, ultimately, you can use an identical lever with a sphere ("test probe" in the paper) and convert sensitivities according the discussion in the paper (basically, account for probe vs. tip location and differences in total signal).

Cantilever Calibration

philip@egberts.com — Wed, 02 Mar 2011 12:57:32 -0500

Hi all,
I am interested in the wedge calibration method.
We are using a UHV-FFM with a scan range of 3x3mu m.

Varenberg (M. Varenberg, I. Etsion & G. Halperin. "An improved wedge calibration method for lateral force in atomic force microscopy". Rev. Sci. Instrum. 74, 3362-7 (2003)) recommends the TGF11 calibration grid. It is rather big for our small scan-ranges but could in principle be used.

What test grids do you recommend?

Thanks for help in advance,
Christian

Best wedge method calibration grating?

christian — Mon, 28 Feb 2011 04:38:51 -0500

Response from: tgoren

Hi Christian, We had good results using the TGF11 in a straightforward way, as described in your paper, so you are on the right track. There is some software on this website that will help you do that work. The problems we hit along the way were 1) making sure the TGF11 surface was clean and smooth - oxygen plasma was the way to go for this (most other cleaning methods only made it dirtier!); 2) we had to choose colloidal spheres small enough to fit in there, so make sure yours does too if you're using one; 3) check the epsilon value of your cantilever/tip (as described in the paper) before you go through the work. Only cantilevers with epsilon << 1 can give physically meaningful results, otherwise in-plane bending is convoluted in with the twisting and the results don't make sense. Again this depends on your tip, it was an issue with our colloidal tips. Good luck, Tolga LSST, ETH Zurich

Response from: carpick

Christian - Tolga makes a lot of good points. I guess with your UHV FFM it is not easy to coarse-position the tip over a desired region. Essentially you'd like to get a flat and a sloped region in one image. Aiming for the flat valley is the best, since it's narrower, so you can get the flat valley and maybe both positive and negative slopes in one image. Unfortunately, WiTec no longer makes the SrTiO3 sample, which was nice for small scans (and regular tips, as opposed to colloidal probe tips). You might also try the TGG01, which has a smaller period (3 um, vs. 10 um for the TGF11). Let us know how it works out!

Back-Scattered Electron Imaging

WillMulhearn — Thu, 24 Feb 2011 23:58:20 GMT

WillMulhearn:

Back-Scattered Electron Imaging utilizes information about the interaction of an electron beam and a target sample in order to detect variations in the elemental composition of the material. Each electron that contacts and atom within the sample has a chance of being deflected in an elastic collision. Elastic collisions deflect the electron back away from the sample with no loss in the electron’s energy. This type of interaction generally results from electrostatic attraction the negatively-charged electron and the positively-charged nucleus of the target atom. If the incident angle of the electron is just right, the attractive interaction will bend the electron’s trajectory around the nucleus with no loss of speed. A helpful visual representation of this trajectory can be seen here:

http://mse.iastate.edu/microscopy/backscat2.html

The probability that an elastic collision will occur depends on the atomic number (Z) of the target atom. Atoms with larger atomic numbers present a greater cross-sectional area to the incident electron beam; so heavier atoms produce more back-scattered electrons Therefore, portions of the sample containing high atomic weight species will generate a stronger signal and appear brighter than portions containing low atomic weight species.

Back-scattered electron imaging allows a compositional map to be generated for a material sample. The map will show brighter regions that correspond to heavy elements, and darker regions that correspond to light elements. This technique is particularly useful for identifying the transition areas in a sample, in which composition changes from one material to another. A sample image can be seen here:

http://serc.carleton.edu/images/research_education/geochemsheets/bse_gray.png

References:

Goodge, John. "Back-scatter Detector (BSE)." SERC. 15 June 2010. Web. 12 Feb. 2011. .

"Backscattered Electrons." Materials Science and Engineering. Web. 12 Feb. 2011. .

Scanning voltage microscopy

Defenestrater — Tue, 22 Feb 2011 05:37:23 GMT

Defenestrater: formatting

Scanning voltage microscopy (SVM), also referred to as nanopotentiometry, is a derivative of atomic force microscopy in that it shares the use of a local probe to measure surfaces. The probe is connected to a voltmeter and a rasterization of the sample’s surface is created. SVM generally does not damage the sample though it is possible that the pressure required to maintain electrical contact could cause damage [1].

SVM is used to analyze micro- and quantum electronic devices such as transistors and quantum well diode lasers due to its nanometer spatial resolution. It has been used to analyze multiquantum-well ridge-waveguide semiconductor lasers [2].

References:

[1]Meyer, E., "Scanning probe microscopy and related methods". Beilstein J. Nanotechnol. 2010, 1, 155–157. doi:10.3762/bjnano.1.18

[2]Ban, D.; Sargent, E.H.; Dixon-Warren, St.J.; Hinzer, K.; White, J.K.; SpringThorpe, A.J.; , "Scanning voltage microscopy on active semiconductor lasers: the impact of doping profile near an epitaxial growth interface on series resistance," Quantum Electronics, IEEE Journal of , vol.40, no.6, pp. 651- 655, June 2004
doi: 10.1109/JQE.2004.828262

Surface Plasmon Resonance (SPR)

Zshurden — Fri, 18 Feb 2011 17:45:25 GMT

Zshurden: Created page with 'Surface plasmon resonance (SPR) is a method to measure the absorption of a material onto planar metal (usually gold or silver) surfaces or onto metal nanoparticles. Surface plasm…'

Surface plasmon resonance (SPR) is a method to measure the absorption of a material onto planar metal (usually gold or silver) surfaces or onto metal nanoparticles. Surface plasmons are surface electromagnetic waves which are set to propagate parallel to the surface. As the wave runs on the boundary of the surface and the external medium (usually air or water), oscillations are very sensitive to any change in the boundary, namely, the absorption of molecules to the metal. In order to excite surface plasmons in a resonant manner (necessary for accurate measurements), an electron or light beam is used.

In addition to measuring molecular absorption, SPR can be used for imaging as well. Since absorption rates vary as the volume of the measured solid varies, SPR measurement can be used to map out nanoscale materials. In addition, SPR can be used to enhance the surface sensitivity of several spectroscopic measurements such as fluorescence, Raman scattering, and second harmonic generation.

Sources:

Stefan Maier (2007). Plasmonics: Fundamentals and Applications. Springer. ISBN 978-0387331508.

http://www.astbury.leeds.ac.uk/facil/SPR/spr_intro2004.htm

Nanocapacitors

Winstonr — Thu, 17 Feb 2011 20:13:49 GMT

Winstonr:

For the last several years, lithium ion batteries have been the golden standard for energy storage in everything from cell phones to laptops and now to cars. As rapidly as technology evolves in this era, the lithium ion battery's rather long life as the best balance of energy storage and cost begs the question, what is the next step for batteries? The answer to this question, however, may not be batteries at all.

Capacitors may indeed be the next step. They charge quickly, are lightweight, and last much longer than batteries, but they lack the crucial ability to retain energy over long periods of time. This shortcoming could potentially be eliminated as a result of current research being conducted on creating micro and nano-scale capacitors with much higher energy density. Arrays of such capacitors could potentially be used to increase the "battery life" and reduce the size and weight of many common electronics. In addition, they would allow for extremely rapid charging as well as rapid discharge. This feature would be extremely beneficial in the electric-car industry as it would allow for charge stations, similar to the current model of gas stations, to be utilized and bursts of energy to be used when called for, much like a turbocharger in current vehicles.

The basis of this technology lies in nanostructures. Tiny holes are made in films only a few nanometers thick. These "nanoholes" are then filled with a layer of insulation sandwiched by two layers of metal. These metal-insulator-metal type capacitors work in the same fashion as typical capacitors but have the added benefit of being able to fit millions of capacitors per square inch.

While many varieties of these nanocapacitor formations are being researched, the next and perhaps more daunting challenge lies in mass producing them. Intel is currently conducting extensive research in this field, as it would have countless applications in their products. Not only would Intel have the ability to produce the capacitors as a battery replacement, but they would also be able to use them in microprocessors and other electronics, allowing them to further decrease the size of key electronic components.

While the full potential of this field is both unrealized and unknown, nanocapacitors may have the potential to serve as the choice energy storage method of the future.

Sources:

http://www.pcworld.com/article/192300/nanoscale_ultra_capacitors_challenge_the_lithiumion_battery.html

http://scitizen.com/nanoscience/nano-capacitors-the-root-towards-the-super-power-battery_a-5-2918.html

[[Category:capacitors]]
[[Category:energy]]
[[Category:battery]]

Induced Grating

Kendavis — Tue, 15 Feb 2011 20:46:52 GMT

Kendavis:

Induced grating is a new method to measure the size and distribution of nanoparticles in a substance. In induced grating, electrodes are connected to a group of nanoparticles. When a voltage is applied to the electrodes, the nanoparticles move due to the attractive and repulsive forces. The nanoparticles distribute themselves into some configuration based on the charges of the electrodes. This distribution can be obtained by passing light through the substance and observing the diffraction pattern of the light as it passes through the nanoparticles. Once this distribution is recorded, the voltages are turned off. The nanoparticles will once again disperse due to the change in attractive and repulsive forces. However, different nanoparticles will move at different rates. Heavier nanoparticles will take longer to move than lighter particles. By observing the light diffraction pattern as the nanoparticles disperse, you can obtain a measurement of the size and distribution of nanoparticles. This method works for nanoparticles ranging from 0.5-500 nanometers and allows for simultaneous measurement of small and large nanoparticles.

References: Canter, Neil "Measuring nanoparticles". Tribology & Lubrication Technology. FindArticles.com. 15 Feb, 2011. http://findarticles.com/p/articles/mi_qa5322/is_201001/ai_n49421435/

Manipulation of Individual Atoms

Sverdugo — Tue, 15 Feb 2011 20:15:29 GMT

Sverdugo: Brief overview of how AFM and STM can be used to move individual atoms on a substrate.

When creating nanostructures with individual atoms, there are two options. The first of which is to have the atoms/molecules self-assemble, while the other is to manipulate them individually. This process seems rather complex, since we cannot actually see atoms, but using tools like atomic force microscopes (AFM) and scanning tunneling microscopes (STM), we can take atoms and move them around as we please. With an AFM, the process simply uses the tip to “push” atoms where we’d like to place them. An STM accomplishes this a bit differently. Instead of pushing atoms, it uses an increase in the tunneling current to create a tunable bond between an atom and the probe tip. It can then use it’s positioning system to place the atom elsewhere, and decrease the current to drop it.

Source:
"Probe Microscopes." http://mrsec.wisc.edu/Edetc/background/STM/#STM

Four Dimensional Microscopy

Romwaite — Tue, 15 Feb 2011 19:56:16 GMT

Romwaite:

Four dimensional microscopy is method of detecting interactions between particles at as they change in time. These interactions which occur within a millionth of a billionth of a second, a femtosecond, are now able to be captured and viewed on a time scale which we can perceive. The resolution of the still images taken with an Electron Beam Microscope can be up to a billionth of meter. The high resolution of still images is due to the fact that the electrons being fired have an extremely small wavelength which allows them to fit into the extremely small spaces between the molecules. In four dimensional microscopy you also use electrons, however, the electrons are fired at specific times and rates in order that they reach the sample at a predesignated time and hit a designated location on the sample. By streaming together the millions of images created from electrons as they bounce off the sample separated by a set amount of time we can see the sample changing in real time.

Source: http://www.sciencedaily.com/releases/2008/11/081120144234.htm

By Romaine Waite

Hooke: Open Source Software Platform for Force Spectroscopy

Insomniaman — Tue, 15 Feb 2011 19:21:48 GMT

Insomniaman:

Hooke is an open source software that allows anyone to contribute to its development to help with the analysis of Atomic Force Microscopy single molecule force spectroscopy. The software, created in 2009, is coded in Python and runs on Windows, Mac OS X, and Linux operating systems. The software is named after Robert Hooke, the famous microscopist who coined the word "cell". The software's purpose is to create a standard for analyzing and sharing data to allow for the better sharing of scientific research. The ultimate goal is for it to be the creation of a general purpose platform for which SFMS algorithms can be incorporated in a standard and open fashion.

Reference
Massimo S, Fabrizio B, Marco B, Alberto G, Bruno S. Hooke: an open software platform for force spectroscopy. Bioinformatics [serial on the Internet]. (2009, June), [cited February 15, 2011]; 25(11): 1428. Available from: Academic Search Premier.

[[Category: AFM]]
[[Category: Software]]

Clean Rooms(ISO Standards)

Ewong11692 — Tue, 15 Feb 2011 19:08:21 GMT

Ewong11692:

The use of cleanrooms is popular and common in the research and manufacturing in nanotechnology. The nature of nanotechnology entails work in a nanoscale level, thus any air particles, bacteria, or any other such contaminants can completely ruin one’s research or product. Therefore, the cleanrooms are essential in keeping extremely clean environments to prevent such disasters. These cleanrooms consist of several major forces such as filters and air flow patterns to maintain a clean environment.

The two most common air filtrations used are highly efficient particulate air (HEPA) or ultralow particulate air(ULPA) filter. These filters are so effective that they can remove about 99.9 percent of any type of microparticles. These filters can only be this effective with the use of two popular air flow systems: laminar and turbulent air flow. Laminar air flow, composed of stainless steel or other non-shed materials, is a stream of air that flows straight down to reduce turbulence and to allow HEPA filters to cleanse the air. Unlike Laminar air flow, turbulent air depends on non-unidirectional airflow, thus when particles are moving in random direction, filters are placed in various random areas to cleanse the air passing in its direction.

Another factor that makes the cleanroom so effective in maintaining an extremely clean environment is the standards in dress code. Employees typically have to change clothes into specially design outfits that entail gloves, breathing masks, and full hood coverings. They also have to take air showers with their special outfits on, and pass items through specially designed chambers.

Cleanrooms are graded by two standards, the ISO and United States federal standards to determine the cleanroom’s cleanliness. ISO grades are calculated by the amount of particles per factor of 10 of an area, thus for a cleanroom with ISO 1, it contains 10 or fewer particles per 0.1 micrometers cubed area, or with ISO 2, containing 100 or fewer particles per 0.1 micrometer cubed area. The level continues to increment as there ten times more particles for 0.1 micrometers.

Reference

"Cleanroom Air Flow Principles." ThomasNet® - CNC Machining, Metal Stamping, Gaskets, Fasteners and Other Industrial Products and Services. Web. 15 Feb. 2011. .

[[Category:Category cleanrooms]]
[[Category:Category HEPA]]
[[Category:Category ULPA]]
[[Category:Category laminarairflow]]

DualBeam Probing

Sissa — Tue, 15 Feb 2011 14:24:42 GMT

Sissa:

One of the most interesting new ideas to probing a sample comes with the advent of the DualBeam. This is a combination of a Scanning Electron Microscope (SEM), and a Focused Ion-Beam (FIB) in the same package. This allows for more accurate positioning of probes because of the ability to view both SEM images and FIB images at the same time. Since FIB’s offer the advantages of: drilling, depositing, and isolating defects, as well as the ability to place insolating or conducting contact areas, they are an invaluable tool for nanocircuit building. From the company website, the following advantages are also available when using DualBeam:

“• Ability to probe very small contact areas, as the high resolution of the
DualBeam imaging allows accurate probe positioning

• Faster real-time probing immediately after FIB preparation including
isolation cuts, addition of interconnects, and localized deprocessing

• The removal of layers to reveal underlying structures within the FIB
chamber—probing can be done immediately, thereby eliminating the need
to transport the sample to a stand-alone lab for fault analysis

• Probing while imaging with either the SEM or the FIB—side views, as well
as top views, are possible, revealing vertical positioning and greatly easing
probe alignment

• FIB preparation and probe testing can be done in sequence—multiple
locations can be probed and new probe locations can be based on initial
results.” (1)

Also since the system is combined, a lot of time is saved and potential human error caused by cleaning and handling is prevented during the transfer to and from different machines. Having this new all-in-one machine proves to be extremely cost and time efficient. As more and more circuits are allowing autonomous FIB analysis, circuit testing, and circuit debugging, the DualBeam solution becomes more and more suited to take full advantage of these new advances. With its highly accurate and easily controllable piezo actuators, it can save a lot of hassle down the line. Creating a new silicon mask can now take just hours instead of weeks, meaning production costs can be lowered extremely.

References:
(1) Young, Richard J. and Carleson, Peter D. DualBeam Solutions for Electrical Nanoprobing. FEI Company 2007. http://www.fei.com/uploadedFiles/Documents/Content/2008_05_ElectricalNanoprobing_wp.pdf

[[Category:SEM]]
[[Category:FIB]]

Nanoprobe Implantation in Cell Membrane

Parthk — Tue, 15 Feb 2011 07:18:21 GMT

Parthk: Created page with 'Researchers at Stanford University recently succeeded in using nanoprobe technology in a novel way to measure electrical activity of individual cells. This probe would detect eve…'

Researchers at Stanford University recently succeeded in using nanoprobe technology in a novel way to measure electrical activity of individual cells. This probe would detect everything from signals between cells to the electronic signals given off by cellular digestive processes. By monitoring these signals for long periods of time, scientists can understand more about how the cell functions under certain conditions. Furthermore, this success will be a stepping stone from which more complicated, multi-functional nanoprobes can be designed which could someday be used in the detection and cure of certain diseases.

The probe itself is made of silicon and is 600 nm long which is an ideal size for integration into cellular membranes. The probe can fuse to either side of the membrane and so it becomes a part of it, shown in that researchers could not remove the probe without breaking apart the whole membrane. Because it “mimics the natural gateways” in the membrane, it can “stealthily” remain in the membrane for up to a week. This method of probing is far better than current ones, which are quite harmful to the cell and cause cell death within hours.

The probe was created using a nanofabrication method specialized for this particular application. The tip of this probe was a trilayer of metal, chromium on the outside and gold coated with carbon in between. The carbon molecules on the gold caused it to have hydrophobic properties which allow it to remain within the cell membrane. This hydrophobic band had to be only a couple nanometers in size and this was done using a metal deposition technique. The fact that the chromium on either side is hydrophilic allows this probe to have similar properties to real cellular membranes. Currently, the device is in testing in human red blood cells. This type of application of nanotechnology is very exciting because it can lead to even more powerful applications of this technology.

Source: Bergeron, Louis. "Nanoscale stealth probe slides into cell walls seamlessly." Stanford Engineering. Stanford University , n.d. Web. 15 Feb. 2011. .

DIC

Srishti — Tue, 15 Feb 2011 06:26:23 GMT

Srishti: Differential interference contrast microscopy

Differential interference contrast microscopy (DIC) is a type of sample illumination developed by Nomarski in 1951. This particular optical microscopy illumination technique enables imaging of transparent sample, by enhancing contrast. Using interferometry, the DIC technique allows for the gathering of information about the optical density of the sample. This in turns allows for the imaging of otherwise invisible features.
DIC first polarizes the light source at a 45° angle. It then, separates the light source into two perpendicular parts, which are first sheared and finally recombined before the image is viewed. This recombination depends largely on the refractive index and the path length. The image does not actually provide a topographically accurate image, but rather gives the impression of the three dimensional object by casting light and dark shadows on appropriate faces. Furthermore, the interference of different wavelengths is what determines the resulting three-dimensional physical relief, which corresponds to the varying optical densities in the sample. The typical wave phase difference is quite small, whether or not interference is constructive or destructive, because of the refractive index of most samples and the media they are in is quite similar.
DIC is considered to be the best in providing high resolution among optical microscopy techniques for illumination. Therefore, DIC is very useful in the imaging of live biological samples. Another area of use of DIC is in the analysis of silicon semiconductor processing. These films of silicon are typically quite thin, ranging from 100-1000 nm, and are thus quite transparent. This enables to DIC to discern whether there are any unwanted depressions or mounds in the film sample. Finally, the DIC is advantageous in that it is completely devoid of artifacts, a problem that often plagues phase contrast.
However, other than this use in silicon analysis, DIC is not suitable for non-biological sample. This is because the polarization of the light source is key to making DIC work. Non-biological samples would surely disrupt this polarization, thus not producing accurate images. DIC also has limited use in biology when samples are not transparent. In these cases, the thick samples do no have fairly similar refractive indices to their surroundings. This causes large phase offsets and disrupts accurate imaging.

1) "Differential Interference Contrast (DIC) Microscopy." Nikon MicroscopyU. Web. 14 Feb. 2011.
2)"Microscopy with Differential Interference Contrast." Rice University Web Calendar. Web. 14 Feb. 2011. .
3)"Molecular Expressions Microscopy Primer: Specialized Microscopy Techniques - Differential Interference Contrast." Molecular Expressions: Images from the Microscope. Web. 14 Feb. 2011. .

Piezoelectric scanners for AFM

Jgmagic — Tue, 15 Feb 2011 05:18:16 GMT

Jgmagic: Created page with 'A piezoelectric material is that which expands and contracts proportionally in response to an applied voltage. Whether a material elongates or contracts depends on the polarity o…'

A piezoelectric material is that which expands and contracts proportionally in response to an applied voltage. Whether a material elongates or contracts depends on the polarity of the voltage applied. Piezoelectric materials are used in Atomic Force Microscopy. The scanner integrates three independent piezo-electrodes for X, Y, and Z into a single tube. This tube forms a scanner, which can manipulate samples and probes with precision in three dimensions. Scanners are characterized by their sensitivity. Sensitivity is the ratio of piezo movement to piezo voltage or how much the material extends or contracts per volt. Sensitivity varies non-linearly with respect to scan size. Piezo scanners often exhibit more sensitivity at the end as opposed to the beginning of a scan. As a result, the forward and reverse scans behave differently and display different results for each scan direction. This can be avoided by applying a non-linear voltage to the piezo electrodes to result in linear scanner movement. The sensitivity of piezoelectric materials decreases exponentially with time. As a result, most of the change in sensitivity occurs early in the scanner’s life. Often, piezoelectric scanners are run before they are shipped from the factory to avoid this change in sensitivity at the buyer. As the scanner ages, the sensitivity will change less with time. Therefore, the scanner would rarely require recalibration.

R. V. Lapshin (1995). "Analytical model for the approximation of hysteresis loop and its application to the scanning tunneling microscope" (PDF). Review of Scientific Instruments (USA: AIP) 66 (9): 4718–4730. doi:10.1063/1.1145314. ISSN 0034-6748.

R. V. Lapshin (1998). "Automatic lateral calibration of tunneling microscope scanners" (PDF).Review of Scientific Instruments (USA: AIP) 69 (9): 3268–3276. doi:10.1063/1.1149091.ISSN 0034-6748.

Fiber Optic Nanoprobe

Ljtao — Tue, 15 Feb 2011 03:01:27 GMT

Ljtao:

Fiber Optic nanoprobes is a new technology in nanotechnology designed to be used to detect and examine living cells. These tips are used in conjunction with near-field optical microscopes (NSOMs). According to a paper written by Yan Zhang, Anuj Dhawan, and Tuan Vo-Dinh, these nanofibers are fabricated via "laser-heated pulling or chemical etching," but the use of focused ion beam (FIB) have been recently implemented for chemical sensing (Zhang 1). In all fabrication methods, metal coatings are applied to the nanofibers to confine the transmittance of light which is used as the detection method of these types of probes. In an independent paper written by Vo-Dinh, the tips of the nanofiber probes are as small as forty nanometers in diameter (Vo-Dinh 1).

The applications of this type of probe with NSOMs are demonstrated in Vo-Dinh's paper where he was able to detect biochemically tagged structures inside cells that were given a fluorescing dye. This type of scope is crucial to analyzing biological organisms at this scale. The marriage of NSOMs with the fiber optic nanoprobe allows investigation without preparing the subject in a fashion that requires plating or slicing, as is the case with other types of microscopes. Vo-Dinh confirms this in his paper, saying "optical nanobiosensors are capable of minimal-to-noninvasive analysis of single living cells." (Vo-Dinh 1).

Zhang, Dhawan, and Vo-Dinh cite issues with tip fabrication that are similar to other tip fabrication drawbacks. They claim that techniques like chemical etching result in a non uniform tip surface, while laser etching has tip angle limitations.

Tuan, Vo-Dinh. "Optical Nanobiosensors and Nanoprobes." 1 Jan 2006. Duke University. Taylor and Francis Group. 14 Feb 2011. < http://docs.google.com/viewer?a=v&q=cache:OKB-J1MFemIJ:www.crcnetbase.com/doi/abs/10.1201/9781420004441.ch17+fiber+optic+nanoprobes&hl=en&gl=us&pid=bl&srcid=ADGEESg-xD0Plhtcgrs-o-bcwTkFJ5PpJAm_hR4_OagyIZtXVrFxPiVkQHyeTMc0qW74285uEOhaHTLD8LWCOU-DPfyAiIirX9VCT-OpfbAfByMh1doy4SWBKZzboFUjoYBAUFYixQYk&sig=AHIEtbTKtbUuI6rK4ioYd-ftotTlhKfPRw>

Zhang, Yan, et al. "Design and Fabrication of Fiber-Optic Nanoprobes for Optical Sensing." 31 Aug 2010. Nanoscale Research Letters. 14 Feb 2011.

Nanoscale Field Effect Transmitters (nanoFET)

Adam.sharaff — Tue, 15 Feb 2011 02:26:04 GMT

Adam.sharaff: Created page with 'Harvard scientists have developed a new type of nano probe that can take measurements of the inside of a living cell. The probe is embedded into a membrane and consists of a tra…'

Harvard scientists have developed a new type of nano probe that can take measurements of the inside of a living cell. The probe is embedded into a membrane and consists of a transistor that takes electrical readings of the inner components of a cell. The probe is essentially an extremely thin bent wire that is positioned to penetrate the cell while still having two tips of the probe hang outside of the cell where they can serve as electrical contacts. The device is coated with lipids to influence the target cell to absorb the probe. This is a very promising technological development considering that it can be used to probe a living cell while being minimally invasive and causing no significant damage to the organism. Nanoscale field-effect transmitters (nanoFETs) have high spatial and temporal resolution. These tiny probes are smaller than the size of most viruses and are the first semiconductor devices to measure the insides of a cell.

The published report can be accessed at:
http://www.sciencemag.org/content/329/5993/830.full

Other reference:
http://www.popsci.com/technology/article/2010-08/nano-wiretap-device-infiltrates-cells-exposing-electrical-signals-and-potential-medical-secrets

Scanning Transmission Electron Microscope (STEM)

Zvrtis — Tue, 15 Feb 2011 01:39:40 GMT

Zvrtis: Scanning Transmission Electron Microscope

The STEM was invented in the 1930s along with the transmission electron microscope (TEM) and offers imaging modes and enhanced microanalysis capabilities not available with a TEM. The STEM also has several similarities to the scanning electron microscope (SEM). One such similarity is that the STEM uses a relatively low electron accelerating voltage of approximately 30 keV. Only thin specimens may be imaged with a STEM; a highly focused beam of electrons is scanned over the specimen and electrons that pass through the sample are collected to fabricate transmission images. In this way, a STEM is very similar to a SEM. Backscattered electrons and x-rays are produced during a STEM scan, which is a similarity to TEM scans. A STEM can be created by adding transmission detectors to an SEM or by adding scanning coils to a TEM. The latter option is usually not employed because the minimum probe diameter is large and the resolution of microanalysis is limited.

One common imaging mode for the STEM is known as bright field imaging. In both a TEM and STEM, transmitted electrons are collected on the axis to create the bright field. By using a large detector and angle of travel, a STEM can be used to image much thicker samples than a TEM is capable of imaging. The reason for this is because there is no objective lens below the sample to cause chromatic aberration as there is in a TEM. For example, a STEM can image a sample up to a few microns thick at 200 keV using the bright field imaging technique, while a TEM can only image an object about 0.5 microns thick using the same energy.

Another advantage of the STEM is its ability to execute High Angle Annular Dark Field (HAADF) imaging. The images collected from this technique are solely from elastically scattered electrons which are repelled by the nuclei of the sample. This is achieved by setting the inner angle of the annular dark field detector to a large value of approximately 30 milliradians so that no Bragg diffracted electrons are collected. With this technique, high resolution is possible without the undesirable diffraction contrast which can mask important structural information. The probe diameter is the primary factor that determines the resolution of the dark field. HAADF is very useful for the imaging of inorganic and organic solids in addition to both crystalline and amorphous materials.

Another important advantage of the STEM over the TEM is its ability to collect secondary electrons in the same way as a SEM. This ability makes it possible to use a STEM to correlate surface information with bulk information from the STEM mode and image samples which are too thick for STEM observation. A major advantage of the STEM over a standard SEM is that an ultra-high resolution can be produced with a STEM because of the comparatively high accelerating voltage used. Overall, a STEM is a very valuable piece of equipment to the nanotechnologist and materials scientist because it blends the advantages of both a TEM and SEM into a single, versatile piece of imaging equipment.

http://www.bruker-axs.se/spectral.nsf/f164f3e9b82f0febc1256dcc004611c1/d4a98a973f4e0290c12571e300376e06/$FILE/208%20Why%20STEM%20Not%20TEM.pdf

Scanning Ion-Conductance Microscopy

Dsobel — Tue, 15 Feb 2011 00:39:00 GMT

Dsobel: Scanning Ion-Conductance Microscopy

Scanning Ion-Conductance Microscopy (SICM) is a form of scanning probe microscopy specially designed for sub-micrometer resolution scanning of non-conductive, soft materials that are in electrolyte solution. Normally, a sample must be killed before being observed using standard SEM techniques. With SICM, living tissues can be scanned and therefore biological processes can be observed whilst in action.

The main component of SICM is the electrically charged glass micro- or nano-pipette probe filled with an electrolytic solution. It is lowered towards a non-conductive sample in a bath of oppositely charged electrolytic solution. As the probe approaches the surface of the sample, ion conductance occurs and therefore a current is observed. By maintaing a constant distance between probe and sample with a controller, a variation in ionic current is observed which directly relates to a mapping of the surface.

Additionally, SICM can be used for sampling and mapping ion currents above a surface. This is very useful for imaging ion currents through membrane channels, another biological application.

Sources:
Hybrid Scanning Ion Conductance and Scanning Near-Field Optical Microscopy for the Study of Living Cells. Biophysics Journal. Volume 7. May 2000.

Nanoprobes Destroy Cancer Cells

Joshtycko — Mon, 14 Feb 2011 21:45:51 GMT

Joshtycko:

UC Davis researchers used heated nanoprobes to slow the growth of human breast cancer tumors in laboratory mice. “We have demonstrated that the system is feasible in laboratory mice. The next step will be clinical testing in patients,” said Sally DeNardo, a professor of internal medicine and radiology at UC Davis and lead author of the study. Heat has long been considered as a potential cancer treatment, but its proven difficult to confine the heat to targeted areas and to predict its effects. The study tried to solve this problem.

The experimental system uses bioprobes created by wedding magnetized iron-oxide nanospheres to radiolabeled monoclonal antibodies. The bioprobes are cloaked in polymers and sugars that render them nearly invisible to the body's immune system. The researchers infused trillions of these nano-scaled probes into the mice's bloodstream where they would seek out and latch onto the receptors of the cancer cells. At this point, the mice's biological systems did not detect or respond to the probes at all.

Three days later, the team applied an alternating magnetic field to the tumor region, causing the magnetic nanospheres latched onto the tumor cells to change polarity thousands of times per second, instantaneously generating heat. As soon as the AMF stopped, the bioprobes cooled down. The duration and amplitude of the magnetic dosage was calculated according to certain formulas in relation to the concentration of the tumorous cells.

Tumor cell growth slowed relative to the heat dosage. Additionally, no toxicity of the nanoprobes was observed.

“Using heat to kill cancer cells isn't a new concept,” DeNardo said. “The biggest problems have been how to apply it to the tumor alone, how to predict the amount needed and how to determine its effectiveness. By combining nanotechnology, focused AMF therapy and quantitative molecular imaging techniques, we have developed a safer technique that could join other modalities as a treatment for breast and other cancers.”

This is just one more example of the exciting and significant applications for nano-scaled devices.

Original Article can be found at: http://nanotechnologytoday.blogspot.com/2007/03/nanoprobes-to-destroy-breast-cancer.html

In Vivo BioSensing with Nanoscale Cantelevers

Ericlamb89 — Mon, 14 Feb 2011 02:50:48 GMT

Ericlamb89: Created page with ' In Vivo biosensing harnesses the ability of nanoscale devices to detect biomolecular processes. Nanoscale devices are perfect in these applications, as detecting cancer for exam…'

In Vivo biosensing harnesses the ability of nanoscale devices to detect biomolecular processes. Nanoscale devices are perfect in these applications, as detecting cancer for example, can require the ability to measure tiny molecular imbalances. Researchers have been able to apply specially designed antibodies to micron-sized cantilevers. When cancer cells release certain proteins, these proteins bind with the antibodies on the cantilevers. These reactions cause the cantilever arms to bend, and the bending causes the conductance of the cantilever to change. The change in conductance is measurable and can indicate the presence of certain proteins and DNA sequences. Furthermore, concentrations, in addition to mere presence, of molecules can be determined in real time. The result is a very accurate and efficient system for detecting various biomolecular compounds.

References:

http://nano.cancer.gov/learn/understanding/nanotech_cantilevers.asp
http://iopscience.iop.org/0957-4484/21/23/230201

Single Crystal Diamond Tips for SPM

Kforce012 — Sun, 13 Feb 2011 23:00:22 GMT

Kforce012: Discussion of the benefits of new single crystal diamond tips for use in SPM

In recent years, the production of diamond probes for scanning probe microscopy has been limited by the inability to manufacture them, because achieving the appropriate geometry has proven very difficult. Recently, Obraztsov et al have developed a method allowing for the mass production of single crystal diamond tips with perfect pyramidal geometry. This new development in SPM has the potential to provide many benefits. In biological applications, the diamond probes offer very high resolution due to the hydrophobicity of their surface, and they possess a much longer lifetime compared to silicon probes. Furthermore, the chemical inertness of diamond allows for better imaging performance, and they feature excellent wear resistance. The developers estimate that the resolution is 50x better compared to silicon tips. These myriad benefits, coupled with the expected inexpensive costs of production, suggest that diamond tip SPM may garner widespread use in the near future [1].

[1] Obraztsov, et al. “Single crystal diamond tips for scanning probe microscopy.” Review of Scientific Instruments. 81, 013703 (2010).

Immunoelectron Microscopy

Mstelt — Sun, 13 Feb 2011 22:33:32 GMT

Mstelt:

Immunoelectron Microscopy is a technique that uses antibodies to detect the location of particular proteins with the use of electron microscopy.[1] The antibody is mixed with an antigen on a specimen grid in order to facilitate the viewing and identification of the type of virus present. The antibody may also be combined with gold in order to visualize and locate specific components of the antigen on a specimen.[2] Gold particles of varying diameters enable the study of more than one protein at once. Immunoelectron microscopy is often executed on ultrathin sections.[3]

The technique is most often applied in a biological facet elucidating the localizations of a variety of active substances. This ability is of great value to medical as well as biological researchers. Progresses in the field have made it possible to observe subcellular organelles. The introduction of confocal laser scanning has facilitated the examination of cell ultrastructures. The confocal laser can mimic the function of an electron microscope in certain special cases.[4]

[1] "Immunoelectron Microscopy". Fred Hutchinson Cancer Research Center.

[2] Saunders Comprehensive Veterinary Dictionary, 3 ed. 2007 Elsevier, Inc.

[3] Lucocq, John Milton and Gawden-Bone, Christian. Quantitative Assessment of Specificity in Immunoelectron Microscopy. J Histochem Cytochem October 1, 2010 vol. 58 no. 10 917-927

[4] Watanabe, Keiichi. Application of Immunoelectron Microscopy to Clinical Medicine. Medical electron microscopy [0918-4287] yr:1994 vol:27 iss:3.

Microfluidic nanoprobes

Abancroft — Sun, 13 Feb 2011 21:40:18 GMT

Abancroft: microfluidic nanoprobe

Microfluidic nanoprobes are used for the measurement of liquids with as small an amount as an atto liter. This is basically the same skill as a pipette but on the nano level. The size of the probe is 10-50 nm in diameter. This tool has overlapping uses with micropipettes and dip-pen lithography since it can both dispense and retrieve liquids. They have volcano shaped tips for dispensing liquid, which are connected with microchannels to an on chip reservoir. This reservoir of liquid is then connected to a remote reservoir. The major benefit of this set up is that there is no need to remove the probe and redip it in ink. While writing with the probe one may continuously refill it so there is no need to change location. This makes it work more like a fountain pen than like a quill. These probes are well suited to be used in an array format.

Moldovan, N., K.-H. Kim, and H.D. Espinosa. "Design and Fabrication of a Novel Microfluidic Nanoprobe." Journal of Microelectromechanical Systems 15.1 (2006): 204-13. Web. 13 Feb. 2011.

Test Article

Brianhorwich — Sun, 13 Feb 2011 20:44:31 GMT

Peter:

Here is a test page.

[[Image:test123]]

{| style="width:80%" border="1"
|-
| This is a table
| Below is blank
|-
| This is row 2
|
|}

Clean Rooms

Brianhorwich — Sun, 13 Feb 2011 19:25:50 GMT

Brianhorwich: Created page with 'In nearly all nanotechnology processes, having an ultra-clean environment is essential. Even small amounts of dust or other particulates in the air can significantly affect the r…'

In nearly all nanotechnology processes, having an ultra-clean environment is essential. Even small amounts of dust or other particulates in the air can significantly affect the results of photolithography, microscopy, etc. As a result, all nanotechnology facilities contain clean rooms in which almost all fabrication is done. These clean rooms are generally installed by private companies that use a variety of technologies and techniques. In order to prevent contamination from surrounding environment, most clean rooms have walls made with reinforced metal (e.g. steel) that is coated with a non-porous material (PortaFab). In order to regulate air cleanliness in these clean rooms, the U.S. government has developed a federally-standardized class system. The six classes range from 1 to 100,000 and are based on the amount of particles and their respective sizes allowed per cubic foot of lab space. There For more information about standards, please see: http://www.engineeringtoolbox.com/clean-rooms-d_932.html . There also exists a second clean room standard called ISO, whose classes range from 1 to 9.

References:

Clean Room Forum, www.cleanroomforum.com/forums

Engineering Toolbox, http://www.engineeringtoolbox.com/clean-rooms-d_932.html

PortaFab Modular Building Systems, http://www.portafab.com/cleanrooms_wall_systems.shtml

Scanning Voltage Microscopy

Sriramr — Sun, 13 Feb 2011 19:10:06 GMT

Sriramr:

[[category: AFM]]

Scanning Voltage Microscopy (SVM) is a method derived from Atomic Force Microscopy (AFM)(Ban, 2004). It is also referred to as nanopotentiometry (Trenkler). While it is still in its infancy, this method has shown promise. SVM measures variations in voltage across a surface, and converts this data into a two-dimensional map. SVM uses a conductive AFM tip to measure the voltages. It has thus far been used in electrical applications, such as characterizing the performance of MOSFETs. For example, in the Trenkler paper, the authors used SVM to determine the I-V characteristics of various transistors to see how different conditions affected them. For example, when biased (e.g. when a gate voltage is applied), the SVM was able to measure the voltages at various points on the transistor (such as throughout the channel), and was thus able to determine things like leakage current. In addition, SVM can be used while devices are functioning (Trenkler). As with other probe methods, the resolution is highly dependent on the size and quality of the tip.

==References==
Ban, Dayan, et al. (2004). Scanning Voltage Microscopy on Active Semiconductor Lasers: The Impact of Doping Profile Near an Epitaxial Growth Interface on Series Resistance. IEEE Journal of Quantum Electronics, 40, 651-655.

Trenkler, T., et al. (1998). Nanopotentiometry: Local potential measurements in complementary metal–oxide–semiconductor transistors using atomic force microscopy. Journal of Vacuum Science & Technology B, 16, 367-372.

Thermal Patterning and the Millipede

Drewkara — Sun, 13 Feb 2011 17:34:08 GMT

Drewkara:

Thermal patterning involves heating the tip of a probe to an extremely high temperature and making small indentions in a material (typically a thin PMMA film) that are ultimately used as data storage bits. At first, a laser diode was used to heat the probe tips, but later a more efficient method using integrated heating circuits was developed [1].

Initially, data transfer rates were limited. But by using sharper tips, higher readout frequency cantilevers, integrated heating, and smoother substrates, the density of bits created by thermal patterning has drastically grown [1].

The biggest jump in thermal patterning technology occurred with the development of multitip systems which allowed larger areas of data to be scanned, and at faster speeds. In 2000, researchers at IBM, Zürich developed a nano probe data storage concept called the millipede "that combines ultrahigh density, terabit capacity, small form factor, and high data rate...resulting in data storage densities up to 1 Tb/in^2" [2]. Although the millipede still has a number of issues that need to be addressed (like tip wear, erasing/rewriting bits, and overall efficiency), its developers believe the millipede's high storage density and low power consumption make it a very realistic data storage possibility in the future [2].

References:

[1] Wouters, Daan, and Ulrich S. Schubert. "Nanolithography and Nanochemistry: Probe-Related Patterning Techniques and Chemical Modification for Nanometer-Sized Devices - Wouters - 2004 - Angewandte Chemie International Edition." Wiley Online Library. 28 May 2004. Web. 11 Feb. 2011. .

[2] Cross, G., M. Despont, U. Drechsler, and B. Gotsmann. "The “Millipede”—Nanotechnology Entering Data Storage." IEEE TRANSACTIONS ON NANOTECHNOLOGY 1.1 (2002): 39-53. Web. 13 Feb. 2011.

Category: Thermal Patterning

Ultrasonic Force Microscopy

Monica Cho — Sun, 13 Feb 2011 02:12:53 GMT

Monica Cho: Created page with 'Ultrasonic Force Microscopy (UFM) is a technique that allows the local mapping of a sample through the creation of a near field acoustic microscopic image. UFM allows the local m…'

Ultrasonic Force Microscopy (UFM) is a technique that allows the local mapping of a sample through the creation of a near field acoustic microscopic image. UFM allows the local mapping of elasticity in atomic force microscopy. It provides a quantitative account of the internal, surface and subsurface properties of a specimen without damaging or destroying the sample.

UFM uses ultrasonic vibration to a cantilever or sample to map local features of a sample due to their elasticity. Different elastic properties helps to differentiate features of the sample. And acoustic standing wave is formed from the interference of a high frequency acoustic wave from the bottom of the specimen and a slightly different frequency wave from the cantilever. A force-distance curve measurement is compared with cantilever dynamics and tip-sample interaction through finite-difference technique. Using ultrasonic frequencies higher than the cantilever resonance, the sample is vertically vibrated so that the tip is cyclically indented into the sample and by varying the vibrational amplitude, subsurface features can be imaged from the cantilever deflection vibration. With low-frequency lateral vibration, the torsional vibration of the cantilever reveals subsurface features with varying degrees of shear rigidity.

==References==
{{Reflist|refs=
Berger, Michael.''New modality of force microscopy advances non-destructive subsurface characterization techniques''. Nanowerk, 2010.
Matsuda, Osamu. Terada, Takuya. Inagaki, Katsuhiko. Wright, Oliver B. ''Cantilever Dynamics in Ultrasonic Force Microscopy''. Jpn. J. Appl. Phys. 41, 2002.
Kolosov, Oleg. Ogiso, Hisato. Yamanaka, Kazushi. 'Ultrasonic force microscopy for nanometer resolution subsurface imaging''. Appl. Phys. Lett. 64, 1994.
}}

Kohler Illumination

Zmazlin — Sat, 12 Feb 2011 16:37:30 GMT

Zmazlin:

Kohler illumination is a method to evenly illuminate of a sample, used in microscopy. It is the most common lighting method used in modern light microscopy even though it requires optics that are not standard in many cheaper microscopes.

This method uses both a field and an aperture iris diaphragm for the illumination. Besides evenly distributed light, this method also produces no glare and minimally heats the specimen.

The field diaphragm allows the user to adjust the amount of light entering the sample, without changing the wavelength of the light. The specimen contrast is altered by changing the condenser diaphragm. You can change the illumination intensity by altering the supplied voltage to the light source.

[[Category:kohler]]

[[Category:illumination]]

References:

[1] http://microscopy.berkeley.edu/Resources/instruction/kohler.html

[2] http://www.gonda.ucla.edu/bri_core/kohler.htm

Photothermal Microspectroscopy

Djabin1 — Thu, 10 Feb 2011 21:07:19 GMT

Djabin1:

Photothermal Microspectroscopy

Photothermal microspectroscopy is the product of infrared spectroscopy and atomic force microscopy. This technique is used to yield infrared spectra from objects below a micrometer in size.

Technique

Using the atomic force microscopy method combined with an infrared spectrometer, a particular portion of the material is located. Once the area absorbs electromagnetic radiation, heat is generated. Temperature fluctuations of this heat are induced by alternating the strength of the excitation beam. This process enables the user to obtain the varying depth measurements of the surface by measuring the heat produced with a thermal probe or resistance thermometer.

Uses

Photothermal microspectroscopy serves as a good method for probing structures in an opaque material and characterizing thermal properties.

Sources

1)http://adsabs.harvard.edu/abs/1993PhDT........48W
2)http://www.ingentaconnect.com/content/sas/sas/1999/00000053/00000007/art00012?token=0054137dbcc39412f415d7666254470234a6c7b4051422530482972715a614f6d4e227a158c5b70bed8b

Conductive atomic force microscopy

Flavahboy — Thu, 10 Feb 2011 21:05:26 GMT

Flavahboy: Created page with 'Conductive atomic force microscopy (C-AFM) is a variation of atomic force microscopy (AFM) and scanning tunneling microscopy (STM), which uses electrical current to construct the…'

Conductive atomic force microscopy (C-AFM) is a variation of atomic force microscopy (AFM) and scanning tunneling microscopy (STM), which uses electrical current to construct the surface profile of the studied sample. The current is flowing through the metal-coated tip of the microscope and the conducting sample. Usual AFM topography, obtained by vibrating the tip, is acquired simultaneously with the current. This enables to correlate a spatial feature on the sample with its conductivity, and distinguishes C-AFM from STM where only current is recorded. A C-AFM microscope uses conventional silicon tips coated with a metal or metallic alloy, such as Pt-Ir alloy.

The C-AFM can be operated in the imaging mode and spectroscopic mode.

==Imaging Mode==

In the conventional imaging mode, vibrating tip is scanned over a small sample area (typically square micrometres); a negative voltage bias is applied to the sample, and the electrons tunneling from the sample to the tip are being collected. This polarity is chosen for several reasons:

The electron barrier in this case is the conduction band onset at the Si/oxide interface, which is better known than the tip/oxide interface.
The emission area for substrate injection is homogeneous and depends mostly on the tip/sample contact area. On the contrary, the emission area in the case of tip injection depends on the shape of the tip.
During the measurement, the tip is in contact with the sample, and many studies materials are hydrophilic. Therefore, the tip drags along water and other contaminants adsorbed at the sample surface. The applied voltage induces a high electrical field between the tip and the substrate. This field ionizes water, producing the OH-. If a negative voltage is applied to the tip, the OH- ions are attracted to the surface of the sample; they oxidize it thereby permanently blocking the current flow. If a positive voltage is applied to the tip, the OH- ions are dragged to the tip, oxidizing it and breaking the electrical circuit. However, whereas the studied sample may be unique, the tips are disposable and easy to replace, but after replacement, it is difficult to relocate exactly the same area. The tip degradation, as well as image quality, also depend on the scanning parameters.

==Spectroscopic Mode==
In the spectroscopic mode, the tip is stationary, while the voltage is being swept. This allows recording conventional current–voltage characteristic from tiny areas of the sample, and thereby to extract information on the local electronic properties, such as local density of states.

==References==
Zhang, L.; T. Sakai, N. Sakuma, T. Ono, K. Nakayama (1999). "Nanostructural conductivity and surface-potential study of low-field-emission carbon films with conductive scanning probe microscopy". Applied Physics Letters 75 (22): 3527–3529. doi:10.1063/1.125377.

Piezoresponse Force Microscopy

Flavahboy — Thu, 10 Feb 2011 20:48:09 GMT

Flavahboy: Blanked the page

Accuracy and calibration

Tatenda — Thu, 10 Feb 2011 18:17:52 GMT

Tatenda:

Accuracy and Calibration of Scanning Probe Microscopy

"Instrumental Factors. The performance of a scanning probe instrument is limited by a number of factors. One of these is the resolution of the mechanical components used to move the tip and measure its position. The sharpness and stability of the probe tip determine the area of contact and the reproducibility of imaging. Obviously, environmental vibrations must be controlled to a high degree. In addition, most positioners depend on piezoelectric drive, which is subject to problems of non-linearity and to overshoot during rapid movements. The major manufacturers of SPM equipment have made substantial improvements in mechanical and electronic design. These improvements and advanced electronic calibration routines result in measurements that are more linear and accurate than the early models. Mark VanLandingham (University of Delaware) has published a discussion of instrumental uncertainties on the Web.
Accurately nanofabricated gratings are the basis for two and three-dimensional calibrations. Such calibration gratings and calibration software are commercially available.

Probe-Related Image Distortions. At very high magnifications and high-relief sample surfaces, the mode of imaging and the geometry of the probe tip can influence the scanned image. Knowledge of the probe geometry then becomes important for interpretation of the image.

To image individual atoms and molecules it is necessary for the tip-surface interaction to depend only on the nearest atom(s) of the tip. This occurs in scanning tunneling microscopy because the tunneling current passes only through the nearest atom of the tip. Tunneling current falls off very steeply with distance from the surface. In atomic force microscopy the tip-surface interaction forces fall off less steeply with distance. Thus an AFM probe responds to the average force of interaction for a number of tip atoms, depending on the sharpness of the tip. An AFM image does not show individual atoms, but rather an averaged surface. For ordered surfaces this will reflect the average unit cell.
Probe Deconvolution (Image Restoration). Imaging very sharp vertical surfaces (surfaces with high relief) is also influenced by the sharpness of the tip. Only a tip with sufficient sharpness can properly image a given z-gradient. Some gradients will be steeper or sharper than any tip can be expected to image without artifact. False images are generated that reflect the self-image of the tip surface, rather than the object surface. Mathematical methods of tip deconvolution can be employed for image restoration. The effectiveness of these methods will depend on the specific characteristics of the sample and the probe tip. A number of scientists have investigated this area."

Time of Flight Secondary Ion Mass Spectrometry

Mansha — Wed, 09 Feb 2011 22:38:28 GMT

Mansha:

Time of Flight Secondary Ion Mass Spectrometry

Description and Use

Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is a surface analytical technique that focuses a pulsed beam of primary ions onto a sample surface, producing secondary ions in a sputtering process. Analyzing these secondary ions provides information about the molecular and elemental species present on the surface. For example, if there were organic contaminants, such as oils adsorbed on the surface, TOF-SIMS would reveal this information. TOF SIMS does not have the spatial resolution of electron beam techniques such as SEM, TEM, or AES however it has an extremely low information depth, in the range of 10 – 20 angstroms, meaning it can successfully provide information from surfaces covered by a monolayer.

Since TOF-SIMS is a survey technique, all the elements in the periodic table, including H, are detected. Moreover, TOF-SIMS can provide mass spectral information; image information in the XY dimension across a sample; and also depth profile information on the Z dimension into a sample.

Process

ToF-SIMS uses a pulsed ion beam (Cs or microfocused Ga) to remove molecules from the very outermost surface of the sample. The particles are removed from atomic monolayers on the surface (secondary ions). These particles are then accelerated into a "flight tube" and their mass is determined by measuring the exact time at which they reach the detector (i.e. time-of-flight). Three operational modes are available using ToF-SIMS: surface spectroscopy, surface imaging and depth profiling.

The Instrument

ToF-SIMS instruments typically include the following components:

• An ultrahigh vacuum system, which is needed to increase the mean free path of ions liberated in the flight path;

• A particle gun, that typically uses a Ga or Cs source;

• The flight path, which is either circular in design, using electrostatic analyzers to direct the particle beam.

• The mass detector system.

ToF-SIMS instruments are also equipped with a powerful computer and software for system control and analysis. ToF-SIMS software is the ability to perform "retrospective" analysis, which means that every molecule from the sample detected by the system can be stored by the computer as a function of the mass and its point of origin. This allows the user to obtain chemical maps or spectra of specific regions not previously defined after the original data has been collected.

Citations

Evans Analytical Group LLC. “Time-of-Flight Secondary Ion Mass Spectrometry.” Analytical Techniques.
http://www.eaglabs.com/techniques/analytical_techniques/tof_sims.php

Mogk, David W. “Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS).” Geochemical Instrumentation and Analysis.
http://serc.carleton.edu/research_education/geochemsheets/techniques/ToFSIMS.html

FMM: Force Modulation Microscopy

Pdsouza — Tue, 08 Feb 2011 01:34:58 GMT

Nos2go:

Force Modulation Microscopy (FMM) is an extension of the AFM technique which is especially useful in detecting specific properties of the substrate such as elasticity, friction, and adhesion. FMM operates in the contact mode of AFM. FMM works by measuring the tip motion after an applied "driving signal" is applied to the cantilever. Essentially, the sample is gently pushed by the tip of the cantilever and "the change in cantilever oscillation amplitude can be related to elasticity of the sample surface." To do this, the subsequent tip motion is transformed into an electric signal and then split into AC and DC components for further investigation.

The DC signal contains the variations just as in regular AFM. However, the AC component measures the tip's response to the driving signal. The amplitude of the AC component is directly influenced by the elastic properties of the substrate. For example, a soft surface would most likely absorb most of the oscillation and produce a smaller amplitude in the AC signal. A hard surface would do the exact opposite.

The phase shift of the AC signal, called ‘FMM Phase,’ also differs according to the elastic properties of the sample. Through this, FMM Phase can be used to generate an FMM image. This technique is the Phase Detection Microscopy (PDM). Often, FMM Phase is more sensitive to the elastic properties of the surface than FMM Amplitude. PDM provides an additional contrast mechanism within a region of homogeneous hardness.

The end result of FMM is a force modulation topographic map of the substrate's elastic properties.

References:
Park Systems. "Park Systems AFM - Advanced SPM Mode, Force Modulation Microscopy, FMM, Variation in Mechanical Properties, Surface Elasticity, Adhesion, Viscosity." Park Systems - Atomic Force Microscope, AFM/SPM, Research, Industrial. Web. 07 Feb. 2011. .
Park AFM Mode Note: Force Modulation Microscopy.

Magnetic Resonance Force Microscopy (MRFM)

Jraines — Sun, 06 Feb 2011 20:52:13 GMT

Mplis:

Magnetic Resonance Force Microscopy (MRFM)

"The magnetic resonance force microscope (MRFM) is a novel scanned probe instrument which combines the three-dimensional imaging capabilities of magnetic resonance imaging with the high sensitivity and resolution of atomic force microscopy. It will enable non-destructive, chemical-specific, high-resolution microscopic studies and imaging of subsurface properties of a broad range of materials. This technology holds clear potential for atomic-scale resolution" (Hammel).

In Magnetic Resonance Force Microscopy (MRFM), the sample which is to be observed is placed on a cantilever near a ferromagnetic tip. The shape of this ferromagnetic tip produces a magnetic field around the sample and the end of the cantilever. Using an RF coil, a second magnetic field is produced around the original field. The interactions of these magnetic fields and the nuclear spins within the samples create noticeable oscillations of the particle. As the sample oscillates back and forth, the cantilever in which the sample is suspended deflects small distances. These distances are measured with an optical-fiber interferometer. However, the magnetic fields produced are not completely uniform. Because of this, the magnetic resonance on the cantilever can not be calculated correctly for the entire sample at the same time. 'In the instances where the magnetic resonance can be calculated, the resonance obeys the following formula.

Wo = g*Bz

where Wo is the frequency of the RF field, Bz is the strength of the inhomogeneous polarizing field, and g is the gyromagnetic radius of the nucleus' (Magnetic Resonance Force Microscopy Detailed Summary).

If the magnetic tip is moved in three dimensions around the sample, and the RF frequency is constantly measured, then an accurate three dimensional picture can be created of the elemental sample.

There are several improvements that could be made to the MRFM scanning method if the right research were done. In order for MRFM to attain its full potential as a scanning method, a better understanding of cantilever damping mechanisms is needed.

There are several articles available that discuss general acoustic and mechanical damping mechanisms, but the mechanisms that have the greatest amount of relevance to MRFM include "mechanical losses associated with gas damping...three-phonon and four-phonon anelastic scattering...thermoelastic damping...and surface containment damping" (Sidles)

There is relatively little literature available that has looked into damping mechanisms that are optimized for MRFM. Mechanisms that can operate at low temperatures, have a very low mass, and a long damping time are ideal for MRFM.

Hammel, Chris. "MRFM." ITS Home. Web. 12 Feb. 2011. .

"Magnetic Resonance Force Microscopy Detailed Summary." Stanford Micromachine. Web. 06 Feb. 2011. .

Sidles, J.A., et al. "Magnetic Resonance Force Microscopy." Rev Mod Phys. 67, 249-265 (1995). 06 Feb 2011.

DPN

Dominique1990 — Sun, 06 Feb 2011 18:42:00 GMT

Dominique1990:

Dip Pen Nanolithography (DPN) utilizes an atomic force microscope tip to deposit nanoscale materials onto a substrate. It is similar to using an ink “dip pen” to write on a piece of paper. The figure to the right is a diagram of DPN showing an AFM tip depositing a material on a substrate. DPN began with the deposition of alkane thiolates onto a gold surface via the method described. DPN has become more widely used in nanotechnology. A major advantage of DPN is that almost any material "ink" and any substrate can be used. However, DPN is much slower than other nanofabrication methods.

The Mirkin Group at Northwestern University is currently using DPN in a variety of applications. One application involves fabricating nanoarrays of proteins via DPN to be used in biological research, proteonomics and pharmaceutical screening. The group has also developed a method for patterning conducting nanoscale polymers on semiconductors by DPN. The Mirkin Group is continuing to investigate the capabilities of DPN as well as optimal inks and substrates.

Citations:

Ratner, Mark, and Daniel Ratner. Nanotechnology: A Gentle Introduction to the Next Big Idea. Upper Saddle River: Pearson Education, 2003. Print.

Son, J, et al. "Dip-Pen Lithography of Ferroelectric PbTiO3 Nanodots." JACS. 131. (2009): Print.

Nanomedicine

Kforce012 — Fri, 04 Feb 2011 07:09:47 GMT

Kforce012:

Nanomedicine, in its broadest sense, refers to nanotechnology that has been applied to the medical field. Nanotechnology has many applications in both biological discovery and clinical practice. The ability of engineered nanoparticles to interact with cells and tissues at a molecular level provides them with a distinct advantage over polymers and other macromolecular substances. Some of the uses of nanotechnology in medicine include fluorescent biological labels, drug and gene delivery agents, bio-detection of pathogens, detection of proteins, probing of DNA structure, tissue engineering, tumor destruction, separation and purification of biomolecules and cells, and magnetic resonance imaging (MRI) contrast enhancement [2].

Nanomedical approaches to drug delivery focus on the development of nanoscale particles and molecules that improve drug bioavailability. One of the major tools used in nanomedicine is the nanocarrier. Nano-scaled carriers have revolutionized drug delivery, allowing for therapeutic agents to be selectively targeted on an organ, tissue and cell specific level. This selectivity minimizes exposure of healthy tissue to often-toxic therapeutic agents. By breaching the blood brain barrier (BBB), a tightly packed layer of endothelial cells that protects the brain by preventing high-molecular weight molecules from entering, nanocarriers promise to provide effective therapies where larger molecules have failed. Thus far, much effort has focused on producing nanoparticles for the delivery of anti-tumor drugs, diagnostic agents, and vaccines. These nanosystems can be further modified to achieve desirable biological properties, including longer circulation in blood, targeted delivery (including intracellular targets), and sensitivity to certain stimuli. Treatments for common neurological disorders, such as stroke, tumours and Alzheimer's, are highly sought-after future applications of nanomedicine [1].

Direct in vivo imaging of nanomaterials is another exciting recent application that can provide real-time tracking of nanocarriers. Tracking the movement of these nanocarriers can help determine how well drugs are being distributed or how substances are metabolized. Quantum dots attached to proteins that penetrate cell membranes are currently being used for this purpose. These dots give off different colors depending on their size. Additionally, the dots are bio-inert, and therefore unlikely to have adverse side effects. The most recent molecular imaging techniques are based on optical and hybrid contrast systems, including fluorescent protein tomography and multispectral optoacoustic tomography. In addition to improvements in overall image quality and spatial resolution, nanotechnology will allow for monitoring of the transmigration ability of various types of biomolecules across the BBB in vivo. Ultimately, such non-invasive fluorescence images may provide insight into both therapeutic and diagnostic targeting of brain tumors.

Thus, nanocarriers have great potential for medical diagnostics, therapeutics and molecular targeting. From a broader perspective, nanocarriers equipped with multiple diagnostic, therapeutic, or targeting molecules should offer successful treatment strategies for a large range of other diseases. Moreover, they have helped scientists understand the mechanisms that govern structural and composition changes in response to various natural BBB transporters, undesirable toxins, infective viruses such as HIV-1, and potential BBB-disrupting molecules. The cutting-edge technologies used in nanomedicine are poised to change the way that medicine is administered [2].

1] Wu, Xiao and Heidi M. Mansour. “Nanopharmaceuticals II: application of nanoparticles and nanocarrier systems in pharmaceutics and nanomedicine”. International Journal of Nanotechnology. Jan 2011; 8: 1-2, 115-145.

2] Bhaskar S. et al. “Multifunctional Nanocarriers for diagnostics, drug delivery and targeted treatment across blood-brain barrier: perspectives on tracking and neuroimaging”. Part Fibre Toxicol. 2010 Mar 3;7:3.

Calculation of the deflection of a cantilever during scanning using a contact mode AFM

Huabin — Wed, 22 Dec 2010 18:22:42 -0500

Response from: mbrukman

In an NS-IV, you might be best off taking force-distance curves immediately before and after your friction images. Use the "before" plot to run the Setpoint Zero function, then apply your normal force with the knowledge of what PSD output corresponds to zero load. Afterwards, take an FD to see how much you've drifted. At the very least, that will put bounds on your normal force uncertainty. You don't need a breakout box to ramp the setpoint in the MFP-3D. I worked with AR to write a couple lines of code to change the SP on a line-by-line basis during an image. Unfortunately it's been a while since I've done this and the exact details escape me. But my discussions with Bemis et al are still up there on the AR forum. I'm sure the code is there too.

Response from: Huabin

Many thanks! Yes, I have noticed the code last year and already used it in my experiments. Here, I would like to mention that the calculation of the normal load stated in the AR forum (see above) is incorrect, and I have discussed it with Bemis recently.

How to determine the deflection of a cantilever during the scanning process using a contact mode AFM

Huabin — Wed, 22 Dec 2010 05:36:43 -0500

Response from: carpick

Huabin - here are my replies, but I will also ask my group members to chime in since they know more about the hands on details - you should trust them more than me! 1) Yes and yes, but with one caveat - when the probe is very far from the surface, the normal force offset will be a little different than when it is close to (but not yet in contact with) the surface. This is because there is some light scattered off the surface and the amount changes with the surface-probe distance. So the best base-line value to take is when the probe is just pulled off from the surface. You'll see this value in a force curve. I believe the value will not be the raw photodiode normal signal, but the normal signal minus the setpoint. For questions 2 and 3, are you referring to a regular friction measurement, or to scanning during the wedge calibration method? 4) Yes, changing the set point will change the deflection value because it is automatically subtracted. So if you are taking a series of discrete images at different set points, write down the value you used for each measurement and use this to reconstruct the true deflection. To get the baseline, do the force curve measurement with the set point set to zero. However, we use another method where we ramp the set point continuously during an image, so each line is taken at a different normal load. This requires using the signal access module. Do you have one? 5) If the feedback is on and optimized, there shouldn't be a large dependence in the deflection signal; you will see a "lag" as the probe goes uphill or downhill. This gets worse if you scan faster, or turn down the feedback. For scanning the wedge sample, it should be possible to have high enough feedback and to scan slowly enough that this does not lead to a large error.

Response from: mbrukman

(1) Did you mean that the signal of the baseline (out of contact) of a force curve can be taken as the offset value? Could the signal of the photo diode when the cantilever is off surface be used as the offset value? I always took a series of force curves right before friction measurements and used the "setpoint zero" function to soft-code the out-of-contact PSD voltage into header of the friction data file (actual setpoint was set using a function generator). Of course you can always just write the value down, but that's not as elegant. Because I only took friction-vs-load measurements, took the liberty of taking the setpoint down below the pulloff force within each image so that some actual out-of-contact data were contained in each image, too. (2) In your work, by which means did you get the deflection signals of the cantilever in a scanning process? Torsional deflection was the "friction" signal, naturally. The "deflection" signal is actually the deflection error signal (deflection minus setpoint) so we used a breakout box, extracted the deflection signal, and ran it into an aux input on the back of the controller. (3) According to the manual of Multimode AFM (please see pages 196-197 of the manual sent to you by email), the data of an image captured with the Data type set to Deflection could be used to calculate the force exerted on a sample (or deflection of the cantilever) if the feedback gains are set low when collecting the image. It seems a bit difficult here, how to set the gains ideally low? I would not use that technique. (4) As you know, in order to calibrate the cantilever, a series of set-point values are usually used in collecting the same image in the friction measurement. In my experiments, I found that the baseline of force curves changes with set-point values. If the offset value mentioned above is obtained by the consideration of the out of contact (baseline) of a force curve (collected immediately upon the completion of imaging), then, at which set-point should a force curve be collected, or how to collect a force curve of which the baseline can be used as the offset value? The green horizontal axis of the force curve plots is not fixed at zero load (or any other load for that matter), it's just a representation of the setpoint. So as you vary the setpoint, the baseline will move up and down. This does not affect the measurement itself. (5) Personally, I think that the deflection (load) of the cantilever in the same fast scan line (same set-point) not only depends on set-point, but also depends on the surface features of a sample. Does it make sense? That's correct. In an ideal measurement, the cantilever deflection always equals the setpoint, and the scanner tracks the topography perfectly. In practice of course there is a lag between topog. changes > cantilever bending > feedback loop > piezo response > cantilever return to desired deflection. The method described in question (3) relies on and exaggerates this lag so that changes in topography force the cantilever into undesired deflections which are then recorded by the "deflection" channel -- which is really the error signal. It's a terrible method that relies on intentionally poor performance of the system as it responds to uncontrolled imperfections in the sample. Like Rob said, we used an external function generator and a breakout box to ramp the setpoint indirectly -- this allowed the feedback loop to function properly. I forget exactly how it was done, but I know it also required a summing amplifier and physically adding a circuit to the feedback board in the controller. (We added a BNC port to the front of the controller with the center lead somehow connected to the setpoint signal.) I think this is because the error signal is actually calculated at the multimode/dimension scanner, but I forget the specifics. Hope that helps Matt Brukman

Lateral force calibration-'offset' value

Huabin — Sun, 12 Dec 2010 20:19:26 -0500

Response from: carpick

Huabin - I'm glad you are using the wedge calibration method for lateral force calibration. For everyone: the latest software for that is available here on the Nanoprobe Network in the Software Library. I have just updated the files there. If you are using a Veeco/Bruker AFM, then the file "friction_v_load_new.m" is set up to import and process the raw data. The user is prompted for an 'Offset' value that is applied to the Normal force signal. This is because often the photodiode is not set so that the normal force signal is actually zero when there is no force on the cantilever. When the tip is out of contact from the sample, the signal should be zero. If it is not, then enter a value close to what you see in the data (assuming your data includes a portion where the tip is out of contact) to offset the normal signal to make it equal to zero when out of contact. This could be a little confusing since the term "offset" is also used to describe the sum of the lateral force trace and lateral force retrace signals. I'm looking for a volunteer to update the Matlab file with some clearer language - any takers? You can post it in the Software Library.

Response from: mbrukman

If you're only doing lateral calibration, then you probably only want to take the data at positive loads anyway (avoids possible artifacts from the nonlinearity at low/tensile loads) so there may not be any out-of-contact data to subtract out, and you can ignore it. (But it is useful for plotting actual friction vs load measurements.) As I recall, the wedge method relies only on the slopes of the four (T+R up, T+R down, T-R up, T-R down; all vs normal force) lines, and those are independent of the fixed normal force offset. So the Matlab script would definitely ignore it. Matt Brukman

Response from: mbrukman

EDIT: The four lines are (T+R up, T+R down, T-R up, T-R down; all/2 and vs normal force)

Response from: JingJing

The 'offset' here really means any normal external load being added to the cantilever. So maybe we can rename the 'offset' to 'external load setpoint', and use the variable 'setpoint' in the code. -Jingjing

Response from: mbrukman

JingJing, There is no external load applied to the cantilever, rather the feedback loop maintains a load equivalent to ([deflection_setpoint] - [out_of_contact_deflection]) x [optical_sensitivity] x [spring_constant]. The "offset" referenced in the code is a correction to the out of contact deflection value and is necessary because cantilever drift causes the OOCD to vary over time. It absolutely, positively should not be renamed "setpoint" in the code. The "offset" you're talking about is another thing entirely, if I'm understanding you correctly. You're talking about something like a function generator output that gets added to either the setpoint or the real-time deflection signal, depending on your setup. This can effectively increase or decrease the tip-sample contact forces, but it is not a load itself. I don't believe this value ever enters into the code at all.

Thanks

dawnbonnell — Fri, 22 May 2009 17:03:04 -0400

The advertised time for the 'Live Forum' has expired. Thanks to all who participated. Please feel free to continue discussions as long as you want and remember that these posting will remain as a resource. We can come back to this forum with future questions and to continue interacting.

If you have ideas for future Forums please let us know.

thanks, Dawn

Physical interpretation of measurements

mbrukman — Fri, 22 May 2009 16:27:33 -0400

Response from: sergeikalinin

Strictly speaking, signal flow in PFM is: excitation signal (khown amplitude and phase) -> electronic circuit (for low frequencies just resisto, but above 1 MHz RLC things can be important) -> electromechnical contact (materials response) -> cantilever transfer function -> detection electronics. Practically, you measure product of all these transfer functions, and osme of them are not separable (eigenresponses of cantilever depend on contact). So, dissipation 9Q factors) can be measure dreliably, but frequency dispersion of signal is very unlikely. As an example, Kathy Wahl reported (JAP or RSI 2001?) a very nice calibration work for nanoindentor, but it was already tough, and nanoindentation is generally much more quantitative then SPM

Response from: kholkin

Sergei, Piezoelectric loss factor originating mostly from the macroscopic domain wall motion is around 5-10\%. Can we say something about the single domain loss by measuring the PFM phase when the tip is located near the domain wall. Or it is indistinguishable from other sources of phase distortion?

Response from: sergeikalinin

Good question. You can do it by measuring band-excitation SS-PFM near domain wall. Good idea. 10\% may actually be measurable.

Response from: mbrukman

If the several loss mechanisms cannot be fully deconvoluted, is the total amplitude R the appropriate value to report, then

Response from: sergeikalinin

whell, the low-frequency value and r_res/Q are only weakly loss-dependent, as in any SHO

Response from: kholkin

Yes, of course. Minute phase changes are difficult to interpret.

Hysteresis mapping

snnnnnn — Fri, 22 May 2009 15:57:46 -0400

Response from: sergeikalinin

Try to acquire hysteresis loops fast:) If your drift is 1 nm/min and loop takes 10 s, you are safe since signal generation volume is ~10-30 nm (caveat is that res frequency can shift, but for low frequency PFM it is not a big deal). Controllers such as Omicron, Asylum, and Nanonis allow you to introduce lienar correction for stationary drift, but modern platforms are good enough to suppress it. E.g. on MultiMode in a good room we were able to collect 6 hour SS-PFM scans over 300 nm region with small drifts (miniscule distortion)

Response from: proksch

As Sergei mentions, having a thermally stable system is important. This can be accomplished with good microscope design and a temperature controlled room. The real world involves microscopes that have metal components and other pieces that move when the temperature changes. To compensate for this, active drift correction can be used. The movie in the link below isn't SSPFM, but it illustrates the results of this type of active compensation. The movie shows a scan of a 250 nm scan of gold on glass was taken at 1 Hz (linescan rate) and at 256x256 pixels. The acoustic hood was left open for 12 hours and closed at the start of imaging. These images were made in attractive mode to keep the tip as constant as possible, as evidenced by comparing the first and last frames. This movie shows images acquired over the period of one week. http://www.AsylumResearch.com/ftp/outgoing/20090522_ImageStabilization.zip File size is ~30MB.

Response from: gruverman

Given that a typical loop rarely takes more than a minute, you would not have any serious problem even with a drift as large as 10 nm/min (your tip-sample contact area is of the order of 10 nm). If your sample requires slow loop measurements (several minutes or more per loop) compensation of a thermal drift would be helpful.

GB's effects in polycrystalline ferroelectric thin films

jingyuanyuan — Fri, 22 May 2009 15:43:10 -0400

Response from: dawnbonnell

Grain boundaries very definitely have an effect on switching in the sense that they provide local variations in lattice structure which a domain wall must negotiate to grow past it. They can also provide nucleation sites. The smaller the grain, the more likely to get single domains.

Response from: sergeikalinin

GBs affect swithcing behavior very strongly by serving as nucleation centers for noew domains, but also as pinning centers for domain wall motion. The degree of influence obviously depends on type of GB (clean vs. with precipitates, orentation angles). On bicrystals, it is possible to explore the mechnisms of domain nucleations at GBs systematically: BRIAN J. RODRIGUEZ, SAMRAT CHOUDHURY, Y.H. CHU, ABHISHEK BHATTACHARYYA, STEPHEN JESSE, KATYAYANI SEAL, ARTHUR P. BADDORF, R. RAMESH, LONG-QINQ CHEN, and SERGEI V. KALININ, Spatially Resolved Polarization Switching at an Engineered Defect: Bicrystal Grain Boundary in Bismuth Ferrite, Adv. Func. Mat. 19, 1 (2009) The pinning was studied by several groups, including Ramesh (papers with Ganpule), Gruverman (I do not have reference at hand, but he is also on this forum), Huey (not sure if published), and Balke (not sure if published). Also, see BRIAN J. RODRIGUEZ, Y.H. CHU R. RAMESH, and SERGEI V. KALININ, Ferroelectric domain wall pinning at a bicrystal grain boundary in bismuth ferrite, Appl. Phys. Lett. 93, 142901 (2008). and some papers by N. Valanoor.

Response from: kholkin

One of the first papers demosntrating domain pinning on grain boundaries and their effect on the polarization relaxation after poling in PZT films: V. V. Shvartsman, A. L. Kholkin, Investigation of switching behavior in PbZr0.45Ti0.55O3 thin films by means of Scanning Probe Microscopy, Ferroelectrics 286, 291 (2003).

Response from: sergeikalinin

Also, Nina Balke at ORNl is doing some spectacular work. Contact her at n2b@ornl.gov

Response from: jingyuanyuan

Great! thanks for the answers and references! If GBs serve as nucleation center, it seems to me that it would be easier to switch the area close to the GBs. If GBs serve as pinning centers, it would be harder to switch the area close to the GBs. If this is true, what determines the role of GBs? whether it's nucleation center or pinning center. How does the orientation angles come into play?

Response from: sergeikalinin

Both. It can be a nucleation and a pinning centers. The mechnisms of nucleation and wall motion are fairly different. There is a very good book by Sidorkin that addresses some of htese issues. Orientation angle comes into play by determining what happens at GB. If it is tilt GB that is formed by parallel dislocation cores, and will affect poalrization weakly since th elattice "almost" continuous. If the GBs are generally misoriented, the supression of poalrization must be much stornger since reocnstructions have to be much more extensive.

Response from: sergeikalinin

There are some great reviews by S. Pennycook and G. Duscher that address structures of tilt GBs in perovskites. Caveat is that electron microscopists (unsurprisingly) prefer GBs where they can get atomic resolutions on both constituent crystals, and this means special orientations.

Response from: dawnbonnell

The grain boundary can induce a local electric field that affects polarization close to the boundary. Gruverman has a nice paper demonstrating this with chemical deposition there. And we know this from theory as well... see Rappe's papers on BTO. The amount of charge will depend on structure, i.e. orientation. This has been measured in non ferroelctric perovskites and will occur in ferroelectrics as well. See Shao et al APL 2004, PRL 2005 and a nice paper by the Stuttgart group is also referenced in the PRL mentioned above.

Response from: gruverman

The role of GB in switching will depend on type of defects it is associated with. Large-angle GB with high dislocation density in its vicinity would pin polarization. Accumulation of vacancies would increase GB conductivity and may make it easier to switch provided that it does not cause too much leakage.

Response from: kholkin

Our recent paper in APL 93, 222905 (2008) directly proves the existence of frozen dipole moments at the grain boundaries in pure SrTiO3 ceramics. These frozen dipoles are responsible for many peculiar phenomena such as forbidden Raman lines, stiffening of soft mode and reduction of the permittivity as compared to single crystals.

Response from: sergeikalinin

Actually, conductivity impedes switching, since field becomes smaller

Signal interpretation in DFRT PFM

snnnnnn — Fri, 22 May 2009 15:19:46 -0400

Response from: sergeikalinin

In DRFT, two things are true if peak is single-harmonic oscillator like: - the resonance frequency is tarcked correctly - the sum of amplitudes is proportional to maximal response If the width of the peak is (a) known and (b) is position independent, both the dissipation and absolute response can be ascertained. Experience with band excitation (which can be interpreted as N-frequency version of DRFT) suggests that - for decent samples (single crystals, films) peak is well behaved -> DRFT should work - for nanopparticles, nanowires, etc. there are very large changes in peak shape - > DRFT not guaranteed to work. However, in any case it will work much better then single-frequency PFM

Response from: snnnnnn

So is that to say that in the case of a nanoparticle or nanowire, the large changes in peak shape result in artifacts within the phase signals? Would there be any post processing required to see negative phase values? As it is collected on the Asylum, the phase only is collected from a 0-360 range.

Response from: sergeikalinin

There are three answers: - the next person to ask is Roger Proksch (roger@asylumresearch.com), who have started the whole DRFT business - band excitation and its equivalents are the only fully reliable way to do these measurements (equivalents inclusing full amplitude-frequency sweeps by Kos and Hurley, and many single-frequency maps by Huey) - better somehting then nothing

Response from: snnnnnn

Are the single frequency maps as immune to topological crosstalk as DFRT?

Response from: sergeikalinin

tak emaps at each frequency (say, from 100 kHz to 200 kHz with 2 kHz step), you will be able to align them (e.g. using imge toolbox in MatLab) and recover resoances. It is not the most easy approach - can be done once, but probably not most productive in long run. Importantly, very often resoannce frequency changes during spectroscopic experiment (i.e. hysteresis loop acquisitions), and there image alighning approach does not work at all.

Response from: snnnnnn

So what measures might one take to make DFRT signal collection more reliable from a non-planar surface? Would changing the cantilever k constant help?

Response from: sergeikalinin

No. Taking several cantilever tunes at "suspect" locations may help.

Response from: snnnnnn

Thanks for the help...I'll have to contact Roger for his thoughts as well.

Response from: proksch

Snnnn, a couple of things regarding your questions... Since the phase it typicaly 90 degrees at resonance, we have adjusted the phase range to be between -90 and +270 degrees. If it goes outside of this, we wrap it back into that range. It is perfectly possible to access the unwrapped data, contact me offline if you would like t play with that. The original idea behind DFRT was to make use of the contact resonance for better SNR while avoiding crosstalk between changes in the contact resonance due to topography. This ends up making nice images at a good SNR. Since then, we've realized that since we have A1, A2, phi1 and phi2 we have enough information to quantify other things. Within the framework of a simple harmonic oscillator, we can get the drive amplitude (proportional to d33), drive phase (polarization direction), resonant frequency (stiffness) and Q (dissipation). One recent nice observation is that solving the transcendental equations to et these quantities also does not converge when the interactions are non-linear. This is a nice safety/reality check on the measurments. Hope this helps, Roger

Friction and PFM

carpick — Fri, 22 May 2009 12:02:19 -0400

Response from: sergeikalinin

There was a paper by Salmeron group on friction vs doping in semiconductors. These are probably related. In PFM, a lot of early work was friction detection of domains in TGS, but eventually the contrast was attributed to surface chemistry differences as mediated by polarization.

Response from: gruverman

In one of the first papers on SPM of ferroelectrics by Luthi et al, they observed domain contrast in the friction mode, which they attributed to the electrostatic intraction between polarization charges and induced charges in the tip. PFM did not exist at that time and after it was developed LFM imaging became less useful, so no direct comparison has been made as far as I know.

Response from: carpick

Thanks - this sounds like it would be a very nice experiment to try. We may give this a shot. I've heard that Andrew Rappe predicts that the hydrophobicity of a surface changes dramatically with polarization.

Response from: sergeikalinin

The problem will be distinguishing chemically-mediated contrast vs. physical polarization effects.

Response from: jestevep

about correlation between friction forces and the charge state on a surface, please check a paper of Miquel Salmeron in Science Materials on the friction across a p-n junction with electrical bias

PFM Reference Samples

mark.d.johnson — Tue, 19 May 2009 23:12:54 -0400

Response from: sergeikalinin

Perhaps the easiest samples to work with are sol-gel PZT films and PZT ceramics. They form easy to observe and reliable domain contrast, and samples can be few 10s $. In many cases, it is possible to get them from old actuators, etc

Response from: gruverman

Most of people use periodically poled lithium niobate (PPLN) as a test sample. The main reason is that it is commercially available. This does not mean that this is the best test sample. Polycrystalline PZT and lead titanate films would be a much better choice.

Response from: dawnbonnell

While PZT is the easiest to pole, is it straightforward to obtain a relevant quantitative electromechanical coupling coefficient? In my experience this varies with processing conditions,etc... so we usually use barium titantate single crystals. It would be great to PZT if possible.

Response from: kholkin

I would also add x-cut quartz as a standard for vertical displacement of the cantilever.

Reference Papers

dawnbonnell — Tue, 19 May 2009 12:29:58 -0400

Response from: carpick

Review paper on dynamic calibration methods: Practical implementation of dynamic methods for measuring atomic force microscope cantilever spring constants Cook, S.M.; Schaffer, T.E.; Chynoweth, K.M.; Wigton, M.; Simmonds, R.W.; Lang, K.M. Source: Nanotechnology, v 17, n 9, p 2135-45, 14 May 2006 http://www.iop.org/EJ/abstract/0957-4484/17/9/010/ Review paper on static calibration methods: The determination of atomic force microscope cantilever spring constants via dimensional methods for nanomechanical analysis Clifford, C.A.; Seah, M.P. Source: Nanotechnology, v 16, n 9, p 1666-80, Sept. 2005 http://www.iop.org/EJ/abstract/0957-4484/16/9/044/

Response from: mattsallen

Here are a few more regarding normal force calibration which I have found helpful: Review paper on static and dynamic methods, written as a tutorial so it is very accessible: B. Ohler, "Application Note #94: Practical Advice on the Determination of Cantilever Spring Constants," in Veeco Application Notes. vol. http://www.veeco.com/library, 2007. Comparison of two dynamic methods: B. Ohler, "Cantilever spring constant calibration using laser Doppler vibrometry," Review of Scientific Instruments, vol. 78, pp. 63701-1, 2007. http://dx.doi.org/10.1063/1.2743272 Here is another comparison, although I believe that Cook (cited by Rob above) notes that they used some inaccurate parameters when implementing the Thermal method. I believe that I have heard this study cited widely because they found significant differences between the spring constants obtained in air and water. N. A. Burnham, X. Chen, C. S. Hodges, G. A. Matei, E. J. Thoreson, C. J. Roberts, M. C. Davies, and S. J. B. Tendler, "Comparison of calibration methods for atomic-force microscopy cantilevers," Nanotechnology, vol. 14, pp. 1-6, 2003. http://dx.doi.org/10.1088/0957-4484/14/1/301

Response from: carpick

Shaw et al., titled "SI-Traceable Spring Constant Calibration of Microfabricated Cantilevers for Small Force Measurements". http://www.springerlink.com/content/231q7614xp704311/

Response from: maclaren

Precision and accuracy of thermal calibration of atomic force microscopy cantilevers, E. J. Thoreson, J. R. Pratt, D. B. Newell, N. A. Burnham. Rev. Sci. Instrum. 77, 083703 (2006). http://link.aip.org/link/?RSINAK/77/083703/1

Response from: carpick

Tilt compensation paper by Cannara; Cantilever tilt compensation for variable-load atomic force microscopy Cannara, R.J.; Brukman, M.J.; Carpick, R.W. Source: Review of Scientific Instruments, v 76, n 5, p 53706-1-6, May 2005 http://link.aip.org/link/?RSINAK/76/053706/1

Response from: carpick

Other papers on tilt issues related to cantilever calibration: Comment on tilt of atomic force microscope cantilevers: Effect on spring constant and adhesion measurements Hutter, Jeffrey L. Source: Langmuir, v 21, n 6, p 2630-2632, March 15, 2005 Heim, L.-O.; Kappl, M.; Butt, H.-J. Langmuir 2004, 20, 2760- 2764.

Response from: oarnould

There is an online article from J.L. Hutter http://www.physics.uwo.ca/~hutter/afmcal.shtml

Response from: oarnould

And an online calibrater with the Sader method (in bending and torsion) http://www.ampc.ms.unimelb.edu.au/afm/calibration.html

Response from: carpick

This came up in the discussion of photodetector sensitivity: Lateral force calibration in atomic force microscopy: a new lateral force calibration method and general guidelines for optimization Cannara, R.J.1; Eglin, M.; Carpick, R.W. Source: Review of Scientific Instruments, v 77, n 5, 53701-1-11, May 2006 http://link.aip.org/link/?RSINAK/77/053701/1

Response from: oarnould

A paper on lateral spring constant calibration : N. Morel, M. Ramonda, Ph. Tordjeman, Cantilever calibration for nanofriction experiments with atomic force microscope, Appl. Phys. Lett. 86, 163103 (2005); DOI:10.1063/1.1905803 http://link.aip.org/link/?APPLAB/86/163103/1

Response from: billly

One paper on Sensitivity of Optic level AFM to correlate the displacement of cantilever and Beam Power received by Photodiode. Useful for determining sensivities between the static and dynamic AFM: Tilman E. Scheffer and Harald Fuchs, Optimized detection of normal vibration modes of atomic force microscope cantilevers with the optical beam deflection method, J. Appl. Phys. 97, 083524 (2005); DOI:10.1063/1.1872202 http://link.aip.org/link/?JAPIAU/97/083524/1

Response from: kholkin

Hi All: I would like to post our recent references that may guide on PFM principles: A. L. Kholkin et al.,Nanoscale piezoelectric characterization of polycrystalline ferroelectrics, J. Electroceram. 19, 81 (2007). A. L. Kholkin et al., Review of ferroelectric domain imaging by Piezoresponse Force Microscopy, in Scanning Probe Microscopy: Electrical and Electromechanical Phenomena at the Nanoscale, Eds. S. Kalinin, A. Gruverman, Springer, 2006, V. 1, pp. 173-214. A. Gruverman, A. L. Kholkin, Nanoscale ferroelectrics: processing, properties and future trends, Rep. Progr. Phys. 69, 2443 (2006). N. Pertsev et al., Dynamics of ferroelectrics domains in BaTiO3 ferroelectric thin films via piezoresponse force microscopy, Nanotechnology 19, 375703 (2008). I. K. Bdikin et al.,Domain dynamics in piezoresponse force spectroscopy: quantitative deconvolution and hysteresis loop fine structure Appl. Phys. Lett. 92, 182909 (2008). A. Kholkin

Response from: gruverman

Greetings! PDF copies of PFM papers (reviews and contributed, recent and not so recent) can be found here: http://physics.unl.edu/~agruverman/publications.shtml

Response from: sergeikalinin

In addition, follwoing references can be useful: General short review on bias-induced phase transitions: S.V. Kalinin, B.J. Rodriguez, S. Jesse, P. Maksymovych, K. Seal, M. Nikiforov, A.P. Baddorf, A.L. Kholkin, and R. Proksch, Local Bias-Induced Phase Transitions, Materials Today 11, 16 (2008). General aspects of electromechnics in nanoscale systems: Sergei V. Kalinin, B.J. Rodriguez, S. Jesse, B. Mirman, E. Karapetian, E.A. Eliseev, and A.N. Morozovska, Nanoscale Electromechanics of Ferroelectric and biological Systems, Annu. Rev. Mat. Sci. 37, 189 (2007). Some instrumental aspects of PFM: Sergei V. Kalinin, A. Rar, and S. Jesse, A Decade of Piezoresponse Force Microscopy: Progress, Challenges, and Opportunities, IEEE Transactions on Ultrasonics and Ferroelectric Materials 53, 2226 (2006). Resolution in PFM and contrast at walls: A.N. Morozovska, S.L. Bravina, E.A. Eliseev, and Sergei V. Kalinin, Resolution-function theory in piezoresponse force microscopy: Wall imaging, spectroscopy, and lateral resolution, Phys. Rev. B 75, 174109 (2007) PFM contrast in anisotropic materials (for standard and dipolar tips): E.A. Eliseev, Sergei V. Kalinin, S. Jesse, S.L. Bravina, and A.N. Morozovska, Electromechanical Detection in Scanning Probe Microscopy: Tip Models and Materials Contrast, J. Appl. Phys. 102, 014109 (2007).

Response from: dawnbonnell

another of Andrei's papers V. V. Shvartsman, A. L. Kholkin, Investigation of switching behavior in PbZr0.45Ti0.55O3 thin films by means of Scanning Probe Microscopy, Ferroelectrics 286, 291 (2003).

relevance of d33 in resonance enhanced PFM?

steef — Sun, 17 May 2009 13:34:16 -0400

Response from: sergeikalinin

The signal at the resonance (maximal amplitude) is the sum of d33 and electrostatic component. For stiff cantilever and tip and surface potentials approximately equal, it will be d33 Q, where Q is a quality factor. The caveats are: - generally the Q factor is unknown and is position dependent - and standard methods (e.g. based on analog phase locked loops) cannot trace the resonance in PFM. AN dresonance frequency is strongly position dependent (resonance frequency can change by 100 kHz for peak wodth of 5 kHz) The theory of the frequency dependent PFM can be found in S. JESSE, A.P. BADDORF, and SERGEI V. KALININ, Dynamic Effects in Electromechanical Scanning Probe Microscopies, Nanotechnology 17, 1615 (2006). This paper also cites several works by C. Harnagea which explore this issue. Also, on Asylum web-ste there is a 24 page support note that discusses this issue (look http://www.asylumresearch.com). The frequency -tracking methods in PFM can be found in: S. JESSE, P. MAKSYMOVYCH, and SERGEI V. KALININ, Rapid Multidimensional Data Acquisition in Scanning Probe Microscopy Applied to Local Polarization Dynamics and Voltage Dependent Contact Mechanics, Appl. Phys. Lett. 93, 112903 (2008). B.J. RODRIGUEZ, C. CALLAHAN, S.V. KALININ, and R. PROKSCH, Dual-Frequency Resonance-Tracking Atomic Force Microscopy, Nanotechnology 18, 475504 (2007). STEPHEN JESSE, SERGEI V. KALININ, R. PROKSCH, A.P. BADDORF, and B.J. RODRIGUEZ, Energy Dissipation Measurements on the Nanoscale: Band Excitation Method in Scanning Probe Microscopy, Nanotechnology 18, 435503 (2007), There was also a very nice concept of two-stage cantilevers developed by Veeco and UCSB folks (you can find it by searching for. papers by B. Pittinger in APL)

PFM in liquid

nn admin — Thu, 07 May 2009 18:44:18 -0400

Response from: dawnbonnell

How can stray currents be eliminated when doing PFM in liquid? One could produce an insulated cantilever-tip with a small metallic end. Or one can operate at high frequency... but I am not convinced that a field can be sustained in that case. How do you do it?

Response from: sergeikalinin

High frequency helps (electrochemistry and diffusion are slow). Insulated tips is a good solution, but they are not commercially avauilable to my knowldge [there was work in ORNL-UT, Stanford, Harvard, LBL on parallel tracks to make them]. There is also company called Nauga Needles that makes something like this

Resonance-Enhanced PFM

nn admin — Thu, 07 May 2009 18:43:23 -0400

What are the advantages and pitfalls of resonance enhanced PFM?

high-resolution spectroscopic data

nn admin — Thu, 07 May 2009 18:42:22 -0400

How to acquire high-resolution spectroscopic data , and how to interpret it?

PFM image from cross-talk

nn admin — Thu, 07 May 2009 18:41:35 -0400

Response from: dawnbonnell

This is an important question. For several of these topics there may be one answer in terms of fundamental physics and an answer that is specific to a particular microscope design. I hope that we will discuss both.

Response from: dconklin

I understand that you would not want to use the softest cantilever to minimize the electrostatic interactions, but do you obtain different PFM responses from using cantilevers with various stiffnesses and can you use these different responses to obtain a more complete picture of the piezo-response?

Response from: sergeikalinin

Theoretically, cantilever stiffness hsould not affect PFM signal in th elow-frequency regime. This is generally true for 1-40 N/m cantilevers, while below 1 N/m electrostatics plays a role. In some cases (e.g. ferroelectric polumers or biomaterials) there is no chois ebut to use 0.03 - 0.1 N/m levers.

Response from: gruverman

There can be several indications that you are dealing with cross-talk. In case of polycrystalline films, if you see contours of grain boundaries in your PFM image it is most likely due to cross-talk. Similarly, if all grains appear in a bipolar state with phase boundaries being almost parallel in all grains - it is cross talk.

Response from: sergeikalinin

Generally, if PFM image "resembles" the error signal for topography it is a bad sign.

PFM on a microsope

nn admin — Thu, 07 May 2009 18:40:08 -0400

Response from: kholkin

Basically, any microscope working in the contact mode can be converted into PFM provided it is equipped with conducting cantilever, external lock-in amplifier and dc/ac voltage source. The ac signal from the photodiode is imaged along with the regular topography. Electrical cross-talk between input and output signals should be avoided.

Response from: sundamey

I have a Veeco multimode III. How can I convert it to PFM?

Response from: mbrukman

Sundamey: Does your NS III have the analog input BNC ports? Not even all NSIIa's have them. Without aux inputs, I think you'll be out of luck.

Response from: sergeikalinin

The easiest way to proceed is to make an alternative tip holder which will allow direct biasing of the tip (this will avoid capacitive cross-talk in older microscopes). But you still need to tap into photodiode signal (so you need a break box or equivalent).

Response from: sundamey

Where do I find the analog input BNC ports? On the controller?

Response from: dawnbonnell

Has anyone had success using 'all metal' cantilevers (such at the ones made by Clayton Williams company) for PFM?

Response from: sundamey

Sergei, Is the "break box" the same as the "exchange box"? I use this for non contact mode.

Response from: mbrukman

Yes, they're probably on the front panel of the nanoscope controller.

Response from: dconklin

When using a external lock-in, does it matter what the value of amplitude setting is when setting the reference signal. Say you put a 5V ac signal on the tip, what should you set the amplitude on the lock-in amp?

Response from: kkathan

I have an alternative tip holder which feeds from a BNC into a thin copper wire attached to the tip holder. Should I be concerned with noise through that thin copper wire? If so, how do you minimize the noise?

Response from: mbrukman

sundamey: break box = signal access module dave: to use the max. dynamic range of the LIA, I think you just want to use the smallest sensitivity value that doesn't overload, and then increase by one or two steps to give yourself some headroom so you don't saturate at a particularly active region during the scan.

Response from: dconklin

Matt: Actually what i was talking about was if you put a 5V signal onto the tip and into the "ref in", it detects the frequency and uses that frequency but then you can control the phase and amplitude for the reference signal and i'm wondering how the amplitude setting on the reference signal affects the output?

Response from: sergeikalinin

Difficult to say. In most cases, intrinsic noise for commercial AFM system is already pretty low (factor of 10 from thermomechnical limit). External noise depends on building, air handling system, etc.

Response from: mbrukman

So you use an external FG, and run that into the LIA "Ref IN" and what to know what you should spin the wheel in that panel to when you set the Amplitude? I think that particular amplitude is irrelevant when you use the Ref In BNC -- the Amplitude dial only controls the "Sine Out." When you use Ref In, the LIA decodes it and generates a digital internal sine wave of fixed amplitude (that the microscope never sees) which it then mixes with the with experimental input signal.

Response from: dconklin

That's what i figured, but just wanted to clarify since doesn't the phase you set on the reference signal affect the output?

Response from: proksch

KKathan, We measure the crosstalk (one important form of noise) by driving the potential of the tip when it is far from any surface and watching the deflection. Ideally, far from the surface you should see no signal at the drive frequency. If you do, this will be a background from which you will need to extract the small PFM signal. Since PFM signals are often on the order of picometers, even a small crosstalk can be a serious problem. The group at ORNL has worked very hard at eliminating this issue in a few other commercial microscopes, Sergei will know the references off the top of his head. Crosstalk can originate from many sources, including the drive signal coupling into the deflection measurement electronics and/or the "shake" piezo commonly used to mechanically excite vibrations in many microscopes.

Response from: dawnbonnell

Sergei, From your experience what are the primary differences in the way PFM is implemented on the most recent microscopes from different vendors? In terms of the electronics specifically.

Response from: kholkin

The phase you set in LIA is just a reference, i.e the the signal phase you measure is a difference between real phase and LIA settings. There is always an offset phase due to processing electronics that adds on the phase produced by the sample.

Response from: dawnbonnell

ok, anybody. Is PFM implemented the same way on all commerical microscopes in terms of electronics? Is it simply a matter of getting a signal to the tip and having internal lock-ins and functional generators? (this is a different question than who does the frequency sweeps and spectroscopy.

Static versus Dynamic calibration

tjacobs — Mon, 20 Apr 2009 15:42:11 -0400

Response from: akonicek

It would seem there are two main issues to consider. For dynamic calibration techniques, the environment the cantilever is in will change the behavior. Calibration done in air will yield a different result than that done in vacuum due to the viscous damping. The other consideration would be calibrating a cantilever with a dynamic method that you are using in contact mode for your experiment. The difference here would be the internal damping that occurs in the cantilever. It seems the best approach is to make sure you calibrate your cantilever in as close to the same environment and same type of nominal motion (static or dynamic) as your experiment.

Response from: carpick

Another point: all AFM's that use the laser beam reflection method (which is almost all of them) measure the slope of the end of the cantilever, not the deflection of the end of the cantilever. These are directly related to one another, but the relation is different for static end loading vs. dynamic oscillation with a free end (a factor 3/2 I believe). This is discussed in: Calculation of thermal noise in atomic force microscopy Butt, H.-J.; Jaschke, M. Source: Nanotechnology, v 6, n 1, p 1-7, Jan. 1995

Response from: carpick

Also, I shouldn't say: "AFM's ... measure the slope of the end of the cantilever". Rather, they measure the average slope of the region on which the cantilever is incident. This of course is not the same location of the tip, nor is it the end of the cantilever. This means that certain calibration methods require you to correct for the difference between the full length of the cantilever and the length to the tip, depending on what you have extracted from your calibration.

Response from: mattsallen

If done correctly (see the Cook et al reference), then the dynamic methods account for the differences in boundary conditions, the deformed shape of the vibrating cantilever, viscous effects, etc..., so I don't think this would be a huge issue. I think that the bigger issue is whether the cantilever obeys the assumptions made in the calibration and whether one knows the boundary conditions for the experiment (e.g. in the actual measurement, is the beam really acting as a cantilever with zero moment on the tip?).