- How to build a plastic AFM -- but can you pick up and move molecules like graphene?
Measurement with Rutherford backscattering spectroscopy
Design and Fabrication of a Rutherford Backscattering Spectrometer and its Use in Measuring Stopping Cross Sections of Aluminum Oxide for Charged Particles.
RBS page with photograph and diagram
RBS instrumentation tutorial
Rutherford backscattering
Harvard RBS page
RBS for thin film characterization
RUMP program- used in calculations of compositions
Quick picture of an RBS setup and two references:
Cherniak, D. J. (1995) Diffusion of lead in plagioclase and K-feldspar: an investigation using Rutherford Backscattering and Resonant Nuclear Reaction Analysis. Contributions to Mineralogy and Petrology, 120, 358-371.[pdf] The use of a 18 O tracer and Rutherford backscattering spectrometry to study the oxidation mechanism of NiAl.
Brenan, J. M., Cherniak, D. J., and Rose, L. A. (2002) Diffusion of osmium in pyrrhotite and pyrite: implications for closure of the Re-Os isotopic system. Earth and Planetary Science Letters, 180, 399-413.
Another short page on RBS
The theory behind RBS is that charged ions are incident upon a sample at energies on the order of MeV's. These ions penetrate the sample to varying depths depending on the type of beam, the type of sample, and the beam energy. A measurable amount of ions are then backscattered by atoms throughout the sample. Using a detector to collect the backscattered ions and their spectrum of energies, this information can provide a depth profile of each element in the sample. The schematic (above) shows the basic experimental setup. The incoming ion beam is passed through a series of microslits which reduce the beam spot size to several microns. This microbeam allows for local probing of non-uniform samples (such as integrated circuits).
Rutherford backscattering spectrometers bombard material specimens with helium ions. Like other systems, this setup requires the typical goniometer to load up samples into the vacuum chamber. Due to the design of these systems, there is this tendency for pulse pile-up to occur. The bombarding helium ions "backscatter" to the solid state detector (see the Harvard link above) and from this we can determine the mass of the atoms and ions in the material sample's surface. To generate the helium ions, the van de Graaff accelerator is used to produce the 2 MeV He+ ions. This involves an elastic scattering process of the helium ions off of the atoms and ions in the thin film being analyzed on the multiple "channels" of energy.
Ellipsometry manuals, tutorials, and an image
List of ellipsometry publications
Colorado State page on ellipsometry
Technische Universiteit Eindhoven brief overview page- discusses the use of ellipsometry as an active view into etching and thin film processes.
Spectroscopic Ellipsometry and Reflectometry: A User�s Perspective (Harland G. Tompkins, Jeffrey H. Baker, Steven Smith, Diana Convey)
When liner polarized light is incident to the film(s), the reflected light becomes ellipsoidally polarized. Ellipsometry determines the phase shift angle, usually abbreviated DELTA or shortly DEL, and the magnetite ratio of total reflection coefficients (Rp and Rs in the above equations). The magnitude ratio is given by angle PSI. Carefully-designed ellipsometry experiments provide a lot of useful information. The reflected light is so sensitive to the surface condition to study the behavior of surface atoms such as recombination and relaxation.The introduction on Wikipedia:
Upon the analysis of the change of polarization of light, which is reflected off a sample, ellipsometry can yield information about layers that are thinner than the wavelength of the probing light itself, even down to a single atomic layer or less. Ellipsometry can probe the complex refractive index or dielectric function tensor, which gives access to fundamental physical parameters and is related to a variety of sample properties, including morphology, crystal quality, chemical composition, or electrical conductivity. It is commonly used to characterize film thickness for single layers or complex multilayer stacks ranging from a few angstroms or tenths of a nanometer to several micrometers with an excellent accuracy.And in the image we see the very typical ellipsometer setup with the one area from which the photons are emitted, and then it hits the sample in the middle, and the light is elliptically polarized (or something) and goes to the light receiver for data storage and analysis. After quickly doing some searches over the WWW, it seems that this tool is largely based off of classical optical principles rather than an understanding of photons in terms of QED. What is "light polarization" in terms of quantum electrodynamics?
The scanning electron microscope is used to characterize surfaces via electrons thermionically emitted from some cathode (maybe of tungsten or lanthanum hexaboride (LaB_6) and accelerated towards an anode, or the electrons can be emitted via field emission. The electron beam has an energy ranging from a few hundred electron volts (eV) to 100 keV, and there are two condenser lenses to focus a beam with a very fine focal spot sized 1 nm to 5 nm. The beam is then further split with different objective lenses, causing the electron beam to be aimed at different locations at the same time. This allows for "raster" scanning (parallel scanning). The electrom beam exchanges energy with the sample and causes electromagnetic radiation, emission of electrons, etc., all of which can be compiled to form the final image. Backscattered electrons can be used to contrast different regions, or be used to form backscattered electronic diffraction ("EBSD") images. The resolution of the SEM is not as high as the TEM machines. Apparently there are some form of "Environmental Scanning Electron Microscopes" in existence that allow for samples to be scanned in environments ranging from 10 to 50 Torr, which is an interesting development because biological samples do not necessarily have to be cryogenically frozen in order to be scanned.
Notes on SEM
Early history and development of SEM
Milestones in the history of electron microscopy
Environmental Scanning Electrom Microscope (ESEM) history
- A simple scanning tunneling microscope for less than $100 USD
- [archived] STM for Students
- Build your own STM @ Advancedphysics.org forums
- Introduction to home brewing an STM
- An amateur scanning tunneling microscope
- Slashdot discussion on DIY build your own Scanning Tunneling Microscope (Vibration damping in STM, and a dupe)
- A significant portion of this content is blatantly stolen from http://www.e-basteln.de/index_r.htm. "All material on this site is Copyright © 1999-2006 Jürgen Müller, juergen@e-basteln.de ... Use for non-commercial purposes is granted free of charge, but I ask that you disclose the source and include a suitable copyright notice, and would appreciate if you let me know when you re-use this stuff."
- Joseph Gatt's amateur STM
An amateur design which has successfully provided scans, although not at atomic resolution to my knowledge. Joseph Gatt initially went for the design choices I was too timid to make: His original design used high voltage supplies/amplifiers (300V) and a slip-stick approach mechanism. The re-designed version now described on his web pages is closer to my concept. Besides describing electronics and software, Joseph's web site also also has information on tip etching and scan results.
- University of M�nster's student STM
While not exactly an amateur effort, the STM designed at the University of M�nster (Germany) is intended to be built and used in schools, and hence avoids hard-to-get or expensive components. The website describes a working STM, based on a piezo tripod scanner and the familiar 3-screw tripod for coarse approach. Feedback loop and tunneling junction parameters are controlled via analog electronics; a PC generates the scanning pattern and samples the scanned image via an AD/DA card. The web site includes mechanical drawings, schematics for the electronics and Visual Basic software. An atomic force microscope has been announced as the group's next project in 2002, but no information has been made available yet (2006).
- Jim Rice's Homebrew STM page
A widely known collection of background information, design considerations, and supplier listings for a home-built STM project. While the project has apparently not been completed, the page still has a load of helpful information. As I mentioned elsewhere, finding this page was what renewed my interest in building an STM. Recommended! Jim's original page has disappeared a few years ago. The link above points to a mirror of the latest state I know about (May 10, 1996).
- Peddie School STM project
An ambitious high-school project, the Peddie school's STM project started sometime in 1997. Very nice site with detailed accounts of their work in progress. Unfortunately, the project has apparently faded away, and after arelaunch of the school's website, only the archived copy linked to above remains.
- Glenn Durden's STM
A recent homebrew project, with the definite advantage of having reached a working prototype! No atomic resolution (yet?). The original web page has disappeared, hence the link above is pointing to an archived version at the internet archive.
- Adam Cohen's STM
Adam Cohen was a high-school student when he won the 1997 Westinghouse science talent search by building an STM from Lego bricks and clay (among other components, I reckon). No atomic resolution, apparently, but certainly an outstanding achievement considering the low-budget approach and his age! I could not find many technical details about this work and would appreciate pointers to more information.
- Uwe Treske's STM
Uwe Treske won a First Prize in the European Union's 2003 Contest for Young Scientists (see link above), and another one at the 2004 Intel International Science Fair, with his low-cost STM design. Not many details about design and performance of his instrument seem to be available on the web � the use of a PC sound card for signal acquisition, and Tungsten filament wire from lightbulbs as the tip wire, is mentioned frequently. Total cost of materials for a computer-controlled STM is quoted as 30 to 50 Euro or US$ in various sources! I would appreciate to learn more details.
- Literature
C. Julian Chen: Introduction to Scanning Tunneling Microscopy, Oxford University Press, New York/Oxford 1993
Best treatment of instrumentation aspects, very practical and detailed, including spectroscopy and AFM. Detailed section on theory; no applications. Nice scan examples showing the range of spatial scales that can be covered.Joseph A. Stroscio, William J. Kaiser (eds.): Scanning Tunneling Microscopy, Academic Press, Boston etc. 1993
Instrumentation chapter written by Sang-Il Park, with specific hints on getting an STM up and running, troubleshooting and optimization of scans, but not many details on design and construction. Comprehensive section on applications, but specializing in solid states physics, i.e. with a strong focus on cryogenic and vacuum applications.Chunli Bai: Scanning Tunneling Microscopy and its Application, Springer, Berlin etc. 1995
Short theory chapter. Instrumentation chapters are shorter than in Chen's book, but with a strong focus on tip preparation (including isolated tips for operation in fluid). Applications: 100 pages of solid state physics, 25 pages biological, 30 pages surface modification.R. Wiesendanger, H.-J. Güntherodt (Eds.): Scanning Tunneling Microscopy III, Springer, Berlin etc. 1996
Explicitly limited to the theory of STM and AFM. I have not managed to get hold of volumes I and II, which sound more interesting to me (I: Applications to metals, adsorbates, semiconductors, layered materials, superconductors; II: Applications in electro-chemistry, biology, scanning force microscopy, magnetic force microscopy, SNOM)Othmar Marti (Ed.): STM and SFM in Biology. Academic Press, 1993
Have not seen the complete book yet. I read and liked the instrumentation chapter (written by Marti himself), which used to be available on the internet, but I can't find it anymore. The book seems to have a strong focus on applications.Papers
Review of Scientific Instruments
Binnig G, Smith DPE: "Single-Tube Three-Dimensional Scanner for Scanning Tunneling Microscopy", Rev. Sci. Instrum. 57, 1688-1689 (1986)
The original paper on the piezo tube scanner. This original design does not drive the opposing electrodes with anti-symmetric voltages, as most later implementations do.Dhirani A, Fisher A, Guyot-Sionnest P, "A simple low-current scanning tunneling microscope", Rev. Sci. Instrum. 67 (8), 2953 (1996)
Hands-on description of the mechanics and pre-amplifier for a low-current STM (10 pA tunneling current). Uses slip-stick mechanics with two piezo tubes, and a Burr-Brown OPA128 with 1 GOhm feedback resistor as the current pre-amp.Kleindiek S, Herrmann K: "A miniaturized scanning tunneling microscope with large operation range," Rev. Sci. Instrum. 64 (3), 692-693 (1993).
Two-tube design - one for the scanning tip, one to support the sample. Sample can be translated via slip-stick motion; for coarse approach, the tip wire can be moved inward/outward via slip-stick motion as well. Very compact (1 cm³) and presumably thermally stable. This design, and a number of nano-drives based on the same slip-stick translator, have also been commercialized by Kleindiek and Klocke. See the link in the Commercial STMs section.Kuk Y, Silverman PV: "Scanning tunneling microscopy instrumentation", Rev. Sci. Instrum. 60, 165-180 (1989)
Review of principles and the full range of instrumentation aspects (vibration isolation, mechanics, feedback electronics, tip and sample preparation), as well as application examples. Many literature references. Good starting point!Nagahara LA, Thundat T, Linsay SM: "Preparation and characterization of STM tips for electrochemical studies", Rev. Sci. Instrum. 60, 3128-3130 (1989)
Describes how to make isolated tips for STM applications in conducting media. Tips are isolated with hot wax - looks like a procedure that could be carried out by the amateur. This could extend the range of applications accessible at room-temperature and ambient air.Pohl DW: "Dynamic piezoelectric translation devices", Rev. Sci. Instrum. 58, 54-57 (1987)
General discussion of inertial sliding (slip-stick) drives. Probably helpful if you want to build a coarse-approach mechanism using that type of design. See Pohl's Surface Science paper for a practical implementation.Park SI, Quate CF: "Theories of the feedback and vibration isolation systems for the scanning tunneling microscope", Rev. Sci. Instrum. 58, 2004-2009 (1987)
Analysis of feedback and vibration isolation, covering roughly the same terrain as Pohl's IBM Journal paper cited below. Like Pohl, they do not describe specific implementations, but clearly have a practical background.Park SI, Quate CF: "Scanning tunneling microscope", Rev. Sci. Instrum. 58 (11), 2010-2017 (1987)
Detailed description of a UHV-compatible STM design, complete with circuit diagrams for feedback, piezo drivers and stepper motor controller. Uses 700V to drive the piezos.Piner R, Reifenberger R: "Computer control of the tunnel barrier width for the scanning tunneling microscope", Rev. Sci. Instrum. 60, 3123-3127 (1989)
An early paper on a digital feedback loop, *very* detailed (and slightly outdated by now).Smith DPE, Binning G: "Ultrasmall scanning tunneling microscope for use in a liquid helium storage dewar", Rev. Sci. Instrum. 57, 2630-2631 (1986)
Compact STM with tube scanner and differential springs for reducing the coarse-approach motion. Looks like another good candidate for a home-built design.Stupian GW, Leung MS: "A scanning tunneling microscope based on a motorized micrometer", Rev. Sci. Instrum. 60, 181 (1988)
STM with a tube scanner and just a motorized micrometer screw for coarse approach (no further motion reduction mechanisms required).Chen YP, Cox AJ, Hagmann MJ and Smith HDA, "Electrometer Preamplifier for Scanning Tunneling Microscopy," Rev. Sci. Instrum. 67, 2652-2653 (1996)
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STM-specific optimization of electrometer pre-amplifiers (as an alternative to the widely used op-amp with large feedback resistor). Thanks to Mark Hagman for pointing this one out!Other journals
Besocke K: "An easily operable scanning tunneling microscope", Surf. Sci. 181, 145-155 (1987)
Four-tube design - one for the scanning tip, and three supporting the sample. Via slip-stick motion, the sample can be translated and height-adjusted (by rotating it's threaded carrier).Drake B, Sonnenfeld R, Schneir J, Hansma PK: "Scanning tunneling microscopy of processes at liquid-solid interfaces", Surf. Sci. 181, 92-97 (1987)
Mainly a report on operation of a standard STM (well, the tip and sample...) inside electrolytic solutions. Also shows an example of a simple and compact STM using the fine-pitch screw tripod for coarse approach.Fink HW: "Mono-atomic tips for scanning tunneling microscopy", IBM J. Res. Develop. 30, 460-465 (1986)
Field-ion microscopy was used to study and create mono-atomic STM tips. Not the ideal procedure for home-making tips...Hansma PK, Elings VB, Marti O, Bracker CE: "Scanning tunnelingmicroscopy and atomic force microscopy: Application to technology and biology", Science 242, 209-242 (1988)
Review, focusing on applications. Includes variations of the STM head design previously published by Hansma and co-workers.Lewis et al.: "Student Scanning Tunneling Microscope", Am. J. Phys. 59 (1), 38-42 (1991)
Low-budget STM, using a mechanical tripod approach and tube scanner design. Electronics described are purely analog, with sawtooth generators for scanning and an oscilloscope or x/y plotter to record the image. No atomic resolution intended.Pohl DW: "Some Design Criteria in Scanning Tunneling Microscopy", IBM J. Res. Develop. 30 (4), 417-427 (1986)
Discussion of mechanical stiffness, vibration damping, and feedback loops. Does not discuss specific implementations, but was clearly influenced by many discussions with STM-builders. (Well, it's from the IBM labs, where these things were invented after all.)Pohl DW: "Sawtooth nanometer slider: A versatile low-voltage piezoelectric translation device", Surf. Sci. 181, 174-175 (1987)
Short paper describing the actual implementation of a slip-stick sliding platform. This might be what the NanoSurf STM uses for coarse approach.Sears RK, Orr BG, Sanders TM: "A Scanning Tunneling Microscope for Undergraduate Laboratories", Computers in Physics 427-430, Jul/Aug (1990)
Describes overall design of an STM that should be within an amateur's reach. Analog feedback loop, scan control and image recording via computer. Manual approach using differential springs (screw compresses soft spring, which pushes stiff spring carryig the piezo tube; scale drawing of mechanics included). Atomic resolution. Paper is not "cookbook" style, but should provide a good guideline for a homebuilt design. Recommended!
Thanks to Razaq Babalola for providing a copy of this paper!
Image from this page on the TecnailF20 field emission transmissions electron microscope. In analytical use, the transmission electron microscope can be used to analyze the spectrum of energy lost when sending some beam of electrons through the material specimen. According to Wikipedia, in TEM machines the electrons are generated via thermionic discharge "in the same manner as the cathode in a cathode ray tube". In other words that's the Edison effect.
Thermionic emission (archaically known as the Edison effect) is the flow of charged particles called thermions from a charged metal or a charged metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. The charge of the thermions (either positive or negative) will be the same as the charge of the metal/metal oxide. The effect increases dramatically with increasing temperature (1000�3000 K).Then the electrons are accelerated via electromagnetic fields and these electrons are measured in volts per meter at this stage of the technique's process. Wikipedia also claims that heavy metals (think osmium, lead, uranium) can be deposited into the specimen to cause electron scattering at the locations of the depositions. However, it mentions nothing of the method of deposting heavy metals nor of how the electrons are accelerated towards the sample- what sort of electromagnets are used?
This page claims that magnetic lenses guide the electrons. And it mentions that there has to be some sort of fluorescent film underneath the specimen so that the electrons that do pass through can hit something. The darker regions on this film represent denser areas whereas the parts of the film that "sparkle" are where the electrons passed through without being absorbed by the material. I would imagine that passing too many electrons through the material specimen would be the equivalent of detailed microwaving: add more energy and eventually the structure will change. So how many passes through the TEM machine could any particular specimen handle?
X-ray diffraction techniques are based off of the diffraction pattern obtained from bouncing x-ray electrons through the ions in some molecule or crystal being studied, consequently resulting in photon emission from the newly placed electrons projecting it (in general) towards the photographic film or screen, making what is known as the diffraction pattern. And from this diffraction pattern one can determine an electron density map over the object. This is much easier in crystals with predictable internal structures. Apparently this technique is not useful for determining the position of hydrogen nuclei because of some need for excessive refinement to get good, reliable diffraction patterns.
Archives of the XRD instrumentation mailing list
A resource page for X-Ray Diffraction
High resolution X-ray diffraction (Paul A. Heiney)
2D X-ray diffraction simulator for crystallography
Tutorial on X-ray diffraction
USGS - X-ray powder diffraction (more at the X-ray analysis of a solid)
Interactive guide to diffraction
Some background on X-ray diffraction
X-ray diffractometers
X-ray diffractometers consist of an x-ray generator, a goniometer and sample holder, and an x-ray detector such as photographic film or a movable proportional counter. X-ray tubes generate x-rays by bombarding a metal target with high-energy (10 - 100 keV) electrons that knock out core electrons. An electron in an outer shell fills thehole in the inner shell and emits an x-ray photon. Two common targets are Mo and Cu, which have strong K(alpha) x-ray emission at 0.71073 and 1.5418 �, respectively. X-rays can also be generated by decelerating electrons in a target or a synchrotron ring. These sources produce a continuous spectrum of x-rays and require a crystal monochromator to select a single wavelength.
