Since I started on my own STM, a number of individual and school or university projects on STM building have become available on the web. While I have not heard about any atomic-resolution STM successfully built by amateurs yet, several designs have reached the stage of producing scanned images.
An amazingly simple and low-cost design aiming for atomic resolution. It uses a "unimorph disk scanner" for X/Y/Z motion, invented by John (patent US 5866902). The scanner can be made from a $2 piezo buzzer, and will give scan ranges on the order of 1µm using just +/- 9V drive voltages from two 9V batteries!
John's design appears to be essentially complete and has taken scans. Complete electronics schematics and a few photographs of the mechanical setup are available. The schematics cover a "core" design with analog feedback loop, requiring an external scan signal generator and an oscilloscope for observing the signal. Adding computer control via a few D/A and A/D converters should be easy enough, if desired.
John used to work for ThermoMicroscopes (so he sure knows what he's doing!), but this design is his own, and apparently intended to be available for non-commercial use. Highly recommended!
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.
While not exactly an amateur effort, the STM designed at the University of Münster (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).
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).
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.
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, www.archive.org.
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 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.
There used to be dozens of companies building commercial STMs and other scanning probe microscopes, but the number was reduced by several rounds of mergers and takeovers. I'm listing a few whose websites provided information I found useful for my project.
Probably the big name in commercial STMs and AFMs today, Veeco has absorbed some other big players over the last few years – including Digital Instruments and ThermoMicroscopes, which was in turn formed by integrating Park Scientific Instruments and TopoMetrix. Digital Instruments' original NanoScope design, still available as the Multimode SPM, is probably the most popular scanning probe microscope worldwide.
Veeco's website has a nice introduction to scanning probe microscopy, the "Practical Guide to SPM", available as a PDF file. Extensive bibliography lists on SPM are offered as well. Last time I checked (2006), these were in the section Products–AFM/SPM–Library. There are also a large number of application notes (which don't give too many technical details away, though) under Products–AFM/SPM–App Notes, and a very nice picture gallery, under Products–AFM/SPM–Nanotheater.
A small Swiss company, founded by graduates of the Güntherodt group at Basel University. Their initial product, the EasyScan STM, was a compact and elegant design with atomic resolution but limited flexibility, apparently targeted at the educational market. This has evolved into a family of modular STM and AFM systems. Nanosurf used to have a nice tutorial on how to make your first scans with their STM, available as a PDF file – now probably hidden in the section reserved for registered users. Maybe still available upon request? Their control software is still available for download, and can be used in a "simulation" mode without the microscope connected. The Applications section has a number of nice examples of what to do with an STM under ambient conditions.
Klocke and Kleindiek seem to have co-operated in developing the dual-tube mini STM. Both are active in the field of micro-manipulation with their own companies, offering nano-translators using piezo elements and slip-stick motion. Klocke Nanotechnik also offers the dual-tube STM and other scanning probe microscopes.
A company co-founded by Jim Rice, the author of the "Homebrew STM page" mentioned below. They intended to build an "affordable STM with atomic resolution", to be available in April 2000. However, in October 1999 Jim Rice has posted a note to the sci.nanotech newsgroup, explaining that AngstromTools is not active any more due to lack of funding. He offered all his STM components and instrumentation to any interested party who would have another go at completing the design and making it available (for free) to the public. Never heard about the outcome, though. Their website has long since disappeared, so the link above points to an (incomplete) copy at archive.org.
Manufacturer of scanning probe miscroscopes, specializing in AFMs. They have a number of helpful, although not too detailed, technical and application notes online. Mark Hagman pointed out their implementation of a clever driving scheme he suggested for the piezo scanner, to allow scanning operation at the resonant frequency (see Quesant's technical note).
The place where I got my piezo tube(s). I chose them because they had the best price (Canadian $100), but also got great service: They sent a very useful brochure on general piezo terms and properties, and they were extremely helpful when something went wrong with the shipping. (For some reason, the German postal service decided they did not know me and returned the package to Canada...) Also, they included an extra piezo tube free of charge! (I understand they make an extra tube in case something goes wrong in the manufacturing process, and were kind enough to let me have it.) Highly recommended!
Staveley used to offer decent piezo data sheets for download; their quote for 'my' piezo tube, as described in the Mechanics section, was US$ 122. This was years ago, and Staveley has since been acquired by Olympus. They don't seem to offer individual piezo elements any more, unless this offering is hidden somewhere deep down in their large web site.
Yet another supplier. Their quote for 1 piezo tube was US$ 500(!!). They have apparently re-organized since I was in touch with them: The sister company specializing in piezo materials (link above) now has a very informative web site with a large set of technical notes.
New Focus makes clever opto-mechanical mounts and opto-electronics products, mostly for research applications. I know (and like) them since I work in optics, which is why I bought the precision screw-and-nut sets for the STM's approach mechanism there. I guess there are many other suppliers for similar screws; theirs have 80 threads per inch and are available with knurled knobs or Allen key receptacles. They handle mail orders worldwide.
Manufacturer of the "CircuitWorks" products, including the conductive epoxy glue I used to contact the piezo tube. (CircuitWorks Conductive Epoxy CW2400). I ordered the epoxy from RS components, by the way.
Burr-Brown used to manufacture a wide range of precision op-amps, including the OPA111, OPA124 and others suitable as tunneling current pre-amps. Also the manufacturer the OPA445 I used as a +/- 40V piezo driver, as well as many other precision or specialised analog ICs. Full range of data sheets on the web site, plus some good application notes, e.g. on high-amplification transimpedance amplifiers (read STM pre-amps, photocurrent amplifiers etc.)
Texas Instruments has acquired Burr-Brown in August 2000. While the Burr-Brown name has disappeared, the products and their names seem largely unchanged. Check the section on 'Amplifiers and Linear' on the TI website.
Integrated-circuit manufacturer with a strong focus on mixed digital/analog ICs. I used their MAX542 D/A converter and the MAX195 A/D converter. As usual, all datasheets are available as PDF files.
Motorola has spun out its semiconductor business under the the Freescale name in 2004. The 56002 DSP is no longer manufactured, but the 'Support–Documentation' section of Freescale's web site still gives plenty of documentation when searching for 'DSP56002' (as of April 2006). Freescale continues to offer DSPs and evaluation boards, but I have not looked into the newer products' specs and pricing.
Specialising in high-voltage op-amps. These things look really tempting, but the price turns out to be out of range for an amateur (on the order of $100 apiece, if I remember correctly). Still interesting to see what's available – check out the section 'Linear Amplifiers–View by Voltage' for a start. The 'Support' section also has a good range of application notes, some specifically discussing how to drive piezos.
International distributor of electronic components, tools etc. Not exactly cheap for most items, but they will sell small quantities, also to private customers. (Maybe it's different in other parts of the world, but in Germany, several specialized electronics distributors sell to commercial customers only.) They have branches around the world, often with web sites and local versions of the catalog. The current German catalog comprises 2 Volumes of more than 1000 pages each; or one CD ROM.
This section lists some software tools I found helpful. Please note that the Software page also contains some information on third-party software, namely image processing packages.
A handy shareware program implementing an oscilloscope, spectrum analyzer, wobble frequency generator and automatic measurements of frequency-dependent amplitude and phase, all via a PC sound card. I do have a "real" oscilloscope (which I would deem a necessity for the STM electronics development), but none of the other equipment. I have used the frequency-plots to characterize the piezo resonances, and intend to use them on the current pre-amp and the complete feedback loop as well. With basic sound cards, everything is limited to the audio range of frequencies, of course, but that is fine for the bandwidth and scan rates obtainable in an STM. With high end sound cards, sample rates up to 192 kHz are supported.
The AudioTester works with full-duplex, 16 or 24 bit sound cards. The unregistered version has full functionality but runs for a limited time per session. Registration fee is EUR 35. HPW-Works is another shareware performing similar functions, with extra functionality in the professional versions. Prices range from US$ 69 to approx. US$ 300 for the full-blown version.
Unfortunately, the complete C compiler and linker, that used to be available for free from the Motorola DSP website seems to have disappeared. I have not used that software, since I sticked with the assembler included in the evaluation kit. Some hints and simple coding examples for the C compiler are available from the KC7WW C programming examples.
That link to KC7WW is pointing to the FTP archive accompanying EA2BAJ's Ham/DSP page. The Motorola DSP56002 used to be quite popular in amateur radio circles. Probably the best starting point is TAPR, the Tucson Amateur Packet Radio association. They have organized a group purchase of DSP56002 evaluation boards a while ago, and have developed a range of ham radio applications for that DSP. Their site also features a nice introductory article on the 56002 evaluation board, also by Johan Forrer, KC7WW.
LabView is a graphical software development system for "virtual instruments": You combine building-blocks like control knobs, a wide selection of displays, and internal "math" blocks, and "wire" them by defining connections, i.e. the data flow between these blocks. I'm thinking about using it for the host PC software, since the current version comes with a nice range of 3D graphics displays.
LabView is expensive, but a LabView student edition, based on LabView 8, is available. It is published by Prentice-Hall, and is hence available from bookstores for around US$90. I am not sure whether there are functional restrictions in the student version. — As mentioned on the software page, I will probably use C++ instead of LabView to implement the PC software for the STM user interface. A matter of personal taste, I guess, so I'll keep the pointer to LabView here.
|Suppliers: Tip and Sample Materials|
Suppliers of microscope laboratory supplies. As part of their "Studen-Tek" series, they offer cheap HOPG (highly-oriented pyrolytic graphite, the STM researcher's guinea pig). I also obtained some PtIr wire from them, which I intend to use for the tip.
Supplier of high-purity materials; recommended by Michael Vogelgesang for both tip and sample material. Michael points out that they offer a wider selection than what's listed on their web site, and that they have competitive prices. The web site has good information on the subset of materials that it does list, but that don't seem to include the 'usual suspects' for STM users, like typical tip wire materials.
Hardly an insider's tip, Goodfellow is probably the best-known supplier of specialty materials for the physical sciences. Very wide selection, good online information – but rather expensive.
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Chunli Bai: Scanning Tunneling Microscopy and its Application, Springer, Berlin etc. 1995
R. Wiesendanger, H.-J. Güntherodt (Eds.): Scanning Tunneling Microscopy III, Springer, Berlin etc. 1996
Othmar Marti (Ed.): STM and SFM in Biology. Academic Press, 1993
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