STMFeynman Machines FMs

STMs utilized to implement Feynman's ideas concerning atomic and molecular level fabrication and machining (Feynman machines: "FMs") have been dubbed by Schneiker as "STM/FMs."

Feynman had noted the possibility of doing chemical synthesis mechanically. In an effort to move in this direction, Schneiker (1986) proposed the following STM experiments (Figure 10.11). 1) Use an STM tip to move a pair of adatoms (or molecular fragments) on a substrate (or STM tip) together so as to induce chemical bonding. 2) Use an STM tip to cleave a chemical bond of a molecule adsorbed on a substrate. 3) Use an enzyme or synthetic catalyst adsorbed on an STM tip to repeat experiments (1) and (2).

Figure 10.12: Nanomilling/nanolithography. By Conrad Schneiker (Schneiker, 1986).

Perhaps the first step in such ambitious proposals has already been accomplished. The Bell Labs group (Becker, Golovchenko and Swartzentruber, 1987) used an STM tip to place a single atom on a germanium surface. Further STM/FM modifications and applications elucidated by Schneiker (1986) include: 1) tip shape modifications (scalpel, chisel, cylindrical, and other configurations) for scanning, scribing, etching, milling, and polishing operations or for electrical interfaces, electrochemical synthesis or machining, 2) attached tip structures (enzymes, synthetic catalysts, shape selective crown ethers, transducer molecules, etc.) for molecular recognition with species selective (and perhaps electrostatic or electromagnetic assisted) pick, place, join, and cleave operations, or nano-environmental sensing, 3) multiple tip configurations (parallel or radial configurations) for use as ultraminiature tweezers, jigs, and arcs or interface electrodes, or to generate rapidly rotating electric fields, and 4) tip materials modification (insulating, semiconducting, ferroelectric or ferromagnetic) for electrostatic, electromagnetic, magnetic, kHz-GHz acoustic (longitudinal, transverse, or torsional) and optical modulation in mono-or multi-polar configurations (Figures 10.12 and 10.13).

Figure 10.13: Nanoscale view of STM nanomilling/nanolithography. By Paul Jablonka (Schneiker and Hameroff, 1987).

In addition to the above modifications, STM/FMs or their tips could be augmented with a wide variety of sensors and transducers; the atomic force microscope of Binnig, Quate and Gerber (1986) is an excellent example. The augmentation of STM/FMs with fiber optic interferometers (or comparable techniques) could provide extremely accurate realtime calibration of absolute and relative STM/FM tip positioning, thus overcoming the problems of electrical noise, creep, ageing and hysteresis inherent in present STM piezo-positioning systems. The technique given in Dietrich, Lanz and Moore (1984) for making tips with uniform tip-to-base conical profiles would be useful for STM/FMs using closely spaced multiple tips. Schneiker conjectures that properly configured and instrumented sets of STM/FMs can operate as machine tools with effectively perfect lead screws and bearings. STM/FMs also can be used as sub-atomic resolution proximity detectors and coordinate measuring machines on conducting surfaces (AFMs would be used for insulators) to monitor nearly perfect superaccurate nanomachining operations (limited by the graininess of atoms and other materials science considerations). Many useful macroscopic mechanical structures and mechanisms may thus be duplicated at the submicron level, and many of these mechanisms may require no lubrication due to force/area scaling and very rapid heat dissipation (Feynman, 1961). For even smaller mechanisms, a switch to Feynman's mechanical chemistry approach would be needed to build up molecular devices in a series of joining and trimming operations. Many presently existing synthetic molecules could be utilized as building blocks; the molecular gear and bearing system of Yamamoto (1985) provides an interesting example and is thought to be capable of rotating about a billion times a second.

STM/FMs may execute many complex mechanical motions for driving such nanomechanisms (Schneiker, 1986). For instance, an essentially infinite series of three dimensional tip motions (single straight lines, circles, spirals, helices, etc.) can be made at speeds presently limited mainly by mechanical resonances in the driving system of current STMs-another motivation for miniaturizing them considerably. Thus it would be possible, for example, to turn a molecular scale mechanical crank (say of 2 nm diameter) at thousands of revolutions per minute. Similar to flagella and cilia of single cell organisms, these could be used for propulsion of nanoscale robots and other uses.

The capabilities of STM/FMs have been heretofore nonexistent; therefore applications may abound in the near future as scientists in many disciplines become aware of this versatile and inexpensive technology.

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