Binnig & Rohrer: Paper1 (Applied Physics Letters, 40 (1982), 178-180):Binnig and Rohrer kept up a schedule of one paper in physics journals every 4-6 months for the first few years and then slowed down to one paper every 8-10 months. In their first publication, Binnig, Rohrer, Gerber and Weibel (the last two were Binnig and Rohrer's personal technicians) address precisely such doubts. They worked in ultra-high vacuum. They employed a very fine piezo drive that had been developed by Binnig in-house in 1979 (IBM Technical Disclosure Bulletin, 22 (1979), 2897). But the piece-de-resistance was a mechanism eliminating vibrations by suspending tip and sample using superconducting levitation. This mechanism was fancy and impressive but immediately showed itself to be cumbersome. For example, superconduction only works at very low temperatures and so the conditions under which the scanning was to take place included extremely low temperature and on a magnetically levitating sample. Binnig and Rohrer gave up the superconducting levitation almost immediately. Nonetheless, this mechanism served an important rhetorical purpose. Most scientists would have expected that only an extraordinary device could have eliminated the extraordinary vibrational problems attending the positioning of macroscopic materials within an atomic distance of each other. Binnig and Rohrer have noted that long after they had abandoned the superconducting levitation, this was the piece of equipment that other scientists remembered. Until the advent of the STM there was an awe of atomic dimensions (cf. Binnig in our interview, members may click here), so that everyone, including Binnig and Rohrer themselves, thought that achieving atomic resolution must require extraordinary means. In retrospect we know that an STM can be supremely simple in comparison with this first, levitating design.The main evidence for the atomic precision of the positioning was that the current measured across the gap varied exponentially with the vertical movement of the tip (that is to say perpendicularly to the surface under investigation). Such an exponentiality is what one expects in quantum tunneling and this tunneling is the only ready explanation. (Most quantum mechanics textbooks calculate the Schrödinger equation of a wavefunction of a particle coming from the left and encountering a potential barrier, whereupon a part of the wavefunction continues into the classically forbidden barrier and beyond. The transmission to the right of the barrier constitutes the tunneling. Within this scheme, it is not difficult to calculate the exponentiality of the transmission as a function of the width of the barrier. There is a website visualizing this tunneling.) So, the argument was that vacuum tunneling had been successfully carried
out, something which in the past had failed because of inadequate suppression
of vibrations.
This page was last updated on 15 May 2001 by Arne Hessenbruch. |
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