Binnig & Rohrer, Paper 3 (Surface Science, 1982):With their third paper (received 30 September 1982), Binnig and Rohrer went straight to the community that mattered most for the acceptance of the STM: surface scientists. The fact that the two technicians, Gerber and Weibel, were now not co-authors may signal that this paper did not focus upon the instrument itself but rather upon its results: images of surfaces. The two previous papers had been published in Applied Physics Letters and in Physical Review Letters, but this paper was sent to Surface Science. Binnig and Rohrer examined several surfaces (Au(110), Si(111), GiAs(111), and Au islands on Si) providing evidence for and against the proposed models for each of these surfaces. They claimed a vertical resolution of less than 1Å and a lateral resolution of a few Å. Again, they argued that vacuum tunneling results need to be compared against results performed on the same samples using different techniques. Again, this is the best (only?) way of showing reliablity of a new instrument; but the point is also to placate hostile adherents of other techniques who felt threatened that their expertise would now be rendered useless (more on this in the interview with Binnig and Rohrer -members may click here). Queries: why these sample surfaces; who were the main investigators of these surfaces at the time; what was the state of play; and how did the STM impinge upon their work?
The cumbersome superconducting levitation was replaced by a less complicated,
but also less flashy, vibration absorber: a two-stage spring system. This
was a much simpler solution and facilitated experimentation. But incredulous
readers who in the first place doubted the feasibility of operations on
an atomic scale may not have been assuaged by the ordinariness of the
apparatus. Despite the simplificationl, the apparatus was still far from
off-the-shelf mundanity. Binnig and Rohrer worked in an ultra-high vacuum
and they had some trouble with the calibration
of the piezodrives (using a capacitance dilatometer), the error of which
they adjudged to be under 5%. And they had problems replicating their
own scans. In their opinion, the tip constituted the main problem. They
suggested that the atomic configuration might change in the course of
the experiment, for example when high electric fields were applied. And
they reiterated that the STM detected a mix of topography and work functions,
and that the two could be separated. Furthermore, they now referred to
a need for a theory of tunneling in small non-planar geometries. The quantum
physics textbook example of exponentiality of tunneling current with the
width of the rectangular potential barrier is an idealized and simplistic
geometry that may not apply to the complex local geometry around the tip
and sample. In the interview, they elaborate on the role of theory in
convincing doubting Thomases.
This page was last updated on 15 May 2001 by Arne Hessenbruch.