Materials Research Activities


Binnig & Rohrer: Paper 2 (Physics Review Letters 49 (1982), 57-61):

The next publication, by the same four authors, combined the tunneling effect with scanning. STM was now tried out on surfaces of CaIrSn4 and Au samples, and they argued that the STM may be applied to two areas: 1) surface studies generally, incorporating space-resolved tunneling spectroscopy, microscopy of adsorbed molecules, and crystal growth; and 2) to fundamental aspects of tunneling. This second area highlights the fact that for the next two years Binnig and Rohrer struggled to achieve a more sophisticated understanding of the tunneling current than the one-dimensional potential barrier calculation of quantum physics textbooks. Rather, the work functions (energy levels) of tip and sample atoms somehow determined the current, and as our interview with them makes clear, this is in fact how they initially thought about the problem. At this stage, Binnig and Rohrer identified such a contribution to the current as a disturbing factor that could be isolated by using high-frequency modulation of the gap length during scanning. (Why these samples? Gold was commonly used in surface science, but we need to know more about the status of these materials in 1982. Can you help?)

How to convince others of the correctness of STM measurements? One way was to compare information gleaned on the surface under investigation with that from other instruments and tools. Binnig, Rohrer, Gerber, and Weibel first used low-energy electron diffraction (LEED) experiments for this purpose. Of course, LEED does not actually measure the same kind of thing as STM; for example while diffraction experiments show results of interactions at the atomic level they necessarily average over these interactions. And diffraction also requires that you infer the material structure from a scattering pattern. By contrast, the claim for the STM was that it revealed individual atomic structures and in real-space (no inference, no Fourier transformation). Hence, there is a limit to the evidential support that the STM could gain from LEED, but the comparison could at least show that STM was not pure imagination. One might wonder what the actual set-up was that allowed simultaneous investigation with STM and LEED? One presumable keeps the sample still, while utilizing STM and LEED one after the other. Sounds straightforward, but was it? The authors did not test their results against sample analyses with other techniques. They merely stated that the STM had greater resolution than the scanning electron microscope (orders of magnitude better), and did not destroy the sample as field ionization microscopy would do.

  • Introduction to Binnig & Rohrer's 1981-1986 publications
  • Paper 1 (Applied Physics Letters 1982)
  • Paper 2 (Physical Review Letters 1982)
  • Paper 3 (Surface Science 1982)
  • Paper 4 (Helvetica Physica Acta 1983)
  • Paper 5 (Surface Science Letters 1983)
  • Paper 6 (Physica 1984)
  • Paper 7 (Surface Science 1984)
  • Paper 8 (Surface Science Letters 1985)
  • Paper 9 (Europhysics Letters 1986)
  • Paper10 (Scientific American 1986)
  • Interview with Binnig and Rohrer, to be featured soon - members may click here.

This page was last updated on 15 May 2001 by Arne Hessenbruch.