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Galina Granek

Postdoctoral Fellow

Philosophy, University of Haifa

Email: granek(at)research.haifa.ac.il

Scanning Tunneling Microscopy (STM): A groundbreaking reliable invention or imagining surfaces?

This research focuses on an episode in the history of technology in which instrumental problems are pushed aside, and imaging processes take center stage. Scanning Tunneling Microscopy (STM) is a novel analytical method for space imaging of surface structures on the atomic scale which Gerd Binnig (b. 1947) and Heinrich Rohrer (b. 1933) of the IBM Zurich research laboratory discovered and developed in 1981-1982.

The goal of this research is to present the history of the STM, clarify historiographical issues, and relate them to historical-philosophical problems pertaining to concept formation and the role of error in experimentation. In particular, the issue of enhancement techniques for amplifying and displaying data electronically will be analyzed and discussed extensively.

Three major issues are addressed:

1) The STM evolved in 1979 - 1981 from Binnig and Rohrer's initial experiments with two conductors: one formed into the shape of a tip and the other was a conducting plate. The tip was mounted on a support moved by a "piezo-motor", and the plate was fixed on a "piezodrive". In 1999 Binnig and Rohrer described their instrument as "an electronic-mechanical hybrid: the probe positioning is mechanics, whereas the interaction is sensed by the tunneling current, which is of quantum mechanical origin". However, in 1982 the two researchers inverted the experimental arrangement: they made one plate act as a surface to be examined ( scanned ) and the other plate play the role of a tip. Binnig and Rohrer changed mechanically the roles of the "piezo-motor" and the "piezodrive"; they mounted the tip on the piezodrive, and fixed the surface to the support moved by the piezo-motor. Two instrumental elements facilitated this inversion: The piezo-motor became a "louse" responsible for the delicate approach of the tip to the sample, and the piezodrive--turned into a "piezoelectric tripod scanner"--could now perform mechanically the scanning. With the introduction of these changes, Binnig and Rohrer turned the instrument into a microscope and called it Scanning Tunneling Microscope.

It is not clear how exactly they came to the idea of transforming their tunneling testing instrument into an STM, displaying images of surfaces on the atomic scale. In 1999 Binnig and Rohrer descried the path to the STM as characterized by a "new appreciation of mechanics". The question then arises: Were Binnig and Rohrer also aware, back in 1981, of the need for a new evaluation of mechanics that could lead them from the first quantum tunneling junction to the second quantum tunneling mechanical microscope? In other words, what was the motivation for this dramatic change that eventually led to the award of the Nobel Prize?

2) It is evident from Binnig and Rohrer's early publications on the STM that what matters to them most was not so much the instrument itself. The principles of the instrument remained the same, while improving it was a patchwork, complicating what was already there. In fact, d uring 1982-1985 Binnig and Rohrer dedicated their enormous efforts almost singularly to imaging.

What is the motivation for this preference for imaging over improving the instrument? The images produced by the STM have revolutionized the new field of surface science, which till then had mainly dealt with systems containing a large number of atoms. The theoretical treatment of such complex systems was traditionally based on simplif ied concepts, averaging, and on neglecting microscopic structures. The STM finally enabled experimentalists to probe physical properties of surface science down to the scale of individual atoms. One could now correlate these physical properties with the microscopic structure of the surface. STM images were expected to reflect qualitatively the atomic surface structure. These surfaces were referred to as having "rounded top hills", "bumps", "ribbons", "flat terraces", "deep valleys", etc. New geographic-topographic terminology was introduced, and a theory of microscopic tunneling of the atomic scale was formulated. The STM has revolutionized the understanding of surface science in such a dramatic manner that Binnig and Rohrer almost "forgot" about improving the STM itself.

3) But there is a more profound lesson. What can we learn from the above preference on the way the scientific community reacts towards a novel technology? During the years 1982-1984 Binnig and Rohrer had the priority and exclusiveness of the STM in the market, both in terms of theory and material culture and they therefore did not bother to improve the instrument. They concentrated rather on the images, which indeed made the whole affair so exciting, and on convincing demonstrations, with which no other existing surface-science tool could then compete. We find that during 1982-1984 there is no prominent criticism of the instrument, and in this case it is not science in the making, but a "closed shop" of believers impressed by flashy STM images.

Is it the case that this lack of criticism during 1982-1985, which was complemented with amazing surface images, was the defining contributing factor to Binnig and Rohrer's ability to gain success in such a short span of time? Could we correlate the lack of criticism of the instrument and thus the non-improvement of the instrument during 1982-1985 with overlooking possible instrumental errors? This issue should be seen within a comprehensive historical-philosophical research devoted to the role of error in STM both on the instrumental level and in the production of images, and generally in enhancement techniques for amplifying and displaying data electronically.

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