STM

Scanning tunneling microscope (STM)

The scanning tunneling microscope (STM) is the research technology that is said to enable nanotechnology and is to this date probably the most effective and transformative nanotechnology, if only because it contributed to the transformation of research practice. The STM brings about a new instrumental concept in microscopy: near-field probing. It consists of approaching the object as closely as possible in order to pick-up the information at the surface of the sample. As one of the pioneers of probe microscopy relates, “traditional scientists shunned this method because its intimacy was seen as a violation of objectivity and distance, a gospel of 19th-century science and epistemology” (Gimzewski 2008, p. 260). The very functioning of the STM itself induces a ‘collapse of distance’ (Nordmann 2006).

Despite its name, the scanning tunneling microscope is an apparatus of manipulation as much as of observation – not only in the sense in which observation always requires some intervention, but more straightforwardly in the sense that it can be used to construct the structure that it then subjects to observation. The STM is both a tool and an instrument, or best: it is an interesting instrument because it is a tool (it individualizes some atomic features of the sample by establishing a sort-circuit between them and the atoms of the tip). And conversely, it is an interesting tool because it is an instrument (it enables collecting data of our intervention in the nanoworld under the form of “manipulation signals”). Finally, it brings together the sensory modalities of touch, hearing, and sight.1

Ian Hacking’s question whether we see through (or with) a microscope served to determine the standing of the instrument as an object entrenched in observational practices, especially by being calibrated to other observational tools (Hacking 1981).2 This entrenchment provides individual observers with a warrant regarding the trustworthy of their more or less inferential visualizations.

But what if we ask whether we see through a scanning tunnelling microscope? In answer to this question, another interesting feature of scanning probe microscopy becomes significant, namely its twofold calibration or immediacy. First of all, experimenting with the STM is always seeking immediacy: Probing in the near-field means going where the object is and recording the very immediate and local interaction of the object with the instrument’s tip. For the purpose of ‘explanation’ the ectoplasm-like images and the manipulation signals that constitute the rough data are then compared with those produced by a simulation of the whole experimental setup. These simulations use models that are calibrated to make theories fit with the experiment. They do not test theories. Rather, they simulate the interpretation of theories in a back-and-forth process with the experiment, until the two present a sufficiently satisfactory likeness.3 And secondly, once this interpretation is done, it is rendered user-friendly by producing a visual kind of immediacy: The rough image is reprocessed numerically with the kind of topographic software that is used in geography, simulation modelling and video gaming – this software is best suited for the representation of what goes on at the surface of a body. Atoms, molecules and surfaces are thus depicted as familiar objects with colours, shadows, foreground and background. Aside from providing the pleasure of experiencing a very familiar-looking space that stands ready to be colonised by nanotechnology, it stacks the deck in favour of inferences from the likeness of STM-images and the visualisations of computer simulations.

Tellingly, this twofold immediacy makes the STM conceptually even more complicated but perceptually even simpler than electron microscopy. In a recent interview, one of the inventors of the STM notes as the most striking feature of nanotechnology that for a new generation of scientists ‘playing with atoms’ has become perfectly straightforward (Binnig 2009) – because perceptual ease and ease of manipulation makes one forget the conceptually complicated inferential structure.

If one reconsiders the history of ‘seeing with microscopes’ one might say that much of it was concerned with realism or truth: Straightforward seeing is associated with seeing how things are, whereas a highly theory-laden and inferential mode of perception suggests that what we see is a construct of sorts.4 The reliability of a way of seeing – with the electron microscope, for example – was judged in comparison to apparently straightforward cases of immediate perception. Calibration, for example, provides a warrant to the effect that one can trust the microscope as much as one normally trusts one’s naked eyes. In contrast, the reliability of observations with the STM does not depend on representational features but on the technical robustness and performance of the system. Seeing with the STM cannot be likened to a human observer who confronts an outside reality and wonders whether a mental image provides a truthful representation – owing to the fact that the STM is an instrument of intervention as well as observation, a tool and an instrument, and due to its twofold calibration. Instead, the STM is coordinated with a multitude of other instruments and procedures and is judged by the way it agrees with and improves upon a whole system of observational and experimental techniques. Firmly entrenched in a variety of contexts and practices, the STM is not a method of seeing atoms on surfaces but an apparatus/world complex that affords perceptual and manipulative access to atoms and molecules on surfaces.5

Footnotes

  1. See Mody/Lynch 2010; Hennig 2006 and 2011; Soentgen 2006; Baird/Shew 2004; Shinn 2008.
  2. This and the next paragraph have been adapted from Nordmann 2010a.
  3. This first production of immediacy can be said to be ‘analogic’ in two senses: it is based on the STM’s operation as an analogue to sensing, and it takes recourse to analogies between the experiment and the model.
  4. To be sure, more sustained reflections of microscopy indicate that the question about realism and truth is based on a misleading dichotomy. For much instrument-aided observation one can say that it does not provide straightforward access to something given, but that it is not therefore an inferential construction of something constructed or contrived.
  5. Compare Rom Harré’s account of the difference between instruments that function like probes (the thermometer, the light microscope) and a complex of apparatus and world that makes a phenomenon available for research and development, for observation and intervention. As we saw above, he says of the latter complexes that they afford a thing or an activity (Harré 2003).

References

  • Baird, D. and Shew, A. (2004). Probing the History of Scanning Tunneling Microscopy. In: Baird, D., Nordmann, A., Schummer, J. (Eds.), Discovering the Nanoscale. Amsterdam: IOS Press, pp. 145–156.
  • Binnig, G. (2009). Interview Statesment. In: Expedition Zukunft/Science Express (exhibition catalogue). Darmstadt: Wissenschaftliche Buchgesellschaft, pp. 239 and 246.
  • Gimzewski, J. K. (2008) Nanotechnology: The Endgame of Materialism, Leonardo, vol. 41(3), pp. 259-264.
  • Hacking, I. (1981). Do we see through a microscope? Pacific Philosophical Quarterly, vol. 62, pp. 305–22.
  • Harré, R. (2003). The Materiality of Instruments in a Metaphysics for Experiments. In: Philosophy of Scientific Experimentation. Radder, H. (Ed), Pittsburgh, PA: University of Pittsburgh Press, pp. 19-38.
  • Hennig, J. (2006). Changes in the Design of Scanning Tunneling Microscopic Images from 1980 to 1990. In: Schummer, J. and Baird, D. (Eds.) Nanotechnology Challenges: Implications for Philosophy, Ethics and Society. Singapore: World Scientific Publishing, pp. 143-163.
  • Hennig, J. (2011) Bildpraxis. Visuelle Strategien in der frühen Nanotechnologie. Bielefeld: Transcript.
  • Mody, Cyrus C. M. and Lynch, M. (2010). Test Objects and other Epistemic Things: A History of a Nanoscale Object. British Society for the History of Science, vol. 43(3), pp. 423-458.
  • Nordmann, A. (2006). Collapse of Distance: Epistemic Strategies of Science and Technoscience. Danish Yearbook of Philosophy, No. 41, pp. 7-34.
  • Nordmann, A. (2010a) Philosophy of Technoscience in the Regime of Vigilance. In: Hodge, G., Bowman, D., Maynard, A. (Eds.), International Handbook of Regulating Nanotechnologies. Cheltenham: Edward Elgar, pp. 25-45.
  • Shinn, T. (2008). Research-Technology and Cultural Change. Instrumentation, Genericity, Transversality. Oxford: The Bardwell Press.
  • Soentgen, J. (2006). Atome Sehen, Atome Hören. In: Nordmann A., Schummer J., Schwarz, A. (Eds.). Nanotechnologien im Kontext. Philosophische, ethische und gesellschaftliche Perspektiven. Berlin: Akademische Verlagsgesellschaft, pp. 97-113.