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PLV: Plenarvorträge

PLV I

PLV I: Plenarvortrag

Montag, 17. März 2025, 08:30–09:15, H1

Seeing dents in the atom — •Franz Giessibl — Exp. and Appl. Phys., University of Regensburg, 93053 Regensburg, Germany

Explaining the emission spectra of atoms was a giant early success of quantum mechanics. Directly seeing atoms remained elusive, though. When Binnig and Rohrer imaged the atoms of the silicon 7x7 reconstructed surface with the scanning tunneling microscope (STM), it came as a surprise. STM relies on a quantum effect, electron tunneling. In 1986, Binnig, Gerber and Quate introduced atomic force microscopy (AFM), a method that also images samples by probing it with, ideally, the single front atom of a sharp tip. Feynman quoted the atomic hypothesis (attracting each other when they are a little distance apart, but repelling upon being squeezed into one another) in chapter 1 of his Lectures on Physics. The AFM uses exactly those forces between atoms to create images line by line. The force sensor needs to probe forces small enough such that neither the tips front atom nor the sample are displaced. AFM passed its acid test when it resolved the silicon 7x7 surface in a non-contact mode using the frequency shift of an oscillating cantilever. The qPlus sensor, a self-sensing quartz cantilever oscillating at sub-A amplitudes resolves molecules with a CO tip. Today, AFM even resolves structures within single atoms. The quantum corral, introduced by Crommie, Lutz and Eigler in 1993, was revisited by AFM, showing that this 2D artificial atom interacts similar with AFM tips as a natural atom. A qPlus sensor with a metal tip reunites STM with AFM and it enables us to do surface science of insulators on the atomic level.

Keywords: Atomic Force Microscopy; Scanning Tunneling Microscopy; Subatomic spatial resolution; Chemical bonding; Surfaces