Graphite Yields to Force

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Science  24 Oct 2003:
Vol. 302, Issue 5645, pp. 535
DOI: 10.1126/science.302.5645.535d

Crystalline graphite serves as a calibration standard for scanning tunneling microscopy (STM), but the images show only every other atom (the β atoms) in the graphite lattice. In contrast, atomic force microscopy (AFM) should, in principle, be able to image all atoms (α and β), yet AFM measurements of attractive forces yield the same incomplete images as STM. Efforts to measure repulsive forces have not been successful because the instrument sensitivity is too low.

Hembacher et al. show that an AFM with enhanced sensitivity to short-range forces can image all of the carbon atoms on a graphite surface. Their instrument can measure tunneling current and force at the same time, and thus serves as both an STM and an AFM. Although the STM image shows only a trigonal lattice, the AFM image reveals the hexagonal carbon rings of the graphite lattice in their entirety. In the AFM images, the forces are different for atoms that lie directly above atoms in the layer underneath than for atoms that are above hollow sites; only the latter atoms are visible to the STM. This instrument may be useful in imaging other soft surfaces at atomic resolution. — JFU

Proc. Natl. Acad. Sci. U.S.A. 10.1073/pnas.2134173100 (2003).

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