Ultrathin Au films studied with the scanning tunneling microscope: Topography of insulating surfaces

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Abstract
The scanning tunneling microscope (STM) can produce high-resolution topographic images of surfaces which, normally, are electrically conducting. We have made STM images of a variety of insulating surfaces which are made conducting by a smooth ultrathin (>20 Å thickness) Au overlay film. Topographic features of the underlying substrate as small as 10 Å are resolved. Surprisingly, no features of the overlay Au film are seen. These films are useful for obtaining topographic images of a wide variety of surfaces and for STM measurements where a stable conducting surface is required for support of molecules or other microscopic structures.