Deposition of metal nanostructures onto Si(111) surfaces by field evaporation in the scanning tunneling microscope

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Abstract
Islands of gold or copper having dimensions as small as 200 Å in diameter and 10 Å in height were prepared by field evaporation from a tip of the appropriate metal in a scanning tunneling microscope (STM). The field emission of metal is induced by the application of tip-negative bias pulses having amplitudes of 6–20 V, and durations of 2 μs to 2 ms. The metallic composition of the protrusions observed by STM are confirmed by ex situ elemental analysis using the field emission scanning Auger microprobe (FE-SAM). Tip-positive bias pulses also produce protrusions, however these are unstable either to STM imaging or to exposure to high-energy electron beams, as in the FE-SAM instrument. It is therefore probable that nonostructures formed via tip-positive bias pulses are not metallic. These data provide the first direct experimental evidence for metal transfer between an STM tip and a surface.