Surface modification in the nanometer range by the scanning tunneling microscope

Abstract

Ar⁺ ion milling reduces the roughness of the surface of a glassy Rh₂₅Zr₇₅sample to a rms value of < 1 Å as proven by studies with the scanning tunneling microscope (STM). Therefore, such metallic glasses provide ideal substrates for nanometer-scale structure fabrication. Here we present a new method to modify, in a reproducible way, the surface of metallic glasses by the STM. The resulting nanometer-scale structures are shown by the STM as well. The high local current density in the STM can raise the temperature in a very small volume near the surface of the metallic glass. An increase in temperature and electric field can lead either to enhanced diffusion of one component or to local crystallization of the glassy state or even to local melting of the surface. Under the influence of the high electric field between the sample and the tip the fluid forms a meniscus similar to a Taylor cone. The nanometer-scale structure is then created upon cooling. It is also possible to similarly produce line-shaped structures by moving the tip across the surface during the heating process. The physics of the formation of these hillocks and lines is discussed.