Application of single crystalline tungsten for fabrication of high resolution STM probes with controlled structure

Abstract

The possibility to fabricate scanning tunneling microscopy (STM) probes with controlled electronic structure using single crystalline tungsten tips is discussed. High resolution power of oriented single crystalline probes is demonstrated in atomic and subatomic resolution STM studies of silicon, gallium telluride and graphite surfaces. The possibility of controllable selection of the tungsten tip atom electron orbitals responsible for the surface imaging in STM experiments is demonstrated. KEYWORDS: tungsten; scanning tunneling microscopy; electron orbital INTRODUCTIONThe invention of scanning tunneling microscopy (STM) allowed investigations of the local electronic structure of conducting surfaces with atomic resolution [1,2]. High spatial resolution of the method is based on exponential dependence of the tunneling current I t on the distance between the probe and the sample atoms (tunneling gap) leading to one order of magnitude decrease in the tunneling current with every 1 Å increase in the gap spacing. Considering the role of the probe in experiments, this dependence means that more than 90% of the tunneling current can be collected by one atom at the apex. The precise knowledge of its electronic structure is crucial for qualitative interpretation of atomically resolved STM data and for further enhancement of the spatial resolution because the electronic structure of the apex atom can modify the electron tunneling conditions in different surface regions. In some cases, the apex orbital structure can also be visualized directly at small tunneling gaps [3][4][5][6][7]. The knowledge of the probe atomic and electronic structure is important for explanation of chemical and spin contrast in atomic scale STM images.Application of oriented single crystalline tips with a priori known orientation of the apex axis appears to be one of the promising methods of fabrication of STM probes with predictable electronic structure. The main objective of this work is related to possibility to control the probe apex atomic and electronic structure and spatial resolution of STM using oriented single crystalline tips.