Scanning tunneling microscopy of layered-structure semiconductors

Abstract

Semiconductors are characterized by atomic resolution imaging and density of states measurements (DOS) obtained through the use of a scanning tunneling microscope (STM). The DOS of the conduction and valence bands can be measured separately with a STM as opposed to an optical measurement which measures only the joint DOS. Layered-structure semiconductors are characterized both in the bulk form and in the isolated cluster form. Images of three bulk layered-structure semiconductors, MoS₂, WSe₂, and SnS₂, were obtained with both positive and negative sample-to-tip bias voltages. Curves of tunneling current as a function of bias voltage were measured, from which the DOS of the valence and conduction bands can be inferred. We obtained an atomically resolved image of an isolated fragment of a semi-conductor cluster which was deposited on a graphite surface from a colloidal suspension of BiI₃. Also imaged were clusters of MoS₂ layered-structure semiconductors.