Tunneling Microscopy of Submonolayer Adsorbates on Si(111)
Abstract
The first real-space observation are reported for several new types of ordered surface structures induced by submonolayer gallium or boron adsorption on Si(111). Where surface doping concentrations can be controlled, one can identify distinct electronic characteristics, spatially localized on the atomic scale, that reflect both average and local dopant distributions and binding configurations. The experiments make use of a scanning tunneling microscope constructed for vacuum operation. For each known, ordered phase of gallium adsorption, multiple-phase-domain images are employed to identify the respective adsorbate binding configurations. For boron adsorption, one finds one ordered surface phase, which can accommodate boron concentrations from very low coverage up to 1/3 monolayer. Local tunneling spectroscopy performed over the available range of boron concentration leads to the identification of distinct current-voltage characteristics with the presence or absence of the dopant at individual atomic sites. Under certain systematic conditions, we observe negative differential conductivity in the microscope's tunnel junction, and we identify spatially localized electronic characteristics that enable single atoms to act as isolated tunnel diodes together with the microscope's tunneling tip. The qualitative corroboration of the results of recent surface energy and stress calculations by our structural and electronic observations suggests that the conceptual approaches behind these computations might eventually offer a substantial predictive capability. (jhd)
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1989
- Accession Number
- ADA216985
Entities
People
- Peter J. Bedrossian
Organizations
- Harvard University