title: Chemically resolved scanning tunneling microscopy imaging of Al on p-type Al0.1Ga0.9As(001)-c(2x8)(2x4).
abstract: The ability to chemically differentiate individual subsurface Al and Ga atoms, when imaging the Al0.1Ga0.9As(001)-c(2x8)(2x4) surface with scanning tunneling microscopy (STM), has been observed for the first time. In filled-state STM images first layer As atoms bonded to second layer Al atoms appear brighter than those bonded to second layer Ga atoms. This effect is only observed experimentally with p-type Al0.1Ga0.9As grown on p-type GaAs substrates and has been computationally modeled with density functional theory (DFT) calculations. It is hypothesized that chemical specificity is not observed on n-type material because the extra surface charge given to first layer As atoms by second layer Al atoms adds negligibly to the filled-state density of the surface, thus preventing the visualization of chemical specificity with filled-state STM imaging. The ability to distinguish whether first layer As atoms are bonded to second layer Ga and/or Al atoms in STM images shows that small differences in bond ionicity affect the local electronic structure of the material.
authors.affiliation: Department of Chemistry, 0358, University of California, San Diego, La Jolla, California 92093, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Hale
authors.forename: D L
authors.initials: DL
authors.lastname: Winn
authors.forename: T J
authors.initials: TJ
authors.lastname: Grassman
authors.forename: A C
authors.initials: AC
authors.lastname: Kummel
authors.forename: R
authors.initials: R
authors.lastname: Droopad