Differential reflectance spectroscopy of monolayer and submonolayer metal deposits on semiconductor and metal electrodes

Abstract

The deposition of metals in monolayer amounts onto semiconductor and metal electrode surfaces was studied by differential reflectance spectroscopy; results are reported for Zn on ZnO, Cd on CdS and Tl on ZnO and Au. The deposition was achieved from electrolytic solutions, either by adding the appropriate metal ions or, in the case of Zn on ZnO, by cathodic decomposition of the semiconductor. The optical constants of the deposited films, ranging from approximately 1 to 3 monolayers in thickness, are given in the photon energy range from 1.8 to 5.2 eV.

It is shown that the optical properties of these metal layers on semiconductors are well interpreted by assuming a transition state between isolated atoms and the bulk phase. With metal electrodes, the substrate often strongly influences the properties of the metal deposit, e.g., by alloying, and vice versa the metal deposit changes the electronic properties of the substrate surface, e.g., by an enhanced electroreflectance effect.