Silicon surface chemistry in aqueous solutions studied with a novel scanning tunneling microscope

I have constructed a novel electrochemical scanning tunneling microscope (STM) that operates in controlled atmospheres. The design is convenient both for in-situ STM observations of air-sensitive electrochemical systems and for ex-situ STM observations of air-sensitive surfaces.;Using this STM as an ex-situ tool, I present a study of the surface chemistry of silicon in aqueous solutions. There are two motivations for this study. First, as the length scales of integrated circuit (IC) devices continue to decrease, it is becoming increasingly important to prepare extremely clean, atomically smooth silicon surfaces during the initial wet processing steps in order to optimize device performance. A better understanding of the chemistry of wet silicon processing is essential to minimize surface roughness and contamination. A second motivation is that hydrogen-terminated silicon is used as a substrate for forming organic self-assembled monolayers, first synthesized by Linford and Chidsey in our laboratory.;I show by ex-situ STM that dissolved oxygen in aqueous 40% ammonium fluoride solution initiates the formation of etch pits in the terraces of the otherwise ideal H-Si(111) surface. I propose that oxygen molecules are reduced to superoxide anion radicals at the negative open-circuit potential of the silicon surface. A small fraction (less than 0.4%) of these superoxide anions abstract hydrogen atoms from the H-Si(111) terraces to form silicon radicals (dangling bonds), which are then susceptible to etching in neutral to basic aqueous solutions.;I next present a more comprehensive study that explores the reactivity of H-Si(111) with dissolved O;Two final studies are presented which explore the reactivity of H-Si(111) related to metal contamination and removal-a key issue for IC's. Photochlorination, an effective metal removal process, is shown here to modify H-Si(111)(1 x 1) to form an ordered Cl-Si(111)(1 x 1) surface. I also present the initial stages of copper deposition on H-Si(111) from aqueous solution.