ABSTRACT
The smallest features on transistors used in computer circuits have approached atomic dimensions: the silicon dioxide gate oxides are between 5 and 8 silicon atoms thick and the concentration of dopant atoms has increased to the point that electrically inactive dopant clusters as small as a few atoms are common enough to affect device performance. At the start of this century, gate oxides thinner than 2 nm were being used in some commercial integrated circuits. Many of the properties of materials are controlled by the distribution and motion of low concentrations of impurity atoms. Techniques such as x-ray absorption spectroscopy or nuclear magnetic resonance can determine the average local environment of impurities in some cases. Atoms on a surface, however, behave very differently from atoms in the bulk. With different local environments, coordination numbers, strains, relaxations and screening responses, states that may have been active in the bulk, may lie mid gap on a surface- or visa-versa.
