Detection of Low-Density Surface Sites on Silica: Experimental Evidence of Intrinsic Oxygen-Vacancy Defects

Abstract

Low-density sites on planar fused silica surfaces are studied by titration with fluorescent probe molecules in an ultrahigh vacuum environment. Intrinsic sites chemically distinct from either hydroxyl or strained siloxane sites are identified by titration with a perylene derivative containing a vinyl functional group. Evidence is presented that these sites are oxygen vacancy defect (OVD) sites, which have previously been difficult to detect experimentally. The density of intrinsic OVD sites is shown to depend on pretreatment temperature, with an estimated density of approximately 1011 sites/cm2 for fused silica heated to 700 °C in vacuum. The influence of molecular and atomic deuterium exposure on various silica surface sites is also explored.