Detection of Low-Density Surface Sites on Silica:
Experimental Evidence of Intrinsic Oxygen-Vacancy Defects
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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 10<sup>11</sup> sites/cm<sup>2</sup> 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