Surface electrical resistivity and wettability study of fused silica

The effect of heat treatment on the room-temperature surface electrical con ductivity of a fused silica plate has been investigated, Water-drop contact -angle measurements were used to assess the area ratio of SIOH (silanol) to Si-O-Si (siloxane) groups generated on the surface. Electrical resistivity values ranging from 10(12) to 10(16) Omega.m were also measured as a funct ion of the generated surface hydration. Three conduction regimes were ident ified corresponding to the following states of a fused silica surface: stro ngly hydrated, fully hydroxylated and increasingly dehydroxylated. The cond uctivity behaviour is interpreted consistently,vith previously proposed cha rge conduction mechanisms involving combinations of protonic and ionic cond uction. A surface region dielectric constant variation of 3.8-3.2 is also d etermined for 20-250 degrees C heat treatments. Resistivity measurements fo r samples treated above 430 degrees C are interpreted in terms of the prese nce of Na+ ions and indicate a surface activation energy of similar to 0.21 eV for labile Na+ ions to be oxidized and surface pinned. Copyright (C) 19 99 John Whey & Sons, Ltd.