Water interaction with thermally oxidized porous silicon layers

Water vapor adsorption and liquid penetration into thermally oxidized porous silicon films were studied by variable angle spectroscopic ellipsometry. Characterization of the surfaces in air combined with multilayer optical modeling showed the existence of a gradient in the volume porosity and bulk-like silicon skeleton in the layers. Films oxidized at 300 degrees C contained a thin oxide layer and further oxidation at 800 degrees C resulted in an almost total oxidation of the silicon skeleton, which yielded an increased hydrophilicity and an almost complete pore filling by water both from saturated atmospheres and from a liquid phase. Total water adsorption per gram adsorbent at saturation was 0.50 cm(3)/g for the 300 degrees C samples and 0.45 cm(3)/g for the totally oxidized films. Oxidation at 800 degrees C resulted in a surface area of 72 m(2)/g deter mined by a modified Brunauer-Emmett-Teller procedure.