X-ray observation of porous-silicon wetting

High-resolution x-ray-diffraction experiments show that the lattice parameter of porous-silicon layers expands when wetted by an alcohol or an alkane. This phenomenon is nearly reversible when the alkane is removed while there is a time-dependent drift during alcohol wetting. The experimental results obtained for several alkanes and for two types of samples (p and p⁺ type) reveal that the magnitude of the lattice-parameter change is correlated with the size of the nanocrystallites rather than with the nature of the alkane. We propose that the lattice expansion is due to a change of the porous-silicon surface stress induced by wetting.