CAPILLARY AND VAN-DER-WAALS FORCES AND MECHANICAL STABILITY OF POROUSSILICON

The evolution of mechanical stress in porous silicon films during dryi ng was investigated. It was found that the dominant factor is capillar y forces which art responsible for high tensile stresses during drying , and which lead to damage and destruction of highly porous films. Bef ore drying, the films are found to be under compression. This can be r elated to the increased lattice parameter observed in porous silicon. After drying, the compressive stress is reduced. The difference in str ess was ascribed to van der Waals forces which lead to attraction betw een the hydrogen-covered pore surfaces.