In situ X-ray diffraction investigation of porous silicon strains induced by the freezing of a confined organic fluid

High resolution X-ray diffraction is used to perform an in situ measurement of the variations of the lattice parameter of the nanometer size crystalli tes of porous silicon, induced by the freezing of a confined organic fluid, dodecane. Two p(+) type PS layers of 60 and 70% porosity are investigated, and the variations of their lattice parameter with the temperature (in the range 150-300 K) are measured. The experimental curves are discussed in re lation with the results of a previous calorimetric study of the freezing of confined dodecane. We explain the observed strains by the presence of capi llary stresses; that appear in the layer due to the formation of internal l iquid-vapour meniscus during the freezing process of the confined fluid.