Porosities of porous silicon layers formed on different types of substrates and under different experimental conditions are compared with and related to the pore size distribution determined by gas adsorption experiments. Results show that porous layers formed on lightly P-doped silicon exhibit a network of very narrow pores, of radii less than 2 nm. Porous films formed on heavily doped silicon present larger radii, ranging between 2 and 9 nm according to the experimental conditions. Larger porosities and larger pore sizes are obtained by increasing the forming current density or by decreasing the HF concentration. Heavily P-doped porous silicon layers are homogeneous in depth and generally present a quite sharp pore size distribution. With heavily N-doped silicon, an increase in porosity with increasing thickness is found, which corresponds to an increase in pore size, leading to a broadening of size distributions. This porosity gradient is attributed to a chemical dissolution of the layer occurring during anodization. In addition, a strong dependence of porosity with small variations in doping level is found.

The evolution of thermally stimulated depolarization current (TSDC) measured on a mordenite Na zeolite is examined as a function of the Na+ exchange degree. According to this investigation, the dipolar reorientation is due to Na+, and the TSDC signal analysis leads to an assessment of the interaction energies between the hopping Na+ ions and the zeolitic lattice. The values of these energies are found to be between 0.7 and 0.9 eV. According to the Na+ exchange degree and the nature of the occupied Na+ sites, a quantitative and qualitative characterization of each site is given.