Structural study of porous silicon and its oxidized states by solid-state high-resolution Si-29 NMR spectroscopy

Si-29 nuclear magnetic resonance spectra were measured to characterize poro us silicon structures. Si-29 nuclei close to surface were selectively detec ted both in cross-polarization and non-cross-polarization spectra. The spec tra were different from those for amorphous silicon and amorphous hydrogena ted silicon. Therefore porous silicon is different from amorphous materials in the structural character. The resonant peaks were, however, much broade r than the peaks observed for crystalline silicon. There exists distributio n of bonding conformation in the porous silicon layer. The origin of the li newidth in the NMR spectra has been discussed. The contribution of each bro adening mechanism to the width has been estimated theoretically and experim entally. The Si-29 NMR spectra for oxidized porous silicon species have bee n assigned as follows: - 50 ppm due to O2SiH2, - 85 ppm due to O3SiH, - 111 ppm due to SiO2, and - 101 ppm due to Si(OH)(x) or Si-29 located between O ySiHx and SiO2. The signals of SiHx species have been assignable to -85 and - 94 ppm; however, further study should be done for the detailed assignmen t. [S0163-1829(98)03426-2].