Spin-lattice relaxation of Si-29 near porous silicon surface

The spin-lattice relaxations of Si-29 at room temperature for as-prepared, annealed, and oxidized porous silicon (PS) surfaces have been investigated. Monoexponential decays fitted well for as-prepared and annealed PS samples . The relaxation times of as-prepared and annealed PS samples were 220 and 190 s, respectively. The relaxations occur through the dipolar coupling wit h H-1. On the other hand, monoexponential decays were not observed for oxid ized PS. Assuming that the decays obey an empirical stretched exponential d ecay function, O3SiH showed the relaxation time of 100 s and the relaxation time of SiO2 was 150 s. The dipolar coupling with proton contributes to th e relaxation of O3SiH. The relaxation of Si-29 Spin is dominated by chemica l shift anisotropy for SiO2. The oxidized PS showed the different relaxatio n behaviors from other PSs: short relaxation time, nonexponential decay, an d the detection of silicons, which do not have direct bonding to proton. Th ese behaviors are due to the oxygen incorporation in PS layer. (C) 2000 Els evier Science B.V. All rights reserved.