Structure of As-prepared and annealed porous silicon surfaces studied by nuclear magnetic resonance spectroscopy

Structures of as-prepared and annealed porous silicon samples have been cha racterized by Si-29 nuclear magnetic resonance (NMR) spectroscopy. Magnetic shielding tensors have also been calculated using ab initio molecular orbi tal calculations to help the characterization. After the annealing at 300 d egrees C for 4 h, the NMR peak position shifted slightly and the chemical s hia anisotropy increased. Hydrogen desorption during the annealing gives (S iH)(2) dimer structure from SiH2 configuration. The assignments of NMR sign als are as follows: -94 ppm due to SM, -85 ppm due to SiH2 and about -85 pp m due to (SiH)(2). The (SiH)(2) dimer has large chemical shift anisotropy a nd small magnetic shielding, which are caused by the strained conformation of the dimer. (C) 1999 The Electrochemical Society. S0013-4651(98)04-077-4. All rights reserved.