Dangling bonds in a-Si:H revisited: A combined Multifrequency EPR and   DFT Study
  Multifrequency pulsed electron paramagnetic resonance (EPR) spectroscopy using S-, X-, Q- and W-Band frequencies (3.6, 9.7, 34, and 94 GHz, respectively) was employed to study paramagnetic coordination defects in undoped hydrogenated amorphous silicon (a-Si:H). The improved spectral resolution at high magnetic field reveals a rhombic splitting of the g-tensor with the following principal values: g_x=2.0079, g_y=2.0061 and g_z=2.0034 and shows pronounced g-strain, i.e., the principal values are widely distributed. The multifrequency approach furthermore yields precise ^{29}Si hyperfine data. Density functional theory (DFT) calculations on 26 computer-generated a-Si:H dangling-bond models yielded g-values close to the experimental data but deviating hyperfine interaction values. We show that paramagnetic coordination defects in a-Si:H are more delocalized than computer-generated dangling-bond defects and discuss models to explain this discrepancy. 
M. Fehr, A. Schnegg, B. Rech, K. Lips, O. Asthakov, F. Finger, G.   Pfanner, C. Freysoldt, J. Neugebauer, R. Bittl, C. Teutloff
cond-mat.mtrl-sci