Detection of texture of nanocrystalline silicon processed by severe plastic deformation by Raman spectroscopy
The angular dependences of the polarized Raman scattering intensity were measured in specimens of nanocrystalline silicon processed by severe plastic deformation. The study was performed on two specimens produced by torsion in Bridgman anvils at pressures of 2 and 6 GPa. Measurements have shown that a part of polarized light related to a strictly oriented crystalline phase is observed against the background of depolarized scattering from a randomly oriented ensemble of crystallites. The degree of order in the ensemble of crystallites is quantitatively described by a model assuming that the specimen consists of crystallites of approximately the same size and the crystallite directions have some mean value and are disordered with respect to the mean value with dispersion σ. The model is applied to the measured values and it is found that the angular dispersions for the specimens processed at pressures of 2 and 6 GPa are equal to 0.51 and 0.53, respectively. A method is proposed for detecting the presence of texture and determining the preferential crystallographic direction in an ensemble of crystallites (texture orientation) by measuring the angular dependence of the polarized Raman scattering intensity. The numerical value characterizing the degree of texture order can be regarded in this case as the variance of disorder in the orientation angle of the crystallites.