| Computer calculations have been made of the scattered x-ray intensity from model structures of poorly crystalline MoS(,2). These are compared with x-ray data collected on MoS(,2) prepared by thermal decomposition of ammonia thiomolybdate. While the initial state appears essentially amorphous, subsequent heat treatment produces material of increasingly crystalline order without, apparently, any intervening crystallization event. Using model crystallites of varying layer extent and number of layers we identify salient features of the diffraction pattern. We then introduce defects to reproduce via calculation the measured diffuse intensity.; On amorphous MoS(,3), prepared through the same process, high resolution data was taken at the Stanford Synchrotron Radiation Lab. The collected data is compared with computer calculations on model structures to which inputs came from prior studies of Liang et. al (18). In his studies chains of metal dimers with polysulfide bonds were proposed. It was considered essential to fit our data both in k-space, over the full range of k, and in r-space out to 4th neighbors. We find that the pairing of the dimerized chains is required and that the prominent 1st peak at k = 1 (ANGSTROM)('-1) arises from planar ribbon-like correlations between pairs of (dimerized) chains. |
