PNNL

Abstract

Significant anisotropy in as-deposited CVD ZnS at several length scales has been demonstrated through investigation of structural and optical properties. Compressive strength of cylinders of CVD ZnS oriented in the growth direction is ~50% higher than cylinders taken perpendicular to the growth direction. Lattice parameter measurements of mandrel side (first-to-grow) material is ~0.4% smaller than growth side (last-to-grow) material in a cored sample representing ~500 hours of CVD growth, indicating significant strain along the growth direction. X-ray diffraction also shows evidence of preferred orientations for hexagonality which differ depending on position in the growth history. In cross-section, the cored sample shows several large bands which are correlated with different degrees of infrared absorption and BTDF scattering. However, no universal trend is found that applies to the whole length from the mandrel to the growth side regarding optical properties. The extinction in the visible and infrared is lower for measurements perpendicular to the growth axis than parallel to it, possibly due to scattering from the growth bands.