On the nature of grain boundary defects in high quality CVD diamond films and their influence on physical properties

Transmission electron microscopy samples have been prepared from high quality, thick (> 100 mu m) CVD diamond films in order to undertake a detailed study of the regions adjacent to the columnar grain boundaries. Using both weak beam and strong matrix diffracted beams and also twin reflections in carefully chosen crystal orientations, it has been possible to show that the boundaries that appear defect-free at first sight are in fact associated with considerable defect densities of characteristic types. These defects have been analysed and the results are presented. An attempt is made to correlate these observations with the anisotropy and temperature dependence of the thermal conductivity of the films and also with their field-emission properties.