Real and apparent grain sizes in chemical vapor deposited diamond

A boron-doped, chemical vapor deposited (CVD) diamond, with a doping level of approximately 10(18) cm(-3), is used to demonstrate the very different grain sizes deduced from the application of various scanning electron microscopy (SEM) techniques to a polished polycrystalline surface. The boron-doped sample was chosen for this investigation because of the very different boron up-take on the {111} and {100} growth sectors and the consequent changes on the physical properties of the underlying crystal. It is shown that SEM contrast resulting from electron channeling gives a gross over-estimate of the grain size, while luminescence microscopy and surface enhanced secondary emission give a better indication, although they can give slight underestimates. The results are consistent with recently published transmission electron microscopy (TEM) observations which show that the grains in thick polycrystalline CVD diamond form clusters with common growth directions [Philos. Mag., A 82 (2002) 1741]. The individual grains within a cluster are related by various twinning operations. This behavior is characteristic of columnar CVD growth and does not depend on boron doping. (C) 2003 Elsevier Science B.V. All rights reserved.