Characterization of ballas diamond depositions

Unfaceted, polycrystalline spherically grown diamond deposits having a radi al structure have been observed since the early days of low pressure CVD di amond synthesis. Because the structure is quite similar to natural ballas s tones, unfaceted CVD diamond is called ballas. So far, the general trend in diamond deposition has focused on well-faceted diamond layers, so CVD ball as deposits have not been systematically investigated. Low pressure growth of ballas always occur under conditions that are "non-o ptimal", i.e. at least one parameter exceeds the range for a diamond growth leading to well-faceted diamond crystals. CVD ballas can consist of more t han 99% of pure diamond; its microstructure reveals high amounts of micro-t wins. Several morphological ballas structures have been observed by varying the deposition conditions, i.e. ballases having faceted areas, Bat ballase s, ballases with graphitic inclusions etc. Various deposits were characteri zed by Raman spectroscopy and impurities were measured by SIMS. Low pressure ballas diamond layers have a hardness quite similar to pure di amond. Of particular interest is the fact that cleavage and crack propagati on along crystallographic planes can - due to the presence of micro-twins - be expected to be much lower in ballas than in single-crystalline diamonds . Thus, ballas structures are of particular interest for wear applications. Ballas type diamonds containing fine graphite particles could also be of in terest for flat panel displays, as the graphite permits high electron emiss ions, (C) 1999 Published by Elsevier Science S.A. All rights reserved.