SHAPING OF DIAMOND FILMS BY ETCHING WITH MOLTEN RARE-EARTH-METALS

DIAMOND films prepared by chemical vapour deposition (CVD) have received considerable attention because of their high thermal conductivity, optical transparency, hardness, inertness and semiconducting properties1,2. The control of film geometry (by thinning, polishing, patterning and shaping) is essential for most applications. Polishing by reaction with oxygen gas or ions usually results in pitting at grain boundaries3,4, and other techniques5-8 are generally slow. Thinning or polishing of single-crystal diamond9 and CVD films4,10 by high-temperature diffusional reaction with solid transition metals has been reported previously. But these approaches require either a hydrogen atmosphere9, which is undesirable industrially, or high pressures (200-3,000 p.s.i.) during the heat treatment4,10. We report here a method for shaping and thinning which does not suffer from these limitations. It involves the use of molten rare-earth metals such as cerium or lanthanum to etch away the diamond film surface. Substantial thinning and shaping can be achieved in just a few hours. We anticipate that this technique may open up new applications of diamond films in optics and biomedicine.