First stages of diamond nucleation on iridium buffer layers

During the first stages of epitaxial diamond nucleation by the bias-enhance d nucleation procedure on monocrystalline iridium films the metal surface s hows a characteristic roughening. Two different types of furrows and ridges along < 100 > and < 110 > develop. From atomic force microscopy images a t ypical structure height of 3 nm is deduced. Transmission electron microscop y indicates {111} faceting. In addition, after 45 min of nucleation 5-10 nm large structures are found with a typical distance of 100-300 nm showing a bright contrast in scanning electron micrographs. While a subsequent 30 mi n growth step results in a similar density of diamond grains with a size of approximately 100 nm, prolonging the biasing step does not increase the si ze of these nucleation centers. It is shown that under the present bias-enh anced nucleation conditions large diamond grains are etched. The fact that diamond can nucleate under conditions under which diamond cannot grow has s trong implications on the nature of the observed nucleation centers and on theoretical models describing the nucleation process. (C) 2001 Elsevier Sci ence B.V. All rights reserved.