Oxidative etching of cleaved synthetic diamond {111} surfaces

In this study, three commonly used methods for oxidative etching of diamond {111} faces are compared: gas phase etching using 'dry' oxygen, gas phase etching using an oxygen/water vapour mixture and liquid etching in molten potassium nitrate. The synthetic diamond surfaces are prepared by cleavage. The morphology of the surfaces is studied using atomic force microscopy and the kinetics of the reactions is determined by measuring the decrease in thickness of the diamond. The atomic arrangement of the {111} surfaces etched in oxygen/water is studied using surface X-ray diffraction. Upon dry oxygen etching, the {111} faces are roughened and become morphologically unstable. This observation conflicts with standard theory, which predicts {111} to be a stable F-face that should etch via a layer mechanism. A possible explanation for this is chemical roughening. The addition of water vapour to the oxygen has a dramatic effect on the etching mechanism of the {111} faces. Now etching proceeds via a layer mechanism involving monoatomic steps. Shallow etch pits are formed, of which the slope increases for increasing etching temperature. Surface X-ray diffraction experiments show that the surface is -OH terminated. For potassium nitrate etching, the {111} face etches also via a layer mechanism and triangular etch pits with rounded corners are formed, hav g point or flat bottoms, This etching technique appears to be the best method to reveal different types of defects ending on diamond {111} surfaces. (C) 2001 Elsevier Science B.V. All rights reserved.