Diamond synthesis by electrolysis of acetates

A new method of electrochemical synthesis of different forms of carbon, including nanocrystalline diamond, is described. The electrolyte consists of a solution of ammonium acetate in acetic acid. The electrolysis is carried out by applying a shifted-square alternating voltage in the 10-100 Hz frequency range. The peak-to-peak voltage amplitude is 60 V and voltage shift is 10 V. The working temperature is 70-75 degreesC. In this work, electrodes are monscrystalline boron-doped silicon plates. The morphology and crystalline structure of the deposit have been examined by scanning (SEM) and transmission electron microscopy (TEM), and Raman spectroscopy. Both TEM and Raman measurements have confirmed unambiguously the formation of diamond nanocrystals in the deposit. As several studies have underlined the role of CH3. and H-. radicals for CVD diamond growth, the basic idea of the present work was to look for the electrochemical production of these radicals. This was achieved by anodic oxiddation of acetate ions (CH; production) and cathodic reduction of ammonium ions (H-. production). Using non-symmetric alternating polarisation conditions, both anodic and cathodic species are alternatively generated and coexist at the electrode surface during a short period of time. Thus, it is believed that, in some areas of the substrate, conditions arise that are quite similar to those that take place in CVD methods of diamond growth. (C) 2001 Elsevier Science B.V. All rights reserved.