X-ray photoelectron diffraction study of bias-treatment for the growth of 1-inch-diameter hetero-epitaxial diamond (001) thick films

Bias-treatment (BT) is widely used as an initial seeding process of chemical vapor deposition (CVD) growth of diamonds. In a BT, substrates are negatively biased by an order of hundred volts so that positive ions in the plasma of CVD gas source bombard the substrate to form 'seeds' of diamond growth. Bias-treated 1-inch-diameter (φ) Ir(001)/MgO(001) substrates were used as the substrates of the CVD growth of 1-inch- φ diamond (001) thick films. XPS (X-ray Photoelectron Spectroscopy) spectra and C 1s and Ir 4f XPD (X-ray Photoelectron Diffraction) patterns were measured for the BT 1-inch- φ samples. 5 typical portions on the sample were measured; one at the central portion and the other 4 were peripheral portions, 90° apart from each other and ∼4 mm from the edge of the sample. The uniformity of the result over the 5 portions was confirmed. The coverage of carbon layers on the sample after BT was evaluated to be ∼ 50 ML in the unit of monolayer of Ir(001)1x1 surface. A quantitative measure of the effect of BT, A _45° (the degree of variation of XPD pattern as defined as I _maxI_min/I_a, where I_max, I _min and I_a are the maximum, minimum and average intensities of photoelectrons in an azimuthal diffraction pattern at the polar angle of 45°, respectively), was examined for C 1s and Ir 4f core-levels for the 1-inch- φ BT samples. The A_45° values appeared to be ∼3% and ∼17% for C 1s and Ir 4f, respectively. The results were compared with those for other bias-treated smaller samples reported so far. The A _45° value of ∼3% for C 1s is found to be very small compared to the corresponding values for the smaller samples reported so far. Thus, the method of BT for the present 1-inch- φ sample was found to have a large margin of improvement in terms of A_45° for C 1s XPD.