Substantial effect of linear velocity of combustion flame on oriented growth of diamond

Abstract

Abstract Diamond coatings were deposited on diamond-polished molybdenum substrates using combustion flame CVD. The total (acetylene plus oxygen) flow rate was between 75 and 310 1 h−1, the acetylene-to-oxygen flow rate ratio was between 1.03 and 1.22 and the substrate temperature was from 620 to 900 °C. A strong dependence of preferred orientation and crystalline order of the coatings, as determined by X-ray diffraction, on the total flow rate is obvious in spite of the wide range of other experimental conditions used for preparation of the samples. A strong (110) preferred orientation observed at low flow rates rapidly decreases and changes to (111) preferred orientation at the highest flow rates. The preferred orientation is apparently restricted to the direction of the coating growth. The change in preferred orientation, which reflects a change in the relative growth rates in the 〈110〉 and 〈111〉 crystal directions, is related to a change in surface morphology: instead of the {111} faces appearing at low flow rates, cubo-octahedral or cubic morphology was observed at high flow rates. The crystalline size values L111 and L220, taken as a measure of crystalline order, behave differently: L111 steadily increases with increasing flow rate, while L220 remains virtually unchanged.