Surface morphology and preferential orientation growth of TaC crystals formed by chemical vapor deposition

TaC film was deposited on (002) graphite sheet by isothermal chemical vapor deposition using TACl(5)-Ar-C(3)H(6) mixtures, with deposition temperature 1200 degrees C and pressure about 200 Pa. The influence of deposition position (or deposition rate) on preferential orientation and surface morphology of TaC crystals were investigated by X-ray diffraction and scanning electron microscopy methods. The deposits are TaC plus trace of C. The crystals are large individual columns with pyramidal-shape at deposition rate of 32.4-37.3 mu m/h, complex columnar at 37.3-45.6 mu m/h, lenticular-like at 45.6-54.6 mu m/h and cauliflower-like at 54.6-77.3 mu m/h, with < 001 > near < 001 >, < 110 > and no clear preferential orientation, respectively. These results agree in part with the preditions of the Pangarov's model of the relationship between deposition rate and preferential growth orientation. The growth mechanism of TaC crystals in < 001 >, near < 001 > < 111 > and no clear preferential orientation can be fairly explained by the growth parameter alpha with Van der Drift's model, deterioration model and Meakin model. Furthermore, a nucleation and coalescence model is also proposed to explain the formation mechanism of < 110 > lenticular-like crystals. (C) 2008 Elsevier B.V. All rights reserved.