Ultra-high vacuum dc magnetron sputter-deposition of 0001-textured trigonal α-Ta2C/Al2O3(0001) thin films

Abstract

We report on the effects of substrate temperature (1073 K ≤ Ts ≤ 1373 K) and deposition time t (= 3 ~ 30 min.) on the crystallinity of Ta2C/Al2O3(0001) thin films grown via ultra-high vacuum direct current magnetron sputtering of TaC target in 20 mTorr (2.7 Pa) pure Ar atmospheres. Using X-ray diffraction and transmission electron microscopy, we determine that the layers are 0001-oriented, trigonal-structured α-Ta2C at all Ts. With increasing Ts, we obtain smoother and thinner layers with enhanced out-of-plane coherency and decreasing unit cell volume. Interestingly, the Ta2C 0001 texture improves with increasing Ts up to 1273 K above which the layers are relatively more polycrystalline. At Ts = 1373 K, during early stages of deposition, the Ta2C layers grow heteroepitaxially on Al2O3(0001) with (0001)Ta2C∥(0001)Al2O3 and [101¯0]Ta2C∥[112¯0]Al2O3. With increasing t, we observe the formation of anti-phase domains and misoriented grains resulting in polycrystalline layers. We attribute the observed enhancement in 0001 texture to increased surface adatom mobilities and the development of polycrystallinity to reduced incorporation of C in the lattice with increasing Ts. We expect that our results help develop methods for the synthesis of high-quality Ta2C thin films.