UCLA

We report on the effects of substrate temperature (1073 K ≤ T _s ≤ 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 T _s. With increasing T _s, 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 T _s up to 1273 K above which the layers are relatively more polycrystalline. At T _s = 1373 K, during early stages of deposition, the Ta₂C layers grow heteroepitaxially on Al₂O₃(0001) with ( 0001 ) Ta 2 C ‖ ( 0001 ) Al 2 O 3 and [ 10 1 ¯ 0 ] Ta 2 C ‖ [ 11 2 ¯ 0 ] Al 2 O 3 . 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 T _s. We expect that our results help develop methods for the synthesis of high-quality Ta₂C thin films.