AVS 65th International Symposium & Exhibition
    Advanced Surface Engineering Division Monday Sessions
       Session SE+NS+TF-MoM

Paper SE+NS+TF-MoM3
Two-dimensional Hexagonal Boron Nitride (hBN) Layer Promoted Growth of Highly-oriented, Trigonal-structured Ta2C(0001) Thin Films via Ultra-high Vacuum Sputter-deposition on Al2O3(0001)

Monday, October 22, 2018, 9:00 am, Room 202C

Session: Nanostructured Thin Films and Coatings
Presenter: Koichi Tanaka, University of California, Los Angeles
Authors: K. Tanaka, University of California, Los Angeles
P. Arias, University of California, Los Angeles
M.E. Liao, University of California, Los Angeles
Y. Wang, University of California, Los Angeles
H. Zaid, University of California, Los Angeles
A. Aleman, University of California, Los Angeles
M.S. Goorsky, University of California, Los Angeles
S. Kodambaka, University of California, Los Angeles
Correspondent: Click to Email
It is generally believed that single-crystalline substrates with either the bulk or surface structure and lattice constant identical or similar to that of the film being deposited are required for the growth of high-quality crystalline thin films. Recent studies have shown that deposition on van der Waals (vdW) layers can lead to highly-oriented thin films of a variety of crystal structures and lattice parameters. Here, we show that two-dimensional (2D) hexagonal boron nitride (hBN) layers (a = 0.250 nm and c = 0.667 nm) improve the crystallinity of trigonal-structured Ta2C (a = 0.310 nm and c = 0.494 nm) thin films sputter-deposited on Al2O3(0001) substrates. Ta2C layers of desired thickness (t = 17 ~ 75 nm) are grown on bare and hBN-covered Al2O3(0001) substrates via ultra-high vacuum direct current magnetron sputtering of TaC compound target in 20 mTorr pure Ar gas atmospheres at 1327 K. hBN layers are deposited via pyrolytic cracking of borazine (~600 L) onto Al2O3(0001) substrates at 1327 K. The as-deposited Ta2C films are characterized in situ using Auger electron spectroscopy and low-energy electron diffraction and ex situ using X-ray diffraction (XRD) and transmission electron microscopy (TEM) based techniques. ω-2θ XRD scans acquired from both Ta2C/Al2O3(0001) and Ta2C/hBN/Al2O3(0001) films with t = 17 nm exhibit only Ta2C 0002n reflections (corresponding to c = 0.494 nm) while thicker layers (t = 75 nm) reveal the presence of additional 10 1 reflections. However, the 0002 reflection peak intensities are 5.4-fold stronger for the Ta2C layers on hBN/Al2O3(0001) than bare Al2O3(0001). High-resolution TEM images and associated Fourier transforms indicate that the layers are single-crystalline. XRD φ scans show six 60°-rotated 1 0 -1 2 peaks of Ta2C at the same ϕ angles for 1 1 -2 6 of Al2O3 based on which we determine the epitaxial crystallographic relationships between the film and the substrate as Ta2C(0002) || Al2O3(0006) with in-plane orientation of Ta2C[1 0 -1 0] || Al2O3[1 1 -2 0]. We further show that 0002-oriented Ta2C thicker films can be obtained by inserting hBN layers at regular intervals during the deposition of thicker Ta2C films.