| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Tuesday Sessions |
| Session TF+PS-TuA |
| Session: | Epitaxial Thin Films |
| 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 K. Hojo, Nagoya University, Japan A. Deshpande, University of California, Los Angeles M.S. Goorsky, University of California, Los Angeles S. Kodambaka, University of California, Los Angeles |
| Correspondent: | Click to Email |
Over the past decade, two-dimensional (2D) layered materials such as graphene, MoS2, etc., have attracted considerable attention for a variety of applications, primarily in nanoelectronics and optoelectronics. An exciting and relatively little explored application of these van der Waals (vdW) layered materials is their use as templates for crystal growth. In the recent years, vdW layers present at the substrate-film interface have been shown to promote 'remote epitaxy', by relaying the epitaxial registry between the film and the substrate.
Here, we demonstrate that the crystallinity of sputter-deposited thin films can be significantly improved using vdW layered materials as buffer layers on growth substrates. Using 2D hexagonal boron nitride (hBN, a = 0.250 nm and c = 0.667 nm) as the buffer layer, we grow hexagonal-MoS2 (a = 0.315 nm and c = 1.23 nm), trigonal-structured Ta2C (a = 0.310 nm and c = 0.494 nm), and NaCl-structured TaC (a = 0.446 nm) of desired thickness on Al2O3(0001) substrates via ultra-high vacuum direct current magnetron sputtering of Mo and TaC targets respectively, in Ar/C2H4 and Ar/H2S gas mixtures. hBN layers are deposited in the same system via pyrolytic cracking of borazine (~600 L) onto the substrates at prior to the growth of the thin films. The as-deposited films are characterized using a combination of in situ using Auger electron spectroscopy and low-energy electron diffraction and ex situ X-ray diffraction (XRD), X-ray photoelectron and Raman spectroscopies, and transmission electron microscopy (TEM) based techniques.
We find notable differences in the layers deposited on hBN-covered Al2O3(0001) compared to those grown on bare substrates: significantly stronger 0002 (or 111 in case of TaC) reflection intensities and observation of Laue oscillations in ω-2θ XRD scans and higher intensity of MoS2 characteristic peaks in Raman spectrum. Furthermore, we show that inserting hBN layers at regular intervals results in highly-0002-oriented growth and suppression of polycrystallinity in thicker Ta2C films. Our results indicate that hBN layers enhance the crystallinity, irrespective of the crystal structure, of sputter-deposited thin films.