Suneel Kodambaka¹, Koichi Tanaka², Aditya Deshpande², Pedro Arias², Angel Aleman², Hicham Zaid², Michael Liao², Cristian Ciobanu³, Mark Goorsky^2
1Virginia Polytechnic Institute and State University, Blacksburg, VA
²University of California Los Angeles, Los Angeles, CA
³Colorado School of Mines, Golden, CO
Composition and crystallinity are probably two of the most important material characteristics that dictate properties and life-time performance of materials. Compositional control in sputter-deposited thin films is typically achieved via changing the deposition parameters, such as partial pressure of the reactive gases, substrate temperature, deposition fluxes, and the target composition. Common approaches to improve crystallinity, to increase grain size and the grain orientation in thin solid films typically involve the use of single-crystalline substrates, high substrate temperatures combined with low deposition fluxes, and energetic ion beams.
In this talk, I will present approaches involving the use of ultra-low (e.g., 0.002%) partial pressures of the reactive gases and van der Waals (vdW) layers as buffer layers to grow thin films of desired composition and enhanced crystallinity. Using Ta-C and Mo-S as model materials systems, we demonstrate compositional tunability and improved crystallinity. We also show that Ta2C thin films grown on Ta₂C(0001) covered with hexagonal boron nitride (hBN), a vdW-bonded material, are more highly oriented than those films grown directly on bare Ta₂C(0001) under identical deposition conditions. That is, heteroepitaxial growth across a vdW layer seemingly yields better crystalline quality than homoepitaxy. We observe similar highly-oriented growth of face-centered cubic Pd, body centered cubic Mo, and hexagonal MoS₂ thin films on hBN-covered substrates. Our results provide new insights into the factors underlying the growth of highly-oriented thin films.