Plasma Assisted Physical Vapor Deposition of 2D Materials

Dr. Andrey Voevodin

University of North Texas

Professor and Chair of Department of Materials Science and

Engineering in The College of Engineering

Plasma assisted physical vapor deposition (PVD) of large area two-dimensional (2D) materials is an emerging technology, which can allow for reproducible, substrate agnostic, and cost effective direct growth of semiconductor and dielectric heterostructures over wafer scale areas. Here we present our recent research into PVD growth of few-layer semiconducting transition metal dichalcogenides (e.g., MoS2, WS2, and others) and dielectric materials (e.g., BN). Pulsed DC magnetron sputtering from MoS2 targets in argon and pulsed laser deposition from BN targets in nitrogen were developed to produce 2D materials on a variety of substrate materials: amorphous silicon dioxide, highly oriented sapphire and graphite, as well as flexible polymers. The thermodynamic tendency toward island formation is overcome by maximizing ad-atom mobility through the control of incident flux, ionization state, energies, and densities, while avoiding defect formation (i.e., vacancy creation by sputtering of S atoms). Plasma assisted PVD processes are shown to yield highly (002) oriented 2D polycrystalline films exhibiting sub-monolayer thickness variability over 40 mm diameter areas when using 30 mm diameter sputtering plasma sources. In-situ XPS and Raman spectroscopy were used to analyze film stoichiometry, structure, and initial growth stages. Pin-hole and gap free 2D MoS2 and BN films were confirmed by TEM, conductive AFM, Raman, and electrical probe measurements. PVD growth methods, coupled with shadow mask patterning, enable fabrication of devices through direct synthesis of 2D semiconducting materials, metallic materials for source-drain and gate electrodes and dielectrics (BN and Al2O3), eliminating a need for 2D layer transfer or photolithography. The challenges of plasma assisted PVD processes in maintaining 2D film stoichiometry and minimizing point defect formation are discussed with possible approaches for their mitigation. Practical routes for room temperature PVD growth of amorphous ultra-thin materials on polymer substrates followed with subsequent laser annealing for selected area conversion to crystalline 2D structures are also outlined.

Host: Dr. Vladimir Drachev

Tuesday, October 27, 2015 3:30 P.M.

3:30 P.M.

Room 104, Physics Building

Refreshments at 3:15 P.M.