| AVS 62nd International Symposium & Exhibition | |
| 2D Materials Focus Topic | Monday Sessions |
| Session 2D+EM+NS+PS+SP+SS+TF-MoM |
| Session: | 2D Materials: Growth and Fabrication |
| Presenter: | Karthik Sridhara, Texas A&M University |
| Authors: | KS. Sridhara, Texas A&M University B.N. Feigelson, US Naval Research Laboratory J.K. Hite, US Naval Research Laboratory A. Nath, George Mason University M. Fuhrer, Monash University, Australia D.K. Gaskill, US Naval Research Laboratory H. Castaneda, Texas A&M University L.O. Nyakiti, Texas A&M University |
| Correspondent: | Click to Email |
The growth of two dimensional (2D) materials such as graphene, hexagonal boron nitride (h-BN) and molybdenum disulphide (MoS2) have been demonstrated by chemical vapor deposition (CVD) on polycrystalline catalytic copper substrates. These Cu foil substrates (25 µm thick) are produced by metallurgical rolling leading to the formation of irregular ridges on the foil surface along with a film of native oxide on the surface. These processing artifacts are a limiting factor for controlled and reproducible large area (several cm2) growth of 2D materials. Greater control of growth can be achieved by controlling the density of nucleation sites and improving the catalytic activity of Cu by removing the Cu native oxide on the surface. Previous attempts to pre-treat the Cu substrate by using wet chemistry or thermal annealing to control growth has been weakly addressed.
In this work, electropolishing combined with prior thermal annealing at 1030°C for 5 hrs under H2 is used to control the degree of roughness of cold rolled polycrystalline Cu foils, and subsequently, to explore the influence of electropolishing on the growth of 2D materials: graphene, h-BN and MoS2. Electropolishing dissolves a thin surface layer of Cu, which contains surface defects and contaminants. This helps in decreasing the density of spontaneous nucleation sites by producing a morphologically uniform and contaminant-free surface. Secondary effects, etch pits which are ascribed to O2 bubbling at random nucleation sites on Cu surface, are mitigated by using additives, such as acetic acid and ethylene glycol, in the H3PO4 electrolyte. Thermal annealing and electropolishing results in this work reveal that a roughness of ~1.2 nm (Rq) can be achieved as measured by Atomic Force Microscope (AFM) along with a greatly planarized Cu foil. AFM will also be used to establish the Cu substrate morphology and its relationship to the growth of 2D materials. Fourier Transform Infrared, and Raman spectroscopy will be used to confirm the existence of the 2D material. Preliminary growth studies of h-BN on these high quality Cu substrates demonstrate improved growth, as assessed by the metrics of size and count of h-BN crystals from Scanning Electron Microscopy (SEM) micrographs [1]. This work will demonstrate that thermal annealing followed by electropolishing leads to optimization of Cu foil surface resulting in the larger crystal size and a reduction in nucleation sites that induce 2D material crystal growth [1].
[1] K. Sridhara. “Growth of hexagonal boron nitride on electrochemically prepared polycrystalline Cu substrates.” M.S. Thesis, University of Maryland, College Park, MD, 2014.