| AVS 64th International Symposium & Exhibition | |
| 2D Materials Focus Topic | Tuesday Sessions |
| Session 2D-TuA |
| Session: | Growth of 2D Materials |
| Presenter: | Arthur Baddorf, Oak Ridge National Laboratory |
| Authors: | C. Ma, Oak Ridge National Laboratory J. Park, Oak Ridge National Laboratory L. Liu, University of Tennessee Y.-S. Kim, Oak Ridge National Laboratory M. Yoon, Oak Ridge National Laboratory A.P. Baddorf, Oak Ridge National Laboratory G. Gu, University of Tennessee A.-P. Li, Oak Ridge National Laboratory |
| Correspondent: | Click to Email |
The interaction of h-BN, the thinnest 2D insulating material, with oxygen is important technologically, but has proven complex. h-BN has strong covalent bonds that exhibit great stability and multilayers have been recommended as an oxidation resistant barrier for both metal and graphene substrates. At the same time, oxygen is predicted to form adsorbed chains and then to cut h-BN sheets along the chains. We have exposed monolayer h-BN on copper substrates to air and then examined the surface with scanning tunneling microcopy (STM) and x-ray photoelectron spectroscopy (XPS) after annealing to 600°C in ultrahigh vacuum. The active adsorbent is identified as oxygen, as expected. More surprising is evidence that oxygen is intercalated between the h-BN and copper and forms both quasi-1D and 2D ordered patterns on the predominantly (100) oriented substrate. STM images display double rows of O in hollow sites forming quasi-1D chains preferably along the moiré patterns and, in areas of higher coverage nucleated by steps, a p(2×2)-O superstructure. Efficient O diffusion along moiré channels is supported by first-principles density functional theory (DFT). Despite searches, a p(2×2)O structure on clean Cu(100) has not been observed; instead, higher density c(2×2)O islands are created there. XPS intensities here are consistent with the lower coverage p(2×2)O stabilized by the h-BN layer. Intercalated O increases the h-BN to Cu distance thereby decreasing the van der Waals interaction. Both STM dI/dV and DFT reflect this increased isolation by a 1.7 eV increase in the monolayer band gap, governed by a decrease in the contribution of the Cu surface to the density of states.
Intercalated oxygen is ultimately not stable and extended annealing at 600°C etches away the h-BN. In contrast to previous models, h-BN is removed by oxygen found underneath rather than adsorbed on the surface. Etching occurs along h-BN zig-zag edges and leads to finally to complete removal of the film. These new mechanisms observed for oxygen introduction, organization, and etching offer opportunities to better understand the stability of h-BN monolayers and to exploit the addition of oxygen to modify electronic properties or for formation of nanoscale structures.
This research was performed at the Center for Nanophase Materials Sciences which is a DOE Office of Science User Facility.