| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2018) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeE |
| Session: | Emerging Topics: Growth and Properties of Electronic Materials, 2D Layers, and Metallic-glass Thin Films |
| Presenter: | Pedro Arias, University of California, Los Angeles |
| Authors: | P. Arias, University of California, Los Angeles A. Abdulslam, Colorado School of Mines A. Ebnonnasir, University of California, Los Angeles C.V. Ciobanu, Colorado School of Mines S. Kodambaka, University of California, Los Angeles |
| Correspondent: | Click to Email |
Using in situ variable-temperature scanning tunneling microscopy (VT-STM) and density functional theory (DFT), we investigated the surface structure and growth kinetics of two-dimensional hexagonal boron nitride (hBN) monolayer on Pd(111). STM images of polydomain hBN monolayers, grown via dissociative chemisorption of borazine on Pd(111)/Al2O3(0001) thin films, reveal moiré patterns with periodicities between 0.6 nm and 2.8 nm corresponding to four different orientations on Pd(111). We observe tunneling-parameter dependent apparent surface corrugation Δz in the STM images of the hBN domains. Furthermore, for the largest moiré pattern periodicities, we observe a bifurcation behavior in which some domains are nearly flat, and others develop significant hill-and-valley geometric corrugations. We suggest that hBN/Pd can have either mainly geometric or mainly electronic corrugation, depending on the domain orientation.1 This behavior is unlike any other monolayer hBN-on-metal system.
Using the VT-STM, we investigated the chemical vapor deposition (CVD) kinetics of hBN monolayers on Pd(111). In each experiment, STM images are acquired while exposing Pd(111) to borazine (10-7 – 10-6 Torr) at temperatures 573 K and 673 K and for times up to 2500 s. The STM images reveal the nucleation and growth of two-dimensional islands on the Pd surfaces. From the images, we measure the areal coverage, island sizes, and island density as a function of time, temperature, and borazine flux. Our STM images reveal an unusual nucleation and growth mode: at lower deposition rate and higher temperature, islands form on terraces; increasing the deposition rate and/or lowering the temperature result in preferential nucleation and growth at the step edges. Interestingly, the attachment of the deposited species is observed on both up and down steps. We attribute this phenomenon to the structure and the highly anisotropic bonding of borazine on Pd(111). Our results provide new insights into the growth dynamics of two-dimensional layered materials.
1P. Arias, A. Abdulslam, A. Ebnonnasir, C. V. Ciobanu and S. Kodambaka, 2D Materials 5 (4), 045001 (2018).