Adsorption, dissociation, and diffusion of borazine on Pt(111)

Using first-principles calculations, we investigate the adsorption, dissociation, and diffusion of borazine, a common precursor for the growth of two-dimensional hexagonal boron nitride (h-BN), on a Pt(111) surface. Our calculations show that borazine adsorbs on Pt(111) both molecularly and dissociatively. The molecular borazine has a planar structure, whereas the dissociated borazine is either in a tilted or vertical configuration. The energy differences between the structures are only similar to 0.1 eV although the dissociated ones are more stable, and the energy barriers for conversion between the structures are also of the order of 0.1 eV. For molecular adsorption, borazine migrates through direct (0.87 eV barrier) or rotational (0.67 eV barrier) mechanisms. In the dissociated state, with alternating parallel and perpendicular structures, the borazine radical can migrate via a "slinky"movement. This results in a much lower diffusion barrier of 0.2 eV. In the case of vertical diffusion, the radical migrates with an energy barrier of 0.29 eV. Our results are consistent with experimental observations of borazine dehydrogenation and may be helpful in understanding h-BN formation at room temperature. We also discuss the atomistic processes for h-BN formation at high growth temperatures.