Thin films of layered materials like hexagonal boron nitride (h-BN) possess unique structural and/or electronic properties due to their two-dimensional nature. Formation of h-BN on hot metal surfaces from molecular precursors has been studied for many years [1]. Nowadays, the renewed interest in h-BN films is caused by the ability of h-BN to form self-assembled nanostructures (nanomesh) on lattice-mismatched transition metal substrates, like Rh(111) [2] or Ru(0001) [3]. This extraordinary ability makes h-BN a promising candidate for creating nanostructured templates for a variety of applications.
In this paper we study electronic structure and bonding of h-BN monolayers adsorbed on Ni(111), Cu(111), Pt(111), Rh(111), Ir(111) and Ru(0001) by the core-level techniques based on synchrotron radiation: x-ray absorption, x-ray emission, core-level and valence-band photoemission. Clear trends in the interfacial chemistry are observed and analyzed. In particular, we reveal the reasons for the h-BN nanomesh formation on rhodium and ruthenium, and its absence on platinum. This is because h-BN is bonded weakly on Pt(111), while on Rh(111) and Ru(0001) the bonding is significantly stronger resulting in a much stronger corrugation of the adsorbed h-BN monolayer (nanomesh) due to larger difference in energy between favorable and unfavorable adsorption sites within the interfacial supercell [4].
Another interesting finding is the existence of occupied and unoccupied interface-induced gap states of h-BN on several substrates, implying that h-BN may become somewhat metallized. The nature of the gap states is different, and depends on the strength of chemical interaction between h-BN and the substrate. For example, at the weakly bound h-BN/Pt(111) interface the gap states are associated with the metal-induced gap states, i.e., states formed by the proximity to the metal, while at the strongly bound h-BN/Ni(111) interface the gap states are induced primarily by chemisorption.
[1] M. T. Paffett et al., Surf. Sci. 232 (1990) 286; A. Nagashima et al., PRL 75 (1995) 3918; E. Rokuta et al., PRL 79 (1997) 4609.
[2] M. Corso et al., Science 303, 217-220 (2004).
[3] A. Goriachko et al., Langmuir, ASAP Article (2007).
[4] A. Preobrajenski et al., submitted to PRB. |