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Single layers of hexagonal boron nitride (h-BN) represent the insulating analogon of graphene sheets. They can be grown in high perfection by thermal decomposition of borazine, the BN analogon of benzene, on transition metal surfaces [1]. The strong intraplanar bonds render the film very stiff with respect to lateral strain. Therefore, it tends to maintain its generic lattice constant, independently of the lattice constant or lattice symmetry of the metal substrate on which it is grown. On lattice-matched Ni(111) a well ordered (1x1) structure forms [1,2], while other substrates produce either a variety of Moiré patterns [3,4], coincidence lattices [5,6], or, as in the cases of Rh(111) and Ru(0001), a strongly corrugated, highly regular superstructure termed a nanomesh [7,8,9].
Angle-resolved photoemission (ARPES) data measured from well characterized h-BN monolayer films show fully occupied s and p bands a few eV below the Fermi energy (EF). The region nearer to EF is dominated by the metal d bands, with no extra h-BN related features appearing, in good agreement with density functional theory calculations [10]. In this sense, the wide band gap of bulk h-BN is preserved in the monolayer. However, due to their single-layer nature, these films are imaged well in scanning tunneling microscopy, reflecting the proximity of the underlying metal states [10]. Femtosecond time-resolved two-photon photoemission experiments reveal unusually long lifetimes for electrons transferrred into the h-BN conduction band states and into an image potential state.
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[4] M. Morscher et al., Surf. Sci. 600, 3280 (2006).
[5] T. Greber et al., e-J. Surf. Sci. Nanotech. 4, 410 (2006).
[6] M. P. Allan et al., Nanoscale Res. Lett. 2, 94 (2007).
[7] M. Corso et al. Science 303, 5655 (2004).
[8] R. Laskowski et al., Phys. Rev. Lett, 98, 106802 (2007).
[9] A. Goriachko et al., Langmuir 23, 2928 (2007).
[10] G. B. Grad et al., Phys. Rev. B 68, 085404 (2003).
[11] M. Muntwiler et al., Phys. Rev. B 75, 075407 (2007).
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