Direct observation of site-selective hydrogenation and spin-polarization in hydrogenated hexagonal boron nitride on Ni(111)

Abstract

We report the structural analysis and spin-dependent band structure of hydrogenated boron nitride adsorbed on Ni(111). The atomic displacement studied by using the normal incidence X-ray standing wave (NIXSW) technique supports the H-B(fcc):N(top) model, in which hydrogen atoms are site-selectively chemisorbed on boron atoms and N atoms remain on top of Ni atoms. The distance between the Ni plane and nitrogen plane did not change after hydrogenation, which implies that the interaction between Ni and N is 3d-π orbital mixing (donation and back-donation) even after hydrogenation of boron. The remaining π* peaks in near-edge X-ray absorption fine structure (NEXAFS) spectra are a manifestation of the rehybridization of sp into sp states, which is consistent with the N-B-N bonding angle derived from NIXSW measurement. The SPMDS measurement revealed the spin asymmetry appearing on hydrogenated h-BN, which was originated from a π related orbital with back donation from the Ni 3d state. Even though the atomic displacement is reproduced by the density functional theory (DFT) calculation with the H-B(fcc):N(top) model, the experimental spin-dependent band structure was not reproduced by DFT possibly due to the self-interaction error (SIE). These results reinforce the site-selective hydrogenation of boron and pave the way for efficient design of BN nanomaterials for hydrogen storage.

Sticking of atomic hydrogen on graphene

“…Koswattage et al (Koswattage et al 2011) examined a deuterated 2-layer sample of h-BN with NEXAFS and XPS, and proved that binding occurs mostly at the B sites. This conclusion was further confirmed by Ohtomo et al, who carried out a more comprehensive experimental and theoretical study, and considered the hydrogenation of a h-BN layer grown epitaxially on Ni(111) (Ohtomo et al 2017). Apart from the selectivity towards the B sites, however, binding of H occurs with an electronic and structural reorganization similar to that found in graphene.…”

Quasi-free-standing monolayer hexagonal boron nitride on Ni

“…[40]. The distance between the N and Ni atoms is 0.21 nm [41]. The translational symmetry and the relatively close N-Ni distance may be essentially important for the chemisorption properties of h-BN/Ni(111).…”

Quantitative determination of a model organic/insulator/metal interface structure

“…In particular, atomic force microscopy and the X-ray standing wave (XSW) technique have proven their potential to yield a detailed and quantitative structure determination, including molecular adsorbates 31–35. However, on metal-supported h -BN only few experimental studies address the geometric interface structure of adsorbates,36,37 and an approach to obtain quantitative information on the molecular conformation of large organic molecules on h -BN is still lacking. This is surprising in view of the manifold studies addressing the electronic properties of organic/ h -BN/metal systems 18,20,21,37–39.…”