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Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates.

ABSTRACT: The effect of point defects and interactions with the substrate are shown by density functional theory calculations to be of significant importance for the structure and functional properties of hexagonal boron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG) and Ni(111) substrates. The structure, surface chemistry, and electronic properties are calculated for h-BN systems with selected intrinsic, oxygen, and carbon defects and with graphene hybrid structures. The electronic structure of a pristine monolayer of h-BN is dependent on the type of substrate, as h-BN is decoupled electronically from the HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111) substrate, metallic-like behavior is predicted. These different film/substrate systems therefore show different reactivities and defect chemistries. The formation energies for substitutional defects are significantly lower than for intrinsic defects regardless of the substrate, and vacancies formed during film deposition are expected to be filled by either ambient oxygen or carbon from impurities. Significantly lower formation energies for intrinsic and oxygen and carbon substitutional defects were predicted for h-BN on Ni(111). In-plane h-BCN hybrid structures were predicted to be terminated by N-C bonding. Substitutional carbon on the boron site imposes n-type semiconductivity in h-BN, and the n-type character increases significantly for h-BN on HOPG. The h-BN film surface becomes electronically decoupled from the substrate when exceeding monolayer thickness, showing that the surface electronic properties and point defect chemistry for multilayer h-BN films should be comparable to those of a freestanding h-BN layer.

SUBMITTER: Smabraten DR

PROVIDER: S-EPMC10357548 | biostudies-literature | 2023 Jul

REPOSITORIES: biostudies-literature

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Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates.

Småbråten Didrik René DR Nylund Inger-Emma IE Marshall Kenneth K Walker Julian J Benelmekki Maria M Einarsrud Mari-Ann MA Kioseoglou Joseph J Selbach Sverre M SM

ACS omega 20230705 28

The effect of point defects and interactions with the substrate are shown by density functional theory calculations to be of significant importance for the structure and functional properties of hexagonal boron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG) and Ni(111) substrates. The structure, surface chemistry, and electronic properties are calculated for h-BN systems with selected intrinsic, oxygen, and carbon defects and with graphene hybrid structures. The electronic stru ...[more]

PMID: 37483195

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Project description:Metal flux methods are excellent for synthesizing high-quality hexagonal boron nitride (hBN) crystals, but the atomic mechanisms of hBN nucleation and growth in these systems are poorly understood and difficult to probe experimentally. Here, we harness classical reactive molecular dynamics (ReaxFF) to unravel the mechanisms of hBN synthesis from liquid nickel solvent over time scales up to 30 ns. These simulations mimic experimental conditions by including relatively large liquid nickel slabs containing dissolved boron and a molecular nitrogen gas phase. Overall, the reaction takes place almost exclusively on the surface of the liquid nickel, owing to the low solubility of nitrogen in bulk nickel and the intermediate species' preference for the metal-gas interface. The formation of hBN invariably begins by reaction of dinitrogen with nickel-solvated boron atoms at the surface, forming intermediate N-N-B species, which typically evolve into B-N-B units through a short-lived intermediate where a single nitrogen atom is coordinated by one nitrogen and two boron atoms. The resulting B-N-B units, in turn, coalesce with growing hBN nuclei and carry nitrogen between hBN nanocrystals in an Ostwald ripening process. The amount of hBN produced on the tens of nanosecond time scale depends critically on the boron concentration, while having a much weaker dependence on the N2 pressure for the regime considered (N2 pressures of 2.5-10 MPa, Ni-B solutions with 6-12% boron by atom fraction). The highest rate of hBN formation occurs at the lowest temperature considered (1750 K, just above the melting point of nickel), while no hBN sheets are formed at 2000 K or above. An analysis of the transition pathways for nitrogen atoms shows that the final step, incorporation of small B-N motifs into larger hBN sheets, is the rate-limiting step in the regimes considered. While raising the temperature from 1750 to 2000 K has little effect on the formation of intermediates (N-N-B, B-N-B, etc.), the lack of large hBN sheets at temperatures >1900 K is explained by decreased probability of the final step and increased probability of breakup of hBN into B-N motifs.

Dataset Information

Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates.

Publications

Electronic Structure and Surface Chemistry of Hexagonal Boron Nitride on HOPG and Nickel Substrates.

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