Epitaxial growth of hexagonal boron nitride on Ag(111)

Abstract

The epitaxial growth of hexagonal boron nitride on a Ag͑111͒ surface by chemical vapor deposition of borazine ͑HBNH͒ 3 was investigated by x-ray photoelectron spectroscopy and low-energy electron diffraction. In contrast to other transition-metal surfaces of hexagonal symmetry, such as Ni͑111͒, Rh͑111͒, or Ru͑0001͒, the hexagonal BN layers form domains of arbitrary orientation, indicating that there is no preferred direction with respect to the Ag͑111͒ lattice. This result is in accordance with recent ab initio calculations that predict vanishing or at least very weak bonding energies for BN on ͑111͒ surfaces of noble metals.After the discovery of the so-called boron nitride nanomesh, 1 as representing a single layer of hexagonal boron nitride ͑h-BN͒ on a Rh͑111͒ surface, 2,3 the epitaxial growth of such boronitrene 4 layers gained new interest, especially since boron nitride and graphene are considered as promising ingredients for the engineering of future nanoelectronic devices. 5 So far, the epitaxial growth of boronitrene layers has been investigated for many transition-metal ͑TM͒ surfaces and, depending on substrate symmetry and lattice misfits, a large variety of superstructures has been observed. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] In this Brief Report, the epitaxial growth of boronitrene layers on Ag͑111͒ is investigated in order to extend the list of experimental studies to the late TM. According to a recent ab initio density-functional study 23 the bonding between boronitrene layers and TM surfaces is largest for the elements in the 4d row but it decreases with an increasing number of d electrons. Compared to the strongest bonding of the BN/ Ru͑0001͒ system, the calculated bonding energies for BN/ Ag͑111͒ range from 0 -20 %, depending on the applied density functional ͓local-density approximation ͑LDA͒, WuCohen ͑WC͒, and Perdew-Burke-Ernzerhof ͑PBE͔͒. In Ref. 23, the bonding between a TM surface and a boronitrene layer correlates with the strength of the TM-d z 2 and B p z and N p z interaction. Between the electropositive B and the TM only the lowest ͑and thus bonding B p z ͒ states are occupied, leading to a bonding interaction for all TM whereas antibonding states become occupied between N and TM, making the interaction in total repulsive. However, in case of strong bonding-antibonding interactions with TM states right at the Fermi energy ͑E F ͒ some of these antibonding states may be shifted above E F , which can reduce the strong Coulomb repulsion between the TM and N. For the case of BN/Ag͑111͒ the d z 2 density of states of the Ag͑111͒ substrate is hardly affected upon the formation of the BN/Ag͑111͒ interface, since all Ag d z 2 states are well below E F and thus fully occupied. Finally the weak bonding comes from a partial cancellation between strong repulsive forces for the N sublattice and weak attractive forces for the B sublattice, which appear at relatively long distances from the Ag͑111͒ surface.Initially, our investigation of growing boronitrene layers on Ag͑...

Boron Nitride on Cu(111): An Electronically Corrugated Monolayer

“…Considerable geometric corrugations can only be achieved by a large lattice mismatch combined with strong electronic BN/metal interactions, which are dictated by the filling of the metal d shell. According to theoretical reports, BN thus has a very low binding energy on Ag(111) and Cu(111), consistent with experimental evidence of a weak interaction in both systems 24,28 . In analogy to the Ni(111) case, where the small lattice mismatch of -0.4 % leads to a commensurate 1x1 structure 26,36 , a slightly stretched commensurate 1x1 overlayer was proposed for Cu(111) which has a 2.6 % larger lattice constant than Ni(111) 28 .…”

“…on various 3d, 4d and 5d transition metals 1,[20][21][22][23][24] . Depending on lattice mismatch, symmetry of the supporting surface and interaction strength between BN and metal, a variety of morphologies can be achieved: Uniform commensurate layers (Ni(111)) [25][26][27][28] , films exhibiting Moiré patterns (Pd(111), Pt(111), Pd(110)) [29][30][31] , strongly corrugated nanomesh topologies (Rh(111), Ru(0001)) 16,32 or one-dimensional superstructures (Cr(110), Fe(110)) 33,34 .…”

“…2b), indicating some strain in the h-BN layer 48 . Nevertheless, it can be concluded that BN on Cu(111) acts neither as a rigid overlayer keeping the bulk lattice constant like on Ag(111) 24 nor does it adapt a commensurate 1x1 structure as on Ni(111) 26 . This finding is in agreement with the observation of randomly oriented triangular BN islands within the same grain of a Cu foil 4 but obviously conflicts with a report claiming a commensurate 1x1 BN monolayer on Cu(111) 28 .…”

Hexagonal boron nitride on transition metal surfaces

“…Similar nanomesh structures have been found on Ru(0001), Pd(111), and Pt(111), which present comparable or even larger lattice constant mismatches. On other metals, like Ag, with a weak interaction and smaller differences in the lattice constants, commensurate structures with no preferred relative orientation [9,12] have been observed. Density functional theory (DFT)-based electronic structure calculations have been instrumental in the understanding of the structure and properties of the h-BN and gr nanomeshes [2,5,12,17,19].…”

“…Chemical vapour deposition of precursor molecules, e.g., borazine in the case of h-BN, on a hot metallic surface leads to a spontaneous formation of the uniform epitaxial monolayers. Originally, the preparation of a single layer of h-BN was achieved on the Rh(111) surface [1,2], but recently similar structures have been grown on Ru(0001) [3][4][5], Pt(111) [4,6,7], Ni(111) [8][9][10], Cu(111) [10], Pd(111) [11], and Ag(111) [12]. One-dimensional structures of h-BN have been produced using the same procedure on Cr(110) [13], Fe(110) [14], and Mo(110) [15].…”