Editing Boron nitride (section)

=== Hexagonal form (h-BN) ===
The most stable crystalline form is the hexagonal one, also called h-BN, α-BN, g-BN, graphitic boron nitride and "white graphene". Hexagonal boron nitride (point group = D<sub>3h</sub>; space group = P6<sub>3</sub>/mmc) has a layered structure similar to graphite. Within each layer, boron and nitrogen atoms are bound by strong [[covalent bond]]s, whereas the layers are held together by weak [[van der Waals force]]s. The interlayer "registry" of these sheets differs, however, from the pattern seen for graphite, because the atoms are eclipsed, with boron atoms lying over and above nitrogen atoms. This registry reflects the local polarity of the B–N bonds, as well as interlayer N-donor/B-acceptor characteristics. Likewise, many metastable forms consisting of differently stacked polytypes exist. Therefore, h-BN and graphite are very close neighbors, and the material can accommodate carbon as a substituent element to form BNCs. BC<sub>6</sub>N hybrids have been synthesized, where carbon substitutes for some B and N atoms.<ref>{{cite journal | author = Kawaguchi, M. | title = Electronic Structure and Intercalation Chemistry of Graphite-Like Layered Material with a Composition of BC6N | journal = Journal of Physics and Chemistry of Solids | volume = 69 | year = 2008 | page = 1171 | doi = 10.1016/j.jpcs.2007.10.076 |issue = 5–6 |bibcode = 2008JPCS...69.1171K |display-authors=etal}}</ref> Hexagonal boron nitride monolayer is analogous to [[graphene]], having a honeycomb lattice structure of nearly the same dimensions. Unlike graphene, which is black and an electrical conductor, h-BN monolayer is white and an insulator. It has been proposed for use as an atomic flat insulating substrate or a [[tunnel diode|tunneling]] dielectric barrier in 2D electronics. .<ref>{{cite journal
| vauthors = Ba K, Jiang W, Cheng J, Bao J, ''et al.''
| date = 2017
| title = Chemical and Bandgap Engineering in Monolayer Hexagonal Boron Nitride
| journal = Scientific Reports
| volume = 7
| issue = 1
| page = 45584
| doi = 10.1038/srep45584
| pmid = 28367992
| bibcode = 2017NatSR...745584B
| s2cid = 22951232
| doi-access = free
| pmc = 5377335
}}</ref>

Studies into the optical properties of [[hexagonal boron nitride|h-BN]] at the few- and mono-layer level have been conducted using specialized techniques like [[deep ultraviolet]] (DUV) [[hyperspectral imaging]] due to its very wide bandgap. Research at low temperatures revealed that [[monolayer]] h-BN exhibits [[photoluminescence]] consistent with a [[direct and indirect bandgaps|direct bandgap]] semiconductor, with emission observed around 6.1 eV. In contrast to observations in other 2D materials like [[transition metal dichalcogenide monolayers|TMDs]], the photoluminescence intensity remains remarkably high in few-layer h-BN, which has been attributed to a high radiative efficiency despite the [[direct and indirect bandgaps|indirect bandgap]] nature of bulk h-BN. Complementary [[atomic force microscopy|AFM]] investigations, particularly in tapping and Kelvin probe modes, have provided nanoscale insight into surface morphology and potential distribution across mono- and few-layer regions. These AFM-based techniques not only assist in confirming flake thickness and uniformity but also support optoelectronic analyses by correlating topographical and electrical variations with luminescence behavior.<ref name="Rousseau2021DUV">{{cite journal | last1=Rousseau | first1=Adrien | last2=Ren | first2=Lei | last3=Durand | first3=Alrik | last4=Valvin | first4=Pierre | last5=Gil | first5=Bernard | last6=Watanabe | first6=Kenji | last7=Taniguchi | first7=Takashi | last8=Urbaszek | first8=Bernhard | last9=Marie | first9=Xavier | last10=Robert | first10=Cédric | last11=Cassabois | first11=Guillaume | title=Monolayer Boron Nitride: Hyperspectral Imaging in the Deep Ultraviolet | journal=Nano Letters | volume=21 | issue=23 | pages=10133–10138 | date=September 16, 2021 | doi=10.1021/acs.nanolett.1c02531 | pmid=34529455 }}</ref>