Scalable Synthesis of Monolayer Hexagonal Boron Nitride on Graphene with Giant Bandgap Renormalization

Abstract

as fundamental building blocks of such 2D devices. Specifically, vertically stacked hBN/ graphene (hBN/G) van der Waals (vdW) heterostructures have been successfully employed to produce emergent properties, such as quantum Hall effect, [8] Hofstadter butterfly spectrum, [9] and plasmon and phonon polaritons. [10] Complementary to the vertical hBN/G vdW heterostructure, the in-plane version forms a covalent hBN/G heterostructure with equally attractive properties, such as transitions between semiconducting, half-metallic, and metallic phases, spin polarization magnetism, and exotic electronic states, [11][12][13][14][15] or even the possibility to reconstruct electronic interfaces similar to those observed in oxide heterostructures. [16,17] The scope of these fascinating properties could be radically expanded by demonstrating epitaxially grown monolayer hBN on graphene with superior structural, electrical, and optical properties, as well as precise control of both the hBN/G out-ofplane and in-plane monolayer interfaces.Recently, intensive efforts have been devoted to the epitaxial growth of hBN on metals, [18][19][20] sapphire, [21] and graphene substrates [22] by using sputtering, [23] chemical vapor deposition (CVD), [24] metal-organic chemical vapor deposition (MOCVD), [25] and molecular beam epitaxy (MBE). [26] Due to the Monolayer hexagonal boron nitride (hBN) has been widely considered a fundamental building block for 2D heterostructures and devices. However, the controlled and scalable synthesis of hBN and its 2D heterostructures has remained a daunting challenge. Here, an hBN/graphene (hBN/G) interface-mediated growth process for the controlled synthesis of high-quality monolayer hBN is proposed and further demonstrated. It is discovered that the in-plane hBN/G interface can be precisely controlled, enabling the scalable epitaxy of unidirectional monolayer hBN on graphene, which exhibits a uniform moiré superlattice consistent with single-domain hBN, aligned to the underlying graphene lattice. Furthermore, it is identified that the deep-ultraviolet emission at 6.12 eV stems from the 1s-exciton state of monolayer hBN with a giant renormalized direct bandgap on graphene. This work provides a viable path for the controlled synthesis of ultraclean, wafer-scale, atomically ordered 2D quantum materials, as well as the fabrication of 2D quantum electronic and optoelectronic devices.

Thickness-Dependent Nonadiabatic Recombination in MoSTe/hBN Heterostructures: An Ultrafast Dynamic Study

“…The optimized lattice parameter of the MoSTe monolayer is 3.35 Å and agrees well with the previously reported theoretical value of 3.34 Å . Similarly, the optimized lattice parameter of the h BN monolayer is 2.51 Å, which also agrees well with the experimental (2.504 Å) and theoretical (2.496 Å) results. To minimize lattice mismatch, a MoSTe supercell with a 3 × 3 × 1 unit cell and an h BN supercell with 4 × 4 × 1 unit cell was employed to form the MoSTe/ h BN supercell.…”

“…Then, we focused on the electronic properties of the MoSTe/ h BN monolayers and heterostructures, which provides a basis for understanding the subsequent processes of photoexcited electron and hole recombination. As depicted in Figure a, the MoSTe monolayer exhibits a band gap of 1.13/1.61 eV (PBE/HSE06), consistent with the reported theoretical values. , Figure b shows that the h BN monolayer possesses a band gap of 4.65/5.71 eV (PBE/HSE06), in accordance with previous theoretical values , albeit slightly smaller than the reported experimental values. ,, Due to its wide band gap, the h BN monolayer exhibits a type-I band alignment when combined with the MoSTe monolayer, as illustrated in Figure d This type-I band alignment is consistently maintained as the number of h BN layers surrounding the MoSTe monolayer increases, with the band gaps remaining nearly constant (see Figure S1). Moreover, the heterostructures possess a direct band gap at the Γ point, where the conduction band minimum (CBM) and valence band maximum (VBM) are exclusively located on the MoSTe layer.…”

Polytypes of sp2-Bonded Boron Nitride

“…In BN, theoretical calculations including the Coulomb correlation predict a direct bandgap at K for the monolayer and an indirect or marginally direct bandgap for stackings of two or more layers [124,[147][148][149]. Photoluminescence experiments [150][151][152] combined with reflectance measurements [150,151] have jointly confirmed using monolayers, deposited by molecular beam epitaxy on highly ordered pyrolytic graphite (HOPG) [150,151] and on suspended membranes [152], that it is a direct bandgap. The photoluminescence of the BN monolayer emits at 6.085 eV at low temperature, which was recently confirmed by the direct measurement of the density of states of a single monolayer of h-BN epitaxially grown on HOPG.…”

Enhanced thermal conductivity and insulation properties of mica tape with BN coating via electrostatic spraying technology

“…[33][34][35][36][37] Thermal conductivity refers to the heat transmitted by the material with a fixed thickness per unit area per unit time and it is the inherent property of the material. [38][39][40][41][42][43] Figure 5 shows the variation of thermal conductivity of high thermal conductivity mica tape with coating mass fraction and temperature. With the increase in temperature, the thermal conductivity of mica tape shows an upward trend, mainly because the increase in temperature will accelerate the thermal movement of molecules and promote the heat conduction between molecules and the heat flow transmission of interfacial pores.…”