Blue emission at atomically sharp 1D heterojunctions between graphene and h-BN

In-plane two-dimensional heterostructures offer atomically sharp one-dimensional heterojunctions that enable unique interfacial functionalities. Lateral heterostructure interfaces have improved device performance in p–n rectification, interlayer excitons, and low-resistance contacts, highlighting emergent phenomena at 2D material junctions. Theoretical works predicted half-metallic or semiconducting behavior for ideal zigzag or armchair graphene/h-BN interfaces, and STM studies observed localized interfacial states near zero bias at zigzag edges. Disordered interfaces are expected in patterned regrowth processes, but their localized states and roles remain unclear. This study investigates whether graphene/h-BN one-dimensional heterojunctions themselves exhibit novel optoelectronic functionality, specifically probing for light emission originating from interfacial localized states in disordered boundaries.

Prior theory suggested localized density of states at random, disordered graphene/h-BN interfaces, whereas ideal zigzag/armchair interfaces were predicted to show half-metallic or semiconducting properties. STM experiments previously detected sharp peaks near zero bias attributed to localized interfacial states at zigzag graphene/h-BN edges and enhanced LDOS at interfaces composed of segments forming 120° angles, with distinct states at −0.6 eV (C–B) and +0.6 eV (C–N) terminations. Disordered interfaces are common in lateral heterostructures from patterned regrowth, yet their optoelectronic signatures were unknown. The current work contrasts with prior reports of light emission in 2D materials arising from doped Pt atoms, hydrogenated edges in large nanoholes, intrinsic point defects in h-BN (e.g., NBVN, carbon substitutions), or point defects in WSe2, by proposing an interfacial-state origin for blue emission at disordered graphene/h-BN boundaries.

Experimental fabrication and characterization: (1) Simple in-plane graphene/h-BN heterostructures were formed by catalytic conversion of monolayer h-BN to graphene on Pt(111). CVD-grown single-layer h-BN on Pt(111) (ammonia borane precursor) was heated in Ar (50 sccm) at 0.21 Torr to 1000 °C; conversion initiated with CH4 (5 sccm) and Ar (50 sccm) for 10 minutes, yielding in-plane graphene/h-BN heterostructures. (2) Graphene quantum dots embedded in h-BN (GQD/h-BN) were prepared by spatially controlled conversion using a Pt nanoparticle (NP) array made via self-patterning PS-b-P4VP micelles loaded with H2PtCl6, followed by annealing at 400 °C in air for 30 min. CVD h-BN grown on Pt was transferred onto the Pt NPs/SiO2 substrate (electrochemical delamination). The conversion was conducted at 0.21 Torr Ar (50 sccm), ramp to 950 °C in 40 min, then CH4 (5 sccm) + Ar (50 sccm) for 10 min, selectively converting h-BN atop Pt NPs to graphene and forming uniform ~7 nm GQD arrays embedded in h-BN. (3) Transfers used a PS support: the GQD/h-BN on Pt NPs/SiO2 was spin-coated with PS, SiO2 removed in 5% HF, Pt NPs removed in aqua regia (HCl:HNO3 = 3:1), then transferred to target substrate and PS removed with toluene. (4) Characterization included SEM (Verios 460), AFM (Bruker Dimension Icon), Raman (532 nm) and PL (266 nm) micro-spectroscopy (alpha 300, WITec). STEM/EELS analysis used JEOL JEM-2100F at 60 kV with aberration correction and Gatan Quantum spectrometer; elemental maps (B, C, N) and annular dark-field images were collected to resolve interface atomic structure. (5) Stacked structures: four-layer GQD/h-BN stacks (4L GQD/h-BN) were assembled by layer-by-layer wet transfer; a second type inserted additional h-BN sheets between each GQD/h-BN layer (4L GQD/h-BN with h-BN intercalation). (6) LED fabrication: Stack was ITO (150 nm)/PEDOT:PSS (40 nm)/PVK (20 nm)/GQD-hBN emitting layer/TPBI (60 nm)/LiF (1 nm)/Al (100 nm). Substrates were cleaned (DI water, acetone, IPA), air plasma treated; PEDOT:PSS spin-coated (3000 rpm, 40 s, 150 °C, 30 min), PVK spin-coated (1500 rpm, 40 s; 15 mg/mL in chlorobenzene; 120 °C, 20 min). TPBI and LiF/Al were thermally evaporated at ~10⁻⁶ Torr. Device J–L–V and EL spectra were measured with a Keithley 2400, calibrated photodiode (FDS100), and fiber spectrometer (FPP2000) in inert atmosphere. Control experiments: PL was measured on bare Pt NPs, bare h-BN, converted h-BN on SiO2/Si without Pt NPs (950 °C, CH4/Ar = 5/50 sccm), bare GQD arrays patterned in graphene via O2 plasma with Pt NP masks, and h-BN with nano-holes produced by H2 etching at 700 °C on Pt NPs (10 sccm H2); none showed the 410 nm PL peak. Theoretical modeling: A polycrystalline in-plane graphene/h-BN heterostructure lattice was constructed via molecular dynamics with orientation mismatch, producing disordered junctions comprised of non-hexagonal rings. A tight-binding Hamiltonian was employed to describe electronic properties. The Kernel Polynomial Method evaluated the Green’s function to compute local density of states (LDOS) projected onto interface sites. Three average grain sizes (10, 20, 40 nm) were studied to assess size dependence.

• Observation of blue photoluminescence (PL) at 410 nm localized at graphene/h-BN interfaces in in-plane heterostructures under 266 nm excitation. No PL observed from pure graphene or h-BN regions.
• PL mapping shows emission exclusively along the circular interface boundary; Raman mapping confirms material regions via graphene 2D band and h-BN E2g peak.
• Embedding graphene quantum dots (GQDs, ~7 nm) in h-BN (GQD/h-BN) increases interface density and enhances PL intensity by ~6× relative to simple G/h-BN interfaces. Quantitatively, interface length per unit area is 0.0082 nm⁻¹ for GQD/h-BN versus 0.0013 nm⁻¹ for G/h-BN (~6.3×), consistent with the PL intensity ratio.
• Control samples (bare Pt NPs, bare h-BN, converted h-BN without Pt NPs, bare GQD arrays on graphene, h-BN with nano-holes) show no 410 nm PL, supporting an interfacial origin linked to G/h-BN junctions.
• Theoretical LDOS at disordered G/h-BN interfaces exhibits two pronounced peaks near −1.2 eV and +2.0 eV, whose energy separation corresponds to ~390 nm emission, close to the experimental 410 nm PL. These localized states are concentrated at structural defects along the disordered interface. The peak energies are insensitive to average grain sizes of 10, 20, and 40 nm.
• ADF-STEM and EELS mapping reveal disordered interface structures with 5- and 7-membered rings comprising C, B, and N atoms, corroborating the structural model for localized interfacial states.
• Vertical stacking: Simply stacking four GQD/h-BN layers (4L GQD/h-BN) reduces PL due to quenching (photon reabsorption and nonradiative energy transfer). Inserting h-BN intercalation layers between GQD/h-BN films significantly improves PL intensity by suppressing interlayer charge transfer, though not to the ideal 4× due to residual reabsorption.
• Proof-of-concept LEDs using GQD/h-BN heterostructures exhibit blue electroluminescence without additional energy donors (details in Supplementary Information).

The results demonstrate that one-dimensional, atomically resolved graphene/h-BN heterojunctions can host localized electronic states that mediate blue light emission. The exclusive PL at interfaces, the scaling of PL with interface density, and the absence of emission in multiple control samples strongly support an interfacial-state mechanism rather than intrinsic defects or nanoparticle-induced effects. Theoretical calculations on disordered interfaces reproduce localized LDOS peaks with an energy spacing matching the observed blue emission, and STEM/EELS directly reveals the disordered 5–7 ring motifs expected to host such states. The size independence of LDOS features with grain size indicates that emission energy is governed by local interface disorder rather than domain dimensions. Vertical stacking with h-BN barriers isolates emitting junctions and mitigates nonradiative interlayer coupling, demonstrating a strategy to enhance emission efficiency and suggesting practical routes for integrating such 1D emitters into optoelectronic architectures. Distinct from previously reported emissions due to dopants, edge hydrogenation, or point defects in h-BN and TMDs, this work establishes disordered G/h-BN interfaces as a new emission platform.

This study establishes blue light emission from atomically sharp one-dimensional heterojunctions between graphene and h-BN, attributed to localized interfacial states at disordered boundaries. By engineering interface density via GQD arrays embedded in h-BN and employing vertical stacks with h-BN intercalation layers, emission intensity is enhanced and quenching mitigated. Atomic-resolution microscopy and theoretical LDOS calculations substantiate the interfacial origin of the emission. These findings introduce disordered G/h-BN junctions as promising building blocks for optoelectronics. Future work could focus on quantitative quantum efficiency optimization, spectral tunability via controlled interface chemistry and strain, improved spatially resolved spectroscopy to isolate single junctions, and integration into device platforms leveraging h-BN barriers for charge and energy management.

• Spatial resolution: Confocal PL measurements probe areas larger than the atomic interface, making it challenging to focus exclusively on the 1D junction; thus, while multiple controls support the assignment, PL cannot be conclusively isolated to only the interface with current PL techniques.
• Theoretical model: Tight-binding Hamiltonian and Kernel Polynomial Method do not capture all many-body effects (electron–electron interactions, excitonic Coulomb screening), leading to a small discrepancy between calculated (~390 nm) and measured (410 nm) emission wavelengths.
• Stacked films: Even with h-BN intercalation layers, PL enhancement is sub-linear due to residual photon reabsorption and nonradiative energy transfer, limiting attainable intensity gains.