Nitride Heterostructures Research Articles

Low-frequency vibration induced piezoelectric boost to photocatalytic hydrogen evolution through 2D-2D-stacked MoS2-carbon nitride

MoS2-carbon nitride heterostructures which are highly sensitive to low-frequency vibration are demonstrated to be the catalysts for piezo-photocatalytic hydrogen evolution reaction (HER). The configuration of MoS2 nanostructure on carbon nitride plays a crucial role in the piezo-photocatalytic HER activity of MoS2-carbon nitride heterostructure. With the cocatalyst of Pt NPs on the carbon nitride portion, 2D-2D stacked MoS2-carbon nitride catalyst exhibits considerably higher HER rate compared to the pristine carbon nitride and MoS2 nanoflower (NF)-carbon nitride catalysts under illumination coupling with the mechanical energy of vortex-induced shearing force. Experimental and calculation results indicate that the MoS2 nanosheets mainly perform as the piezopotential generator to induce an electric field in the carbon nitride counterpart. With the configuration of 2D-2D stacking, the light harvesting of carbon nitride in the heterostructure remains the same as the pristine one. Nevertheless, the recombination of photogenerated electron-hole pairs in the carbon nitride portion of the MoS2-carbon nitride heterostructure is inhibited due to the electric field induced by MoS2 nanosheet under low-frequency vortex vibration, resulting in the significantly boosted HER rate obtained from the 2D-2D stacked MoS2-carbon nitride heterostructure.

Porous heterostructure of graphene/hexagonal boron nitride as an efficient electrocatalyst for hydrogen peroxide generation

AbstractCompared with the traditional heteroatom doping, employing heterostructure is a new modulating approach for carbon‐based electrocatalysts. Herein, a facile ball milling‐assisted route is proposed to synthesize porous carbon materials composed of abundant graphene/hexagonal boron nitride (G/h‐BN) heterostructures. Metal Ni powder and nanoscale h‐BN sheets are used as a catalytic substrate/hard template and “nucleation seed” for the formation of the heterostructure, respectively. As‐prepared G/h‐BN heterostructures exhibit enhanced electrocatalytic activity toward H2O2 generation with 86%–95% selectivity at the range of 0.45–0.75 V versus reversible hydrogen electrode (RHE) and a positive onset potential of 0.79 versus RHE (defined at a ring current density of 0.3 mA cm−2) in the alkaline solution. In a flow cell, G/h‐BN heterostructured electrocatalyst has a H2O2 production rate of up to 762 mmol gcatalyst−1 h−1 and Faradaic efficiency of over 75% during 12 h testing, superior to the reported carbon‐based electrocatalysts. The density functional theory simulation suggests that the B atoms at the interface of the G/h‐BN heterostructure are the key active sites. This research provides a new route to activate carbon catalysts toward highly active and selective O2‐to‐H2O2 conversion.

Interfacial charge transfer and electronic structure of diamond/c-BN heterointerface

In this work, the interfacial structures and electronic properties of diamond and cubic boron nitride heterostructures are investigated using first principles calculation. It is found that the n-type (p-type) surface doping appears at the heterostructures with interface CN (C—B) bonds, which is attributed to the interface charge transfer. The doping feature of heterostructures is determined by the interface bonds, and it is not related to the surface functionalization and crystal orientation. The areal electron (hole) density values are 6.57 × 1013 — 1.57 × 1014 cm−2 (2.24 × 1014 — 3.72 × 1014 cm−2). This work is helpful for promoting diamond applied in electronic and opto-electronic devices.

Molecular dynamics study of tensile properties of graphene/GaN heterostructures

Graphene/GaN nanocomposites have been widely used in high-power and high-frequency optoelectronic devices. At present, the thermal transport characteristics of graphene/gallium nitride heterostructures have been investigated by many scholars, but their mechanical properties have not been systematically studied. In this paper, the effects of graphene layer number, temperature and interfacial structure on the mechanical properties of graphene/GaN heterostructures were investigated by molecular dynamics method. The mechanical properties of materials were analyzed by failure stress, failure strain and Young’s modulus. The simulation results show that the heterogeneous structure is very sensitive to temperature. When the temperature is set at 2000K, the Young’s modulus of the heterostructure decreases by 25.11% compared with that at 300K, which indicates that the increase of temperature will reduce the mechanical properties of graphene composites, However, when the number of graphene layers increases, the mechanical properties of the heterostructures also improved. With the number of graphene layers is set from 1 layer to 5 layers, the performance of the heterostructure is improved, and its Young’s modulus increases by 48.46%. In addition, the effect of interface structure on the young’s modulus of the heterostructure structure is not obvious, but it will affect the maximum failure stress and maximum failure strain of the material. The mechanical properties of graphene in cross section contact with gallium atom are better than those of nitrogen atom. It is beneficial to improve the reliability of microelectronic devices to control and design heterogeneous structures based on the research results.

Graphene and 2D Hexagonal Boron Nitride Heterostructure for Thermal Management in Actively Tunable Manner.

Thermal management is a critical task for highly integrated or high-power semiconductor devices. Low dimensional materials including graphene and single-layer hexagonal boron nitride (BN) are attractive candidates for this task because of their high thermal conductivity, semi-conductivity and other excellent physical properties. The similarities in crystal structure and chemistry between graphene and boron nitride provide the possibility of constructing graphene/BN heterostructures bearing unique functions. In this paper, we investigated the interfacial thermal transport properties of graphene/BN nanosheets via non-equilibrium molecular dynamics (NEMD) simulations. We observed a significant thermal rectification behavior of these graphene/BN nanosheets, and the rectification ratio increased with the system length increases up to 117%. This phenomenon is attributed to the mismatch of out-of-plane phonon vibration modes in two directions at the interface. In addition, we explored the underlying mechanism of the length dependence of the thermal transport properties. The results show promise for the thermal management of this two-dimensional heterostructure in an actively tunable manner.

Wrinkle-mediated CVD synthesis of wafer scale Graphene/h-BN heterostructures

The combination of two-dimensional materials (2D) into heterostructures enables their integration in tunable ultrathin devices. For applications in electronics and optoelectronics, direct growth of wafer-scale and vertically stacked graphene/hexagonal boron nitride (h-BN) heterostructures is vital. The fundamental problem, however, is the catalytically inert nature of h-BN substrates, which typically provide a low rate of carbon precursor breakdown and consequently a poor rate of graphene synthesis. Furthermore, out-of-plane deformations such as wrinkles are commonly seen in 2D materials grown by chemical vapor deposition (CVD). Herein, a wrinkle-facilitated route is developed for the fast growth of graphene/h-BN vertical heterostructures on Cu foils. The key advantage of this synthetic pathway is the exploitation of the increased reactivity from inevitable line defects arising from the CVD process, which can act as active sites for graphene nucleation. The resulted heterostructures are found to exhibit superlubric properties with increased bending stiffness, as well as directional electronic properties, as revealed from atomic force microscopy measurements. This work offers a brand-new route for the fast growth of Gr/h-BN heterostructures with practical scalability, thus propelling applications in electronics and nanomechanical systems.

Plasmon-Induced Enhanced Light Emission and Ultrafast Carrier Dynamics in a Tunable Molybdenum Disulfide-Gallium Nitride Heterostructure.

The effect of localized plasmon on the photoemission and absorption in hybrid molybdenum disulfide-Gallium nitride (MoS2-GaN) heterostructure has been studied. Localized plasmon induced by platinum nanoparticles was resonantly coupled to the bandedge states of GaN to enhance the UV emission from the hybrid semiconductor system. The presence of the platinum nanoparticles also increases the effective absorption and the transient gain of the excitonic absorption in MoS2. Localized plasmons were also resonantly coupled to the defect states of GaN and the exciton states using gold nanoparticles. The transfer of hot carriers from Au plasmons to the conduction band of MoS2 and the trapping of excited carriers in MoS2 within GaN defects results in transient plasmon-induced transparency at ~1.28 ps. Selective optical excitation of the specific resonances in the presence of the localized plasmons can be used to tune the absorption or emission properties of this layered 2D-3D semiconductor material system.

Interface engineering of bimetallic nitrides nanowires as a highly efficient bifunctional electrocatalyst for water splitting

Electrolytic water splitting offers a prodigious amount of hydrogen and oxygen production, which could satisfy the demand for clean energy for building the community of human destiny. Thus, as the key technology barrier, the development of a low-cost and high-performance bifunctional transition metal electrocatalyst toward water splitting is still a challenge. In this work, aiming to enhance electrocatalytic performance, the nickel molybdenum nitride heterostructure nanowire arrays were synthesized on nickel foam (Ni 3 N-Mo 2 N/NF) via hydrothermal strategy followed by a direct nitridation, from which the heterostructure nanowire was achieved. The self-supporting Ni 3 N-Mo 2 N/NF electrodes exhibits very low overpotentials of 66 and 252 mV at 10 mA cm −2 for the hydrogen evolution reaction and oxygen evolution reaction, respectively. When the cathode and anode were both Ni 3 N-Mo 2 N/NF, a current density of 10 mA cm −2 was achieved with only 1.55 V. This work provides a new idea for the design and preparation of non-precious metal-based transition metal nitride catalysts. • Nickel molybdenum nitride heterostructure arrays was designed as efficient bifunctional electrocatalysts. • The Ni 3 N-Mo 2 N/NF catalyst only needs a cell voltage of 1.55 V to drive 10 mA cm −2 . • Catalytic performance is enhanced by optimization of heterostructure interfaces.

Hierarchical ternary layered double hydroxide/graphitic carbon nitride heterostructures as visible-light photocatalysts for efficient reduction of CO2

The development and synthesis of high-efficient, stable, and cost-effective photocatalysts to reduce both world-wide energy and environmental issues are the most significant challenge in CO2 reduction. Herein, we explore the photocatalytic performance over NiFeV layered double hydroxide (LDH) nanosheets, g-C3N4, and NiFeV-LDH/g-C3N4 heterostructures, which convert CO2 into high value-added fuels, such as CO and CH4. The 2D/2D hierarchical flower-like structure created an outstanding heterosystem with close interfaces and prominently exposed catalytic active sites to dramatically improve light-harvesting ability. The charge transfer among the individual components made the separation of photogenerated charge carriers easier and lessened their recombination rate, enhancing the photoreduction of CO2. The ratio of g-C3N4 to NiFeV-LDH in term of weight had a significant impact on the photocatalytic activity of the NiFeV-LDH/g-C3N4 heterostructure. The photocatalyst generated the maximum yields of CH4 (15.2 µmol h−1g−1) when the weight ratio of g-C3N4 to NiFeV-LDHs was 15%, which was 4.04 times that of pure NiFeV-LDH. The yield of CO was 13.05 µmol h−1g−1, 3.15 times that of pure NiFeV-LDH. Furthermore, during cycling experimental runs, the optimized NiFeV-LDH/g-C3N4-15% heterostructure exhibited a remarkable photostability with no discernible change in the amounts of CO and CH4 formation. The significantly improved photocatalytic performance towards CO2 reduction was confirmed by the XPS and HRTEM analyses, which showed strong electronic interactions and promoted charge transfer between heterostructure components. The current study provides a feasible way to enhance the photocatalytic performance of LDH-based heterostructures and opens up new prospects for developing LDH-based photocatalysts towards CO2 reduction.

Boron nitride-graphene in-plane hexagonal heterostructure in oxygen environment

Aiming to improve fabrication protocols for boron nitride and graphene (h-BNG) lateral heterostructures, we studied the growth of h-BNG thin films on platinum and their behavior in an oxygen environment. We employed a surface science approach based on advanced spectroscopy and imaging techniques to investigate the evolution of surface stoichiometry and chemical intermediates at each reaction step. During oxygen exposure at increasing temperatures, we observed progressive and subsequent intercalation of oxygen, and selective etching of graphene accompanied by the oxidation of boron.Additionally, by exploiting the O2 etching selectivity towards graphene at 250 °C and repeating growth cycles, we obtained in-plane h-BNG layers with controllable compositions and vertically stacked h-BN/Gr heterostructures without the use of consecutive transfer procedures. The growth using a single precursor molecule can be beneficial for the development of versatile atomically thin layers for electronic devices.

Terahertz photodetection in scalable single-layer-graphene and hexagonal boron nitride heterostructures

The unique optoelectronic properties of single layer graphene (SLG) are ideal for the development of photonic devices across a broad range of frequencies from x rays to microwaves. In the terahertz (THz) frequency range (0.1–10 THz), this has led to the development of optical modulators, nonlinear sources, and photodetectors with state-of-the-art performances. A key challenge is the integration of SLG-based active elements with pre-existing technological platforms in a scalable way, while maintaining performance level unperturbed. Here, we report room temperature THz detectors made of large-area SLG, grown by chemical vapor deposition (CVD) and integrated in antenna-coupled field effect transistors. We selectively activate the photo-thermoelectric detection dynamics, and we employ different dielectric configurations of SLG on Al2O3 with and without large-area CVD hexagonal boron nitride capping to investigate their effect on SLG thermoelectric properties underpinning photodetection. With these scalable architectures, response times ∼5 ns and noise equivalent powers (NEPs) ∼1 nW Hz−1/2 are achieved under zero-bias operation. This shows the feasibility of scalable, large-area, layered material heterostructures for THz detection.

Airy Function-Based Model for 2-DEG Charge and Surface Potential in N-Polar Gallium Nitride Heterostructures

A systematic, analytical method to obtain the charge density and surface potential in an N-polar GaN/AlGaN heterostructure is presented. This method also provides the wave functions, subband energies, and band diagram. The model accounts for the greater leakage of the wave functions into the spacer and barrier layers in the N-polar structure as compared to the Ga-polar structure. The framework is based on the solution of Schrödinger–Poisson equations for an approximately triangular well potential with finite confinement, achieved using first-order perturbation theory. No fitting parameters are used. Results obtained using our model are in good agreement with numerical results (obtained using the finite difference method) for a wide range of bias conditions (from OFF- to ON-states) and Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{1}-{x}}\text{N}$ </tex-math></inline-formula> spacer mole fractions.

Overdamped phase diffusion in hBN encapsulated graphene Josephson junctions

We investigate the zero-bias behavior of Josephson junctions made of encapsulated graphene boron nitride heterostructures in the long ballistic junction regime. For temperatures down to $2.7$ K, the junctions appear nonhysteretic with respect to the switching and retrapping currents ${I}_{C}$ and ${I}_{R}$. A small nonzero resistance is observed even around zero-bias current and scales with temperature as dictated by the phase diffusion mechanism. By varying the graphene carrier concentration we are able to confirm that the observed phase diffusion mechanism follows the trend for an overdamped Josephson junction. This is in contrast with the majority of graphene-based junctions which are underdamped and shorted by the environment at high frequencies.

Synergistically enhanced solar light‐driven degradation of hazardous food colorants by ultrasonically derived MgFe2O4/S‐doped g‐C3N4 nanocomposite: A Z‐scheme system‐based heterojunction approach

Magnesium ferrite/sulfur‐doped graphitic nitride (MFO/SCNNS) heterostructure has been developed via sonication‐assisted deposition of zero‐dimensional MFO over the surface of two‐dimensional SCN nanosheets. Additionally, the prepared nanocomposite material has been characterized by several analytical characterization techniques including XRD, Fourier transform infrared (FT‐IR), high‐resolution transmission electron microscopy (HR‐TEM), selected‐area electron diffraction (SAED), energy‐dispersive spectrometry (EDS), Brunauer–Emmett–Teller (BET), vibrating sample magnetometer (VSM), UV–Vis. spectroscopy, electron spin resonance(ESR), and X‐ray photoelectron spectroscopy (XPS) which indicated the existence of strong interfacial interactions via heterojunction formation between MFO and SCNNS. The as prepared nanocomposite, especially MFO:SCNNS (1:1) (having 1:1 mass ratio of MFO to SCNNS), offered impressive photo‐response for the complete degradation of Erythrosine B and Indigo Carmine within 30 min under direct solar light irradiation. The enhanced photoactivity of the MFO:SCNNS (1:1) was also confirmed by the photoluminescence, photocurrent and electrochemical impedance spectroscopy. The Mott–Schottky analysis also depicts the formation of p‐n heterojunction at the interface of MFO and SCNNS, responsible for the enhanced photoactivity. Additionally, the degradation process has also been studied using mass spectrometry, UV–Vis, and ESR spectral analysis. The trapping experiments were also conducted to confirm the formation of active radical species during the photodegradation reaction. Furthermore, the nanocomposite photocatalytic material offered excellent stability and reusability and thus can serve as an effective candidate for environmental remediation application such as real waste water treatment.

Exploring the structural and optoelectronic properties of natural insulating phlogopite in van der Waals heterostructures

Naturally occurring van der Waals crystals have brought unprecedented interest to nanomaterial researchers in recent years. So far, more than 1800 layered materials (LMs) have been identified but only a few insulating and naturally occurring LMs were deeply investigated. Phyllosilicate minerals, which are a class of natural and abundant LMs, have been recently considered as a low-cost source of insulating nanomaterials. Within this family an almost barely explored material emerges: phlogopite (KMg3(AlSi3)O10(OH)2). Here we carry out a high throughput characterization of this LM by employing several experimental techniques, corroborating the major findings with first-principles calculations. We show that monolayers (1L) and few-layers of this material are air and temperature stable, as well as easily obtained by the standard mechanical exfoliation technique, have an atomically flat surface, and lower bandgap than its bulk counterpart, an unusual trend in LMs. We also systematically study the basic properties of ultrathin phlogopite and demonstrate that natural phlogopite presents iron impurities in its crystal lattice, which decreases its bandgap from about 7 eV to 3.6 eV. Finally, we combine phlogopite crystals with 1L-WS2 in ultrathin van der Waals heterostructures and present a photoluminescence study, revealing a significant enhancement on the 1L-WS2 optical quality (i.e. higher recombination efficiency through neutral excitons) similarly to that obtained on 1L-WS2/hexagonal boron nitride heterostructures. Our proof-of-concept study shows that phlogopite should be regarded as a good and promising candidate for LM-based applications as a low-cost layered nanomaterial.

Self-powered, low-noise and high-speed nanolayered MoSe2/p-GaN heterojunction photodetector from ultraviolet to near-infrared wavelengths

Integration of nanolayered metal chalcogenides with wide-bandgap semiconductors forming pn heterojunction leads to the way of high-performance photodetection. This work demonstrates the fabrication of a few nanometer thick Molybdenum diselenide (MoSe2)/Mg-doped Gallium Nitride (p-GaN) heterostructure for light detection purposes. The device exhibits low noise broadband spectral response from ultraviolet to near-infrared range (300–950 nm). The band-alignment and the charge transfer at the MoSe2/p-GaN interface promote self-powered photodetection with high photocurrent to dark current ratio of 2000 and 1000 at 365 nm and 640 nm, respectively. A high responsivity of 130 A W−1, detectivity of 4.8 × 1010 Jones, and low noise equivalent power of 18 fW/Hz1/2 at 365 nm is achieved at an applied bias of 1 V. Moreover, the transient measurements reveal a fast rise/fall time of 407/710 μsec for the fabricated device. These outcomes exemplify the viability of MoSe2/p-GaN heterostructure for high-speed and low-noise broadband photodetector applications.

A Qualitative Study of the Disorder Effect on the Phonon Transport in a Two-Dimensional Graphene/h-BN Heterostructure

Recently, massive efforts have been made to control phonon transport via introducing disorder. Meanwhile, materials informatics, an advanced material-discovery technology that combines data-driven search algorithms and material property simulations, has made significant progress and shown accurate prediction ability in studying the target properties of new materials. However, with the introduction of disorder, the design space of random structures is greatly expanded. Global optimization for the entire domain is nearly impossible with the current computer resource even when materials informatics reduces the design space to a few percent. Toward the goal of reducing design space, we investigate the effect of different types of disorders on phonon transport in two-dimensional graphene/hexagonal boron nitride heterostructure using non-equilibrium molecular dynamics simulation. The simulation results show that when the hexagonal boron nitride is distributed disorderly in the coherent phonon-dominated structure, that is, the structure with a period length of 1.23 nm, the thermal conductivity is significantly reduced due to the appearance of coherent phonon localization. By qualitatively analyzing different types of disorder, we found that the introduction of disordered structure in the cross direction with a larger shift distance can further reduce the thermal conductivity. Further physical mechanism analysis revealed that the structures with lower thermal conductivity were caused by weak propagation and strong localization of phonon. Our findings have implications for accelerating machine learning in the search for structures with the lowest thermal conductivity, and provide some guidance for the future synthesis of 2D heterostructures with unique thermal properties.

High-Performance All-Optical Modulator Based on Graphene-HBN Heterostructures

Graphene has emerged as an ultrafast photonic material for on-chip all-optical modulation. However, its atomic thickness limits its interaction with guided optical modes, which results in a high switching energy per bit or low modulation efficiencies. Nonetheless, it is possible to enhance the interaction of guided light with graphene by nanophotonic means. Herein, we present a practical design of an all-optical modulator that is based on graphene and hexagonal boron nitride (hBN) heterostructures that are hybrid integrated into silicon slot waveguides. Using this device, a high extinction ratio (ER) of 7.3 dB, an ultralow insertion loss (IL) of <0.6 dB, and energy-efficient switching (<0.33 pJ/bit) are attainable for a 20{\mu}m long modulator with double layer graphene. In addition, the device performs ultrafast switching with a recovery time of <600 fs, and could potentially be employed as a high-performance all-optical modulator with an ultra-high bandwidth in the hundreds of GHz. Moreover, the modulation efficiency of the device is further enhanced by stacking additional layers of graphene-hBN heterostructures, while theoretically maintaining an ultrafast response. The proposed device exhibits highly promising performance metrics, which are expected to serve the needs of next-generation photonic computing systems.

Potential-resolved wavelength tunable electrochemiluminescence from graphitic carbon nitride heterostructure

Biocompatible and water-dispersible electrochemiluminescence (ECL) phosphors with potential/spectrum-resolved ECL emission are highly desired to underpin ECL-based multiplex detection in a spot-free format. In this work, we develop a band structure engineered graphitic carbon nitride, CN425-PDI0.5, to achieve potential-resolved wavelength tunable ECL emission. The covalent incorporation of pyromellitic diimide (PDI) with high electron affinity and mobility endows CN425-PDI0.5 with the coexistence of polymeric melem motifs and melem-PDI motifs. The melem-PDI motifs show lower lowest unoccupied molecular orbital energy level and narrower bandgap, as compared to polymeric melem motifs. By pulsing the CN425-PDI0.5 nanosheets modified glassy carbon electrode at the increasing reduction potential in phosphate buffer solution containing S2O82‒ as coreactant, the cathode ECL gradually tunes the maximum emission wavelength from 540 nm to 440 nm. The CN425-PDI0.5 nanosheets with potential-resolved wavelength tunable ECL emission may provide a promising prospect for promoting solid-state ECL-based multiple detection and extending CN application in the sensing fields.

Epitaxially Grown Ru Clusters–Nickel Nitride Heterostructure Advances Water Electrolysis Kinetics in Alkaline and Seawater Media

The epitaxial heterostructure can be rationally designed based on the in situ growth of two compatible phases with lattice similarity, in which the modulated electronic states and tuned adsorption behaviors are conducive to the enhancement of electrocatalytic activity. Herein, theoretical simulations first disclose the charge transfer trend and reinforced inherent electron conduction around the epitaxial heterointerface between Ru clusters and Ni3N substrate (cRu‐Ni3N), thus leading to the optimized adsorption behaviors and reduced activation energy barriers. Subsequently, the defect‐rich nanosheets with the epitaxially grown cRu‐Ni3N heterointerface are successfully constructed. Impressively, by virtue of the superiority of intrinsic activity and reaction kinetics, such unique epitaxial heterostructure exhibits remarkable bifunctional catalytic activity toward electrocatalytic OER (226 mV @ 20 mA cm−2) and HER (32 mV @ 10 mA cm−2) in alkaline media. Furthermore, it also shows great application prospect in alkaline freshwater and seawater splitting, as well as solar‐to‐hydrogen integrated system. This work could provide beneficial enlightenment for the establishment of advanced electrocatalysts with epitaxial heterointerfaces.