Graphene Heterojunctions Research Articles

Self-Powered Photodetectors with High Stability Based on Se Paper/P3HT:Graphene Heterojunction

Self-Powered Photodetectors with High Stability Based on Se Paper/P3HT:Graphene Heterojunction

N-P type charge compensatory synergistic effect for Schottky and efficient photoelectrocatalysis applications: Doping mechanism in (Nb/Re)@WS2/graphene heterojunctions.

Band gap engineering based on doped two-dimensional (2D) transition metal dichalcogenides (TMDs) has shown great potential in the design and development of new nano photoelectronic devices and their application in photoelectrocatalysis. However, there are two key issues that are difficult to take into account, namely the impurity levels induced by dopant atoms appear in the forbidden band of the doping system, which can become the recombination center of photogenerated carriers, thereby reducing the photocatalytic efficiency. Compared with the carrier mobility of the corresponding doped systems, that of intrinsic 2D TMDs is too low. Understanding the doping mechanism of heteroatoms in these systems and designing corresponding crystal structures rationally is important for solving these problems. In this study, the crystal structures of co-doped monolayer WS2 with Nb and Re atoms were designed using density functional theory, and doping systems with graphene (high carrier mobility) were assembled into a heterostructure using the concept of heterorecombination. The N-P type co-doping of Nb and Re atoms retained the continuous band characteristics of the original monolayer WS2 while also providing the high carrier mobility of graphene, yielding an excellent multipurpose material for manufacturing high-speed Schottky devices and efficient water-splitting H evolution catalysts.

SnO2–SnS2/graphene heterojunction composite promotes high-performance sodium ion storage

The design of electrode material nanostructures including reducing material sizes and designing appropriate heterostructures, has great potential in improving charge storage dynamics and enhancing practical performance. In this study, we present the innovative synthesis of SnO2-SnS2/graphene heterojunction composite materials via a controlled vulcanization reaction process. The unique structure endows the composite with high electronic conductivity, rapid ion diffusion rates, elevated electrochemical activity, excellent structural stability, and abundant reaction sites, making it a highly efficient anode material for sodium-ion batteries (SIBs). Half-cell tests demonstrate that the SnO2–SnS2/r–G composite achieves a first Coulombic efficiency of 77.3% at a high current density of 5 A/g, showing remarkable cycling stability. Remarkably, the composite retains a reversible capacity of 330 mA·h/g after 1000 cycles, with a capacity retention rate of 77.5%. Moreover, we elucidate the specific sodium storage mechanisms of the heterojunction composite electrode via in-situ and ex-situ characterization methods. Furthermore, a full battery utilizing Na0.53MnO2 as the cathode and SnO2–SnS2/r–G composite as the anode exhibits outstanding rate performance and long-term cycling stability. This method of heterostructure design and fabrication, coupled with the exceptional performance metrics, suggests that the SnO2–SnS2/r–G heterostructure is a promising candidate for advanced anode materials in SIBs applications.

Electronic and Optical Properties of 2D Heterostructure Bilayers of Graphene, Borophene and 2D Boron Carbides from First Principles.

In the present work the atomic, electronic and optical properties of two-dimensional graphene, borophene, and boron carbide heterojunction bilayer systems (Graphene-BC3, Graphene-Borophene and Graphene-B4C3) as well as their constituent monolayers are investigated on the basis of first-principles calculations using the HSE06 hybrid functional. Our calculations show that while borophene is metallic, both monolayer BC3 and B4C3 are indirect semiconductors, with band-gaps of 1.822 eV and 2.381 eV as obtained using HSE06. The Graphene-BC3 and Graphene-B4C3 bilayer heterojunction systems maintain the Dirac point-like character of graphene at the K-point with the opening of a very small gap (20-50 meV) and are essentially semi-metals, while Graphene-Borophene is metallic. All bilayer heterostructure systems possess absorbance in the visible region where the resonance frequency and resonance absorption peak intensity vary between structures. Remarkably, all heterojunctions support plasmons within the range 16.5-18.5 eV, while Graphene-B4C3 and Graphene-Borophene exhibit a π-type plasmon within the region 4-6 eV, with the latter possessing an additional plasmon at the lower energy of 1.5-3 eV. The dielectric tensor for Graphene-B4C3 exhibits complex off-diagonal elements due to the lower P3 space group symmetry indicating it has anisotropic dielectric properties and could exhibit optically active (chiral) effects. Our study shows that the two-dimensional heterostructures have desirable optical properties broadening the potential applications of the constituent monolayers.

Design and Construction of Carbon-Coated Bimetallic Selenide Heterostructures Loaded on Reduced Graphene Oxide Substrate for Superior Lithium-Ion Storage.

In this work, carbon-coated bimetallic tin-nickel selenide heterostructures loaded on reduced graphene oxide composites were prepared through a metal-organic framework-assisted strategy. The carbon coating mitigates the volume expansion and maintains the structural stability, while the introduction of reduced graphene oxide and heterojunction enhances electrical conductivity and reaction kinetics, thereby together contributing to the enhanced lithium-ion storage performance. As expected, the optimal material delivers excellent lithium-ion storage performance in terms of a high reversible capacity of 1033.4 mAh g-1 at 0.2 A g-1, outstanding rate capability, and long-term cyclability with the capacity of 726.2 mAh g-1 after 500 cycles at 1.0 A g-1 and 452.4 mAh g-1 after 1000 cycles at 2.0 A g-1. Furthermore, the electrochemical reaction mechanism of the composite is analyzed.

Exploring the Structural Stability of 1T-PdO2 and the Interface Properties of the 1T-PdO2/Graphene Heterojunction.

Motivated by a recent study on the air stability of PdSe2, which also reports the metastability of the PdO2 monolayer [Hoffman A. N.. npj 2D Mater. Appl.2019, 3( (1), ), 50.], in this work, we use density functional theory (DFT) to further explore the thermal, dynamic, and mechanical stability of monolayer PdO2 and study its structural and electronic properties. We further studied its vertical heterojunction composed of 1T-PdO2 and graphene monolayers. We show that both the monolayer and the heterojunction are energetically and dynamically stable with no negative frequencies in the phonon spectrum and belong to the vdW-type. 1T-PdO2 is an indirect-band-gap semiconductor with band-gap values of 0.5 eV (GGA) and 1.54 eV (HSE06). The interface properties of the heterojunction show that the n-type Schottky barrier height (SBH) becomes negative at the vertical interface in the PdO2/graphene contact, forming an Ohmic contact and mainly suggesting the potential of graphene for efficient electrical contact with the PdO2 monolayer. However, at the same time, a negative band bending occurs at the lateral interface based on the current-in-plane model. Moreover, the optical absorption of the PdO2/graphene heterojunction under visible-light irradiation is significantly enhanced compared to the situation in their free-standing monolayers.

Enhancing the Performance of Titanium Dioxide Compact Layer on Epitaxial Graphene and Fluorine Tin Oxide Heterojunctions

Enhancing the Performance of Titanium Dioxide Compact Layer on Epitaxial Graphene and Fluorine Tin Oxide Heterojunctions

Novel iodide-modified bismuth molybdate quantum dot/monolayer graphene (0D/2D) heterojunction for efficient photothermal catalytic reduction of CO2

The main influencing factor in photothermal catalytic reduction of CO2 is carrier migration limitation. To further enhance the carrier transport rate, iodide-modified Bi2MoO6 quantum dots (BMO QDs) were constructed and deposited on a monolayer of reduced graphene oxide surface (rGO) to construct a BMO-I QDs/rGO heterojunction. Quantum dots have short carrier migration distances due to their ultra-small bulk phase thickness, allowing carrier migration to occur quickly and electron-hole complexation to be reduced. rGO heterojunction can promote the formation of thin stacked structures in BMO-I QDs and a photothermal conversion temperature of 74. 6 °C. The rGO and BMO-I QDs can form a C–I–Bi interfacial electron bridge, and the I- playing transport channel provides a bridge for carrier interfacial transport, which enables the electrons in the BMO QDs to migrate to the surface of the rGO, formation of an electron cloud on the rGO for rapid catalytic reduction of CO2, and the CO production on BMO-I QDs/5rGO was 2.02 times higher than that on BMO-I QDs. The construction of heterojunctions is demonstrated to accelerate CO2 cleavage and CO desorption by DFT calculations of CO2 adsorption, electronic energy band structure and density of states.

Designing S-scheme of TiO2@g-C3N4/graphene Heterojunction with enhanced photocatalytic activity under visible light: Experiments and DFT calculations

Using a dual hydrothermal pathway, this study investigated an S-scheme heterojunction of synthesized TiO2, g-C3N4, and graphene. The enhanced photocatalytic performance of the composite with an optimized graphene content of 0.1 wt% was clarified due to the improved charge transfer following the S-scheme and formation of the built-in electric field, which is supported by both experiment and density functional theory results. Furthermore, the decomposition pathway of Rhodamine B was investigated using the liquid chromatography-mass spectroscopy (LC-MS/MS) technique with a proposed mechanism.

Engineering the flexibility and elastic modulus of graphene by heterojunctions

Graphene shows both superior flexibility and excellent mechanical strength. The fabricated graphene samples usually contain various defects like grain boundaries, which can either enhance or weaken the mechanical strength of graphene. So, exploring the effects of grain boundaries on the flexibility of graphene is useful in designing graphene-based flexible devices. Employing the first-principles calculation, flexibilities of graphene heterojunctions were studied, aiming to tailor the flexibility of graphene by heterojunctions. Here, by connecting armchair (AC) and zigzag (ZZ) graphene through grain boundaries, graphene heterojunctions with tunable AC to ZZ ratio were constructed. It was found that bending moduli, as well as Young’s moduli, of graphene heterojunctions are lower than the pristine graphene and can be further tailored by the AC to ZZ ratio, making graphene heterojunctions more flexible than graphene. Particularly, changing the AC to ZZ ratio can even alter the relative flexibility of graphene heterojunctions in different directions. Therefore, graphene heterojunction provides an approach to engineer the flexibility of graphene, which is helpful in understanding the mechanical properties of two-dimensional materials and designing the flexible devices.

Charge transport through the multiple end zigzag edge states of armchair graphene nanoribbons and heterojunctions.

This comprehensive study investigates charge transport through the multiple end zigzag edge states of finite-size armchair graphene nanoribbons/boron nitride nanoribbons (n-AGNR/w-BNNR) junctions under a longitudinal electric field, where n and w denote the widths of the AGNRs and the BNNRs, respectively. In 13-atom wide AGNR segments, the edge states exhibit a blue Stark shift in response to the electric field, with only the long decay length zigzag edge states showing significant interaction with the red Stark shift subband states. Charge tunneling through such edge states assisted by the subband states is elucidated in the spectra of the transmission coefficient. In the 13-AGNR/6-BNNR heterojunction, notable influences on the energy levels of the end zigzag edge states of 13-AGNRs induced by BNNR segments are observed. We demonstrate the modulation of these energy levels in resonant tunneling situations, as depicted by bias-dependent transmission coefficient spectra. Intriguing nonthermal broadening of tunneling current shows a significant peak-to-valley ratio. Our findings highlight the promising potential of n-AGNR/w-BNNR heterojunctions with long decay length edge states in the realm of GNR-based single electron transistors at room temperature.

Achieving ultralow friction under high pressure through operando formation of PbS QDs/graphene heterojunction with 0D/1D nanostructure

It is a great challenge to utilize graphene for practical applications in moving parts, which meet high contact pressure and atmosphere environments. In this work, ultralow friction (0.054) of graphene was achieved under high contact pressure (1.03 GPa) and atmosphere environment via the operando formation of PbS quantum dots (QDs)/graphene heterojunction at the frictional interface. It is found that PbS QDs are trapped in graphene nanosheets via shear-induced rearrangement for obtaining the PbS QDs/graphene heterojunctions, which provide an excellent rolling effect to lower friction. It is also found that the heterogeneous PbS QDs/graphene tribofilms have a strong Pb-enriched function and heterojunction nanorod phase. Our objective is to uncover the physical and chemical mechanisms governing the friction of 0D/1D nanostructures within PbS QDs/graphene heterostructures through our studies. This research will enhance our comprehension of nanomaterials' frictional behavior while offering valuable guidance and optimization strategies for their application in mechanical engineering and functional nanomaterials. Consequently, our efforts aim to foster the advancement of nanoscience and technology, leading to additional scientific and technological breakthroughs.

Ultrafast and Broad-Band Graphene Heterojunction Photodetectors with High Gain.

Graphene possesses an exotic band structure that spans a wide range of important technological wavelength regimes for photodetection, all within a single material. Conventional methods aimed at enhancing detection efficiency often suffer from an extended response time when the light is switched off. The task of achieving ultrafast broad-band photodetection with a high gain remains challenging. Here, we propose a devised architecture that combines graphene with a photosensitizer composed of an alternating strip superstructure of WS2-WSe2. Upon illumination, n+-WS2 and p+-WSe2 strips create alternating electron- and hole-conduction channels in graphene, effectively overcoming the tradeoff between the responsivity and switch time. This configuration allows for achieving a responsivity of 1.7 × 107 mA/W, with an extrinsic response time of 3-4 μs. The inclusion of the superstructure booster enables photodetection across a wide range from the near-ultraviolet to mid-infrared regime and offers a distinctive photogating route for high responsivity and fast temporal response in the pursuit of broad-band detection.

Ultra‐High Responsivity Black‐Si/Graphene Heterojunction Photodetectors Enabled by Enhanced Light Absorption and Local Electric Fields

AbstractPhotodetectors with high responsivity, fast response, and broad spectral response are of great importance for a wide range of applications in fundamental science and various industries. However, conventional photodiodes operating at low bias voltage do not provide any gain. The graphene (Gr)/Si van der Waals heterostructure, on the other hand, offers a potential gain due to the limited density of states near the Dirac point. In this work, a highly photoresponsive broadband pyramidal black‐Si/Gr heterojunction photodetector is presented. The device, with an active area of 5×5 mm2 and a bias voltage of −5 V, exhibits an ultra‐high responsivity of 4.1 A W−1. The photoresponsivity can be further increased to 1379 A W−1 by reducing the device area. Comparative experiments reveal that the pyramidal black‐Si/Gr photodetectors exhibit the largest responsivity compared with pyramidal‐Si/Gr and flat‐Si/Gr photodetectors. The gain in pyramidal black‐Si/Gr photodetectors is attributed to both the pyramidal nanoporous structures and the shift of the Fermi level of Gr under bias. Furthermore, the high responsivity and stable operation of the photodetectors enable the demonstration of imaging applications. The results provide a new strategy for enhancing the performance of photodetectors based on 2D materials.

Effect of Andreev processes on the Goos–Hänchen (GH) shift in the Graphene–Superconductor–Graphene (GSG) junctions

In this article, we study the transport properties of Graphene–Superconductor–Graphene (GSG) heterojunction where the superconducting region is created in the middle of a graphene sheet, as contrasted to widely studied transport properties through a Superconductor–Graphene–Superconductor (SGS) type of Josephson junction. We particularly analyse in detail the Goos–Hänchen shift of the electron and the hole at the GS interface in such a junction, due to normal as well as Andreev reflection, using a transfer matrix-based approach. Additionally, we evaluate the normalised differential conductance as a function of bias voltage that characterises the transport through such junction and point out how they are influenced by Andreev and normal reflection. In the subsequent parts of the article we demonstrate how the GH shift for both electron and hole changes with the width of the superconducting region. The behaviour of the differential conductance in such junctions as a function of the bias voltage in the region, dominated by Andreev and normal reflection, is also presented and analysed.

A flexible PI/graphene heterojunction optoelectronic device modulated by TENG and UV light for neuromorphic vision system

Artificial neural visual electronic devices have attracted great research interest in the fields of low-power and high-efficiency pattern recognition. However, emulating the hyperpolarized behavior of cone and rod cells and further developing image recognition functionalities encounter formidable challenges due to the inherent optoelectronic effects in semiconductors. Here, a flexible optoelectronic synapse device based on polyimide (PI)/Graphene heterojunction is proposed to effectively emulate human visual functionalities. The PI not only serves as a flexible substrate but also exhibits remarkable UV light absorption capability. Furthermore, the electrical conductivity of graphene channel can be bidirectionally regulated through UV light irradiation and triboelectric nanogenerator (TENG) induced negative gas ions adsorption, corresponding to inhibitory and excitatory behaviors, respectively. The negative photoconductance effect, stemming from the recombination between photogenerated electrons in PI and holes in graphene, endows the emulation of hyperpolarized behavior of cone and rod cells. Various synaptic behaviors, such as paired-pulse facilitation, spike-rate dependent plasticity, short-term depression, and long-term depression, can be achieved by modulating light pulses parameters. Additionally, the TENG-induced gas ions adsorbed on the graphene surface act as floating gate, leading to an increase in graphene conductivity. Continuous pulse stimulation through corona discharge enables long-term potentiation behavior in the synaptic device. Ultimately, combining opto-electrically coupled weight updates with artificial neural network algorithms allows for real-time handwritten digit recognition. This work presents a novel pathway for constructing simple flexible artificial visual electronic systems.

Graphene/Heterojunction Composite Prepared by Carbon Thermal Reduction as a Sulfur Host for Lithium-Sulfur Batteries.

An interlayer nanocomposite (CC@rGO) consisting of a graphene heterojunction with CoO and Co9S8 was prepared using a simple and low-cost hydrothermal calcination method, which was tested as a cathode sulfur carrier for lithium-sulfur batteries. The CC@rGO composite comprises a spherical heterostructure uniformly distributed between graphene sheet layers, preventing stacking the graphene sheet layer. After the introduction of cobalt heterojunction on a graphene substrate, the Co element content increases the reactive sites of the composite and improves its electrochemical properties to some extent. The composite exhibited good cycling performance with an initial discharge capacity of 847.51 mAh/g at 0.5 C and a capacity decay rate of 0.0448% after 500 cycles, which also kept 452.91 mAh/g at 1 C and in the rate test from 3 C back to 0.1 C maintained 993.27 mAh/g. This article provides insight into the design of cathode materials for lithium-sulfur batteries.

Electrochemical mechanisms of the reduction of N2 to NH3 catalyzed by TM anchored on Nvs-g-C3N4/graphene van der Waals heterostructure: Insights from a first-principles study

Nitrogen fixation is one of the most critical issues in chemical science and technology. However, developing efficient and stable electro(photo)catalysts remains a comprehensive challenge. Here, we constructed 21 single-atom heterostructures consisting of g-C3N4 with nitrogen vacancies and graphene (TM@Nvs-g-C3N4/graphene, TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Pd, Cd and Pt) and systematically investigated their stabilities and catalytic activities for the conversion from N2 to NH3. The calculations indicate that all heterostructures are thermodynamically stable. Among of them, 15 TM@Nvs-g-C3N4/graphene heterojunctions can activate N2, and effectively reduce N2 into NH3 by a distal or alternating mechanism. The Cr, Mo and Nb atoms anchored in Nvs-g-C3N4/graphene heterojunctions have higher activities and selectivities for nitrogen reduction reaction (NRR). In particular, Mo@Nvs-g-C3N4/graphene has the highest NRR performance. The Bader charge and PDOS analysis elucidate that the d-π* feedback bonds formed by 4d orbitals of Mo atom and π* orbitals of N2 plays a dominant role in the activation of N2. Altogether, the results obtained in this study could provide new avenues for the development of electrochemical catalyst for the reduction of N2 to NH3.

Manipulate the interfacial friction of χ3-borophene on graphene heterojunction via rotation

Manipulating friction between two-dimensional (2D) material heterojunctions is crucial for their application in microscale functional devices. In this study, we have systematically investigated the frictional properties of χ3-Borophene(Bo)/Bo, Bo/Graphene(Gr), and Bo/Gr(30°) by first-principles calculations. The results indicate that the formation of Bo/Gr heterojunctions indeed reduces interfacial sliding potential energy corrugation of Borophene. Interestingly, friction anisotropy appears when commensurate state forms between Gr and Bo along armchair direction of Bo/Gr heterojunction. In addition, this anisotropy vanishes after rotating the heterojunction with an angle of 30°. The Fourier transformation method is applied to illustrate the commensurability of heterojunctions along specific directions. Finally, the interfacial friction behavior is further confirmed to be consistent with the fluctuation of interfacial charge transfer, which emphasizes the atomic stacking and chemical property of heterojunctions.

Theoretical Design of an Mox W1-x S2 /Graphene (x=0.25/0.75) Heterojunction with Adjustable Band Gap: Potential Candidate Materials for the Next Generation of Optoelectronic Devices.

Multicomponent two-dimensional (2D) transition metal dichalcogenides (TMDCs) semiconductors based on adjustable band gap are increasingly used to design optoelectronic devices with specific spectral response. Here, we have designed the Mox W1-x S2 /graphene heterostructure with adjustable band gap by adopting the combination idea of alloying and multiple heterogeneous recombination. The contact type, stability and photoelectric properties of Mox W1-x S2 /graphene heterojunction were investigated theoretically. At the same time, by applying external vertical electric field to Mox W1-x S2 /graphene, the regulate of heterojunction Schottky contact type was realized. The results show that Mox W1-x S2 /graphene heterojunction has broad application prospects in the field of photocatalysis and Schottky devices, and is suitable for being a potential candidate material for next generation of optoelectronic devices. The design of Mox W1-x S2 /graphene heterostructure enables it to obtain the advanced characteristics that are lacking in the one-component intrinsic 2D TMDCs semiconductors or graphene materials, and provides a theoretical basis for the experimental preparation of such heterojunctions.