Graphene Heterostructures Research Articles

Tunable hybridized plasmons-phonons in a graphene/mica-nanofilm heterostructure.

Graphene plasmons exhibit significant potential across diverse fields, including optoelectronics, metamaterials, and biosensing. However, the exposure of all surface atoms in graphene makes it susceptible to surrounding interference, including losses stemming from charged impurity scattering, the dielectric environment, and the substrate roughness. Thus, designing a dielectric environment with a long lifetime and tunability is essential. In this study, we created a van der Waals (vdW) heterostructure with graphene nanoribbons and mica nano-films. Through Fourier-transform infrared spectroscopy, we identified hybrid modes resulting from the interaction between graphene plasmons and mica phonons. By doping and manipulating the structure of graphene, we achieved control over the phonon-plasmon ratio, thereby influencing the characteristics of these modes. Phonon-dominated modes exhibited stable resonant frequencies, whereas plasmon-dominated modes demonstrated continuous tuning from 1140 to 1360 cm-1 in resonance frequency, accompanied by an increase in extinction intensity from 0.1% to 1.2%. Multiple phonon couplings limited frequency modulation, yielding stable resonances unaffected by the gate voltage. Mica substrates offer atomic level flatness, long phonon lifetimes, and dielectric functionality, enabling hybrid modes with high confinement, extended lifetimes (up to 1.9 picoseconds), and a broad frequency range (from 750 cm-1 to 1450 cm-1). These properties make our graphene and mica heterostructure promising for applications in chemical sensing and integrated photonic devices.

Enhanced thermoelectric performance of a wide-bandgap twisted heterostructure of graphene and boron nitride.

The manipulation of the relative twist angle between consecutive layers in two-dimensional (2D) materials dramatically modulates their electronic characteristics. Twisted bilayer graphene (tblg) and twisted boron nitride (tBN) exhibit Moiré patterns that have the potential to revolutionize various fields, from electronics to quantum materials. Here, the electronic and thermoelectric properties of 21.8° tblg and 21.8° tBN and a 21.8° twisted graphene/boron nitride (Gr/BN) heterostructure were investigated using density functional theory and Boltzmann transport theory. The twisted Gr/BN heterostructure possesses a wide band gap of 1.95 eV, which overcomes the limitations of the absence of a band gap of graphene and boron nitride's extremely wide band gap. A significant increase in thermoelectric power factor was obtained for the heterostructure compared to its parent materials, 21.8° tblg and 21.8° tBN. It has a thermal conductivity of 5.88 W m-1 K-1 at 300 K, which is much lower than those of 21.8° tblg and 21.8° tBN. It is observed that graphene plays an important role in electron transport or power factor enhancement, whereas BN helps in reducing the thermal conductivity in twisted Gr/BN systems. A strong role of boundary scattering in thermal transport compared to electrical transport was observed. A high figure of merit (ZT) of 1.28 for the twisted Gr/BN heterostructure at a ribbon width of L = 10 nm and T = 900 K was obtained. This suggests its suitability as an effective material for thermoelectric applications.

Visible-light-driven photoelectrochemical sensor based on conjugated microporous polymer-grafted graphene for o-aminophenol detection.

The pollutant o-aminophenol (o-AP) presents considerable risk to environmental safety, and its detection is therefore critical. Although various optical and electrochemical methods have been proposed for the detection of o-AP, there are a limited number of detection methods based on photoelectrochemical (PEC) sensors. In this study, a sensitive visible-light-driven PEC sensor was developed for o-AP detection in water. A conjugated microporous polymer (CMP)-coated graphene heterostructure (CMP-rGO) was synthesized and used to develop a PEC sensor. Under optimal conditions, the proposed sensor exhibited a high sensitivity of 0.03 μM with a wide linear range of 0.0034-37.6 μM. The PEC sensor also displayed acceptable repeatability and reproducibility, good long-term stability, and excellent recovery (98-102%). In addition, the binding patterns of CMP to o-AP and o-AP analog molecules were analyzed by molecular docking. Therefore, this study provides a new and feasible PEC sensor-based detection scheme for o-AP detection.

Molecular dynamics study of interfacial thermal transport properties of graphene/GaN heterostructure

The performance of interfacial thermal transport in heterostructure determines the reliability of micro- and nano-scale device. In this study, a molecular dynamics method is used to investigate the interfacial thermal transport properties of graphene/GaN sandwich heterostructure. The effects of temperature, defect, and size on the interface thermal conductance at the heterostructure are analyzed. It is found that the interface thermal conductance increases with temperature rising; at 1100 K, the interface thermal conductance of the 3-layer graphene heterostructure is increased by 61%. This increase is mainly attributed to the enhanced lattice vibrations at higher temperature, which excites more out-of-plane phonons. The presence of minor vacancy defects in GaN leads interface thermal conductance to increase, reaching a maximum value of 0.0357 GW/(m<sup>2</sup>·K) at a defect rate of 20%. This enhancement is believed to be due to additional thermal transport pathways created by the defects. However, as the defect rate increases further, the interface thermal conductance begins to decrease, which is thought to be due to interfacial coupling strength decreasing. With the number of GaN layers increasing from 8 to 24, the interface thermal conductance decreases, the change is attributed to the decrease of the number of phonons participating in the thermal transport across the interface. Conversely, with the number of graphene layers increasing from 2 to 6, the interface thermal conductance initially increases and then decreases. This behavior is related to initial improvements of phonon matching and coupling strength, followed by the increase in phonon scattering and localization. The results of this study provide a theoretical basis for regulating the interfacial thermal transport in microelectronic devices.

Zero field fractional Hall states, now in graphene heterostructures

Zero field fractional Hall states, now in graphene heterostructures

Magnetic heterostructure of graphene with a submonolayer magnet on silicon

Graphene provides a wealth of advantageous functionalities but lags behind in spintronic applications due to lack of magnetism. A solution currently explored is proximity coupling of graphene with a 2D magnet. Recently, a class of submonolayer 2D magnets – superstructures of metal atoms on semiconductor surfaces – has been discovered. In these materials, magnetic metal atoms are not screened by anions; therefore, such 2D magnets can be employed in formation of magnetic heterostructures. Here, we report synthesis of a submonolayer 2D magnet – a superstructure of Gd on silicon – and its integration with graphene to induce spin-related phenomena. Magnetic properties of the 2D magnet and its heterostructure with graphene are rather similar with the exception that the heterostructure acquires significant magnetic coercivity. Proximity to the 2D magnet strongly affects the transport properties of graphene; in particular, the anomalous Hall effect emerges signifying spin-polarization of the carriers. Quantum oscillations are tracked across the magnetic transition; their evolution can be rationalized as an order of magnitude increase in the effective mass in the magnetic state. Being seamlessly integrated with the silicon technological platform, the heterostructure makes a prospective material for graphene spintronics.

Twist- and gate-tunable proximity spin-orbit coupling, spin relaxation anisotropy, and charge-to-spin conversion in heterostructures of graphene and transition metal dichalcogenides

Twist- and gate-tunable proximity spin-orbit coupling, spin relaxation anisotropy, and charge-to-spin conversion in heterostructures of graphene and transition metal dichalcogenides

Trans-dimensionality of electron/hole channels in multilayer in-plane heterostructures comprising graphene and hBN superlattice

Abstract Using density functional theory, we investigated trilayer in-plane heterostructures consisting of graphene and hBN strips in terms of their interlayer stacking arrangements. The trilayer hBN/graphene superlattices possess flat dispersion bands at their band edges, the wave function distribution of which strongly depends on the interlayer stacking arrangement. The wave functions of the valence and conduction band edges of the trilayer heterostructure with AA’ stacking are distributed throughout the layers implying a two-dimensional carrier distribution. In contrast, we found one-dimensional carrier channels along the border between graphene and hBN for electrons and holes in the trilayer heterosheet with rhombohedral interlayer stacking. These unique carrier distributions are ascribed to the interlayer dipole moment arising from asymmetric arrangements of B and N atoms across the layers. Therefore, the trilayer in-plane heterostructures of graphene and hBN superlattice possess trans-dimensional carriers in terms of their interlayer stacking arrangement.

Photoexcited electron transfer in hydrophobic fluorescent FAPbBr3 perovskite nanocrystals and graphene heterostructures

Photoexcited electron transfer in hydrophobic fluorescent FAPbBr3 perovskite nanocrystals and graphene heterostructures

First-Principles Study on Nb2C–X (X = S, Cl, F)/Graphene Heterostructures: Assessing Aqueous Stability and Implications for Electrocatalysis

First-Principles Study on Nb₂C–X (X = S, Cl, F)/Graphene Heterostructures: Assessing Aqueous Stability and Implications for Electrocatalysis

Effect of strain on electronic properties of tri-layer MoS2/h-BN/graphene van der Waals heterostructures

The two-dimensional materials have grabbed the attention of researchers because of their high functionality and widely controllable properties. Due to the dimensionality reduction, the external factors have a significant influence on their properties. The density functional theory calculations have been performed on the heterostructures of single-layer graphene (G), boron nitride (BN) and molybdenum disulfide (MoS2) to investigate the alteration in their electronic properties. Our calculations predict that electronic properties such as bandgap, work function, Schottky barrier height and tunnelling barrier probability can be modulated by applying mechanical strain. The application of strain resulted in a band gap opening of about 1 eV in trilayer heterostructures. At low values of strain, heterostructures maintained a low resistance ohmic contact. At −9% strain, the p-to-n-type transition of Schottky contact was observed indicating the flow of electrons from semiconductor to metal. The MoS2 monolayer was found to be more electron deficient and exhibited a greater charge accumulation. MoS2/BN/G heterostructure can be used for the fabrication of capacitive devices. Whereas BN/G/MoS2 and BN/MoS2/G heterostructures can act as potential candidates for trilayer Schottky devices due to the presence of low-barrier metal-semiconductor junction.

Spin and valley-polarized multiple Fermi surfaces of α -RuCl3/bilayer graphene heterostructure

We report the transport properties of α-RuCl3/bilayer graphene heterostructures, where carrier doping is induced by a work function difference, resulting in distinct electron and hole populations in α-RuCl3 and bilayer graphene, respectively. Through a comprehensive analysis of multi-channel transport signatures, including Hall measurements and quantum oscillation, we unveil significant band modifications within the system. In particular, we observe the emergence of spin and valley-polarized multiple hole-type Fermi pockets, originating from the spin-selective band hybridization between α-RuCl3 and bilayer graphene, breaking the spin degree of freedom. Unlike the α-RuCl3/monolayer graphene system, the presence of different hybridization strengths between α-RuCl3 and the top and bottom graphene layers leads to an asymmetric behavior of the two layers, confirmed by effective mass experiments, resulting in the manifestation of valley-polarized Fermi pockets. These compelling findings establish α-RuCl3 proximitized to bilayer graphene as an outstanding platform for engineering its unique low-energy band structure.

Synergistic Combination of Reductive Covalent Functionalization and Atomic Layer Deposition—Towards Spatially Defined Graphene‐Organic‐Inorganic Heterostructures

AbstractThree‐dimensionally (3D) well‐ordered and highly integrated graphene hybrid architectures are considered to be next‐generation multifunctional graphene materials but still remain elusive. Here, we report the first realization of unprecedented 3D‐patterned graphene nano‐ensembles composed of a graphene monolayer, a tailor‐made structured organophenyl layer, and three metal oxide films, providing the first example of such a hybrid nano‐architecture. These spatially resolved and hierarchically structured quinary hybrids are generated via a two‐dimensional (2D)‐functionalization‐mediated atomic layer deposition growth process, involving an initial lateral molecular programming of the graphene lattice via lithography‐assisted 2D functionalization and a subsequent stepwise molecular assembly in these regions in the z‐direction. Our breakthrough lays the foundation for the construction of emerging 3D‐patterned graphene heterostructures.

Synergistic Combination of Reductive Covalent Functionalization and Atomic Layer Deposition-Towards Spatially Defined Graphene-Organic-Inorganic Heterostructures.

Three-dimensionally (3D) well-ordered and highly integrated graphene hybrid architectures are considered to be next-generation multifunctional graphene materials but still remain elusive. Here, we report the first realization of unprecedented 3D-patterned graphene nano-ensembles composed of a graphene monolayer, a tailor-made structured organophenyl layer, and three metal oxide films, providing the first example of such a hybrid nano-architecture. These spatially resolved and hierarchically structured quinary hybrids are generated via a two-dimensional (2D)-functionalization-mediated atomic layer deposition growth process, involving an initial lateral molecular programming of the graphene lattice via lithography-assisted 2D functionalization and a subsequent stepwise molecular assembly in these regions in the z-direction. Our breakthrough lays the foundation for the construction of emerging 3D-patterned graphene heterostructures.

A potential candidate material for quantum anomalous Hall effect: Heterostructures of ferromagnetic insulator and graphene

Discovery of novel topological materials have motivated tremendous research owing to their peculiar energy bands and potential fundamental and practical prospects. In contrast to conventional nonmagnetic topological insulators (TIs), new type of magnetic TIs, such as Cr2Ge2Te6, revealed a quantum Hall effect (QHE) at zero magnetic field. The phenomenon is called anomalous QHE. In the magnetic TIs showing QAHE, the interaction of spontaneous magnetism with conducting surface states opens an insulating band gap at the Dirac points by breaking the time-reversal symmetry. In contrast to inducing the phenomenon of QHE through spontaneous magnetism by chemical doping, the alternative suitable option is the heterostructure engineering of 2D Dirac materials with semiconductor magnetic insulators. In this study, we first time investigate the phenomenon of QAHE in semiconducting magnetic insulator Cr2Ge2Te6 by proposing its bulk and monolayer heterostructure with graphene by the first-principles calculations. We employed density functional theory to compute electronic properties of Cr2Ge2Te6 and its heterostructure with graphene. The exchange-correlation in view of meta-generalized gradient approximations with tight binding method reveal the results for bulk Cr2Ge2Te6 are close to the experimental values. The maximum achieved energy gap in the heterostructure is up to 5 meV.

Top-gate engineering of field-effect transistors based on single layers of MoS2 and graphene

Field-effect transistors (FETs) were fabricated with use of vertical heterostructures of graphene and MoS2 monolayers with top-gate and back-gate configurations. Nanodiamonds/poly(vinylidene difluoride) (1:1) and SiO2 were used as the top-gate and back-gate dielectric, respectively. The novel top-gate electrode and gate dielectric assembly consisting of polyaniline and nanodiamonds/poly(vinylidene difluoride) were synthesized by a chemical oxidative polymerization approach. Our MoS2 FETs showed a high linear mobility of approximately 212 cm2/V s and a high on/off current ratio of up to 107 at 10 V for top-gated FETs, which is much greater than for conventional back-gated FETs. The devices were stable under elevated temperatures up to 100 °C, with a decrease in the on/off current ratio. The devices showed good stability without any additional encapsulation after an elapsed time of 10 days, as the results on the first and tenth days were identical. This work will pave the way for the design of high-performance FETs for applications in electronics and optoelectronics.

Independent-regulated double-edge Janus angular absorber for terahertz waves based on photonic edge band gaps and graphene wide-angle absorption

In this paper, three categories of Janus angle absorption structures for terahertz (THz) waves are realized by operating the edge hopping property of the photonic band gaps (PBGs) and the wide-angle absorption of graphene heterostructure. The left and right edges of the angle window are determined by the PBGs generated by photonic crystals 1 (PC1) and photonic crystals 2 (PC2), respectively. The appropriate combination of the two can obtain a transmission angle window (TAW), and the edges can be independently manipulated, which makes it possible to construct arbitrary angle filtering structures, making up for the shortage of rigid angle windows in traditional research. Graphene material has absorption potential, and when it is introduced into ternary photonic crystals 3 (PC3), high absorption at large angles will occur. The combination of PC3 and TAW will produce an absorption angle window (AAW) by using the energy cascade transmission features of photonic crystals (PCs). Contributing to the strong absorption properties, the energy transfer on both sides of PC3 is isolated. Consequently, the Janus angle absorption phenomenon will be remarkable by mirroring the PCs structures with different TAWs on both sides of PC3. Through the unique parameter design, the three relationships between the forward AAW and the backward one are investigated, that is inclusion, partial coincidence, and incoherence.

Drift current-induced tunable near-field energy transfer between twist magnetic Weyl semimetals and graphene

Abstract Both the nonreciprocal surface modes in Weyl semimetal (WSM) with a large anomalous Hall effect and the nonreciprocal photon occupation number on a graphene surface induced by the drift current provide a promising way to manipulate the nonreciprocal near-field energy transfer. Interestingly, the interactions between nonreciprocities are highly important for research in (thermal) photonics but remain challenging. In this study, we theoretically investigated the near-field radiative heat flux transfer between a graphene heterostructure supported by a magnetic WSM and a twist-Weyl semimetal (T-WSM). The nonreciprocal surface mode could be changed by the separation space between two Weyl nodes and the twist angle. Notably, we found that in the absence of a temperature difference between two parallel plates, nonequilibrium fluctuations caused by drift currents led to the transfer of near-field radiative heat flux. Furthermore, these nonreciprocal surface modes interacted with the nonreciprocal photon occupation number in graphene to achieve flexible manipulation of the near-field heat flux size and direction. Additionally, graphene adjustable flux in the case of a temperature difference between the two plates was also discussed. Our scheme can provide a reference for near-field heat flux regulation in nonequilibrium systems.

Electrically-driven ultrafast out-of-equilibrium light emission from hot electrons in suspended graphene/hBN heterostructures

Nanoscale light sources with high speed of electrical modulation and low energy consumption are key components for nanophotonics and optoelectronics. The record-high carrier mobility and ultrafast carrier dynamics of graphene make it promising as an atomically thin light emitter, which can be further integrated into arbitrary platforms by van der Waals forces. However, due to the zero bandgap, graphene is difficult to emit light through the interband recombination of carriers like conventional semiconductors. Here, we demonstrate ultrafast thermal light emitters based on suspended graphene/hexagonal boron nitride (Gr/hBN) heterostructures. Electrons in biased graphene are significantly heated up to 2800 K at modest electric fields, emitting bright photons from the near-infrared to the visible spectral range. By eliminating the heat dissipation channel of the substrate, the radiation efficiency of the suspended Gr/hBN device is about two orders of magnitude greater than that of graphene devices supported on SiO2 or hBN. We further demonstrate that hot electrons and low-energy acoustic phonons in graphene are weakly coupled to each other and are not in full thermal equilibrium. Direct cooling of high-temperature hot electrons to low-temperature acoustic phonons is enabled by the significant near-field heat transfer at the highly localized Gr/hBN interface, resulting in ultrafast thermal emission with up to 1 GHz bandwidth under electrical excitation. It is found that suspending the Gr/hBN heterostructures on the SiO2 trenches significantly modifies the light emission due to the formation of the optical cavity and showed a ∼440% enhancement in intensity at the peak wavelength of 940 nm compared to the black-body thermal radiation. The demonstration of electrically driven ultrafast light emission from suspended Gr/hBN heterostructures sheds the light on applications of graphene heterostructures in photonic integrated circuits, such as broadband light sources and ultrafast thermo-optic phase modulators.

Interface engineering of CoSe2/N-doped graphene heterostructure with ultrafast pseudocapacitive kinetics for high-performance lithium-ion capacitors

Interface engineering of CoSe2/N-doped graphene heterostructure with ultrafast pseudocapacitive kinetics for high-performance lithium-ion capacitors