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We investigate two-dimensional (2D) position-dependent probe absorption in monolayer graphene. Specifically, we consider quantized three-level graphene driven by an infrared probe field, two orthogonal terahertz standing-wave fields, and a coupling field. Our results demonstrate that the spatial distribution of probe absorption can be effectively controlled by adjusting the detunings of the probe and standing-wave fields, as well as the Rabi frequency of the coupling field. The absorption spectrum of the probe field exhibits some interesting features, such as crater-like structures and spikes. Our findings provide new insights into the manipulation of optical properties in graphene and have potential applications in solid-state quantum information. [ABSTRACT FROM AUTHOR]

The quest for scalable integration of monolayer graphene into functional composites confronts the bottleneck of high-fidelity transfer onto substrates, crucial for unlocking graphene's full potential in advanced applications. Addressing this, our research introduces the camphor-assisted transfer (CAT) method, a novel approach that surmounts common issues of residue and structural deformation endemic to existing techniques. Grounded in the sublimation dynamics of camphor, the CAT method achieves a clean, contiguous transfer of centimeter-scale monolayer graphene onto an array of polymer films, including ultra-thin polyethylene films. The resultant ultrathin graphene-polyethylene (gPE) films, characterized by their exceptional transparency and conductivity, reveal the CAT method's unique ability to preserve the pristine quality of graphene, underscoring its practicality for preparing flexible transparent electrodes by monolayer graphene. In-depth mechanism investigation into the camphor sublimation during CAT has led to a pivotal realization: the porosity of the target polymer substrate is a determinant in achieving high-quality graphene transfer. Ensuring that camphor sublimates initially from the polymer side is crucial to prevent the formation of wrinkles or delamination of graphene. By extensive examination of CAT on a spectrum of commonly used polymer films, including PE, PP, PTFE, PI and PET, we have confirmed this important conclusion. This discovery offers crucial guidance for fabricating monolayer graphene-polymer composite films using methods akin to CAT, underscoring the significance of substrate selection in the transfer process. [ABSTRACT FROM AUTHOR]

First-principles simulations are conducted to explore the structural stability, electronic properties, and optical responses of pristine and boron- or nitrogen-doped monolayers graphene. The computed electronic density of states revealed that the substitutional doping of boron impurity atoms on monolayer graphene (MLG) shifts the Dirac point upward, although the substitution of nitrogen impurity atoms in graphene pushes the Dirac point downward the Fermi level. This could exhibit that upon the doping of MLG with boron or nitrogen, respectively, p-type or n-type semimetal is acquired. The overall optical spectral properties of the substituted graphene with boron or nitrogen atoms are simulated and compared with the optical spectra results of pure graphene. The optical features of pristine and doped MLG are determined by taking the interband and intra-band transitions into account ranging from the far-infrared to the ultraviolet regime of the electromagnetic radiation. A remarkable red shift in the optical spectra of the doped MLG towards the visible regime of radiation is established. An enhanced reflectivity illustrated that concentration-dependent optical properties of boron and nitrogen-doped MLG happen at lower electromagnetic radiation regimes. In addition, we explored the thermoelectric behaviors of the pristine/doped graphene monolayers with 4 × 4 supercells. We found a significant improvement in the electrical conductivity of graphene when doped with boron or nitrogen impurities. However, an increase in the electrical conductivity has textured a decrease in the Seebeck coefficients. Improvement in the electrical conductivity is attributed to an interesting effect on the graphene monolayers' power factor (PF). These findings indicate a positive impact of the dopants on the thermoelectric properties of graphene monolayers and reveal that they are potential materials for thermoelectric applications and nanodevices. [ABSTRACT FROM AUTHOR]

Two‐dimensional materials have been widely used to tune the growth and energy‐level alignment of perovskites. However, their incomplete passivation and chaotic usage amounts are not conducive to the preparation of high‐quality perovskite films. Herein, we succeeded in obtaining higher‐quality CsPbBr3 films by introducing large‐area monolayer graphene as a stable physical overlay on top of TiO2 substrates. Benefiting from the inert and atomic smooth graphene surface, the CsPbBr3 film grown on top by the van der Waal epitaxy has higher crystallinity, improved (100) orientation, and an average domain size of up to 1.22 μm. Meanwhile, a strong downward band bending is observed at the graphene/perovskite interface, improving the electron extraction to the electron transport layers (ETL). As a result, perovskite film grown on graphene has lower photoluminescence (PL) intensity, shorter carrier lifetime, and fewer defects. Finally, a photovoltaic device based on epitaxy CsPbBr3 film is fabricated, exhibiting power conversion efficiency (PCE) of up to 10.64% and stability over 2000 h in the air. [ABSTRACT FROM AUTHOR]

This study systematically explores the influence of charged impurities on static screening in monolayer graphene and extends the investigation to AA-stacked and AB-stacked bilayer graphene (BLG). Applying the random phase approximation (RPA), monolayer graphene displays unique beating Friedel oscillations (FOs) in inter-valley and intra-valley channels. Shifting to BLG, the study emphasizes layer-specific responses on each layer by considering self-consistent field interactions between layers. It also explores the derived multimode FOs, elucidating distinctions from monolayer behavior. In AA-stacked BLG, distinct metallic screening behaviors are revealed, uncovering unique oscillatory patterns in induced charge density, providing insights into static Coulomb scattering effects between two Dirac cones. The exploration extends to AB-stacked BLG, unveiling layer-specific responses of parabolic bands in multimode FOs with increasing Fermi energy. This comprehensive investigation, integrating RPA considerations, significantly advances our understanding of layer-dependent static screening in the broader context of FOs in graphene, providing valuable contributions to the field of condensed matter physics. [ABSTRACT FROM AUTHOR]

We successfully fabricated a pair of microgap monolayer graphene electrodes (MMGEs), in which the basal planes of two monolayer graphenes are arranged in parallel facing each other across a small gap of 20 μm, without using a microfabrication process. We measured the redox cycling in the MMGEs using (ferrocenylmethyl) trimethylammonium bromide and observed an excellent redox cycling under low-speed scanning conditions of 0.005 V/s. The collection efficiency reached 97% and was almost independent of the scan rate. [ABSTRACT FROM AUTHOR]

Within the maximum entropy principle, we present a general theory able to describe in a dynamical context the transport properties of hot carriers in monolayer graphene under electric fields of arbitrary strength. Therefore, we obtain a closed extended hyperbolic system of hydrodynamic (HD) equations in which all the unknown constitutive functions are completely determined. In particular, we consider the different scattering mechanisms used in the literature in the kinetic approaches. The closed extended HD system is applied to monolayer graphene at 300 K and is validated by comparing numerical calculations with ensemble Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Graphene, known for its high carrier mobility and broad spectral response range, has proven to be a promising material in photodetection applications. However, its high dark current has limited its application as a high-sensitivity photodetector at room temperature, particularly for the detection of low-energy photons. Our research proposes a new approach for overcoming this challenge by designing lattice antennas with an asymmetric structure for use in combination with high-quality monolayers of graphene. This configuration is capable of sensitive detection of low-energy photons. The results show that the graphene terahertz detector-based microstructure antenna has a responsivity of 29 V·W−1 at 0.12 THz, a fast response time of 7 μs, and a noise equivalent power of less than 8.5 pW/Hz1/2. These results provide a new strategy for the development of graphene array-based room-temperature terahertz photodetectors. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) is generally observed by the excitation of surface plasmon polaritons on the metal (Au/Ag) surface. In order to utilize the SPR phenomenon for sensing application, the metal surface is functionalized with suitable ligands. Although such functionalization can enhance the specific adsorption capability of the sensor however due to the large thickness of the ligands, the plasmonic field of the metal surface becomes less sensitive towards the adsorption of analytes. In the next generation SPR-based sensor, graphene can be utilized not only as plasmonic material but also as a suitable ligand for attracting analytes through π-π interaction. In this article, we present our theoretical simulation studies on the observation of the SPR phenomenon using graphene monolayer (MLG), bilayer graphene (BLG), and in-plane twisted layers of BLG (T-BLG) as plasmonic materials deposited over zinc-selenide substrate. The Kretschmann configuration under wavelength interrogation setup was simulated, and SPR wavelength for graphene systems/water interface was estimated. The bio-sensing simulation was performed, and the sensing parameters viz. sensitivity, figure-of-merit (FOM), and plasmonic field for different graphene systems were obtained. Interestingly, the excellent sensing parameters were found in T-BLG system with relative in-plane twist angle near to magic angle viz. 1°. The enhancement is due to strong coupling between the layers twisted at the magic angle. This study demonstrates that the MLG, BLG and T-BLG can be employed as a standalone layer system for not only the generation of plasmonic fields but also enhanced sensing due to its intrinsic interactions with bio-analytes. [ABSTRACT FROM AUTHOR]

A near-perfect narrow-band graphene-based absorber was fabricated using a resonant system integrated with an asymmetric meta-grating at a wavelength of 1550 nm. By optimizing the gap between the two grating strips, the absorption of monolayer graphene can be increased to 99.6% owing to the strong field confinement of the bottom zero-contrast grating (ZCG). The position of the absorption spectrum could be adjusted by tailoring the grating period or the thickness of the waveguide layer. Interestingly, absorption spectrum linewidth can be tailored by changing the thickness of the spacer layer. The accidental bound states in the continuum (BICs) are then demonstrated in the structure. Moreover, the designed structure realizes the dynamic adjustment of the absorption efficiency at a specific wavelength, which has excellent potential in integrated optical devices and systems. [ABSTRACT FROM AUTHOR]

High‐quality customized monolayer graphene structures are a prerequisite for various applications such as electronics, optoelectronics, and energy devices. Top‐down photolithography is the main method for graphene patterning, but it is greatly affected by complex manufacturing processes and residual photoresist. Recently, bottom‐up methods based on catalyst or precursor patterning have been developed. Although these methods can achieve high‐resolution graphene patterns, it is difficult to control the number of graphene layers and has a high defect density. Here, the authors propose a selective area reconstruction method for in‐situ growth of high‐quality monolayer graphene structures on copper substrates. The method utilizes selective oxidation and high‐temperature reduction technologies, which can effectively regulate the surface characteristics of the copper substrate, thereby precisely controlling the nucleation and growth behavior of the customized graphene structure. The feature size of the fabricated graphene structure is less than 1 µm and it has high monolayer coverage and extremely low defect density. The performance of the photoluminescence device and photodetector based on the customized monolayer graphene structure is characterized. The method provides a new approach for the direct growth of high‐quality, scalable, and high‐precision functional graphene structures, which is expected to have great potential in the optoelectronic applications. [ABSTRACT FROM AUTHOR]

Two-dimensional materials are easily affected by radiation. So far, there is no work to predict the neutron irradiation effects of AA bilayer graphene. Furthermore, the differences and comparisons of various properties between monolayer graphene and AA bilayer graphene after irradiation in the approximately same neutron environment have not been reported. In this study, the neutron irradiation processes on monolayer graphene and AA bilayer graphene were simulated in ab initio molecular dynamics. The mechanical, and optoelectronic properties of monolayer and AA bilayer systems before and after irradiation were calculated using the method based on density functional theory. The results indicate that the AA bilayer system is more resistant to neutron irradiation than the monolayer system. The bandgap of the monolayer (bilayer) system after irradiation will reach the order of 0.1 eV. This article has important value in exploring the methods of radiation reinforcement technology for carbon-based devices. [ABSTRACT FROM AUTHOR]

Inverted planar perovskite solar cells (PSCs) have intrigued great promise in negative hysteresis, simple fabrication process, and flexible substrate implementation, in which the shared hole transport materiel is NiOx. However, the low‐temperature solution processing of the NiOx film is usually accompanied by defect formation, which deteriorates the perovskite quality and device performance. Meanwhile, the energy‐level offset between the NiOx and perovskite films is relatively large, limiting the interfacial charge transport. To suppress those setbacks, a defect‐free monolayer graphene sheet is transferred onto the NiOx film surface as a template for van der Waals epitaxial growth of perovskite films for the first time, leading to enhancing crystallinity with a large grain size of perovskite layer, 0.20 eV energy level offset drop, and accelerating charge transfer for the devices. Finally, the power conversion efficiency of 19.21% without hysteresis is achieved, exceeding 18.35% of the control device. [ABSTRACT FROM AUTHOR]

Monolayer graphene (1LG) is frequently unpredictably modified by supporting material so that it limits development of devices. Van der Waals interaction is dominant in the models describing the in-plane processes, including the electrical charge transport. However, the current flow perpendicular to the plane of the graphene is still less understood. This report analysed specific aspect of the perpendicular current and disclosed an original way to create transport bridges perpendicular to the plane across the 1LG. The most extraordinary finding is that the electron transport between two parallel metal surfaces can be shut down and opened if the metals are separated by the 1LG. The electron transmission can be intentionally varied in this metalâ€"1LGâ€"metal (Mâ€"Gâ€"M) system by pressure. In the experimental study the AFM force curve and tunnelling current measurements were combined when the external load force (0â€"1200 nN) and electrical potential (âˆ'1.5 V to +1.5 V) were used. It is proved that for low voltages (<±9 mV) a bridge is opened perpendicular to the graphene across the Mâ€"Gâ€"M systems by the external force, if the compression dependent Fermi level crosses electronic states in the interfaces and graphene. The localised bridges with diameter about 10â€"40 nm can be opened and kept continuously by the stabilised force in separated points of the system. However, the predictable changes can be produced in the system if the voltage and the force exceeded critical magnitudes. A combined model was proposed acceptable to explain the bridging and predictably modify the characteristics. [ABSTRACT FROM AUTHOR]

Graphene is an excellent piezoresistive material. The gauge factor of graphene mirrors the sensitivity of electromechanical devices. This paper mainly studies the gauge factors of different layers of graphene under different deformation conditions. Specifically, a theoretical model was combined with linearized Boltzmann transport equation, and the density function theory (DFT) to explore how the layer number of graphene affects sensitivity. The results show that monolayer graphene is slightly more sensitive than two-layer graphene, and significantly more sensitive than three-layer graphene and fourlayer graphene. In particular, monolayer graphene remains highly sensitive under large deformation conditions, which gives monolayer graphene a significant advantage over other layers of graphene. Furthermore, a microelectromechanical system (MEMS) pressure sensor was proposed with monolayer graphene, and compared with previous similar sensors with multilayer graphene in terms of sensitivity. [ABSTRACT FROM AUTHOR]

Emerging high-entropy alloy (HEA) films achieve high strength but generally show ineludible brittle fractures, strongly restricting their micro/nano-mechanical and functional applications. Nanolayered (NL) CoCrFeNi/graphene composites are elaborately fabricated via magnetron sputtering and the transfer process. It is uncovered that NL CoCrFeNi/graphene composite pillars exhibit a simultaneous ultra-high strength of 4.73 GPa and considerable compressive plasticity of over 20%. Detailed electron microscope observations and simulations reveal that the monolayer graphene interface can effectively block the crack propagation and stimulate dislocations to accommodate further deformation. Our findings open avenues for the fabrication of high-performance, HEA-based composites, thereby addressing the challenges and unmet needs in flexible electronics and mechanical metamaterials. [ABSTRACT FROM AUTHOR]

We investigate the plasmonic excitations and the broadening functions of the plasmon dispersions in multilayer structures consisting of four parallel monolayer graphene (4-MLG) sheets on an inhomogeneous background dielectric within the random-phase approximation. By finding the zeroes of the frequency-dependent dielectric function, we determine one optical and three acoustic plasmon modes in the system. We observed that the dependence of plasmon properties in the inhomogeneous 4-MLG system on the parameters differs significantly from that in the homogeneous one. Once the inhomogeneity of the background dielectric is taken into account, the plasmon frequencies get smaller values, compared to those in the homogeneous situation as well as in the MLG at the same parameters. As the interlayer separation increases, the plasmon branches in the inhomogeneous system move downward while only the optical branch in the homogeneous one does this, the acoustic plasmon branches shift to the opposite direction. With the efficiently large separations, plasmon lines in the homogeneous case become identical while those in the inhomogeneous case separate from each other in the large momentum region. For homogeneous 4-MLG systems, the decrease in carrier density leads to the decrease in plasmon frequency, but for inhomogeneous 4-MLG structures, the decrease in the doping density of the first graphene layer increases remarkably the frequencies of all plasmon branches. Finally, the broadening function of the plasmon dispersions gets the larger values as plasmon lines go far away from the inter single-particle excitation boundary. [ABSTRACT FROM AUTHOR]

Electron-electron interactions (EEI) play a pivotal role in the transport behavior of carriers confined in a two-dimensional system. The strength of the interaction can be tuned by changing carrier concentration in a conventional two-dimensional system, while it expectedly cannot be controlled in monolayer graphene with a linear dispersion relation since the interaction parameter is not related to carrier concentration. Here, an anomalous carrier-concentration dependence of the EEI is observed in epitaxial graphene on SiC. From quantum transport measurement, a logarithmic temperature dependence of the Hall coefficient is obtained, which is a manifestation of the EEI. From the logarithmic temperature dependence, the EEI-related factor K e e is extracted. Unexpectedly, the extracted K e e shows an increase on increasing carrier concentration, which is further confirmed by analyzing logarithmic correction to the Drude conductivity. This can be attributed to the carrier-concentration dependence of Fermi-liquid constant F 0 σ due to gas absorption, which offers a route to control the EEI in graphene. [Display omitted] [ABSTRACT FROM AUTHOR]

We study the supercontinuum (SC) generation from a passively mode-locked erbium-doped fiber laser (ML-EDFL) using two different samples of monolayer graphene saturable absorber (SA) onto the side-polished surface of a D-shaped fiber, characterized with 98% and 65% polarization dependent loss (PDL), respectively. By using the first 98% PDL graphene SA (setup-1), output pulse spectral profile with 11.6 nm bandwidth was obtained from the ML-EDFL and subsequently amplified using an erbium-doped fiber amplifier (EDFA) to pump 2-m highly nonlinear fiber (HNLF) and 5-m ZBLAN lengths, both fibers operating at the normal dispersion regime, which resulted in individual SC generation of 350 and 245 nm, respectively. Furthermore, the EDFA was spectrally characterized by observing their SC blue shift of the central wavelength, reaching a value of 6.9 nm at 12 dB due to dispersion gain. With the second 65% PDL graphene SA (setup-2), we could generate SC with 227 and 351 nm bandwidths using 0.5 and 2 m HNLF lengths, respectively. Because the two SC setups were highly dependent on the polarization state of the input pulse, we optimized the SC generation from setup-2 using an external polarization controller (PC), which allowed us to adjust both the spectral brightness and the broadening of the SC. • SC generation using two samples of monolayer graphene on D-shaped fibers as SA. • SC generation seeded by both different solitons profiles and polarization states. • The two previous SC generation studies were analyzed using HNLF and ZBLAN fibers. [ABSTRACT FROM AUTHOR]

The excellent thermal and chemical stability of monolayer graphene makes it an ideal material for separations at high temperatures and in harsh organic solvents. Here, based on understanding of solvent permeation through nanoporous graphene via molecular dynamics simulation, a resistance model was established to guide the design of a defect-tolerant graphene composite membrane consisting of monolayer graphene on a porous supporting substrate. Guided by the model, we experimentally engineered polyimide (PI) supporting substrates with appropriate pore size, permeance, and excellent solvent resistance and investigated transport across the resulting graphene-covered membranes. The cross-linked PI substrate could effectively mitigate the impacts of leakage through defects across graphene to allow selective transport without defect sealing. The graphene-covered membrane showed pure solvent permeance of 24.1 L m-2 h-1 bar-1 and stable rejection (~90%) of Allura Red AC (496.42 g mol-1) in a harsh polar solvent, dimethylformamide (DMF), at 100 °C for 10 d. [ABSTRACT FROM AUTHOR]

Large-area graphene synthesized by a chemical vapor deposition (CVD) method is promising for a flexible, stretchable transparent electrode but suffers from structural defects such as grain boundaries, which causes to degrade its physical properties. Recently, preparation methods of large-scale growth templates for single-crystalline graphene (SCG) were reported, but the macroscopic properties of SCG have not been adequately examined yet. Here, an SCG-based flexible, stretchable graphene transparent electrode is successfully demonstrated, which shows superior optoelectrical, electromechanical, and barrier properties compared to polycrystalline graphene (PCG)-based transparent electrodes. The result exhibits the grain boundary effect of graphene on soft substrates on a macroscopic scale and a great promise toward realizing a tremendous performance improvement of graphene-based flexible transparent electrodes on a large scale. [Display omitted] • The macroscopic properties of SCG and PCG related to transparent electrode application are examined. • SCG and PCG were synthesized and confirmed with various methods both in microscopic and macroscopic scale. • According to the scaling law, graphene without GBs may not have advantages in its physical properties. • The graphene GBs highly affect electromechanical and barrier properties, as well as electrical conductivity. • Using SCG instead of PCG for flexible transparent electrodes is worth it for its improved long-term stability. [ABSTRACT FROM AUTHOR]

Converting biomass waste into high-value products presents a challenging task in the environmental field. Growth of graphene from solid-state precursors is cost-effective and is becoming a hot research topic. However, the underlying mechanisms are as yet unclear. In this work, we report a novel method for directly growing adlayer-free large area graphene from cellulose acetate, the main component of cigarette filter waste. The evolution of cellulose acetate to reduced graphene oxide and finally to graphene is shown in this work for the first time. The effect of various growth parameters, hydrogen concentration and Cu grain boundaries on the size and qualities of the monolayer graphene domains is clarified. Finally, the mechanism for the growth of graphene from a solid-state precursor is proposed. The field-effect-transistor fabricated from transferred monolayer graphene demonstrated high electron and hole mobilities ∼1500 cm2/(V·s). This work presents a new opportunity for converting biomass waste into high-value graphene products. Image 1 [ABSTRACT FROM AUTHOR]

In this work we have critically reviewed the processes in high-temperature sublimation growth of graphene in Ar atmosphere using closed graphite crucible. Special focus is put on buffer layer formation and free charge carrier properties of monolayer graphene and quasi-freestanding monolayer graphene on 4H–SiC. We show that by introducing Ar at higher temperatures, T Ar , one can shift the formation of the buffer layer to higher temperatures for both n-type and semi-insulating substrates. A scenario explaining the observed suppressed formation of buffer layer at higher T Ar is proposed and discussed. Increased T Ar is also shown to reduce the s p 3 hybridization content and defect densities in the buffer layer on n-type conductive substrates. Growth on semi-insulating substrates results in ordered buffer layer with significantly improved structural properties, for which T Ar plays only a minor role. The free charge density and mobility parameters of monolayer graphene and quasi-freestanding monolayer graphene with different T Ar and different environmental treatment conditions are determined by contactless terahertz optical Hall effect. An efficient annealing of donors on and near the SiC surface is suggested to take place for intrinsic monolayer graphene grown at 2000 ∘ C, and which is found to be independent of T Ar . Higher T Ar leads to higher free charge carrier mobility parameters in both intrinsically n-type and ambient p-type doped monolayer graphene. T Ar is also found to have a profound effect on the free hole parameters of quasi-freestanding monolayer graphene. These findings are discussed in view of interface and buffer layer properties in order to construct a comprehensive picture of high-temperature sublimation growth and provide guidance for growth parameters optimization depending on the targeted graphene application. [ABSTRACT FROM AUTHOR]

The most attractive application of graphene in the RF area is low-noise amplifier (LNA) due to its amazing properties. But, design and fabrication of graphene LNA Monolithic Microwave Integrated Circuits (MMICs) are still blank. In this work, 200 nm gate-length chemical vapor deposition (CVD) monolayer graphene transistors were fabricated on a sapphire substrate. The graphene transistor shows an intrinsic gain of ${g} _{\text{m}}/{g} _{\text{ds}}= {1.1}$ , and high extrinsic maximum oscillation frequency with ${f} _{\text{max}}$ (48 GHz) > cutoff frequency ${f} _{\text{T}}$ (43 GHz). The graphene transistors show low extrinsic minimum noise figure of 2–7 dB in the measured frequency range of 6–50 GHz. A C-band graphene LNA MMIC was designed and fabricated and shows a maximum gain of 8.34 dB at 5.5 GHz, and minimum noise figure of 4.96 dB at 5.8 GHz. This work demonstrates the application potential of graphene for future RF high-speed electronics. [ABSTRACT FROM AUTHOR]

The introduction of graphene (Gr) with high thermal conductivity between GaAs and metal electrode can reduce the internal temperature rise and thermal stress accumulation of high-power chips, such as photoconductive switches, protect the contact electrode, and improve the device stability. Meanwhile, the introduction of graphene has the potential to decrease the interface contact resistance. It is valuable to study the effect of graphene on the contact characteristics of the metal–semiconductor interface. The metallic composite Ni/Ge/Au/Ni/Au was obtained by electron beam evaporation, and the graphene was grown by CVD. The current–voltage (${I}$ – ${V}$) characteristics of the devices over a high-temperature range 300 K–420 K were measured by a semiconductor parameter analyzer. The Schottky barrier properties of metal/semi-insulating GaAs (M/SI-GaAs) with and without graphene interlayer were analyzed by some analysis techniques, such as forward ${I}$ – ${V}$ and Norde’s methods. It was observed that the barrier heights (BHs) were inhomogeneous in the high-temperature range. The mean BHs were extracted by the experimental BH versus 1/T. We found that the homogeneous BH of M/Gr/SI-GaAs was lower that of M/SI-GaAs. It is helpful to improve the performance of semiconductor devices, as we realized the specific contact resistivity lower by two orders of magnitudes via graphene insertion. [ABSTRACT FROM AUTHOR]

The results of experiments aimed at fabricating and studying the properties of photodetector structures based on single-layer graphene produced by chemical vapor deposition are presented. The configuration of a Ta2O5 vertical microcavity with a resonance wavelength of about 850 nm and a lower dielectric SiO2/Ta2O5 distributed Bragg reflector is taken as the base structure. The conditions for the transfer and fabrication of mesas in the graphene layer on the microcavity surface are optimized. The diagnostics by Raman spectroscopy of the structural quality of graphene after fabrication of the mesas in the graphene layer and contact pads are indicative of the single-layer structure of graphene with a low intensity of features in its spectrum, responsible for imperfection of the structure. The photocurrent is measured under local optical pumping. [ABSTRACT FROM AUTHOR]

Graphene‐based materials are considered as one of the promising photocatalysts for hydrogen production from solar‐driven water splitting yet subject to zero bandgap limitation. Here, we report an efficient one‐step pyrolysis for preparing p‐type boron‐doped monolayer graphene. Through varying the dopant content, the bandgap of the boron‐doped graphene can be tuned. Moreover, a p‐type conductivity behavior of the boron‐doped monolayer graphene is demonstrated by the four‐probe measurement and Hall effect measurement. The boron‐doped graphene can service as an efficient semiconductor photocatalyst for hydrogen production from water splitting under visible‐light irradiation. The optimized boron‐doped graphene can deliver a high H2 production rate of 219.3 μmol h−1 g−1 without any cocatalyst. The photocatalyst can be recycled at least four times without obvious activity decay and maintain high H2 production rate of 215.3 μmol h−1 g−1 after 60 h reaction, indicative of excellent stability. This work may open up a new avenue for fabrication of new photocatalysts based on p‐type boron‐doped monolayer graphene. [ABSTRACT FROM AUTHOR]

This paper presents the influence of top-gate dielectric material for graphene field-effect transistor (GFET) using TCAD simulation. Apart from silicon-based dielectric that is typically used for top-gate structure, other high-dielectric constant (high-k) dielectric materials namely aluminum oxide and hafnium oxide are also involved in the analysis deliberately to improve the electrical properties of the GFET. The unique GFET current-voltage characteristics against several top-gate dielectric thicknesses are also investigated to guide the wafer fabrication engineers during the process optimization stage. The improvement to critical electrical parameters of GFET in terms of higher saturation drain current and greater on/off current ratio shows that the use of high-k dielectric material with very thin oxide layer is absolutely necessary. [ABSTRACT FROM AUTHOR]

High-Q chiral resonances have attracted great interest recently due to their practical photonic applications. For generating such resonances, chiral quasi-bound states in the continuum (quasi-BICs) have recently been proposed and experimentally demonstrated by many researchers, while their dynamic tunability has still not been discussed. In this work, we show multiband circular dichroism and asymmetric transmission based on high-Q chiral quasi-BICs in dielectric metasurfaces, which are dynamically tunable in the mid-infrared range by using graphene monolayers covering the metasurfaces. By changing the Fermi energy, the surface conductivity of graphene is tunable in a wide range, resulting in tunable chiroptical responses of the metasurfaces. Since the metasurfaces exhibit high-Q resonances with narrow linewidths, tuning the metasurfaces results in large modulation depths of circular dichroism and asymmetric transmission, which is of great importance for photonic applications, including tunable polarization manipulation and polarization-dependent detection. • Tunable circular dichroism and asymmetric transmission. • High-Q multiband chiral quasi-BICs in the mid-IR range. • Simultaneously broken in-plane inversion and mirror symmetries. • Tunable chirality by changing conductance of graphene. • Dielectric metasurfaces covered with monolayer graphene. [ABSTRACT FROM AUTHOR]

Abstract Among carbon nanomaterials, graphene has emerged as promising novel membrane material for enhancing desalination performance. However, realistic prospects for industrial-scale production of graphene membranes has been limited. Here we take steps forward in exploring methods to increase the size and enhance the mechanical stability of the single layer graphene membranes. Using Transmission Electron Microscopy (TEM) grids as porous mechanical support and oxygen plasma treatment for creating nanopores, freestanding graphene with large total area was fabricated. 1 m column of salty water was used as the driving force for water desalination measurements in these membranes. High water permeation (1.64 × 107 Lm− 2 h− 1 bar− 1) and acceptable NaCl rejection rate (~ 76%) was achieved over an active area of 2.77 × 104 μm2. Without an ideal porous support, large area freestanding graphene with significant number of cracks, wrinkles, pinholes and defects cannot withstand pressures (~ 50–80 bar) required for water desalination. Fine mesh grids with small holes as inexpensive mechanical supports can be utilized to increase the rupture strength of large area suspended graphene for many purposes including desalination and filtration of multivalent ions or larger molecules. Graphical abstract Image 2 Highlights • Large area single layer graphene membranes fabricated with support of TEM grids. • Acceptable NaCl rejection and high water permeation are achieved. • Grids with larger bars and smaller holes provide better mechanical support. [ABSTRACT FROM AUTHOR]

Graphene has originally low absorption at telecommunication wavelengths. Therefore, it is necessary to overcome this hurdle to use graphene as an absorption media in many optoelectronic devices. In this paper, a narrow-bandwidth graphene-based total absorber is numerically and theoretically investigated. The proposed structure consists of a graphene sheet on a Si rectangular grating, which is placed on $\mathrm{\text{SiO}}_{{\bf 2}}$ spacer backed with the gold substrate. Due to the absence of plasmonic response of graphene in near infrared wavelengths, the method of critical coupling with guided mode resonance is employed to realize highly efficient absorption of light in the graphene sheet. The simulation results show that the maximum magnitude of absorption reaches near 100% (43-fold enhancement compared to isolated monolayer graphene absorption of 2.3%). Also, based on calculated results, the absorption of the proposed structure can be controlled by altering the geometrical parameters and chemical potential of graphene. In particular, the absorption spectrum is modulated by the external gate voltage. Moreover, we find that the operating wavelength is adjusted flexibly by an incident source angle. As a result, the proposed absorber has high directivity and can act similar to an antenna. The control ability of total absorption in the proposed structure provides potential applications for the realization of ultra-compact and high-performance optoelectronic devices, such as sensors and narrow-band filters. [ABSTRACT FROM AUTHOR]

Although there are several kinds of thermal interfacial materials used in the electronic semiconductor industry, such as thermal grease, thermal glue, thermal gap filler, thermal pad and thermal adhesive, the problem of heat dissipation still remains a challenge. In this context, chemical vapor deposition of graphene on copper foils in vacuum has recently become considered as a wonderful hybrid material (graphene/copper/graphene) for more demanding thermal management applications, thanks to the unique properties of graphene in comparison with other materials. We found that the thermal properties of copper films change as graphene is deposited on top of the copper surface. Especially, a single atomic plane of graphene can significantly increase the film’s thermal conductivity. Our graphene on copper foil was analyzed and measured by optical microscopy, Raman spectroscopy, scanning electron microscopy and heat transfer technique. This stack of graphene/copper/graphene materials may play a very important role as a potential material with superior thermal conductivity to replace traditional copper shim thermal pads in current electronic devices. [ABSTRACT FROM AUTHOR]

Abstract Temperature effect of the bound magnetopolaron on the bandgap are discussed in monolayer graphene (MG). The Lee-Low-Pine unitary variational method and linear-combination operator are used to derive the average number of acoustic phonons of ground state and the energy gap of MG. We used quantum statistical theory to study the temperature effect of the bound magnetopolaron on the bandgap in MG. The relationships of the mean number of the acoustic phonons versus the temperature, cut-off wave number (CW), the magnetic field strength are simulated, and the energy gap (EG) of the bound magnetopolaron has a linear relationship with the temperature, the CW, the magnetic field strength, and the Coulomb bound parameter. Highlights • Temperature effect of mean phonon number in monolayer graphene (MG) is studied. • The energy gap (EG) of MG depends on the magnetic field and temperature. • The EG can be tunable by controlling of Coulomb bound potential. • The MG become a topological insulator under the magnetic field and temperature. • Temperature effect supplies theory for self-heating effect of the devices. [ABSTRACT FROM AUTHOR]

We propose using a liquid crystal (LC) layer placed on top of graphene ribbons or a graphene monolayer to control surface plasmons. The plasmon frequency depends on the LC director orientation which can be controlled by an applied voltage. The surface plasmons excitation is sensitive to the light polarisation and can be manipulated using the orientation properties of LCs. We further suggest using periodically anchored LCs instead of a relief grating to excite and control the plasmons in monolayer graphene. The suggested scheme can be used as the basis for a tunable optical filter or a modulator. [ABSTRACT FROM AUTHOR]

In this paper we present a theoretical work on the influence of doped and co-doped Al, Al - S , Al - N and Al - P heteroatoms in the mono layer graphene surface. The Density functional study reveals that , Al , P and S co-doping significantly modifies the neighborhood bonding arrangement of the graphene sheet. The Natural population analysis revels that Al , P and S co-doping makes the graphene surface as electron rich system. From the molecular orbital analysis it is found that HOMO-LUMO energy gap decreases by starting from the pristine graphene in following manner Al doping > Al - S co-doping> Al - N co-doping > Al - P co-doping. On the other hand, the time dependent density functional theory (TD-DFT) calculation shows that the maximum absorbing wavelength of Al-P and Al-N co-doped graphene systems shifted towards the lower wavelength range with respect to Al doped graphene. [ABSTRACT FROM AUTHOR]

Abstract: We report the effect of electrochemical anodization on the properties of monolayer graphene as the main aim of this research and consequently using the resulting label‐free impedimetric biosensor for DNA sequences detection. Monolayer graphene was grown by chemical vapor deposition (CVD) with methane as precursor on copper foil, transferred onto a glassy carbon electrode and electrochemically anodized. Raman spectroscopy and X‐Ray photo electron spectroscopy revealed enhancement of defect density, roughness and formation of C−O−C, C−O−H and C=O functional groups after anodization. Amine‐terminated poly T probe was linked covalently to the carboxylic groups of anodized graphene by the zero‐length linker to fabricate the impedance‐based DNA biosensor. The anodized graphene electrode demonstrated a superior performance for electrochemical impedance detection of DNA. The DNA biosensor showed a large linear dynamic range from 2.0×10−18 to 1.0×10−12 M with a limit of detection of 1.0×10−18 M using electrochemical impedance spectroscopy (EIS) method. Equivalent circuit modeling shows that DNA hybridization is detected through a change in charge transfer resistance. [ABSTRACT FROM AUTHOR]

A wavelength tunable perfect absorber with graphene-hexagonal gold (Au) cylinder array on a ground plate is investigated theoretically. The interactions between electromagnetic (EM) waves and monolayer graphene are analyzed through the field distributions and spectral responses in detail. The finite-difference-time-domain (FDTD) method is used to investigate the tunable properties of the absorber. It is demonstrated that in an optimized configuration, monolayer graphene can interact with light via critical coupling, and the absorptance can be greatly enhanced and reach to 100% for both transverse magnetic (TM) and transverse electronic (TE) polarizations. Furthermore, the influence of geometrical parameters of the structure on the response of the hybrid structure is studied. It is expected that the proposed graphene perfect absorbers can be applied for many applications in the visible (VIS) and the near-infrared (NIR) spectral ranges such as wavelength selective infrared photodetectors and plasmonic sensors. [ABSTRACT FROM AUTHOR]

We propose a simple structure based on monolayer graphene with two layers dielectric grating. The effect of structural parameters on the optical behavior is studied by using the rigorous couple wave analysis method. The situation of changing incident angle for TM polarization is considered without changing the geometrical parameters. The absorption of about 77% and the Q-factor value of about 3390 can be obtained. In order to enhance absorption, we further design perfect absorption based on monolayer graphene with multiple-layer dielectric grating structure. The guide-mode resonances of both the grating and the dielectric layers are excited to achieve perfect multi-peak absorption. The proposed structure uses relatively less layers to achieve the perfect absorption, which can provide a reference for the further development of high sensitive modulators. [ABSTRACT FROM AUTHOR]

The efficiency of graphene-based optoelectronic devices is typically limited by the poor absolute absorption of light. A hybrid structure of monolayer graphene with cylindrical titanium dioxide (TiO 2 ) array and aluminum oxide (Al 2 O 3 ) spacer layer on aluminum (Al) substrate has been proposed to enhance the absorption for two-dimensional (2D) materials. By combining dielectric array with metal substrate, the structure achieves multiple absorption peaks with near unity absorbance at near-infrared wavelengths due to the resonant effect of dielectric array. Completed monolayer graphene is utilized in the design without any demand of manufacture process to form the periodic patterns. Further analysis indicates that the near-field enhancement induced by surface modes gives rise to the high absorption. This favorable field enhancement and tunability of absorption not only open up new approaches to accelerate the light-graphene interaction, but also show great potential for practical applications in high-performance optoelectronic devices, such as modulators and sensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Low-cost and industry-compatible MATLAB-based image analysis is employed to assess macroscopic coverage, uniformity and residues of graphene transferred onto Si/SiO 2 and ITO-covered glass substrates from optical microscopy images. • PMMA-, TRT- and PDMS-assisted transfer processes yield coverages exceeding 80 % on a Si/SiO 2 target substrate and are quantitatively compared using MATLAB-based image analysis of optical microscopy images of the transferred graphene. • Deeper insight into changes in fundamental properties of graphene induced by the transfer process itself is gained by detailed analysis of Raman spectra of pristine and transferred graphene. • MATLAB-based image analysis evaluation method for graphene transfer processes is validated by comparing the results obtained with it to Raman mapping results, both being in good agreement. The use of CVD-grown graphene requires a transfer method to transport this material from the metal foil on top of which it is grown onto a target substrate. In many cases this transfer changes its properties, leading to variations from one zone of the target substrate to another. Here we present a simple semi-automatic method for a quantitative study of the coverage, uniformity and residues of graphene transferred onto Si/SiO 2 substrates whose operation is not dependent on costly equipment, making it low-cost oriented. The method can be extrapolated to different target substrates, e.g., ITO-coated glass, and serves as an evaluation tool for graphene transfer processes. This is achieved by calculating a figure of merit, based on 2 proposed quantitative parameters (accounting for the coverage and the uniformity of the transferred graphene), while simultaneously determining the residues left by the transfer substrate using MATLAB-based image analysis of optical microscopy images. To corroborate the proposed method, a comparison between polydimethylsiloxane (PDMS), thermal release tape- (TRT) and polymethylmethacrylate- (PMMA) assisted transfer processes is performed, demonstrating that the methodology is valid for all cases. Coverages over 80 % are obtained, being in good agreement with results from the same transfer processes studied via Raman mapping. [ABSTRACT FROM AUTHOR]

Monolayer graphene-based composites are of immense importance for research and applications in the microelectronic and thermal-management fields. For the current continuous production of monolayer graphene protocols, chemical etching of the catalyst layer acts as the bottleneck, which is tedious, expensive, and polluting. Thus in this work, by combining chemical etching and mechanical exfoliation, copper foil etching has been compressed from hours to 30 s, with the foil entirely recyclable and reusable. Furthermore, the whole transfer process could be confined within 7 min, including all pre- and post-treatments, without the usage of any intermediate, glue, electricity, vacuum, heat, or pressure. And this minute-level-fast monolayer graphene transfer could be performed continuously multiple times. The key to this novel transfer method is the superficial etching and the subsequent delamination of copper foil off graphene. In-situ OM, AFM, SEM, Raman, and UV–vis spectra have been employed to carefully inspect the transfer mechanism, effectiveness, and quality. The prepared monolayer graphene/polymer composite membrane is ultrathin (∼200 nm), conductive, highly transparent (93.9%), and flexible simultaneously. Its application as an ultrathin, efficient, and conformable Joule heating membrane-form device has been demonstrated. This minute-level-fast transfer is well-adapted to continuous monolayer graphene production and could considerably improve their practicality and efficiency. Additionally, this study provides more understanding of the interface between graphene-polymer and graphene-catalyst and a minute-level-fast route to fabricate 2D-based polymeric composite materials. Ultrafast monolayer graphene transfer onto polymers. [Display omitted] • Minute-level-fast monolayer graphene transfer with etching compressed from hours to 30 s. • The minute-level-fast transfer could be performed several times, with each round as rapid as 7 min. • A facile route to fabricate graphene/polymeric ultrathin membranes is provided. [ABSTRACT FROM AUTHOR]

In this paper, we study collective excitations in an M-BLG heterostructure, consisting of one BLG and one parallel MLG sheet on an inhomogeneous background dielectric. Theoretical calculations are carried out within the random-phase approximation, taking into account temperature effects. The results illustrate that two solutions, corresponding to optical and acoustical modes, admit the zero equation of the temperature-dependent dynamical dielectric function of the structure. The energy of these collective modes is significantly larger (smaller) than that in DBLG (DLG) systems with similar parameters. As temperature increases, the frequency of the acoustical mode steadily increases while that of the optical mode only increases in large wave vector regions, found differently with different interlayer separations. Interestingly, we explore that the effects of carrier density in graphene on plasmon properties of M-BLG heterostructures sharply differ from those in both BLG and DLG systems. • Two plasmon modes, corresponding to optical and acoustical modes, are found. • Plasmon frequencies are significantly larger (smaller) than that in DBLG (DLG). • The AC mode frequency steadily with increasing temperature. • The OP mode frequency increases in small wave vector regions. • Carrier density causes different effects on plasmon properties of M-BLG heterostructures. [ABSTRACT FROM AUTHOR]

[Display omitted] • The purification of industrial oils such as methane with monolayer graphene and Bilayer graphene has been studied. • The influence of silver impurities has been studied to provide the correct filter suitable for industrial oils. • Calculations are made based on density functional theory. • Silver impurities on graphene may be suitable to filter methane impurities. Graphene sensors have high sensitivity and selectivity and are commonly used to detect and clean oil breakdown resulting gas contaminants. Silver impurities on Graphene sheet vacancy were simulated for Methane interaction with vacant Graphene layers, with and without silver impurities, based on density functional theory with Quantum ESPRESSO. PBE exchange–correlation function with GGA function and vdW-DF corrections were used. Analyzing adsorption energies revealed the effects of the additives on Graphene, and showed Graphene with silver impurities was a good option. Analyzes of methane (CH 4 /MVG, CH 4 /BVG, CH 4 /MVG_Ag, and CH 4 /BVG_Ag) show that adsorption strengths of the structures were the relationship MVG_Ag > BVG > MVG > BVG_Ag. Adding Ag impurity to the foil greatly increases the CH 4 adsorption strength of MVG_Ag and decreases the adsorption strength of BVG_Ag. Due to CH 4 ′s symmetry, orientation relative to Graphene makes no difference as it interacts with carbon atoms from any side. [ABSTRACT FROM AUTHOR]