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We demonstrated the sensing properties and adsorption mechanism of NO2 molecules of monolayer graphene and multilayer graphene encapsulated ZnO QDs for NO2 gas adsorption. The gas response value of ZnO-multilayer graphene (ZMLG) QDs was approximately 23 % and 7.2 and 25.5 times higher than that with ZnO-monolayer graphene (ZG) and ZnO QDs, respectively. The surface potential change of ZMLG QDs increased up to 14.25 times compared to ZnO QDs and 6.33 times increased compared to ZG QDs. We proposed an accurate adsorption mechanism for the improvement of the detection behavior that is occured by covering the graphene shells into ZnO QDs by the Brunauer–Emmett–Teller (BET), X-ray photoelectron spectroscopy (XPS), and SKPM measurement. These results are expected to increase the accuracy of gas sensor characteristic analysis.

The alloy catalysts have been introduced in synthesizing highly oriented and monolayer graphene because of the combination of excellent features of different metals. However, precise manipulation o...

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.

Bilayer graphene has attracted interest for its unique properties, including interesting electrical behavior when one layer is slightly rotated relative to the other. However, the quality of large-area bilayer graphene is often limited by the layer-plus-island growth mode in which islands of thicker graphene present as unavoidable impurities. Here, we report the observation of the layer-by-layer, Frank-van der Merwe (FM) growth mode in bilayer graphene where multilayer impurities are suppressed. Instead of the conventional surface adhesive energy, it is found that interface adhesive energy is possible to be tuned with an oxidative pretreatment. The FM-grown bilayer graphene is of AB-stacking or with small-twisting-angle (θ = 0-5°), which is more mechanically robust compared to monolayer graphene, facilitating a free-standing wet transfer technology.

Graphene oxide (GO) contains various types of oxygen functional groups (e.g., C–OH, C–O–C, C=O, and O=C–OH groups), which provide superior functions such as proton conductivity, catalytic activity,...

The use of conductive polyaniline (PANI) in energy storage has been extensively explored during the past several decades. Despite the significant progress, there is still a need for effective and s...

We report on magnetotransport in a high-quality graphene device, which is based on monolayer graphene (Gr) encapsulated by hexagonal boron nitride (hBN) layers, i.e., hBN/Gr/hBN stacks. In the vicinity of the Dirac point, a negative magnetoconductance is observed for high temperatures > ~ 40 K, whereas it becomes positive for low temperatures ≤ ~ 40 K, which implies an interplay of quantum interferences in Dirac materials. The elastic scattering mechanism in hBN/Gr/hBN stacks contrasts with that of conventional graphene on SiO2, and our ultra-clean graphene device shows nonzero magnetoconductance for high temperatures of up to 300 K.

Purpose The authors designed those experiments to test the sensitivity of graphene when it is exposed to NO2 gas, to find a way to decrease the recovery time of graphene and to find the difference effect between monolayer and bilayer graphene in the experiments. Design/methodology/approach The authors transferred graphene from film on Cu foil to NO2 sensor sample and measured the resistances of on monolayer and bilayer graphene when they were exposed to NO2 gas under different concentration; then, the authors obtained the results. Findings The results show that monolayer graphene exhibits a linear response when the NO2 concentration is below 20 ppm. But the monolayer graphene will not be so sensitive to NO2 gas when the concentration continues to reduce. The desorption time of monolayer graphene is longer when compared with bilayer graphene. It shows faster recovery time and higher response of bilayer graphene under low NO2 concentration. And the limit detectable NO2 concentration of bilayer graphene is 50 ppb. Desorption time of bilayer graphene is shortened to below 20 s under UV light. Originality/value The authors found a reliable way to decrease the recovery time of graphene when it is exposed NO2 gas and got the concrete data.

Two-dimensional (2D) materials such as graphene prefer to interact in a face-to-face manner when colloidally suspended but are forced to interact in an edge-to-edge manner when trapped at a fluid–f...

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.

Though much effort has been dedicated to the development of graphene-based optoelectronic devices, its birefringent properties need further investigation. Here, a monolayer graphene is thoroughly s...

A label-free biosensor is described based on the Raman spectroscopic signatures of monolayer graphene, which are modified in the compartment of cancer cells because of electron-phonon coupling in monolayer graphene. Specifically, the Raman spectra of electrostatically gated monolayer graphene on SiO

The transfer of chemical vapor deposited (CVD) monolayer graphene by using poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF1600) fluoropolymer (FP) as a sac...

We investigated the thermoelectric (TE) properties of the MoS2 monolayer-graphene heterostructure which consists of the MoS2 monolayer and graphene. The electronic structures of the MoS2 monolayer-graphene heterostructure are mainly contributed from graphene and the MoS2 monolayer for the valence band maximum and conduction band minimum, respectively. The change in the electronic structures near the Fermi level is responsible for the fact that the calculated Seebeck coefficients S and electrical conductivity σ/τ of MoS2 monolayer-graphene are largely affected from those of graphene and the MoS2 monolayer. Its power factor S 2σ/τ is increased compared to those of graphene and the MoS2 monolayer at an electron concentration of 1011 to 1012 cm-2, which corresponds to a three-dimensional concentration of 3 × 1018 to 3 × 1019 cm-3. We also demonstrated that the MoS2 monolayer shows the p-type TE behavior, while the MoS2 monolayer-graphene heterostructure is given to the n-type TE material. The current study provides a strategy to improve TE properties of the MoS2 monolayer through the formation of the MoS2 monolayer-graphene heterostructure.

Graphene as a truly 2-dimensional (2D) system is a promising candidate material for various optoelectronic applications. Implementing graphene as the main building material in ultra-broadband photodetectors has been the center of extensive research due to its unique absorption spectrum which covers most of the electro-magnetic spectra. However, one of the main challenges facing the wide application of pure graphene photodetectors has been the small optical absorption of monolayer graphene. Although novel designs were proposed to overcome this drawback, they often need complicated fabrication processes in order to integrate with the graphene photodetector. In this regard, fabrication of purely graphene photodetectors is a promising approach towards the manufacturing of simple, inexpensive, and high photosensitive devices. The fabrication of full graphene photodetectors (FGPDs) is mainly based on obtaining an optimal technique for the growth of high quality graphene, modification of electronic and optical properties of the graphene, appropriate techniques for transfer of graphene from the grown substrate to the desire position, and a proper design for photodetection. Therefore, the available states of the art techniques for each step of device fabrication, along with their pros and cons, are reviewed and the possible approaches for optimization of FGPDs have been proposed.

We report a facile and efficient method for the covalent 2D‐patterning of monolayer graphene via laser irradiation. We utilized the photo‐cleavage of dibenzoylperoxide (DBPO) and optimized the subsequent radical additions to non‐activated graphene up to that level where controlled covalent 2D‐patterning of graphene initiated by spatially resolved laser writing is possible. The covalent 2D‐functionalization of graphene, which is monitored by scanning Raman microscopy (SRM) is completely reversible. This new concept enables write/read/erase control over the covalent chemical information stored on the graphene surface., A write/read/erase concept for spatially controlled patterning utilizing covalent functionalization of monolayer graphene on a Si/SiO2 substrate is made possible by laser decomposition of benzoyl peroxide. The introduced chemical information and its reversible binding were investigated by Raman spectroscopy. This method allows the production of a wide array of highly specialized graphene surfaces.

A high-speed residue-free transfer method using PDMS (polydimethylsiloxane) stamp and water infiltration between graphene and a hydrophilic surface is reported. Monolayer graphene was transferred from an enhanced fluorinated Al2O3 surface using PDMS. Water infiltration dramatically reduced the time required to separate the graphene from the Al2O3 substrate to a few minutes. The graphene was then successfully transferred to a target substrate (SiO2) using the PDMS stamp. Atomic force microscopy and lateral force microscopy was used to confirm the absence of residue on the transferred graphene surface.

This study presents chemical vapor deposition (CVD) growth of high-quality monolayer graphene on 100 nm-thick Pt thin films deposited on TiO2-coated silicon wafers. Conventional graphene growth on ...

GaN-based light-emitting diodes (LEDs) are extremely promising and highly efficient solid-state light sources with long lifetimes. In this study, a stress-free GaN film with optimal quality and a l...

The submitted work is focused on graphene preparation using the chemical vapour deposition method employing a cost-saving cold-wall reactor. Optimization of the parameters and conditions of the growth technology was pursued. We succeeded in preparing and transferring monolayer graphene onto a dielectric substrate and in studying its properties by various analytical methods in great detail. The transferred graphene material displays well-resolved band structure. The band structure evidences that undoped material was prepared, with Dirac points lying at the Fermi level.

Load-dependent friction hysteresis is an intriguing phenomenon that occurs in many materials, where the friction measured during unloading is larger than that measured during loading for a given normal load. However, the mechanism underlying this behavior is still not well understood. In this work, temperature-controlled friction force microscopy was utilized to explore the origin of friction hysteresis on exfoliated monolayer graphene. The experimental observations show that environmental adsorbates from ambient air play an important role in the load dependence of friction. Specifically, the existence of environmental adsorbates between the tip and graphene surface gives rise to an enhanced tip-graphene adhesion force, which leads to a positive friction hysteresis where the friction force is larger during unloading than during loading. In contrast to positive friction hysteresis, a negative friction hysteresis where the friction force is smaller during unloading than during loading is observed through the removal of the environmental adsorbates upon in situ annealing. It is proposed that the measured friction hysteresis originates from the hysteresis in the contact area caused by environmental adsorbates between the tip and graphene. These findings provide a revised understanding of the friction hysteresis in monolayer graphene in terms of environmental adsorbates.

The controllable manipulation of graphene to create three-dimensional (3D) structures is an intriguing approach for favorably tuning its properties and creating new types of 3D devices. However, due to extremely low bending stiffnesses, it is rather challenging to construct monolayer graphene into stable 3D structures. Here, we demonstrate the stable formation of monolayer graphene microtubes with accompanying pre-patterned strain layers. The diameter of graphene microtubes can be effectively tuned by changing the thickness of the strain layers. Benefiting from a high surface-to-volume ratio of the tubular geometry, the 3D geometry leads to a prominent Raman enhancement, which was further applied to molecular sensing. The R6G molecules on graphene microtubes can be detected even for a concentration as low as 10-11 M. We believe that this method can be a generalized way to realize the 3D tubular structure of other 2D materials.

Phase contrast transmission electron microscopy (TEM) is a powerful tool for imaging the local atomic structure of materials. TEM has been used heavily in studies of defect structures of 2D materials such as monolayer graphene due to its high dose efficiency. However, phase contrast imaging can produce complex nonlinear contrast, even for weakly-scattering samples. It is therefore difficult to develop fully-automated analysis routines for phase contrast TEM studies using conventional image processing tools. For automated analysis of large sample regions of graphene, one of the key problems is segmentation between the structure of interest and unwanted structures such as surface contaminant layers. In this study, we compare the performance of a conventional Bragg filtering method to a deep learning routine based on the U-Net architecture. We show that the deep learning method is more general, simpler to apply in practice, and produces more accurate and robust results than the conventional algorithm. We provide easily-adaptable source code for all results in this paper, and discuss potential applications for deep learning in fully-automated TEM image analysis., 12 pages, 6 figures

Purpose The purpose of this paper is to simulate charge transport in monolayer graphene on a substrate made of hexagonal boron nitride (h-BN). This choice is motivated by the fact that h-BN is one of the most promising substrates on account of the reduced degradation of the velocity due to the remote impurities. Design/methodology/approach The semiclassical Boltzmann equations for electrons in the monolayer graphene are numerically solved by an approach based on a discontinuous Galerkin (DG) method. Both the conduction and valence bands are included, and the inter-band scatterings are taken into account as well. Findings The importance of the inter-band scatterings is accurately evaluated for several values of the Fermi energy, addressing the issue related to the validity of neglecting the generation-recombination terms. It is found out that the inclusion of the inter-band scatterings produces sizable variations in the average values, like the current density, at zero Fermi energy, whereas, as expected, the effect of the inter-band scattering becomes negligible by increasing the absolute value of the Fermi energy. Research limitations/implications The correct evaluation of the influence of the inter-band scatterings on the electronic performances is deeply important not only from a theoretical point of view but also for the applications. In particular, it will be shown that the time necessary to reach the steady state is greatly affected by the inter-band scatterings, with not negligible consequences on the switching on/off processes of realistic devices. As a limitation of the present work, the proposed approach refers to the spatially homogeneous case. For the simulation of electron devices, non-homogenous numerical solutions are required. This last case will be tackled in a forthcoming paper. Originality/value As observed in Majorana et al. (2019), the use of a Direct Simulation Monte Carlo (DSMC) approach, which properly describes the inter-band scatterings, is computationally very expensive because the valence band is highly populated and a huge number of particles is needed. Even by simulating holes instead of electrons does not overcome the problem because there is a certain degree of ambiguity in the generation and recombination terms of electron-hole pairs. The DG approach, used in this paper, does not suffer from the previous drawbacks and requires a reasonable computing effort.

Chemical vapor deposition (CVD) is one of the most important methods for the preparation of graphene. Graphene is usually prepared using horizontal tube CVD (HT-CVD) method. However, the preparation of this method is too long, generally more than 2 h. In this article, a method called vertical cold-wall CVD (VCW-CVD) method was introduced for graphene preparation. Due to the vertical angle between direction of gas flow and sample surface, the reaction process of this method for graphene preparation is only 1 min. Accordingly, in this article, the modified parameter of graphene preparation by this method was discussed. Besides, the VCW-CVD graphene had an equal quality with the HT-CVD graphene, which was proved by measurement of conductivity, transmittance and heat stability.

We experimentally demonstrated the broadband absorption enhancement of monolayer graphene embedded in the center of a dielectric cavity of the prism coupling configuration in the visible spectral range. The absorption peak is enhanced up to 86.1% at λ = 650 nm with a 3 dB bandwidth of 314 nm (from 542 nm to 856 nm). The absorption performance is the best experimental result for monolayer graphene in the visible range, to the best of knowledge. The improved absorption is attributed to enhanced light-graphene interaction via the cavity mode formed in the dielectric layer with the properly chosen graphene position. The proposed structure is suitable to a high-efficiency broadband photodetector based on monolayer graphene due to the simple fabrication process and the high fabrication tolerance.

Exceptional mechanical properties of graphene have been extensively studied and leveraged in applications of a broad variety. The fine-tuning of the degree of graphene mechanical anisotropy, however, remains not well understood today. In this paper, a defect engineering strategy is adopted to tune the anisotropic property of monolayer graphene. Mechanical properties of various defect designs, from defect designs consisting of basic elements to more complex patterned graphene kirigami, are systematically discussed and numerically studied using molecular dynamics simulations. A novel stress-ratio-versus-strain-ratio graph is proposed to visualize and rationalize the tuning of mechanical anisotropy of defected graphene sheet. Through our defect designs, all the four quadrants of the 2D ratio graph are covered, indicating a high capability and versatility of fine-tuning the mechanical properties of graphene in different directions. This research, which investigates the tunability of graphene mechanical anisotropy via defect design, sheds light on the new possibility of fine-tuning mechanical properties of other 2D materials and has the potential to improve materials for applications such as stretchable electronics and supercapacitor devices.

We consider a problem of obtaining information about the scattering potentials of the monolayer graphene sample using available experimental data on its resistance. For this purpose, we study theor...

Mono-, few-, and multilayer graphene is explored towards the electrochemical Hydrogen Evolution Reaction (HER). Careful physicochemical characterisation is undertaken during electrochemical perturbation revealing that the integrity of graphene is structurally compromised. Electrochemical perturbation, in the form of electrochemical potential scanning (linear sweep voltammetry), as induced when exploring the HER using monolayer graphene, creates defects upon the basal plane surface that increases the coverage of edge plane sites/defects resulting in an increase in the electrochemical reversibility of the HER process. This process of improved HER performance occurs up to a threshold, where substantial break-up of the basal sheet occurs, after which the electrochemical response decreases; this is due to the destruction of the sheet integrity and lack of electrical conductive pathways. Importantly, the severity of these changes is structurally dependent on the graphene variant utilised. This work indicates that multilayer graphene has more potential as an electrochemical platform for the HER, rather than that of mono- and few-layer graphene. There is huge potential for this knowledge to be usefully exploited within the energy sector and beyond.

The probability of terahertz transitions between Landau levels for various magnetic fields at 4.2 K is calculated at different positions of Fermi levels corresponding to different concentrations of...

A scanning transmission electron diffraction method is developed for use in the scanning electron microscope to perform orientational characterization of 2D materials. The method can generate orientation maps of monolayer graphene over a field of view up to ≈ 50 μ m in just a few minutes and can distinguish twisted bilayers from aligned bilayers. This method holds promise to bring electron-diffraction-based orientation measurements of 2D materials to a broader audience.

Controllable directional transport of liquid droplets on a functionalized surface has been a challenge in the field of microfluidics because it does not require energy supply, and the physical mechanism of such self-driving transport exhibits extraordinary contribution to fundamental understanding of some biological processes and the design of microfluidic apparatus. In this paper, we report a novel design of a surface microstructure that can realize unidirectional self-driving liquid mercury (Hg) droplet transport on a graphene-covered copper (Cu) substrate with a three-dimensional surface microstructure. We have demonstrated that a liquid Hg droplet spontaneously propagates on a grooved Cu substrate covered by a monolayer graphene without any external force fields. Classical molecular dynamics results provide a profound insight on the self-driving process of Hg droplets. It shows that the Hg droplet undergoes acceleration, deceleration, and return stages successively from the narrow to wide ends of the gradient groove. Intriguingly, Hg droplets can move continuously and unidirectionally on the three-dimensional graphene-covered surface microstructure when they accumulate enough kinetic energy from the gradient groove to break the energy barrier at the step junctions between the two neighboring unit cells. The design of the zigzag textured surface covered by a monolayer graphene artfully uses the facts; (1) the monolayer graphene can effectively reduce the droplet pinning on the textured surface, (2) the hydrophobic graphene layer reduces the friction between Hg droplets and the substrate, and (3) the textured surface can permeably interact with the droplets through the monolayer graphene to achieve a continuous self-driving process. The findings reported here open a door to explore the graphene-covered functional surface to directional transport of liquid droplets and provide an in-depth understanding of the self-driving mechanism for liquid droplets on graphene-covered textured substrates.

We experimentally demonstrate actively tunable infrared absorption based on graphene-covered SiC metasurfaces. A dry transfer method is employed to coat monolayer graphene on the metasurface charac...

We investigate the hybrid structure composed of single-walled carbon nanotubes (SWCNTs) and monolayer graphene to highly increase flow-induced voltage generation by an ionic droplet on these hybrid carbon membranes. These properties were characterized by Raman spectra, a field-emission-scanning probe, and optical microscope. We demonstrated flow-induced voltage generation on the hybrid structure at various ion concentrations of NaCl. The generated voltage for the membrane of SWCNTs/graphene/SWCNTs was 8.636 and 4.92 times larger than for the SWCNTs, and graphene/SWCNTs membranes, respectively, based on the highly increased electron dragging mechanism.

Significance Single-particle electron cryomicroscopy (cryoEM) has now proved to be the method of choice for determining the structure of biological macromolecules and complexes. Yet success in determining a structure by cryoEM depends on being able to prepare a frozen specimen on a small metal support called a grid. This process is poorly controlled at present because of molecule–surface interactions. Here we used a modified form of graphene, in conjunction with a stable grid made of gold, to control these surface effects. Functionalized graphene-on-gold grids improve the reliability of specimen preparation and enhance image quality. This technology has the potential to take specimen preparation for cryoEM from a trial and error art to a controlled and reproducible process., With recent technological advances, the atomic resolution structure of any purified biomolecular complex can, in principle, be determined by single-particle electron cryomicroscopy (cryoEM). In practice, the primary barrier to structure determination is the preparation of a frozen specimen suitable for high-resolution imaging. To address this, we present a multifunctional specimen support for cryoEM, comprising large-crystal monolayer graphene suspended across the surface of an ultrastable gold specimen support. Using a low-energy plasma surface modification system, we tune the surface of this support to the specimen by patterning a range of covalent functionalizations across the graphene layer on a single grid. This support design reduces specimen movement during imaging, improves image quality, and allows high-resolution structure determination with a minimum of material and data.

We calculate the plasmon frequency and damping rate in a double-layer system made of monolayer graphene and GaAs quantum well at finite temperature using the random-phase-approximation dielectric function and taking into account the inhomogeneity of the dielectric background of the system. We show that the temperature, interlayer correlation parameters and dielectric background inhomogeneity affect significantly the plasmon frequencies and damping rates of the system. At low temperatures, acoustic (optical) plasmon frequency increases (decreases) with the increase of temperature. We also find that damping rates of both plasmon modes increase remarkably compared to the zero-temperature case.

We propose the monolayer graphene with a periodic stack of the dielectric materials to achieve comb-like absorption enhancement. The number of absorption peaks corresponds to the stacked period number of two dielectric materials. The simulation and theoretical results illustrate that the appearance of multiple absorption peaks is attributed to the excitation of multiple waveguide modes confirmed by using the multiple waveguide theory. The perfect absorption peaks at any desired wavelength in the visible range can be tuned by carefully optimizing the structural parameters and the stacked period number of two dielectric materials.

Contamination on graphene is a critical problem that has limited the applications of graphene despite its innate versatility. However, the structures of such contamination remain unclear. In this study, we investigated the structure of a contaminated region growing on free-standing monolayer graphene in situ at room temperature using an aberration-corrected scanning transmission electron microscope. Energy-dispersive X-ray spectroscopy showed that carbon atoms were the dominant element of the growing contamination. We quantitatively confirmed that the growing contamination consisted of several layers of nanoscale graphene flakes on pristine single-layer graphene. Electron energy-loss spectroscopy indicated that the hexagonal carbon lattice deforms considerably from the pristine one at the higher layers. Analysis of the three-dimensional atomic structure revealed that the atoms in the third layer were the suppliers of the second layer at the step edge. In addition, we found that the lattice constant of pristine graphene in the region of the first layer was larger than that of the bulk graphite crystals, and that it gradually decreased as the second layer grew on the first layer. The findings of this paper will be helpful not only for the control of nanographene but also for a basic understanding of the intrinsic features of graphene.

The conventional thermal chemical vapor deposition (T-CVD) equipment takes a long time to synthesize a thin film, which is the stumbling block in the commercialization of monolayer graphene. Rapid thermal chemical vapor deposition (RT-CVD) equipment is suitable for rapid graphene synthesis on most surfaces of large area transition metals. The initial graphene domains synthesized by RT-CVD were visualized and compared with graphene synthesized by T-CVD. The number of graphene domains grown by RT-CVD was approximately 12.31% larger than those synthesized by T-CVD. The surface of the thermally treated metal substrate determines the density and shape of the graphene domains due to the reduced surface irregularities and hence flattens. As a result of the thermal treatment of the copper foil, the ID/IG value of RT-CVD graphene decreased by 12.5%. Thus, it was confirmed that the electrical characteristics were improved as the average value of the sheet resistance reduced by 15.8%.

Monolayer graphene aligned with hexagonal boron nitride ($h\text{\ensuremath{-}}\mathrm{BN}$) develops a gap at the charge neutrality point (CNP). This gap has previously been extensively studied by electrical transport through thermal activation measurements. Here, we report the determination of the gap size at the CNP of $\mathrm{graphene}/h\text{\ensuremath{-}}\mathrm{BN}$ superlattice through photocurrent spectroscopy study. We demonstrate two distinct measurement approaches to extract the gap size. A maximum of $\ensuremath{\sim}14\text{ }\text{ }\mathrm{meV}$ gap is observed for devices with a twist angle of less than 1\ifmmode^\circ\else\textdegree\fi{}. This value is significantly smaller than that obtained from thermal activation measurements, yet larger than the theoretically predicted single-particle gap. Our results suggest that lattice relaxation and moderate electron-electron interaction effects may enhance the CNP gap in $\mathrm{graphene}/h\text{\ensuremath{-}}\mathrm{BN}$ superlattice.

Quantum optical lithography, a diffraction-unlimited method, was applied to pattern monolayer graphene at 10 nm resolution. In our tests with chemical vapor deposition monolayer graphene samples, we have succeeded in producing flat surfaces of a sandwich of monolayer graphene-resist on Si, S i 3 N 4 , or glass substrates. Complex patterns have been written on monolayer graphene samples by a nanoablation process. The method could be used to realize monolayer graphene nanodevices.

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, TAr, 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 TAr is proposed and discussed. Increased TAr is also shown to reduce the sp3 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 TAr plays only a minor role. The free charge density and mobility parameters of monolayer graphene and quasi-freestanding monolayer graphene with different TAr 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 TAr. Higher TAr leads to higher free charge carrier mobility parameters in both intrinsically n-type and ambient p-type doped monolayer graphene. TAr 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.

In the domain of condensed matter physics the monolayer graphene material is of interest. Researchers have started to develop new quantum circuit models that rely on this material properties. Unfortunately, the process to obtain pieces of monolayer graphene useable for nanocomponent design produces a lot of undesired other structures on the same substrate. In this paper, we have developed an approach to target and detect monolayer graphene from alternating layers of graphene and other particles (corrugated crystals and tape residues). We describe a region of interest-based image segmentation process to extract 2D atomic crystals; however, some unwanted particles remain in the segmented region. An intensity-based discrimination of monolayer graphene from other particles is applied and it is observed that the red color space of the monolayer graphene differs 1.8–6%, green 2.5–8% and blue differ 2.5% to 3% from the surrounding background pixel.

We report an ellipsometric study of the monolayer graphene prepared by the chemical vapor deposition (CVD). The investigation was carried over a broad spectral range spanning the ultraviolet to the near-infrared at variable incidence angles. Comparison with graphite and previously published graphene data shows a high degree of similarity in the optical properties of these two materials.

The Boltzmann equation for charge transport in monolayer graphene is numerically solved by using a discontinuous Galerkin method. The numerical fluxes are based on a uniform non oscillatory reconstruction. The numerical scheme has been tested by simulating the electron dynamics in a graphene field effect transistor. To the best of our knowledge the presented simulations are the first ones using a full Boltzmann equation in graphene devices.

During recent years, graphene has attracted growing interest for application in biology, particularly in the biosensing field for sensitivity enhancement. For the biosensing purpose, the graphene layers have to be uniform and have an accurately controlled thickness. Graphene quality may vary depending on the method of its production. Using Raman spectroscopy, an assessment was made of the quality and suitability of the use of CVD and exfoliated graphene for biosensors. The Raman spectra of graphene obtained by the chemical vapor deposition method were measured before and after transferring. We found that CVD graphene with single and bi-layer thickness has a uniform structure with lager area and a small number of defects. But the number of defects increases with an increase of the number of layers. Also, we found that for some samples with CVD graphene, sometimes it is difficult to determine the number of layers since the specific shape of the 2D peak is not always explicitly expressed. Furthermore, it was shown that the exfoliated graphene, although having fewer defects, have non-uniform structure, with smaller areas of monolayer graphene.

An attempt to include the Pauli principle in the Monte Carlo method by also acting on the free-flight step and not only at the end of each collision is investigated. The charge transport in suspended monolayer graphene is considered as a test case. The results are compared with those obtained with the standard ensemble Monte Carlo technique and with the updated direct simulation Monte Carlo algorithm which is able to correctly handle with Pauli's principle. The physical aspects of the investigated approach are analyzed as well.

Ultra thin two-dimensional materials have attracted lots of attention since the monolayer graphene was first successfully deposited by mechanical exfoliation in 2004 by British scientists. Since then, grapheme-like-materials, such as $\mathrm{MoS}_{2}$ have become a new research hotspot. Based on the Web of Science Core collection database, this study visually analyzed the research status of application of $\mathrm{MoS}_{2}$ in the sensors since 1996 to 2019 by using co-citation, citation burst, and keyword co-occurrence functions of software CiteSpace. This paper aims to scientifically and accurately recognize the trends and challenges in the development of $\mathrm{MoS}_{2}$ -based gas sensors.

Thermal rectification (TR) in graphene/boron nitride (GBN) monolayer heterosheets containing various types of interfacial structures has been studied using molecular dynamic simulations. The TR effect is ascribed to the asymmetric heat flow caused by mismatched PDOS of graphene and BN in the boundary. Additionally, the dependences of TR effects on boundary structures and defects are discussed. At a temperature difference of 240 K and interfacial chirality angle of 30°, a TR ratio as high as 334% is obtained. Our studies prove that the TR effect of GBN could be effectively regulated by controlling the interfacial structures and defects, and our analyses provide guidance on the structural designs of unique thermal management materials.