Monolayer Graphene Research Articles

Adsorption of magnesium porphyrin on Au(111)-supported graphene and hexagonal boron nitride monolayers: A first-principles study

Adsorption of magnesium porphyrin on Au(111)-supported graphene and hexagonal boron nitride monolayers: A first-principles study

8-Inch Wafer Scale, Transfer-Free, High-Quality Monolayer Graphene Growth on Ti-Buffered Si (001) Substrates At 100 ºC via Plasma-Assisted Chemical Vapor Deposition

8-Inch Wafer Scale, Transfer-Free, High-Quality Monolayer Graphene Growth on Ti-Buffered Si (001) Substrates At 100 ºC via Plasma-Assisted Chemical Vapor Deposition

A low quantum defect and power scalable Yb-doped glass waveguide laser

We present a continuous wave laser action in ytterbium (Yb)-doped phosphate glass buried channel waveguides. The 25 mm long waveguides were fabricated by the standard ion exchange method. When pumped with a 976 nm laser diode, the waveguide laser emits at 982.4 nm, yielding an ultralow quantum defect of 0.66 %. The impact of coupling and pump power variation on the laser emission wavelengths is demonstrated. Furthermore, the results of pulsing using a monolayer graphene as a saturable absorber (SA) are presented and a pulse train with a repetition rate of 1 MHz and a pulse width of 700 ns was obtained.

Theoretical insights into the essential role of weak interactions in the electrocatalytic reduction of nitrobenzene: Ag-anchored graphene electrode

We used identical transition metal dimer with six coordinated nitrogen atoms to dope a monolayer graphene to construct homonuclear double-atom catalysts (DACs) and probed their catalytic efficiency for nitrobenzene reduction reaction (Ph-NO2RR) using density functional theory. The findings predict that Ag2N6@G possesses significant activity and selectivity, whose potential determining step (PDS) and competitive hydrogen evolution reaction (HER) process have the Gibbs free energy changes of 0.31 and −1.49 eV, respectively. An analysis of IRI (interaction region indicator) and IGMH (independent gradient model (IGM) based on Hirshfeld partition of molecular density) indicates a pronounced van der Waals interactions between Ph-NO2 and Ag2N6@G due to the benzene ring. When silver atom is introduced, the Gibbs free energy change of its PDS is reduced by 0.09 eV compared to the pure graphene as a catalyst. Through IRI, IGMH, and charge transfer analysis, it is confirmed that the van der Waals interactions between the catalyst and nitrobenzene crucially influences the activation of Ph-NO2.

Effective interlaminar toughening of carbon fiber/epoxy composite laminates by extremely low loadings of monolayer graphene oxide

AbstractAn interlaminar ultrafine spraying method was proposed for monolayer graphene oxide (GO) modified CFRP nanocomposite laminates. The well‐dispersed monolayer GO nano‐solutions were prepared by multi‐level dispersion and then sprayed on carbon fiber/epoxy prepreg by the ultrafine atomizing technique. A series of GO/CFRP laminate specimens with different GO loadings were fabricated for our fracture toughness tests and SEM characterization. The test results indicated that the Mode I fracture toughness () was enhanced by 140% with quite a low fraction of monolayer GO nanosheets. The distinct toughening effect at such a low level of nano‐contents was attributed to the sufficient quantity of monolayer GO nanosheets and also a uniform distribution, which was found to be more important than the volume/weight fraction as the principal structural parameter. Thus, the proposed interlaminar toughening approach owns the virtues of good effectiveness and especially low cost owing to the largely reduced weight percentage of nanographene, showing a promising potential of industrial scale‐up.Highlights Proposed an interlaminar ultrafine spraying method for monolayer GO nanosheets. Found that the quantity of GO nanosheets is vital in polymer toughening. Realized significant toughening with extremely low loadings of monolayer GO. Provided a way with high toughening effect and low cost for industrial scale‐up.

Electrically tunable graded photonic crystal lens based on graphene plasmons.

Controlling the nonlinear relationship between surface plasmon polariton (SPP) mode index and chemical potential of graphene can be used in the field of active transformation optics. Here, we propose an electrically tunable 2D Graded Photonic Crystal (GPC) lens based on graphene SPP platform. Our platform comprises a graphene monolayer integrated into a back-gated structure with nano-patterned gate insulators. When the chemical potential of the graphene surface is designed to operate in the nonlinear region, the designed GPC lens can be continuously transformed between a Maxwell's fish-eye lens and a Luneburg lens by tuning the gate voltage. The range of the lens background chemical potential for allowing this transformation is systematically studied. To compensate for the significant errors inherent in the conventional effective medium theory (EMT) during the homogenization of photonic crystals (PCs), we propose a generalized effective medium theory (GEMT). The validity and accuracy of this approach are verified through comparisons with true values (based on rigorous eigenvalue solutions) and EMT values. Due to its advantages of on-site controls and easy fabrication characteristics, the proposed graphene GPC provides a new way for practical on-chip light manipulation.

Vanishing bulk heat flow in the ν = 0 quantum Hall ferromagnet in monolayer graphene

Vanishing bulk heat flow in the ν = 0 quantum Hall ferromagnet in monolayer graphene

Scalable and High-Quality Monolayer Graphene Transfer onto Polymer Membranes Assisted by Camphor

Scalable and High-Quality Monolayer Graphene Transfer onto Polymer Membranes Assisted by Camphor

Mutant amplitude modulation behavior of MIS-like structure of few-layer graphene/SiO2/p-Si in 500–750 GHz band

Graphene has great application potential in the field of electromagnetic modulation field because of its excellent physical and electronic properties. Studies have demonstrated that the properties of graphene films with different layers are also different due to the difference in energy band structure. Nowadays, the modulation mechanism of monolayer graphene (MLG) and bilayer graphene (BLG) has been gradually discovered, but for graphene with more than three layers, the mechanism of whether it is tunable remains to be explored, especially on the proving from an experimental perspective. In this study, the CVD-prepared highly homogeneous few-layer graphene (FLG) film was combined with SiO2 nanolayers and P-doped Si substrate to form an MIS-like capacitor structure, a unique electromagnetic behavior of mutant amplitude modulation exhibited by FLG film was found, which was different from that of mono- and bi-layers of graphene. The results show that the structure exhibits obvious modulation behavior in the ultra-wideband frequency of 500–750 GHz and the bias of 0.9 V, up to 3.1 dB. This study makes a new supplement to a gap in the EM modulation system of graphene series material.

A Tunable Transparent Graphene Absorber with Multifrequency Resonance

AbstractThe demand for multinarrowband absorber has attracted increasing interest among researchers in recent years. However, integrating multifrequency absorption, tunability, and high optical transparency into an absorber remains a crucial challenge. In this study, a multiband, tunable, and transparent microwave meta‐absorber is theoretically proposed and experimentally demonstrated. This meta‐absorber is composed of resonant patterns made from graphene and indium tin oxide (ITO), placed on a substrate of lithium niobate (LN). By introducing P‐type doping to reduce the resistance of monolayer graphene to around 300 Ω, the impedance matching of the absorber is promoted, consequently manifesting ten absorption points within 40 GHz. The electric field distribution analysis and an equivalent circuit model are employed to elucidate the physical mechanisms of the multiband absorber. Additionally, the lithium niobate dielectric layer possesses a substantial dielectric constant and exhibits phase transition characteristics with temperature changes. When the temperature increases to 250 °C, a comprehensive tuning range of more than 5.49 GHz within 40 GHz range is realized. The maximum tuning range for a single frequency point is 1.33 GHz. With the broadening of the band, the meta‐absorber can provide multiple tunable ranges, making it more favorable for practical applications in optical modulator and sensor.

Electrical Transport Properties of PbS Quantum Dot/Graphene Heterostructures.

The integration of PbS quantum dots (QDs) with graphene represents a notable advancement in enhancing the optoelectronic properties of quantum-dot-based devices. This study investigated the electrical transport properties of PbS quantum dot (QD)/graphene heterostructures, leveraging the high carrier mobility of graphene. We fabricated QD/graphene/SiO2/Si heterostructures by synthesizing p-type monolayer graphene via chemical vapor deposition and spin-coating PbS QDs on the surface. Then, we used a low-temperature electrical transport measurement system to study the electrical transport properties of the heterostructure under different temperature, gate voltage, and light conditions and compared them with bare graphene samples. The results indicated that the QD/graphene samples exhibited higher resistance than graphene alone, with both resistances slightly increasing with temperature. The QD/graphene samples exhibited significant hole doping, with conductivity increasing from 0.0002 Ω-1 to 0.0007 Ω-1 under gate voltage modulation. As the temperature increased from 5 K to 300 K, hole mobility decreased from 1200 cm2V-1s-1 to 400 cm2V-1s-1 and electron mobility decreased from 800 cm2V-1s-1 to 200 cm2V-1s-1. Infrared illumination reduced resistance, thereby enhancing conductivity, with a resistance change of about 0.4%/mW at a gate voltage of 125 V, demonstrating the potential of these heterostructures for infrared photodetector applications. These findings offer significant insights into the charge transport mechanisms in low-dimensional materials, paving the way for high-performance optoelectronic devices.

The incorporation of armchair and zigzag boron nitride nanoribbons in graphene monolayers: An examination of the structural, electronic, and magnetic properties

The opening of an energy gap and generating magnetism in graphene are certainly the most significant and urgent topics in your current research. The majority of proposed applications for it require the ability to modify its electronic structure and induce magnetism in it. Here, using first-principles calculations utilizing the PBE and HSE06 functionals, we examine the structural, energetic, electronic, magnetic, and phonon transport characteristics of armchair graphene and boron nitride nanoribbons (aGNRs and aBNNRs), and zigzag graphene and boron nitride nanoribbons (zGNRs and zBNNRs) with varying widths. We shall emphasize the impact of incorporating aBNNRs and zBNNRs of varying widths into graphene monolayers (GMLs). The findings suggest that zBNNRs are easier to insert into GMLs than aBNNRs. A study of the average formation energies of graphene and boron nitride nanoribbons reveals that BNNRs have a formation energy that is at least twenty times greater than GNRs. We have observed energy gaps that can be classified into three distinct families in aGNRs, aBNNRs, and aBNNRs inserted into GML. In the zGNRs and zBNNRs inserted in GML, depending on the width, different magnetic orderings (antiferromagnetic, ferrimagnetic, and ferromagnetic), and electronic behaviors are observed (metallic, semimetallic, semiconductor, and topological insulator).

RF NEMS switches based on graphene for low pull-in voltage and excellent RF performance

This study introduces a novel graphene RF NEMS capacitive switch and conducts an extensive analysis of its RF performance using CST and COMSOL Multiphysics software. The switch’s characteristic impedance matching is accomplished through a coplanar waveguide (CPW) structure, incorporating a dielectric layer topped with conductive graphene beam electrodes. Simulation results reveal that the monolayer graphene RF NEMS switch maintains an insertion loss of 0.003 ~ 0.015 dB and an isolation greater than 40 dB across an ultra-wideband (UWB) frequency range of DC ~ 140 GHz. Moreover, the switch demonstrates a switching time of 4.03 ps at a pull-in voltage of 1 V. The performance of multilayer graphene RF NEMS switches was also evaluated. The study further investigates the operational mechanism of the graphene RF NEMS switch and performs finite element analysis on the proposed design. The graphene RF NEMS switch discussed herein offers significant advantages, including minimal size, lightweight, cost-effectiveness, low pull-in voltage, rapid response time, excellent RF performance, and reduced space consumption in circuitry. Its potential applications span a range from L to F bands, encompassing data storage, communication systems, sensors, remote sensing and military uses.

Cumulated Effects of Magnetic Field, Electron–Phonon and Spin–Orbit Interaction on Thermodynamics Properties of Mono Layer Graphene

Cumulated Effects of Magnetic Field, Electron–Phonon and Spin–Orbit Interaction on Thermodynamics Properties of Mono Layer Graphene

Investigating the role of graphene in the formation and stability of [formula omitted]-phase antimonene islands

Two-dimensional materials have shown tremendous potential for various technological applications. Particularly, 2D antimony exhibits high applicability in electronics, sensors, and batteries. This 2D material, known as antimonene, presents two stable phases: α (rectangular lattice) and β (honeycomb lattice), whose formation depends on the substrate where antimony is deposited. In this study, we investigated the growth of antimonene islands on graphene, forming an antimonene/graphene heterostructure. To demonstrate the significance of graphene in the synthesis of antimonene, we also studied antimony deposited on a bare copper foil similar to the one used for the graphene substrate. Antimony deposition exhibits the β phase antimonene structure when deposited on top of monolayer graphene, but not when deposited on a bare copper foil, nor on top of multilayer graphene. Additionally, we investigated the stability of the heterostructure after exposure to air. Pure antimony islands are formed when evaporated in high vacuum on top of graphene and copper substrates, and antimony atoms oxidize upon exposure to air. After annealing the sample in ultra-high-vacuum at temperatures lower than 200 °C, more than half of pure antimony is recovered and almost all oxidized antimony is desorbed from the graphene substrate. In contrast, almost none of the oxidized antimony is desorbed from the bare copper substrate, highlighting the key role of the heterostructure on the formation and preservation of the physical and chemical properties of the deposited 2D material.

Ultrafast Silicon/Graphene Optical Nonlinear Activator for Neuromorphic Computing

AbstractOptical neural networks (ONNs) have shown great promise in overcoming the speed and efficiency bottlenecks of artificial neural networks. However, the absence of high‐speed, energy‐efficient nonlinear activators significantly impedes the advancement of ONNs and their extension to ultrafast application scenarios like real‐time intelligent signal processing. In this work, a novel silicon/graphene ultrafast all‐optical nonlinear activator, leveraging the hybrid integration of silicon slot waveguides, plasmonic slot waveguides, and monolayer graphene is demonstrated. Exploiting the exceptional picosecond‐scale photogenerated carrier relaxation time of graphene, the response time of the activator is markedly reduced to ≈93.6 ps, establishing all‐optical activator as the fastest known in silicon photonics to knowledge. Moreover, the all‐optical nonlinear activator holds a low threshold power of 5.49 mW and a corresponding power consumption per activation of 0.51 pJ. Its feasibility and capability for use in ONNs, manifesting performance comparable with commonly used activation functions are experimentally confirmed. This breakthrough in speed and energy efficiency of all‐optical nonlinear activators opens the door to significant improvements in the performance and applicability of ONNs.

Singular photon spin Hall effect in chiral-graphene heterostructures and its application in chirality detection.

In this paper, we consider the singular photonic spin Hall effect (PSHE) in a chiral-graphene-chiral (CGC) heterostructure in the THz band. We investigate the impact of a chiral medium on reflectance spectra and the modulation of the Fermi energy on the surface conductivity of graphene. Our study shows that placing a chiral medium on both sides of a monolayer of graphene results in an enhanced transverse shift (TS) compared to placing a non-chiral medium. Moreover, the direction of the TS of the PSHE can be altered by adjusting the sign of the chirality parameter and the Fermi energy of graphene. Finally, we establish a quantitative relationship between the PSHE and the chirality parameter and the Fermi energy of graphene. By dynamically modulating the PSHE in graphene, it is possible to flexibly detect chirality parameters. This work opens up new avenues for chiral molecular detection and graphene-PSHE dynamic modulation.

Correlation of Valence electron structure and properties of monolayer graphene and MX2 (M=Mo, W; X=S, Se, Te): Empirical Electron Theory (EET) investigation

The atomically thin layers of transition-metal dichalcogenide (TMDC) materials have garnered considerable attention due to their exceptional electrical, optical, mechanical, and thermal properties. Hence, it is important to investigate the mechanism of their excellent properties. In this paper, the study is focused on the correlation between valence electron structures (VESs) and mechanical as well as thermal properties of graphene and MX2 (M = Mo, W; X = S, Se, Te) for revealing their essential mechanisms of properties with an empirical electron theory (EET). A model of Young's modulus is built for the monolayer graphene and MX2 (M = Mo, W; X = S, Se, Te) based on the VES, which has been verified by the observed ones of elements in the 4th to 6th periods in the periodic table of elements. The calculated bond lengths and mechanical and thermal properties of graphene and MX2 are in good agreement with experimental ones. The study reveals that the thermal and mechanical properties of MX2 strongly depend on their valence electron structures. It shows that the melting point, cohesive energy, thermal conductivity, and Young's modulus are modulated by covalence electron pair nA, the averaged covalence electron per atom nc/atom, covalence electron pair nA and linear density of covalent electron on the strongest bond ρl, respectively. The study helps explain the thermal and mechanical properties of two-dimensional (2D) materials and also supplies a reference for their design with high performance by modulating their valence electron structures.

Electronic Properties of Monolayer Graphene with Doping of Nitrogen Atom: A Density Functional Theory Study

Abstract As a material that has been widely researched, graphene is certainly interesting because it has many unique features. In its development, graphene is very promising as an optoelectronic material. However, in theory, graphene has obstacles in its development because its band gap position is zero. With various modifications in opening the band gap so that it does not have a value of zero. In the current research, structural modifications were carried out on graphene layers by doping with a number of Nitrogen atoms. The modeling was carried out using graphene with a supercell size of 4 x 4 x 1. Our calculations are based on Density Functional Theory using the PBE – GGA function for potential exchange correlation. The result is the Fermi level shifting and emergence of magnetic moment through doping with Nitrogen atoms. The results obtained certainly open up opportunities for the development of graphene.

Fabrication of sandwich nanostructured substrates with Au@Ag NCs/Graphene/AgMP for ultrasensitive SERS detection

This paper presents the design of a bottom-up "sandwich" configuration substrate via electrostatic self-assembly. A silver microplate (AgMP) serves as the stable structural base, onto which monolayer graphene is wet-transferred. Au@Ag nanocubes (Au@Ag NCs) are then assembled on the upper layer through liquid-liquid three-phase self-assembly, forming a Au@AgNCs/G/AgMP “sandwich” substrate. The combination of electromagnetic enhancement from noble metal nanoparticles and chemical enhancement from graphene synergistically amplifies the signal of detected molecules, leading to significant Surface-Enhanced Raman Scattering (SERS) enhancement. Experimental results demonstrate that this substrate can detect Rhodamine 6 G (R6G) at concentrations as low as 10–12 M and Crystal Violet (CV) at 10–9 M. Moreover, the substrate can detect Aspartame (APM) at concentrations as low as 0.0625 g/L, well below the typical daily intake levels for humans. These findings indicate that the substrate exhibits excellent SERS performance and holds significant potential for broad applications.