Graphene Layers Research Articles

Few-layered-graphene - Si3N4 composite powders prepared by decomposition of methane onto a Si3N4 powder bed: Control of the average number of layers in the graphene stack

The chemical vapor deposition of carbon is performed onto a commercial silicon nitride powder bed. This produces few-layered-graphene (FLG) films or islands on the Si3N4 particles. The samples are characterized by several techniques including Raman spectroscopy, scanning and transmission electron microscopy. The experimental parameters of the methane (CH4) decomposition (temperature, CH4 concentration, dwell time) are correlated to the average number of graphene layers (N). Complete coverage of the Si3N4 particles is achieved for FLG with N controlled in the range 5–12, corresponding to 4–12 wt%. of carbon. Below that, for stacks with N = 3–4, the coverage of the surface by FLG islands is not total. The value found for the activation energy of CH4 conversion into carbon shows that island-growth is favored over layer-growth. A macroscopical method based on a carbon proportion evaluation gives an approximation of both the coverage ratio and the average number of layers in the stack.

Mechanism simulation of polar and nonpolar organic solvent vapor adsorption on a multiwall carbon nanotubes paper gas sensor.

We investigate the adsorption behavior of polar and nonpolar molecules on carbon nanotube interfaces through computational simulations. Gaussian 16 was utilized to calculate the total energy of each possible molecular structure and analyze the adsorption mechanisms in stacked and inline configurations. The study reveals that nonpolar molecules favor stacked adsorption on two graphene interfaces, while polar molecules prefer inline adsorption. The findings suggest that inline adsorption of polar molecules results in minimal changes to the local dielectric constant, which may explain the absence of multi-step adsorption isotherms. The research examines the stability and energetics of molecular adsorption on graphene layers simulating CNT interfaces. Different types of molecules (polar and nonpolar) exhibit distinct adsorption behaviors, with nonpolar molecules aligning with the IUPAC type VI isotherm model and polar molecules following the Langmuir isotherm model (IUPAC type I). This study provides insight into how molecules are likely to adsorb on CNT surfaces and the impact on the local dielectric constant. This understanding has implications for the design and optimization of CNT-based sensors, particularly in detecting organic solvents and gases in various environments.

Graphene-Based Tunable Polarization Conversion Metasurface for Array Antenna Radar Cross-Section Reduction.

A graphene-based tunable polarization conversion metasurface (PCM) was designed and analyzed for the purpose of reducing the radar cross-section (RCS) of array antennas. The metasurface comprises periodic shuttle-shaped metal patches, square-patterned graphene, and inclined grating-patterned graphene. By adjusting the Fermi energy levels of the upper (μ1) and lower (μ2) graphene layers, different states were achieved. In State 1, with μ1 = 0 eV and μ2 = 0.5 eV, the polarization conversion ratio (PCR) exceeded 0.9 in the bandwidths of 1.65-2.19 THz and 2.29-2.45 THz. In State 2, with μ1 = μ2 = 0.5 eV, the PCR was greater than 0.9 in the 1.23-1.85 THz and 2.24-2.60 THz bands. In State 3, with μ1 = μ2 = 1 eV, the PCR exceeded 0.9 in the 2.56-2.75 THz and 3.73-4.05 THz bands. By integrating the PCM with the array antenna, tunable RCS reduction was obtained without affecting the basic radiation functionality of the antenna. In State 1, RCS reduction was greater than 10 dB in the 1.60-2.43 THz and 3.63-3.72 THz frequency ranges. In State 2, the RCS reduction exceeded 10 dB in the 2.07-2.53 THz, 2.78-2.98 THz, and 3.70-3.81 THz bands. In State 3, RCS reduction was greater than 10 dB in the 1.32-1.43 THz, 2.51-2.76 THz, and 3.76-4.13 THz frequency ranges. This polarization conversion metasurface shows significant potential for applications in switchable and tunable antenna RCS reduction.

The Tunable Parameters of Graphene-Based Biosensors.

Graphene-based surface plasmon resonance (SPR) biosensors have emerged as a promising technology for the highly sensitive and accurate detection of biomolecules. This study presents a comprehensive theoretical analysis of graphene-based SPR biosensors, focusing on configurations with single and bimetallic metallic layers. In this study, we investigated the impact of various metallic substrates, including gold and silver, and the number of graphene layers on key performance metrics: sensitivity of detection, detection accuracy, and quality factor. Our findings reveal that configurations with graphene first supported on gold exhibit superior performance, with sensitivity of detection enhancements up to 30% for ten graphene layers. In contrast, silver-supported configurations, while demonstrating high sensitivity, face challenges in maintaining detection accuracy. Additionally, reducing the thickness of metallic layers by 30% optimizes light coupling and enhances sensor performance. These insights highlight the significant potential of graphene-based SPR biosensors in achieving high sensitivity of detection and reliability, paving the way for their application in diverse biosensing technologies. Our findings pretend to motivate future research focusing on optimizing metallic layer thickness, improving the stability of silver-supported configurations, and experimentally validating the theoretical findings to further advance the development of high-performance SPR biosensors.

Tunable terahertz filter based on graphene photonic crystals with defective layers

In this paper, we design a high-precision tunable terahertz filter by using transfer matrix method. The filter structure mainly consists of graphene embedded photonic crystals (GPCs). The front part of the GPCs contains artificial synthetic material and air layer, the back part of the GPCs is composed by and periodic stack of isotropic dielectric slabs (MgF2) embedded with graphene sheets, where air defect layer is located in the middle of the GPC as a central layer. Our simulation reveals that graphene layer and air defective layer strongly affect the filter performance. And we can get a relatively pure transmission peak in a wide frequency region. Additionally, the influence of incidence angle of terahertz wave, thickness of air layer, the unit number of front periodic structure and chemical potential of the graphene sheets can also modulate the function of the filter. And the filter has strong stability when the temperature changes from 150 K to 350 K.The results indicate that single channel, dual and multiple channels filter in a narrow frequency can be obtained by optimizing the structure parameter.

Lignocellulosic Biomass‐Derived Graphene: Fabrication, Challenges and Its Potential for Hydrogen Storage Application

ABSTRACTThis review explores the utilization of lignocellulosic biomass (LCB) waste in the fabrication of graphene and its applications in hydrogen storage. Several LCB wastes, such as rice straws, coconut shells, wheat straws, and sugarcane bagasse, along with the methodology used and the characteristics of the final graphene, have been discussed in detail. It was found that the coconut shells produced crumpled multilayered graphene, rice husks (RHs) provided a mix of graphene layers and amorphous carbon, wheat straw yielded few‐layered graphene, and sugarcane bagasse contributed to different graphene‐like materials. This review has also focused on the various synthesis processes, such as carbonization, hydrothermal carbonization (HTC), chemical activation, pyrolysis, chemical vapor deposition (CVD), and Hummers' method for graphene fabrication from LCB waste, along with their advantages and disadvantages, for a better understanding. Various results have been discussed exploring the use of lignocellulosic biomass‐derived graphene (LCB‐G) and its various modified forms for hydrogen storage applications. Various challenges in graphene fabrication from LCB, such as low yield, product quality, scalability, use of expensive synthesis methods, and toxic chemicals, along with some potential solutions, have been mentioned. Finally, the review concludes with insights into the future of LCB‐G and its role in hydrogen storage while identifying some gaps, such as scalability and product quality, for further research and development.

Sucrose‐Based Dense, Pure, and Highly‐Crystalline Graphitic Materials for Lithium‐Ion Batteries

AbstractAt present, most synthetic graphite materials commonly used as anode active ingredients in lithium‐ion cells are produced by graphitization of petroleum cokes. The carbon footprint associated with synthetic graphite production is significant. Thus, bio‐derived and cheap precursors, such as saccharides, would be an attractive alternative for the sustainable production of graphitic carbons. However, they are non‐graphitizing at temperatures as high as 3000 °C, preserving the curved, fullerene‐like structure of graphene layers and microporosity. Consequently, many lithium ions are consumed during the formation of solid electrolyte interphase films and passivated in the nanovoids. Here, a method for the production of pure, crystalline, graphitic materials based on sucrose disposed of microporosity is presented, which also works with a variety of saccharides and other organic precursors of hard carbons—generally considered incapable of such transformation. This process employs catalytic graphitization by Si particles at high temperatures. The electrochemical response of such derived sucrose‐based graphite in Li‐ion half‐cells demonstrated its feasibility to serve as an anode active material for rechargeable Li‐ion batteries.

Thermal Rectification in Graphene-Boron Nitride Nanotube Hybrid Structures: An Independent Control Mechanism for Forward and Backward Heat Flux.

The weak van der Waals interactions in the out-of-plane direction result in markedly low thermal conductivity in one-dimensional (1D) and two-dimensional (2D) materials, which substantially restricts their applications. Developing three-dimensional (3D) columnar hybrid structures, featuring high thermal conductivity both within and beyond the plane, effectively addresses this challenge. This study investigated a 3D hybrid structure composed of graphene and boron nitride nanotubes (GR-BNNTs) using non-equilibrium molecular dynamics simulations. This approach allowed the examination of the formation mechanisms and key factors influencing thermal rectification (TR) in these materials. Our findings reveal a novel mechanism for independently regulating forward and backward heat fluxes in GR-BNNTs. By manipulating the thermal properties of the BNNTs and the graphene layer, the TR ratio can be controlled flexibly. Additionally, we identify specific strategies for independently adjusting the heat flux, such as altering the intercolumn distance of BNNTs, which impacts the backward flux merely, while applying strain to affect the forward flux merely. This research introduces a novel concept of independent regulation of forward and backward heat fluxes, providing significant insights into phonon thermal transport in 3D hybrid structures.

Fe2N5P dual-atom catalysts: A pathway to efficient hydrogen evolution in renewable energy applications

Dual-atom catalysts (DACs) are expected to improve the catalytic activity compared to single-atom catalysts (SACs). This improvement is attributed to the synergistic interaction between adjacent bimetallic atoms in DACs. Recently, the highly active Fe2N5P sites embedded in covalent organic framework-derived carbon have been demonstrated to catalyze oxygen reduction reaction (doi:10.1021/acscatal.3c02186). Motivated by this fascinating finding of Fe2N5P-based DACs, their potential for catalyzing hydrogen evolution reaction (HER) has been investigated. Thus, electrocatalytic activities of the Fe2N6 and Fe2N5P-based DACs embedded in graphene layer were systematically investigated toward the HER. Our results show that the Fe2N6 site embedded in graphene shows high catalytic activity and selectivity toward the HER. However, our results reveal that the P atom in the Fe2N5P dual-site facilitates the × H formation and thus improves its catalytic activity toward HER due to a greater degree of synergistic effect. The computed Gibbs free energies confirm the higher feasibility of HER on the Fe center of Fe2N5P compared to the Fe2N6 DAC.

Synergistically Tuning Graphene Layer and Active Sites for Flexible Zn–Air Batteries

Synergistically Tuning Graphene Layer and Active Sites for Flexible Zn–Air Batteries

Positron unveiling high mobility graphene stack interfaces in Li-ion cathodes

Carbon-based coatings in Li-ion battery cathodes improve electron conductivity and enable rapid charging. However, the mechanism is not well understood. Here, we address this question by using positrons as non-destructive probes to investigate nano-interfaces within cathodes. We calculate the positron annihilation lifetime in a graphene stack LiCoO2 heterojunction using an ab initio method with a non-local density approximation to accurately describe the electron-positron correlation. This ideal heterostructure represents the standard carbon-based coating performed on cathode nanoparticles to improve the conduction properties of the cathode. We characterize the interface between LiCoO2 and graphene as a p-type Schottky junction and find positron surface states. The intensity of the lifetime component for these positron surface states serves as a descriptor for positive ion ultra-fast mobility. Consequently, optimizing the carbon layer by enhancing this intensity and by analogizing Li-ion adatoms on graphene layers with positrons at surfaces can improve the design of fast-charging channels.

Graphene-based tunable broadband metamaterial absorber for terahertz waves

In order to overcome the limitations exhibited by traditional absorbers in electromagnetic wave absorption, such as the extremely narrow absorption bandwidth and uncontrollable absorption results, this paper proposes a novel tunable broadband metamaterial absorber based on graphene. Compared to other terahertz absorbers, the absorber designed in this study exhibits simpler structural design, compact form, thin thickness, efficient absorption performance, and a broader bandwidth. This absorber adopts a three-layer structure, including a patterned monolayer graphene metasurface, a dielectric layer, and a metal substrate. The structure of this patterned graphene consists of four triangular graphene resonators, achieving both high absorption efficiency and maintaining an exceptionally wide absorption bandwidth. The simulation results indicate that at a Fermi energy level Ef of 0.45 eV, the absorber achieves a broadband absorption rate of over 90 % in the 3.287 THz to 5.247 THz frequency range under normal terahertz wave incidence conditions. By analyzing different quantities of the triangular graphene structure on the top of the absorber, we found that the wide absorption bandwidth of the absorber is mainly attributed to the structural coupling of the top-layer graphene in the absorber. Furthermore, through the study of electric field amplitude and current distribution, we stumbled upon that when terahertz waves are incident on the absorber, due to the structural coupling between the graphene layers, electric resonance and magnetic resonance occur within the absorber, resulting in the absorption effect. Finally, through the study of geometric parameters, different polarization angles and oblique incidence angles of the incident waves, as well as different Fermi energy levels of graphene, we discovered that by adjusting the Fermi energy level of graphene, the bandwidth and absorption performance of the absorber can be flexibly tuned. In addition, this absorber exhibits wide-angle absorption characteristics and polarization-insensitive properties, providing potential application prospects in fields such as terahertz thermal imaging and stealth technology.

Design of encoded graphene-gold metasurface-based circular ring and square sensors for brain tumor detection and optimization using XGBoost algorithm

This study introduces a circular ring and square metasurfaces-based sensor employing graphene and gold layers for enhanced brain tumor detection. The sensor architecture includes dual graphene circular metasurfaces and a gold square resonator layer on a silicon dioxide substrate. A comprehensive parametric investigation explores the influence of geometric parameters and graphene chemical potential on sensor performance. The sensor achieves a remarkable sensitivity of 769 GHzRIU−1, a high-quality factor of 6.514, a low detection limit of 0.182 RIU, and an FOM of 1.148RIU−1. Electric field intensity analysis identifies optimal transmission frequencies. By employing the XGBoost regressor, the analysis significantly reduces simulation time and resource consumption by at least 80 %. Simulation validation confirms that despite 80 % reduction in simulation time, high prediction accuracy remains achievable, with an impressive R2 score ranging from 0.9 to 1. The proposed sensor presents a promising non-invasive approach for early brain tumor diagnosis, with potential applications in biomedical imaging and other related fields.

Influence of Graphene on Sheet Resistivity and Urbach Enery of Nano TiO<sub>2</sub> for DSSC Electrode

Importance of renewable energy cannot be over emphasized. Titanium IV oxide (TiO<sub>2</sub>) is the most suitable semiconductor for dye sensitized solar cell (DSSC) due to its chemical stability, non toxicity and excellent optoelectronic properties. In this research TiO<sub>2</sub> is coated on graphene to enhance its charge transport aiming to reduce recombination which is a main set back in DSSCs. undestanding graphene- TiO<sub>2 </sub>contact is therefore essential for DSSC application. TiO<sub>2</sub> thin films were deposited on single layer graphene (SLG) as well as on flourine tin oxide (FTO) using doctor blading technique. The films were annealed at rates of 2°C /min and 1°C/min up to a temperature of 450°C followed by sintering at this temperature for 30 minutes. Four point probe SRM-232 was used to measure sheet resistance of the samples. The film thickness were obtained from transmittance using pointwise unconstrained minimization approximation (PUMA). UV –VIS spectrophotometer was employed to measure transmittance. Resistivity of TiO<sub>2</sub> on both FTO and Graphene were of order 10<sup>-4</sup> Ωcm. However, TiO<sub>2</sub> annealed on graphene matrix exhibited a slightly lower resistivity 5.6 x10<sup>-4</sup> Ωcm as compared to 6.0x10<sup>-4 </sup>Ωcm on FTO. Optical transmittance on visible region was lower for TiO<sub>2</sub> on FTO than on SLG, 71.48% and 80.11% respectively. Urbach energy (Eu) for weak absorption region decreased with annealing rate. Urbach energies for 1°C/min TiO<sub>2 </sub>on FTO and SLG were 361 meV and 261meV respectively. This was used to account for decrease of disoders of films due to annealing. A striking relation between sheet resistivity and urbach was reported suggesting SLG as a suitable candidate for photoanode of a DSSC.

Joule heating for structure reconstruction of hard carbon with superior sodium ion storage performance

Hard carbon anode for sodium ion batteries still remains many challenges including insufficient cycling life and initial Coulombic efficiency (ICE), weak rate capability and poor compatibility in common ester electrolytes. Here, we propose a Joule heating post-treatment including multifield sintering method to reconstruct the structure of hard carbon from thick graphene layers to more disordered vortex layer structure composed of thin and curved graphite-like domains. The molecular dynamics simulation and differential charge density distribution demonstrate the crucial effect of electric field in strengthening the interaction between the polar molecule groups and the graphene layer, leading to the distortion and expanding of graphene layer. This is a universal and highly efficient strategy to modify various hard carbons within minutes. The optimized hard carbon anode exhibits exceptional rate capability and cycling stability with a high retention rate of 88.4% after 15,000 cycles at 10C in ether electrolyte. It also displays remarkably improved reversible capacity, initial Coulombic efficiency ICE of 89.5% and cycling stability in ester electrolyte. It is revealed by in-situ electrochemical impedance spectroscopy and atomic force microscopy that the spontaneous formation of a thin, stable and inorganic substance-rich solid electrolyte interface layer with significantly improved mechanical property is largely responsible for the outstanding sodium-ion transport kinetics and long lifespan.

Optical Sensitive Detection of Cervical Cancer Based on Surface Plasmon Resonance Nanostructure

Cervical cancer is a disease that affects a lot of people all over the world. The success of treatment is significantly increased by early detection. The new surface plasmon resonance sensor (SPRS) described in this article is constructed from layers of silver, BaTiO3, and graphene, as well as a coupling prism. The transfer matrix (TM) approach is used to evaluate the SPRS structure. To obtain the highest sensitivity of the suggested SPRS, the thicknesses of the Ag and BaTiO3 and the number of Gr sheets are evaluated. Investigations are done on all factors of performance of the proposed device. Exemplary efficiency is achieved using 4 nm (BaTiO3) and 60 nm (Ag) materials. Three layers are chosen as the optimal amount of graphene after investigation. When the optimal thicknesses are employed, the suggested SPRS's greatest sensitivity of 300° RIU−1 has been attained. The suggested SPRS displays better sensitivity when compared to SPRS structures that have already been published in the literature. This SPRS is promising to be used in different biosensing applications due to its high performance.

Raman spectroscopy and photoluminescence study of PN junction p-graphene/n-GaAs.

Single layer graphene (SLG) was synthesized via high-quality chemical vapor deposition (CVD) on high-quality copper and subsequently transferred onto SiO2 and on n-GaAs substrates with varying doping electron concentrations (n = 1016, 1017, 5 × 1017, 1018, and 5 × 1018cm-3). The n-GaAs substrates were grown by molecular beam epitaxy. The optical properties of the SLG were investigated through photoluminescence (PL) and Raman spectroscopy measurements. Carrier concentration n or p and Fermi energy (EF) values in SLG were determined both before and after the transfer onto n-GaAs, and these findings were validated through PL studies. The Raman spectroscopy results indicated an increase in the transfer of electrons from n-GaAs to SLG as the doping electron density in n-GaAs increased. PL analysis revealed a significant change in the bandgap energy (Eg) of n-GaAs due to bandgap narrowing and the Burstein-Moss shift. Our data enable us to determine the energy band diagrams. Upon aligning the energy bands, an increase in transferred carrier density is accompanied by changes in Fermi energies and an increase in the potential barrier (∆U). The increase in ∆U is of significant interest to ensure that charges are directed more efficiently toward the cell's electrical contacts in the case of photovoltaic application. There, they can contribute significantly to the generated electric current, thereby enhancing the performance of a cell. Our results can provide insights into the interaction in graphene-based heterostructures and aid in selecting the best parameters for developing new advanced devices.

Exploring novel methods: Acid treatment, metal nanoparticle doping, and graphene insertion for enhanced electrical conductivity of nm thin PEDOT:PSS films

This study builds upon our previous research aimed at enhancing the electrical conductivity of Poly(3,4-ethylenedioxythiophene) Polystyrene Sulfonate (PEDOT:PSS). We investigate a range of techniques, including acid treatments, doping with metal nanoparticles (Cu and Ag), deposition of multiple PEDOT:PSS layers, and incorporation of mono/multiatomic layer graphene. Our investigations reveal that optimizing the deposition of PEDOT:PSS multilayers and treating them with nitric acid yields superior results compared to alternative methods employing metal nanoparticles and graphene. This optimized process not only enhances the electrical conductivity of PEDOT:PSS but also offers advantages in terms of reduced errors, increased stability, and cost-effectiveness when compared to the use of graphene layers and metal nanoparticles. Optimization parameters such as spinning speed, etchant concentration, and etching time are crucial factors in achieving these outcomes. Compared to single-layer PEDOT:PSS films of the same thickness, the optimized nine-layer PEDOT:PSS treated with nitric acid demonstrates a significant enhancement of conductivity from 0.18 S/cm to 15,699 S/cm. Furthermore, we address film aging to mitigate reliability issues induced by ambient conditions.

Graphene-Based Field-Effect Photodetector with HgCdTe Absorber

A field-effect photodetector structure composed of an Al2O3-encapsulated bilayer graphene conductive channel attached to an Al2O3 dielectric layer deposited on a HgCdTe absorbing layer on CdTe/Si <211> was studied. Ti/Au ohmic contacts to the graphene layer were used as drain and source electrodes and back-gate voltage was applied to the Si substrate. It was demonstrated that 80% and 10% modulation of the graphene channel conductivity can be achieved under blue (50 W/cm2) and infrared (IR) (0.02 W/cm2) illumination, respectively, at a gate voltage of 7 V. Detector responsivity was measured as 406 A/W and 1.83 A/W under IR lamp and 405-nm laser irradiation, respectively, with corresponding gain values of 340 and 5.6. The detectivity of the 4 × 4 photodetector arrays was on the order of 1010 Jones for the mid-wave infrared wavelength range (3–5 μm).

The oxidation of carbon nanostructures imaged by electron microscopy: Comparison between in-situ TEM and TGA experiments

The development of a model of carbon oxidation has engaged researchers for decades. Yet many outstanding questions remain due to the inability to experimentally study the details of the oxidation. Today, novel techniques such as environmental transmission electron microscopy (ETEM), allowing for in-situ nanoscale observations of the oxidation process, can help illuminate some of these questions. In this study of few layer graphene (FLG), multi-walled carbon nanotubes (MWCNTs), buckminsterfullerene (C60), and nanodiamonds (NDs) oxidizing in temperatures up to 1100 °C and we analyze the importance of nanostructure for the thermal stability of nanocarbons. The study was complemented with thermogravimetric analysis (TGA) and the experiments were in good agreement with oxidation rates increasing sharply with temperature and the thermal stability of the materials MWCNTs, FLG, C60 and NDs in descending order. Based on the direct nanoscale visualization obtained in the ETEM the materials can be divided into two overall categories: materials with low strain sp2-bonds (FLG and MWCNT); and materials with high strain sp2-bonds (C60) or sp3-bonds (NDs). For materials in the first category, it is possible to identify several different phenomena as their oxidation rate increases as a function of temperatures whereas materials in the second category appear to be more influenced by extrinsic factors such as the electron beam and by structural transformation upon heating. This study clearly shows the value of adding ETEM results to traditional TGA investigations since it gives both a complementary and more detailed information about the dynamic oxidation process.