Graphene Silicon Research Articles

Surface-wave-sustained plasma synthesis of graphene@Fe–Si nanoparticles for lithium-ion battery anodes

Silicon encapsulated in conductive layers has proven to be an excellent method for retaining the high capacity of silicon in lithium-ion batteries (LIBs) throughout cycling. This study presents an ultra-fast, single-step, and scalable method for synthesizing graphene@Fe–Si nanoparticles via an atmospheric pressure surface-wave-sustained plasma. The verification of the synthesized nanoparticles, encompassing graphene cladding and silicon nanoparticles encapsulated in iron, was conducted through energy-dispersive x-ray spectroscopy mapping, line scanning in the transmission electron microscopy mode, and high-resolution transmission electron microscopy. Additionally, Raman spectroscopy corroborated the identity of the cladding as graphene. This study provides a viable strategy for the industrial production of anode materials for high-performance LIBs.

Modeling and characterization studies of wear behavior of aluminium metal matrix composites reinforced with reduced graphene oxide, silicon carbide, and alumina

In the current study, we report on the modeling and characterization studies of wear behavior of aluminium metal matrix composites reinforced with reduced graphene oxide (rGO), silicon carbide (SiC), and alumina (Al2O3). A double stir casting process was utilized in the production of the metal matrix composites using a 10 wt% ratio of the reinforcements. The wear test was performed using a pin-on-disc at room temperature, by varying loads and sliding speed. The results show that the sliding speed, load, and interactions between the sliding speed and load as well as the load and the composition were significant model terms. The optimum predicted conditions were attained at a sliding speed of 750 rpm at a of load 750 g for composition C. The P-values was less than 0.0500, indicating that the model terms are significant. At lower load, a rubbing type of debris feature characterizes the debris morphology. However, at higher loads, a severe sliding feature with striations and straight edges was evident. The EDX peak suggests a mechanically mixed layer comprising Al2O3 on the surface.

The effect of graphene layers on the optoelectronic properties of graphene–silicon photodetector

The effect of graphene layers on the optoelectronic properties of graphene–silicon photodetector

First-principles study on the electronic structure of siligraphene on a ZnO monolayer

Density functional theory was employed to investigate the electronic structures of atomic bilayer materials that form between graphene (g-C) or graphitic silicon carbide (also known as siligraphene: g-SiC and g-SiC2) and graphitic zinc oxide (g-ZnO). The results indicate that g-C/g-ZnO bilayers have semimetallic properties with an energy band gap of zero like in graphene. For a g-SiC/g-ZnO bilayer, an ensemble of three sp 2-hybridized carbon atoms periodically separated by three silicon atoms on g-ZnO has indirect and direct band gaps of 3.32 and 3.78 eV, respectively, which is suitable for use in light-emitting diode applications. For a g-SiC2/g-ZnO bilayer, an ensemble of four sp 2-hybridized carbon atoms periodically separated by two silicon atoms on g-ZnO has a direct band gap of 1.15 eV, which approaches the optimal value of the band gap (E opt ≃ 1.3 eV) for solar cell applications. The results show that increasing Si content in siligraphene can help to open the band gap of graphene and enhance the band gap of graphitic silicon carbide. The band gaps of siligraphene/g-ZnO bilayers depend on a smaller band gap from the monolayer component. Therefore, adjusting the Si content in siligraphene permits tuning of the band gap, and constructing a bilayer in the presence of a g-ZnO monolayer can slightly decrease the band gap. These results could lead to a new design of heterostructures with tunable band gaps for various applications.

Highly Sensitive, Wide-Range Pressure Sensor Based on Negative Poisson’s Ratio for Human Motion Detection

Flexible wearable materials can be attached to human skin to collect a range of health information, such as wrist rotation, finger joint movement, knee flexion, and so on. Moreover, facial muscle-based signal monitoring can infer people’s emotional expressions, which has a wide range of applications. At present, it is difficult for one sensor to realize the interactive information monitoring of multiple parts of the human body, which is caused by the contradiction between sensitivity and range. In this work, an innovative method of mechanical structure is proposed. A PDMS elastomer with negative Poisson’s ratio (NPR) is embedded in the graphene–silicon rubber foam composite (rGO-PDMS/SR) in a simple and low-cost process, which improves the mechanical performance and resistance variation range effectively. The performance test results show that compared with ordinary graphene–silicon rubber composites (rGO-SR), the resistance variation range of the rGO-PDMS/SR has expanded by six times, which has high linear sensitivities of 7.0838 kPa−1 at 0–50 kPa and 0.0168 kPa−1 at 50–250 kPa. In addition, the composite shows reliable stability during cyclic compression. By analyzing the resistance change mechanism of the sensor, the explicit expression between the composite material performance parameters and the resistance is obtained. The results of human interaction experiments show that the sensor can meet the requirements of signal detection at nine different positions of the human body, including facial expression judgment, motion state monitoring, and other fields, which indicates good human interaction performance.

Development of a tunable broadband metamaterial absorber based on joint modulation of graphene and photosensitive silicon in the terahertz region

In this paper, a tunable broadband metamaterial absorber based on joint modulation of graphene and photosensitive silicon have been proposed in the terahertz region. While σSi = 2000 S/m and Ef = 0.6 eV, the overall bandwidth of over 90% absorption is 0.896 THz and the relative bandwidth is 53%. As is known to all, the conductivity of graphene can be adjusted by bias voltage, and that of photosensitive silicon by optical pumping. So, through regulating the Fermi energy of graphene, central frequency modulation of the broadband absorption can be achieved. By means of laser pumping on photosensitive silicon, we can control the absorption amplitude conveniently. Through joint modulation of Fermi energy and silicon conductivity, manipulation of absorption bandwidth can be obtained. Thus, the absorber can realize active modulation of central frequency, absorption amplitude and absorption bandwidth at the same time. Besides, other influencing factors on absorption performance, such as the polarization angle, the incidence angle, as well as structure parameters are also studied in details. All the simulation results indicate that the proposed absorber possesses fine performance, which could be dynamically modified to fit different application areas.

Current crowding in graphene–silicon schottky diodes

The performance of the Graphene/Si (Gr/Si) Schottky interface and its potential in future electronics strongly rely on the quality of interconnecting contacts with external circuitry. In this work, we investigate the dominating and limiting factors of Gr/Si interfaces designed for high light absorption, paying particular attention to the nature of the contact failure under high electrostatic discharge (ESD) conditions. Our findings indicate that severe current crowding at contact edges of the graphene is the dominating factor for the device breakdown. Material degradation and electrical breakdown are systematically analyzed by atomic force, Raman, scanning electron, and energy-dispersive x-ray spectroscopies. This work enlists the robustness and limitations of Gr/Si junction in photodiode architecture under high ESD conditions that can be used as general guidelines for 2D–3D electronic and optoelectronic devices.

Integrated metamaterial with the functionalities of an absorption and polarization converter.

A switchable and tunable dual-function absorber/polarization converter is presented in this work. The constitution of the structure, which incorporates patterned graphene and photosensitive silicon (Si), can minimize undesired optical losses. Simulated results show that when the Si is metallic, the structure behaves as a broadband absorption of more than 90% in the range of 1.45-3.36THz. Its peak absorption can be tuned from 22% to 99.8% by changing the Fermi energy of graphene. Furthermore, the interference theory analyzes the physical mechanism for broadband absorption. When the Si is in the dielectric state, the structure has a transmission polarization conversion function, which realizes the conversion from linear to cross-polarized waves. The polarization conversion ratio (PCR) is greater than 90% in the 3.82-4.43THz range. Meanwhile, the cross-polarization transmission can be dynamically tuned from 28% to 97%, and the PCR can also be tuned from 17% to 99.9% by adjusting the conductivity of the Si. The reason for realizing polarization conversion is explained by the polarization decomposition method. This study provides a design opinion of high-performance multifunctional tunable terahertz devices.

Optimization of graphene dose for improved electrochemical performance of silicon–graphene negative electrodes in lithium batteries

Different percentages of nanoparticles graphene (G) were mixed with nano-micron sized silicon (Si) particles as follows: 10, 20, 30 and 40 wt% graphene to silicon ratios. The crystal structure of pure Si powder pattern has cubic phase SEM, TEM/SAED and XPS equipments were implemented to study the surface properties of the prepared G@Si composites. Cyclic voltammetry (CV) measurement for the G@Si cell revealed two broad cathodic peaks, related to the deposition of Li2O thin layer on Si particles and the lithiation process of Si to form lithium silicide. Meanwhile, the oxidation of LixSi into Si and Li ionis confirmed by the anodic strong peak at 0.56 V. Electrochemical impedance spectroscopy (EIS) measurements revealed high interfacial resistance ~ 1825 Ω for pure Si anode in comparison with that of G@Si composite anode. It is concluded that graphene acts as a conductive shielding pathway to inhibit the large volume change and minimize the capacity fading during successive galvanostatic cycling of G@Si composite anode materials versus Li/Li+. Accordingly, the specific discharge capacity of 30%G@Si cell delivered about 1240 and 900 mAhg−1 for 1st and 100th charge–discharge cycles, respectively.

Tunable and switchable common-frequency broadband terahertz absorption, reflection and transmission based on graphene-photosensitive silicon metamaterials

In this paper, we present a switchable and tunable common-frequency broadband terahertz (THz) absorption/reflection/transmission functional device based on graphene and photosensitive silicon. When photosensitive silicon is in the metallic state and graphene Fermi energy level is at EF=1 eV, the absorptance (A) is greater than 90% in the range of 1.42 to 3.34 THz, and adjusting graphene Fermi energy level to EF=0 eV, the reflectance (R) is greater than 80% from 0.5 to 4.5 THz. While photosensitive silicon switches to the dielectric state and graphene Fermi energy level at EF=0 eV, the transmittance (T) is greater than 80% in the range of 1.42 to 3.34 THz. Simulated data were verified by the coupled-mode theory (CMT). We believe that the proposed structure can be applied to wireless communication, sensing and imaging.

The impact of various carbon nanomaterials on the morphological, behavioural, and biochemical parameters of rainbow trout in the early life stages

With the increasing production and the number of potential applications of carbon nanomaterials, mainly from the graphene family, their release into the natural environment, especially to aquatic ecosystems, is inevitable. The aim of the study was to determine the effects of various carbon nanomaterials (graphene nanoflakes (GNF), graphene oxide (GO), reduced graphene oxide (RGO) and silicon carbide nanofibers (NFSiC) in the concentration of 4 mg L−1 on the early life stages of the rainbow trout Oncorhynchus mykiss. The survival rates of O. mykiss were not affected after 36 days of exposure to studied materials, except for RGO, which caused significant mortality of both embryos and larvae compared to the control conditions. Larvae exposed to GO and NFSiC were characterized by a smaller standard body length at hatch, whereas at the end of the experiment, the growth of fish exposed to all materials was accelerated, especially in GO and RGO treatment, in which higher body weight and length were accompanied by lower volume of the yolk sac. Neither the markers of the oxidative damage nor the antioxidant enzymes activities were significantly affected in embryos, newly hatched larvae and larvae after 26-day exposure to studied carbon nanomaterials. Also, no neurotoxic effect expressed by the activity of the whole-body acetylcholinesterase was observed. Nevertheless, the significant increase in the velocity and the overall activity of larvae exposed to GNF (not investigated after exposure to other materials) must be highlighted. The most pronounced effect of RGO might be connected with its large particle size, sharp edges, and the presence of TiO2 nanoparticles. The results indicate for the first time that various carbon nanomaterials potentially released into aquatic ecosystems may have serious developmental implications for the early life stages of salmonid fish.

Fundamental optical logic gate operations using optically controlled two surfaces plasmonic polariton mode coupler based on graphene clad waveguide

Here, an optical pulse controlled 2 × 2 surface–plasmon–polariton (SPP) mode interference coupler based on graphene clad is designed for the operation of optical fundamental gates. Exploiting the light–matter interactions on graphene–silicon interface and nonlinear optical property of graphene, coupling characteristics are obtained as a function of extra phase change between the excited SPP modes (fundamental and first order) modes with incidence of optical pulse. The device with a very small coupling length of ∼4.3 μm shows optical NOT, AND, and OR gate operation. Our compact design with high fabrication tolerance opens an avenue for the development of a complex optical processor.

Tribological Behaviour and Microstructure of an Aluminium Alloy-Based g-SiC Hybrid Surface Composite Produced by FSP

In this work, the microstructure and wear characteristics of a surface-reinforced composite based on an aluminium alloy with a mixture of graphene nanoplatelets (GNP) and silicon carbide (SiC), referred to as g-SiC, fabricated by Friction Stir Processing (FSP), are investigated. To further improve the tribological performance, different volume fractions (0 vol%, 5 vol%, 10 vol% and 15 vol%) of g-SiC-reinforced aluminium alloy are prepared by FSP. It is concluded that the Friction Stir Processed (FSPed) AA5083/g-SiC (15 vol%) specimen has optimum reduction in average friction coefficient (61.13%) and optimum reduction in specimen weight (72.97%). In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of metals with minimal negative impact on the environment and humans, while reducing material loss and overall manufacturing costs.

Enhanced Electrical Properties of Optimized Vertical Graphene-Base Hot Electron Transistors

The arrival of high-mobility two-dimensional materials like graphene leads to the renaissance of former vertical semiconductor–metal–semiconductor (SMS) hot electron transistors. Because of the monolayer thickness of graphene, improved SMS transistors with a semimetallic graphene-base electrode are now feasible for high-frequency applications. In this study we report about a device that consists of amorphous silicon, graphene, and crystalline silicon. For the first time, this device is fabricated by a four-mask lithography process which leads to significant improvements in the device performance. A strongly increased common-emitter current gain of 2% could be achieved while the on–off ratio improved to 1.6 × 105, which is already higher than predicted theoretically. This could be mainly attributed to better interface characteristics and decreased lateral dimensions of the devices. A cutoff frequency of approximately 26 MHz could be forecasted based on the DC measurements of the device.

High‐Speed Graphene–Silicon–Graphene Waveguide PDs with High Photo‐to‐Dark‐Current Ratio and Large Linear Dynamic Range

Abstract2D materials (2DMs) meet the demand of broadband and low‐cost photodetection on silicon for many applications. Currently, it is still very challenging to realize excellent silicon‐2DM photodetectors (PDs). Here, graphene–silicon–graphene waveguide PDs operating at the wavelength bands of 1.55 and 2 µm, showing the potential for large‐scale integration, are demonstrated. For the fabricated PDs, the measured responsivities are ≈0.15 and ≈0.015 mA W−1 for the wavelengths of 1.55 and 1.96 µm, respectively. In particular, the PDs exhibit a high bandwidth of ≈30 GHz, an ultra‐low dark current of tens of pico‐amperes, a high normalized photo‐to‐dark‐current ratio of 1.63 × 106 W−1, as well as a high linear dynamic range of 3 µW to 1.86 mW (and beyond) at 1.55 µm. According to the measurement results for the wavelength bands of 1.55/2.0 µm and the theoretical modeling for the silicon–graphene heterostructure, it is revealed that internal photoemission and photo‐assisted thermionic field emission dominantly contribute to the photoresponse in the graphene–silicon Schottky junctions under moderately high bias voltage, which helps the future work to further improve the performance.

Enhanced photovoltaic effect in graphene–silicon Schottky junction under mechanical manipulation

A graphene–silicon Schottky junction (GSJ), which has potentials of large-scale manufacturing and integration, can bring new opportunities to Schottky solar cells for photovoltaic (PV) power conversion. However, the essential power conversion limitation for these devices lies in a small open-circuit voltage (Voc), which depends on the Schottky barrier height. In this study, we introduce an electromechanical method based on a flexoelectric effect to enhance the PV efficiency in GSJ. By atomic force microscope (AFM) tip-based indentation and in situ current measurement, the current–voltage (I–V) responses under a flexoelectric strain gradient are obtained. The Voc is observed to increase for up to 20%, leading to an evident improvement of the power conversion efficiency. Our studies suggest that the strain gradient may offer unprecedented opportunities for the development of GSJ-based flexo-photovoltaic applications.

Defect mediated lithium adsorption on graphene-based silicon composite electrode for high capacity and high stability lithium-ion battery

Carbon-coated silicon materials are considered as promising anode materials in high-capacity lithium-ion batteries (LIBs). Theoretically, using graphene as the anode material in the LIB would afford high electrical conductivity, mechanical stability of Si, and suppression of the unstable solid–electrolyte interface. However, its usage is hindered by its electrochemical characteristic, which is not electrochemically active when combined with lithium. Therefore, research on graphene as the anode and coated material in LIBs has been conducted using defect engineering to enhance the storage capacity of graphene. Although the electrochemical characteristics of various defects in graphene have been studied experimentally and theoretically, graphene-based composite anode materials such as graphene–silicon composite electrodes have rarely been studied from the electrochemical and mechanical perspectives. In this study, lithium adsorptions are conducted on various defected graphene and graphene–silicon composites using density functional theory calculation. The formation energies of Li on the various defected graphene are assessed, and the mechanical strengths of the graphene–silicon composites are analyzed. Our calculations validate that the defects in graphene enhance the electrochemical adsorptions and interfacial mechanical strengths of the graphene and graphene–silicon composites. During lithiation, the defects mediate greater interfacial adhesion of the silicon–graphene composite. Hence, we elucidate that defected graphene increases the electro-chemo mechanical stabilities of silicon composites in high-capacity LIBs.

Performance Evaluation of Silica–Graphene Quantum Dots for Enhanced Oil Recovery from Carbonate Reservoirs

Nanomaterials have shown significant performances in enhancing oil recovery by reducing the interfacial tension (IFT) and contact angle (CA) of the rock/crude oil/water system in porous media. This is evaluated by the synergistic impact of silica–graphene quantum dots (Si–GQDs) on IFT reduction and wettability alteration for the purpose of enhancing oil recovery from carbonate reservoirs. The silica–graphene quantum dots (Si–GQDs) were synthesized by combining graphene oxide and silicon oxide nanoparticles (NPs) and characterized using several analytical techniques. Both distilled water and brine, as dispersion media, were used to prepare nanofluids by dispersing the synthesized Si–GQDs at different concentrations from 1000 to 10,000 ppm. The main properties of the nanofluids including pH, density, and conductivity were measured to evaluate their quality and the performance of Si–GQDs. In addition, the prepared nanofluids were used in the measurements of IFT and contact angles at different concentrations of the synthesized Si–GQDs in both types of used water. The obtained results show that the DWN1000 nanofluid formulated from dispersing 1000 ppm Si–GQDs in distilled water enables an additional 14.4% OOIP oil recovery due to a significant reduction in the value of IFT from 28.3 to 9.5 mN m–1, improving rheology behavior and wettability alteration toward a strong water-wet system from 134 to 61° contact angles.

EXPERIMENTAL AND MODELING ANALYSES OF STABILITY AND THERMOPHYSICAL CHARACTERISTICS OF GRAPHENE OXIDE, CARBON NANOTUBE, AND SILICON CARBIDE DISPERSION IN PROPYLENE GLYCOL

Determining nanofluids' properties by theoretical or experimental analysis has attracted significant attention. This study synthesizes and characterizes propylene glycol-graphene oxide (PG-GO), PG-carbon nanotubes (PG-CNT), and PG-silicon carbide (PG-SiC) nanofluids. All nanofluids were prepared by a two-step procedure with the nanoparticles' concentrations of 0.10, 1.05, and 2.00 wt.%. The nanofluids' stability, thermophysical (heat capacity and surface tension), and transport (thermal conductivity and viscosity) properties are measured at a temperature range of 20-80°C. Zeta potential and average nanocluster size approved that the nanofluids are stable. Increasing the temperature enhances thermal conductivity and heat capacity and reduces viscosity and surface tension. Nanoparticles addition to PG decreases surface tension and heat capacity and increases the viscosity and thermal conductivity. The PG-GO nanofluids have the best average values for viscosity, heat capacity, and thermal conductivity. Several simple models are also suggested to relate nanofluids' thermophysical properties to the temperature and nanoparticles' dose. These correlations simulate the experimental data with reasonable accuracy (correlation coefficient > 0.93).

Modeling the Interaction of Anticancer Protein Azurin with the Nanosheets for Medical Applications

AbstractAzurin as an electron transfer protein plays a vital role in the degradation of cancerous cells, but due to the destruction of its structure by stomach acid, finding safe and efficient techniques such as nano material to protect Azurin for drug delivery purposes is in high demand. In the present study, molecular dynamics techniques are exploited to examine the interaction and immobilization of Azurin on the surface of nanosheets such as graphene monoxide, silicon carbide and boron nitride at 310 K. To analyze the simulation results, structural parameters such as root mean square fluctuation (RMSF), root mean square deviation (RMSD), radius of gyration (Rg), the distance between the center of mass of immobilized protein and surface of the considered nanosheets, and surface accessible solvent area (SASA) are measured. Additionally, the interaction energy of the protein with the nanosheet surface is investigated using structural and energetic parameters of the protein and nanosheets including residue polarity, charge density, hydrophilicity, and hydrophobicity. The simulation results exhibit the adsorption and immobilization of Azurin on the targeted surfaces while maintaining its native structure. As an initial step, these results reveal a promising potential application of studied nanosheets in aqueous condition for the smart delivery, medicine and cancer therapy of Azurin.