Deposited Graphene Films Research Articles

Direct Graphene Deposition via a Modified Laser-Assisted Method for Interdigitated Microflexible Supercapacitors.

The transcendence toward smarter technologies and the rapid expansion of the Internet of Things requires miniaturized energy storage systems, which may also be shape-conformable, such as microflexible supercapacitors. Their fabrication must be compatible with emerging manufacturing platforms with regard to scalability and sustainability. Here, we modify a laser-based method we recently developed for simultaneously synthesizing and transferring graphene onto a selected substrate. The modification of the method lies in the tuning of two key parameters, namely, the inclination of the laser beam and the distance between the precursor material and the acceptor substrate. A proper combination of these parameters enables the displacement of the trace of the transmitted laser beam from the deposited graphene film area. This mitigates the negative effects that arise from the laser-induced ablation of graphene on heat-sensitive substrates and significantly improves the electrical conductivity of the graphene films. The optimized graphene exhibits very high C/O (36) and sp2/sp3 (13) ratios. Post-transport irradiation was used to transform the continuous graphene films to interdigitated electrodes. The capacitance of the microflexible supercapacitor was measured to be among the highest reported ones in relation to interdigitated supercapacitors with electrodes based on laser-grown graphene. The device shows good cycling stability, retaining 91% of its capacitance after 10,000 cycles, showing no substantial degradation after applying bending conditions. This promising laser-based approach emerges as a viable alternative for the fabrication of microflexible interdigitated supercapacitors for paper electronics and smart textiles.

Features of electrochemical behavior of graphene films on metal foams

ABSTRACT Electrochemical behaviour of 4.8 ± 0.2 nm graphene films on nickel and copper foams was investigated by cyclic voltammetry (CV). The graphene films were prepared by chemical vapor deposition and characterized by electron energy loss spectroscopy, elastic peak electron spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The CV of the [Ru(NH3)6]+2/+3 redox reaction was performed using these substrates. The obtained results demonstrated a high continuity of the deposited graphene film and independence of the electron transfer rate on them from the metal substrate used. The rate of outer-sphere electron transfer on the graphene surface appeared to be substantially less than that on the polished glassy carbon. Partial splitting of graphene layers due to wedged action of 2D adsorption layers, formed by camphor solution, led to the increase in double-layer capacitance.

Molecular dynamics simulation of the amorphous graphite-like membrane deposited on ideal graphite substrate.

To understand the growth mechanism of pyrolytic graphite on ideal graphite substrate by chemical vapor deposition (CVD), the process simulated by molecular dynamics is performed. The simulation revealed that only an amorphous graphite-like membrane (a-GLM) can be obtained using the Tersoff potential function. It is revealed that the formation process for the first layer of the a-GLM initiates from the firstly deposited carbon monomers, dimers, and trimers as growth points, on which Y-shaped long chain is formed, and then the network with pores are developed, and finally the graphene-like layer with six-membered dominated rings appears after repair treatment. The following deposition simulation for more deposited carbon atoms indicates that a second layer like-graphene is more prone to superpose onto the microdomains of the first layer like-graphene until the formation of the island-like bumps, and the concave zone around the bumps will be filled by deposited atoms and modified by defect repair. The growth mechanism for pyrolytic graphite prepared by CVD can be deduced by the simulation inspiration. The optimal deposition temperature of 2400 K is acquired by evaluating the integrity of the first deposited graphene film by statistics of five-to-seven-membered carbon ring number. This study can provide theoretical references for the design of the pyrolytic graphite production process.

Fragmented graphene synthesized on a dielectric substrate for THz applications

Fragmented multi-layered graphene films were directly synthesized via chemical vapor deposition (CVD) on dielectric substrates with a pre-deposited copper catalyst. We demonstrate that the thickness of the sacrificial copper film, process temperature, and growth time essentially influence the integrity, quality, and disorder of the synthesized graphene. Atomic force microscopy and Kelvin probe force microscopy measurements revealed the presence of nano-agglomerates and charge puddles. The potential gradients measured over the sample surface confirmed that the deposited graphene film possessed a multilayered structure, which was modelled as an ensemble of randomly oriented conductive prolate ellipsoids. THz time domain spectroscopy measurements gave the ac conductivity of the graphene flakes and homogenized graphitic films as being around 1200 S cm−1 and 1000 S cm−1, respectively. Our approach offers a scalable fabrication of graphene structures composed of graphene flakes, which have effective conductivity sufficient for a wide variety of THz applications.

Growth of wrinkle-free and ultra-flat Bi-layer graphene on sapphire substrate using Cu sacrificial layer

The transfer process of chemical vapor deposition graphene film leads to unavoidable crack, wrinkles, doping, and contamination, which limits its function to establish stable and high-performance devices. It raises a growing interest to fabricate high-quality graphene on the target substrate directly. Here, bi-layer graphene (BLG) film can be grown on sapphire substrate by a Cu sacrificial layer using atmospheric-pressure chemical vapor deposition. The as-obtained BLG at the interface between sapphire and Cu layer is free of wrinkles, and the corresponding surface roughness Ra is as low as 0.66 nm. The square resistance of the graphene is 898.1 ohm sq−1, which is the lowest among the records of graphene film directly grown on nonmetal substrates.

Breaking the Rate‐Integrity Dilemma in Large‐Area Bubbling Transfer of Graphene by Strain Engineering

AbstractEfficient electrochemical bubbling delamination is highly promising for realizing the scalable transfer of high‐quality chemical vapor deposition (CVD) graphene film. However, it remains a challenge to significantly improve the low delamination rate of large‐area graphene without causing structural damage. Here, a strain‐engineering strategy is reported to break this rate‐integrity dilemma by introducing appreciable compressive strain into graphene to dramatically accelerate the delamination of CVD graphene from Cu foil in a non‐destructive manner. An astonishing 25‐fold improvement in the delamination rate is achieved by hot bubbling graphene coated with a post‐cured UV‐epoxy adhesive. Meanwhile, the inherent structural integrity of delaminated graphene films is well preserved. The strategy is superior to the prevalent methods by simultaneously realizing the unprecedented high‐rate delamination and intact transfer. It is further demonstrated that it allows the highly efficient roll‐to‐roll bubbling transfer of meter‐scale high‐quality graphene films.

Graphene oxide/graphene hybrid film with ultrahigh ammonia sensing performance

In this paper, a novel ammonia detection hybrid film is proposed based on a graphene oxide (GO)/graphene stack, which shows excellent sensing characteristics at room temperature. It is attributed to the cooperation of GO layer serving as molecular capture layer while graphene serving as conductive layer. GO layer is obtained on chemical vapor deposited graphene film by a simple drop-casting method. The prepared GO/graphene hybrid film is directly transferred to the target substrate without any additional transfer vehicle to reduce possible contamination. The success of the transfer depends on the mechanical strength of GO layer. The thickness of GO layer can scale down to 55 nm while sustaining the transfer process. The best ammonia gas sensing performance is obtained at about 275 nm GO layer thickness and the ammonia detection limit is calculated to be 1.5 ppb. In conclusion, the ammonia gas sensing performance of GO/graphene hybrid film can be significantly improved through GO layer thickness optimization.

Photocatalytic Degradation of Phenol Using Chemical Vapor Desposition Graphene Column

In the field of wastewater treatment, the advanced oxidation process (AOP) is a widely employed method. It uses reactive oxygen species (ROS) to degrade harmful organic and inorganic chemicals. Metal catalysts are the conventional standard when using these methods. However, they have drawbacks such as harsh activation conditions and poor recyclability. We previously suggested chemical vapor deposition (CVD) graphene film as an alternative metal-free catalyst. In this study, we enhanced the catalytic activity of the CVD graphene film by synergistically adding UV light irradiation. The result was complete degradation of phenol on a wafer-scale in a reduced timeframe. To further enhance the degradation process, we devised a graphene-based column for continuous in situ chemical oxidation and analyzed the intermediates over time, proving the potential of graphene-assisted AOP in industrial wastewater applications.

A Flexible Electrochemical Sensor Based on L-Arginine Modified Chemical Vapor Deposition Graphene Platform Electrode for Selective Determination of Xanthine

Abstract A flexible graphene platform electrode (GPE) was prepared by transferring chemical vapor deposition graphene film from Cu foil to polyethylene terephthalate substrate with the help of polymethyl-methacrylate. L-Arginine (L-Arg) was electrodeposited on GPE to form a poly(L-Arg)/GPE (P(L-Arg)/GPE) which was characterized by scanning electron microscopy, energy dispersive spectroscopy and Raman spectroscopy. The electrocatalytic activity and enhanced conductivity of P(L-Arg)/GPE sensor was evaluated by determining xanthine (XA) in the presence of uric acid (UA) and hypoxanthine (HX) in phosphate buffer solution. The electrochemical behaviors of XA on P(L-Arg)/GPE were studied by cyclic voltammetry and differential pulse voltammetry in comparison with those on bare GPE. The proposed sensor not only achieved the selective determination of XA, but also separated the voltammetric signals of UA and HX with potential differences of 420 and 384 mV, respectively. Under the optimized conditions, the proposed sensor displayed superb sensing property towards XA in a wide linear range of 0.5-140 μmol/L with corresponding detection limit of 0.083 μmol/L (S/N = 3). With good stability, reproducibility, high sensitivity, low cost as well as high resistance to interferences, the P(L-Arg)/GPE had been applied to determine XA in human serum successfully.

Thickness effect of graphene film on optimizing the interface and mechanical properties of Cu/Ni multilayer composites

In the present work, laminated Cu/Ni samples reinforced by graphene film with various thicknesses were produced via electrophoretic depositing graphene oxide (GO) on Cu foil by controlling deposition voltage, and the effect of thickness of graphene film on strengthening Cu/Ni multilayer composites were investigated in detail. Microstructural examination revealed that the fragments of graphene film were dispersed at the interface between Cu and Ni layer after hot rolling, with a range of thickness from 0.76 to 5.13 μm. The graphene film showed an excellent strengthening effect in the composites regardless of their thickness according to the tensile testing. However, the toughing effect achieved optimal as the thickness of 4.12 μm. The role of deposited graphene film played in determining the load transfer and optimizing the interface was discussed. Graphene film with appropriate thickness can effectively inhibit the severe asymmetric diffusion behavior of Cu and Ni elements, which plays an important role in strengthening and toughening clad interfaces by inhibiting the formation of Kirkendall voids. This study provides novel insights into understanding the strengthening and toughing behaviors of graphene reinforced multilayer composites, which can be developed into a technical strategy for fabricating high performance laminated metal matrix composites.

Chemical vapour deposited graphene: substrate pre-treatment, growth and demonstration as a simple graphene-based SERS substrate

In chemical vapour deposition (CVD) of graphene, surface roughness and purity of the copper substrate are very crucial for obtaining uniform films. Even though electrochemical polishing is an effective technique for obtaining homogeneous graphene films, most of the experiments adopt complex experimental parameters like electrolyte heating, stirring and use of additives for better results. These are not applicable to thin copper foils used in CVD of graphene. In the present study, a simple electrochemical procedure is developed for deposition of high-quality graphene films with good coverage. The depositions of graphene films on bare and polished copper foils for the same growth conditions are analysed using various microscopic techniques. The uniformly grown graphene on copper is then directly employed as a surface-enhanced Raman scattering (SERS) substrate along with plasmonic silver nanoparticles. A simple SERS substrate having a reasonable detection limit of $$10^{-10}$$ M for R6G is achieved with uniform SERS signals over a large area. The homogeneity of SERS substrate can be attributed to the uniformity of the deposited graphene film. A simple and efficient SERS substrate using conventional methods is achieved through the incorporation of chemical vapour deposited graphene. The study covers the growth of CVD graphene film starting from substrate pre-treatment, various analyses of the film and finally the application in SERS.

Through-substrate terahertz time-domain reflection spectroscopy for environmental graphene conductivity mapping

We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapor deposited graphene films through silicon support. We validate the technique against measurements performed using the established transmission based THz-TDS. Our through-substrate approach allows unhindered access to the graphene top surface and thus, as we discuss, opens up pathways to perform in situ and in-operando THz-TDS using environmental cells.

Development and Characterization of Freestanding Poly (Methyl Methacrylate)/Monolayer Graphene Membrane

Graphene-polymer based materials are gaining more popularity among researchers due to its mechanical properties that are found to be suitable to be used in various micro/nanoscale application requiring highly sensitive sensors. This research ventured into the fabrication and characterization process of a freestanding poly (methyl methacrylate) (PMMA) on monolayer graphene (Gr) yielding a (PMMA/Gr) membrane. In the process of transferring the chemical vapor deposition (CVD) graphene film over a cavity that was developed on a silicon substrate, the wet transfer method was used. Five repetitions of the nanoindentation testing had been carried out on the flexible membrane which resulted in a reproducible deflection, when exerted with a maximum loading of 10 mN. The indented (PMMA/Gr) membrane showed an identical elastic behavior with Young's modulus of 0.18 GPa. The highest deflection of approximately 22 μm at 1.6 mN maximum loads and the tensile stress of 0.58 MPa was obtained from the indentation testing analysis. The combination of PMMA-Graphene materials as a membrane has shown impressive changes to its mechanical properties. Besides maintaining its viscoelastic-plastic behavior which contributed to its flexibility, the presence of a graphene layer provided strong support to prevent damages to the membrane. Meanwhile, PMMA properties with low elastic modulus have contributed to the increased of the mechanical sensitivity of the membrane. Based on this research, the mechanical sensitivity of (PMMA/Gr) is reported to be 0.15 nm/Pa, which is much higher compared to a typical conventional membrane. It was proven that the hybrid (PMMA/Gr) membrane was extremely sensitive to the subjected pressures, thus, shown its potential to be applied as a micro-electro-mechanical systems (MEMS) capacitive pressure sensor.

No Tilt Angle Dependence of Grain Boundary on Mechanical Strength of Chemically Deposited Graphene Film

No Tilt Angle Dependence of Grain Boundary on Mechanical Strength of Chemically Deposited Graphene Film

Transfer-free CVD graphene for highly sensitive glucose sensors

Chemical vapor deposition (CVD) graphene film is a promising electrode-modifying material for fabricating high-performance glucose sensor due to its high electrical conductivity and two-dimensional structure over large area. However, the use of typical metal-based CVD graphene suffers from the residue contamination of polymer transfer-support and heavy metal ions. In this work, we directly grew few-layer graphene on the SiO2/Si substrate without transfer process and then fabricated graphene-based glucose sensors by sequentially immobilizing glucose oxidase and depositing Nafion layer on its surface that was functionalized by oxygen-plasma treatment. Our transfer- and metal-free process shows distinct advantage over the common metal-CVD method in improving the electrochemical performance by eliminating the contamination of transfer-residue. Thus-obtained glucose sensor shows a high sensitivity (16.16 μA mM−1 cm-2) with a detection limit of 124.19 μM. This method is simple and promising for the development of highly sensitive glucose sensors.

Ultraviolet light induced electrical hysteresis effect in graphene-GaN heterojunction

Fabrication of a two- and three-dimensional (2D/3D) heterojunction device has attracted significant attention for developing high performance photodiodes, light emitting diodes, solar cells, and other electronic devices. Here, we reveal the effect of ultraviolet (UV) illumination on electrical hysteresis in a graphene/gallium nitride (GaN) vertical heterojunction Schottky device. A chemical vapor deposited graphene film was transferred onto a free-standing n-type GaN substrate for Schottky diode fabrication, where the interfacial states play a significant role in the occurrence of electrical hysteresis in diode characteristics. A fabricated graphene/GaN Schottky device free from electrical hysteresis under no illumination condition showed the appearance of hysteresis with the illumination of UV light. The residual impurities of graphene and the surface defects of the GaN act as trap sites for the photocarriers; as a result, interface dependent photoresponsivity was observed. Capacitance-voltage analysis also showed the effect of residual impurities on the space charge dependent capacitance and the occurrence of hysteresis due to interface traps of the graphene/GaN heterojunction. Our findings can be significant in understanding the highly sensitive graphene/GaN and other 2D/3D heterojunction interfaces by the UV illumination process for developing high performance devices.

Clean transfer of chemical vapor deposition graphene film

Graphene is believed to have promising applications in many fields because of its unique properties. At present, graphene films are mainly prepared on Cu substrates by chemical vapor deposition. The graphene films prepared in this way need to be transferred to the target substrates for further applications, while the transfer process inevitably induces contamination on graphene, which affects the properties of graphene and the performance of devices. Therefore, how to reduce or avoid contamination and realize the clean transfer of graphene is an important topic for the development of graphene transfer technology, which is the major topic of this review. Here, firstly, the transfer techniques of graphene are briefly reviewed, which can be classified according to different rules. For example, it can be classified as direct transfer, with which graphene is directly stuck to the target substrate, and indirect transfer, with which graphene is indirectly transferred to the target substrate with a carrier film. According to the way of separating graphene and the growth substrate, it can also be classified as dissolving transfer, with which the substrate is dissolved by chemical etchant, and delaminating transfer, with which graphene is delaminated from the substrate. Then the origins of contamination are discussed followed with how contamination affects graphene properties. The main contaminations induced by transfer are ions from the etchant and electrolyte, undissolved metal or metal oxide particles, and organic residues from carrier films. Contaminations have a great influence on the electrical, thermal and optical properties of graphene. Then the up-to-date progress of techniques for clean transfer is reviewed, including modifying the cleaning process or using alternative etchant/electrolyte to remove or suppress metal contamination and annealing graphene or using alternative carrier films (e.g., more dissoluble materials) to remove or suppress organic residues. Finally, the challenges of clean transfer of graphene are summarized, and future research directions and opportunities are prospected. This review not only contributes to the research of graphene film transfer technology, but also has great reference value for the clean fabrication of the whole two-dimensional materials and devices.

A novel free-standing CVD graphene platform electrode modified with AuPt hybrid nanoparticles and l-cysteine for the selective determination of epinephrine

A novel free-standing graphene platform electrode (GPE) was prepared directly by transferring a chemical vapor deposition (CVD) graphene film from Cu foils to polyethylene terephthalate substrates with the aid of polymethyl-methacrylate. AuPt hybrid nanoparticles (AuPtNPs) and l-cysteine (l-Cys) were electrodeposited simultaneously on the GPE. The successful formation of AuPtNPs-Cys/GPE was confirmed by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Raman microscope and X-ray diffraction (XRD). The electrocatalytic activity and enhanced conductivity of AuPtNPs-Cys/GPE sensor was evaluated by determining epinephrine (EP) in the presence of ascorbic acid (AA), dopamine (DA), uric acid (UA) in phosphate buffer solution by various techniques, including cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry. Further, the proposed sensor not only achieved the selective determination of EP, but also separated the voltammetric signals of AA, DA, EP and UA with potential differences of 266, 250 and 183 mV, respectively. The amperometric current response was increased linearly with increasing EP concentration in the range of 0.2 to 1000 μM with a detection limit of 0.0157 μM (S/N = 3). In addition, the as-obtained sensor delivered extraordinary stability, reproducibility, as well as high resistance to interferences, and was successfully utilized in determining real samples.

Implementation of graphene as hole transport electrode in flexible CIGS solar cells fabricated on Cu foil

Graphene has great potential to be used as electrode in many opto-electronic devices, owing to its superior optical and electrical properties. Graphene films have been employed as window electrode in various thin film solar cells. However, to date graphene film has not been used as hole transport electrode, particularly in CIGS solar cell. In this work, we have demonstrated a novel structure for graphene-based flexible CIGS solar cell, in which graphene film on flexible Cu foil was implemented as hole transport electrode. CIGS solar cells were directly fabricated on the chemical vapor deposited graphene film on Cu foil, without any transfer process. Several techniques, including Raman spectroscopy, X-ray diffraction, scanning electron microscopy, external quantum efficiency and J-V characteristics under illumination, have been used to investigate the device performance. The graphene-based device displayed power conversion efficiency of 9.91 ± 0.89% with a fill factor of 64.75 ± 7.34%, which are substantially higher compared to reference cell fabricated using conventional Mo/stainless steel electrode. High open circuit voltage together with substantially large fill factor is primarily responsible for high cell efficiency of graphene/Cu foil based device. This study provides a plausible implication of graphene as hole transport electrode in flexible CIGS photovoltaic devices.

Contactless graphene conductivity mapping on a wide range of substrates with terahertz time-domain reflection spectroscopy

We demonstrate how terahertz time-domain spectroscopy (THz-TDS) operating in reflection geometry can be used for quantitative conductivity mapping of large area chemical vapour deposited graphene films on sapphire, silicon dioxide/silicon and germanium. We validate the technique against measurements performed with previously established conventional transmission based THz-TDS and are able to resolve conductivity changes in response to induced back-gate voltages. Compared to the transmission geometry, measurement in reflection mode requires careful alignment and complex analysis, but circumvents the need of a terahertz transparent substrate, potentially enabling fast, contactless, in-line characterisation of graphene films on non-insulating substrates such as germanium.