Uniform Graphene Research Articles

Detection of terahertz radiation using topological graphene micro- nanoribbon structures with transverse plasmonic resonant cavities

The lateral interdigital array of the graphene microribbons (GMRs) on the h-BN substrate connected by narrow graphene nanoribbon (GNR) bridges serves as an efficient detector of terahertz (THz) radiation. The detection is enabled by the nonlinear GNR elements providing the rectification of the THz signals. The excitation of plasmonic waves along the GMRs (transverse plasmonic oscillations) by impinging THz radiation can lead to a strong resonant amplification of the rectified signal current and substantial enhancement of the detector response. The GMR arrays with the GNR bridges can be formed by the perforation of uniform graphene layers.

Improved Conductivity of Low‐Temperature‐Synthesized Graphene/Cu for CMOS Backend‐of‐Line Interconnect Applications

AbstractThis study proposes a synthesis strategy of high‐quality graphene films on the copper foil at a temperature of 400 °C throughout the graphene growth process without employing high‐temperature annealing. Through continuous CO2 laser pretreatment of the copper foil, the surface smoothness improves, and the removal of copper particles and copper oxide results in fewer defects on the foil. Therefore, the nucleation density of graphene is reduced, leading to a more uniform and continuous graphene film and showing an outstanding quality of graphene with low defects and low resistivity compared with other groups. After laser treatment, the copper foil's resistivity decreases from 1.71 ×10−8 to 1.51 ×10−8 Ω·m. The graphene‐coated on laser‐treated foil experiences an even more substantial decrease in resistivity, from 1.34 ×10−8 to 1.18 ×10−8 Ω·m, marking a significant 11.94% reduction. Excitingly, the groundbreaking technique is taken to the next level by applying it to fine copper interconnects as narrow as 0.4 µm. The experiments confirm the successful cultivation of graphene on these miniature scales, showing the immense potential of the approach. The proposed approach aligns with the demands of contemporary CMOS backend‐of‐line processes, facilitating the seamless incorporation of graphene in advanced chip technologies.

Modulating growth of graphene on sapphire by chemical vapor deposition

The direct growth of graphene on insulating substrates presents significant promise for the advancement of next-generation semiconductor technologies. Here, the synthesis of graphene directly on sapphire substrates via chemical vapor deposition (CVD) is reported. The CVD growth parameters are systematically manipulated to optimize the crystal quality of graphene. Furthermore, the dependency of graphene growth on the crystallographic orientation of the sapphire substrate is explored to elucidate the underlying mechanisms. It is found that robust C-O chemical bonds are established between the oxygen atoms on the sapphire surface and the carbon atoms in the graphene, predominantly influencing the nucleation process. The oxygen-rich nature of the c-plane sapphire surface contributes to a higher graphene nucleation density and the formation of smaller grains comparing to r-plane sapphire. Accordingly, high quality and uniform monolayer graphene is successfully obtained on both c-plane and r-plane sapphire.

Site-Selective Synthesis of Bilayer Graphene on Cu Substrates Using Titanium as a Carbon Diffusion Barrier.

Chemical vapor deposition (CVD) is a widely used method for graphene synthesis, but it struggles to produce large-area uniform bilayer graphene (BLG). This study introduces a novel approach to meet the demands of large-scale integrated circuit applications, challenging the conventional reliance on uniform BLG over extensive areas. We developed a unique method involving the direct growth of bilayer graphene arrays (BLGA) on Cu foil substrates using patterned titanium (Ti) as a diffusion barrier. The use of the Ti layer can effectively control carbon atom diffusion through the Cu foil without altering the growth conditions or compromising the graphene quality, thereby showcasing its versatility. The approach allows for targeted BLG growth and achieved a yield of 100% for a 10 × 10 BLG units array. Then a 10 × 10 BLG memristor array was fabricated, and a yield of 96% was achieved. The performances of these devices show good uniformity, evidenced by the set voltages concentrated around 4 V, and a high resistance state (HRS) to low resistance state (LRS) ratio predominantly around 107, reflecting the spatial uniformity of the prepared BLGA. This study provides insight into the BLG growth mechanism and opens new possibilities for BLG-based electronics.

Surface modification of mild steel to circumvent challenges in chemical vapour deposition of graphene coating for durable corrosion resistance

Graphene possesses unique combination of characteristics (i.e., inertness, impermeability and toughness) to qualify as ideal coating material for corrosion resistance, and graphene coatings on nickel and copper have been shown to provide excellent and durable corrosion resistances. However, growing graphene directly on mild steel by chemical vapour deposition (CVD), is prohibitively challenging due to high solubility of carbon in mild steel at high temperatures. The non-trivial challenge was circumvented through surface modification of steel by electroplating with Cu and Ni, accounting for the critical consideration, i.e., the inter-diffusivity of iron in nickel or copper. However, the key finding was that the undesirably high thicknesses of the electroplated Cu and Ni layers were detrimental, and optimization of their thicknesses was essential for successful deposition of the required quality graphene. The optimised thicknesses were derived on the basis of the fundamental diffusion calculations. The uniform multi-layered graphene coating on the suitably modified mild steel surface provided remarkable corrosion resistance in an aqueous chloride solution, and electrochemically validation of the corrosion durability for extended exposure (>1000 h) was characterised.

Tuning cross-plane thermal conductivity of multilayer graphene/h-BN vdW heterostructures via composition distribution

Nanomaterials with low thermal conductivity (TC) are ideal candidates as thermoelectric materials. In this direction, we design innovative multilayer graphene/h-BN (GBN) van der Waals (vdW) heterostructures with gradient composition distribution (C, B and N atoms), inspired by the newly synthesized boron carbonitride nanosheets. Three types of 26-layer GBN models are constructed and investigated, i.e. U-shape, X-shape, A-shape, representing uniform, symmetrical, and asymmetrical distributions of carbon atoms along the cross-plane direction, respectively. Based on non-equilibrium molecular dynamics (NEMD) simulation, we confirm that X-shape GBN model possess the lowest cross-plane TC, approximately 7 times smaller than that of the uniform U-shape graphene. The cross-plane TC can be further reduced by applying tensile strains or decreasing interlayer coupling strength. These findings elucidate the significant role the composition distribution plays in the thermal transport of GBN vdW heterostructures. However, the mechanical properties (Young's nodulus and tensile strength) of the new vdW heterostructures are insensitive to the composition distribution. Our work provides a new perspective for manipulating the interfacial thermal transport of multilayer GBN vdW heterostructures by means of material design and offers a useful guide for rationally designing thermoelectric materials with tailored thermal properties based on vdW heterostructures.

Highly Efficient Growth of Large‐Sized Uniform Graphene Glass in Air by Scanning Electromagnetic Induction Quenching Method

AbstractThe scalable, efficient, and cost‐economic preparation method of graphene is the key to promoting the real applications of graphene. In recent years researchers have made intensive efforts to enhance the synthesis efficiency and reduce the production costs of the manufacturing processes, especially for the chemical vapor deposition methods. However, the efficiency and uniformity are difficult to further improve due to its complicated synthesis conditions. A high‐efficiency synthesis method to provide a large uniform production area suitable for graphene growth remains a great challenge until now. In this work, a facile and scalable ultrafast quenching method for growing graphene in air is developed by using scanning electromagnetic induction (SEMI) equipment. This method is successfully applied to grow a 400 mm × 400 mm graphene glass within 2 min in the air with a lab‐grade instrument. Thus‐produced multiple‐layered graphene glass is of a high uniformity, film adhesion, and full coverage, showing a surface resistance (Rs) below 500 Ω sq−1. Outstanding electrothermal capabilities up to 1000 °C are demonstrated for their promising potential for transparent heating devices. The SEMI method, including the product size and growth rate, can be easily up‐scaled, which is believed to provide an effective route to grow graphene aiming at its real applications.

Flexible field-effect transistors with high-quality and uniform single-layer graphene for high mobility

In this work, a fully flexible graphene field-effect transistor with high carrier mobility is reported. Patterned high-quality and uniform single-layer graphene films are successfully realized by combining the selective growth on a patterned copper foil and the direct transfer method to minimize degradation factors. The selectively grown single-layer graphene is directly transferred to the target substrate through the deposition of poly-para-xylylene (Parylene) C. The quality of the graphene films is confirmed by Raman spectroscopy. The analysis reveals that the use of Parylene C as the substrate, gate dielectric, and encapsulation layer has the advantage of reducing the scattering by the optical phonons and charge puddles. The estimated residual carrier density is 1.72 × 1011 cm−2, and the intrinsic hole and electron carrier mobilities are found to be as high as 10 260 and 10 010 cm2 V−1 s−1, respectively. This study can pave the way for the development and mass production of high-performance and fully flexible graphene electronics.

Ultrathin damage-tolerant flexible metal interconnects reinforced by in-situ graphene synthesis

Conductive patterned metal films bonded to compliant elastomeric substrates form meshes which enable flexible electronic interconnects for various applications. However, while bottom-up deposition of thin films by sputtering or growth is well-developed for rigid electronics, maintaining good electrical conductivity in sub-micron thin metal films upon large deformations or cyclic loading remains a significant challenge. Here, we propose a strategy to improve the electromechanical performance of nanometer-thin palladium films by in-situ synthesis of a conformal graphene coating using chemical vapor deposition (CVD). The uniform graphene coverage improves the thin film’s damage tolerance, electro-mechanical fatigue, and fracture toughness owing to the high stiffness of graphene and the conformal CVD-grown graphene-metal interface. Graphene-coated Pd thin film interconnects exhibit stable increase in electrical resistance even when strained beyond 60% and longer fatigue life up to a strain range of 20%. The effect of graphene is more significant for thinner films of < 300 nm, particularly at high strains. The experimental observations are well described by the thin film electro-fragmentation model and the Coffin-Manson relationship. These findings demonstrate the potential of CVD-grown graphene nanocomposite materials in improving the damage tolerance and electromechanical robustness of flexible electronics. The proposed approach offers opportunities for the development of reliable and high-performance ultra-conformable flexible electronic devices.

Magnetoresistance properties in nickel-catalyzed, air-stable, uniform, and transfer-free graphene

A transfer-free graphene with high magnetoresistance (MR) and air stability has been synthesized using nickel-catalyzed atmospheric pressure chemical vapor deposition. The Raman spectrum and Raman mapping reveal the monolayer structure of the transfer-free graphene, which has low defect density, high uniformity, and high coverage (>90%). The temperature-dependent (from 5 to 300 K) current–voltage (I–V) and resistance measurements are performed, showing the semiconductor properties of the transfer-free graphene. Moreover, the MR of the transfer-free graphene has been measured over a wide temperature range (5–300 K) under a magnetic field of 0 to 1 T. As a result of the Lorentz force dominating above 30 K, the transfer-free graphene exhibits positive MR values, reaching ∼8.7% at 300 K under a magnetic field (1 Tesla). On the other hand, MR values are negative below 30 K due to the predominance of the weak localization effect. Furthermore, the temperature-dependent MR values of transfer-free graphene are almost identical with and without a vacuum annealing process, indicating that there are low density of defects and impurities after graphene fabrication processes so as to apply in air-stable sensor applications. This study opens avenues to develop 2D nanomaterial-based sensors for commercial applications in future devices.

Hydrophobic Surface Array Structure Based on Laser-Induced Graphene for Deicing and Anti-Icing Applications.

The exceptional performance of graphene has driven the advancement of its preparation techniques and applications. Laser-induced graphene (LIG), as a novel graphene preparation technique, has been applied in various fields. Graphene periodic structures created by the LIG technique exhibit superhydrophobic characteristics and can be used for deicing and anti-icing applications, which are significantly influenced by the laser parameters. The laser surface treatment process was simulated by a finite element software analysis (COMSOL Multiphysics) to optimize the scanning parameter range, and the linear array surface structure was subsequently fabricated by the LIG technique. The generation of graphene was confirmed by Raman spectroscopy and energy-dispersive X-ray spectroscopy. The periodic linear array structure was observed by scanning electron microscopy (SEM) and confocal laser imaging (CLSM). In addition, CLSM testings, contact angle measurements, and delayed icing experiments were systematically performed to investigate the effect of scanning speed on surface hydrophobicity. The results show that high-quality and uniform graphene can be achieved using the laser scanning speed of 125 mm/s. The periodic linear array structures can obviously increase the contact angle and suppress delayed icing. Furthermore, these structures have the enhanced ability of the electric heating deicing, which can reach 100 °C and 240 °C within 15 s and within 60 s under the DC voltage power supply ranging from 3 to 7 V, respectively. These results indicate that the LIG technique can be developed to provide an efficient, economical, and convenient approach for preparing graphene and that the hydrophobic surface array structure based on LIG has considerable potential for deicing and anti-icing applications.

Electrochemical exfoliation of graphene without drying for direct preparation of Ag/graphene coating

The high production cost and agglomeration of graphene are the primary challenges limiting the large-scale practical application of graphene-enhanced nanocomposites. In this study, graphite rods were electrochemically exfoliated in the nitric acid solution, and the undried exfoliated graphene was directly dispensed into the deposition solution. The esterification reaction of hydroxyl and carboxyl groups was blunted due to the spatial site-barrier effect of water molecules present in graphene. Irreversible agglomeration due to drying in the usual graphene preparation process was avoided, resulting in a composite electroplating solution with uniform graphene dispersion. On this basis, Ag/graphene composite coatings were electrochemically deposited. The graphene in the composite coating was uniformly distributed, and the surface was smooth and free of agglomeration. At the same time, the incorporation of graphene changed the coating grain orientation shift from (220) crystal plane to low-energy (111), (200) crystal plane orientation. The surface energy of the composite coating was dramatically reduced, the hardness was increased, and the wear resistance was significantly improved. This study provides a low-cost and high-quality solution for preparing graphene composites.

Ultrasensitive Biochemical Sensing Platform Enabled by Directly Grown Graphene on Insulator.

To fabricate label-free and rapid-resulting semiconducting biosensor devices incorporating graphene, it is pertinent to directly grow uniform graphene films on technologically important dielectric and semiconducting substrates. However, it has long been intuitively believed that the nonideal disordered structures formed during direct growth, and the resulted inferior electrical properties will inevitably lead to deteriorated sensing performance. Here, graphene biosensor chips are constructed based on direct plasma-enhanced chemical vapor deposition (PECVD) grown graphene on a 4-inch silicon wafer with excellent film uniformity and high yield. To surprise, optimal operations of graphene biosensors permit ultrasensitive detection of SARS-CoV-2 virus nucleocapsid protein with dilutions down to sub-femtomolar concentrations. Such impressive limit of detection (LOD) is comparable to or even outperforms that of the state-of-the-art biosensor devices based on high-quality graphene. Further noise spectral characterizations and analysis confirms that the LOD is limited by molecular diffusion and/or known interference signals such as drift and instability of the sensors, rather than the electrical merits of the graphene devices along. Hence, result sheds light on processing directly grown PECVD graphene into high-performance sensor devices with important economic benefits and social significance.

Silicon Radical-Induced CH4 Dissociation for Uniform Graphene Coating on Silica Surface.

Due to the manufacturability of highly well-defined structures and wide-range versatility in its microstructure, SiO2 is an attractive template for synthesizing graphene frameworks with the desired pore structure. However, its intrinsic inertness constrains the graphene formation via methane chemical vapor deposition. This work overcomes this challenge by successfully achieving uniform graphene coating on a trimethylsilyl-modified SiO2 (denote TMS-MPS). Remarkably, the onset temperature for graphene growth dropped to 720°C for the TMS-MPS, as compared to the 885°C of the pristine SiO2. This is found to be mainly from the Si radicals formed from the decomposition of the surface TMS groups. Both experimental and computational results suggest a strong catalytic effect of the Si radicals on the CH4 dissociation. The surface engineering of SiO2 templates facilitates the synthesis of high-quality graphene sheets. As a result, the graphene-coated SiO2 composite exhibits a high electrical conductivity of 0.25Scm-1. Moreover, the removal of the TMP-MPS template has released a graphene framework that replicates the parental TMS-MPS template on both micro- and nano- scales. This study provides tremendous insights into graphene growth chemistries as well as establishes a promising methodology for synthesizing graphene-based materials with pre-designed microstructures and porosity.

Electro-mechanical coupling model and interlaminar stress analysis of laminated plates containing GSR actuator

Due to its remarkable physical features, graphene nanosheets (GPN) are one of the most appealing reinforcing materials for composites. For polyvinylidene fluoride (PVDF), GPN reinforced composites can dramatically increase its piezoelectric and mechanical characteristics. If the interlaminar shear deformation of laminated plates containing uniform graphene sheets reinforced (GSR) smart piezoelectric layer, which material properties vary widely from layer to layer and subjected to electromechanical loading cannot be accurately predicted, the interlaminar stresses may be very high, eventually leading to interlaminar failure. In light of this, an effective mechanoelectrical coupling model for the accurate prediction of interlaminar stress for composite plates contains GSR actuators is developed in present study. Meanwhile, the finite element formulation (FEF) can be substantially simplified due to the expression of transverse shear stress components becoming more succinct. Therefore, by using the suggested electro-mechanical coupling theory, a three-node FEF is easily constructed. The refinement of transverse shear stress prediction in the context of electromechanical coupling can be accomplished through the application of the Reissner mixed variation theory (RMVT). The performance of the recommended plate model will be evaluated using the results derived from three-dimensional (3D) elastic theory and the selected model. By employing the RMVT method, we improve predictions of transverse shear stresses while considering the electromechanical coupling effect. The results from our model are compared with alternative models and 3D elasticity theory, demonstrating its superiority in satisfying the continuity requirements of transverse shear stresses and exhibiting excellent agreement with exact solutions. This validates the accuracy and applicability of our proposed model. Further to that, the prediction of mechanical characteristics for laminated plates with GSR actuators were systematically studied from the thoroughly perspectives of electromechanical load, piezoelectric layer thickness, graphene volume fraction, and some other parameters.

Molecular-scale grinding of uniform small-size graphene flakes for use as lubricating oil additives

Molecular-scale grinding of uniform small-size graphene flakes for use as lubricating oil additives

Fabrication of Hydroxyl‐Group‐Rich Reduced Graphene Oxide Film and its Application for Electrochemical Detection of Hydrogen Peroxide

AbstractGraphene oxide (GO) can be obtained economically from graphite, and it has, therefore, been used for energy storage, conversion, and biosensor fabrication. To overcome the limitations associated with the poor electrical conductivity of GO, mild thermal reduction is widely used. However, owing to considerable variations in GO in terms of size and shape, uniform reduction of GO films is highly challenging. Herein, it reports a mildly reduced uniform graphene oxide thin film (mrUG) that is enriched with functional hydroxyl groups. This film is effective for electrochemical H2O2 decomposition and detection. A uniform graphene oxide thin film (UGTF) is first fabricated on an indium tin oxide (ITO) substrate and subjected to mild thermal annealing at 300 °C. Remarkably, the variations in all important parameters, including film thickness, surface roughness, reduction level, are significantly low in the case of mrUG. Moreover, It is found that unlike GO, UGTF undergoes structural rearrangement easily and possesses many hydroxyl groups (─OH) when reduced for a specific duration (t = 10 s, mrUG(10)). mrUG(10) is highly stable and effectively decomposed H2O2, which is advantageous for the electrochemical detection of H2O2 with extremely low signal variations. Therefore, mrUG(10) can be used as a carbon‐based metal‐free electrocatalyst in biosensors, energy, and electronic applications.

Molecular-scale grinding of uniform small-size graphene flakes for use as lubricating oil additives

A variety of industrial preparation methods to obtain graphene from graphite have been developed, the most prominent of which are the chemical reduction of graphene oxide and intercalation-exfoliation methods. However, the low-cost, thin-layer, large-scale production of graphene with a radial dimension smaller than 1 μm (SG) remains a great challenge, which has limited the industrial development and application of small-scale graphene in areas such as textile fibers, engine oil additives, and graphene-polymer composites. We have developed a novel way to solve this problem by improved ball milling methods which form molecular-scale grinding aids between the graphite layers. This method can produce uniform, small-size (less than 1 μm) and thin-layer graphene nanosheets at a low cost, while ensuring minimal damage to the internal graphene structure. We also show that using this SG as an additive in lubricating oil not only solves the current dispersion stability of graphene, but also reduces the friction coefficient by more than 27% and wear by more than 38.8%. The SG preparation method reported is simple, low-cost, and has a significant effect in lubricating applications, which is of great commercial value.

Laser-induced reduction and pattern regulation of graphene oxide film with high biosafety for wearable micro-supercapacitors

A two-step laser process consisting of surface treatment and pattern scribing was developed to prepare micro-supercapacitors (MSCs) with high electrochemical performance and structural robustness. First, an ultrathin and uniform graphene oxide (GO) film was deposited onto a copper foil by electrophoretic deposition, after which a laser beam with a wavelength of 450 nm was used to remove the oxygen-containing functional groups and introduce porous structures into the GO film. Subsequently, another laser beam with a wavelength of 1064 nm was used to scribe the film to form finger-patterned electrodes. After being assembled into flexible MSCs, the volume specific capacity of the MSCs reached 1.94 F cm−3, and the power and energy densities reached 4 mW cm−3 and 0.172 mWh cm−3, respectively. After 7000 charge-discharge cycles, the device showed excellent cycling stability with a capacitance retention rate of ∼87.5%. Moreover, the MSCs could be bent into different forms with marginal capacitance loss, confirming their high structural tolerance. Remarkably, the laser-irradiated GO (L-GO) film showed high biosafety toward human empirical cells in the biotoxicity tests, indicating that the devices could be adopted as reliable micro-devices with high biosafety for fabricating wearable electronics on human skin.

Low T direct plasma assisted growth of graphene on sapphire and its integration in graphene/MoS2 heterostructure-based photodetectors

We report on outstanding photo-responsivity, R > 103 A/W, fast response (~0.1 s), and broadband sensitivity ranging from the UV to the NIR in two terminal graphene/MoS2 photodetectors. Our devices are based on the deterministic transfer of MoS2 on top of directly grown graphene on sapphire, and their performance outperforms previous similar photodetectors using large-scale grown graphene. Here we devise a protocol for the direct growth of transparent (transmittance, Tr > 90%), highly conductive (sheet resistance, R□ < 1 kΩ) uniform and continuous graphene films on sapphire at 700 °C by using plasma-assisted chemical vapor deposition (CVD) with C2H2/H2 gas mixtures. Our study demonstrates the successful use of plasma-assisted low-temperature CVD techniques to directly grow graphene on insulators for optoelectronic applications.