Graphite Films Research Articles

Laser‐Patterned Graphite‐Based Strain and Temperature Sensor on Disposable Paper Cup

Flexible sensors have versatile applications in a home environment to create better ambient intelligence, which still have high fabrication costs and disposable value. As a proof‐of‐concept example to resolve these problems, the graphite‐based sensors on a disposable paper cup by laser patterning to measure the water level and temperature are proposed. The optimal process parameters of graphitic film, sensing mechanisms, and the sensor performance are investigated in the experiments. Moreover, the paper cup with graphitic sensors is simulated by the finite element method to analyze the experimental results. This fast and low‐cost manufacturing method may open up avenues for the development of disposable flexible electronics in smart home necessities.

CVD Synthesis of Graphitic Carbon Nitride Films from Melamine

A CVD technique has been developed for the deposition of homogeneous graphitic carbon nitride films on silicon and quartz glass substrates using melamine as a precursor. Layer-by-layer deposition at low precursor loadings makes it possible to deposit a film up to 1.4 µm thick; however, it is possible to achieve large thicknesses by multiple repetition of the experimental cycle. The effect of synthesis parameters on the surface morphology of deposited layers has been studied by scanning electron microscopy. The chemical composition and structure of graphitic carbon nitride films are confirmed by a set of spectroscopic methods and X-ray diffraction. The optical properties have been studied using diffuse reflectance spectroscopy. Scanning electron microscopy and X-ray diffraction analysis have shown that films deposited at temperatures of 550–650°C have a layered microcrystalline structure. The bandgap of the obtained samples was 2.76–2.93 eV.

CVD Synthesis of Graphitic Carbon Nitride Films from Melamine

CVD Synthesis of Graphitic Carbon Nitride Films from Melamine

Heat Dissipation Performance Research of Power Lithium Battery Based on High Thermal Conductivity Graphite Film

Heat will be generated inside the power lithium-ion battery during operation, if heat dissipation is not carried out in time, its temperature will rise continuously, causing thermal safety accidents once the temperature exceeds its normal work temperature range. In addition, the uniformity of the battery temperature will affect its performance, life, and even safety. Therefore, research on the heat dissipation performance of lithium battery can effectively improve its safety characteristics and working performance. To improve the temperature uniformity of single battery, different high thermal conductivity graphite films are used as the thermal conductivity enhanced scheme, the heat production and heat generation rate model of single battery was established, and its temperature simulation model was built by Ansys software to simulate heat dissipation performance. The results show that the high thermal conductivity graphite film can significantly enhance the battery heat dissipation performance, and its thickness, specific heat capacity and density have important effects on its performance.

Diamond-like carbon graphene nanoplatelet nanocomposites for lubricated environments

The tribological behaviour of diamond-like carbon (DLC) and graphene nanoplatelets (GNP) nanocomposite has not been previously explored in a lubricated environment, with some previous studies reporting only on graphene materials on the surface of the DLC. In this study DLC-GNP nanocomposite films with various GNP coverages were synthesised by a 3 step process: spin coating a GNP suspension, heat treatment, and DLC deposition. In this study, the effect of the GNP coverage on the mechanical properties, and tribological response of the DLC-GNP nanocomposite film were studied at elevated temperatures against a cast iron pin in a base-oil lubricated environment. The study shows decrease in friction and wear of the DLC-GNP nanocomposites as the GNP coverage increased, with the lowest friction (COF ∼0.03) and wear (∼1.6 × 10−19 m3/Nm−1) achieved with a 4.5% coverage. This study reports the addition of GNP into the DLC matrix reduced both friction and wear by creating a highly graphitic transfer film on the counter-body, but for higher GNP coverages agglomeration during the spin coating of GNP islands were recorded, leading to removal of the GNP during sliding wear negating the friction reduction effect of the GNP.

Star-shaped furoate-PCL: An effective compound for the development of graphite nanoplatelets-based films

The aim of this study was to improve the dispersibility of graphite nanoplatelets (GNP) in films based on poly(ε-caprolactone) (PCL). To this end, a star-shaped PCL with furoate-like end groups (PCL-Fur), potentially capable of interacting/reacting with the surface of the graphene layers through Diels-Alder reactions, was synthesized by enzymatic catalysis. PCL-Fur was applied for film development by blending it with a commercial high molecular weight PCL (PCL-L) and GNP. The reactivity of GNP with respect to furoate groups was demonstrated by studying the thermal behavior of the GNP/methyl 2-furoate system, while the dispersibility of graphite in the solution containing PCL-Fur was studied by UV–Vis measurements. GNP proved to be well dispersed and adhered to the polymer matrix in the PCL-L/PCL-Fur/GNP composite films prepared by casting, in contrast to the films based on the neat PCL-L. This fine GNP dispersion resulted in films characterized by high electrical conductivity.

Operando formation of multiphase heterostructure for achieving macroscale superlubricity with ultra-long lifetime under high contact stress

Pressure-induced reactions in situ at the sliding interface for carbon-based or disulfide-based films are well-known to yield structural evolution or chemical modifications for obtaining low friction. However, the underlying lubrication mechanisms between them remain poorly understood, and it poses indeterminacy in realizing the long-lasting heterointerface superlubricity. Here, we achieve the macroscale superlubricity (∼0.0055) with an ultra-long lifetime of at least 340,000 cycles and the ultra-mild wear (∼1.2 × 10−8 mm3/N·m) by sliding of diamond-like a-C:H (DLCH) against MoS2 under a high pressure of 1.28 GPa in nitrogen. Detailed studies reveal that a composite shear band based on tribo-induced graphitized nano-carbon films (GNCF) with disordered or local sp2 ordering structure and the layered MoS2 transfer film is formed on DLCH ball surface. Meanwhile, the slip interface of MoS2 disc encounters structural transformation to form a harder and smoother tribolayer parallel to sliding direction by stress-motivated tribochemical reactions. At micro-contact areas, in-situ formation of sliding heterostructure between the GNCF/MoS2 shear band and the reoriented MoS2 tribolayer is speculated to mainly provide the easy-shearing interface as well as incommensurate contact for the occurrence of microscale superlow friction. Macroscale superlubricity is then established as a result of the combination effect of numberless micro-asperities superlubricity. The findings provide fundamental insights into heterointerface friction and design pathway for long-term superlubricity.

Flat Bands for Electrons in Rhombohedral Graphene Multilayers with a Twin Boundary

AbstractTopologically protected flat surface bands make thin films of rhombohedral graphite an appealing platform for searching for strongly correlated states of 2D electrons. In this work, rhombohedral graphite is studied with a twin boundary stacking fault and the semimetallic and topological properties of low‐energy bands, localized at the surfaces and at the twinned interface, are analyzed. An effective 4‐band low energy model is derived, where the full set of Slonczewski–Weiss–McClure (SWMcC) parameters is implemented, and the conditions for the bands are found to be localized at the twin boundary, protected from the environment‐induced disorder. This protection together with a high density of states at the charge neutrality point, in some cases—due to a Lifshitz transition, makes this system a promising candidate for hosting strongly‐correlated effects.

Effect of Graphitization Degree of Mesocarbon Microbeads (MCMBs) on the Microstructure and Properties of MCMB-SiC Composites.

Mesocarbon microbead-silicon carbide (MCMB-SiC) composites were prepared by hot-press sintering (2100 °C/40 MPa/1 h) with two different graphitized MCMBs as the second phase, which exhibited good self-lubricating properties. The effects of the graphitization degree of the MCMBs on the microstructure and properties of the composites were investigated contrastively. The results showed that the composites that added raw MCMBs with a low degree of graphitization had excellent self-sintering properties, higher densities, and better mechanical properties; by comparison, the composites that added mature MCMBs with a high degree of graphitization, which has regular and orderly lamellar structures, not only had good mechanical properties but also exhibited a lower and more stable dry friction coefficient (0.35), despite the higher wear rate (2.66 × 10-6 mm3·N-1·m-1). Large amounts of mature MCMBs were peeled off during the friction process to form a uniform and flat graphite lubricating film, which was the main reason for reducing the dry friction coefficient of the self-lubricating composites and making the friction coefficient more stable.

Ultrahigh thermal conductive graphite film via the in-situ construction of aligned nanographene skeleton using chemical vapor deposition

Both high thermal conductivity (K) and large cross-sectional area are essential for thermal dissipation materials to maximize their heat transfer capability. However, the drastic decrease of K values with the increased thickness makes the existing graphite/graphene films less favored for practical applications. In this work, graphite film with both large thickness and high K value is produced based on an in-situ composition strategy between nanographene (G) and pyrocarbon (PyC) via chemical vapor deposition (CVD) using CH3OH/C2H5OH mixed precursors. It's found that an optimized O/C ratio of precursors facilitates the construction of ordered G skeletons within the deposited G/PyC composites. Such G/PyC composites can be completely graphitized at a lower temperature than the existing products. After 2400 °C annealing, dense, thick, and highly aligned graphite films were prepared. Their K values reach 1350 and 1010 W m–1 K–1 at the thickness of 40 and 120 μm, respectively, surpassing the existing records with similar thicknesses. More importantly, the proposed method is insensitive to the deposition substrates, and the G/PyC can be infiltrated into large-size fiber preforms as a matrix for preparing centimeter-thick high K materials. Besides, the G/PyC also exhibits better mechanical and electromagnetic shielding performances than the existing products, indicating a promising multifunctional application prospect.

Investigation on thermal conduction of graphite film enhanced carbon fiber polymer composite by laser flash analysis

Laser flash analysis (LFA) is an advantageous transient method, widely used for measuring thermal diffusivity of solid materials nowadays. In this paper, the thermal conductivity of graphite film enhanced carbon fiber composite was measured by LFA and the results show an unusual size-dependent effect which was considered to be due to violation of homogeneous assumptions. To investigate the size effect, numerical analyses based on the representative volume element (RVE) models were implemented to evaluate the thermal conductivities of composites with periodic microstructures. Transient periodic boundary conditions (PBCs) were proposed and applied to the RVEs for simulating the LFA. Transient simulative results obtained by applying PBCs verify the size effect and are in better agreement with the experimental data than those obtained by applying conventional adiabatic conditions. Moreover, the classical steady-state analyses on RVEs were performed for comparison. The reason for size effect was discussed in details. The present work expands the application scope of LFA to measuring thermal conductivity of complex composite and provides a perception of discreetly selecting specimen size and modifying the general LFA technique.

Flexible graphite films with high cross-plane thermal conductivity prepared by graphitization of polyimide catalyzed by Ni-coated-CNTs

Graphite films are widely used in microelectronic devices as heat-dissipation materials due to their high thermal conductivity, low thermal expansion coefficient and lightweight.

Recent progress of graphitic carbon nitride films and their application in photoelectrochemical water splitting

This review summarizes the progress in the synthesis of CN electrodes spanning from top-down and bottom-up categories, carrier dynamics modulation, and surface water oxidation reaction kinetics.

An SECM-Based Spot Analysis for Redoxmer-Electrode Kinetics: Identifying Redox Asymmetries on Model Graphitic Carbon Interfaces.

The fundamental process in non-aqueous redox flow battery (NRFB) operation revolves around electron transfer (ET) between a current collector electrode and redox-active organic molecules (redoxmers) in solution. Here, we present an approach utilizing scanning electrochemical microscopy (SECM) to evaluate interfacial ET kinetics between redoxmers and various electrode materials of interest at desired locations. This spot-analysis method relies on the measurement of heterogeneous electron transfer rate constants (kf or kb ) as a function of applied potential (E-E0 '). As demonstrated by COMSOL simulations, this method enables the quantification of Butler-Volmer kinetic parameters, the standard heterogeneous rate constant, k0 , and the transfer coefficient, α. Our method enabled the identification of inherent asymmetries in the ET kinetics arising during the reduction of ferrocene-based redoxmers, compared to their oxidation which displayed faster rate constants. Similar behavior was observed on a wide variety of carbon electrodes such as multi-layer graphene, highly ordered pyrolytic graphite, glassy carbon, and chemical vapor deposition-grown graphite films. However, aqueous systems and Pt do not exhibit such kinetic effects. Our analysis suggests that differential adsorption of the redoxmers is insufficient to account for our observations. Displaying a greater versatility than conventional electroanalytical methods, we demonstrate the operation of our spot analysis at concentrations up to 100 mM of redoxmer over graphite films. Looking forward, our method can be used to assess non-idealities in a variety of redoxmer/electrode/solvent systems with quantitative evaluation of kinetics for applications in redox-flow battery research.

Structural Modeling and Thermal Conductivity of Graphite Film Reinforced Aluminum Matrix Laminated Composites

Abstract: Excellent thermal conductivities of thermal management materials are expected to ensure the timely heat dissipation in lots of engineering applications and electronic devices. High in-plane thermal conductivity of laminated composites has become increasing significant for high energy and power density electronic devices. In this study, the continuous graphite film/aluminum (Gr film/Al) laminated composites were fabricated by vacuum hot pressing. In-plane and out-of-plane thermal conductivity of Gr film/Al laminated composites are tested. Two-dimensional structural models of Gr film/Al laminated composites are established, in which volume fraction, interfacial property, punching zone and orientation angle of Gr films can be controlled according to their actual composite microstructures. The effects of volume fraction and interfacial property on the thermal conductivity of Gr film/Al laminated composites are investigated. Two ways to reduce anisotropy of thermal conductivity are introduction of punching zones and control of Gr orientation, which are verified to be effective. On basis of the analysis above, a good understanding can be brought out for extensive thermal management applications of Gr/Al composites.

Probing the tribological behaviors of diamond-like carbon film in water-based drilling fluid environment by varying normal loads

This paper investigates the friction behavior and mechanism of diamond-like carbon (DLC) film and 26CrMo alloy steel under different loads in water-based drilling fluid environment. The results show that the coefficient friction and wear degree of DLC film in water-based drilling fluid environment are significantly lower than that of 26CrMo alloy steel under both low and high load. Raman, SEM and other test results suggest that the graphitization degree of worn DLC surface and the transfer layer on the surface of friction pair will increase with the increase of load. DLC film shows superior lubrication and wear resistance in water-based drilling fluid environment. Meanwhile, further investigation suggests that the friction and wear behavior of DLC film in water-based drilling fluid environment is also affected by the synergy of rolling effect, filling effect and polishing effect. Moreover, the barite particles wrapped in graphene dust will produce a low-friction synergy at the friction interface even if the DLC film is worn through. The relevant research results not only help to enrich the basic theory of lubrication and wear resistance technology of DLC film, but also help to promote the practical engineering application of DLC film in oil and gas environment. • DLC film exhibits lower COF and wear in water-based drilling fluid environment. • Graphitization of DLC film and transfer layer increase with the increase of load. • Friction behaviors are affected by rolling effect, filling effect and polishing effect.

Systematic Investigations on the Thermal Management Performance of Graphite Thin Films for High-Electron-Mobility Transistors

Self-heating is a severe problem for high-electron-mobility transistors (HEMTs). Graphene and thin graphite films are attractive candidates for heat spreader materials at the transistor level due to their ultrahigh in-plane thermal conductivity. However, a realistic and systematic simulation study of how they can improve the thermal management of HEMTs has not been carried out yet and is needed to push the method into practical use and realize industrialization. This study systematically investigated the effect of graphene and thin graphite films, and the most practical boundary condition in the simulations was primarily selected with comparisons. Then, the thermal properties consisting of thermal conductivity and interfacial thermal resistance (ITR) between graphite and other materials were fully investigated, which may bottleneck the actual improvement of the thermal management in applications. Our steady-state results indicated that the ITR between graphite and SiO2 determined the whole improvement in thermal management performance through the added graphite heat bridge. Subsequently, the transient thermal analysis was conducted on the HEMTs to explore the effect of graphene and thin graphite films under repeated joule heating pulses on a microsecond time scale, and we obtained the effect of graphene and thin graphite films on each heating and cooling process. Finally, based on all the results and analysis mentioned above, we can confirm that the graphite-based heat-spreader structures can still offer efficient heat dissipation under near-real conditions, thereby indicating ways of the optimization of HEMTs heat dissipation.

Macroscopic superlubricity enabled by the tribopair of nc-Ag/MoS2 and hydrogenated graphitic-like carbon films under high contact stress

Solid lubricants have superior environmental adaptability and can be widely used in space machinery under extreme harsh working conditions, including high contact pressure, high or cryogenic temperature, long working duration, etc. Loose-structured molybdenum disulfide (MoS2) film usually has poor load-bearing capacity, while low-hydrogenated graphitic-like carbon (GLCH) film is difficult to construct low-sheared frictional interfaces under dry inert atmosphere. In this paper, the heterogeneous interface was built up by combining nano-crystallized silver-doped MoS2 (nc-Ag/MoS2) and GLCH films to achieve superlubricity (coefficient of friction, COF = 0.006) under the ultra-high contact stress of 2.33 GPa. The results emphasize that the GLCH film with a low hydrogen content among the hydrogenated amorphous carbon (a-C:H) films is more likely to be low-friction and anti-wear when paired with nc-Ag/MoS2 film. Moreover, the nc-Ag/MoS2 film has potential to obtain the high load-bearing capacities and induce an appropriate graphitization of GLCH film in the heterogeneous interface system, obtaining superlow friction in contrast to the homogeneous self-mated GLCH tribopair. Additionally, this heterogeneous interface can achieve superlubricity (COF = 0.007) for more than 50,000 sliding cycles without failure. This study has important application significance in space machinery and can provide theoretical guidance and new paths for future solid lubrication technology.

Synthesis of a flexible self-standing graphene-like graphite thin film and its application to anode materials for thin-film all-solid-state lithium-ion batteries

Synthesis of a flexible self-standing graphene-like graphite thin film and its application to anode materials for thin-film all-solid-state lithium-ion batteries

Electrically conducting films prepared from graphite and lignin in pure water.

In this study, we present electrically conducting self-standing graphite films consisting of lignin derivatives extracted by simultaneous enzymatic saccharification and comminution (SESC). Sonication of graphite powder in the presence of SESC lignin and pure water allows dispersion of the SESC-lignin-attached graphite without addition of other chemicals. The SESC-lignin-attached graphite having a diameter of several micrometers can be used as a surface electroconductive coating and molded into self-standing films by drying. The SESC-lignin-attached graphite film exhibits higher conductivity (∼2,075 S/cm) than graphite-based composites consisting of ordinary lignin derivatives. Manufacturing self-standing films of micrometer-sized graphite using SESC lignin enables high electrical conductivity of the SESC-lignin-attached graphite film. The size of the SESC-lignin-attached graphite is proportional to the conductivity of the film. The SESC-lignin-attached graphite also acts as an antiplasticizer and a conductive filler for polymer films, i.e., conductive films consisting of poly(ethylene glycol) or Li+ montmorillonite can be obtained through a water-based process.