Graphene-based Films Research Articles

Rapid and facile fabrication of conducting monolayer reduced graphene oxide films by methane plasma-assisted reduction

In this research article, we report a method to fabricate conducting reduced graphene oxide (rGO) monolayer films reduced by methane plasma treatment within few minutes and the nanoscale characterization of local conductivity via conductive atomic force microscopy (C-AFM), realizing their applicability in highly transparent conducting electrodes. Continuous monolayer graphene oxide (GO) films were fabricated by a simple spin-coating method and reduction of oxygen-containing groups with simultaneous lattice defect restoration was done by methane plasma treatment. Current images obtained by C-AFM provide detailed information about the conductivity through the flakes depending on the plasma irradiation time. Moreover, lattice defect restoration was confirmed by the appearance of the G’-band in Raman spectra, which is in correlation with current images, whereas no G’-band or current image was observed in vacuum annealed samples at similar durations in the absence of methane. This rapid and facile method offers a way to fabricate conductive monolayer rGO films by a short-term plasma treatment allowing to utilize low melting point substrates to form flexible conductive graphene-based films.

Plasticization stretching strategy towards high strength nacre-like graphene-based composites

Introducing graphene into polymers is a common method to prepare nacre-like functional composites with enhanced mechanical strength and conductive properties. However, the soft nature of graphene sheets makes it easy to form chaotic wrinkles and degrade the mechanical performance of the composites by hindering interlayer stress transfer. Here, we use a simple plasticization and stretching method to flatten the sheet wrinkles and obtain a highly oriented and crystalline graphene-based nacre-like composite film. The composite film shows excellent mechanical properties (tensile strength of 709.2 MPa, toughness of 11.1 MJ m-3), as well as high electrical conductivity of 7671 S m-1, which are much higher than those of as-prepared films without plasticization and stretching. This low cost and facile method opens an avenue to prepare graphene and other 2D nanosheet based composites with enhanced performance.

Hybrid Supercapacitors Based on Self-Assembled Electrochemical Deposition of Reduced Graphene Oxide/Polypyrrole Composite Electrodes

Conductive polymers (CPs) have potential application to commercial energy storage because of their high electrochemical activity and low cost. However, an obstacle in developing CP-based supercapacitors is the degradation in their capacitance during the charge-discharge process that leads to poor rate performance. This study fabricates layers of a high-performance self-assembled polypyrrole/reduced graphene oxide (PPY/RGO) composite material on a carbon cloth through electrochemical deposition. The layered graphene improved the electrochemical properties of PPY. Carbon fiber rods were coated with the PPY/RGO composite layer, the thickness of which depends on the deposition time. Adequate capacitive behaviors were achieved by using 16 layers of polypyrrole/reduced graphene oxide, with a specific capacitance of 490 F g−1 (0.6 A g−1) and good rate performance. The results here provide a novel means of preparing graphene-based nanocomposites films for a variety of functions. A symmetric device was subsequently assembled by using electrodes featuring 16 layers of the polypyrrole/reduced graphene oxide composite. It yielded a specific capacitance of 205 F g−1 and a high energy density of 16.4 Wh kg−1. It also exhibited good cycle stability, with a capacitance retention rate of 85% for 5,000 cycles.

Novel Data Science Driven Chemical Agent Sensors: Towards Better Discrimination in Complex Environments

Chemical agents remain a persistent threat to both Warfighters and civilian personnel in both combat and non-combat environments. While many useful detection technologies exist to provide early warning, many of them suffer from similar drawbacks. Most common are unacceptable false positive response rates and inability to discriminate target analytes in complex or obscurant-laden environments. A typical approach to this problem is to develop material solutions for more specific and sensitive sensors. While useful, these solutions are often too expensive, not practical, or non-deployable. Our approach fuses both material and data science to extend the power of multiplexed sensor arrays towards more accurate and faster detection and discrimination.This presentation will discuss our approach towards vapor analyte detection using multiplex array systems combined with novel data science approaches. For vapor phase detection, sorptive and conductive graphene-based nanocomposite polymer films as well as select 2D conductive materials are used for semi-selective affinity towards chemical agent simulants in binary mixtures with common obscurants. Response data are pre-processed using a novel algorithm called the Variational Autoencoder Kalman Filter and the entire response dataset is used to train neural networks for analyte discrimination. To inform the neural networks to facilitate accurate and fast analyte discrimination, datasets far exceeding the capability of laboratory measurements are needed. Here too we describe our approach to generate simulated data to supplement and augment the classification algorithm machine learning process. We lastly demonstrate this approach to discriminate binary and tertiary mixtures of analytes with both similar and different chemical similarity both in and out of the precise of common environmental interferents.

Antimicrobial Effect of Chitosan Films on Food Spoilage Bacteria.

Synthetic materials commonly used in the packaging industry generate a considerable amount of waste each year. Chitosan is a promising feedstock for the production of functional biomaterials. From a biological point of view, chitosan is very attractive for food packaging. The purposes of this study were to evaluate the antibacterial activity of a set of chitosan-metal oxide films and different chitosan-modified graphene (oxide) films against two foodborne pathogens: Campylobacter jejuni ATCC 33560 and Listeria monocytogenes 19115. Moreover, we wanted to check whether the incorporation of antimicrobial constituents such as TiO2, ZnO, Fe2O3, Ag, and graphene oxide (GO) into the polymer matrices can improve the antibacterial properties of these nanocomposite films. Finally, this research helps elucidate the interactions of these materials with eukaryotic cells. All chitosan-metal oxide films and chitosan-modified graphene (oxide) films displayed improved antibacterial (C. jejuni ATCC 33560 and L. monocytogenes 19115) properties compared to native chitosan films. The CS-ZnO films had excellent antibacterial activity towards L. monocytogenes (90% growth inhibition). Moreover, graphene-based chitosan films caused high inhibition of both tested strains. Chitosan films with graphene (GO, GOP, GOP-HMDS, rGO, GO-HMDS, rGOP), titanium dioxide (CS-TiO2 20:1a, CS-TiO2 20:1b, CS-TiO2 2:1, CS-TiO2 1:1a, CS-TiO2 1:1b) and zinc oxide (CS-ZnO 20:1a, CS-ZnO 20:1b) may be considered as a safe, non-cytotoxic packaging materials in the future.

Variable-Angle Spectroscopic Ellipsometry of Graphene-Based Films

A review of the authors’ research works on Variable-Angle Spectroscopy (VASE) of graphene-based films is presented. The interaction of graphene oxide (GO) with magnetron-sputtered metals is a promising research area. VASE optical models of GO thin films deposited on magnetron-sputtered titanium (Ti), silver (Ag) and gold (Au) are discussed. Moreover, the optical properties of graphene nanoplatelet (GNPS) films and reduced graphene oxide (RGO) stabilized with Poly(Sodium 4-Styrenesulfonate) (PSS) films, which are less studied graphene-related materials, are shown. Finally, different optical behaviors of chemical vapor deposition (CVD)-grown monolayer, bilayer, and trilayer graphene films on silicon and polyethylene terephthalate (PET) substrates are recapitulated.

Thermal management of graphene-induced high-power semiconductor laser package with bidirectional conduction structure

A graphene-based film acted as thermal dissipation channel is introduced to design the package of high-power single-emitter laser diodes. Here we show that heat conduction of high-power laser diodes can be greatly improved via introduction of additional transverse heat dissipation channel with graphene-based film through thermal management. The finite element analysis method is employed to analyse the heat dissipation performance of laser diodes. The epi-up package coupled with graphene is proposed to reduce the thermal stress of laser diodes. In order to increase the thermal dissipation while reducing thermal stress, the effect of the temperature of the active region on account of the thickness of graphene-based film of the package of high-power single-emitter laser diodes is discussed, and the relationship between the output power of semiconductor laser and the heat dissipation effect of graphene-based film is analyzed. The results show that the junction temperature of the active region of graphene-induced package structure is reduced by 9.1 K and the thermal resistance is reduced by 1.52 K/W by using bidirectional conduction graphene-based film compared with the non-graphene-based structure.

Laser scribing of Ag-decorated graphene for high-performance and flexible heaters

In this article, Ag nanoparticle decorated graphene-based film heaters are fabricated using a CO2 infrared laser writing technology. In this process, we use the commercial polyimide (PI) as carbon sources which can be directly converted into graphene during the laser irradiation. To prepare the Ag decorated graphene, the PI films are modified with KOH into potassium polyamate and incorporation of Ag+ ions through subsequent ion exchange prior to the laser irradiation. While the laser is irradiating on silvered PI, the temperature of the irradiated silvered PI increases in a flash leading to the reduction of Ag+ ions on the PI derived graphene (PDG) surface. The resultant Ag-decorated PDG (Ag-PDG) composites reveal an enhanced electric conductivity (16.2 Ω/sq.) with excellent mechanical properties. The flexible heaters constructed from the Ag-PDG film also show remarkable electrothermal performance in terms of saturated temperature (Ts, 248.3 °C), heating efficiency (142.8 °C cm2/W), response time (2.14 s) and durability with a small temperature deviation (1.3 °C) after 2000 bending cycles.

Flexible, graphene-based films with three-dimensional conductive network via simple drop-casting toward electromagnetic interference shielding

Fabricating flexible and large-scale graphene-based films through a simple process to achieve excellent electromagnetic interference (EMI) shielding performance is still a daunting challenge. Herein, the flexible and large-area EMI shielding films with ultrathin coating thickness (i.e., 10 μm) and low coating density (i.e., 2.4 mg/cm2) were fabricated through a simple drop-casting approach by using graphene-based conductive ink at room temperature. With the aid of electromagnetic simulation, the optimal square resistance of conductive film for desirable EMI shielding effectiveness is predicted, avoiding the unnecessary costs of error and trial. To solve the vital issue of poor conductivity of reduced graphene oxide (RGO) arising from defects and the serious agglomeration of each filler in ink, a three-dimensional network was constructed by connecting RGO with flexible one-dimensional (1D) conductive fibers (i.e., carbon nanotubes (CNT) and Ag nanowire (AgNW)). The square resistance of the RGO/CNT@Epoxy/AgNW composite film could reach as low as 1.94 ± 0.63 Ω/sq, which exhibited the shielding effectiveness value of 40 dB at a minimum in 8.2–12.5 GHz. These attributes could satisfy the EMI shielding and flexibly conformal demands of most communication equipment.

Facile Synthesis and Characterization of Few-Layer Multifunctional Graphene from Sustainable Precursors by Controlled Pyrolysis, Understanding of the Graphitization Pathway, and Its Potential Application in Polymer Nanocomposites.

The key feature of the present work is the dexterous utilization of an apparently destructive process, pyrolysis, for the synthesis of the most esteemed nanomaterial, graphene. This work is an attempt to synthesize graphene from nonconventional sources such as tannic acid, alginic acid, and green tea by a controlled pyrolysis technique. The precursors used in this work are not petroleum-derived and hence are green. A set of pyrolysis experiments was carried out at different temperatures, followed by a thorough step-by-step analysis of the product morphology, enabling the optimization of the graphitization conditions. A time-dependent morphological analysis was also carried out along with isothermal thermogravimetric studies to optimize the ideal pyrolysis time for graphitization. The specific capacitance of the graphene obtained from alginic acid was 315 F/g, which makes it fairly suitable for application as green supercapacitors. The same graphene was also used to fabricate a rubber-latex-based flexible supercapacitor film with 137 F/g specific capacitance. The graphene and graphene-based latex film exhibited room-temperature magnetic hysteresis, indicating their ferromagnetic nature, which also supports their spintronic applications.

Graphene‐Based Hybrid Carbons: Ultrahigh Strength and Modulus Graphene‐Based Hybrid Carbons with AB‐Stacked and Turbostratic Structures (Adv. Funct. Mater. 50/2020)

In article number 2005381, Sunghwan Jin, Rodney S. Ruoff, Seongwoo Ryu, and co-workers show a graphene-based hybrid carbon film composed of AB-stacked and turbostratic structure by heat-treating graphene/poly(catecholamine) composites. The graphene/poly(catecholamine) composites have a brick-mortar structure that the composite films are transformed to have both AB-stacked (mainly from graphene oxide) and turbostratic (mainly from poly(catecholamines)) structures.

Bioproduced Polymers Self-Assemble with Graphene Oxide into Nanocomposite Films with Enhanced Mechanical Performance.

Graphene oxide (GO) has recently been highlighted as a promising multipurpose two-dimensional material. However, free-standing graphene oxide films suffer from poor strength and flexibility, which limits scaling-up of production and lifetime structural robustness in applications. Inspired by the relationship between the organic and inorganic components of the hierarchical structure of nacre found in mollusk shells, we have fabricated self-assembled, layered graphene-based composite films. The organic phase of our composite is produced via environmentally friendly and economical methods based on bacterial production of γ-poly(glutamic acid) (PGA). Composite films made of GO, PGA, and divalent cations (Ca2+) were prepared through a slow solvent evaporation method at ambient temperature, resulting in a nacre-like layered structure. These biobased nanocomposite films showed impressive mechanical properties, which resulted from a synergistic combination of hydrogen bonding with the bacterially produced PGA and ionic bonding with calcium ions (Ca2+). The GO/PGA/Ca2+ composite films possessed a high strength of 150 ± 51.9 MPa and a high Young’s modulus of 21.4 ± 8.7 GPa, which represents an increase of 120% and over 70% with respect to pure GO films. We provide rational design strategies for the production of graphene-based films with improved mechanical performance, which can be applied in filtration purification of wastewater in the paper, food, beverage, pigment, and pharmaceuticals industries, as well as for manufacturing of functional membranes and surface coatings.

Graphene-based film heater fabricated by laser writing

In this work, a graphene-based film heater is proposed based on laser-reduced graphene oxide (LRGO) fabricated by the simple and eco-friendly laser direct writing technology at ambient conditions. Benefiting from high photothermal effect of CO2 laser with wavelength of 10.6 um, the LRGO-based film heater has a high heating rate of 15.3 °C/s up to 196 °C with a fast response of 12.84 s at a low power density of 1 W/cm2. Moreover, it exhibits good anti-interference ability to the mechanical effect and shows potential important application for de-icing. This work is helpful for the development of graphene-based device in practical application.

Self-assembled perylenetetracarboxylic acid-reduced graphene oxide film for high-sensitive impedimetric determination of thrombin

Graphene-based thin film has been widely used as signal conductor and platform material in electrochemical sensors. For commonly used reduced graphene oxide (rGO), oxygen-containing functional groups can provide coupling sites to conjugate with bio-cognitive elements, but high degree of oxidation can harm its structural integrity and signal conductivity. In this work, a new strategy is developed to balance the conductivity and functionality of rGO. The PTCA-rGO composite film was prepared by self-assembly and used to fabricate electrochemical biosensor. To form reusable thrombin aptasensor, an in situ layer-by-layer self-assembling method was adopted to stepwise deposit reduced graphene oxide (rGO), 3, 4, 9, 10-perylenetetracarboxylic acid (PTCA), and thrombin aptamer (TBA) onto 3-aminopropyltriethoxy silane (APTES)-modified glassy carbon electrode (GCE). The as-prepared aptasensor was used to determine thrombin in response to impedimetric signal by electrochemical impedance spectroscopy (EIS). The as-prepared GCE/rGO/PTCA/TBA sensor provided outstanding performance for determination of thrombin concentration with wide linear range (1 pM-100 nM), low detection limit (0.2 pM), reusability, and good specificity to thrombin. The good performance of GCE/rGO/PTCA/TBA aptasensor can be attributed to the electrochemical property of rGO-PTCA composite film and the in situ layer-by-layer fabricated strategy. This PTCA-modification method is promising to be widely used in the fabrication of graphene-based electrochemical devices.

Mechano-adaptive thin film of graphene-based polymeric nanocomposite for enhancement of lubrication properties

Intriguing low frictional properties of 2D materials can be harnessed for thin-film lubrication in small-scale devices by making their mechano-adaptive coatings. Herein, the reduced graphene oxide-polystyrene (rGO-PS) nanocomposite synthesized by single-step chemical processing of graphene oxide and polystyrene is applied to prepare self-lubricating thin film over the silicon substrate. The non-covalent π-π interaction between the aromatic rings of polystyrene and the π-electron network of rGO furnished excellent interfacial adhesion and extended the mechanical strengthening and lubrication properties. The interfacial interaction is further supported by higher glass transition and thermal decomposition temperatures of the rGO-PS nanocomposite. The rGO-PS thin film with a uniform thickness of 850 nm is coated on a silicon surface by a spray pyrolysis deposition technique. The rGO-PS thin film showed significantly low friction (μ = 0.12) compared to the silicon substrate (μ = 0.6). The microscopic and spectroscopic analyses confirmed the deposition of a graphene-based thin film on the counter interface of the steel ball. Furthermore, the rGO-PS thin film couldn’t damage/rupture even after 100,000 cyclic contacts, which revealed its remarkable wear-resistivity. The excellent mechano-adaptability and low frictional properties of rGO-PS thin film promise the potential of 2D nanomaterials for thin-film lubrication applications.

A Review of Electron Emitters for High-Power and High-Frequency Vacuum Electron Devices

This work reviews the progress in the area of high current density electron emitters, specifically for use in high frequency and high-power microwave vacuum electron devices. The review is divided into two subsections: 1) thermionic cathodes and 2) field emission cathodes. The thermionic cathode section includes the discussion on the M-type, MM-type, Scandate and the CPD cathodes. CPD cathode promises better usability in a practical device as compared to the Scandate cathodes which are limited by emission nonuniformity, poor resistance to poisoning/ion bombardment and low life. With the increasing demand for miniaturized and high power VEDs in the near future, the development of high current density field emission cathodes is of immediate interest to the VED community. The Spindt, CNT, and graphene-based emitters are the potential candidates in the field emitters section. Graphene-based film cathodes, when compared to the Mo/Si FEAs and the CNTs, offer larger emission area as well as high current carrying capability. This review includes the evolution of the emission capabilities of the emitters, state-of-the-art performances, and possible future developments.

A highly flexible and porous graphene-based hybrid film with superior mechanical strength for effective electromagnetic interference shielding

There is usually a tough trade-off between the mechanical property and the shielding performance in electromagnetic interference shielding (EMI) materials, especially for those ultrathin and porous film-based devices. Herein, we report an ultrathin and flexible RGO/CNF@Ag–Fe3O4 (RGCF) porous film for EMI shielding application by a vacuum-assisted filtration method and a hydrazine-induced foaming process. The RGCF-3 porous film exhibits outstanding mechanical properties with a tensile strength of 175.5 MPa. As expected, the EMI shielding effectiveness of the lightweight RGCF-3 porous film (21.0 dB) is much higher than that of the compact film (10.4 dB), due to the improved efficient wave attenuation within the cellular space. Therefore, the flexible and lightweight RGCF porous film with applicable EMI shielding and superior mechanical strength is highly promising for applications in wearable electronics.

Size-Dependent Liquid Crystal Behavior of Graphene Oxides for Preparation of Highly Ordered Graphene-Based Films

We report the preparation of a highly-oriented graphene-based film prepared from liquid crystal dispersion of graphene oxides (GOs). We observed that the liquid crystal behavior of GOs is highly affected by the lateral size of GO flakes: the critical concentration for liquid crystal formation decreased with the increase of the lateral size of GO flakes, which is in a good agreement with Onsager’s theory. As a result, we were able to obtain highly-ordered graphene assemblies with large-sized GO flakes (150 ± 29 μm) at relatively low concentrations. By applying the shear force, we were able to obtain highly-oriented films from liquid crystal GO flakes. After hydrogen iodide (HI) reduction, GO films showed excellent mechanical strength and electrical conductivity, which were 278% and 283% higher, respectively, than those of films made from smaller sized GO flakes (28 ± 24 μm).

Graphene-based vertical thin film transistors

Vertical field effect transistors (VFETs), where the channel material is sandwiched between source-drain electrodes and the channel length is simply determined by its body thickness, have attracted considerable interest for high performance electronics owning to their intrinsic short channel length. To enable the effective gate modulation and current switching behavior, the electrode of conventional VFET is largely based on perforated metals, in which the gate electrical field could penetrate through. Recently, with the emerge of graphene, a new type of graphene based VFETs has been developed. With finite density of states and the weak electrostatic screening effect, graphene exhibits a field-tunable work-function and partial electrostatic transparency, it can thus function as an “active" contact with tunable graphene-channel junction, enabling entirely new transistor functions or higher device performance not previously possible. In this review, we discuss the research progresses of graphene-based VFET, including the its basic device structure, carrier transport mechanism, device performance and novel properties demonstrated.

Single-layer graphene-based surface plasmon resonance sensor with dynamic evanescent field enhancement for biomarker study

ABSTRACTIn this work, we have developed a kind of single-layer graphene-based surface plasmon resonance (SLG-SPR) biosensor to detect C-reactive protein (CRP) and Prostate-specific antigen (PSA). In the experiment of testing CPR, the results obtained revealed that the changes in resonance wavelength of SLG-SPR biosensors are higher than that of the gold-film based SPR (Au-SPR) biosensors. Moreover, for the experiment of testing PSA, due to the dynamic evanescent field enhancement produced by a strong electric field coupling between the localized SPR (LSPR) of AuNPs and SPR of single-layer graphene-based film (SLG-film) that further amplify the evanescent field signal. We verified the SLG-SPR biosensors exhibited higher sensitivity than the Au-SPR biosensors and the SLG-SPR biosensor exceeded the traditional biosensor detection limit. Accordingly, the SLG-SPR biosensor based on dynamic optical enhancement can realize high sensitivity detection of low concentration biomarkers and can be applied to most of the trace biomarkers in theory.