Graphene Laminates Research Articles

Ultimate Charge Transport Regimes in Doping-Controlled Graphene Laminates: Phonon-Assisted Processes Revealed by the Linear Magnetoresistance.

Understanding and controlling the electrical properties of solution-processed 2D materials is key to further printed electronics progress. Here, we demonstrate that the thermolysis of the aromatic intercalants utilized in nanosheet exfoliation for graphene laminates allows for high intrinsic mobility and the simultaneous control of doping type (n- and p-) and concentration over a wide range. We establish that the intraflake mobility is high by observing a linear magnetoresistance of such solution-processed graphene laminates and using it to devolve the interflake tunneling and intralayer magnetotransport. Consequently, we determine the temperature dependencies of the inter- and intralayer characteristics. The intraflake transport appears to be dominated by electron-phonon scattering processes at temperatures T > 20 K, while the interflake transport is governed by phonon-assisted tunneling. In particular, we identify the efficiency of phonon-assisted tunneling as the main limiting factor for electrical conductivity in graphene laminates at room temperature. We also demonstrate a thermoelectric sensitivity of around 50 μV·K-1 in a solution-processed metal-free graphene-based thermocouple.

Effect of densification process on mechanical enhancement of graphene laminates

Graphene nanosheets have attracted great attention in the field of nanotechnology applications due to their extraordinary mechanical properties. While the structural defects such as gaps will occur during the preparation of graphene laminates, which will greatly damage the performance of the macroscopic material. Hence, a simple and promising mechanical compression method is used to improve the mechanical properties of graphene laminates. However, the roles of the densification process in the mechanical enhancement mechanism of graphene laminates are not clear. In our work, the mechanical enhancement of the compressed graphene (PG) laminates was investigated by the coarse-grained molecular dynamics simulation method. The tensile strength of PG model could be increased by increasing the graphene nanosheet size and the degree of compression in the system. And the model has the stronger van der Waals effect between graphene sheets due to the larger graphene size as well as the higher overlap ratio. Furthermore, two kinds of PG laminates were prepared by densification method, and the tensile strength was consistent with the upward trend of the PG model. This work provides an in-depth understanding on the mechanical enhancement of the densification process and lays a foundation for the future practical application of graphene laminates.

Structural colored water rewritable paper enabled by assembled graphene laminates/ SiO2 amorphous colloidal arrays hierarchical structure

Rewritable paper is of great significance for environmental and sustainable development. Specially, the water rewritable paper based on hydrochromism has aroused extensive research interesting for being clean, convenient and compatible with the current ink jet printer. Nevertheless, previously reported water rewritable paper requires complex and time-consuming fabricating process. Here, we report a facile strategy to fabricate structural colored water rewritable paper simply via two step infiltration on commercially available paper. After infiltration of graphene laminates and SiO2 colloidal spheres in sequence, the obtained paper is integrated with assembled graphene laminates (AGLs)/amorphous colloidal arrays (ACAs) hierarchical composite structure. Owing to the advantageous micro-topography, selective separation capacity and high visible light absorption property of the underlying AGLs, SiO2 ACAs with vivid structure color can be realized. Moreover, the hydrochomism of the hierarchical composite structure is resulted from the synergistic contribution of the hydrophilic structural color and the visible light absorption property of AGLs. Our strategy is based on the environmental-friendly structural color and convenient to realized, which offers a promising alternative to rapidly fabricate colored water rewritable paper.

Controlling Graphene Sheet Resistance for Broadband Printable and Flexible Artificial Magnetic Conductor-Based Microwave Radar Absorber Applications

Current artificial magnetic conductor (AMC) designs use metallic patterns on rigid substrates and focus on shapes and sizes of AMC structures, rather than on material performance, which has hindered operation bandwidth and design flexibility. Here, we introduce printed graphene AMC-based broadband and flexible microwave radar absorbers, which not only redirect but also absorb the incident wave so to broaden the operation bandwidth. Contrasting to other reported works, the phase characteristics of the AMCs are realized through the control of the surface resistance provided by printed graphene laminates. We produced a variety of AMC structures, composed of printed graphene circular ring arrays with exactly the same shape and size, but different sheet resistances. By carefully designing the sheet resistance of printed graphene laminates, the optimized anti-phase reflection cancellation between AMCs can be achieved. With printed graphene AMCs and flexible dielectric substrate, the absorber presented in this work has a broadband effective absorption (above 90% absorptivity) from 7.58 GHz to 18, is polarization insensitive under normal incident, and can work at relatively wide incident angles. Furthermore, this absorber is capable of bending easily with notable performance, which makes it ideal for applications with irregular and uneven shapes.

Infiltration-Assisted Assembly of Flexible Noniridescent Amorphous Colloidal Arrays on Exfoliated Graphene Laminates for Structural Color Applications

Amorphous colloidal arrays (ACAs) have stimulated considerable interest owing to noniridescent structural colors and feasibility in color mixing. Here, we develop a method for the rapid fabrication...

Construction of three-dimensional all-carbon C60/graphene hybrids and their use in high performance supercapacitors

Control of the three-dimensional (3D) pore structure of all-carbon C60/graphene hybrids was conducted by introducing C60 molecules into graphene laminates by a simple hydrothermal method to improve their performance as electrodes in supercapacitors. Results indicate that the strong π-π interaction between carbon hexagons in C60 and graphene skeletons favors the self-assembly of the 3D pore structure of the C60/graphene hybrids under hydrothermal conditions. The addition of C60 molecules gives the hybrids a hierarchical pore structure and redox-active sites, which contribute remarkably to the improved electrochemical performance. A specific capacitance of 332.3 F·g-1 at a current density of 1 A·g-1 was obtained in a 6 mol·L-1 potassium hydroxide solution for a hybrid optimized by an orthogonal experimental design method, which is 54.5% higher than that of the graphene without C60. This finding indicates that the all-carbon hybrids may be used as more competitive and promising electrodes for the fabrication of high performance supercapacitors.

Graphene film for thermal management: A review

Abstract Thermal conductivity and thermal dissipation are of great importance for modern electronics due to the increased transistor density and operation frequency of contemporary integrated circuits. Due to its exceptionally high thermal conductivity, graphene has drawn considerable interests worldwide for heat spreading and dissipation. However, maintaining high thermal conductivity in graphene laminates (the basic technological unit) is a significant technological challenge. Aiming at highly thermal conductive graphene films (GFs), this prospective review outlines the most recent progress in the production of GFs originated from graphene oxide due to its great convenience in film processing. Additionally, we also consider such issues as film assembly, defect repair and mechanical compression during the post-treatment. We also discuss the thermal conductivity in in-plane and through-plane direction and mechanical properties of GFs. Further, the current typical applications of GFs are presented in thermal management. Finally, perspectives are given for future work on GFs for thermal management.

Ballistic impact analysis of graphene nanosheets reinforced kevlar-29

The bulletproof vests used by law enforcement officials can be appropriately termed as “Bullet-resistant” vests instead of bulletproof vests since they are not completely threat proof. The bullets released from handgun calibers such as 0.357 SIG or 9 mm guns travel at a very high velocity which the vests cannot withstand. These vests are mostly made of ceramic or steel plates backed with para-aramids such as kevlar, spectra, and dyneema. Kevlar is an organic fiber from an aromatic polyamide family. Kevlar has a unique molecular structure that distinguishes it from other polyamide families. The para-aramid structure gives kevlar an optimum combination of high tensile strength, high modulus, resilience, thermal stability, and toughness [1]. Different varieties of Kevlar are produced to be used in different applications. Kevlar-29 has been the most widely used material in bulletproof vests for ballistic protection. Despite its strength and resilience kevlar has its disadvantages such as poor compression strength, which makes it less reliable for ballistic protection. Although kevlar fibers are strong and have high tensile strength its ability to cope with the force of compression is poor [2]. Also, the inclusion of these plates significantly increases the weight of the jackets. Graphene, on the other hand, is a two-dimensional allotrope of carbon atoms arranged in a hexagonal lattice structure [3]. It is found to be the strongest material ever found yet weighs much less than a paper [4]. In this work, graphene nanoparticles are inserted as laminates in-between the kevlar fiber layers and dynamic ballistic impact analysis is done on this reinforced material. The equivalent stresses, total deformation, maximum principal stress and directional velocity of the vests and bullet are investigated and the results show a significant increase in the ballistic performance of vests reinforced with graphene laminates.

Flexible transparent graphene laminates via direct lamination of graphene onto polyethylene naphthalate substrates.

Graphene, with its excellent electrical, mechanical, and optical properties, has emerged as an exceptional material for flexible and transparent nanoelectronics. Such versatility makes it compelling to find new pathways to lay graphene sheets onto smooth, flexible substrates to create large-scale flexible transparent graphene conductors. Here, we report the realization of flexible transparent graphene laminates by direct adhesion of chemical vapor deposition (CVD) graphene on a polyethylene naphthalate (PEN) substrate, which is an emerging standard for flexible electronics. By systematically optimizing the conditions of a hot-press technique, we have identified that applying optimum temperature and pressure can make graphene directly adhere to flexible PEN substrates without any intermediate layer. The resultant flexible graphene films are transparent, have a standard sheet resistance of 1 kΩ with high bending resilience, and high optical transmittance of 85%. Our direct hot-press method is achieved below the glass transition temperature of the PEN substrate. Furthermore, we demonstrate press-assisted embossing for patterned transfer of graphene, and hence it can serve as a reliable new means for creating universal, transparent conducting patterned films for designing flexible nanoelectronic and optoelectronic components.

Stamped multilayer graphene laminates for disposable in-field electrodes: application to electrochemical sensing of hydrogen peroxide and glucose.

A multi-step approach is described for the fabrication of multi-layer graphene-based electrodes without the need for ink binders or post-print annealing. Graphite and nanoplatelet graphene were chemically exfoliated using a modified Hummers' method and the dried material was thermally expanded. Expanded materials were used in a 3D printed mold and stamp to create laminate electrodes on various substrates. The laminates were examined for potential sensing applications using model systems of peroxide (H2O2) and enzymatic glucose detection. Within the context of these two assay systems, platinum nanoparticle electrodeposition and oxygen plasma treatment were examined as methods for improving sensitivity. Electrodes made from both materials displayed excellent H2O2 sensing capability compared to screen-printed carbon electrodes. Laminates made from expanded graphite and treated with platinum, detected H2O2 at a working potential of 0.3V (vs. Ag/AgCl [0.1M KCl]) with a 1.91μM detection limit and sensitivity of 64nA·μM-1·cm-2. Electrodes made from platinum treated nanoplatelet graphene had a H2O2 detection limit of 1.98μM (at 0.3V), and a sensitivity of 16.5nA·μM-1·cm-2. Both types of laminate electrodes were also tested as glucose sensors via immobilization of the enzyme glucose oxidase. The expanded nanographene material exhibited a wide analytical range for glucose (3.7μM to 9.9mM) and a detection limit of 1.2μM. The sensing range of laminates made from expanded graphite was slightly reduced (9.8μM to 9.9mM) and the detection limit for glucose was higher (18.5μM). When tested on flexible substrates, the expanded graphite laminates demonstrated excellent adhesion and durability during testing. These properties make the electrodes adaptable to a variety of tests for field-based or wearable sensing applications. Graphical abstract Expanded graphite (eGR) and expanded nanoplatelet graphene (nGN) were chemically exfoliated, thermally expanded, and manually stamped into flexible multi-layer graphene laminate electrodes. Hydrogen peroxide amperometric testing of eGR laminates compared to nGN laminates and a screen printed carbon (SPC) electrode.

Ultrathin flexible graphene films with high thermal conductivity and excellent EMI shielding performance using large-sized graphene oxide flakes.

As the demand for wearable and foldable electronic devices increases rapidly, ultrathin and flexible thermal conducting films with exceptional electromagnetic interference (EMI) shielding effectiveness (SE) are greatly needed. Large-sized graphene oxide flakes and thermal treatment were employed to fabricate lightweight, flexible and highly conductive graphene films. Compared to graphene films made of smaller-sized flakes, the graphene film made of large-sized flakes possesses less defects and more conjugated domains, leading to higher electrical and higher thermal conductivities, as well as higher EMI SE. By compressing four-layer porous graphene films together, a 14 μm-thick graphene film (LG-4) was obtained, possessing EMI SE of 73.7 dB and the specific SE divided by thickness (SSE/t) of 25 680 dB cm2 g−1. The ultrahigh EMI shielding property of the LG-4 film originates from the excellent electrical conductivity (6740 S cm−1), as well as multi-layer structure composed of graphene laminates and insulated air pores. Moreover, the LG-4 film shows excellent flexibility and high thermal conductivity (803.1 W m−1 K−1), indicating that the film is a promising candidate for lightweight, flexible thermal conducting film with exceptional EMI shielding performance.

Tuning the nanostructure of nitrogen-doped graphene laminates for forward osmosis desalination.

Studies have concentrated on the physicochemical properties of graphene-based membranes that can replace polymeric membranes for use in forward osmosis (FO) systems. However, recent research studies have focused on mixtures of two or more different materials (e.g., graphene oxide and polymers) due to the need to reinforce underwater stability. Alternatives include reduced forms such as reduced graphene oxide to improve the stability and size-based selectivity, which have resulted in a narrow nanochannel that restricts water permeability. Herein, we propose the use of a novel nitrogen-doped graphene (NG) membrane to solve a trade-off between permeability and selectivity, investigating the nanostructure via N-doping reaction time. In an FO process, NG membranes achieved an outstanding specific salt flux of 0.18 g L-1, compared to commercial membranes (0.55 g L-1). The pyridinic-N bonding structure improved the permeability and selectivity under a similar nanochannel size because of its negatively polarized hole defects with the moderate energy barrier enabling water passage while blocking ions. Our results confirm the possibility of fabricating novel graphene-based FO membranes by tailoring the nitrogen-bonding structure, which will significantly help develop a process for improving the scalability of membrane materials.

Pop-Up Conducting Large-Area Biographene Kirigami.

We demonstrate the rapid, large-area transformation of bioenabled graphene laminates into multidimensional geometries for pop-up and stretchable applications. Water-vapor annealing facilitates the controlled plasticization of the multilayered silk-graphene morphologies, allowing highly localized kirigami cuts by programmable drag knife with diverse type and depth of cuts. By adjusting drag-knife depth, we can generate a microscale array of full and partial cuts, enabling a purely topological approach toward the control of metastable fold-unfold states and crack fracture paths in kirigami structures. Through orthogonal control over the graphene-silk composite's nanoscale morphology, cut pattern, and semimetal-like conductivity, we showcase bioenabled laminates as a platform for prospective soft and shape-transforming electronics as flexible interconnects and stretchable energy harvesters.

Graphene and poly(methyl methacrylate) composite laminates on flexible substrates for volatile organic compound detection

In this paper, we present a gas sensor for volatile organic compound (VOC) detection based on graphene and poly(methyl methacrylate) (GR/PMMA) composite laminates fabricated using CVD-grown graphene. Graphene was transferred to a poly(ethylene terephthalate) (PET) substrate by PMMA-supported wet transfer process without PMMA removal in order to achieve the deposition of GR/PMMA composite laminates on PET. The GR/PMMA and graphene sensors show completely different sensitivities to VOC vapors. The GR/PMMA and graphene sensors showed the highest sensitivities to dichloromethane (DCM). The response of the GR/PMMA sensor to DCM was 3 times higher than that of the graphene sensor but the GR/PMMA sensor hardly responded to acetone, chloroform, or benzene. The sensing mechanism of the graphene sensor can be based on the dielectric constant of VOCs, the size of VOC molecule, and electron hopping effects on defect graphene, while that of the GR/PMMA sensor can be explained in terms of the polymer swelling owing to the Hansen solubility parameter.

Anomalous molecular infiltration in graphene laminates.

Graphene laminated (GL) coatings formed by stacked few layer graphene (FLG) nanocrystals were deposited on low-density polyethylene (PE) films by the mechanical rubbing technique. Molecular transport through the bilayer membrane was studied by the gas phase permeation technique by monitoring the CO2, N2 and 2H2 transport fluxes in transient conditions. The results evidenced that the transport exhibited anomalous character. The experimental data could be reproduced assuming that the penetrant concentration in the GL coating, cint(t), reached a saturation value cs following compressed exponential kinetics cint(t) = cs[1 - e-(λrelt)β]. The relaxation time τrel = 1/λrel showed thermally activated behavior, and its value increased with the kinetic diameter of the penetrant molecules. The critical exponent β = 1.5 ± 0.1 for CO2 and N2 and β = 2.0 ± 0.1 for 2H2 did not change with temperature. Positron annihilation lifetime spectroscopy (PALS) analysis indicated that the average cross-section (hg) of the cavities in the GL coating exhibited comparable size to the kinetic diameter (σk) of the penetrant molecules. The results could be explained by assuming that the molecular infiltration in the GL structure occurred in nano-channels having distributed path lengths where the penetrant transport obeyed a configurational diffusion mechanism.

3D nanoporous crystals enabled 2D channels in graphene membrane with enhanced water purification performance

Two-dimensional (2D) materials have been received increasing attention in various fields such as physics, material science, chemistry and engineering. In particular, the graphene-based membrane is an emerging subject mainly due to the atomic thickness, simple processing and the compatibility with other materials. In the case of water treatment, stable graphene-based laminar structures as well as high separation performance are pursued. In this work, nanoporous crystals embedded graphene laminate membranes was reported for water purification. Reduced graphene oxide (rGO) nanosheets obtained from a solution chemical process act as building blocks to construct the 2D channels through a pressure-driven filtration process. By incorporating three-dimensional (3D) nanoporous crystals with sub-nano sized aperture size into the 2D graphene laminates, both the inter-layer spacing and numbers of nanofluidic channels are increased, leading to greatly-enhanced water separation performance. The optimized 3D/2D membranes exhibit 15 times higher water permeability than that of the rGO membrane with similar high dye retention rate. The significance of such 3D nanoporous structure and transport mechanism through the 3D/2D membranes is systematically studied. This general approach of enhancing the molecular transport through 2D nanofluidic channels proposed here may also find application in gas separation and battery membranes.

Design optimization of graphene laminates for maximum fundamental frequency

Design optimization of graphene laminates for maximum fundamental frequency

Superconductivity in Ca-doped graphene laminates.

Despite graphene’s long list of exceptional electronic properties and many theoretical predictions regarding the possibility of superconductivity in graphene, its direct and unambiguous experimental observation has not been achieved. We searched for superconductivity in weakly interacting, metal decorated graphene crystals assembled into so-called graphene laminates, consisting of well separated and electronically decoupled graphene crystallites. We report robust superconductivity in all Ca-doped graphene laminates. They become superconducting at temperatures (Tc) between ≈4 and ≈6 K, with Tc’s strongly dependent on the confinement of the Ca layer and the induced charge carrier concentration in graphene. We find that Ca is the only dopant that induces superconductivity in graphene laminates above 1.8 K among several dopants used in our experiments, such as potassium, caesium and lithium. By revealing the tunability of the superconducting response through doping and confinement of the metal layer, our work shows that achieving superconductivity in free-standing, metal decorated monolayer graphene is conditional on an optimum confinement of the metal layer and sufficient doping, thereby bringing its experimental realization within grasp.

Strong and electrically conductive graphene-based composite fibers and laminates.

Graphene is an ideal candidate for lightweight, high-strength composite materials given its superior mechanical properties (specific strength of 130 GPa and stiffness of 1 TPa). To date, easily scalable graphene-like materials in a form of separated flakes (exfoliated graphene, graphene oxide, and reduced graphene oxide) have been investigated as candidates for large-scale applications such as material reinforcement. These graphene-like materials do not fully exhibit all the capabilities of graphene in composite materials. In the current study, we show that macro (2 inch × 2 inch) graphene laminates and fibers can be produced using large continuous sheets of single-layer graphene grown by chemical vapor deposition. The resulting composite structures have potential to outperform the current state-of-the-art composite materials in both mechanical properties and electrical conductivities (>8 S/cm with only 0.13% volumetric graphene loading and 5 × 10(3) S/cm for pure graphene fibers) with estimated graphene contributions of >10 GPa in strength and 1 TPa in stiffness.

Embedding SiO2into graphene oxide in situ to generate 3D hierarchical porous graphene laminates for high performance lithium–sulfur batteries

3D hierarchical porous graphene laminates through self-assembly of functionalized graphene oxide embedded with SiO2in situas a carbon host material for sulfur cathode, exhibits high reversible capacity, stable cycling performance as well as excellent rate capabilities.