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3D printing technologies have expanded the possibilities of fabricating new composite materials with tailored properties, which depend on both the materials selected and the structural design at multiple length scales. Here, a catalyst-free CVD method has been used to produce hybrid materials based on 3D printed cellular α-Al 2 O 3 substrates decorated by either nanocrystalline graphene or nanocrystalline graphitic films of tunable number of layers. Graphene-based coatings of variable thickness and crystallinity have been controlled by the alteration of the parameters of CVD processing, performed under CH 4 /H 2 flux. Transmission electron microscopy has confirmed the effective growth of nanocrystalline graphene layers on the scaffolds due to the penetration of CVD gases into the open pores. The fully-connected and highly conductive 3D pathways have displayed a room temperature electrical conductivity in the range of 101–103 S m−1. Furthermore, the thermal conductivity has also increased by 50% for the specimen decorated with a 20 nm thick graphitic coating as compared to a bare 3D ceramic scaffold. The developed structures open up new possibilities for expanding the field of application of graphene/ceramic composites for conditions requiring dielectric substrates of various shapes coated with conductive films or graphene-based catalytic supports with good structural stability. [Display omitted] • Highly porous 3D-printed Al 2 O 3 supports coated for the first time by CVD nanocrystalline multilayer graphene. • Tunable electrical and thermal properties of graphene-alumina hybrids. • Electrical conductivity up to 103 S m−1, 50% augmented thermal conductivity and hydrophobic surfaces. [ABSTRACT FROM AUTHOR]

The interfacial adhesion energy of as-grown graphene on its metal growth substrate is an important variable in designing, monitoring, and controlling a roll-to-roll (R2R) graphene transfer process using mechanical peeling. In this study, we develop a novel method to estimate the adhesion energy of as-grown graphene during the R2R dry transfer process. An energy balance model is established to derive the adhesion energy based on web tension and bending curvature measurements. Experiments were conducted under various mechanical peeling conditions. The adhesion energy of as-grown graphene on copper foil was determined to be from 1.22 J/m2 to 2.58 J/m2 depending on the peeling front geometry. The developed adhesion energy estimation method is compatible with the R2R process and can be used to monitor and control the large-scale graphene transfer process with in-process measurements. [Display omitted] • A novel method to estimate adhesion energy of as-grown graphene in a roll-to-roll dry transfer process is developed. • Adhesion energy of as-grown graphene on copper is determined to be from 1.22 to 2.58 J/m2 due to web bending. • This is the first study to report the adhesion energy of as-grown graphene in a R2R dry transfer process. [ABSTRACT FROM AUTHOR]

Graphene/Cu composites are promising materials for future electrodes because of their mechanical, electrical, and thermal stability. However, the presence of graphene accelerates oxidation of the underlying Cu surface, which affects the various properties of graphene/Cu composites. Therefore, investigating the effects of Cu oxidation on the interfacial properties of graphene/Cu composite is critical. Here, the time-dependent doping and strain of large-area graphene on a Cu surface were analyzed through characterization of both the degree of oxidation and the crystallographic orientation of Cu using Raman spectroscopy. Moreover, we proposed a model for describing the Fermi level of graphene depending on the state of the Cu, such as its crystallographic orientation and degree of surface oxidation. [Display omitted] [ABSTRACT FROM AUTHOR]

Large-area and high-quality graphene grown on metal by chemical vapor deposition (CVD) has great potential applications in electronics and photo electronics. After more than 10 years of development, great progress has been made in the growth of graphene, and the role of various factors in the growth of graphene has been gradually clear. In this review, the role of hydrogen and oxygen in the formation and elimination of carbon-based impurities and silicon oxide particles and in the formation, observation, and control of grain boundary, point defects, and wrinkles is introduced. The content focuses on the specific experimental methods, results, and mechanism. Finally, the challenges of hydrogen and oxygen in the study of graphene growth on metal are introduced. This review can increase the theoretical knowledge and experimental design ability related to hydrogen and oxygen in CVD graphene grown on metal. • The concept of carbon-based impurity, silicon oxide particle, grain boundary, point defect and wrinkle, and their effects on the CVD graphene growth on metal are introduced in detail. • The role and the mechanism of hydrogen and oxygen in the study of carbon-based impurities, silicon oxide particles, grain boundaries, point defects and wrinkles are introduced. • We systematically share our experience and suggestions on the research of impurities and defects in CVD graphene growth on metal. [ABSTRACT FROM AUTHOR]

Degradation/corrosion of metallic bi-polar plates in proton exchange membrane fuel cell (PEMFC) environment is a vexing problem in durable performance of PEMFCs. Graphene coatings have been demonstrated to provide robust and durable corrosion resistance in PEMFC environment, without compromising the essential criterion, i.e., high electric conductivity. Multilayer graphene coatings were deposited on nickel and a commercial Ni–Cu alloy by chemical vapour deposition technique. Time dependent electrochemical tests carried out in the simulated PEMFC environment (0.5 M H 2 SO 4 solution) showed up to two orders of magnitude improvement in corrosion resistance of the metal substrate, and this resistance sustained for the entire test duration of 750 h. The magnitude of corrosion resistance of graphene-coated Ni was considerably superior than that for graphene-coated Monel 400 (investigated in this study) or graphene-coated Cu (reported in an earlier study). As suggested by the post-corrosion scanning electron microscopy, the graphene coatings on Ni and Monel 400 remained largely intact after long exposures to the aggressive H 2 SO 4 solution. The durable corrosion resistance of nickel and a nickel-copper alloy due to graphene coating is attributed to the ability of nickel to develop multilayer graphene (however, the nickel-copper alloy is less efficient in developing a robust multilayer graphene). Image 1 [ABSTRACT FROM AUTHOR]

We employed conventional and time-resolved Raman spectroscopy to study the effects of electron-phonon and phonon-phonon interactions on the linewidth of the G phonon in both unintentionally and intentionally doped polycrystalline chemical vapor deposited (CVD) graphene samples. We directly measured the G phonon lifetime, observing a ≈14% decrease with doping up to E F = 270 meV. The anticipated reduction of G phonon linewidth due to a decrement in electron-phonon contribution deviates from first principles calculations. CVD samples exhibit a ≈30% decrease in the electron-phonon coupling constant, λ Γ (E F = 0), compared to exfoliated graphene samples. Additionally, phonon-defect scattering makes a significant contribution to the G band linewidth in CVD graphene samples, owing to their lower crystal quality compared to exfoliated graphene. [Display omitted] [ABSTRACT FROM AUTHOR]

Graphene was grown on copper and repeatedly transferred onto a GaAs semi-insulating substrate to form multilayers (1–10). These manually stacked graphene layers resulted in appreciable local variations of optical properties due to the local differences of stacking orders. In addition, most of the observed 2D/G intensity and area ratios of an n-multilayer CVD graphene is consistent with the characteristics of a single layer repeated n-times. However, multilayer graphene has many kinds of advantages for applications to optoelectronic devices. First, the G band shift is not related to the stacking order, proving that multilayer graphene reduces doping and strain effect from the substrate, which is confirmed by Raman results after metal electrode deposition. Second, the sheet resistance decreases with increasing number of layers and after thermal annealing. Another benefit of multilayer graphene is that each layer can be annealed after transfer, which greatly improves the sheet resistance and its lateral uniformity without intentional doping. We therefore conclude that multilayer CVD graphene is a good candidate for various GaAs-based electrical applications and its good electrical uniformity allows fabrication of devices on large scales. [ABSTRACT FROM AUTHOR]