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The comparative analysis of the structural, morphological, and local electrical properties of CVD graphene films synthesized at atmospheric and low pressure CVD growth conditions was carried out. The use of electrical techniques of scanning probe microscopy, such as Kelvin probe force microscopy, scanning capacitance microscopy, electrostatic force microscopy, and conductive atomic-force microscopy for investigation of heterogeneous graphene coverage was discussed. A significant change in the surface potential values was observed indicating the formation of p-type multilayered graphene domains on single layer graphene at low pressure and n-type multilayered graphene films at atmospheric pressure CVD. The effect of Ar flow rate increasing during cooling stage in the temperature range of 700–200 °C causing graphite formation was described. The employment of surface potential spectroscopy allows to indicate the presence of nonlinear phenomena in heterogeneous graphene. [ABSTRACT FROM AUTHOR]

Graphene is extremely sensitive to its surrounding environment. In fact, any modification on its surface, such as an adsorption of a molecule, can change its properties. The conductivity of graphene is a crucial parameter to be examined for potential graphene-based applications, especially biosensors. In this paper, we have investigated the effects of non-covalent functionalization based on π–π interaction, using 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBASE), on the conductivity of graphene-based electrodes by electrochemical techniques. Graphene layers were obtained by chemical vapor deposition (CVD) and characterized by Raman spectroscopy, Scanning Electron Microscopy (SEM), and X-Ray Diffraction (XRD). The results demonstrate the synthesis of a high quality and continuous monolayer graphene with an I2D/IG ratio = 2.71 and ID = 0. After the functionalization of graphene-based electrode with PBASE, the electrochemical analyses confirmed a p-doping effect existence influencing the conductivity by increasing the charge transfer resistance Rct from 816.5 to 2213 Ω. Furthermore, increasing the concentration of PBASE from 5 mM to 10 mM did not affect the conductivity as the Rct did not change. Solvent adsorption was found to be the main cause of the decrease in conductivity during the functionalization process. This study highlights the effect of non-covalent π-π stacking of PBASE on graphene to tune the electrical properties of graphene through functionalization processes for a better performance for their use as biosensors. [ABSTRACT FROM AUTHOR]

Emerging nanotechnologies offer numerous opportunities in the field of regenerative medicine and have been widely explored to design novel scaffolds for the regeneration and stimulation of nerve tissue. In this review, we focus on peripheral nerve regeneration. First, we introduce the biomedical problem and the present status of nerve conduits that can be used to guide, fasten and enhance regeneration. Then, we thoroughly discuss graphene as an emerging candidate in nerve tissue engineering, in light of its chemical, tribological and electrical properties. We introduce the graphene forms commonly used as neural interfaces, briefly review their applications, and discuss their potential toxicity. We then focus on the adoption of graphene in peripheral nervous system applications, a research field that has gained in the last years ever-increasing attention. We discuss the potential integration of graphene in guidance conduits, and critically review graphene interaction not only with peripheral neurons, but also with non-neural cells involved in nerve regeneration; indeed, the latter have recently emerged as central players in modulating the immune and inflammatory response and accelerating the growth of new tissue.

The synaptic devices based on various electronic materials have been widely investigated to realize functions of artificial information processing with low power consumption. In this work, a novel CVD graphene field-effect transistor is fabricated with ionic liquid gate to study the synaptic behaviors based on the electrical-double-layer mechanism. It is found that the excitative current is enhanced with the pulse width, voltage amplitude and frequency. With different situations of the applied pulse voltage, the inhibitory and excitatory behaviors are successfully simulated, at the same time the short-term memory is also realized. The corresponding ions migration and charge density variation are analyzed in the different time segments. This work provides the guidance for the design of artificial synaptic electronics with ionic liquid gate for low-power computing application. [ABSTRACT FROM AUTHOR]

In this work, we report a novel method for the label-free detection of cyanotoxin molecules based on a direct assay utilizing a graphene-modified surface plasmon resonance (SPR) aptasensor. Molecular dynamic simulation of the aptamer's interaction with cylindrospermopsin (CYN) reveals the strongest binding sites between C18–C26 pairs. To modify the SPR sensor, the wet transfer method of CVD monolayer graphene was used. For the first time, we report the use of graphene functionalized by an aptamer as a bioreceptor in conjunction with SPR for the detection of CYN. In a direct assay with an anti-CYN aptamer, we demonstrated a noticeable change in the optical signal in response to the concentrations far below the maximum tolerable level of 1 µg/L and high specificity. [ABSTRACT FROM AUTHOR]

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]

Large area graphene patterning is critical for applications. Current graphene patterning techniques, such as electron beam lithography and nano imprint lithography, are time consuming and can scale unfavorably with sample size. Resist-based masking and subsequent dry plasma etching can lead to high roughness edges with no alignment to the underlying graphene crystal orientations. In this study, we present hot punching as a novel and feasible method for patterning of chemical vapor deposition (CVD) graphene sheets supported by a polyvinylalcohol (PVA) layer. Additionally, we observe the effect of such hot punching on graphene supported by PVA via optical microscopy, Raman spectroscopy, AFM, and TEM, including wrinkling, strain and the formation of nanoribbons with crystallographically aligned and smooth edges due to fracturing. We present hot punching as a facile technique for the production of arrays of such nanoribbons., (Creative Commons Attribution license.)

Remote epitaxy is an emerging materials synthesis technique which employs a 2D interface layer, often graphene, to enable the epitaxial deposition of low defect single crystal films while restricting bonding between the growth layer and the underlying substrate. This allows for the subsequent release of the epitaxial film for integration with other systems and reuse of growth substrates. This approach is applicable to material systems with an ionic component to their bonding, making it notably appealing for IIIâ€"V alloys, which are a technologically important family of materials. Chemical vapour deposition growth of graphene and wet transfer to a IIIâ€"V substrate with a polymer handle is a potentially scalable and low cost approach to producing the required growth surface for remote epitaxy of these materials, however, the presence of water promotes the formation of a IIIâ€"V oxide layer, which degrades the quality of subsequently grown epitaxial films. This work demonstrates the use of an argon ion beam for the controlled introduction of defects in a monolayer graphene interface layer to enable the growth of a single crystal GaAs film by molecular beam epitaxy, despite the presence of a native oxide at the substrate/graphene interface. A hybrid mechanism of defect seeded lateral overgrowth with remote epitaxy contributing the coalescence of the film is indicated. The exfoliation of the GaAs films reveals the presence of defect seeded nucleation sites, highlighting the need to balance the benefits of defect seeding on crystal quality against the requirement for subsequent exfoliation of the film, for future large area development of this approach. [ABSTRACT FROM AUTHOR]

Single-layer (SLG)/few-layer (FLG) and multilayer graphene (MLG) (>15 layers) samples were obtained using the CVD method on high-textured Cu foil catalysts. In turn, plasma-assisted molecular beam epitaxy was applied to carry out the GaN graphene-assisted growth. A thin AlN layer was used at the initial stage to promote the nucleation process. The effect of graphene defectiveness and thickness on the quality of the GaN epilayers was studied. The bilayer graphene showed the lowest strain and provided optimal conditions for the growth of GaN/AlN. Theoretical studies based on the density functional theory have shown that the energy of interaction between graphene and AlN is almost the same as between graphite sheets (194 mJ/m2). However, the presence of vacancies and other defects as well as compression-induced ripples and nitrogen doping leads to a significant change in this energy. [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]

In this work, the effect of the ion fluence-dependent defect formation on the modification of surface electronic and optical properties of graphene has been investigated. The chemical vapor deposited (CVD) graphene samples were irradiated with 70 MeV Si+5 swift heavy ions (SHI) with varying fluence to study the defect formation mechanism and the role of ion beam fluence in modulating its surface electronic property such as work function. At a low ion dose, acceptor doping via vacancy creation was observed. The redshift in absorption peak position, the blueshift in Raman peak position, and the enhancement in work function values are indicators of such doping effect at low fluence. In contrast, the dense electronic excitation-dominated extended defects were realized at a higher ion dose showing strain-induced modifications in the optoelectronic properties of graphene. This work offers an effective strategy to control defect formation and systematically alter graphene's optical and electronic properties. The experimental findings will be useful for the applicability of graphene under extreme radiation conditions and space research. [ABSTRACT FROM AUTHOR]

Large-area high-quality graphene enabled by chemical vapor deposition (CVD) can possibly pave the path for advanced flexible electronics and spintronics. CVD-grown method utilizing liquid carbon precursor has recently been demonstrated as an appealing choice for mass graphene production, thanks to its low cost and safe operation. However, the quality of the graphene film has been the major obstacle for the implementation of the liquid-precursor-based CVD method. Here we report the growth of centimeter-scale easily-transferable single-layer graphene (SLG) using acetone as a liquid carbon precursor. The dry-transfer technique was used to prepare the graphene device. The typical mobility of the dry-transferred SLG device is as high as 12 500 cm2 Vâˆ'1 sâˆ'1 at room temperature. Thanks to the high quality of the device, the robust quantum Hall effect can survive up to room temperature. The excellent device quality also enables us to observe the Shubnikovâ€"de Haas oscillation in the low magnetic field regime and systemically study the leading scattering mechanism. We extracted both the transport scattering time Ď„ t and the quantum scattering time Ď„ q over a wide range of carrier density. The ratio of the scattering times suggests that the charged-impurity resided near the surface of the graphene restricted the device performance. [ABSTRACT FROM AUTHOR]

The growth of high-quality continuous film of graphene on less than 1 μ m-thick Cu film is proven to be a challenging task due to the solid-state dewetting of Cu during the high-temperature chemical vapor deposition (CVD) process. In this paper, we introduce the use of nanostructured black Si (b-Si) as a template for Cu evaporation to mitigate the dewetting of Cu thin film. Using a cold-wall CVD system at a process temperature of 825 ∘ C, even Cu thickness, t Cu = 6 0 0 nm on polished SiO2/Si substrate is poor for maintaining Cu as a continuous film. If the polished SiO2/Si is replaced with SiO2/b-Si, the minimum t Cu = 4 0 0 nm is sufficient. According to the Cu trapping mechanism, moving Cu particle is trapped in the nanostructured trenches of SiO2/b-Si during annealing and CVD growth processes. Continuous monolayer graphene with a grain size of ∼ 1 μ m without defect is obtained on Cu/SiO2/b-Si substrate. The improved adhesion of Cu to the SiO2/b-Si enables dry-transfer of graphene by mechanical peeling using a polyvinyl alcohol (PVA) film. Our solution is promising for obtaining flat graphene and a recyclable Cu/SiO2/b-Si substrate. [ABSTRACT FROM AUTHOR]

Stability is a vitally important criterion to measure the effectiveness of a membrane, especially in the engineering fields. Although polymeric membranes are widely used, stability problems frequently arise in long-term applications. Two-dimensional atomically thin materials, especially graphene, have aroused wide interest from membrane science due to the excellent physical and chemical properties and, most importantly, the ability to simultaneously achieve high selectivity and high permeability. However, defects are generated in the growth and transfer process, impairing the desired properties and resulting in unstable performance of graphene membranes. Therefore, overcoming the negative effects from defects is urgent for their applications. Here, we report a facile route to produce stability-enhanced double-layer graphene membranes and provide an application paradigm of graphene in a membrane-based precision instrument, the membrane-based total organic carbon (TOC) analyzer. The first layer and the second layer of graphene were respectively transferred onto the polymer substrate through phase inversion and heat pressing methods. Then, Ar plasma was employed to accurately create high-density (1011–1012 cm–2) nanopores in the graphene lattice. The obtained double-layer graphene membranes could function normally in the TOC analyzer with a higher precision (signal linear correlation R2 of 99.64%) than the polymeric membranes (99.16% for poly-(vinylidene fluoride) and 99.33% for Teflon). Furthermore, the stability of double-layer graphene was evidently better (RSD (relative standard deviation) of 1.93%) than that of the single-layer graphene membrane (3.12%) in the continuous measurement for 7 days. Moreover, the stability-enhanced double-layer graphene membranes could work properly for more than 30 days (RSD of 2.50%), which have potential to satisfy the industry standards. Therefore, our work not only provides a solution to enhance the stability of membranes, which is significant in engineering fields, but also bridges the gap between the "proof-of-concept" in the laboratory and the application of graphene in membrane-based precision instruments. [ABSTRACT FROM AUTHOR]

We report on nano-infrared (IR) imaging studies of confined plasmon modes inside patterned graphene nanoribbons (GNRs) fabricated with high-quality chemical-vapor-deposited (CVD) graphene on Al2O3 substrates. The confined geometry of these ribbons leads to distinct mode patterns and strong field enhancement, both of which evolve systematically with the ribbon width. In addition, spectroscopic nanoimaging in the mid-infrared range 850-1450 cm(-1) allowed us to evaluate the effect of the substrate phonons on the plasmon damping. Furthermore, we observed edge plasmons: peculiar one-dimensional modes propagating strictly along the edges of our patterned graphene nanostructures.

Graphene transfer onto ceramics, like Si/SiO2, is well-developed and described in the literature. However, it is problematic for other ceramic materials (e.g., Al2O3 and ZrO2), especially porous ones. In this case, it is mainly due to poor adhesion to the substrate, resulting in strong degradation of the graphene. For these reasons, the research topic of this study was undertaken. This article presents research on the development of the methodology of graphene transfer onto ceramic Al2O3 surfaces. Polycrystalline graphene chemical vapour deposition (CVD) monolayer and quasimonocrystalline high-strength metallurgical graphene (HSMG®) synthesised on liquid copper were used. When developing the transfer methodology, the focus was on solving the problem of graphene adhesion to the surface of this type of ceramic, and thus reducing the degree of graphene deterioration at the stage of producing a ceramic–graphene composite, which stands in the way of its practical use. Plasma and chemical ceramic surface modification were applied to change its hydrophobicity, and thus to improve the adhesion between the graphene and ceramic. The modification included the use of dielectric barrier discharge (DBD) plasma, oxygen plasma (RF PACVD method - Radio Frequency Plasma Assisted Chemical Vapour Deposition), and hydrofluoric acid treatment. Changes in surface properties caused by the modifications were determined by measuring the contact angle and (in the case of chemical modification) measuring the degree of surface development. The effectiveness of the applied surface preparation methodology was evaluated based on the damage degree of CVD and HSMG® graphene layer transferred onto modified Al2O3 using optical microscopy and Raman spectroscopy. The best average ID/IG ratio for the transferred HSMG® graphene was obtained after oxygen plasma modification (0.63 ± 0.18) and for CVD, graphene DBD plasma was the most appropriate method (0.17 ± 0.09). The total area of graphene defects after transfer to Al2O3 was the smallest for HSMG® graphene after modification with O2 plasma (0.251 mm2/cm2), and for CVD graphene after surface modification with DBD plasma (0.083 mm2/cm2).

Graphene has received much attention in multiple fields due to its unique physical and electrical properties, especially in the microelectronic application. Nowadays, graphene can be catalytically produced on active substrates by chemical vapor deposition and then transferred to the target substrates. However, the widely used wet transfer technique often causes inevitable structural damage and surface contamination to the synthetic CVD graphene, thus hindering its application in high-performance devices. There have been numerous reviews on graphene growth and transfer techniques. Thus, this review is not intended to be comprehensive; instead, we focus on the advanced plasma treatment, which may play an important role in the quality improvement throughout the growth and transfer of graphene. Promising pathways for future applications are also provided.

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]

There is a constant need for Hall-effect magnetic sensors with lower noise and lower offset for the high accuracy analog applications driven primarily by industrial and automotive markets, for example, high dynamic range current sensing for battery management in electric vehicles. Graphene-based Hall sensors (GHSs) demonstrate low thermal noise due to their high carrier mobility but suffer from large low-frequency flicker noise and offset limiting the prevalent low-frequency applications. In this paper, we present the results of a recently proposed gate modulation scheme for GHSs that uses dynamic ambipolar operation to up-convert the input magnetic signal to higher modulating frequencies while the offset and flicker noise remain spectrally unchanged and thus enabling thermal noise limited performance. We implement a prototype GHS using a scalable fabrication process with CVD graphene transferred on to silicon-oxide and followed by standard thin film and subsequent photolithographic processes. The measurement results confirm the effectiveness of dynamic ambipolar gate modulation technique in producing low offset of $- 524\,\,\mu \mathrm{T}$ in conjunction with three orders of magnitude estimated improvement in the low frequency noise performance. [ABSTRACT FROM AUTHOR]

Single-layer (SLG)/few-layer (FLG) and multilayer graphene (MLG) (>15 layers) samples were obtained using the CVD method on high-textured Cu foil catalysts. In turn, plasma-assisted molecular beam epitaxy was applied to carry out the GaN graphene-assisted growth. A thin AlN layer was used at the initial stage to promote the nucleation process. The effect of graphene defectiveness and thickness on the quality of the GaN epilayers was studied. The bilayer graphene showed the lowest strain and provided optimal conditions for the growth of GaN/AlN. Theoretical studies based on the density functional theory have shown that the energy of interaction between graphene and AlN is almost the same as between graphite sheets (194 mJ/m2). However, the presence of vacancies and other defects as well as compression-induced ripples and nitrogen doping leads to a significant change in this energy.

Bidirectional interdependency between graphene doping level and ferroelectric polarization is demonstrated in graphene/PbZr0.2Ti0.8O3 hybrid structures. The polarization of the PbZr0.2Ti0.8O3 can be effectively switched with graphene electrodes and can in turn alter carrier type and density in the graphene. A complete reversal of the current-voltage hysteresis direction is observed in the graphene when external environmental factors are minimized, converting p-type graphene into n-type with an estimated carrier density change as large as ~10(13) cm(-2). Nonvolatility and reversibility are also demonstrated.

As an atomically thin electric conductor with a low density of highly mobile charge carriers, graphene is a suitable transducer for molecular adsorption. In this study, we demonstrate that the adsorption properties can be significantly enhanced with a laser-deposited TiO 2 nanolayer on top of single-layer CVD graphene, whereas the effective charge transfer between the TiO 2 -adsorbed gas molecules and graphene is retained through the interface. The formation of such a heterostructure with optimally a monolayer thick oxide combined with ultraviolet irradiation (wavelength 365 nm, intensity <1 mW/mm 2 ) dramatically enhances the gas-sensing properties. It provides an outstanding sensitivity for detecting NO 2 in the range of a few ppb to a few hundred ppb-s in air, with response times below 30 s at room temperature. The effect of visible light (436 and 546 nm) was much weaker, indicating that the excitations due to light absorption in TiO 2 play an essential role, while the characteristics of gas responses imply the involvement of both photoinduced adsorption and desorption. The sensing mechanism was confirmed by theoretical simulations on a NO 2 @Ti 8 O 16 C 50 complex under periodic boundary conditions. The proposed sensor structure has significant additional merits, such as relative insensitivity to other polluting gases (CO, SO 2 , NH 3 ) and air humidity, as well as long-term stability (>2 years) in ambient air. The results pave the way for an emerging class of gas sensor structures based on stacked 2D materials incorporating highly charge-sensitive transducer and selective receptor layers.

The large-scale production of high-quality and clean graphene devices, aiming at technological applications, has been a great challenge over the last decade. This is due to the high affinity of graphene with polymers that are usually applied in standard lithography processes and that, inevitably, modify the electrical proprieties of graphene. By Raman spectroscopy and electrical-transport investigations, we correlate the room-temperature carrier mobility of graphene devices with the size of well-ordered domains in graphene. In addition, we show that the size of these well-ordered domains is highly influenced by post-photolithography cleaning processes. Finally, we show that by using poly(dimethylglutarimide) (PMGI) as a protection layer, the production yield of CVD graphene devices is enhanced. Conversely, their electrical properties are deteriorated as compared with devices fabricated by conventional production methods.

Scanning tunneling microscopy (STM) and atomic force microscopy (AFM) images of graphene reveal either a triangular or honeycomb pattern at the atomic scale depending on the imaging parameters. The triangular patterns at the atomic scale are particularly difficult to interpret, as the maxima in the images could be every other carbon atom in the six-fold hexagonal array or even a hollow site. Carbon sites exhibit an inequivalent electronic structure in HOPG or multilayer graphene due to the presence of a carbon atom or a hollow site underneath. In this work, we report small-amplitude, simultaneous STM/AFM imaging using a metallic (tungsten) tip, of the graphene surface as-grown by chemical vapor deposition (CVD) on Cu foils. Truly simultaneous operation is possible only with the use of small oscillation amplitudes. Under a typical STM imaging regime the force interaction is found to be repulsive. Force–distance spectroscopy revealed a maximum attractive force of about 7 nN between the tip and carbon/hollow sites. We obtained different contrast between force and STM topography images for atomic features. A honeycomb pattern showing all six carbon atoms is revealed in AFM images. In one contrast type, simultaneously acquired STM topography revealed hollow sites to be brighter. In another, a triangular array with maxima located in between the two carbon atoms was acquired in STM topography.

The transfer of chemical vapor deposited (CVD) monolayer graphene by using poly-[4,5-difluoro-2,2-bis-(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF1600) fluoropolymer (FP) as a sacrificial nanolayer is demonstrated. Owing to the chemical inertness of FPs, the AF1600-assisted transfer produces an ultraclean surface with excellent transfer integrity. Compared with the widely used poly-(methyl methacrylate)-assisted transfer, AF1600-assisted transfer produces better overall transfer quality as measured by root-mean-square (RMS) roughness. Adding a noncovalent surface monolayer between the graphene and the FP facilitates the FP removal after graphene transfer, resulting in a surface with RMS roughness of 0.4–0.5 nm due to a better reduction of the surface residue after transfer. The remaining residue is found to be primarily associated with thermal-expansion ripples in the graphene that act as trapping sites for the low-molecular-weight FP particles. This work provides a scalable solution to clean CVD graphene transfer for many applications, particularly in sensors where surface cleanliness is paramount. The use of prefunctionalized graphene via self-assembled monolayers as molecular scale passivation layer could further enhance its utility as an integration scheme for graphene sensors. [ABSTRACT FROM AUTHOR]

For the first time, CVD graphene supported cobalt (II) phthalocyanine (CoPc) is investigated as a possible catalyst to replace Pt cathode in polymer electrolyte membrane (PEM) fuel cells. Impregnation method is utilized for the synthesis of CVD graphene supported CoPc catalyst. Higher heat-treatment temperatures for CoPc/CVD graphene mixtures have resulted with better electrochemical activity and stability. 5% Co/CoPc-G electrode compare to 9.3% Co/CoPc-G for 0.3 mg Co/cm2 loading has resulted reduced voltage-current characteristics due to kinetic and mass transfer limitations. Operational parameters are evaluated resulting maximum power density of 186 mW/cm2 with 9.3Co%/CoPc-Graphene, 25-psi backpressure, 100% RH and 80 °C operational temperature. Image 1 • CoPc/CVD graphene electrode is developed for acid electrolytes. • Electrochemical activity of CoPc/CVD graphene proceeds with less than 4-electron. • Heat treatment of CoPc/Graphene at 800 °C gives the best polarization response. • CoPc/Graphene has lower performance compare to CoPc/C and Pt/C electrocatalyst. [ABSTRACT FROM AUTHOR]

A method for graphene transfer which is referred to as "bifacial transfer" that allows transfer of multilayer chemical vapor deposition (CVD) graphene from both sides of a native metal substrate, such as an as‐received nickel catalyst, is presented. In traditional transfer methods, the graphene on the "non‐preferred" side, that is, the bottom of the substrate, is removed with oxygen plasma before removal of the metal catalyst in etchant solution. Although this treatment prevents undesired aggregation of the graphene films, it fails to utilize both sides of CVD‐grown graphene. The bifacial transfer method reduces the cost of multilayer graphene by allowing the transfer of graphene from both sides of the substrate. The quality of graphene transferred from both sides onto target glass and polymer substrates is compared. The results of optical microscopy, confocal Raman spectroscopy, atomic force microscopy, and electronic transport measurements suggest that the quality of the multilayer graphene on the "non‐preferred" side does not differ significantly from that of the "preferred" side. This method will allow more efficient and cost‐effective use of graphene by doubling the usable graphene per area of growth substrate, and by eliminating the need for intermediate sacrificial transfer substrates such as poly(methyl methacrylate). [ABSTRACT FROM AUTHOR]

The rarely reported defects with crack-and-fold (CAF) style graphene grown on raw Cu foils substrates by chemical vapor deposition (CVD) were examined in this study. Factors for the formation of CAF defects were explored by performing different substrate treatments and varied hydrogen inflow. A clear relationship was found between CAF defects and Cu (110) facets by electron back-scattered diffraction measurement. CAF defects were affected by the interaction between graphene and the substrate. A model with a two-step process, including cracking and folding, is established to elucidate the formation of CAF defects. CAF defects can be reduced by performing substrate treatment, varying hydrogen flow and controlling the orientation of the Cu substrate. This study was performed to improve the quality of graphene grown by CVD for industrial production. [ABSTRACT FROM AUTHOR]

The electrical properties of polycrystalline graphene grown by chemical vapor deposition (CVD) are determined by grain-related parameters—average grain size, single-crystalline grain sheet resistance, and grain boundary (GB) resistivity. However, extracting these parameters still remains challenging because of the difficulty in observing graphene GBs and decoupling the grain sheet resistance and GB resistivity. In this work, we developed an electrical characterization method that can extract the average grain size, single-crystalline grain sheet resistance, and GB resistivity simultaneously. We observed that the material property, graphene sheet resistance, could depend on the device dimension and developed an analytical resistance model based on the cumulative distribution function of the gamma distribution, explaining the effect of the GB density and distribution in the graphene channel. We applied this model to CVD-grown monolayer graphene by characterizing transmission-line model patterns and simultaneously extracted the average grain size (~5.95 μm), single-crystalline grain sheet resistance (~321 Ω/sq), and GB resistivity (~18.16 kΩ-μm) of the CVD-graphene layer. The extracted values agreed well with those obtained from scanning electron microscopy images of ultraviolet/ozone-treated GBs and the electrical characterization of graphene devices with sub-micrometer channel lengths.

Single-crystal graphene (SCG) wafers are needed to enable mass-electronics and optoelectronics owing to their excellent properties and compatibility with silicon-based technology. Controlled synthesis of high-quality SCG wafers can be done exploiting single-crystal Cu(111) substrates as epitaxial growth substrates recently. However, current Cu(111) films prepared by magnetron sputtering on single-crystal sapphire wafers still suffer from in-plane twin boundaries, which degrade the SCG chemical vapor deposition. Here, it is shown how to eliminate twin boundaries on Cu and achieve 4 in. Cu(111) wafers with ≈95% crystallinity. The introduction of a temperature gradient on Cu films with designed texture during annealing drives abnormal grain growth across the whole Cu wafer. In-plane twin boundaries are eliminated via migration of out-of-plane grain boundaries. SCG wafers grown on the resulting single-crystal Cu(111) substrates exhibit improved crystallinity with >97% aligned graphene domains. As-synthesized SCG wafers exhibit an average carrier mobility up to 7284 cm 2 V -1 s -1 at room temperature from 103 devices and a uniform sheet resistance with only 5% deviation in 4 in. region., (© 2023 Wiley‐VCH GmbH.)

Graphene as an atom-thick carbon material is promising for the detection of gaseous molecules owing to extremely high surface-to-volume ratio. However, the majority of graphene-based gas sensors, prepared by chemical vapor deposition (CVD), have suffered from non-uniformity in their responses. Such a high sensor-to-sensor variation in responses has not been systematically studied, limiting application of graphene gas sensors. Here we report processes that lead to a highly sensitive and uniform graphene gas sensor. We examined four types of graphene sensors by varying two conditions: (1) whether or not there is a carbon precursor while cooling down the reactor after graphene synthesis and (2) whether poly-(methyl methacrylate) (PMMA), a polymer for transferring the graphene onto another substrate, is removed by annealing at high temperature or by rinsing with acetone. Using 5 ppm dimethyl methylphosphonate (DMMP), a nerve agent simulant, as a model analyte, we found that uniform responses are obtained by cooling down the reactor without carbon precursor and by removing PMMA by annealing. Additional heat treatment of the graphene in air greatly enhances the sensitivity, regardless of the synthesis conditions, by removing residual PMMA and impurities from the graphene surface. The uniform graphene sensors enabled us to find that the edge-to-surface ratio of graphene does not affect sensitivity, whereas noise increases at higher edge-to-surface ratio. Our study presents a design rule for fabricating sensitive and uniform graphene gas sensors, which may facilitate their applications in detecting a broad range of analytes. [ABSTRACT FROM AUTHOR]

The transfer of CVD graphene grown on catalytic copper with an additional supporting substrate is different from that grown on the standalone copper foils, and the flexible polymer-based transfer supports are not quite suitable. For this purpose, we invented a wax-assisted crack-free graphene transfer method by taking advantage of the low polarity, high rigidity, and molecular-mixing nature of wax. Unlike other small-molecule transfer supports, the amorphous wax effectively mitigates the interfacial thermal stress caused by phase transition, enabling a clean and integral graphene transfer. Microscopic and spectroscopic characterizations reveal less doping defects of the wax-transferred graphene than its PMMA-transferred counterpart, demonstrating great electric properties with high electron and hole mobilities. Consequently, this new transfer method provides a universal solution for CVD graphene grown on various substrates, and paves the way for further extending their applications. Unlabelled Image • A novel solution for transfering CVD graphene grown on catalytic copper with an additional supporting substrate. • The molecular-mixing nature of wax allows alleviating the interfacial thermal stress typically incurred by small-molecule based transfer supports. [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]

This study presents a solution-gated graphene field effect transistor (GFET) for a TP53 DNA sensor using a unique coplanar electrode array integrated with a microfluidic chip. The integrated microfluidic channel controls the exact amount of solution to be delivered. The cancer-related gene, TP53, was applied over the graphene active layers to monitor the sensing performance of the solution-gated GFET. After immobilization of the probe DNA, we hybridized the target DNA with different concentrations (10 μM–1 nM) onto each electrode array. The limit of the detection value obtained herein was 1 nM. To validate the selectivity, when the noncomplementary and one-mismatched DNA molecules were injected into the microchannel, the Dirac point shift values were not significant. The shift of the Dirac point occurs owing to the doping effect caused by the negative charges of the DNA over the graphene surface. When the measurements were reproduced in eight other electrode pairs in the array structure, the transfer curves presented similar Dirac point values, i.e., approximately ±1 mV, indicating the stability of the device. The developed solution-gated GFET sensor provides a reliable measurement of the electrical characteristics and a multiplex detection for cancer diagnostics using a large area of the graphene platform. [ABSTRACT FROM AUTHOR]

Summary: Chemical vapor deposition (CVD) grown graphene‐supported PtCo catalyst was developed as a polymer electrolyte membrane fuel cell (PEMFC) cathode. The effects of cell temperature, back pressure, relative humidity, anode, and cathode flow rates on the fuel cell performance were investigated utilizing Design Expert software for statistical analysis. Cell temperature, back pressure, and relative humidity were shown to be the most critical factors to improve fuel cell performance in the presence of PtCo on CVD grown graphene. The maximum current density of 1779.5 mAcm−2 and power density of 785.38 mWcm−2 are obtained at cell temperature of 79.99°C, back pressure of 4.99 psi, relative humidity of 50%, anode flow rate of 0.156 dm3min−1, and cathode flow rate of 0.199 dm3min−1. [ABSTRACT FROM AUTHOR]

Nano carbon-semiconductor hybrid materials such as graphene and zinc oxide (ZnO) have been vigorously explored for their direct electron transfer properties and high specific surface areas. We fabricated a three-dimensional anodic electrode catalyst nanostructure for a direct glucose fuel cell (DGFC) utilizing two-dimensional monolayer graphene and one-dimensional ZnO nanorods, which accommodate silver/nickel (Ag/Ni) nanoparticle catalyst. Glucose, as an unlimited and safe natural energy resource, has become the most popular fuel for energy storage. Ag and Ni nanoparticles, having superior catalytic activities and anti-poisoning effect, respectively, demonstrate a 73-times enhanced cell performance (550 µW cm−2 or 8 mW mg−1) when deposited on zinc oxide nanorods with a small amount of ∼0.069 mg in 0.5 M of glucose and 1 M of KOH solution at 60 oC. This three-dimensional anodic electrode catalyst nanostructure presents promise to open up a new generation of fuel cells with non-Pt, low mass loading of catalyst, and 3D nanostructure electrodes for high electrochemical performances. [ABSTRACT FROM AUTHOR]

Electrochemical deposition of cobalt nanoparticles was used to modify carrier transport properties of single-layered CVD graphene at the SiO2-on-Si substrate. The structure of graphene with cobalt nanoparticles was analyzed by Raman spectroscopy and scanning electron microscopy. The effect of the deposited cobalt nanoparticles on the sheet resistance of graphene was studied in the temperature range of 4–300 K. [ABSTRACT FROM AUTHOR]

This work aims to investigate the influence of various electrode materials on the signal‐to‐noise ratio (SNR) of passive microelectrode arrays (MEAs) intended for use in neural interfaces. Noise reduction substantially improves the performance of systems which electrically interface with extracellular solutions. The MEAs are fabricated using gold, indium tin oxide (ITO), inkjet printed (IJP) graphene, and chemical vapor deposited (CVD) graphene. 3D‐printed Nylon reservoirs are adhered to glass substrates with identical MEA patterns and filled with neuronal cell culture media. To precisely control the electrode area and minimize the parasitic coupling of metal interconnects and solution, SU‐8 photoresist is patterned to expose only the area of the electrode to solution and cap the remainder of the sample. Voltage signals with varying amplitude and frequencies are applied to the solution using glass micropipettes, and the response is measured on an oscilloscope from a microprobe placed on the contact pad external to the reservoir. The time domain response signal is transformed into a frequency spectrum, and SNR is calculated. As the magnitude or the frequency of the input signal gets larger, a significantly increased signal‐to‐noise ratio was observed in CVD graphene MEAs compared to others. This result indicates that 2‐dimensional nanomaterials such as graphene can provide better signal integrity and potentially lead to improved performance in hybrid neural interface systems. [ABSTRACT FROM AUTHOR]

Abstract The development of miniaturized and portable electronic devices urgently demands the miniaturization and integration of power sources. Micro-supercapacitors have caught increasing attention in considering their special performance. Herein, we report a type of planar MSC based on the graphene network and nickel hydroxide nanoplates by chemical vapor deposition, mask-free patterning and spray-coating methods. Different interdigital width of graphene network based micro-supercapacitors are researched and the optimized micro-supercapacitor exhibits a high capacitance of 0.34 mF/cm2 at 10 mV/s. Aiming at improving the capacitance and performance of the micro-device, NiOOH/Ni(OH) 2 nanoplates are uniformly deposited on CVD graphene surfaces to obtain all-solid-state graphene/NiOOH/Ni(OH) 2 micro-supercapacitors. This optimal micro-device displays an outstanding capacitance of 0.75 mF/cm2 at 5 mV/s (7.54 F/cm3), a maximum energy density of 1.04 mWh/cm3 and retention of 80% of its original capacity value after 3000 charge-discharge cycles. The enhancement of electrochemical performance of graphene/NiOOH/Ni(OH) 2 micro-supercapacitor is profit by the reversible redox involving two kind of phase transformation of Ni(OH) 2 and NiOOH in both positive and negative. These results demonstrate that our graphene based MSCs provide the potential as self-charging power unit for future integrated electronic applications. Graphical abstract Image 1 Highlights • Graphene and graphene/NiOOH/Ni(OH) 2 composites were the active materials of MSCs. • The optimal GMSC and GNMSC were obtained and analyzed. • The electrochemical mechanism in GNMSC was discussed in detail. [ABSTRACT FROM AUTHOR]

In this work, we report a novel method of label-free detection of small molecules based on direct observation of interferometric signal change in graphene-modified glasses. The interferometric sensor chips are fabricated via a conventional wet transfer method of CVD-grown graphene onto the glass coverslips, lowering the device cost and allowing for upscaling the sensor fabrication. For the first time, we report the use of graphene functionalized by the aptamer as the bioreceptor, in conjunction with Spectral-Phase Interferometry (SPI) for detection of ochratoxin A (OTA). In a direct assay with an OTA-specific aptamer, we demonstrated a quick and significant change of the optical signal in response to the maximum tolerable level of OTA concentration. The sensor regeneration is possible in urea solution. The developed platform enables a direct method of kinetic analysis of small molecules using a low-cost optical chip with a graphene-aptamer sensing layer.

We report improved control over the quality and uniformity of CVD graphene devices through a novel fabrication technique. An overlying HSQ pinning dielectric is used to physically anchor and protect the graphene sheet, resulting in electron and hole motilities of 25 600 and 23 700 cm2/Vs, respectively, record-breaking values for CVD graphene devices. Transitioning from traditional 3-D bulk materials to loosely adhered 2-D graphene sheets, the presented process is expected to bring new focus to post-transfer passivation as a means of fabricating graphene devices closer to their theoretical limits. Based on the extracted mean-free-path (MFP) from the experimental data, the graphene interconnect is benchmarked against the copper interconnect at various widths and edge roughness. Results demonstrate the importance of edge smoothness and MFP, which dictate the potential benefits of graphene interconnects at a narrow dimension.

Flexible strain sensors, as the core member of the family of smart electronic devices, along with reasonable sensing range and sensitivity plus low cost, have rose a huge consumer market and also immense interests in fundamental studies and technological applications, especially in the field of biomimetic robots movement detection and human health condition monitoring. In this paper, we propose a new flexible strain sensor based on thick CVD graphene film and its low-cost fabrication strategy by using the commercial adhesive tape as flexible substrate. The tensile tests in a strain range of ∼ 30% were implemented, and a gage factor of 30 was achieved under high strain condition. The optical microscopic observation with different strains showed the evolution of cracks in graphene film. Together with commonly used platelet overlap theory and percolation network theory for sensor resistance modeling, we established an overlap destructive resistance model to analyze the sensing mechanism of our devices, which fitted the experimental data very well. The finding of difference of fitting parameters in small and large strain ranges revealed the multiple stage feature of graphene crack evolution. The resistance fallback phenomenon due to the viscoelasticity of flexible substrate was analyzed. Our flexible strain sensor with low cost and simple fabrication process exhibits great potential for commercial applications. Using a commercial 3M tape as a flexible substrate, a low-cost flexible strain sensor has been successfully fabricated with thick nickel-based CVD graphene as a sensitive material. It was found by optical microscopy that the graphene film showed large-scale cracks under tensile strain. Such graphene flexible sensor achieves a balance between gauge factor and sensing range, and reduces costs with a simple process. [ABSTRACT FROM AUTHOR]

Abstract Continuous-phase, porous graphene was produced by CVD process and tested for suitability as catalyst and catalyst support for polymer electrolyte membrane (PEM) fuel cells. N-doping of CVD graphene was carried by NH 3 gas flown over graphene for a given time. Ultralow Pt was sputter deposited onto porous, continuous phase N-doped graphene. Oxygen reduction reaction (ORR) activity by Rotating Disc Electrode (RDE) in 0,1 M HClO 4 electrolyte and PEM fuel cell performance were measured. N-doping and thicker Pt sputtering increases reduction current in RDE measurements. Sputter deposition of 1 nm and 10 nm Pt on CVD graphene (2.1 and 21.45 μgPt/cm2 loading) has shown orders of magnitude increase in current compare to only-graphene samples. In fuel cell testing, sputter deposited Pt layer of 10 nm has provided 2.5 A/mgPt at 0.5 V polarization while 1 nm samples shows 15 A/mgPt performance at the same voltage. Graphical abstract Image 1 Highlights • Continuous phase CVD graphene utilized as PEM fuel cell electrode. • PEM fuel cell operation with N-dopped graphene without any metal catalyst gives current. • Sputter deposition of 1 nm Pt has shown orders of magnitude increase in fuel cell current. • 10 nm Pt deposition has provided 2,5 A/mgPt versus 1 nm gives 15 A/mgPt in fuel cell operation. [ABSTRACT FROM AUTHOR]