The synthesis of graphene on cubic silicon carbide on silicon pseudosubstrates draws enormous interest due to the potential integration of the 2D material with the well-established silicon technology and processing. However, the control of transport properties over large scales on this platform, essential for integrated electronics and photonics applications, has lagged behind so far, due to limitations such as 3C-SiC/Si interface instability and nonuniform graphene coverage. We address these issues by obtaining an epitaxial graphene (EG) onto 3C-SiC on a highly resistive silicon substrate using an alloy-mediated, solidsource graphene synthesis. We report the transport properties of EG grown over large areas directly on 3C-SiC(100) and 3C-SiC(111) substrates, and we present the corresponding physical models. We observe that the carrier transport of EG/3C-SiC is dominated by the graphene−substrate interaction rather than the EG grain size, sharing the same conductivity and same inverse power law as EG on 4H-or 6H-SiC(0001) substrates although the grain sizes for the latter are vastly different. In addition, we show that the induced oxidation/silicates at the EG/ 3C-SiC interface generate a p-type charge in this graphene, particularly high for the EG/3C-SiC(001). When silicates are at the interface, the presence of a buffer layer in the EG/3C-SiC(111) system is found to reduce somewhat the charge transfer. This work also indicates that a renewed focus on the understanding and engineering of the EG interfaces could very well enable the long sought-after graphene-based electronics and photonics integrated on silicon.

Brain-machine interfaces are key components for the development of hands-free, brain -controlled devices. Electroencephalogram (EEG) electrodes are particularly attractive for harvesting the neural signals in a non-invasive fashion. Here, we explore the use of epitaxial graphene grown on silicon carbide on silicon for detecting the electroencephalogram signals with high sensitivity. This dry and non-invasive approach exhibits a markedly improved skin contact impedance when benchmarked to commercial dry electrodes, as well as superior robustness, allowing prolonged and repeated use also in a highly saline environment. In addition, we report the newly -observed phenomenon of surface conditioning of the epitaxial graphene electrodes. The prolonged contact of the epitaxial graphene with the skin electrolytes functionalize the grain boundaries of the graphene, leading to the formation of a thin surface film of water through physisorption and consequently reducing its contact impedance by more than 75%. This effect is primed in highly saline environments, and could be also further tailored as pre-conditioning to enhance the performance and reliability of the epitaxial graphene sensors.

The formation of liquid crystal (LC) phases in graphene oxide (GO) aqueous solution is utilized to develop high-performance supercapacitors. To investigate the effect of LC formation on the properties of subsequently reduced GO (rGO), we compare films prepared through blade-coating of viscous LC-GO solution and ultrasonic spray-coating of diluted GO aqueous dispersion. After hydrothermal reduction under identical conditions, the films show different morphology, oxygen content, and specific capacitance. Trapped water in the LC GO film plays a role in preventing restacking of sheets and facilitating the removal of oxygenated groups during the reduction process. In device architectures with either liquid or polymer electrolyte, the specific capacitance of the blade-coated film is twice as high as that of the spray-coated one. For a blade-coated film with mass loading of 0.115 mg/cm(2), the specific capacitance reaches 286 F/g in aqueous electrolyte and 263 F/g in gelled electrolyte, respectively. This study suggests a route to pilot-scale production of high-performance graphene supercapacitors through blade-coated LC-GO films.

A novel approach to improve the specific capacitance of reduced graphene oxide (rGO) films is reported. We combine the aqueous dispersion of liquid-crystalline GO incorporating salt and urea with a blade-coating technique to make hybrid films. After drying, stacked GO sheets mediated by solidified NaCl and urea are hydrothermally reduced, resulting in a nanoporous film consisting of rumpled N-doped rGO sheets. As a supercapacitor electrode, the film exhibits a high gravimetric specific capacitance of 425 F g and a record volumetric specific capacitance of 693 F cm at 1 A g in 1 M HSO aqueous electrolyte when integrated into a symmetric cell. When using LiSO aqueous electrolyte, which can extend the potential window to 1.6 V, the device exhibits high energy densities up to 35 Wh kg, and high power densities up to 10 W kg. This novel strategy to intercalate solidified chemicals into stacked GO sheets to functionalize them and prevent them from restacking provides a promising route toward supercapacitors with high specific capacitance and energy density.

Growing graphene on SiC thin films on Si is a cheaper alternative to the growth on bulk SiC, and for this reason it has been recently intensively investigated. Here we study the effect of hydrogen intercalation on epitaxial graphene obtained by high temperature annealing on 3C-SiC/Si(111) in ultra-high vacuum. By using a combination of core-level photoelectron spectroscopy, low energy electron diffraction, and near-edge x-ray absorption fine structure (NEXAFS) we find that hydrogen saturates the Si atoms at the topmost layer of the substrate, leading to free-standing graphene on 3C-SiC/Si(111). The intercalated hydrogen fully desorbs after heating the sample at 850 °C and the buffer layer appears again, similar to what has been reported for bulk SiC. However, the NEXAFS analysis sheds new light on the effect of hydrogen intercalation, showing an improvement of graphene's flatness after annealing in atomic H at 600 °C. These results provide new insight into free-standing graphene fabrication on SiC/Si thin films.

Epitaxial growth of graphene on SiC is a scalable procedure that does not require any further transfer step, making this an ideal platform for graphene nanostructure fabrication. Focused ion beam (FIB) is a very promising tool for exploring the reduction of the lateral dimension of graphene on SiC to the nanometre scale. However, exposure of graphene to the Ga beam causes significant surface damage through amorphisation and contamination, preventing epitaxial graphene growth. In this paper we demonstrate that combining a protective silicon layer with FIB patterning implemented prior to graphene growth can significantly reduce the damage associated with FIB milling. Using this approach, we successfully achieved graphene growth over 3C-SiC/Si FIB patterned nanostructures.

The quest for supercapacitors that can hold both high energy and power density is of increasing significance as the need for green and reliable energy storage devices grows, for both large-scale and integrated systems. While supercapacitors for integrated technologies require a solid-state approach, gel-based electrolytes are generally not as efficient as their aqueous counterparts. Here we demonstrate a strategy to enhance the performance of quasi-solid-state supercapacitors made by graphitized silicon carbide on silicon electrodes and polyvinyl alcohol (PVA) + H2SO4 gel electrolyte. The electrochemical characterization shows an increase of the specific capacitance of the cell up to 3-fold resulting from a simple agent-free, in-situ, electrochemical treatment leading to functionalization of the graphitic electrodes. The functionalization of the electrodes simultaneously enables redox reactions, without adding any redox agent, and increases the double layer contribution to the overall capacitance. The strategy and insights offered by this work hold great promise for improving quasi-solid-state, miniaturized on-chip energy storage systems, which 3 are compatible with silicon electronics. 4

The inelastic mean free path (IMFP) for carbon-based materials is notoriously challenging to model, and moving from bulk materials to 2D materials may exacerbate this problem, making the measurement of IMFP in 2D carbon materials quite critical. We present an experimental measurement for IMFP in epitaxial graphene on SiC using photoelectron spectroscopy (PES) over an electron kinetic energy range of 50-1150 eV. The results suggest that the existing models for IMFP may not adequately capture the physics of electron interactions in 2D materials. Our experimental values exceed the theoretical predictions and experimental values of the IMFP in graphite for all energies through this range. We emphasize the significant effect of interface and demonstrate that the IMFP in the so-called 'buffer layer' is smaller than for free-standing graphene.