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Abstract Aiming at the production of light, porous, conductive, biosafe composites, in this paper we are presenting a novel fabrication method for monolithic, three-dimensional (3D) graphene foam (GF)/porous polymer composites. The synthesis adopts a novel process architecture by using Ni foam templates in an inductive heating chemical vapor deposition growth process, and by removing Ni chemically while retaining graphene integrity by the reversible application of cyclododecane (CD); finally, nondestructive coating procedures with polycaprolactone (PCL) solutions have been developed. The composites can be optimized to enhance electrical conduction, flexibility and mechanical properties, while mixing PCL and CD allows to coat the GF with a novel mesoporous polymer coating. By tuning the GF properties, the typical electrical resistance of the 3D forms can be reduced to a few 10 s of Ohms, values that are maintained after the PCL coatings. The current study achieved a GF fraction ranging between 1 and 7.3 wt%, with even the lower graphene content composites showing acceptable electrical and mechanical properties. The properties of these conductive 3D-GF/PCL composites are in line with the requirements for applications in the field of nerve tissue engineering. Graphical abstract

Carbon-based nanomaterials, such as carbon dots (CDs) and graphene (Gr), feature outstanding optical and electronic properties. Hence, their integration in optoelectronic and photonic devices is easier thanks to their low dimensionality and offers the possibility to reach high-quality performances. In this context, the combination of CDs and Gr into new nanocomposite materials CDs/Gr can further improve their optoelectronic properties and eventually create new ones, paving the way for the development of advanced carbon nanotechnology. In this work, we have thoroughly investigated the structural and emission properties of CDs deposited on single-layer and bilayer graphene lying on a SiO2/Si substrate. A systematic Raman analysis points out that bilayer (BL) graphene grown by chemical vapor deposition does not always respect the Bernal (AB) stacking, but it is rather a mixture of twisted bilayer (t-BL) featuring domains with different twist angles. Moreover, in-depth micro-photoluminescence measurements, combined with atomic force microscopy (AFM) morphological analysis, show that CD emission efficiency is strongly depleted by the presence of graphene and in particular is dependent on the number of layers as well as on the twist angle of BL graphene. Finally, we propose a model which explains these results on the basis of photoinduced charge-transfer processes, taking into account the energy levels of the hybrid nanosystem formed by coupling CDs with t-BL/SiO2.

In this paper, a novel 4H-SiC metal–semiconductor-metal photodetector design based on Graphene electrode engineering and gold nanoparticles is proposed. The benefits of using an intense light trapping formalism to improve the optical performance of the 4H-SiC PD are investigated by means of an accurate optoelectronic model. The developed model is based on the EMT and avoids the difficulty of considering all nanoparticles. The precision assessment of the built model is carried out by comparison with the experimental data. The findings shed light on the ability of the proposed design to realize the dual task of reducing the unwanted shadowing effect and improving the absorption through Graphene electrode formalism and the Surface Plasmon Resonance effect in the 4H-SiC layer. Furthermore, to optimize the design sensing capability, the proposed model is adopted to formulate fitness functions for the multi-objective genetic algorithm. It is found that for a filling fraction of 0.02 and 7.5 nm radius, the optimized design yields 50 % increase in absorption compared to the standard designs where responsivity of 458 mA/W, PDCR of 3.05 × 106 and response time of 4.7 µs are achieved. These findings confirm the outstanding ability of the proposed design approach to boost up the PD active area for low-cost and high sensing capability, making it valuable for optoelectronic application.

Schottky-barrier solar cells (SBSCs) represent low-cost candidates for photovoltaics applications. The engineering of the interface between absorber and front electrode is crucial for reducing the dark current, blocking the majority carriers injected into the electrode, and reducing surface recombination. The presence of tailored interfacial layers between the metal electrode and the semiconductor absorber can improve the cell performance. In this work, the interface of a graphene/n-type Si SBSC by introducing a graphene-based derivative (GBD) layer meant to reduce the Schottky-barrier height (SBH) and ease the charge collection are engineered. The chemical vapor deposition (CVD) parameters are tuned to obtain the two graphene films with different structure and electrical properties: few-layer graphene (FLG) working as transparent conductive electrode and GBD layer with electron-blocking and hole-transporting properties. Test SBSCs are fabricated to evaluate the effect of the introduction of GBD as interlayer into the FLG/n-Si junction. The GBD layer reduces the recombination at the interface between graphene and n-Si, and improves the external quantum efficiency (EQE) with optical bias from 50 to 60%. The FLG/GBD/n-Si cell attains a power conversion efficiency (PCE) of ≈5%, which increase to 6.7% after a doping treatment by nitric acid vapor.

High conductive graphene films can be grown on metal foils by chemical vapor deposition (CVD). We here analyzed the use of ethanol, an economic precursor, which results also safer than commonly-used methane. A comprehensive range of process parameters were explored in order to obtain graphene films with optimal characteristics in view of their use in optoelectronics and photovoltaics. Commercially-available and electro-polished copper foils were used as substrates. By finely tuning the CVD conditions, we obtained few-layer (2-4) graphene films with good conductivity (∼500 Ohm/sq) and optical transmittance around 92-94% at 550 nm on unpolished copper foils. The growth on electro-polished copper provides instead predominantly mono-layer films with lower conductivity (≥1000 Ohm/sq) and with a transmittance of 97.4% at 550 nm. As for the device properties, graphene with optimal properties as transparent conductive film were produced by CVD on standard copper with specific process conditions.

In this work, a Raman and photoluminescence (PL) study of synthetic diamond films grown by hot filament chemical vapor deposition (CVD) on WC-Co is presented. The changes in the Raman spectrum induced by the different pretreatments of the substrate and/or different growth parameters of the films are discussed. In particular, the spectra of the films grown at 740 degrees C substrate temperature, 36 mbar pressure and 1.7% methane content in the CH4-H-2 gas mixture and after different substrate pretreatments show all the features commonly observed in nanocrystalline diamond films, overlapped with a large PL background. A significant level of compressive stress is qualitatively deduced by the shift of the diamond Raman peaks. The different pretreatments of the substrates seem to have no influence on the quality of the diamond films. On the contrary, in samples grown at 700 degrees C substrate temperature, 10 mbar pressure and 1% methane content in the CH4-H-2 gas mixture, the contribution of the non-diamond carbon phases to the Raman spectrum substantially decreases, even though the diamond Raman peak remains shifted and broad. Impurities in the films have been identified by means of low-temperature PL measurements. Wand Si-related optical centers have been clearly observed, together with a band at approximately 1.967 eV probably connected to a nitrogen-related defect center. Copyright (C) 2008 John Wiley & Sons, Ltd.

Graphene-based materials represent a useful tool for the realization of novel neural interfaces. Several studies have demonstrated the biocompatibility of graphene-based supports, but the biological interactions between graphene and neurons still pose open questions. In this work, the influence of graphene films with different characteristics on the growth and maturation of primary cortical neurons is investigated. Graphene films are grown by chemical vapor deposition progressively lowering the temperature range from 1070 to 650 °C to change the lattice structure and corresponding electrical conductivity. Two graphene-based films with different electrical properties are selected and used as substrate for growing primary cortical neurons: i) highly crystalline and conductive (grown at 1070 °C) and ii) highly disordered and 140-times less conductive (grown at 790 °C). Electron and fluorescence microscopy imaging reveal an excellent neuronal viability and the development of a mature, structured, and excitable network onto both substrates, regardless of their microstructure and electrical conductivity. The results underline that high electrical conductivity by itself is not fundamental for graphene-based neuronal interfaces, while other physico– chemical characteristics, including the atomic structure, should be also considered in the design of functional, bio-friendly templates. This finding widens the spectrum of carbon-based materials suitable for neuroscience applications., European Union (EU) 785219-Graphene Flagship-Core2, Ministero degli Affari Esteri e Cooperazione Internazionale of Italy (Farnesina-MAECI) MAE0057294, Basic Science Research Program, Creative Materials Discovery Program, International Research & Development Program through the NRF of Korea 2016M3A7B4910940 2018M3D1A1058793 2019K1A3A1A25000267, European Union's Horizon 2020 under the Marie Skodowska-Curie Action-COFUND Athenea3i grant 754446, European Union's Horizon 2020 research and innovation program under the Marie Skodowska-Curie grant 713640