Fabrication of flexible and free-standing graphene fiber based microelectrode arrays with a thin platinum coating, as a current collector, results in a structure with low impedance, high surface area and excellent electrochemical properties. This modification results in a strong synergistic effect between these two constituents consequently leading to a robust and superior hybrid material with better performance compared to either graphene electrode or Pt electrode. Low impedance and porous structure of the graphene fiber results in an unrivalled charge injection capacity of 10.34 mC/cm 2 with ability to record and detect neuronal activity. Then, the thin Pt layer transfers the collected signals along the microelectrode efficiently. In-vivo studies show that microelectrodes implanted in the rat cerebral cortex can detect neuronal activity with remarkably high signal-to-noise ratio of 9.2 dB at area as small as an individual neuron.
Stoichiometric and pure Al2O3 gate dielectric films were grown on n-type 4H-SiC by a thermal atomic layer deposition process. The electrical properties of both amorphous and epitaxial Al2O3 films were studied by capacitance-voltage and current-voltage measurements of metal-oxide-semiconductor capacitors. A dielectric constant of 9 and a flatband voltage shift of +1.3V were determined. A leakage current density of 10−3A∕cm2 at 8MV∕cm was obtained for the amorphous Al2O3 films, lower than that of any high-κ gate oxide on 4H-SiC reported to date. A Fowler-Nordheim tunneling mechanism was used to determine an Al2O3∕4H-SiC barrier height of 1.58eV. Higher leakage current was obtained for the epitaxial γ-Al2O3 films, likely due to grain boundary conduction.
Crystalline silicon carbide (SiC) and silicon (Si) biocompatibility was evaluated in vitro by directly culturing three skin and connective tissue cell lines, two immortalized neural cell lines, and platelet-rich plasma (PRP) on these semiconducting substrates. The experiments were performed specifically for the three adopted SiC polytypes, namely 3C-, 4H- and 6H-SiC, and the results were compared to those obtained for Si crystals. Cell proliferation and adhesion quality were studied using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays and fluorescent microscopy. For the neural cells studied AFM was also used to quantify the filopodia and lamellipodia extensions on the surface of the tested materials. Fluorescent microscopy was also used to assess platelet adhesion to the semiconductor surfaces where significantly lower values of platelet adhesion to 3C-SiC was observed compared to Si. The reported results show that SiC is indeed a more biocompatible substrate than Si. While there were some differences among the degree of biocompatibility of the various SiC polytypes tested, SiC appears to be a highly biocompatible material in vitro that is also somewhat hemocompatible. This extremely intriguing result appears to put SiC into a unique class of materials that is both bio- and hemo-compatible and is, to the best of our knowledge, the only semiconductor with this property.
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