Field emission (FE) has been extensively explored from various exotic low dimensional carbon nanomaterials, such as amorphous carbon films, 1 single and multiwalled carbon nanotubes (CNTs), 2 tubular graphitic cones, 3 vertically aligned nanowalls, 4 few-layered graphene (FLG) nanoflakes, 5,6 and, more recently, from doped and pristine graphene. 7,8 Graphene, a two-dimensional monatomic plane layer of hexagonally arrayed sp 2-hybridized carbon atoms forms the backbone of all the above-mentioned carbon nanostructures. 9 The highly desirable properties of graphene, such as atomic thickness, excellent electrical conductivity, and high aspect ratio, make it an ideal candidate for field emission applications. 7-9 Also, as compared to CNTs, the presence of a large number of edges may render graphene superior for electron tunneling. 7 Although FE in CNTs is highly efficient, it has been shown that heteroatom doping by elements, such as nitrogen, can further reduce the effective tunneling potential barrier, thereby reducing the turn-on field and significantly increasing the electron emission current. 10,11 Nitrogen acts as an electron donor in CNTs because it has five valence electrons and causes a shift in the Fermi level (E F) to the conduction band and increases the electron density of states (DOS). In the case of graphene, theoretical studies have shown that substitutional heteroatom doping can modulate the band structure of graphene, leading to a metal-semiconductor transition, thereby expanding the applications of graphene. 12,13 Although Malesevic et al. 5 and Qi et al. 6 have shown the field emission behavior of pristine and Ar plasma-treated FLG nanoflakes, respectively, to the best of our knowledge, until now, there ' EXPERIMENTAL SECTION The synthesis of FLGs was carried out in a SEKI MPECVD deposition system, equipped with a 1.5 kW, 2.45 GHz microwave source. The substrates used were bare n-type heavily doped Si wafers (resistivity < 0.005 Ω cm) (10 mm  10 mm). Prior to growth, the substrates were pretreated with N 2 plasma at 650 W at 40 Torr while the substrate temperature was maintained at 900°C. Synthesis was then carried out using CH 4 /N 2 (gas flow

We report the development of a semiconductor nanorod-carbon nanotube based platform for wire-free, light induced retina stimulation. A plasma polymerized acrylic acid midlayer was used to achieve covalent conjugation of semiconductor nanorods directly onto neuro-adhesive, three-dimensional carbon nanotube surfaces. Photocurrent, photovoltage, and fluorescence lifetime measurements validate efficient charge transfer between the nanorods and the carbon nanotube films. Successful stimulation of a light-insensitive chick retina suggests the potential use of this novel platform in future artificial retina applications.

Composites of few layered graphene (G) and platinum (Pt) nanoparticles (NP) with different loadings of Pt were used as counter electrode (CE) in dye-sensitized solar cell (DSSC). NPs were deposited directly on to G using pulsed laser ablation method (PLD). DSSCs formed using the composite CEs show improved performance compared to conventional Pt thin film electrode (Std Pt) and unsupported Pt NPs. Composite with 27% loading of Pt shows 45% higher efficiency (η = 2.9%), greater short circuit current (J(sc) = 6.67 mA cm(-2)), and open circuit voltage (V(oc) = 0.74 V) without any loss of the fill factor (FF = 58%) as compared to the cells fabricated using Std Pt electrodes. Values of η, J(sc) and V(oc) for DSSC using Std Pt CE were 2%, 5.05 mA cm(-2) and 0.68 V, respectively. Electrochemical impedance spectroscopy using I(-)(3)/I(-) redox couple confirm lower values of charge transfer resistance for the composite electrodes, e.g., 2.36 Ω cm(2) as opposed to 7.73 Ω cm(2) of Std Pt. The better catalytic activity of these composite materials is also reflected in the stronger I(-)(3) reduction peaks in cyclic voltammetry scans.

A platinum free counter electrode for dye sensitized solar cells was developed using graphene platelets (GP) supported nickel nanoparticles (NPs) as the active catalyst. Few layered GP were prepared by chemical oxidation of graphite powders followed by thermal exfoliation and reduction. The nanoparticles of nickel were deposited directly onto the platelets by pulsed laser ablation. The composite electrodes of GP and Ni nanoparticles (GP-Ni) thus obtained showed better performance compared to conventional Pt thin film electrodes (Std Pt) and unsupported Ni NPs. The efficiencies of the cells fabricated using GP-Ni, Std Pt and Ni NP CEs were 2.19%, 2% and 1.62%, respectively. The GP-Ni composite solar cell operated with an open circuit voltage of 0.7 V and a fill factor of 0.6. Electrochemical impedance spectroscopy using the I(3)(-)/I(-) redox couple confirms lower values of charge transfer resistance for the composite electrodes, 4.67 Ω cm(2) as opposed to 7.73 Ω cm(2) of Std Pt. The better catalytic capability of these composite materials is also reflected in the stronger I(3)(-) reduction peaks in cyclic voltammetry scans.

Wearable electronics offer new opportunities in a wide range of applications, especially sweat analysis using skin sensors. A fundamental challenge in these applications is the formation of sensitive and stable electrodes. In this article we report the development of a wearable sensor based on carbon nanotube (CNT) electrode arrays for sweat sensing. Solid-state ion selective electrodes (ISEs), sensitive to Na ions, were prepared by drop coating plasticized poly(vinyl chloride) (PVC) doped with ionophore and ion exchanger on CNT electrodes. The ion selective membrane (ISM) filled the intertubular spaces of the highly porous CNT film and formed an attachment that was stronger than that achieved with flat Au, Pt, or carbon electrodes. Concentration of the ISM solution used influenced the attachment to the CNT film, the ISM surface morphology, and the overall performance of the sensor. Sensitivity of 56 ± 3 mV/decade to Na ions was achieved. Optimized solid-state reference electrodes (REs), suitable for wearable applications, were prepared by coating CNT electrodes with colloidal dispersion of Ag/AgCl, agarose hydrogel with 0.5 M NaCl, and a passivation layer of PVC doped with NaCl. The CNT-based REs had low sensitivity (-1.7 ± 1.2 mV/decade) toward the NaCl solution and high repeatability and were superior to bare Ag/AgCl, metals, carbon, and CNT films, reported previously as REs. CNT-based ISEs were calibrated against CNT-based REs, and the short-term stability of the system was tested. We demonstrate that CNT-based devices implemented on a flexible support are a very attractive platform for future wearable technology devices.