S. Ravi P. Silva

Bio: S. Ravi P. Silva is an academic researcher from University of Surrey. The author has contributed to research in topics: Carbon nanotube & Graphene. The author has an hindex of 40, co-authored 226 publications receiving 6036 citations. Previous affiliations of S. Ravi P. Silva include Shanghai Jiao Tong University & Zhengzhou University.

Low-threshold cold cathodes made of nitrogen-doped chemical-vapour-deposited diamond

Abstract: BECAUSE diamond surfaces terminated with hydrogen have a negative electron affinity1–4 (the conduction band minimum lies below the vacuum level), they are expected to emit electrons spontaneously. This has led to attempts to develop 'cold cathodes'—miniaturized vacuum diodes that might have applications in microelectronics and flat-panel displays. In previous studies of electron emission from diamond grown by chemical vapour deposition5–9 (CVD), the threshold voltages for emission were more than an order of magnitude too large for use in battery-driven cold cathodes. Although low-threshold emission from caesium-coated, nitrogen-doped high-pressure synthetic diamond was reported recently10, ultimately diamond thin films grown by chemical vapour deposition (CVD) look to be the most promising material for cold-cathode applications. But to obtain low-threshold emission, it is necessary to introduce high concentrations of donor dopants such as nitrogen—something that is difficult for CVD diamond. Here we report that high concentrations of nitrogen can be incorporated into diamond films by using urea as the gaseous nitrogen source, and that such heavily doped films shown very-low-threshold electron emission, which augurs well for cold-cathode technology.

From 1D and 2D ZnO nanostructures to 3D hierarchical structures with enhanced gas sensing properties

Abstract: Facile and low cost hydrothermal routes are developed to fabricate three-dimensional (3D) hierarchical ZnO structures with high surface-to-volume ratios and an increased fraction of (0001) polar surfaces. Hierarchical ZnO nanowires (ZNWs) and nanodisks (ZNDs) assembled from initial ZnO nanostructures are prepared from sequential nucleation and growth following a hydrothermal process. These hierarchical ZnO structures display an enhancement of gas sensing performance and exhibit significantly improved sensitivity and fast response to acetone in comparison to other mono-morphological ZnO, such as nanoparticles, NWs, or NDs. In addition to the high surface-to-volume ratio due to its small size, the nanowire building blocks show the enhanced gas sensing properties mainly ascribed to the increased proportion of exposed active (0001) planes, and the formation of many nanojunctions at the interface between the initial ZnO nanostructure and secondary NWs. This work provides the route for structure induced enhancement of gas sensing performance by designing a desirable nanostructure, which could also be extended to synthesize other metal oxide nanostructures with superior gas sensing performance.

Large-area synthesis of carbon nanofibres at room temperature.

Abstract: Carbon nanotubes, first identified by Iijima1, require for their production a source of elemental carbon and a transfer of energy that is specific to the type of source and the growth environment. Methods developed so far involve arc discharge2, and vaporization using laser3,4, pyrolysis5,6 and chemical vapour deposition of hydrocarbons7. Here, we show growth of carbon nanofibres from radio-frequency plasma-enhanced chemical vapour deposition at room temperature, which was made possible by substituting the thermal energy requirements for the growth with plasma decomposition of methane on the Ni catalyst. Electron microscopy analysis provides evidence for a 'tip' growth model8, with the Ni catalyst particle attached to the tip of the nanofibre. Energy-filtered imaging shows the Ni catalyst has a surface layer rich in carbon, consistent with the formation of a eutectic Ni–C droplet as a nucleation site for the carbon nanofibres9, so that the carbon diffuses across the surface. The reduced distortion of the catalyst particles at low temperatures leads to a more uniform growth of the carbon nanofibres over large areas. The lower growth temperature allows for the removal of the silicon dioxide barrier layer associated with catalytic growth, and should allow in situ growth of nanofibres on relatively large areas of temperature-sensitive substrates, such as plastics, organics and even paper.

Higher Dispersion Efficacy of Functionalized Carbon Nanotubes in Chemical and Biological Environments

Abstract: Aqueous dispersions of functionalized carbon nanotubes (CNTs) are now widely used for biomedical applications. Their stability in different in vitro or in vivo environments, however, depends on a wide range of parameters, such as pH and salt concentrations of the surrounding medium, and length, aspect ratio, surface charge, and functionalization of the applied CNTs. Although many of these aspects have been investigated separately, no study is available in the literature to date, which examines these parameters simultaneously. Therefore, we have chosen five types of carbon nanotubes, varying in their dimensions and surface properties, for a multidimensional analysis of dispersion stability in salt solutions of differing pH and concentrations. Furthermore, we examine the dispersion stability of oxidized CNTs in biological fluids, such as cellular growth media and human plasma, and their toxicity toward cancer cells. To enhance dispersibility and biocompatibility, the influence of different functionalization schemes is studied. The results of our investigations indicate that both CNT dimensions and surface functionalization have a significant influence on their dispersion and in vitro behavior. In particular, factors such as a short aspect ratio, presence of oxidation debris and serum proteins, low salt concentration, and an appropriate pH are shown to improve the dispersion stability. Furthermore, covalent surface functionalization with amine-terminated polyethylene glycol (PEG) is demonstrated to stabilize CNT dispersions in various media and to reduce deleterious effects on cultured cells. These findings provide crucial data for the development of biofunctionalization protocols, for example, for future cancer theranostics, and optimizing the stability of functionalized CNTs in varied biological environments.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Dispersion and functionalization of carbon nanotubes for polymer-based nanocomposites: a review

Abstract: Carbon nanotubes (CNTs) hold the promise of delivering exceptional mechanical properties and multi-functional characteristics. Ever-increasing interest in applying CNTs in many different fields has led to continued efforts to develop dispersion and functionalization techniques. To employ CNTs as effective reinforcement in polymer nanocomposites, proper dispersion and appropriate interfacial adhesion between the CNTs and polymer matrix have to be guaranteed. This paper reviews the current understanding of CNTs and CNT/polymer nanocomposites with two particular topics: (i) the principles and techniques for CNT dispersion and functionalization and (ii) the effects of CNT dispersion and functionalization on the properties of CNT/polymer nanocomposites. The fabrication techniques and potential applications of CNT/polymer nanocomposites are also highlighted.

Chemically derived graphene oxide: towards large-area thin-film electronics and optoelectronics.

Abstract: Chemically derived graphene oxide (GO) possesses a unique set of properties arising from oxygen functional groups that are introduced during chemical exfoliation of graphite. Large-area thin-film deposition of GO, enabled by its solubility in a variety of solvents, offers a route towards GO-based thin-film electronics and optoelectronics. The electrical and optical properties of GO are strongly dependent on its chemical and atomic structure and are tunable over a wide range via chemical engineering. In this Review, the fundamental structure and properties of GO-based thin films are discussed in relation to their potential applications in electronics and optoelectronics.

Efficient and stable large-area perovskite solar cells with inorganic charge extraction layers

Abstract: The recent dramatic rise in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has triggered intense research worldwide. However, high PCE values have often been reached with poor stability at an illuminated area of typically less than 0.1 square centimeter. We used heavily doped inorganic charge extraction layers in planar PSCs to achieve very rapid carrier extraction, even with 10- to 20-nanometer-thick layers, avoiding pinholes and eliminating local structural defects over large areas. The robust inorganic nature of the layers allowed for the fabrication of PSCs with an aperture area >1 square centimeter that have a PCE >15%, as certified by an accredited photovoltaic calibration laboratory. Hysteresis in the current-voltage characteristics was eliminated; the PSCs were stable, with >90% of the initial PCE remaining after 1000 hours of light soaking.