Low-temperature, solution-based self-assembly of vanadia nanofibers yields a free-standing, ceramic paper with an outstanding combination of high strength, stiffness, and macroscopic flexibility. Its excellent mechanical performance results from a brick-and-mortar like architecture, which combines strong covalent bonding within the single-crystalline nanofibers with an intricate hydrogen bonding network between them.
communications GrapheneIn order to realize solar cells with technologically useful performance, intensive efforts are being directed towards the development of novel device architectures and components. So far, high power conversion effi ciencies exceeding 5% have been reached with dye-sensitized [ 1 ] or polymer blend-based solar cells, [ 2 ] wherein very fast interfacial charge transfer occurs. However, charge transport is often limiting the performance of these devices. In particular for blendbased solar cells, the photocurrent depends strongly on the properties of the percolation network. [ 3 ] A promising strategy to overcome this limitation involves nano-structured solar cells which provide well-defi ned, separate pathways for carrier transport, thus minimizing recombination losses. Examples include vertically aligned arrays of ZnO, [ 4 ] TiO 2 , [ 5 ] Si nanowires, [ 6 ] or TiO 2 functionalized CNTs. [ 7 ] Especially promising are CNTs decorated with semiconductor nanoparticles, since the former provide a close-to-ideal transport pathway for carriers. However, it is diffi cult to obtain a high quality electrical connection between nanotube and semiconductor without disrupting the carbon framework of the nanotubes. Accordingly, studying the interface between sp 2 -bonded carbon materials and semiconductors is important for further improving the performance of CNT based solar cells. More recently, also the closely related graphene has attracted increasing interest toward photovoltaic applications. [ 8 ] It has been chemically modifi ed by the attachment of TiO 2 nanoparticles [ 9 ] or CdS quantum dots, [ 10 ] albeit only little is known about the interface between graphene and inorganic or organic semiconductors, in contrast to the metal-graphene interaction. [ 11 -13 ] In fact, while ultrafast electron transfer from CdS dots to graphene has been detected by time-resolved photoluminescence spectroscopy, [ 14 ] the suitability of these nanocomposites for light harvesting applications remains to be evaluated.Here, we investigate the photoelectric properties of the interface between graphene as a carbon nanostructure and CdS as a widely used II-VI semiconductor. In this model system, the graphene sheet is contacted with a CdS nanowire which serves to transport electrons to the opposite metal contact. The lateral device confi guration allows scanning photocurrent microscopy (SPCM) to be used to map the generated photocurrents with sub-micrometer resolution. In contrast to bulk solar cells, this opens the possibility to distinguish between photoresponses of the involved interfaces at the nanoscale. Although due to the ultrasmall photoactive interfacial area in these devices, they naturally exhibit only low photoconversion effi ciencies, they provide a valuable platform to explore strategies for chemical interface tailoring.The fi nal device structure is illustrated by the atomic force microscopy (AFM), optical microscopy and optical refl ection images in Figure 1 a. In this device, the contacted graphene consist...
Charge recombination dynamics in semiconductor nanostructures is of vital importance for photovoltaic or photodetector device applications. We use local photocurrent measurements to explore spatially separated drift- and diffusion-currents close to the edge of gold contacts on top of cadmium sulfide nanowires. By theoretical modeling of the experimental photocurrent profiles, the electron diffusion length and lifetime in the wires are obtained to 0.8 μm and 1 ns, respectively. In contrast to bulk devices, the nanoscale dimensions of the involved Schottky contacts enable a highly efficient charge carrier extraction from below the electrodes. This finding paves the way for designing nanostructured optoelectronic devices of improved performance.
The second-life concept helps to reduce the cost for electric vehicles by adding monetary value to disused automotive batteries. However, the sudden-death effect, a change in ageing behaviour limits the total lifetime and might reduce the second-life timespan. In this paper, we utilize a common pseudo two-dimensional (P2D) cell model to investigate the influence of different porosity profiles in the graphite electrode on the battery’s ageing. Ageing is modeled by two irreversible side reactions at the anode, the formation of solid electrolyte interface (SEI) and lithium plating. We use parameters of a high-energy cell with thick electrodes. A constant initial anode porosity as a reference is compared with two optimized porosity profiles. Simulation results show that by using a layered anode, a two-stage porosity profile with higher porosity at the separator side, the cycle count until sudden-death and especially the cycles for second-life applications can both almost be doubled.
We have investigated the near-field coupling of surface plasmons to a titanium/CdS nanowire interface for two different device configurations. A bare aluminum grating on an underlying aluminum layer exhibited the expected stronger electrical signal for perpendicular versus parallel light polarization. An opposite intensity ratio was detected when the grating and the Schottky contact are connected via an aluminum-silica-aluminum sandwich structure. Based upon finite difference time domain device simulations, the enhanced coupling for parallel polarization is attributed to the emergence of a transversal electric wave within the metal-insulator-metal structure.
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