Microstructure and dielectric function modelling by spectroscopic ellipsometry and energy electron loss spectroscopy of In₂O₃:Sn thin films

Indium tin oxide (ITO) is a semiconducting material combining high conductivity and high transparency in the visible range. It is the most widely used transparent conducting oxide in applications such as flat panel displays. In this work, ITO thin films were deposited by pulsed laser deposition (PLD) onto transparent glass substrates. The substrate temperature and oxygen pressure during deposition were controlled to generate a variety of microstructures and electro-optical properties. Similar film thicknesses were used to avoid any change of carrier concentration. The dielectric function and complex refractive index were derived using spectroscopic ellipsometry and electron energy loss spectroscopy

Multilayer multifunctional advanced coatings for receivers of concentrated solar power plants

International audienceThe extending market of concentrated solar power plants requires high-temperature materials for solar surface receivers that would ideally heat an air coolant beyond 1300 K. This work presents investigation on high-temperature alloys with ceramic coatings (AlN or SiC/AlN stacking) to combine the properties of the substrate (creep resistance, machinability) and of the coating (slow oxidation kinetics, high solar absorptivity). The first results showed that high temperature oxidation resistance and optical properties of metallic alloys were improved by the different coatings. However, the fast thermal shocks led to high stress levels not compatible due to the differences in thermal expansion coefficients

Flexible transparent conductive materials based on silver nanowire networks: a review

The class of materials combining high electrical or thermal conductivity, optical transparency and flexibility is crucial for the development of many future electronic and optoelectronic devices. Silver nanowire networks show very promising results and represent a viable alternative to the commonly used, scarce and brittle indium tin oxide. The science and technology research of such networks are reviewed to provide a better understanding of the physical and chemical properties of this nanowire-based material while opening attractive new applications

Collection Efficiency and Design Requirements for Metallic Nanowire Networks in Solar Cells

In using TCMs based on metallic nanowires it is important to determine the effect of nanowire geometry and spatial arrangement on the resulting network. To this end we have extensively simulated the effect of wire length and device size on the percolation properties of the network produced. We have performed Monte Carlo simulations of 2D conductive stick networks including for the first time stick lengths approximating nanowires which are produced experimentally. Each simulation is performed based on an average stick length but the actual lengths of the nanowires in the simulation are randomly generated with a normal distribution around the defined average length. The effects of density and length distribution on the percolation threshold are also explored. The results of such simulations are also employed to determine an elementary representative volume, which can be directly applied to a device design by allowing the determination of the nanowire density required to produce a conductive network associated with a characteristic length, such as diffusion length or pixel size. We also extend this work to the specific application of metallic nanowire networks as front electrodes in dye sensitized solar cells (DSSC), allowing a calculation of the collection efficiency as a function of network density. These calculations were based on the diffusion length of electrons generated within a DSSC and a spatial mapping of the collection efficiency function on the solar cell surface

Prediction of dislocation density in AlN or GaN films deposited on (0001) sapphire

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Thermal annealing effects on silver nanowire networks

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Physical properties of silver nanowire networks: effects of percolation and thermal annealing

Silver nanowire networks have recently been a heavily researched subject due to their potential use as transparent electrodes in solar cells or flat panel displays. Currently, the most commonly used material for such applications (Tin-doped Indium oxide) suffers from two major drawbacks: indium scarcity and brittleness. However, metallic nanowire networks can be deposited by low cost deposition techniques and exhibit simultaneously very promising optical, electrical and electro-mechanical properties. To enhance these properties, nanowire density should be considered. For a given nanowire aspect ratio, lower nanowire densities result in higher optical transparency but demonstrate lower electrical conductivity. As the density of nanowires is increased the relationship is reversed, resulting in high electrical conductivity but low optical transparency. Numerical Montecarlo simulations on stick percolation shed light on the percolative nature of these 2D networks. Relations between simulation and experimental observations are discussed. We also show that thermal annealing can efficiently improve the electrical properties without significantly changing the optical response2. However, above a certain temperature threshold, morphological instabilities occur and induce a cancelling out of the beneficial effects. The physical mechanisms involved in thermal annealing of Ag nanowire networks are addressed as well as their effects on electro-optical properties. Finally the potential integration of Ag nanowire networks into devices is evaluated