Electrochromic (EC) materials change their optical properties (darken/lighten) in the presence of a small electric potential difference, and are suitable for application in energy-efficient windows, antiglare automobile rear-view mirrors, sunroofs, displays, and hydrogen sensors. [1][2][3][4] There are two important criteria for selecting an EC material. The first is the time constant of the ion-intercalation reaction, which is limited both by the diffusion coefficient and by the length of the diffusion path. While the former depends on the chemical structure and crystal structure of the metal oxide, the latter is determined by the material's microstructure. [11] In the case of a nanoparticle, the smallest dimension is represented by the diffusion path length. Thus, designing a nanostructure with a small radius, while maintaining the proper crystal structure, is key to obtaining a material with fast insertion kinetics, enhanced durability, and superior performance. The second important criterion is coloration efficiency (CE), the change in optical density (OD) per unit inserted charge (Q), that is, CE = D(OD)/DQ. [12] A high CE provides large optical modulation with a small charge insertion or extraction. This is a crucial parameter for EC devices, since a lower charge-insertion or -extraction rate enhances the longterm cycling stability. Among inorganic materials, tungsten oxides have been most extensively studied. Up until now, amorphous WO 3 films have exhibited the highest CE in the visible region of the electromagnetic spectrum. However, because of their high dissolution rate in acidic electrolyte solutions, these films can only be used in lithium-based electrolytes, resulting in slower response times. Furthermore, extended durability, even in Li + systems, has not yet been demonstrated. Inexpensive conducting and redox polymers have attracted increased attention for use as EC materials because of their fast response times and high contrast ratios. [13][14][15] However, disadvantages include multiple coloration in the visible spectral range and poor UV stability. By fabricating EC films from crystalline WO 3 nanoparticles, the state-of-the-art technology of producing EC materials has been profoundly advanced. Crystalline WO 3 nanoparticles have been grown by an economical hot-wire chemical-vapordeposition (HWCVD) process, and a unique electrophoresis technique is employed for the fabrication of porous nanoparticle films. The porosity of the films not only increases the surface area and ion-insertion kinetics, but also reduces the overall material cost, leading to an inexpensive, large-area EC material. Compared to conventional amorphous WO 3 films prepared by vacuum deposition, nanoparticle films deposited by electrophoresis exhibit vastly superior electrochemical-cycling stability in acidic electrolytes, a higher charge density, and comparable CE. This greatly enhanced stability and charge capacity are attributed to the crystalline nanoparticles employed in this work. These initial results will ultimately ...

Lithium-ion batteries are current power sources of choice for portable electronics, offering high energy density and longer lifespan than comparable technologies. Significant improvements in rate and durability for inexpensive, safe and non-toxic electrode materials may enable utilization in hybrid electric or plug-in hybrid electric vehicles (PHEVs). Furthermore, recent efforts for hybrid electric vehicle applications have been focused on new anode materials with slightly more positive insertion voltages with respect to Li/Li þ to minimize any risks of high-surface-area Li plating while charging at high rates, a major safety concern.[1] In hybrid electric vehicles, batteries are cycled with $10% charge/discharge from the point where the cell is at 50% capacity. when cycled in a voltage window of 3.0-0.005 V, but this material suffered from poor cycling stability, with the capacity degrading to 400 mA h g À1 in $100 cycles. [8] By increasing the cut-off potential to 0.2 V and employing a slow rate (discharge and charge at C/15 and C/20, respectively), the cycling was more stable, ranging from 600-400 mA h g À1 in 100 cycles.[8] A tin-doped MoO 3 system was also explored, and the average charge potential was lowered, but at the expense of capacity fading.[9] Here we report on anodes fabricated from crystalline MoO 3 nanoparticles that display both a durable reversible capacity of 630 mA h g À1 and durable high rate capability.The nanoparticle anodes show no capacity degradation for 150 cycles between 3.5 to 0.005 V with both charge and discharge at C/2, compared to micrometer-sized particles where the capacity quickly fades. (Typically both decreased capacity and rapid degradation are observed when deep cycles are employed at higher rates.) Upon cycling, long-range order in the MoO 3 nanostructures is lost. First-principle calculations are employed in order to explain the nanoparticle durability despite the loss of structural order. The crystalline molybdenum oxide nanoparticles are grown at high density by a previously described economical hot-wire chemical vapor deposition (HWCVD) technique.[10] Figure 1a shows a representative transmission electron microscopy (TEM) image of the as-synthesized nanoparticles. Extensive TEM analyses reveal that the bulk powder contains almost exclusively nanospheroids with diameters of 5-20 nm, thus providing a short solid-state Li-ion diffusion path. A highresolution TEM image of a nanoparticle where the lattice fringes are visible is shown in Figure 1b. A simple electrophoresis deposition process [11] is employed to fabricate high-surface area porous nanoparticle films on a stainless steel electrode with a thickness of $2 mm. Figure 1c displays a scanning electron microscopy (SEM) image of an electrophoresis-deposited film. The mass density of the nanoparticle film was found to be $3.3 g cm À3 from mass and thickness data compared to 4.7 g cm À3 for the bulk material. Furthermore, the electrode is comprised of entirely COMMUNICATION

Device-quality hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device-quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament. These low H content films show an Urbach edge width of 50 mV and a spin density of ∼1/100 as large as that of glow discharge films containing comparable amounts of H. High substrate temperatures, deposition in a high flux of atomic H, and lack of energetic particle bombardment are suggested as reasons for this behavior.

We have measured the low temperature internal friction ͑Q 21 ͒ of amorphous silicon ͑a-Si͒ films. e-beam evaporation or 28 Si 1 implantation leads to the temperature-independent Q 21

High-hydrogen-diluted films of hydrogenated amorphous Si (a-Si:H) 0.5 μm in thickness and optimized for solar cell efficiency and stability, are found to be partially microcrystalline (μc) if deposited directly on stainless steel (SS) substrates but are fully amorphous if a thin n layer of a-Si:H or μc-Si:H is first deposited on the SS. In these latter cases, partial microcrystallinity develops as the films are grown thicker (1.5–2.5 μm) and this is accompanied by sharp drops in solar cell open circuit voltage. For the fully amorphous films, x-ray diffraction (XRD) shows improved medium-range order compared to undiluted films and this correlates with better light stability. Capacitance profiling shows a decrease in deep defect density as growth proceeds further from the substrate, consistent with the XRD evidence of improved order for thicker films.