Metal nanoplasmas as bright sources of hard X-ray pulses

We report significant enhancements in light coupling to intense-laser-created solid plasmas via surface plasmon and "lightning rod" effects. We demonstrate this in metal nanoparticle-coated solid targets irradiated with 100 fs, 806 nm laser pulses, focused to intensities approximately 10(14)-10(15) W cm(-2). Our experiments show a 13-fold enhancement in hard x-ray yield (10-200 keV) emitted by copper nanoparticle plasmas formed at the focal volume. A simple model explains the observed enhancement quantitatively and provides pointers to the design of structured surfaces for maximizing such emissions.     

Aligned Nanorod Arrays: Additive and Emergent Properties

Studies of one-dimensional nanostructures of various types (such as quantum wires, nanorods, nanotubes and nanobelts) have progressed substantially during the past decade and have been reviewed by a number of authors. Here, we provide a concise overview of the synthesis and special properties of arrays of parallel nanorods, whose behavior is often quite distinct from that of individual nanorods of the same material. We show that the distinctive behavior of such nanorod arrays may occur due to their exhibiting either additive or emergent properties. The former originates from a simple amplification of some advantageous property shown by a single nanorod, thus making it usable in a practical device; while the latter necessarily involves the presence of the array, and would not be observable from a single nanorod. Nanorod arrays have been shown to have possible applications in diverse areas that include nanolasers, microcavities, surface enhanced Raman effect, photovoltaic cells, field emission sources, gas sensing, electrical discharge and in hydrophobic surfaces. We first present an overview of some of the physical and chemical synthesis strategies for nanorod arrays, followed by a brief review of their applications in the areas just mentioned.     

Structural and optoelectronic properties of vacuum evaporated SnS thin films annealed in argon ambient

In this work, 650 nm polycrystalline SnS thin films were grown by thermal evaporation of high purity tin sulfide powder at 250 °C substrate temperature, followed by post deposition annealing at 200 °C and 300 °C for 2, 4 and 6 h, and at 400 °C for 2 and 4 h in argon ambient. The XRD pattern of the as-deposited and annealed SnS films led to the conclusion that the as-deposited films were polycrystalline in nature with preferentially oriented along (1 1 1) direction. The direct bandgap of all the films was found to be observed between 1.33 and 1.53 eV. Except for annealing at 400 °C all the films were nearly stoichiometric in nature, suggesting lower rate of desulfurization at that ambient. However, higher annealing temperature has resulted in the segregation of tin phase. All the films showed good absorption in the visible range. The as-deposited and annealed films showed p-type conductivity. Hall measurement revealed the carrier concentration and mobility ranging from 10¹⁵ to 10¹⁶ cm⁻³ and 0.8 to 31.6 cm² V⁻¹ s⁻¹ respectively. The photoconductivity measurements of all the SnS films were carried out by recording the lowering of resistance of the respective films with time under illumination.     

Template-based fabrication of Ag–ZnO core–shell nanorod arrays

We report a simple, versatile, two-step fabrication technique for synthesizing a core–shell nanorod array whose architecture is specifically suited for use as an electrode in a dye sensitized solar cell (DSSC). The particular structure fabricated by us consists of a parallel array of 5 μm long and 150–200 nm wide Ag nanorod cores, each coated with a 15–20 nm thick ZnO shell. Importantly, the shell thickness is roughly uniform throughout the length of the rods, which are free standing but distinctly separated from each other. This would allow the dye to penetrate freely and cover the ZnO surface completely in a DSSC.     

Polyimide-free homogeneous photoalignment induced by polymerisable liquid crystal containing cinnamate moiety

We designed and synthesised a reactive mesogen (CRM) containing cinnamate moiety in the core and two acrylate groups at both ends. The structure was characterised by ¹H NMR and FT-IR, and its liquid crystalline property was investigated by DSC and POM. The compound showed a nematic phase between 175.2 – 97.5 ^oC, followed by a smectic C phase between 97.5 and 57.9 ^oC during the cooling cycle. We proposed a fabrication method to achieve uniaxial homogeneous alignment of liquid crystals by irradiating the CRM-doped LC mixture in a sandwich cell of in-plane switching mode (CRM-IPS) with linearly polarised ultraviolet light. The results indicated that the CRM-IPS cell showed excellent initial dark state with a good alignment state, electro-optical performance and durability. This confirmed that the photo-induced alignment of LCs by CRM possesses outstanding alignment capability compared to the conventional rubbed polyimide alignment layer. We expect that this fabrication method is a promising candidate for cost-effective, green-manufacturing, and high-quality alignment method for the manufacturing of high-resolution liquid crystal displays (LCDs).     

Proximity effect in Nb/Zr multilayers with variable Nb/Zr ratio

We have investigated the effect of varying the individual layer thickness on the superconducting transition temperature (T_C) of Nb/Zr multilayers. These thin film multilayer structures were deposited using UHV magnetron sputtering with layer thickness ranging from 0.5 to 8 nm. In conformity with the predictions of the de Gennes equations in the Cooper limit (layer thickness small compared to coherence length), we find that the T_C increases with increasing thickness of the Nb layer (when the Zr layer thickness is constant), and decreases with increasing thickness of the Zr layer (when the Nb layer thickness is constant). The possible effect of the existence of an interfacial Nb-Zr layer is discussed. We also point out the marked influence of the in-plane grain dimension on the T_C in these multilayers.     

O implantation in ZnSe: lattice distortion by Raman measurement

We probe the “bulk” and near-surface regions of O-implanted heteroepitaxial ZnSe films, using the full-width at half-maximum (FWHM) of the Raman line. The results are compared to those after N implantation. A tensile stress attributed to a deformation in the lattice around O is found. Under rapid thermal annealing, the optimum temperature for the recovery of the implantation damage without suffering from thermally generated point defects is T_a = 500°C. It corresponds here to the maximum FWHM from the uncompensated tensile stress, while identical FWHM's are found for the top and the “bulk” part of the film just after implantation, and after implantation and T_a = 600°C.     

Suppression of superconductivity in submicron La1.85Sr0.15CuO4?δ

Bulk La_1.85Sr_0.15CuO_4– (LSCO) superconducts below 36K. But microcrystalline LSCO with mean particle size 700nm (prepared by rapid liquid dehydration) is not superconducting down to 4.2K. This may be due to a size-induced structural distortion and an accompanying reduction in the oxygen occupancy.     

Lattice size induced moment formation on isolated Fe atoms in nanocrystalline Nb

Measurements of the local susceptibility and 3d spin relaxation rate for single Fe impurities embedded in a nanocrystalline Nb host indicates the emergence of a local moment on Fe at and below a critical size of 11?nm. Our ab?initio electronic structure calculations show that the moment formation occurs due to Stoner enhancement arising from a size dependent lattice expansion and a consequent shift in the Fermi level. We also show that a size-induced positive host spin polarization of the Nb-4d band electrons strongly influences the fluctuation rate of the Fe moment.