Abstract: The effects of thermal annealing on vanadium oxide (VOx) thin films prepared by pulsed-dc magnetron sputtering were studied to explore methods of improving the efficiency of uncooled IR imaging microbolometers, particularly with respect to maximizing the temperature coefficients of resistance (TCR) (typically ~2%) while minimizing resistivity values (typically 0.05–5 Ω cm). Since high TCR values are usually associated with high resistivities, the experiments were designed to find processing conditions that provide an optimal balance in these properties and to then determine the underlying structural correlations which would enable rational design of thin films for this specific application. VOx films of different compositions were deposited by pulsed-dc reactive sputtering from a vanadium target at different oxygen flow rates. The deposited films were further modified by annealing in inert (nitrogen) and oxidizing (oxygen) atmospheres at four different temperatures for 10, 20, or 30 min at a time. The resistivities of the as-deposited films ranged from 0.2 to 13 Ω cm and the TCR values varied from –1.6% to –2.2%. Depending on the exact annealing conditions, several orders of magnitude change in resistance and significant variations in TCR were observed. Optimal results were obtained with annealing in a nitrogen atmosphere. Structural characterization by x-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, and Raman spectroscopy indicated changes in the film crystallinity and phase for annealing conditions over 300 °C with the onset and extent of the changes dependent on which annealing atmosphere was used.

Abstract: We describe a novel effect involving odd-order dispersion cancellation. We demonstrate that odd- and even-order dispersion cancellation may be obtained in different regions of a single quantum interferogram using frequency-anticorrelated entangled photons and a new type of quantum interferometer. This offers new opportunities for quantum communication and metrology in dispersive media.

Abstract: We present a new photon number resolving detector (PNR), the Parallel Nanowire Detector (PND), which uses spatial multiplexing on a subwavelength scale to provide a single electrical output proportional to the photon number. The basic structure of the PND is the parallel connection of several NbN superconducting nanowires (100 nm-wide, few nm-thick), folded in a meander pattern. Electrical and optical equivalents of the device were developed in order to gain insight on its working principle. PNDs were fabricated on 3-4 nm thick NbN films grown on sapphire (substrate temperature TS=900C) or MgO (TS=400C) substrates by reactive magnetron sputtering in an Ar/N2 gas mixture. The device performance was characterized in terms of speed and sensitivity. The photoresponse shows a full width at half maximum (FWHM) as low as 660ps. PNDs showed counting performance at 80 MHz repetition rate. Building the histograms of the photoresponse peak, no multiplication noise buildup is observable and a one photon quantum efficiency can be estimated to be QE=3% (at 700 nm wavelength and 4.2 K temperature). The PND significantly outperforms existing PNR detectors in terms of simplicity, sensitivity, speed, and multiplication noise.

Abstract: It is established that, in preparing p-Bi0.5Sb1.5Te3 by vertical zone melting, in addition to the directional texture (characteristic of materials exhibiting a highly anisotropic growth rate) in which the cleavage planes of crystal grains are parallel to the direction of propagation of the crystallization front, other texture types can arise, in which the orientation of grain cleavage planes is ordered in a cross-sectional plane of the ingot. Two types of such textures, “radial” and “circular,” were observed. In a radial texture, the lines of intersection of grain cleavage planes with a cross-sectional plane of the ingot are oriented along radii of this cross section and, in a circular texture, these lines of intersection are oriented approximately perpendicular to a radius crossing the grain. The formation of a radial texture is associated with rotation of the ampoule with the crystallizing substance about its vertical axis causing centrifugal flows of the melt. The formation of a circular texture is associated with the orientation effect of the ampoule walls and with circular motion of the melt during torsional oscillations of the ampoule about the vertical axis. Ingots with a radial texture exhibit much lower resistance to splitting along their axis than ingots with a circular texture do. An explanation is provided for this fact.