Superconductivity in disordered thin films: giant mesoscopic fluctuations

We discuss the intrinsic inhomogeneities of superconductive properties of uniformly disordered thin films with a large dimensionless conductance g. It is shown that mesoscopic fluctuations, which usually contain a small factor 1/g, are crucially enhanced near the critical conductance g(cF) > 1 where superconductivity is destroyed at T = 0 due to Coulomb suppression of the Cooper attraction. This leads to strong spatial fluctuations of the local transition temperature and thus to the percolative nature of the thermal superconductive transition.     

Superconductivity in sputtered thin films of Tl-Ba-Ca-Cu-O

Films of Tl-Ba-Ca-Cu-O have been made by multi-target magnetron sputtering. The best films show an onset of superconductivity at ≈ 110 K and zero resistance at 96 K. Preliminary X-ray diffraction analysis suggests the films to be predominantly oriented with the c-axis perpendicular to the film surface with the lowest multiple of lattice spacing along the c-axis being ∼ 2.94 nm, consistent with the Tl₂Ba₂CaCu₂O_x (2212) phase.     

Superconductivity of thin films of lead,indium, and tin prepared in the presence of oxygen

We have studied the influence of oxygen on the superconducting properties of thin films of lead, indium and tin deposited on glass or sapphire substrates. In addition, the morphological microstructure was investigated by scanning electron microscopy. The film thickness was 1.0 μm, and the partial pressure of O₂ during the film deposition was raised up to 1×10⁻⁴ Torr. In all three materials the development of a granular structure and a strong increase in the residual electric resistivity was observed due to the O₂-treatment. Whereas in the Pb films no change of the critical temperature was found, the In films deposited on glass substrates showed a slight increase ofT _c due to the oxygen. The strongest increase ofT _c (up to 8%) was observed in the O₂-treated Sn films. These results are discussed in terms of the McMillan theory. From our measurements of the critical current densityj _c we conclude that edge pinning is dominant in the undoped films. All three materials showed a strong increase ofj _c due to the O₂-treatment which must be interpreted in terms of bulk pinning.     

Superconductivity in thin films of boron-doped carbon nanotubes

Superconductivity in carbon nanotubes (CNTs) is attracting considerable attention. However, its correlation with carrier doping has not been reported. We report on the Meissner effect found in thin films consisting of assembled boron (B)-doped single-walled CNTs (B-SWNTs). We find that only B-SWNT films consisting of low boron concentration leads to evident Meissner effect with Tc=12 K and also that a highly homogeneous ensemble of the B-SWNTs is crucial. The first-principles electronic-structure study of the B-SWNTs strongly supports these results.     

Superconductivity in tin -group V trichalcogenides

Superconductivity has been found for the tetragonal compounds SnNbS₃, SnTaS₃ and SnNbSe₃ at 2.75, 2.90 and 3.02, respectively. Crystallographic data and results of low temperature specific heat measurements are reported.     

The origin of haze in CVD tin oxide thin films

The origin of haze was investigated in antimony-doped tin oxide thin films, and in double-stack thin films of fluorine-doped tin oxide/antimony-doped tin oxide, both deposited by chemical vapor deposition onto soda-lime–silica float glass substrates. These transparent conductive oxide thin films are of great importance in the production of solar control architectural glazing units. Therefore, understanding the origins of haze is necessary to the development of coated, IR-reflecting glass windows with low overall haze levels. Haze measurements of as-prepared and polished samples were correlated with surface roughness and concentration of internal hole defects. Surface roughnesses were evaluated by atomic force microscopy, and characterized by estimated RMS values. In thin tin oxide films (<2000 Å) internal hole defects caused haze, while in thick tin oxide films (>4000 Å) surface roughness was the primary source of haze.     

Synthesis and characterisation of co-evaporated tin sulphide thin films

Tin sulphide films were grown at different substrate temperatures by a thermal co-evaporation technique. The crystallinity of the films was evaluated from X-ray diffraction studies. Single-phase SnS films showed a strong (040) orientation with an orthorhombic crystal structure and a grain size of 0.12 μm. The films showed an electrical resistivity of 6.1 Ω cm with an activation energy of 0.26 eV. These films exhibited an optical band gap of 1.37 eV and had a high optical absorption coefficient (>10⁴ cm^-1) above the band-gap energy. The results obtained were analysed to evaluate the potentiality of the co-evaporated SnS films as an absorber layer in solar photovoltaic devices. PACS 78.40.Fy; 68.60.-p; 61.10.Nz; 68.55.-a; 78.66.-w     

Substrate-assisted laser patterning of indium tin oxide thin films

Maskless laser patterning of indium tin oxide (ITO) thin films was studied by the use of a diode-pumped Q-switched Nd:YLF laser. The ITO films were sputter-deposited either on lime glass, the standard substrate material for flat panel display applications, or fused quartz so that the efficiency of laser patterning as a function of substrate absorption could be studied. The laser wavelength was varied among infrared (5=1047 nm), visible (5=523 nm), and ultraviolet (5=349 nm and 5=262 nm). It is observed that strong light absorption by the substrate is a crucial requirement for a residue-free patterning of the ITO film. Observations and numerical calculations of the laser-induced surface temperature indicate that material removal occurs via thermal vaporization and that other mechanisms such as photochemical decomposition or spallation can be neglected.     

Superconductivity in ultrathin films

It is shown that the pair breaking parameter of the Maki-Thompson contributions to the fluctuation conductivity above the superconducting transition temperature has the same thickness dependence as the transition temperature depression in very thin amorphous Be-Al films. Both can be ascribed to an extremely thin surface sheath with suppressed superconductivity.Supported by the Swedish Natural Science Research Board.     

BiFeO3 thin films: Novel effects

In this paper we report synthesis of phase-pure highly resistive magnetoelectric BiFeO₃ thin films on Pt/TiO₂/SiO₂/Si substrate by using pulsed laser deposition technique. For the first time saturated ferroelectric hysteresis loop has been observed. It has confirmed the presence of ferroelectricity in BiFeO₃ compound. The films exhibit dielectric anomaly near Neel temperature. This anomaly is related to the influence of vanishing magnetic order on the electric order. In situ domain alignment occurs during observation of the films under transmission electron microscope.     

溶胶凝胶法制备参氟二氧化锡薄膜

利用溶胶凝胶方法，在硅碱玻璃底板上制备的透明低电阻SnO2:F薄膜，是一种低辐射导电薄膜。将SnCl4·5H2O 和 NH4F 溶解在50%乙醇和50%水的溶液中。制备条件为底板温度450℃，喷嘴与底板之间的距离60mm,载气流速8 L/min，制备时间5分钟。制成的SnO2:F薄膜面电阻为2Ω/□，可重复性好。并且文中还定性给出了SnO2:F薄膜其红外反射率与面电阻之间的关系。     

Interface effects in perovskite thin films

The control of matter properties (transport, magnetic, dielectric,…) using synthesis as thin films is strongly hindered by the lack of reliable theories, able to guide the design of new systems, through the understanding of the interface effects and of the way the substrate constraints are imposed on the material. The present Letter analyzes the energetic contributions at the interfaces, and proposes a model describing the microscopic mechanisms governing the interactions at an epitaxial interface between a manganite and another transition metal oxide in perovskite structure (as for instance SrTiO3). The model is checked against experimental results and literature analysis.     

Superconductivity in amorphous Cr films

Superconducting transition has been observed for the first time in amorphous Cr films prepared by co-sputtering of Cr and BN. Superconducting transition temperatures (Tc) up to 1.14 K have been observed with an orbital contribution (i.e.(dH_c2⊥/dT)_Tc) as large as 49 kOe K^-1. The electronic specific heat coefficient (γ) has been estimated to be about 1.6 times as large as that of amorphous Mo-BN (or Mo-metalloid) alloys. This finding, i.e. the low Tc with the large γ for amorphous Cr is inconsistent with data reported for amorphous alloys of 4d and 5d transition elements. This inconsistency implies a formation of local magnetic moments or spin fluctuation in the amorphous Cr film.     

Tuning the properties of tin oxide thin films for device fabrications

Tin oxide thin films were deposited on well cleaned glass substrates by thermal evaporation in vacuum and were annealed at 500?^°C in the open atmosphere inside a furnace for 90 min for promoting the sensitivity of the films. The X-ray diffraction studies revealed that the as-deposited films were amorphous in nature and the annealed films showed appreciable crystalline behavior. The annealed thin films were then irradiated using ⁶⁰Co gamma source. The radiation induced changes were then studied by X-ray diffraction, scanning electron microscopy, UV–vis spectroscopy and I–V characterization. The remarkable increase in the average grain size, the decrement in the energy band gap and resistivity due to the gamma irradiations up to a certain dose and the reversal of these properties at higher doses are the important observations. The large changes in the conductivity and energy band gap of the annealed thin films due to gamma irradiation make these films quite important device material for the fabrication of gamma sensors and dosimeters.     

The kinetics of the photolysis of thin films of tin diiodide

The kinetics of photolysis of thin films of SnI₂ have been followed using a quartz crystal microbalance technique. The products of photolysis are iodine gas generated at the surface and tin formed within the SnI₂ (which appears as α-Sn even up to ~400 K). Rate as a function of extent of reaction, film thickness, light intensity and wavelength, temperature, doping agents and substrate and finally thin film microstructure have been investigated for both high and low temperature polymorphic forms of SnI₂. The extent of photolysis, which always starts by being linear in time, goes via an intermediate regime to being proportional to $\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ .The kinetics of photolysis are similar to PbI₂ studied previously[1] and, as for that case, the photolysis mechanism is consistent with a rate determining anion motion.