A Method for Forming Very Small Diameter Wires

Measurements of the critical field $\stackrel{^}{H}$ and transition temperature $\stackrel{^}{T}$ of superconducting indium in porous glass have been made using a low-frequency mutual-inductance technique. The pore sizes of the glasses are well characterized, so that 96% of the pore volume is within \ifmmode\pm\else\textpm\fi{}10% of the mean pore diameter $d$. Pore diameters from 65 to 250 \AA{} were used. Below $t (\ensuremath{\equiv}\frac{T}{\stackrel{^}{T}})=0.5$, $\stackrel{^}{H}$ can be represented approximately by $\stackrel{^}{H}=\frac{(3415\ifmmode\pm\else\textpm\fi{}40)(1\ensuremath{-}{t}^{2})}{{d}^{(1.00\ifmmode\pm\else\textpm\fi{}0.14)}},$where $\stackrel{^}{H}$ is in kilo-oersteds and $d$ is in Angstrom units. This is in agreement with the predictions of de Gennes and Maki of ${H}_{c2}$ for type II superconductors in the dirty limit, assuming that the electronic mean free path is proportional to $d$. Above $t=0.6$, there are deviations from de Gennes's prediction for the $d$ dependence and the $t$ dependence of $\stackrel{^}{H}$. For the small pore sizes the temperature dependence of $\stackrel{^}{H}$ is qualitatively similar to the Abrikosov prediction of ${H}_{c2}$ for type II superconductors; however, near $t=1$ for the largest pore size the temperature dependence of $\stackrel{^}{H}$ is similar to that for a type I superconductor. The superconducting transition temperature $\stackrel{^}{T}$ shows a strong dependence upon $d$, so that $\stackrel{^}{T}(65 \AA{})$ is 4.23\ifmmode^\circ\else\textdegree\fi{}K compared with 3.4\ifmmode^\circ\else\textdegree\fi{}K for the bulk indium. The dependence of $\stackrel{^}{T}$ on $d$ is conveniently represented by $\stackrel{^}{T}\ensuremath{-}{T}_{\mathrm{bulk}}=1\ensuremath{-}0.0028 d,$where $d$ is in Angstrom units. The change in $\stackrel{^}{T}$ may be due to strain, mean-free-path, or surface effects. The samples are similar to inhomogeneous type II superconductors in their magnetic properties, showing hysteresis and flux jumping.

Critical Magnetic Field and Transition Temperature of Synthetic High-Field Superconductors

We report on the structural and electrical characterization of Mo thin films deposited at room temperature by RF magnetron sputtering. The effect of RF power on the morphology and residual stress of the films is analyzed. The films are under compressive stress and consist of densely packed columns with a lateral size on the order of 20 nm. The stress, critical temperature, and resistivity of the films are found to rise when increasing the ejected ion energy during the sputtering process. The changes in critical temperature and resistivity are discussed in terms of the observed morphology and stress changes.

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Effects of Stress and Morphology on the Resistivity and Critical Temperature of Room-Temperature-Sputtered Mo Thin Films

Superconductivity in nearly one-dimensional tin wires

Tantalum films have been epitaxially deposited on cleaved MgO (001) surfaces at temperatures above 700°C under high‐vacuum conditions The interstitial impurity content is below 05 at% for thicknesses greater than 1000 A; the impurity concentration increases with decreasing film thickness, and severe lattice dilation occurs in the very thin film region (250–350 A) Films of thicknesses greater than 1000 A have specific resistivities and critical temperatures (160 μΩ·cm and 430°K, respectively) close to bulk values Two impurity‐stabilized phase transitions produced by electron microscope beam heating are described

Electrical and Structural Properties of Epitaxial bcc Tantalum Films

Factors which affect the superconducting transition temperature (Tc) of thin tin films are of considerable importance in the design of thin film devices. This paper reports an investigation of one such factor, the stress state of the film. Two approaches were used. First, the transition temperature was correlated with the differential thermal contraction between film and substrate. Six different types of glass were used for substrates, and the six films were evaporated simultaneously to ensure similar conditions of evaporation. Secondly, a substrate‐bending technique was used to stress the film while holding it near its transition temperature. For both of these methods, shifts of the transition temperature greater than 0.1°K have been observed. However, it was found that agglomeration of the film can greatly reduce the dependence of the transition temperature on stresses transmitted to the film by the substrate.When agglomeration was negligible, both these approaches yielded a linear increase in Tc with t...

P. M. Hall

Papers

Effect of Stress on the Superconducting Transition Temperature of Thin Films of Tin