10 research outputs found
Effect of layer thickness on structural, morphological and superconducting properties of NbSn films fabricated by multilayer sequential sputtering
Superconducting Nb3Sn films can be synthesized by controlling the atomic
concentration of Sn. Multilayer sequential sputtering of Nb and Sn thin films
followed by high temperature annealing is considered as a method to fabricate
Nb3Sn films, where the Sn composition of the deposited films can be controlled
by the thickness of alternating Nb and Sn layers. We report on the structural,
morphological and superconducting properties of Nb3Sn films fabricated by
multilayer sequential sputtering of Nb and Sn films on sapphire substrates
followed by annealing at 950 {\deg}C for 3 h. We have investigated the effect
of Nb and Sn layer thickness and Nb:Sn ratio on the properties of the Nb3Sn
films. The crystal structure, surface morphology, surface topography, and film
composition were characterized by X-ray diffraction (XRD), scanning electron
microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray
spectroscopy (EDS). The results showed Sn loss from the surface due to
evaporation during annealing. Superconducting Nb3Sn films of critical
temperature up to 17.93 K were fabricated
Selective thermal evolution of native oxide layer in Nb and Nb3Sn-coated SRF grade Nb: An in-situ angular XPS study
This contribution discusses the results of an in-situ angular XPS study on
the thermal evolution of the native oxide layer on Nb3Sn and pure Nb. XPS data
were recorded with conventional spectrometers using an AlK(alpha) X-ray source
for spectra collected up to 600 C, and an MgK(Alpha) X-rays source for
temperatures above 600 C. The effect of the thickness, composition, and thermal
stability of that oxide layer is relevant to understanding the functional
properties of superconducting radiofrequency (SRF) cavities used in particle
accelerators. There is a consensus that oxide plays a role in surface
resistance (Rs). The focus of this study is Nb3Sn, which is a promising
material that is used in the manufacturing of superconducting radiofrequency
(SRF) cavities as well as in quantum sensing, and pure Nb, which was included
in the study for comparison. The thermal evolution of the oxide layer in these
two materials is found to be quite different, which is ascribed to the
influence of the Sn atom on the reactivity of the Nb atom in Nb3Sn films. Nb
and Sn atoms in this intermetallic solid have different electronegativity, and
the Sn atom can reduce electron density around neighbouring Nb atoms in the
solid, thus reducing their reactivity for oxygen. This is shown in the
thickness, composition, and thermal stability of the oxide layer formed on
Nb3Sn. The XPS spectra were complemented by grazing incident XRD patterns
collected using the ESRF synchrotron radiation facility. The results discussed
herein shed light on oxide evolution in the Nb3Sn compound and guide its
processing for potential applications of the Nb3Sn-based SRF cavities in
accelerators and other superconducting devices
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Development of NbSn Cavity Vapor Diffusion Deposition System
NbSn is a BCS superconductors with the superconducting critical temperature higher than that of niobium, so theoretically it surpasses the limitations of niobium in RF fields. The feasibility of technology has been demonstrated at 1.5 GHz with NbSn vapor deposition technique at Wuppertal University~\cite{Wuppertalthebest}. The benefit at these frequencies is more pronounced at 4.2 K, where NbSn coated cavities show RF resistances an order of magnitude lower than that of niobium. At Jefferson Lab we started the development of NbSn vapor diffusion deposition system within an R\&D development program towards compact light sources. Here we present the current progress of the system development
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RF Surface Impedance Characterization of Potential New Materials for SRF-based Accelerators
In the development of new superconducting materials for possible use in SRF-based accelerators, it is useful to work with small candidate samples rather than complete resonant cavities. The recently commissioned Jefferson Lab RF Surface Impedance Characterization (SIC) system can presently characterize the central region of 50 mm diameter disk samples of various materials from 2 to 40 K exposed to RF magnetic fields up to 14 mT at 7.4 GHz. We report the recent measurement results of bulk Nb, thin film Nb on Cu and sapphire substrates, Nb{sub 3}Sn sample, and thin film MgB{sub 2} on sapphire substrate provided by colleagues at JLab and Temple University
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Characterization Of Superconducting Samples With SIC System For Thin Film Developments: Status And Recent Results
Within any thin film development program directed towards SRF accelerating structures, there is a need for an RF characterization device that can provide information about RF properties of small samples. The current installation of the RF characterization device at Jefferson Lab is Surface Impedance Characterization (SIC) system. The data acquisition environment for the system has recently been improved to allow for automated measurement, and the system has been routinely used for characterization of bulk Nb, films of Nb on Cu, MgB, NbTiN, NbSn films, etc. We present some of the recent results that illustrate present capabilities and limitations of the system
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ECR Nb Films Grown on Amorphous and Crystalline Cu Substrates: Influence of Ion Energy
In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. Using energetic condensation of ions extracted from plasma generated by Electron Cyclotron Resonance, it has been demonstrated that Nb films with good structural properties and RRR comparable to bulk values can be produced on metallic substrates. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. Particular attention is given to the nucleation conditions to create a favourable template for growing the final surface exposed to SRF fields. The influence of the deposition energy on film growth on copper substrates is investigated with the characterization of the film surface, structure, superconducting properties and RF performance