An energetic vacuum deposition system has been used to study deposition energy effects on the properties of niobium thin films on copper and sapphire substrates. The absence of a working gas avoids the gaseous inclusions commonly seen with sputtering deposition. A biased substrate holder controls the deposition energy. Transition temperature and residual resistivity ratio of the niobium thin films at several deposition energies are obtained together with surface morphology and crystal orientation measurements by atomic force microscope inspection, X-ray diffraction analysis and transmitted electron microscope (TEM) analysis. The results show that niobium thin films on a sapphire substrate exhibit the best cryogenic properties at a deposition energy of around 123 eV. The TEM analysis revealed that epitaxial growth of film was evident when the deposition energy reached 163 eV for a sapphire substrate. Similarly, niobium thin films on copper substrates show that the film grows more oriented with higher deposition energy and the grain size reaches the scale of the film thickness at a deposition energy of around 153 eV. D
An electron cyclotron resonance (ECR)-plasma reactor has been built to do energetic ion deposition of refractory metals in vacuum. The system uses an E-beam gun to create refractory metal flux. The neutral metal flux feeds into a microwave resonator and forms pure metal plasma created by electron cyclotron resonance. The metal ions are extracted to a biased substrate for direct deposition. A retarding field energy analyzer is developed and used to measure the kinetic energy of metal ions at the substrate location. A high-quality niobium thin film is obtained through this deposition system. The niobium film exhibits an excellent superconducting transition. The niobium ion energy distribution has been measured. The niobium ion at the substrate location has a median kinetic energy of 64 eV with an energy spread of 20 eV under certain plasma conditions.
Niobium (Nb) thin film deposited on copper (Cu) cavities through electron cyclotron resonance (ECR) plasma appears to be an attractive alternative technique for fabricating superconducting radio frequency cavities to be used in particle accelerators. The performance of these obtained Nb/Cu cavities is expected to depend on the surface characteristics of the Nb films. In this report, we investigate the influence of deposition energy on surface morphology, microstructure, and chemical composition of Nb films deposited on small Cu disks employing a metallographic optical microscope, a 3-D profilometer, a scanning electron microscope, and a dynamic secondary ion mass spectrometry. The results will be compared with those obtained on Nb surfaces treated by BCP, EP, and BEP.
A system using an Electron Cyclotron Resonance (ECR) plasma source for the deposition of a thin niobium film inside a copper cavity for superconducting accelerator applications has been designed and is being constructed. The system uses a 500-MHz copper cavity as both substrate and vacuum chamber. The ECR plasma will be created to produce direct niobium ion deposition. The central cylindrical grid is DC biased to control the deposition energy. This paper describes the design of several subcomponents including the vacuum chamber, RF supply, biasing grid and magnet coils. Operational parameters are compared between an operating sample deposition system and this system. Engineering progress toward the first plasma creation will be reported here.
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