MgB₂films fabricated on molybdenum substrate by hybrid physical–chemical vapor deposition for superconducting RF cavity applications

Abstract

Magnesium diboride (MgB2) is a good candidate material for superconducting RF cavities because of its higher transition temperature of ∼39 K and because of the absence of weak links between grains which prevents other high-Tc superconducting materials, such as YBCO, from being used for SRF cavities. Differently from MgB2 films fabricated on Cu or stainless steel(SS), we have fabricated MgB2 films on Mo substrate by hybrid physical–chemical vapor deposition. The films are about 0.7 µm thick and the Tc (onset) is as high as 38 K, with a corresponding transition width of 0.9 K. The upper critical field at T = 0 K, HC2(0), is extrapolated as 13.5 T and the critical current density at 5 K, JC (5 K, 0 T), is 6.5 × 105 A cm−2. Analysis results indicate that MgB2 film on molybdenum substrate has suitable superconducting properties and does not show the problems which often occur for MgB2 films fabricated on other metal substrates, such as the large cracks on SS substrate and the reaction between the substrate and the Mg on Cu substrate.

MgB2 thin films grown on graphene/Ni–Mo alloy system

“…5 shows us the M-H curve at 5 K. The critical current density j c is calculated by the Bean model j c = 20DM/Va(1Àa/3b), where DM is the width of the M-H loop, and V, a and b are the volume, width and length (a < b) of the sample, respectively. We can calculate j c (5 K, 0 T) is 9.6 Â 10 6 A/cm 2 , which is higher than He et al [17]. However, the graphene layer may become a carbon source that doping into MgB 2 film, meanwhile, the polycrystalline MgB 2 films may induce many defects, both situations will decrease the critical current density, which means a smaller j c than those have been reported [23,24].…”

“…3a and b shows the MgB 2 films deposited with 5% and 25% concentration flow of B 2 H 6 (8 sccm) respectively, we can see the films in this system are superconducting, and the transition temperature are 36.4 K and 37 K. Contrast to Ref. [17], we can easily get the superconducting MgB 2 films at a lower concentration and a less B 2 H 6 gas flow, which lays a good foundation of depositing thick films. The M-T curve shows us a higher concentration of B 2 H 6 has a steeper transition, which means it makes a better MgB 2 film.…”

“…Those predictions show us MgB 2 -graphene system may have a great potential in the area of electronic applications. At the same time, MgB 2 film fabricated on molybdenum substrate is also a good candidate for Superconducting Radio Frequency (SRF) cavity, because its higher transition temperature of 39 K and the absence of weak links between grains which prevents other high-T c superconducting materials, such as YBCO, from being used for SRF cavity [17].…”

A possibility of enhancing Jcin MgB2film grown on metallic hastelloy tape with the use of SiC buffer layer

“…Wide variety of metallic substrates has been applied in the making of MgB 2 superconducting tapes throughout the years [12][13][14]. All of which were made without inserting any buffer layer.…”

Microwave Response of Coaxial Cavities Made of Bulk Magnesium Diboride

“…Still now, several groups investigate the properties of MgB 2 with the aim to demonstrate its suitability for mw applications, particularly in films [8]- [10]. The advantage in using MgB 2 rather than conventional superconductors is its higher T c , which can be easily reached by little expensive closed-cycle cryocoolers.…”