Magnetron sputtering of Superconducting Multilayer Nb3Sn Thin Film

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(MgB 2 ), which is a simple ionic binary compound that has proven to be aninexpensive and useful superconducting material. Its crystal structure is shown in Fig.1.8.The superconductivity of MgB 2 was announced in the journal Nature in March2001 by Nagamatzu and Akimitsu [20] . Its Tc of 39 K for a sp-bonded is the highestamongst conventional superconductors. This material was first synthesized and itsstructure confirmed in 1953, [21] but its superconducting properties were not discovereduntil 2001. The discovery caused great excitement and led to the general interest inthis material, since it opens the way to a new class of simple and low-cost binaryintermetallic superconductors with a record HTCs for non-oxide and non C-60 basedcompounds.Fig. 1.9 Temperature dependence of the upper critical field, the region near T c isenlarged in the inset.Though generally believed to be a conventional superconductor and mostexperimental works, as Raman Spectroscopy, Boron-isotope effect, Spin latticerelaxation time, tunneling measurements and optical conductivity data, are allconsistent with the existence of phonon mediated superconductivity, it is a ratherunusual one. But an unusual superconducting gap behavior has been observedindicating the existence of a double gap [22] and the presence of a smaller gap is aserious drawback for RF applications. Its electronic structure is such that there exist16
two types of electrons at the Fermi level with widely differing behaviours, one ofthem (σ-bonding) being much more strongly superconducting than the other(π-bonding). This is at odds with usual theories of phonon-mediatedsuperconductivity which assume that all electrons behave in the same manner.Theoretical understanding of the properties of MgB 2 has almost been achieved withtwo energy gaps. It was regarded as behaving more like a metallic than a cupratesuperconductor.On the other side the material appears promising for RF, since it is ratherinsensitive to impurity content; it is highly metallic and has strong linked grainboundaries. Its properties depend greatly on composition and fabrication process.Many properties are anisotropic due to the layered structure. 'Dirty' samples, e.g., withoxides at the crystal boundaries, are different from 'clean' samples. [23]The maximum critical current (Jc) is: 10 5 A/m² at 20 T, 10 6 A/m² at 18 T, 10 7A/m² at 15 T, 10 8 A/m² at 10 T, 10 9 A/m² at 5 T [23] .Up to 2008, the parallel upper critical field (H c2 ) obtained is about 14.8 T, andthe perpendicular upper critical field is about 3.3 T as shown in Fig. 1.10 [23] . In thinfilms the field is up to 74 T, and in fibres up to 55 T [23] .MgB 2 thin film produced by the hybrid physical chemical vapour deposition(HPCVD) has the good performance, which characterized by T c0 = 41.8 K, ρ 0 = 0.26μΩ cm, RRR > 30 [24,25] , and self-field J c = 3.4×10 7 A cm −2 [26] .As far assuperconducting cavities are concerned, still many problems must be solved: thedegradation of superconducting properties of MgB 2 after the immersion in water.Fig.1.10 R BCS of different material17
Page 1: UNIVERSITÀ DEGLISTUDI DI PADOVAFac
Page 7 and 8: IndexINDEX ........................
Page 9 and 10: IntroductionThe superconductor acce
Page 11 and 12: Fig. 1.1 Disc-loaded traveling-wave
Page 13 and 14: In Type-II superconductors, vortex
Page 15 and 16: needed for preventing the supercond
Page 17 and 18: The B1 crystal structure has a cubi
Page 19 and 20: NbN cavities literature, is often h
Page 21 and 22: superconducting magnet construction
Page 23: 775°C. From the same diagram, it i
Page 27 and 28: Of course, there are some other kin
Page 29 and 30: as shown in Fig.2.3. The four opera
Page 31 and 32: Fig.2.8 turbomolecular pumpFig. 2.9
Page 33 and 34: Fig. 2.14 The chamber covered with
Page 35 and 36: Fig. 2.17 the gasket and the magnet
Page 37 and 38: shown in Fig. 2.21 and Fig. 2.22. T
Page 39 and 40: Fig. 2.26 The interface of the surf
Page 41 and 42: Fig. 2.30 put the sample into the T
Page 43 and 44: Fig. 2.34 the performance of the th
Page 45 and 46: 1008038.5°{110}69.6°{211}sample1s
Page 47 and 48: 2dsinθ= nλ (2.3)Fig.2.44 the diff
Page 49 and 50: Chapter 3 Multilayer deposition of
Page 51 and 52: 1 minute. The time of depositing mu
Page 53 and 54: chamber 1 and is connected to the s
Page 55 and 56: 3.2.2.2 Analysis resultⅠ The thic
Page 57 and 58: In order to detect the component of
Page 59 and 60: measure the RRR. So the resistance
Page 61 and 62: 110100903480relative Intensity70605
Page 63 and 64: frequency of the cavity which is in
Page 65 and 66: Fig. 3.28 the inductor coilDuring t
Page 67 and 68: Fig. 3.32 fixing the sample with Nb
Page 69 and 70: second transition temperature is th
Page 71 and 72: source is the bulk Nb sample. Altho
Page 73 and 74: of 1A in the Fig. 3.37 and Fig. 3.4
Page 75 and 76:
Table 3.10 the description of the p
Page 77 and 78:
1101001.0A10'-IND3 45 6 7 9 1011 12
Page 79 and 80:
1101009080341.8A10'INDrelative inte
Page 81 and 82:
Reference1. A. Godeke, Nb3Sn FOR RA
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Magnetron sputtering of Superconducting Multilayer Nb3Sn Thin Film

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