Magnetron sputtering of Superconducting Multilayer Nb3Sn Thin Film

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Unfortunately even if no grain boundaries are present and a δ-phase singlecrystal is considered the single grain resistivity is not so low: A minimum value ofρ n = 30μΩcm is expected, due to both metallic and gaseous vacancies in thelattice. This problem that is common to all the other B1 compounds consists in thefact that what corresponds to the equiatomic composition is not the formulaNb 1.0 N 1.0 , but Nb 0.987 N 0.987 : vacancies randomly distributed in both sublatticesamounts to 1.3% respectively.In order to improve the performance of NbN, the Titanium is added into. Itpresents all the advantages of the NbN, in the meanwhile it shows electricalconduction properties as more metallic as higher the titanium percentages is.Titanium is a good Nitrogen getter and the more Titanium we have the lowerlattice vacancies will be. The Nitrogen stoichiometry hence is closer to 1 than forNbN. Moreover the critical temperature is even higher than that of NbN forTitanium content up to 40%. The resistivity instead decreases steeply versus theTitanium content [15-17] . This last phenomenon is the main reason under NbTiNchoice. NbTiN cavities have been sputtered at CERN and at Saclay. The Q 0 , atzero field, is higher than the Q-value of Niobium cavities, but the acceleratingfield achieved does not overcome the 10 Mv/m limit [18] .V 3 GaThe A15 phase forms by a congruent reaction from the bcc solid solution at1295°C and is stable from 20 at. % to 32 at. % gallium. The T C shows a markedmaximum of 15.9K at stoichiometry and decreases almost linearly on both sizes.V 3 Ga has the highest electronic density of states of all known A15 compounds. Incontrast to the latter, however, it does not exhibit a low temperature phasetransformation, which is explained by the fact that perfect ordering in thiscompound cannot be reached.V 3 AlIt shows a T C up to 14K, but it is a metastable compound, superconductingonly under thin film form. In principle metastability would be not a problem forRF applications construction, if V-Al is sputtered into a resonator, and moreover ithas the advantage of a relatively low temperature of deposition. It should deservefurther investigation, being a relatively little studied compound. The real problemindeed is that, because of metastability, this compound is not applicable to12
superconducting magnet construction, and then it has been generally neglected inA15 treatises.V 3 SiThis material is one of the few examples of an A15 compound that formcongruently from the melt. The A15 phase in the Vanadium-Silicon system isstable between 19 and 25 at. % Silicon. Large single crystals can be grown in thewhole range either by zone melting or by recrystallization at 1870°C. There is alinear increase in T C from 19 at. % to 25 at. % silicon, where a maximum T C of17.1K is achieved. For this compound, the RRR value of 80 can be obtained.One problem must be solved before to apply this material to cavities: aproper substrate should be chosen. Niobium is not the right choice, because of thelarge diffusion coefficient of Vanadium into Niobium at high temperatures. Thechoice of Vanadium itself, as a substrate, should be more deeply considered, dueto the drawback of lower thermal conductivity than Niobium, and this is aproblem for the achievement of high gradients.Fig.1.6 A15 phase fields and superconductivity in a) Nb-Ga, b) Nb-Ge, and c) Nb-Al SystemsNb 3 AlThis compound is formed by a peritectoid reaction from the bcc solidsolution and sigma (Nb 2 Al) phase at 1730°C, and contains 26 at. % Al. The13
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: NbN cavities literature, is often h
Page 23 and 24: 775°C. From the same diagram, it i
Page 25 and 26: two types of electrons at the Fermi
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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