Superconducting thin films of MgB2 on (001)-Si by pulsed laser deposition

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Hyper Tech(美国Hyper公司MgB2超导材料介绍)

FCL- 2 organizations for both resistive and inductive type plus Hyper Tech’s internal resistive FCL program
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Typical multifilament MgB2 conductor
MgB2 Nb
Cu
Monel
Lengths currently up to 6 km @ 0.8 mm, scaling up to over 60 km.
9
Wire Performance
Commercial 1st Generation MgB2 Wire
0 0 2 4 6 8 10 12 14
B (T)
Peak bore fields: 4.6 T at 4.2 K, 2.2 T at 20 K
11
Improving connectivity, continued
106 36 fil [CTFF-1] 1 fil [CTFF-2] 1 fil [CTFF-2] Interpolated 18 fil [CTFF-2] 105
Third , the superconductor needs to operate at a wire performance level that can significantly reduce the weight and cost of the generator.
Fourth- superconducting generator design needs to be easily manufactured, maintained and repaired in the field.

On the Decoupling of Layered Superconducting Films in Parallel Magnetic Field

a r X i v :c o n d -m a t /9604182v 2 24 J u n 1996ON THE DECOUPLING OF LAYERED SUPERCONDUCTINGFILMS IN PARALLEL MAGNETIC FIELDJ.P.Rodriguez Theoretical Division,Los Alamos National Laboratory,Los Alamos,NM 87545and Dept.of Physics and Astronomy,California State University,Los Angeles,CA 90032.*Abstract The issue of the decoupling of extreme type-II superconducting thin ﬁlms (λL →∞)with weakly Josephson-coupled layers in magnetic ﬁeld parallel to the layers is considered via the corresponding frustrated XY model used to describe the mixed phase in the critical regime.For the general case of arbitrary ﬁeld orientations such that the perpendicular magnetic ﬁeld component is larger than the decoupling cross-over scale characteristic of layered superconductors,we obtain independent parallel and perpendicular vortex lattices.Specializing to the double-layer case,we compute the parallel lower-critical ﬁeld with entropic eﬀects included,and ﬁnd that it vanishes exponentially as temperature approaches the layer decoupling transition in zero-ﬁeld.The parallel reversible magnetization is also calculated in this case,where we ﬁnd that it shows a cross-over phenomenon as a functionof parallel ﬁeld in the intermediate regime of the mixed phase in lieu of a true layer-decoupling transition.It is argued that such is the case for any ﬁnite number of layers,since the isolated double layer represents the weakest link.PACS Indices:74.60.Ec,74.20.De,11.10.Lm,75.10.HkI.IntroductionThe study of layered superconductivity has been reinvigorated by the discovery of the high-temperature oxide superconductors.1In the case of the Bismuth(Bi)and Thallium (Tl)based compounds,for example,the superconducting coherence lengthξc perpendicular to the conducting planes is less than the separation between layers,and London theory fails.1Hence a Lawrence-Doniach(LD)type of description in terms of weakly Josephson-coupled layers becomes necessary.2The following question then naturally arises:does a layer decoupling transition,aided perhaps by the introduction of a parallel magneticﬁeld,3 occur in such systems in addition to or in place of the conventional type-II superconducting ones marked by the lower and upper criticalﬁelds,4H c1(T)and H c2(T)?In the absence of external magneticﬁeld parallel to the layers,a layer decoupling transition is indeed predicted to exist theoretically at a critical temperature T∗that lies above that of the intra-layer Kosterlitz-Thouless(KT)transition temperature,T c.5−8This result is based on studies of the XY model with weakly coupled layers,which accurately describes a layered superconductor in the absence ofﬂuctuations of the magneticﬁeld;9,10 e.g.,in the intermediate regime of the mixed phase found in extreme type-II superconduc-tors,where it is appropriate to take the limitλL→∞for the London penetration length λL.Also,recent experiments on Bi-based high-temperature superconductorsﬁnd evidence for a superconducting transition at T c c,where the c-axis resistivity vanishes,that lies a few tenths of a degree Kelvin above a second superconducting transition temperature T ab c, where the resistivity in the ab-planes vanishes.11,12Hence both theory and experiment ﬁnd an extraordinary regime in temperature,T c=T ab c<T<T∗=T c c,where Josephson tunneling between layers exists while the layers themselves are resistive and show no intra-layer phase coherence.(It has recently been argued in ref.13that T c c in fact marks a sharp crossover for the bulk case.)Last,it is worth pointing out that Monte-Carlo simulations of the three-dimensional(3D)XY model obtain similar behavior in the presence of a large magneticﬁeld perpendicular to the layers.10The nature of layer decoupling in the presence of magneticﬁeld parallel to the layers, on the other hand,is less well understood.Early work by Efetov suggests that supercon-ducting layers decouple at high parallelﬁelds B >B ∗(0)∼Φ0/d2γ,whereΦ0denotes theﬂux quantum,γ=(m c/m ab)1/2is the mass anisotropy parameter,and d denotes theseparation between layers.3The latter calculation is based on a high-temperature series expansion analysis of the LD model.A recent study of the same model by Korshunov and Larkin that employs a Coulomb gas representation,however,ﬁnds no such layer decoupling in the high-ﬁeld limit for temperatures below the decoupling transition.14In this scenario, therefore,the layers remain eﬀectively Josephson coupled up to the parallel upper-critical ﬁeld,H c2(T).In this paper,we shall also examine the decoupling of layered superconductors in parallel magneticﬁeld,but inﬁlm geometries of thickness much less than the in-plane London penetration length,and at temperatures near the zero-ﬁeld decoupling transition at T∗.5−7Speciﬁcally,we consider thinﬁlms of extreme type-II layered superconductors (λL→∞)in the intermediate regime(H c1≪H≪H c2)of the mixed phase,which can be described by a frustrated XY model with aﬁnite number of N weakly coupled layers.10 By working with the Villain form of the latter,7,15we obtainﬁrst that the thermodynamics factorizes into independent perpendicular and parallel parts in the presence of magnetic ﬁeld at arbitrary orientation so long as the perpendicular component,H⊥,of the latter is larger than the Glazman-Koshelev decoupling cross-over scale,16B⊥∗∼Φ0/d2γ2.The perpendicular thermodynamics is characterized by the melting of two-dimensional(2D) vortices17that are decoupled from the parallel Josephson vortices,as well as from the perpendicular2D vortices in adjacent layers.This is a result of the fact that well-formed vortex loops traversing a few or more layers within theﬁlm are absent in the present limit of weak inter-layer coupling.7In particular,the parallel Josephson vortices are unable to make connections between perpendicular2D vortices in the same or in adjacent layer if the nearest-neighbor spacings between these perpendicular2D vortices is much less than the zero-temperature Josephson penetration length,λJ(0)∼γd.This situation occurs precisely for perpendicularﬁelds that satisfy H⊥≫B⊥∗,as stipulated above.Also,since weﬁrst take the limit of extreme type-II superconductivity,we then have the inequality B⊥∗≫H⊥c1∼Φ0/λ2L.This means that the former requirement guarantees that the distance between perpendicular vortices is within the London penetration length,which in turn guarantees that magnetic screening transverse to the perpendicularﬁeld component is negligible.The parallel thermodynamics,on the other hand,is described by a LD model in parallel magneticﬁeld H ,with a heavily renormalized anisotropy parameterγ(T)thatdiverges exponentially as T approaches the decoupling transition temperature T∗from below.The renormalization down of the inter-layer coupling is due physically to the excitation of vortex rings5(ﬂuxons)that lie in between consecutive layers.Second,we compute the line tension of a single Josephson vortex in the simplest case of an isolated weakly coupled double-layer XY-model,where weﬁnd that the parallel lower-criticalﬁeld H c1(T)of the double-layer vanishes exponentially as T approaches T∗from below.This result agrees up to a numerical factor with a recent calculation by the author of the same that employs an alternate“frozen”superconductor description of the Meissner phase in layered superconductors.8Related results have also been obtained by Browne and Horovitz in the setting of long Josephson junctions18and by Horovitz via a fermion analogy for layered superconductors in parallel magneticﬁeld.6The former coinci-dence is not surprising since the present double-layer type-II superconductor is equivalent to a(dynamical)long Josephson junction at zero temperature,19−22wherein no current is allowed to pass between the junction.In fact,the above analysis proceeds byﬁrst consid-ering the length of the vortex as imaginary time.Semi-classical quantum corrections to the energy of the fundamental sine-Gordon soliton,23−25which corresponds to the Josephson vortex in the double layer,are then computed.Entropic wandering of the vortex therefore translates into quantumﬂuctuations of the soliton.Note that the wandering of Josephson vortices is equivalent to the excitation of double-layerﬂuxons,which are again the physical origin of this phenomenon.We next consider a one-dimensional lattice of Josephson vortices in the double layer. After adapting certain elements from the analysis of long Josephson junctions in external ﬁeld19−22to the“semi-classical”analysis discussed above in the case of a periodic array of sine-Gordon solitons,we are able to compute the reversible magnetization as a function of parallel magneticﬁeld.Notably,we obtain a cross-overﬁeld B ∗(T)∼Φ0/d2γ(T), beyond which the magnetization displays a B−3tail characteristic of both long Josephsonjunctions19and of layered superconductors in high parallelﬁeld,26generally(see Fig.1 and ref.27).Unlike long Josephson junctions,however,this cross-overﬁeld is much larger than the lower-criticalﬁeld.Thus weﬁnd no evidence forﬁeld dependence in the layer decoupling transition temperature,T∗,within the present“semi-classical”approximation, which is in agreement with the results of Korshunov and Larkin.14Last,we argue thatsuch is the case for anyﬁnite number of layers,since the isolated double layer represents the weakest link.The remainder of the paper is organized as follows:in part II we introduce the frus-trated XY model in the Villain form,from which we derive the renormalized LD model for T<T∗.The double-layer case is the focal point of section III,where we compute the parallel lower-criticalﬁeld and the parallel reversible magnetization from the above LD model,in addition to the compressibility modulus of the corresponding vortex array and the eﬀective inter-vortex interaction potential in the dilute limit.We then apply these results to the phenomenology of layered type-II superconductors in section IV,as summa-rized by st,we assess the validity of the present“semi-classical”approximation, as well as discuss the general case of N layers,in section V.II.Frustrated XY ModelThe object now is to understand extreme type-II superconductingﬁlms composed of a ﬁnite number N of weakly coupled layers in the presence of external magneticﬁeld.In the intermediate regime of the mixed phase,where the magneticﬁeld satisﬁes H c1≪H≪H c2, the London penetration length is in general much larger than the inter-vortex spacing. Following Li and Teitel,10magnetic screening eﬀects are then negligible,and we may describe the system by a uniformly frustrated layered XY model with an energy functional given byE XY=JNl=1 r µ=x,y{1−cos[∆µφ( r,l)−Aµ( r,l)]}+J⊥N−1l=1 r{1−cos[φ( r,l+1)−φ( r,l)−A z( r,l)]}.(1)Hereφ( r,l)is the phase of the superconducting order-parameter on the layered structure, where r ranges over the square lattice with lattice constant a,and l is the index for the layers separated by a distance d.We presume that the lattice constant a is larger than the size of a typical Cooper pair.The magneticﬂux threading the plaquette at site( r,l) perpendicular to theµ=x,y,z direction readsΦµ=(Φ0/2π) ν,γǫµνγ∆νAγ,where Φ0=hc/2e is theﬂux quantum.Also,∆µφ(r)=φ(r+ˆµ)−φ(r)is the lattice diﬀerenceoperator.The nearest-neighbor Josephson couplings are related to the respective masses in Ginzburg-Landau theory byJ =(¯h2/2m a2)(n s a2d),(2a)J⊥=(¯h2/2m⊥d2)(n s a2d),(2b)where n s labels the superﬂuid density.Notice that J is independent of the lattice constant, a,as required by scale invariance in two dimensions.Hence the anisotropy parameter,γ′=(J /J⊥)1/2,of the XY model is related to that of the mass,γ=(m⊥/m )1/2,byγ′=γd2βNl=1 r n2( r,l)−1(2π)2e i k· ris(formally)the Greens function for the square lattice.In the limit of weak coupling,γ′→∞,the interlayerﬁeld n−vanishes,which implies that n′is indeed an integerﬁeld. After making a suitable(lattice)integration by parts of the energy functional in Eq.(4), we then obtain the factorization Z=Z CGΠN l=1Z(l)DG for the partition function in the limit of weakly coupled layers,whereZ(l)DG= { n′( r,l)}Π rδ[ ∇· n′| r,l]exp −12βNl=1 r, r′[n z( r,l−1)−n z( r,l)]G(2)( r− r′)[n z( r′,l−1)−n z( r′,l)]−iN−1l=1 r n z( r,l)A z( r,l)−12J ,while the inter-layer links n z( r)undergo an inverted2DCoulomb gas binding transition at k B T∗=4πJ in the limit of weak inter-layer coupling,γ′→∞.7(It is understood that the limit of vanishing Josephson coupling is taken beforethat of vanishing perpendicularﬁeld.)The latter high-temperature transition,which oc-curs well inside the normal phase of each individual layer,corresponds to the decoupling of layers mediated by the binding of oppositely(n z)charged vortex rings lying in between consecutive layers.5Notice this implies that Josephson coupling between resistive layers exists in the temperature regime T c<T<T∗!8,11,12Forγ′large butﬁnite,the form(7) of the layered Coulomb gas ensemble indicates that each set of consecutive double layers is dielectrically screened by itself as well as by the neighboring N−2such double layers. Hence,they each can be considered in isolation from their neighbors as long as one makesβ ,whereǫ0−1is the polarization of an isolated double layer. the replacementβ →ǫN−1Since the latter is directly proportional to the fugacity,y∗=exp(−2πγ′2),of the Coulomb gas(7)at T∗[see Eq.(11)],8and since the decoupling transition temperature is then given by k B T∗∼=4πJ [1+(N−1)(ǫ0−1)]in the limit of weak inter-layer coupling,we obtain an implicit linear dependence for the corrections to the value of T∗with the fugacity y∗. Such a linear dependence agrees with the standard renormalization-groupﬂows that cor-respond to the2D Coulomb gas.30As expected,the above formula for T∗also indicates that the decoupling transition temperature increases without bound with the number of layers.In particular,the former linear increase crosses over to an exponetial increase at N0∼(ǫ0−1)−1layers,which is far beyond the2D-3D cross-over point expected to occur at N c/0∼γ′layers for the layered XY model.31This is then consistent with the fact that the bulk layered XY model exhibits only a3D superﬂuid transition at the bulk T c.Note that the present factorization into parallel and perpendicular parts is unable to obtain corrections for the value of T c in the case of large butﬁnite anisotropy parametersγ′.32 Consider now Eqs.(6)and(7)in the presence of a homogeneous magnetic induction,Φ0B =b⊥,(9b)2πawith the parallel component directed along the y-axis,and with B⊥≫B⊥∗to insure the decoupling between2D perpendicular vortices and parallel Josephson vortices explicit in the previous factorization of(4).16This decoupling becomes evident if we choose the gaugeA x=0,A y=b⊥x,and A z=−b x,where b and b⊥are the parallel(7)and perpendicular(6)magneticﬂux densities.In particular,each layer independently experiences the per-pendicular component B⊥=H⊥of the magnetic induction,33which sets the intra-layervortex density to be n V=|H⊥|/Φ0.The fact that n V≫λ−2J≫λ−2L in the present limit of extreme type-II superconductivity insures that magnetic screening eﬀects transverse to the perpendicularﬁeld component can be neglected.Each layer will then independently follow the2D vortex lattice melting scenario,17with a melting temperature T m<T c.Since the issue of2D vortex lattice melting has already been discussed extensively in the literature with respect to the phenomenon of high-temperature superconductivity,1we shall end the present discussion here and focus our attention below on the thermodynamics connected with the parallel component to the magnetic induction.We now derive the renormalized LD theory2−4mentioned in the introduction.It is usefulﬁrst to make the following Hubbard-Stratonovich transformation of the Coulomb gas ensemble(7):34Z CG= Dθ( r,l) {n z( r,l)}exp −β2β⊥N−1l=1 r n2z( r,l) .(10)Hereθ( r,l)represents a real scalarﬁeld that lives on each layer.Suppose now that we operate in the low-temperature regime,T<T∗,where the layers are coupled.5−7Then inter-layer n z charges in the Coulomb gas ensemble are screened,which means that global charge conservation is no longer enforced.Following the standard prescription,34we in-dependently sum over charge conﬁgurations at each site,with the restriction to values n z=0,±1.In the limit that the fugacityy0=exp(−1/2β⊥)(11)is small,we thenﬁnd that the original Coulomb gas ensemble(7)is equivalent to a renor-malized Lawrence-Doniach model Z CG= Dθ( r,l)exp(−E LD/k B T)with energy func-tionalE LD=JN l=1 r1At the decoupling transition in particular,we have that the fugacity(11)is given by y∗=exp(−2πγ′2).Hence,the anisotropy parameter is renormalized up toγ′∗= J( ∇¯θ)2 ,(14)2where¯θ( r)=2−1/2[θ( r,1)+θ( r,2)].Here,L SG[φ]= dx 1∂y 2+1∂x−b 2+Λ−20(1−cosφ) (15) represents the“Lagrangian”for the sine-Gordon model in one space(x)and one imaginary time(y=i¯t)dimension,with a bare Josephson penetration lengthΛ0=a(β /4y0)1/2,(16)while the eﬀective dimensionless Planck constant is¯¯hF=2/β .(17) Notice that we have taken the continuum limit of the LD model(12),as well as made the change of variableφ( r)=θ( r,2)−θ( r,1)−A z( r).The integration over¯θon the right of Eq.(14)results in a trivial gaussian factor.Below,we shall exploit the quantum mechanical analogy suggested above for the nontrivial sine-Gordon factor in order to compute the parallel lower-criticalﬁeld8and the parallel reversible magnetization of the double-layer system.A.Single Josephson VortexWe now set ourselves to the task of computing the parallel lower-criticalﬁeld,H c1,of the double layer system,which is in general related to the free energy per unit length of a single Josephson vortex,ε ,by1H c1=4πε /Φ0.Let us therefore consider the eﬀective sine-Gordon model(15)in the presence of a single Josephson vortex aligned along the y-axis;i.e.,the homogeneous magneticﬂux is set to b =0,while the phase-diﬀerence ﬁeld winds once along the x-axis; ∞−∞dx∂φ/∂x=2π.In the absence of thermal(or “quantum”)ﬂuctuations,the vortex line tension is given by the Ginzburg-Landau energyε0 =JΛ0(18)of the“static”fundamental sine-Gordon solitonφ0(x,y)=4tan−1e x/Λ0,(19) which is a solution of theﬁeld equation−∂2φWe shall now include the eﬀects of thermal wandering in the double-layer Josephson vortex(19)byﬁrst Wick rotating the y coordinate to a real time-like coordinate,y= i¯t.Second,we observe that the free energy per unit length of the Josephson vortex is equal to the product of12 dxφ∗1 ∂2∂x2+Λ−20cosφ0 φ1(21)to second order in the deviation.Hence in the presence of the soliton,we obtain a spectrum of harmonic oscillators of the formφ1(x,¯t)=ψ(x)e iω¯t,where−∂22 (25) gives the corresponding amplitude of each harmonic oscillator.After Wick rotating back to imaginary time L y=i¯T0,we observe that only the n=0terms above survive the limit of a long vortex,L y→∞.Yet the ratio of the partition functions in the presence of a single Josephson vortex to that in its absence is in general related to the vortex linetension,ε ,by Z SG[1]/Z SG[0]=exp(−L yε /k B T).In the“semi-classical”limit,therefore, we obtaink B Tε =ε0 += r0λJJosephson penetration lengthλJ diverges exponentially as it approaches the decoupling transition likeλJ/a=C exp[D/(β −β∗)1/2].(31)Here,C and D are non-universal numerical constants.In conclusion,the parallel lower-criticalﬁeld H c1=4πε /Φ0vanishes exponentially fast near the decoupling transition of the double layer following Eqs.(29)and(31). Horovitz has obtained this result employing a fermion analogy for layered superconductors in parallel magneticﬁeld.6A similar dependence has also been proposed by Browne and Horovitz for the lower-criticalﬁeld of long Josephson junctions.18Combining Eq.(2a) with the identity(Φ0/λL)2=(2π)3(¯h2/2m )n s for the bulk(N→∞)in-plane London penetration lengthλL yieldsJλ2L,(32) from which we obtain the useful expressionε (T)=84πλL(T)2λJ(0)characterized by a spin-gap.35Second,notice that we have essentially recovered the stan-dard renormalization group results for the KT transition30via the present semi-classical quantization of the sine-Gordon soliton energy in one space and one time dimension.Fi-nally,also observe that the entropic correction to the line-tension in Eq.(28)indicates that the number of microstates per unit length a of a Josephson vortex in thermal equilibrium isλJ/r0.Given that r0∼a,thenλJ can be naturally interpreted as the eﬀective width of the Josephson vortex.B.Array of Josephson VorticesConsider now the case of a nonzero homogeneous magnetic induction aligned parallel to the y-axis of the double layer;i.e.,b =0.Then it is easily seen from Eq.(15)that the superﬂuid portion,G s−G n=−k B T ln Dφe−¯¯h−1F dyL SG[φ],(34) of the Gibbs free energy36is minimized with respect to b at b =L−1x ∞−∞∂φ/∂x.In other words,the average winding per unit length in any conﬁguration of the phase diﬀerence between the double-layers is set by the magnetic induction.In the particular case of the low-temperature“classical”conﬁguration,we then have that the parallel magnetic induction is related to the lattice constant a0of the corresponding array of Josephson vortices by2πb =∂B G s−G nof the double layer in the intermediate regime of the mixed phase,H c 1≪B ≪Hc 2,where H ∼=B .Consider ﬁrst the lowest order Ginzburg-Landau contributionG 0s −G n =L y J dx =2κΛ0κ2 ,(38)where the parameter κlies in the interval between zero and unity,and is set by the period a 0followinga 0=2Λ0κK (κ2).(39)Above,dn(u |κ2)represents the appropriate Jacobian Elliptic function,while K (κ2)rep-resents the complete Elliptic integral of the ﬁrst kind.37Conservation of energy,E 0=2Λ−20(κ−2−1),in the corresponding pendulum system yields L SG [φ0]2 dφ02b 2 .We obtain,therefore,that the zero-order Gibbs free energy density is equal toG 0s −G n Λ20 2K (κ2)+1−κ−2 −J 2,(40)where E (κ2)represents the complete Elliptic integral of the second kind.37Standard manipulations 19then yield that the reversible magnetization (36)is given by−4πM =H c 1 E (κ2)41Λ0 a 02Λ0for the reversible magnetization (41).Hence,the low-ﬁeld magnetization extrapolates to zero atB 0=2Λ0d,(43)which deﬁnes a bare crossover ﬁeld.At high-ﬁelds a 0≪Λ0,on the other hand,(39)dictates that κ∼=π−1a 0/Λ0.We then obtain that the limiting behavior for the reversible magnetization (41)is given by−4πM ∼=H c 1Λ0 3(44)in such case.This implies a B −3tail at high ﬁelds B ≫B 0that is characteristic of long Josephson junctions and of layered superconductors in general.19,26A plot of result (41)spanning both the high-ﬁeld and low-ﬁeld limits is shown in Fig.1.Notice that the bare crossover ﬁeld B 0is much larger than the Ginzburg-Landau lower-critical ﬁeld Hc 1in the present double-layer extreme type-II superconductor [see Eq.(51)].This is qualitatively diﬀerent from the case of a long Josephson junction,19where B 0∼H c 1.In analogy with the previous analysis of a single Josephson vortex,let us now consider the eﬀect of “semi-classical”corrections to the reversible magnetization in parallel ﬁeld(41).We again have a spectrum (21)of harmonic oscillators φ1(x,¯t )=ψ(x )e iω¯t that satisfy the linearized ﬁeld equation (22),but with a periodic conﬁguration for the phase diﬀerence set by 20,21cos 1κΛ0 κ2 ,(45)where sn(u |κ2)represents the appropriate Jacobian Elliptic function.37To be more speciﬁc,the spatial factors of each oscillator satisfy Lam´e ’s equation,21−∂2κΛ0 κ2 −Λ−20 ψ=ω2ψ.(46)To make contact with the previous discussion of a single Josephson vortex,let us now focus our attention on the (bare)low-ﬁeld regime B ≪B 0,where the parameter κisexponentially close to unity,since a 0≫Λ0.This allows us to approximate the potential terms in Lam´e ’s equation [−∂2Λ0,(47)where each term above corresponds to the potential associated with a fundamental sine-Gordon soliton centered at x0+na0.In general,the band structure corresponding to Lam´e’s equation(46)is composed of a continuum and a zero-mode band separated by a gap.21,37A curious feature particular to each potential term in Eq.(47),however,is its transparency;23i.e.,the continuum oscillators(24)of the fundamental sine-Gordon soliton have no reﬂected wave component.Therefore in the present(bare)low-ﬁeld limit, the upper continuum band is essentially the same as that of a fundamental soliton(24). Repeating the renormalization group arguments made in the previous section for the line energy of a single Josephson vortex then indicates that the entropic correction due to the latter continuum band can be accounted for by simply replacingΛ0(16)withλJ(31)in the original Ginzburg-Landau free energy of the vortex lattice;i.e.,G s−G n=J2 ∂φ02∂φ02b2 +λ−2J(1−cosφ0) ,(48)with the lattice constant of the vortex array(38)set by Eq.(35).In general,however,the eﬀects of the zero-mode band must also be included in the present semi-classical analysis. The corresponding states are given by the tight-binding anzats|k0 = n e ik0a0n|n in the present(bare)low-ﬁeld limit,where x|n =ψb(x−x0−na0)is the(normalized)bound state(23)of the fundamental soliton located at the n th well.The hopping matrix element is therefore−t0= n|−∂22k0a0)|that is exponentially narrow.By(25), the zero-mode band results in an entropic pressure contribution to the Gibbs free energy density given byP0=k B T2ω0(k0)=2a0dt1/2.(49)Hence,the magnetization(36)acquires a diamagnetic correction−∂P0/∂B of order e−a0/2Λ0,which is negligibly small in the present(bare)low-ﬁeld limit.Eq.(42)indi-cates,however,that the low-ﬁeld correction to the initial linear increase of the parallel magnetization varies as e−a0/Λ0in the Ginzburg-Landau regime.Unlike the case of a single Josephson vortex,then no obvious renormalization group appears to exist for the above entropic pressure contribution.In conclusion,double-layer extreme type-II superconductors in parallel magneticﬁeld are described by the eﬀective Ginzburg-Landau free energy(48),along with the boundary condition(35),in the bare lowﬁeld limit B ≪B 0of the intermediate regime,H c1≪B ≪H c2.This means that the reversible magnetization is determined by the original Ginzburg-Landau theory analysis[Eqs.(36)-(44)],where the bare Josephson penetration lengthΛ0is replaced by the renormalized lengthλJ throughout.In particular,the true parallel cross-overﬁeld(see Fig.1)of the double layer is given byB ∗=2λJ d(50)instead of by Eq.(43).However,our inability toﬁnd a renormalization group for the entropic pressure contribution(49)to the parallel magnetization suggests that the present renormalized Ginzburg-Landau theory result for−4πM serves only as a strong lower bound in the critical regime.27We thereforeﬁnd evidence for at best a crossover as a function of magneticﬁeld below the bare scale B 0,and no evidence for a decoupling phase transition atﬁxed st,it is easily shown after employing relation(32)thatB ∗d2.(51) This of course indicates that the crossoverﬁeld is much larger than the lower-criticalﬁeld, which validates a posteriori the assumption(36)that H ∼=B in the intermediate regime of the mixed phase.It also illustrates the qualitative diﬀerence between a double-layer superconductor and a long Josephson junction,19where B ∗∼H c1.We shall close this section by computing the compression modulus of the parallel array of Josephson vortices,as well as the interaction energy between widely spaced vortices.The local change in the elastic free-energy density due to a localﬂuctuationδn V in the vortex density is given byδf SG=1λ2J d 2K(κ2)+1−κ−2 (52)is the Gibbs free-energy density(48)modulo the−1。

High critical current densities in superconducting MgB2 thin films

High critical current densities in superconducting MgB2 thin filmsS. H. Moon a), J. H. Yun, H. N. Lee, J. I. Kye, H. G. Kim, W. Chung, and B. OhLG Electronics Institute of Technology, Seoul 137-724, KoreaSuperconducting MgB2thin films were prepared on Al2O3(0001) and MgO(100) substrates. Boron thin films were deposited by the electron-beam evaporation followed by post-annealing process with magnesium. Proper post annealing conditions were investigated to grow good superconducting MgB2 thin films. The X-ray diffraction patterns showed randomly orientated growth of MgB2 phase in our thin films. The surface morphology was examined by scanning electron microscope (SEM) and atomic force microscope (AFM). Critical current density (J c) measured by transport method was about 107 A/cm2 at 15 K, and superconducting transition temperature (T c) was ~ 39 K in the MgB2 thin films on Al2O3.PACS numbers: 74.25.Fy, 74.60.Jg, 74.70.Ad, 74.76.Dba) Corresponding author, e-mail: smoon@The recent discovery of the superconductivity above 39 K in magnesium boride (MgB2) material attracts many researchers in scientific as well as technical reasons.1 This material seems to have conventional BCS type superconductivity, and it has the simple structure.2 The possibility of making good superconducting MgB2 wires with low-cost was reported by several groups, because the weak-link problem between grains does not seem to be the case in this material.3-5 The possibility of the electronic device application is also wide open, since it becomes possible to operate devices made of MgB2 thin films with a low-cost refrigerator because of the higher T c ~ 39 K than other conventional superconductors. In addition, it may be easy to make very reliable electronic devices and Josephson junctions with this material, because of its simpler crystal structure and longer coherence length compared with the oxide superconductors. To make electronic devices, MgB2 thin films with good superconducting properties are essential. Several groups have reported MgB2 thin films made by pulsed laser deposition (PLD) method or e-beam evaporation followed by post annealing.6-11 In this paper, we report our results on the growth of MgB2 thin films by the electron-beam evaporation method followed by post-annealing process. The evaporation method has an advantage to the PLD method to make large area thin films. We investigated optimum growth conditions to make good superconducting MgB2thin films on Al2O3(0001) and MgO(100) substrates. Some superconducting transport properties (T c and J c) and surface morphology of the MgB2 thin films were also investigated.To make MgB2 thin films, we have started with the boron thin films deposited on the substrates, similar to the MgB2 wire formation by Canfield et al.4 The boron thin film was deposited by the electron beam evaporation from boron source in crucible. We have used two different substrate temperatures for the boron deposition, room temperature and 750 °C. The background pressure of the deposition chamber was below 1 x 10-6 Torr. Typically 250 ~ 300 nm thick boron films were made with the deposition rate of ~ 2 Å/sec. The boron films as deposited were insulating and had brown color, and the broad boron peak was observed in X-ray diffraction pattern.To obtain superconducting MgB2 phase, the boron films were annealed under magnesium vapor environment. In order to maintain sufficient magnesium vapor environment during annealing, the boron films together with magnesium pieces were wrapped in a tantalum foil. Several pieces of titanium were also wrapped together with them as a spacer to prevent the direct contact of the boron film to the tantalum foil. Then, this whole thing was encapsulated in a quartz tube. To find an optimum annealing condition, we have varied annealing temperature and annealing time. The thickness of thin films has increased about 70 ~ 80 % due to the annealing. Final MgB2 thin film thickness was in the range of 450 ~ 500 nm, starting from 250 ~ 300 nm thick boron films.Figure 1 shows the normalized resistance data as a function of temperature (R vs. T) for the MgB2 thin films on Al2O3(0001)and MgO(100) substrates annealed at 800 o C for 30 minutes. The MgB2 thin films on Al2O3 substrate has been made from two kinds of boron films, deposited at room temperature or 750 o C. The MgB2 thin film made from the room temperature deposited boron film has shown higher T c than the other one. We have obtained the superconducting transition temperature (T c) of ~39 K with the transition width (∆T c) of about 0.3 K in the MgB2 thin film on Al2O3. The MgB2 thin film on Al2O3, made from the boron film deposited at 750 o C, has shown T c of ~ 37.4 K with?∆T c of about 0.7 K. Resistivity of this sample is about 2 times larger than the previous one, and it has a small tail in the R vs. T curve. This implies that the less formation of a crystalline phase of boron as a starting material was the better to form MgB2 phase during the post-annealing. The MgB2 film on MgO substrate has T c of ~ 38 K and ∆T c of about 0.5 K. MgB2 thin films on both Al2O3 and MgO have shown very similar R vs. T results, and the resistivity was in the range of 20 ~ 30 µΩ-cm at room temperature for both films.Figure 2 shows the glancing angle (incident angle of 5 degrees with sample rotation) X-ray diffraction patterns of the MgB2 thin films, which is basically the powder pattern of the thin films. Mainly MgB2 phase was observed, and there was no significant amount of MgO or MgB4 phases, which was often observed in thin films made by e-beam evaporation with MgB2 pressed pellets.9There was also no evidence of preferred orientation from theta-two-theta X-ray diffraction patterns which are not shown here, in which the main peak of MgB2 was overlapped with the substrate peak near ~ 43 degrees. From the X-ray diffraction patterns, we found that our MgB2 thin films have grown in random orientation on Al2O3(0001) and MgO(100) substrates. The MgB2 thin film made from the boron film deposited at 750 o C on Al2O3 has shown the similar random orientation growth.Figure 3(a) and 3(b) show the scanning electron microscope (SEM) and atomic force microscope (AFM) images of the MgB2 thin films on Al2O3 substrate with T c ~ 39 K. The surface of the boron film as deposited at room temperature was very flat and smooth from the SEM image. But the surface morphology of the MgB2 thin films formed by the post-annealing process became a little rough as in Fig. 3. This MgB2 thin film has the root mean square (RMS) roughness of ~ 20 nm according to the AFM image. Similar behavior was observed in MgB2 thin films on MgO substrates. We note that the thin film looks very dense and its grain size is smaller than about 100 nm.Figure 4 shows the critical current density (J c) as a function of temperature for several MgB2 thin films measured by four-point probe method. The inset shows the optical microscope image of the stripline used for the transport J c measurement. The J c criteria were less than 0.1 µV which was the noise level in the current-voltage characteristics (I-V curve). This stripline of 2 µm x 20 µm size was formed by photo-lithographic patterning and argon ion-milling with the milling rate of ~ 30 nm/min. The electrical contact was made by aluminum wire bonded directly to the contact pads. The contact resistance was less than ~ 1 Ω at 10 K.The thickness of the MgB2 thin films for J c measurement was in the range of 440 ~ 490 nm, and the error of the thickness measurement is estimated to be less than 20 %. The two films on Al2O3 were annealed at 800 o C for 30 minutes, and the thin film on MgO was annealed at 825 o C for 20 minutes. The transport J c of MgB2 thin films on Al2O3 and MgO was about 107 A/cm2 in the temperature range of 10 ~ 15 K, which is the highest J c at zero field reported so far. The reason of this large J c is not clear yet, but we speculate the pinning at the grain boundary or at the interface between thin film andsubstrate may be very strong in our films. The T c’s and J c’s of MgB2 thin films for various annealing conditions are summarized in Table I. In this table, we note very similar results were obtained from the two different substrates of Al2O3(0001) and MgO(100). We have obtained T c of 38 ~ 39 K and J c of ~ 107 A/cm2 in temperature range of 10 ~ 15 K from MgB2 thin films on two different substrates of Al2O3(0001) and MgO(100).In summary, we have made 450 ~ 500 nm thick MgB2 thin films on Al2O3(0001) and MgO(100) substrates by the electron beam evaporation of boron and the post-annealing process. They have grown in random orientation. MgB2 thin films of T c of ~ 39 K with ∆T c ~ 0.3 K and the critical current density of 1.1 x 107 A/cm2 at 15 K was obtained on Al2O3(0001) substrates.AcknowledgementsThe authors acknowledge Mr. H. H. Kim for SEM, and Dr. S. M. Lee, Dr. J. H. Ahn, and Dr. H. J. Lee for helpful discussions. This work was supported by the Korean Ministry of Science & Technology under the National Research Laboratory project.References1 J. Nagamatsu N. Nakagawa, T. Muranaka, Y. Zenitani, and J. Akimitsu, Nature 410, 63(2001).2 S. L. Bud'ko, G. Lapertot, C. Petrovic, C. E. Cunningham, N. Anderson, and P. C. Canfield,Phys. Rev. Lett. 86, 1877 (2001).3 D. C. Larbalestier, M. O. Rikel, L. D. Cooley, A. A. Polyanskii, J. Y. Jiang, S. Patnaik, X.Y. Cai, D. M. Feldmann, A. Gurevich, A. A. Squitieri, M. T. Naus, C. B. Eom, E. E.Hellstrom, R. J. Cava, K. A. Regan, N. Rogado, M. A. Hayward, T. He, J. S. Slusky, P.Khalifah, K. Inumaru, and M. Haas, Nature 410, 186 (2001).4 P. C. Canfield, D. K. Finnemore, S. L. Bud’ko, J. E. Ostenson, G. Lapertot, C. E.Cunningham, and C. Petrovic, Phys. Rev. Lett. 86, 2423 (2001).5 M. Kambara, N. Hari Babu, E. S. Sadki, J. R. Cooper, H. Minami, D. A. Cardwell, A. M.Campbell, and I. H. Inoue, Supercond. Sci. Technol. 14, L5 (2001).6 W. N. Kang, H. -J. Kim, E. -M. Choi, C. U. Jung, S. I. Lee, cond-mat/0103179 (2001).7 C. B. Eom, M. K. Lee, J. H. Choi, L. Belenky, S. Patnaik, A. A. Polyanskii, E. E. Hellstrom,D. C. Larbalestier, N. Rogado, K. A. Regan, M. A. Hayward, T. He, J. S. Slusky, K.Inumaru, M. K. Haas, and R. J. Cava, cond-mat/0103425 (2001) (submitted to Nature).8 H. M. Christen, H. Y. Zhai, C. Cantoni, M. Paranthaman, B. C. Sales, C. Rouleau, D. P.Norton, D. K. Christen, and D. H. Lowndes, submitted to Physica C (March 22, 2001).9 S. Moon, J. H. Yun, J. I. Kye, H. K. Kim, and B. Oh, presented at the APS Meeting, Seattle,Washington, /meet/MAR01/mgb2/talk3.html#talk56 (March 12, 2001).10 A. Brinkman, D. Mijatovic, G. Rijnders, V. Leca, H. J. H. Smilde, I. Oomen, A. A.Golubov, F. Roesthuis, S. Harkema, H. Hilgenkamp, D. H. A. Blank, and H. Rogalla, cond-mat/0103198 (2001).11 M. Paranthaman, C. Cantoni, H. Y. Zhai, H. M. Christen, T. Aytug, S. Sathyamurthy, E. D. Specht, J. R. Thompson, D. H. Lowndes, H. R. Kerchner, and D. K. Christen, cond-mat/0103569 (2001) (submitted to Appl. Phys. Lett.).Table I. The effect of the annealing temperature and time on the superconducting transition temperature (T c) and critical current (J c) of MgB2 thin films on Al2O3(0001) and MgO(100) substrates. The MgB2 thin films were formed from the boron thin films deposited at either room temperature (R.T.) or 750 o C.BoronDeposition Temperature SubstrateAnnealingTemperature(o C)AnnealingTime(minutes)T c (K)Onset ZeroJ c(15 K, 0T)(107 A/cm2)R. T.Al2O370030- -R. T.Al2O37503038.7 37.3R. T.Al2O37753038.7 38.4R. T.Al2O38003039.2 38.9 1.1 R. T.Al2O38253039.0 38.7R. T.Al2O38503039.0 38.7R. T.Al2O39003038.9 38.5R. T.Al2O39503038.6 37.3R. T.Al2O38002039.1 38.8R. T.Al2O38006039.1 38.8R. T.MgO8003038.5 38.0R. T.MgO8253038.6 38.1 1.0 750 o C Al2O38003037.7 37.00.5 750 o C MgO8003038.1 37.4Figure captions:FIG. 1. The normalized resistance as a function of temperature of MgB2 thin films on Al2O3(0001) and MgO(100) substrates. The circle indicates the thin films were made from the boron film deposited at 750 o C, and the other two samples were made from the boron films deposited at room temperature. All three samples were annealed at 800 o C for 30 minutes as explained in the text.FIG. 2. The glancing angle (thin film) X-ray diffraction patterns of three MgB2 thin films. MgB2 films made from boron films deposited on Al2O3(0001) (a) at RT and (b) at 750 o C followed by annealing at 800 o C for 30 minutes, and (c) deposited on MgO(100) at RT annealed at 825 o C for 20 minutes. We note mainly MgB2 phase with small unknown phases.FIG. 3. (a) SEM and (b) AFM images of the MgB2 thin film with T c ~ 39 K on Al2O3(0001) substrate.FIG. 4. Transport critical current density (J c) of MgB2 thin films as a function of temperature. The inset shows the narrow stripline of 2 µm x 20 µm size used for J c measurement by the four-point probe method.0501001502002500.00.20.40.60.81.0N o r m a l i z e d R e s i s t a n c e Temperature (K)Fig. 1. S. H. MoonFig. 2. S. H. Moon2030405060708090*(001)*(102)*(112)(201)(110)(002)(101)(100)(110)(002)(101)(100)*(112)(201)(111)(110)(002)(101)(100)(c)(b)(a)I n t e n s i t y (A r b . U n i t )2-theta (degrees)(a)(b)Fig. 3. S. H. Moon104105106107J c (A /c m 2)Temperature(K)Fig. 4. S. H. Moon。

MgB_2超导材料的制备_王醒东

电工材料2014No.21引言超导技术作为高新技术之一，历经百余年的发展，已有多种产品问世，在强电领域和弱电领域得以应用，如超导电缆和超导滤波器等。

2013年3月，德国铺设了目前世界上最长的高温超导电缆，该条电缆以二代钇-钡-氧化铜（YBCO）高温超导材料为核心材料，长度为1km，直径仅15cm，输电功率和输电电压分别为40MW和10kV；同年4月，世界上载流能力最强的350m长、载流10kA的直流超导电缆在河南中孚实业有限公司投入工程示范运行，并为该公司的电解铝车间供电，该条电缆以一代铋-锶-钙-氧化铜（BSCCO-2223）高温超导材料为载流层；超导滤波器方面，江苏综艺超导有限公司是国内唯一一家开发超导滤波器的企业，产品已达到军用标准，但尚未量产。

现有的超导产品或样机，基本以YBCO或BSCCO-2223为超导材料，最主要原因是其临界温度（T c）在液氮沸点之上，可以用液氮作为制冷剂，成本低。

但目前有能力制造商用YBCO或BSCCO-2223超导材料的厂家不多，最根本的原因是受制于复杂的工艺及设备的要求：①YBCO和BSCCO-2223均属于陶瓷材料，组成元素多，原子比例多变，只有满足一定的原子比时，材料才具有优异的超导特性，此外，超导材料对压力、氧含量及湿度等工艺参数敏感，这些都增加了工艺的难度；②采用粉末套管法（PIT法）制备BSCCO-2223的工艺已比较成熟[1]，与之相比，YBCO材料制备工艺不成熟，对设备真空度、精密度和自动化程度等要求高，导致其价格较高。

2001年，二硼化镁（MgB2）化合物的发现，改变了人们的传统思维。

MgB2为AlB2型六方晶格结构，B原子呈石墨蜂窝型排列，Mg原子则呈一定规MgB2超导材料的制备王醒东1,2（1.富通集团有限公司浙江省光纤制备技术工程技术研究中心，浙江富阳311400；2.富通集团（天津）超导技术应用有限公司，天津300384）摘要：二硼化镁（MgB2）是重要的超导材料，在超导磁体等领域有着潜在的应用。

钛掺杂氧化镁薄膜二次电子发射倍增特性研究

钛掺杂氧化镁薄膜二次电子发射倍增特性研究崔乃元，王思展，王志浩，刘宇明，李蔓，王璐（北京卫星环境工程研究所，北京 100094）摘要：氧化镁具有较高的二次电子发射系数，适合作为制备多级放大装置的二次电子发射材料。

文章采用磁控溅射法制备高质量氧化镁薄膜和钛掺杂氧化镁薄膜，并对薄膜进行形貌表征，研究其二次电子发射倍增特性，包括氧化镁薄膜电子倍增器的增益特性以及增益衰减情况。

结果表明：高压源电压和电流的增大均可提高电子倍增器的电流增益倍数；掺杂Ti 不仅能提高电子倍增器的增益效能，且相比纯氧化镁薄膜，钛掺杂氧化镁薄膜的增益衰减明显放缓，能够将倍增器的寿命延长2倍以上。

关键词：氧化镁薄膜；钛掺杂；磁控溅射；二次电子发射；电子倍增特性中图分类号：TB34文献标志码：A 文章编号：1673-1379(2021)06-0687-06DOI: 10.12126/see.2021.06.012The secondary electron emission multiplication characteristics oftitanium-doped magnesium oxide thin filmsCUI Naiyuan, WANG Sizhan, WANG Zhihao, LIU Yuming, LI Man, WANG Lu(Beijing Institute of Spacecraft Environment Engineering, Beijing 100094, China)Abstract: The magnesium oxide, due to its high secondary electron emission coefficient, is suitable as asecondary electron emission material for the preparation of multi-stage amplification devices. In this paper, the high-quality magnesium oxide films and the titanium-doped magnesium oxide films are prepared by the magnetron sputtering, and the morphology of the films is characterized. In addition, the secondary electron emission multiplication characteristics of the films used in the MgO film electron multiplier are studied. The gain characteristics and the gain reduction of the electron multiplier are also analyzed. It is shown that the increase of the voltage or the current of the high voltage source can both increase the current gain multiple of the electron multiplier; the titanium doping, for example, the Ti-doped MgO film in comparison with the pure MgO film, can not only increase the gain of the electron multiplier, but also extend the working life of the multiplier more than two times.Keywords: magnesium oxide thin films; titanium doping; magnetron sputtering; secondary electron emission; electron multiplication characteristics收稿日期：2021-06-29；修回日期：2021-12-14基金项目：国家自然科学基金项目（编号：1187021136）引用格式：崔乃元, 王思展, 王志浩, 等. 钛掺杂氧化镁薄膜二次电子发射倍增特性研究[J]. 航天器环境工程, 2021, 38(6):687-692CUI N Y, WANG S Z, WANG Z H, et al. The secondary electron emission multiplication characteristics of titanium-doped magnesium oxide thin films[J]. Spacecraft Environment Engineering, 2021, 38(6): 687-692第 38 卷第 6 期航天器环境工程Vol. 38, No. 62021 年 12 月SPACECRAFT ENVIRONMENT ENGINEERING 687E-mail: ***************Tel: (010)68116407, 68116408, 68116544. All Rights Reserved.0 引言原子频率标准（以下简称频标）技术被广泛应用于守时和授时服务，常见的原子频标有铷原子频标、铯原子频标和氢原子频标等。

The Physics and Properties of Thin Films

The Physics and Properties of ThinFilmsIntroductionThin films are layers of material that range in thickness from fractions of a nanometre to several micrometres. They are used in many applications, including electronics, optics, and coatings. The properties of thin films are determined by their structure and composition, which can be controlled during deposition. The physics of thin films is complex and requires an understanding of surface and materials science, as well as solid-state physics. In this article, we will explore the physics and properties of thin films.Surface ScienceSurface science is the study of the properties of surfaces and interfaces. Thin films are of interest to surface scientists because they have a high surface-to-volume ratio, which means that surface properties dominate the behaviour of the material. The surface of a thin film can be modified to change its properties, such as its wettability or adhesion. Surface science techniques, such as scanning probe microscopy and X-ray photoelectron spectroscopy, can be used to study the surface of thin films and to understand how it affects their properties.Materials ScienceMaterials science is the study of the properties of materials and how they can be used to create new materials. Thin films are a class of materials that can be engineered to have specific properties. For example, thin films can be made of different materials, such as metals, semiconductors, or insulators, by selecting the appropriate deposition technique. Materials science techniques, such as X-ray diffraction and transmission electron microscopy, can be used to study the internal structure of thin films and to understand how it affects their properties.Solid-State PhysicsSolid-state physics is the study of the behaviour of solids, particularly their electronic and magnetic properties. Thin films are of interest to solid-state physicists because their properties can be tailored by changing their composition and structure. For example, a thin film of a semiconductor can be doped to create a p-n junction, which is the basis of many electronic devices. Solid-state physics techniques, such as electrical conductivity measurements and magnetization measurements, can be used to study the properties of thin films.Properties of Thin FilmsThe properties of thin films depend on their structure, composition, and thickness. Some of the properties of thin films are discussed below.Optical PropertiesThin films can have different optical properties depending on their composition and thickness. For example, a thin film of gold can be used as a reflective coating, while a thin film of silicon dioxide can be used as an anti-reflective coating. Thin films can also exhibit interference effects, such as the colours seen in soap bubbles or oil slicks. These effects are due to the different optical paths taken by light as it reflects off the top and bottom surfaces of the thin film.Electrical PropertiesThin films can have different electrical properties depending on their composition and structure. For example, a thin film of a metal can be conductive, while a thin film of an insulator can be electrically insulating. Thin films can also be semiconducting, which means that their electrical conductivity can be controlled by doping. Thin films of semiconductors are the basis of many electronic devices, such as solar cells and transistors.Mechanical PropertiesThin films can have different mechanical properties depending on their composition and thickness. For example, a thin film of diamond can be very hard, while a thin film of polymer can be flexible. Thin films can also be used as coatings to improve the mechanical properties of a substrate, such as corrosion resistance or wear resistance.ConclusionThin films are a class of materials that have unique properties due to their structure and composition. The physics of thin films is complex and requires an understanding of surface and materials science, as well as solid-state physics. The properties of thin films can be tailored to meet specific requirements, such as optical or electrical properties. Thin films are used in many applications, including microelectronics, sensors, and coatings.。

Study of superconducting properties of MgB2

a r X i v :c o n d -m a t /0207658v 2 [c o n d -m a t .s u p r -c o n ] 30 J u l 2002Study of superconducting properties of MgB 2Y.Machida ∗and S.SasakiMaterials and Structures Laboratory,Tokyo Institute of Technology4259Nagatsuta,Midori-ku,Yokohama 226-8503,JapanH.FujiiNational Institute for Materials Science,1-2-1,Sengen,Tsukuba 305-0047,JapanM.Furuyama,I.Kakeya and K.KadowakiInstitute of Materials Science,University of Tsukuba,1-1-1,Tennoudai,Tsukuba 305-8573,Japan(Dated:February 1,2008)We synthesized single crystalline and policrystalline MgB 2under ambient pressures.The single crystals of MgB 2were of good quality,where the crystal structure reﬁnements were successfully converged with R =0.020.The speciﬁc heat of policrystalline MgB 2samples has been measured in a temperature range between 2and 60K in magnetic ﬁeld up to 6T.The measurement gave the coeﬃcient of the linear term in the electronic speciﬁc heat,γ=3.51mJ/K 2mol,and the jump of the speciﬁc heat,2.8mJ/K 2mol at 38.5K.It is shown from the analysis of the speciﬁc heat that the electronic speciﬁc heat in the superconducting state diﬀers largely from the conventional BCS weak coupling theory.From the results of measurements of the magnetic properties on single crystal samples,we found a sharp superconducting transition at 38K with transition width ∆Tc =0.8K and the superconducting anisotropy ratio γincreasing from about 1near T c to 4.0at 25K.PACS numbers:74.25.Bt,74.25.Ha,74.62.Bf,74.60.EcThe recent discovery of superconductivity at 39K in magnesium diboride MgB 21has attracted great scien-tiﬁc interest.Several experiments indicated a phonon-mediated s -wave BCS superconductivity 2,3and the ap-pearance of a double energy gap was predicted 4,5.Spe-ciﬁc heat 6and spectroscopic 7measurements,scanning tunneling spectroscopy 8,9gave evidence for this pre-diction.However,several key parameters such as the upper critical ﬁelds H c 2and their anisotropy ratio γ,the magnetic penetration λ,the coherence lengths ξand Ginzburg-Landau parameters κare not well estab-lished because of the diﬃculty of growing high qual-ity MgB 2single crystals.Especially the anisotropy ra-tio γ=H ab c 2/H cc 2is important to clarify the supercon-ducting mechanism and applications of MgB 2.Here H ab c 2and H c c 2are the in-plane and the out-of-plane up-per critical ﬁelds respectively.Reported γ-values vary widely depending on the measurement methods or on the sample types.The values determined from resistiv-ity on pollycrystallie 10,aligned crystallites 11,c-axis ori-ented ﬁlms 12,13,14and single crystals 15,16,17,18,19,20,21,22have been reported to be 6-9,1.7,1.3-2and 2.6-3,re-spectively.In this paper,we present a study of the speciﬁc and the magnetization measurements on single crystalline and policrystalline MgB 2.The polycrystals for the spe-ciﬁc measurement were synthesized as follows.The Mg (99.99%,Furuya Metal Co.)ingot and the B (99.9%,Fu-ruuchi Chemical Co.)powder were pressed into a cylin-der with a diameter of 13mm and a length of 15mm.This was put in the BN crucible with a lid,and this crucible was encapsulated in a stainless (SUS304)tube in argon atmosphere.Then,this was reacted for threehours at 1100◦C in an electric furnace.The sample after reaction was a form of sintered porous lump.This was not so hard that the sample was cut from this lump in a shape of thin,square plate for the speciﬁc heat measure-ment.The single crystals were grown in the stainless (SUS304)tube.The SUS304tube had an outside di-ameter of 32mm,a wall thickness of 1.5mm,and a length of 110mm.The inner surface of the tube was sealed by Mo sheet (99.95%,Nilaco Co.)with the size of 0.05×100×200mm 3.One end of the SUS304tube was pressed with a vise and sealed in an Ar gas atmosphere by arc welding.The starting materials of Mg chunk with the size of 3∼5mm and B chunk which was cut out with the size of about 1cm 3from B block was ﬁlled inside of the tube.Then the other end of the tube was pressed with a vise and sealed in an Ar gas atmosphere by arc welding,as well.The samples were heated from room tempera-ture to 1200◦C for 40minutes and kept at 1200◦C for 12hours,then slowly cooled to room temperature for 12hours.The single crystals ﬁnally obtained were about 100∼300µm,which had irregular shapes with shiny gold color when observed under a optical microscope.The single crystal images observed by a scanning electron microscope (SEM)is shown in Fig 1(a).The crystals were found to have very ﬂat surfaces.Struc-tural analysis was carried out using a x-ray precession camera,a four-circle diﬀractometer and a transmission electron microscope (TEM).The x-ray precession photograph indicated that the crystal has the hexag-onal structure,as shown in Fig 1(b).The diﬀraction data were collected by using graphite monochromated Mo K αradiation at room temperature and reﬁned byFIG.1:(a)SEM image of a MgB2single crystal with a size of about100µm.(b)X-ray precession photograph of the single crystal.the least-square procedure using86reﬂections as the average of the measured866reﬂections.The obtained cell and structural parameters were a=b=3.0863(4)˚A, c=3.5178(4)˚A,(x,y,z)=(0,0,0)(Mg),(1/3,2/3,1/2)(B), U11(Mg)=0.0078(2)˚A2,U33(Mg)=0.0054(2)˚A2, B eq(Mg)=0.382(2)˚A2,U11(B)=0.0068(2)˚A2, U33(B)=0.0058(2)˚A2and B eq(B)=0.371(2)˚A2 with small agreement factors R=0.020,R w=0.027 (w=weight).To conﬁrm the structure of the MgB2 phase,we took plane-view HRTEM images and electron diﬀraction patterns in selected areasfor beam directions of[001]and[100]as shown in Fig2,which indicated atomic arrangement with P6/mmm cell of MgB2.Nei-ther extra spots nor streaks were not found,indicating that the crystal is of high quality.The temperature dependence of the magnetization curve was measured at1mT along the c-axis and the ab-plane by a superconducting quantum interference de-vice(SQUID)magnetometer.Figure3(a)is the results for the MgB2single crystal.It shows the M(T)curves in the zero-ﬁeld-cooling(ZFC)and theﬁeld-cooling(FC) modes.The onset of superconducting transition was ob-FIG.2:Electron diﬀraction patterns and HRTEM images of a MgB2single crystal for a beam direction of[001]and[110] in the hexagonal structure.served at Tc=38K with transition width∆Tc=0.8K both for H//ab and for H//c,indicating high quality of the samples,where//ab(//c)indicates theﬁeld H perpendicular(parallel)to the c-axis of the sample,paring to the transition temperatures (≈39K)for polycrystal samples23,24,25,single crystal samples15,16,17,18,26formerly reported have a little bit lower transition temperature at around38K.It is noted that our samples are not an exceptional case.This lower Tc in single crystals was thought to be caused by contam-ination from container materials(BN,Mo,Nb).From the quantitative analysis using an electron prove micro-analyzer(EPMA),however we found that there was no contamination in the samples from the container,which was Mo and SUS304in our case.According to this anal-ysis,the composition in rather ideal without particular stoichiometry shift,therefore,the quality check of the single crystals is an urgent need in more detail.Figure 3(b)shows the magnetic hysteresis curves M(H)at5K for appliedﬁelds up to2T for H//ab and for H//c,in-dicating the characteristic curve of type-II superconduc-tors.There is an asymmetry between the ascending and the descending branches at H≤0.1T,which has been also observed in the magnetic hysteresis measurements on single crystals21.Figure4shows the temperature dependence of mag-netization M(T)curves on warming afterﬁeld cooling the sample for(a)H//ab in magneticﬁeld up to5T and(b)H//c in magneticﬁeld up to2.5T.The super-conducting transition shifts to lower temperatures as the ﬁeld increased.The superconducting transition inﬁelds is determined by extrapolating the M(T)curve lineally and byﬁnding the crossing point to the horizontal lineTABLE I:Comparison of physical parameters with single crystals prepared by diﬀerent methods.Parameter Our sample J.Karpinski et al19,21,27S.Lee et al15,28M.Xu et al18K.H.P.Kim et al17,20FIG.5:(a)Upper criticalﬁeld for H ab c2and H c c2determined from the onset of the superconductivity in Fig4(a)and(b)as a function of the temperature.(b)Temperature dependence of upper criticalﬁeld anisotropyγ=H ab c2/H c c2.Tc deﬁned by the mid point of the jump in the speciﬁc heat is38.5K,and the width of the jump is about1K. The value∆C(Tc)/Tc of the jump of speciﬁc heat is 2.8mJ/K2mol.However,the jump of the speciﬁc heat was not observed in the magneticﬁeld of6T in this scale. It is important to separate electronic speciﬁc heat from the entire speciﬁc heat to know the excitation of the elec-tron system.It is assumed that the entire speciﬁc heat is composed of the speciﬁc heat of the electron system and the lattice system,C(T)=C e(T)+C ph(T).The speciﬁc heat of the lattice system is expressed by C ph(T)=βT3 within the range of the temperature which is suﬃciently lower than that of the Debye temperatureθD.The elec-tron speciﬁc heat is assumed to be C e(T)=γT in the normal state.The plot of C(T)/T vs.T2is shown in Fig.7.However,it is clear that the expression of C(T)/T=γ+βT2in the normal state between40and 60K in0T magneticﬁeld and between30and50K in6T magneticﬁeld.The higher-order term is then added in the expression to correct the speciﬁc heat of the lattice:it is approximated by C ph(T)=βT3+β5T5. The electronic speciﬁc heat was separated by extrapolat-FIG.6:Speciﬁc heat of MgB2under magneticﬁeld of range 2-60K of temperature,0and6T.Inset:Expansion of Tc neighborhood.ing it to a lower temperature region by using the spe-ciﬁc heat of the lattice by which the speciﬁc heat of the normal state was corrected.Thisﬁtting gave the result ofγ=3.51mJ/K2mol,β=6.76×10−6J/K4mol andβ5=1.08×10−9J/K6mol,giving0.8to the jump ∆C(Tc)/γTc of the speciﬁc heat normalized byγTc,and is diﬀerent from1.43of BCS theory.The temperature de-pendence of the superconducting electronic speciﬁc heat C es(T)which had been obtained by subtracting the spe-ciﬁc heat of the lattice from the entire speciﬁc heat of the superconducting state was shown in Fig.8.The temperature dependence of the electronic speciﬁc heat of the superconducting state in zero magneticﬁeld de-viates strongly from the speciﬁc heat of the BCS theory as seen in Fig.8.It is smaller than the value of the BCS theory in20K≤T≤Tc.But it is larger than the value of the BCS theory in T≤20K.A gradual jump of the speciﬁc heat,which extended in a wide range of tem-perature20-28K under the magneticﬁeld of6Tesla was observed.The critical temperature in this magneticﬁeld agrees roughly to the one obtained by the experimental result of the upper critical magneticﬁeld measurement18. The entropy in the superconducting state can be ob-tained by using S(T)= C e(T)/TdT under the condi-tion that the entropy of superconducting state and nor-mal state should be equal at Tc,i.e.,S s(Tc)=S n(Tc). The temperature dependencies of the entropy in both states are shown in Fig.9.Furthermore,the critical magneticﬁeld Hc(T)was obtained from the entropy of superconducting state and normal state by using the ex-pression S n(T)-S s(T)dT=H c(T)2/8π.In order to make the diﬀerence from the BCS theory clear,the deviation function D(t)=H c(t)/H c(0)-(1-t2) as shown in Fig.10where t=T/Tc.The BCS the-FIG.7:C(t)/T in magneticﬁeld0and6T plotted as a function of T2.The solid line is a curve by which theﬁtting is done by C n(T)=γT+βT3+β5T5and the speciﬁc heat of normal state is extended to the low temperature.FIG.8:Temperature dependence of the electronic speciﬁc heat C es in magneticﬁeld0and6T.The BCS theory was shown in the solid line and the speciﬁc heat of normal state was shown in the horizontal dotted line.ory assumes the weak electron-phonon interaction,the isotropic Fermi surface and the isotropic interaction.The diﬀerence between the superconducting electronic spe-ciﬁc heat and the one of the BCS theory shown in Figure 10may be caused by the strong coupling eﬀect,and/or the anisotropy of the Fermi surface and the anisotropy of the interaction.However,the eﬀect of the electron-phonon coupling and anisotropy cause the opposite eﬀect in the normalized jump of the speciﬁc heat∆C(Tc)/γTc and the deviation function D(t).That is,when the cou-pling becomes stronger,the value of∆C(Tc)/γTc grows more than the BCS value of1.43,and the deviation func-tion D(t)shifts from the BCS curve to a positive direc-tion.On the other hand,when the anisotropy becomes ,the value of∆C(Tc)/γTc becomes smaller than the values of BCS,and D(t)is changed in a negative di-rection31,32,33.Value0.8of the jump of the normalized speciﬁc heat was smaller than the value of BCS and show the deviation function D(t)in Fig.10which appeared FIG.9:Entropy as function of temperature in magneticﬁeld of0and6T.The entropy of normal state and the BCS theory was shown.FIG.10:Temperature dependence of the deviation function D(t):D(t)=H c(t)/H c(0)-(1-t2),t=T/Tc.in more negative direction than the BCS curve. According to the results shown above the supercon-ducting state of MgB2exhibits rather strong anisotropy of order4at low temperature.This result agrees with the result of the speciﬁc heat measurement in other groups6. The experimental result predicting the existence of two gaps has been reported in the result of tunneling mi-croscopy8.Models of the two-zone or the multi-zone where the anisotropy is treated by dividing the Fermi sur-face,when the anisotropy of both the Fermi surface and the coupling becomes stronger,might be a good model. The anisotropy eﬀect in the framework of the two-zone model was discussed34.In that case,the value of the en-ergy gap is diﬀerent in each zone.Therefore,the speciﬁc heat would have the jump at a diﬀerent temperature to which the energy gap of each zone opens.Though the temperature dependency of speciﬁc heat changes largely by the inter-zone scattering of conduction electrons,it6diﬀers largely from speciﬁc heat of the single-zone(single-band)isotropic superconductor.Part of the large elec-tronic speciﬁc heat C es at the low temperature in Fig.8 depends on the existence of a small energy gap it to be possible to excite even at the low temperature.In summary,we reported on the results of measure-ment and the analysis of the speciﬁc heat of polycrys-talline MgB2and the magnetic properties of single crys-talline MgB2.The behavior of the superconducting elec-tronic speciﬁc heat and the deviation function indicate that the superconducting state of this MgB2is a strong anisotropy superconducting state,which is diﬀerent from the BCS theory.From the magnetization measurement on single crystals,the upper criticalﬁeld anisotropy ratio γ=H ab c2/H c c2is found to be increased from about1near Tc to4.0at25K.We would like to thank K.Yamawaki,K.Noda,K. Ishikawa,H.Saito,Y.Takano,and K.Ohshima for useful discussions.∗Corresponding author:Tel.+81-45-924-5383;Fax.+81-45-924-5339E-mail address:machida@lipro.rlem.titech.ac.jp1J.Nagamatsu,N.Nakagawa,T.Muranaka,Y.Zenitani, and J.Akimitsu,Nature410,63(2001).2S.L.Bud’ko,pertot,C.Petrovic,C.E.Cunningham, N.Anderson,and P.C.Canﬁeld,Phys.Rev.Lett.86,1877 (2001).3J.W.Quilty,A.Yamamoto,and S.Tajima,Phys.Rev.Lett.88,087001(2002).4J.Kortus,I.I.Marzin,K. D.Belashchenko,V.P.Antropov,and L.L.Boyer,Phys.Rev.Lett.86,4656 (2001).5A.Y.Liu,I.I.Marzin,and J.Kortus,Phys.Rev.Lett.87,087005(2001).6F.Bouquet,R.A.Fisher,N.E.Phillips,D.G.Hinks,and J.D.Jorgensen,Phys.Rev.Lett.87,047001(2001).7P.Szab´o,P.Samuely,J.Ka˘c mar˘c´ık,T.Klein,J.Marcus,D.Fruchart,and S.Miraglia,Phys.Rev.Lett.87,137005(2001).8F.Giubileo, D.Roditchev,W.Sacks,my, D.X.Thanh,and J.Klein,Phys.Rev.Lett.87,177008(2001). 9M.Iavarone,G.Karapetrov,A.E.Koshelev,W.K.Kwok,G.W.Crabtree,and D.G.Hinks,cond-mat/0203329.10F.Simon,A.J´a nossy,T.Feh´e r,F.Mur´a nyi,S.Garaj, L.Forr´o,C.Petrovic,S.L.Bud’ko,pertot,V.G.Kogan,et al.,Phys.Rev.Lett.87,047002(2001).11O.F.de Lima,R.A.Ribeiro,M.A.Avila,C.A.Cardoso, and A.A.Coelho,Phys.Rev.Lett.86,5974(2001).12S.Patnaik,L.D.Cooley,A.Gurevich,A.A.Polyanskii, J.Jiang,X.Y.Cai,A.A.Squitieri,M.T.Naus,M.K.Lee,J.H.Choi,et al.,Superconduct.Science Techn.14, 315(2001).13M.H.Jung,M.Jaime,cerda,G.S.Boebinger, W.N.Kang,H.J.Kim,E.M.Choi,and S.I.Lee,Chem.Phys.Lett.343,447(2001).14R.J.Olsson,W.K.Kwok,G.Karapetrov,M.Iavarone,H.Claus,C.Peterson,G.W.Crabtree,W.N.Kang,H.J.Kim,E.M.Choi,et al.,cond-mat/0201022.15S.Lee,H.Mori,T.Masui,Y.Eltsev,A.Yamamota,and S.Tajima,J.Phys.Soc.Jpn.70,2255(2001).16A.K.Pradhan,Z.X.Shi,M.Tokunaga,T.Tamegai,Y.Takano,K.Togano,H.Kito,and H.Ihara,Phys.Rev.B.64,212509(2001).17K.H.P.Kim,J.H.Choi,C.U.Jung,P.Chowdhury,H.S.Lee,M.S.Park,H.J.Kim,J.Y.Kim,Z.Du,E.M.Choi, et al.,Phys.Rev.B.65,100510(2002).18M.Xu,H.Kitazawa,Y.Takano,J.Ye,K.Nishida,H.Abe,A.Matsushita,N.Tsujii,and G.Kido,Appl.Phys.Lett.79,2779(2001).19M.Angst,R.Puzniak,A.Wisniewski,J.Jun,S.M.Kaza-kov,J.Karpinski,J.Roos,and H.Keller,Phys.Rev.Lett.88,167004(2001).20U.Welp,G.Karapetrov,W.K.Kwok,G.W.Crabtree,C.Marcenat,L.Paulius,T.Klein,J.Marcus,K.H.P.Kim,C.U.Jung,et al.,cond-mat/0203337.21M.Zehetmayer,M.Eisterer,H.W.Weber,J.Jun, S.M.Kazakov,J.Karpinski,and A.Wisniewski,cond-mat/0204199.22A.V.Sologubenko,J.Jun,S.M.Kazakov,J.Karpinski, and H.R.Ott,Phys.Rev.B.65,180505(2002).23C.U.Jung,M.S.Park,W.N.Kang,M.S.Kim,S.Y.Lee,and S.I.Lee,Physica C353,162(2001).24Y.Takano,H.Takeya,H.Fujii,H.Kumakura,T.Hatano, and K.Togano,Appl.Phys.Lett.78,2914(2001).25J.D.Jorgensen,D.G.Hinks,and S.Short,Phys.Rev.B.63,224522(2001).26A.V.Sologubenko,J.Jun,S.M.Kazakov,J.Karpinski, and H.R.Ott,cond-mat/0111273.27J.Karpinski,M.Angst,J.Jun,S.M.Kazakov,R.Puzniak,A.Wisniewski,J.Roos,H.Keller,A.Perucchi,L.Degiorgi,et al.,cond-mat/0207263.28Y.Eltsev,S.Lee,K.Nakao,N.Chikumoto,S.Tajima, N.Koshizuka,and M.Murakami,cond-mat/0202133.29S.L.Bud’ko and P.C.Canﬁeld,cond-mat/0201085.30G.K.Perkins,J.Moore,Y.Bugoslavsky,L.F.Cohen, J.Jun,S.M.Kazakov,J.Karpinski,and A.D.Caplin, cond-mat/0205036.31J.R.Clem,Ann.Rev.40,286(1966).32H.Padamsee,J.E.Neighbor,and C.A.Shiﬀman,J.Low Temp.Phys.12,387(1973).33D.G.Gubser,Phys.Rev.B.6,827(1972).34P.Entel,Z.Physik.B.24,263(1976).。

超导材料研发及近期应用情况

超导材料研发应用近期概况德国著名学府和研究院近期发表的一篇文章[1]，共70页，全面从详介绍了当前超导材料的科研和应用现状。

加拿大皇后大学发表了一篇文章[2]，系统的总结了元素和简单化合物的超导行为。

现试将其部分主要内容，结合一些相关资料，简要归纳如下，供参考A/，引言。

超导现象，自从1911年被发现后，始终是引起人们强烈兴趣的主题。

没有电阻的电流意味著在节能，高效和环保等多方面难以想象的巨大经济利益。

同时他又不是一个简单的完全导体，还具有在1933年发现的超导体排斥磁场的麦斯纳(Meissner)效应。

这是完全导体所无法解释的现象。

因此应该把它看作是一种物质的全新热力学状态。

[1,2]随着制冷技术和高压实验技术的发展，特别是1968年时，实验装置所允许的最高压力为25GPa, 而今已达260GPa. (1 GPa=10197.16 kg/cm2~10000kg/cm2). 于是越来越多的元素和化合物，都已观察到超导现象。

超导已不再是稀有罕见的奇迹，而是相对普偏现象。

Fig.1, 超导元素周期表[2]Fig.2, 在某些情况下，可能诱导产生超导现象的不同途径[2]Fig.1用周期表的形式标明了那些元素在常压下，就有超导行为（粽色，标明了Tc值），那些元素在加压条件下，表现出超导行为（绿色，标明了Tc值及所需压力GPa）。

白色标明了那些元素尚未观察到超导现象。

Fig.2表明。

许多通常没有超导行为的物质，可能有多种途径使之表现出超导现象来, 例如加压[3]，辐照[4]，掺杂[5], 冷淬沉积薄膜[2]，接近效应诱导[6]，结构物象诱导[2]等。

见图2。

虽然Fig.1,2能增进我们对超导现象的认识，但其使用价值自然远不如高温超导。

1987年Tc=93 K的YBCO的出现，震动了全世界。

从此可用液氮取代液氦。

实现了巨大的经济利益。

同时也掀起了寻找更高转变温度新材料的高潮。

由于科研人员克服了重重困难，目前高温超导的最高临界温度已在常压下达到135 K, 在31 GPa高压下，达到164 K[7].Fig.3, 高温超导的研发进展1956年Cooper 提出了基于电子与声子地相互作用而形成的cooper pair 理论[8]， 1957年, Bardeen, Cooper 及 Schrieffer 通过复杂的数学推导提出的超导理论简称BCS理论，是超导理论研究方面的重要成就[9]。

MgB_2超导电性的发现及其特性

MgB2超导电性的发现及其特性学生姓名：高宁学号：20095040202单位：物理电子工程学院专业：物理学指导老师：刘慧职称：实验师摘要：本文介绍了超导发展的历史和最有可能首先实现大规模工业应用的超导材超导电性的发现，详细介绍了MgB2中的超导电性的特性和研究现状，MgB2料MgB2的发现实现了高温超导技术的实用化进程。

关键词：超导; 二硼化镁; 晶体结构; 研究现状The found and characteristics of MgB2’s superconductivity Abstract：This article introduces the development history of superconductor and the found of MgB2’s superconductivity, MgB2 is a superconducting material, which is most probably to be firstly realized in large-scale industrial application. This article also describes the feature and characteristics of MgB2. The found of MgB2 realizes the superconducting technique’s practical applications.Key words：Superconducting,MgB2, Crystal structure, Research status引言自从在铜氧化物中发现了高转变温度的超导体以后，新的高温超导的研发引起了人们极大的兴趣，MgB2超导体以其39K的高转变点打破了Bardeen-Cooper-Schriefler 的理论预言[1]，为研究超导的微观机理提供了一种新型的材料。

发明纳米涂层眼睛作文四百字

发明纳米涂层眼睛作文四百字英文回答：Nano-coating for the eyes is a revolutionary invention that has transformed the way we see the world. This innovative technology involves applying a thin layer of nanoparticles onto the surface of the eye, which enhances vision and provides various benefits.One of the main advantages of nano-coating for the eyes is improved clarity and sharpness of vision. The nanoparticles act as a protective shield, reducing glare and enhancing contrast. This means that even in bright sunlight or low-light conditions, our vision remains clear and focused. For example, when I went hiking in the mountains, the nano-coating on my eyes allowed me to see every detail of the breathtaking scenery, from the distant peaks to the intricate patterns on the leaves.Another benefit of nano-coating for the eyes isincreased resistance to dust and dirt. The nanoparticles create a hydrophobic layer that repels water and prevents particles from sticking to the eye's surface. This is particularly useful in dusty or polluted environments, as it reduces the need for constant eye rubbing or cleaning. For instance, when I visited a construction site, the nano-coating on my eyes prevented dust particles from irritating my eyes, allowing me to focus on my work without any discomfort.Furthermore, nano-coating for the eyes offersprotection against harmful UV rays. The nanoparticles have the ability to absorb and block UV radiation, reducing the risk of eye damage and conditions such as cataracts. This is especially important for individuals who spend a lot of time outdoors or in sunny climates. For example, when I went to the beach, the nano-coating on my eyes provided an extra layer of protection against the intense UV rays, ensuring that my eyes remained safe and healthy.In addition to these benefits, nano-coating for the eyes can also be customized to address specific visionproblems. By adjusting the composition and properties ofthe nanoparticles, it is possible to correct refractive errors such as nearsightedness or farsightedness. This eliminates the need for traditional eyeglasses or contact lenses, providing a more convenient and comfortable solution. For instance, my friend had a mild case of astigmatism, and after getting the nano-coating treatment, his vision improved significantly, allowing him to see clearly without the need for corrective lenses.中文回答：纳米涂层眼睛是一项革命性的发明，改变了我们看世界的方式。

Mechanical Properties of Thin Films

Mechanical Properties of Thin FilmsIntroductionThin films refer to layers of material with thicknesses ranging from a few nanometers to several micrometers, which are typically deposited onto a substrate using various techniques. Thin films have become increasingly important in recent years, due to their unique mechanical, electrical, magnetic, and optical properties that make them highly useful in a range of applications. In this article, we will explore the mechanical properties of thin films and their relevance in various fields.Mechanical Properties of Thin FilmsThe mechanical properties of thin films are determined by their composition, microstructure, and bonding characteristics. Some of the key mechanical properties that are of interest for thin films include hardness, elasticity, toughness, adhesion, and wear resistance, among others. Understanding these properties is critical for optimizing the performance of thin films across a variety of applications.HardnessThe hardness of a material is a measure of its resistance to deformation or indentation under an applied load. In thin films, hardness can be influenced by factors such as composition, grain boundary structure, and defect density. Hardness is typically measured using indentation techniques such as nanoindentation, which involve applying a small load to the film surface and measuring the resulting deformation. Hardness is a critical property for materials used in applications such as wear-resistant coatings, cutting tools, and microelectromechanical systems (MEMS).ElasticityElasticity is a measure of a material's ability to recover its original shape after being subjected to deformation. In thin films, elasticity is influenced by factors such as grain size, crystal structure, and defects. Elasticity can be measured using various techniques,such as acoustic methods, which involve measuring the speed of sound through the film, or in situ indentation methods, which involve measuring the deformation and recovery of the film under load. Understanding the elasticity of thin films is critical for applications such as flexible electronics, micro-optics, and energy conversion systems.ToughnessToughness is a measure of a material's ability to withstand fracture under an applied load. In thin films, toughness can be influenced by factors such as film thickness, adhesion, and microstructure. Toughness can be measured using various methods, such as indentation or scratch testing, or using fracture mechanics techniques such as the critical load method or the indentation fracture method. Toughness is an important property for materials used in applications such as protective coatings, thin-film solar cells, and biomedical implants.AdhesionAdhesion is a measure of the strength of the interface between a thin film and its substrate. In thin films, adhesion can be influenced by factors such as surface energy, interfacial chemistry, and film thickness. Adhesion can be measured using various techniques, such as peel testing, scratch testing, or the four-point bending method. Adhesion is a critical property for materials used in applications such as protective coatings, microelectronic devices, and MEMS.Wear ResistanceWear resistance is a measure of a material's ability to resist surface damage under sliding or rolling contact. In thin films, wear resistance can be influenced by factors such as film composition, microstructure, and surface morphology. Wear resistance can be measured using various techniques, such as ball-on-disk or pin-on-disk testing. Wear resistance is an important property for materials used in applications such as cutting tools, microelectronic devices, and biomedical implants.Applications of Thin FilmsThin films have found numerous applications across a diverse range of fields, including microelectronics, optics, energy, and biomedical engineering, among others. Some of the key applications of thin films include:- Microelectronics: Thin films are used in the fabrication of microelectronic devices, such as transistors, diodes, and sensors.- Optics: Thin films are used in the fabrication of optical coatings, such as anti-reflection coatings, dichroic filters, and high-reflectivity mirrors.- Energy: Thin films are used in the fabrication of thin-film solar cells, fuel cells, and batteries.- Biomedical engineering: Thin films are used in the fabrication of biomedical implants, drug delivery systems, and biosensors.ConclusionThin films have unique mechanical properties that make them highly useful across a range of applications. Understanding these properties is critical for optimizing the performance of thin films in various fields. By exploring the mechanical properties of thin films and their relevance in different applications, we can gain insights into the potential of thin films to drive technological innovation and scientific progress.。

超级计算机

目录
¾ 超级计算机...............................................................................................................................1 超级计算环境 2007 年 3 季度运行情况简报 .........................................................................1
深腾6800
● 共197名用户，3季度增加用户6名。 ● 有134名用户利用LSF提交作业，共完成.51000多个作业，用户作业平均规模为5.9个CPU，累计使用机时112万CPU小时（按Walltime计算）。 ● 2007年3季度，深腾6800的磁盘阵列系统与QsNet网络系统先后发生故障，导致深腾6800的平均整体使用率有所下降，为83.5%（按Walltime计算），平均CPU利用率69.1%（按CPUtime计算）。CPUtim e与Walltime之比平均为82.7%。 ● 2007年3季度，作业平均等待时间为23.3小时。 ● 已完成作业按规模分布情况：串行作业数量占62.6%，4处理器节点内并行作业数量占21.1%。而根据作业使用的CPU小时计算，占用机时最多的并行作业规模分别为16处理器、33-63处理器、32处理器、64处理器，其比例分别为21.8%，18.1%，17.9%和12.4%，串行作业仅使用总机时的2.1%，表明深腾6 800的计算机时还是主要用于较大规模的并行作业计算。
1. Introduction ...................................................................................................................2

Superconducting Microwave Cavity Made of Bulk MgB2

a rX iv:c ond-ma t/612159v2[c ond-m at.s upr-con]16Fe b27Superconducting Microwave Cavity Made of Bulk MgB 2G.Giunchi EDISON SpA R &D,Foro Buonaparte 31,I-20121Milano (Italy)A.Agliolo Gallitto,G.Bonsignore,M.Bonura,M.Li Vigni CNISM and Dipartimento di Scienze Fisiche e Astronomiche,Universit`a di Palermo,Via Archiraﬁ36,I-90123Palermo (Italy)Abstract.We report the successful manufacture and characterization of a microwave resonant cylindrical cavity made of bulk MgB 2superconductor (T c ≈38.5K),which has been produced by the Reactive Liquid Mg Inﬁltration technique.The quality factor of the cavity for the TE 011mode,resonating at 9.79GHz,has been measured as a function of the temperature.At T =4.2K,the unloaded quality factor is ≈2.2×105;it remains of the order of ×105up to T ∼30K.We discuss the potential performance improvements of microwave cavities built from bulk MgB 2materials produced by reactive liquid Mg inﬁltration.PACS numbers:74.25.Nf;74.70.AdThe very low surface resistance of superconducting materials makes them particularly suitable for designing high-performance microwave(mw)devices,with considerably reduced sizes.The advent of high-temperature superconductors(HTS) further improved the expectancy for such applications,oﬀering a potential reduction of the cryogenic-refrigeration limit,with respect to low-temperature superconductors.A comprehensive review on the mw device applications of HTS was given by Lancaster [1].Among the various devices,the superconducting resonant cavity is one of the most important applications in the systems requiring high selectivity in the signal frequency, such asﬁlters for communication systems[2],particle accelerators[3,4],equipments for material characterization at mw frequencies[1,5].Nowadays,one of the commercial applications of HTS electronic devices are planar-microstripﬁlters for transmission line,based on YBa2Cu3O7thin or thickﬁlms[1,6], whose manufacturing process allows having an high degree of device miniaturization. Nevertheless,the need of high performance,in many cases,overcomes the drawback of the device sizes,as, e.g.,in the satellite-transmission systems,radars,particle accelerators,and demands for cavities with the highest quality factors.Since the discovery of HTS,several attempts have been done to manufacture mw cavities made of these materials in bulk form[2,7,8];however,limitations in the performance were encountered.Firstly,because of the small coherence length of HTS,grain boundaries in these materials are weakly coupled giving rise to reduction of the critical current and/or nonlinear eﬀects[9],which worsen the device performance;furthermore,the process necessary to obtain bulk HTS in a performing textured form is very elaborated. For these reasons,in several applications,such as particle accelerators and equipments for mw characterization of materials,most of the superconducting cavities are still manufactured by Nb,requiring liquid helium as refrigerator.Since the discovery of superconductivity at39K in MgB2[10],several authors have indicated this material as promising for technological applications[4,11,12]. Indeed,it has been shown that bulk MgB2,contrary to oxide HTS,can be used in the polycrystalline form without a signiﬁcant degradation of its critical current[11,12,13]. This property has been ascribed to the large coherence length,which makes the material less susceptible to structural defects like grain boundaries.Actually,it has been shown that in MgB2only a small amount of grain boundaries act as weak links[14,15,16,17]. Furthermore,MgB2can be processed very easily as high-density bulk material[18], showing very high mechanical strength.Due to these amazing properties,MgB2has been recommended for manufacturing mw cavities[4,19],and investigation is carried out to test the potential of diﬀerent MgB2materials for this purpose.However,papers discussing the realization and/or characterization of mw cavities made of MgB2have not yet been reported.Recently,we have investigated the mw response of MgB2samples prepared by diﬀerent methods,in the linear and nonlinear regimes[17,20].Our results have shown that the residual surface resistance strongly depends on the preparation technique and the purity and/or morphology of the components used in the synthesis process.Inparticular,the investigation of small plate-like samples of MgB2prepared by ReactiveLiquid Mg Inﬁltration(RLI)process,has highlighted a weak nonlinear response,as wellas relatively small values of the residual surface resistance.Furthermore,bulk samplesproduced by RLI maintain the surface staining unchanged for years,without controlled-atmosphere protection.This worthwhile property is most likely related to the highdensity,and consequently high grain connectivity,achieved with the RLI process,aswell as to the small and controlled amount of impurity phases[21].On the contrary,samples prepared by other techniques,though exhibiting lower values of the residualsurface resistance,need to be kept in protected atmosphere to avoid their degradation.These interesting results have driven us to build a mw resonant cavity using MgB2produced by the RLI process.In this work,we discuss the properties of theﬁrst mwresonant cavity made of bulk MgB2.As theﬁrst attempt to apply the MgB2to the cavity-ﬁlter technology,we havemanufactured a simple cylindrical cavity and have investigated its microwave responsein a wide range of temperatures.All the parts of the cavity,cylinder and lids,aremade of bulk MgB2with T c≈38.5K and density≈2.33g/cm3.The MgB2material has been produced by the RLI process[18,22],which consists in the reaction of Bpowder and pure liquid Mg inside a sealed stainless steel container.In particular,thepresent cylindrical cavity(inner diameter40mm,outer diameter48mm,height42.5mm)was cut by electroerosion from a thicker bulk MgB2cylinder prepared as describedin Sec.4.3of Ref.[22],internally polished up to a surface roughness of about300nm.A photograph of the parts,cylinder and lids,composing the superconducting cavity isshown in Fig.1.cmFigure1.Photograph of the cylinder and the lids composing the bulk MgB2cavity.The holes in one of the lids are used to insert the coupling loops.As it is well known,resonant cylindrical cavities support both TE and TM modes.In the TE 01n modes,the wall currents are purely circumferential and no currents ﬂow between the lids and the cylinder,requiring no electrical contact between them;for this reason,the TE 01n are the most extensively used modes.The TE 01n modes are degenerate in frequency with the TM 11n modes and this should be avoided to have a well deﬁned ﬁeld conﬁguration.In order to remove the degeneracy,we have incorporated a “mode trap”in the form of circular grooves (1mm thick,2mm wide)on the inside of the cylinder at the outer edges.This shifts the resonant frequency of the TM 11n modes downwards,leaving the TE 01n modes nearly unperturbed.Two small loop antennas,inserted into the cavity through one of the lids,couple the cavity with the excitation and detection lines.The loop antenna was constructed on the end of the lines,soldering the central conductor to the outer shielding of the semirigid cables.The ratio between the energy stored in the cavity and the energy dissipated determines the quality factor,Q ,of the resonant cavity.When the cavity is coupled to an external circuit,besides the power losses associated with the conduction currents in the cavity walls,additional losses out of the coupling ports occur.The overall or loaded Q (denoted by Q L )can be deﬁned by1Q U+12π√ nπa 2,(2)Q U 01n =1µ2z 201d 3+4n 2π2a 3,(3)where µand ǫare the permeability and dielectric constant of the medium ﬁlling the cavity;a and d are the radius and length of the cavity;R s is the surface resistance of the material from which the cavity is built;z 01=3.83170is the ﬁrst zero of the derivative of the zero-order Bessel function.Q U can be determined by taking into account the coupling coeﬃcients,β1and β2for both the coupling lines;these coeﬃcients can be calculated by directly measuring the reﬂected power at each line,as described in Ref.[1],Chap.IV.Thus,Q U can be calculated asQ U =(1+β1+β2)Q L .(4)The frequency response of the cavity has been measured in the range of frequencies 8÷13GHz by an hp -8719D Network Analyzer.Transmission by two probes has been successfully used for measuring the loaded quality factor in a wide range of temperatures.Among the various modes detected,two of them have shown the highest quality factors;at room temperature and with the cavity ﬁlled by helium gas,the resonant frequencies of these modes are 9.79GHz and 11.54GHz;according to Eq.(2),they correspond to the TE 011and TE 012modes.The coupling coeﬃcients β1and β2have been measured as a function of the temperature;they result ≈0.2at T =4.2K and reduce to ≈0.05when the superconductor goes to the normal state.At T =4.2K (without liquid helium inside the cavity)the unloaded quality factors,determined by using Eq.(4),areQ U 011≈220000and Q U 012≈190000;both decrease by a factor ≈20when the material goes to the normal state.Fig.2shows the temperature dependence of the measured (loaded)and thecalculated (unloaded)Q values for the TE 011mode,Q L 011and Q U 011;in the same plot(right scale)it is shown the mw surface resistance deduced from Q U 011using Eq.(3).As one can note,the quality factor maintains values of the order of 105up to T ≈30K and reduces by a factor ≈20at T =T c .0510152025303540104105Q u a l i t y F a c t o r Temperature (K)R s (m Ω)Figure 2.Temperature dependence of the loaded and unloaded quality factor,Q L 011and Q U 011,(left scale);mw surface resistance R s deduced from Q U 011(right scale).The results of Fig.2have been obtained at low input power level (≈−15dBm).In order to reveal possible nonlinear eﬀects,we have investigated the TE 011resonant curve at higher power levels.In this case,to avoid possible heating eﬀects,the measurements have been performed with the cavity immersed into liquid helium.At input power level of ≈15dBm,we have observed that the quality factor reduces by about 10%,indicating that,at these input power levels,nonlinear eﬀects on the surface resistance are weak.Our results show that MgB 2produced by RLI is a very promising material for building mw resonant cavities.We have obtained a quality factor higher than those reported in the literature for mw cylindrical cavities manufactured by HTS,both bulk and ﬁlms [2,6,7,8].Moreover,Q takes on values of the order of 105from T =4.2K up to T ≈30K,temperature easily reachable by modern closed-cycle cryocoolers.We would remark that this is theﬁrst attempt to realize a superconducting cavitymade of bulk MgB2;we expect that the performance would improve if the cavity weremanufactured with material produced by liquid Mg inﬁltration in micrometric B powder.The present cavity is made of MgB2material obtained using crystalline B powder withgrain mean size≈100µm.On the other hand,previous studies have shown that thegrain size of the B powder,used in the RLI process,aﬀects the morphology[23]and thesuperconducting characteristics[20,23]of the material,including the mw properties.Investigation of the microwave response of bulk MgB2obtained by the RLI methodhas been performed in the linear and nonlinear regimes[20,17].In the linear regime,we have measured the temperature dependence of the mw surface impedance[20]at9.4GHz;the results have shown that the sample obtained using microcrystalline Bpowder(≈1µm in size)exhibits smaller residual surface resistance(<0.5mΩ)thanthose measured in samples prepared by crystalline B powder with larger grain sizes[20].Since the residual surface resistance obtained from the Q U011data is R s(4.2K)≈3.5mΩ,we infer that by using microcrystalline B powder in the RLI process the Q factor couldincrease by one order of magnitude.In the nonlinear regime(input peak power∼30dBm),we have investigated thepower radiated at the second-harmonic frequency of the drivingﬁeld[17].Since ithas been widely shown that the second-harmonic emission by superconductors at lowtemperatures is due to nonlinear processes in weak links[9,25,26],these studiesallow to check the presence of weak links in the samples.Our results have shownthat MgB2samples produced by RLI exhibit very weak second-harmonic emission atlow temperatures.In particular,the sample obtained using microcrystalline B powderdoes not show detectable second-harmonic signal in a wide range of temperatures,fromT=4.2K up to T≈35K[17].So,we infer that eventual nonlinear eﬀects in the cavityresponse can be reduced by using microcrystalline B powder.Because of the shorter percolation length of the liquid Mg into veryﬁne B powder(1µm in size),the production of massive MgB2samples by RLI using microcrystallineB powder turns out to be more elaborated.In this work,we have devoted the attentionto explore the potential of bulk MgB2materials prepared by RLI for manufacturing mwresonant cavities;work is in progress to improve the preparation process in order tomanufacture large specimens using microcrystalline B powder.In summary,we have successfully built and characterized a mw resonant cavitymade of bulk MgB2.We have measured the quality factor of the cavity for the TE011mode as a function of the temperature,from T=4.2K up to T≈45K.At T=4.2K,the unloaded quality factor is Q U011≈2.2×105;it maintains values of the order of105 up to T∼30K and reduces by a factor≈20when the superconductor goes to thenormal state.To our knowledge,these Q values are larger than those obtained in HTSbulk cavities in the same temperature range.The results show that the RLI processprovides a useful method for designing high-performance mw cavities,which may havelarge scale application.We have also indicated a way to further improve the MgB2mwcavity technology.The authors acknowledge Yu. A.Nefyodov and A.F.Shevchun for critical reading of the manuscript.References[1]ncaster,Passive Microwave Device Applications of High-Temperature Superconductors,Cambridge University Press(Cambridge1997).[2]H.Pandit,D.Shi,N.H.Babu,X.Chaud,D.A.Cardwell,P.He,D.Isfort,R.Tournier,D.Mast,and A.M.Ferendeci,Physica C425(2005)44.[3]H.Padamsee,Supercond.Sci.Technol.14(2001)R28.[4]E.W.Collings,M.D.Sumption,and T.Tajima,Supercond.Sci.Technol.17(2004)S595.[5]Z.Zhai,C.Kusko,N.Hakim,and S.Sridhar,Rev.Sci.Instrum.71(2000)3151.[6]M.Hein,High-Temperature Superconductor Thin Films at Microwave Frequencies,Springer Tractsof Modern Physics,vol.155,Springer(Heidelberg1999).[7]C.Zahopoulos,W.L.Kennedy,S.Sridhar,Appl.Phys.Lett.52(1988)2168.[8]ncaster,T.S.M.Maclean,Z.Wu,A.Porch,P.Woodall,N.NcN.Alford,IEE Proceedings-H,vol.139(1992)149.[9]M.Golosovsky,Particle Accelerators351(1998)87.[10]J.Nagamatsu,N.Nakagawa,T.Muranaka,Y.Zenitani,and J.Akimitsu,Nature(London)410(2001)63.[11]Y.Bugoslavsky,G.K.Perkins,X.Qi,L.F.Cohen,and A.D.Caplin,Nature410(2001)563.[12]M.A.Hein,Proceedings of URSI-GA,Maastricht2002;e-print arXiv:cond-mat/0207226.[13]rbalestier,L.D.Cooley,M.O.Rikel,A.A.Polyanskii,J.Jiang,S.Patnaik,X.Y.Cai,D.M.Feldmann,A.Gurevich,A.A.Squitieri,M.T.Naus,C.B.Eom,E.E.Hellstrom,R.J.Cava,K.A.Regan,N.Rogado,M.A.Hayward,T.He,J.S.Slusky,P.Khalifah,K.Inumaru, and M.Haas,Nature,410(2001)186.[14]S.B.Samanta,H.Narayan,A.Gupta,A.V.Narlikar,T.Muranaka,and J.Akimtsu,Phys.Rev.B65(2002)092510.[15]J.M.Rowell,Supercond.Sci.Technol.16(2003)R17.[16]Neeraj Khare,D.P.Singh,A.K.Gupta,Shashawati Sen,D.K.Aswal,S.K.Gupta,and L.C.Gupta,J.Appl.Phys.97(2005)07613.[17]A.Agliolo Gallitto,G.Bonsignore,G.Giunchi,and M.Li Vigni,J.Supercond.,in press;e-printarXiv:cond-mat/0606576.[18]G.Giunchi,Int.J.Mod.Phys.B17(2003)453.[19]T.Tajima,Proceedings of EPAC Conf.,p.2289,Paris2002.[20]A.Agliolo Gallitto,G.Bonsignore,G.Giunchi,M.Li Vigni,and Yu.A.Nefyodov,J.Phys.:Conf.Ser.43(2006)480.[21]G.Giunchi,C.Orecchia,L.Malpezzi,and N.Masciocchi,Physica C433(2006)182.[22]G.Giunchi,G.Ripamonti,T.Cavallin,E.Bassani,Cryogenics46(2006)237.[23]G.Giunchi,S.Ginocchio,S.Rainieri,D.Botta,R.Gerbaldo,B.Minetti,R.Quarantiello,and A.Matrone,IEEE Trans.Appl.Supercond.15(2005)3230.[24]A.Agliolo Gallitto,G.Bonsignore,G.Giunchi,and M.Li Vigni,Eur.Phys.J.B51(2006)537.[25]T.B.Samoilova,Supercond.Sci.Technol.8,(1995)259,and references therein.[26]S.-C Lee,S.-Y.Lee,S.M.Anlage,Phys.Rev.B72,(2005)024527.。

Growth methods of c-axis oriented MgB2 thin films by pulsed laser deposition

c
INFM-Coherentia, Dipartimento di Scienze Fisiche, Università di Napoli, Via Cintia, I-80126 Napoli, Italy
d
INFM, Dipartimento di Chimica e Chimica Industriale, via Dodecaneso 31, 16146 Genova Italy
Growth methods of c-axis oriented MgB2 thin films by pulsed laser deposition
V.Ferrando a, S.Amoruso b, E.Bellingeri a, R.Bruzzese c, P.Manfrinetti d, D.Marrè a, R.Velottac, X. Wang c, C.Ferdeghinia
a
INFM-LAMIA, Dipartimento di Fisica, Università di Genova, via Dodecaneso 33, 16146 Genova Italy
b
INFM-Coherentia and Dipartimento di Ingegneria e Fisica dell'Ambiente, Università della Basilicata, C.da Macchia Romana, I-85100 Potenza, Italy
In this paper we present results in thin films deposition by both methods. In the first section we describe the single step meth

MgB2 superconducting thin film wire material and i

专利内容由知识产权出版社提供
专利名称：MgB2 superconducting thin film wire material and its manufacturing method
发明人：岩中拓夢,小瀧博司,楠敏明申请号：JP2017093226 申请日：20170509 公开号：JP6751369B2 公开日：20200902
申请人：株式会社日立製作所地址：東京都千代田区丸の内一丁目６番６号国籍：JP 代理人：PROBLEM TO BE SOLVED: To provide a MgBsuperconducting thin film wire capable of reducing cost compared to conventional one while securing superconducting property similar to or more than conventional MgBsuperconducting thin film wire, and a manufacturing method of the superconducting thin film wire.SOLUTION: The MgBsuperconducting thin film wire is a superconducting wire in which a MgBthin film is formed on a long sized metallic substrate, the MgBthin film exhibits critical temperature of 30K or more, and has a fine structure in which MgBcolumnar crystal particle stands and aggregates to a surface of the long sized metallic substrate, and a layer of Mg oxide is formed so as to surround the MgBcolumnar crystal particle in a particle boundary area of the MgBcolumnar crystal particle.SELECTED DRAWING: Figure 3

Method of preparing oxide superconducting thin fil

专利名称：Method of preparing oxide superconductingthin film发明人：Takano, Satoshi,Okuda, Shigeru,Yoshida,Noriyuki,Hayashi, Noriki,Sato, Kenichi申请号：EP91105090.4申请日：19910328公开号：EP0449317A2公开日：19911002专利内容由知识产权出版社提供专利附图：摘要：When an oxide superconducting thin film is formed on a substrate by a vapor phase method such as laser ablation, for example, a plurality of grooves are formed onthe substrate by photolithography or beam application in the same direction with an average groove-to-groove pitch of not more than 10 µm, so that the oxide superconducting thin film is formed on a surface provided with such a plurality of grooves. Thus promoted is growth of crystals of the oxide superconducting thin film in parallel with the grooves, whereby respective directions of a-axes and c-axes are regulated to some extent. This improves critical current density of the oxide superconducting thin film.申请人：SUMITOMO ELECTRIC INDUSTRIES, LTD.地址：5-33, Kitahama 4-chome, Chuo-ku Osaka-shi, Osaka 541 JP国籍：JP代理机构：KUHNEN, WACKER & PARTNER更多信息请下载全文后查看。

发明纳米涂层眼镜作文

发明纳米涂层眼镜作文英文回答：Invention of Nano-Coated Glasses.With the rapid development of technology, the invention of nano-coated glasses has revolutionized the eyewear industry. Nano-coated glasses are glasses that have been treated with a thin layer of nano-sized particles, which provide a range of benefits such as improved scratch resistance, water repellence, and anti-reflective properties.The nano-coating process involves the deposition of nano-sized particles onto the surface of the glasses using advanced techniques such as chemical vapor deposition or physical vapor deposition. This results in a thin,invisible layer that enhances the overall durability and performance of the glasses.One of the key advantages of nano-coated glasses is their improved scratch resistance. The nano-sized particles form a protective barrier on the surface of the glasses, making them more resistant to scratches from everyday wear and tear. This not only extends the lifespan of the glasses but also ensures that the wearer can enjoy clear vision without any distracting scratches.Furthermore, the nano-coating provides water repellent properties, which means that water droplets are less likely to cling to the surface of the glasses. This isparticularly beneficial during rainy or humid conditions, as it helps to maintain clear visibility without the need for constant wiping or cleaning.Another significant benefit of nano-coated glasses is their anti-reflective properties. The nano-sized particles help to reduce glare and reflections, allowing for better vision in bright environments and minimizing eye strain. This is especially advantageous for individuals who spend a significant amount of time outdoors or in front of digital screens.In addition to these benefits, nano-coated glasses are also easier to clean and maintain, as the smooth surface repels dust and dirt particles. This not only saves time and effort for the wearer but also ensures that the glasses remain in pristine condition for longer periods.Overall, the invention of nano-coated glasses has significantly improved the quality and functionality of eyewear, providing wearers with enhanced durability, clarity, and comfort.中文回答：纳米涂层眼镜的发明。

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Superconducting thin films of MgB2 on (001)-Si by pulsed laser depositionA. Brinkman, D. Mijatovic, G. Rijnders, V. Leca, H.J.H. Smilde, I. Oomen,A.A. Golubov, F. Roesthuis, S. Harkema, H. Hilgenkamp, D.H.A. Blank and H. Rogalla.Low Temperature Division, MESA+ Research Instituteand Faculty of Applied PhysicsUniversity of TwenteP.O. Box 2177500 AE EnschedeThe NetherlandsSuperconducting thin films have been prepared on Si-substrates, using pulsed laser deposition from a target composed of a mixture of Mg and MgB2 powders. The films were deposited at room temperature and post-annealed at 600 ºC. The zero resistance transition temperatures were 12 K, with an onset transition temperature of 27 K. Special care has been taken to avoid oxidation of Mg in the laser plasma and deposited film, by optimizing the background pressure of Ar gas in the deposition chamber. For this the optical emission in the visible range from the plasma has been used as indicator. Preventing Mg from oxidation was found to be essential to obtain superconducting films.In January 2001, J. Akimitsu et al. [1,2] reported the discovery of superconductivity in the intermetallic compound MgB2. The remarkably high critical temperature at which this material undergoes the transition to the superconducting state, T c≈ 40 K, has aroused great interest and has spurred many groups to explore the properties and application-potential of this novel superconductor. The initial reports were soon confirmed, e.g. by Bud’ko et al., [3] who described the occurrence of an isotope-effect, hinting towards a phonon-mediated pairing-mechanism. Band-structure calculations also point in this direction [4]. Various scientific and technological milestones are now being reached, such as first spectroscopic studies [5], measurements of the specific heat [6], investigations on the intergranular coupling [7], and the realization of MgB2 superconducting wires, as accomplished by Canfield et al. [8]. For many electronic applications and further basic studies, the availability of superconducting thin films will be of great importance. Here we report the fabrication of superconducting thin films of MgB2 on Si-substrates by pulsed laser deposition (PLD) using a target composed of a mixture of Mg and MgB2.Two complicating factors for the fabrication of superconducting films of MgB2 are the high vapor pressures at low temperatures of the magnesium and the high sensitivity of magnesium to oxidation, requiring very low oxygen partial pressures in the deposition system. In order to compensate for a possible loss of Mg in the deposition-process we have used targets composed of MgB2-powder enriched with Mg. The targets were prepared from a mixture of 50 Vol. % Mg powder (Alfa Aesar, purity 99.6 %) and 50 Vol. % MgB2-powder (Alfa Aesar, purity 98.0 %). These powders were carefully mixed and uniaxially pressed in the form of a pellet. Then the pellets were sintered in anitrogen-flow for 3 hours at 640 ºC and subsequently for 10 hours at 500 ºC. It was observed that during the sintering process at 640 ºC some Mg evaporated from the pellet. For this reason we removed a surface-layer of the pellet of about 1-2 mm by grinding. It is estimated that the Mg:B ratio in the final target is considerably larger than 2 Initially, using these targets as well as using targets prepared from MgB2 powders only, we did not succeed in fabricating superconducting films. Numerous attempts were made, varying the deposition temperature from room temperature to ∼ 600 ºC and using various post-anneal procedures. Also depositing multi-layer stacks from elemental boron and magnesium-targets by PLD and subsequent post-annealing did not lead to superconducting films, although in few cases the resistance versus temperature curves displayed small dips in the temperature range of 30 K-40 K.While doing these experiments it was noticed that the plasma-plume invoked by the laser-ablation mostly showed a green color, which is also typically observed in the growth of MgO. For the growth of elemental Mg a blue plasma is rather to be expected. This suggested that the Mg was likely oxidized during the deposition process, explaining the absence of superconductivity in the films. Remarkably, it was found that by varying the background-pressure of Argon gas, the color of the plasma-plume could be altered from intense green for low pressures, to a bright blue for intermediate pressures and a mixture of green and blue for higher Ar pressures. Optimal Ar pressures to obtain the blue plasma were found to depend on the target composition and the laser-energy. Using a target prepared from MgB2 powder only, the optimal Ar-pressure was 0.3 mbar with a laser energy E= 500 mJ, and 0.15 mbar at E= 660 mJ. Using a pure Mg-target, the pressure was 0.22 mbar at E= 500 mJ and 0.2 mbar at E = 660 mJ. Finally, using the target prepared from the mixture of Mg and MgB2 the optimal pressure was found to be 0.17 mbar at E = 500 mJ. The latter values were used in the deposition of the films that showed the transition to the superconducting state.The deposition of the films took place at room temperature. A KrF excimer-laser was used with a wavelength of 248 nm. As the laser spot-size on the target was approximately 8 mm2, and the energy losses in the laser beam-path are estimated to be about 30%, the energy-density at the target was about 4 J/cm2. As a substrate, (001)-oriented Si was used. Prior to the deposition the native SiO x layer was removed from the substrate surface using a 1% vol. HF-etching. Before growing the film, first a Mg-target was pre-ablated for 2 minutes at 10 Hz. This was done with the purpose to reduce the oxygen background pressure in the chamber by the gettering action of the Mg. Before the pre-ablation the chamber was filled with 0.2 mbar of Ar, using an Ar-flow rate of 20 ml/min.. Subsequently, the target composed of the Mg-MgB2 mixture was pre-ablated under the same conditions, first for 2 minutes at 3 Hz and then for 1 minute at 10 Hz.For the actual deposition, the pressure in the chamber was adjusted to the optimal value of 0.17 mbar and the Si-substrate was placed in front of the target at a distance of 4.5cm (on-axis geometry). The films were deposited at a repetition-rate of 10 Hz for 6 minutes, yielding an approximate layer-thickness of 220 nm. After deposition, the Ar-gas was pumped out of the system, which then displayed a background-pressure of 2 × 10-7 mbar. This is below the usual background pressure of our system of about 5 × 10-7 mbar.A high-temperature annealing step was needed to form the superconducting phase. The ex-situ annealing procedure took place in a 0.2 mbar Ar-atmosphere and consisted of a rapid increase (in 4 minutes) to T ann = 600 ºC followed by a quick cool-down to room temperature. The total annealing procedure was kept short to avoid Mg-evaporation out of the film.Figure 1 shows a resistance versus temperature curve for a film before and after the annealing. The graph was recorded using a four-point measurement configuration with voltage-pins placed approximately 2 mm apart. The film was not structured and its dimensions were about 10 × 5 mm2. The bias current used in the measurement was 100 µA. Prior to annealing, the film does not show signs of superconductivity. After annealing, clearly a transition to zero resistance is observed with a zero resistance T c of 12 K. Remarkably, the room temperature resistance increased by the annealing procedure. It is noted that before annealing the film looked shiny like silver and after annealing shiny black.From Figure 1 it appears likely that the film contains multiple phases, characterized by different temperature dependencies of the resistivity. Also, in these measurements the shunting path formed by the Si-substrate is expected to influence the measured temperature dependence.In a second measurement on the same film (shown in Fig.2), we used ultrasonically bonded Al-wires, placed about 1 mm apart. Clearly in this measurement the large hump in the resistance that was observed in Fig. 1b at around 30K is absent. The zero-resistance critical temperature deduced from this measurement was 11 K, with an onset transition temperature of about 27 K. We expect that by optimizing the deposition conditions and the annealing procedure the critical temperature can be further enhanced.In conclusion, we have fabricated superconducting films by pulsed laser deposition using targets prepared from a mixture of Mg and MgB2 powders. An essential aspect to attain superconductivity in the films is to prevent oxidation of the Mg in the laser plasma and deposited film. This was achieved by optimizing the back-ground pressure of Ar gas in the deposition-chamber and using the color of the plasma as an indicator. The availability of superconducting films is an important step towards the realization of superconducting electronics based on this intermetallic compound, for which it is especially noteworthy that the films could be prepared on Si-substrates. Also, the films can be of great value for further basic studies on this intruiging material.The authors thank G.J. van Hummel and C.A.J. Damen for assistance and O. Dolgov and J.G.J. van den Brink for valuable discussions. This work was supported by the Dutch Foundation for Research on Matter (FOM) and the Royal Dutch Academy of Arts and Sciences.[1]: J. Akimitsu, presentation at ‘Symposium on Transition Metal Oxides’, Sendai, January 10, 2001.[2]: J. Nagamatsu et al., Nature410, 63 (2001); See also R.J. Cava, Nature410, 23 (2001).[3]: S.L. Bud’ko et al., Phys. Rev. Lett.86, 1877 (2001).[4]: J. Kortus et al., cond-mat/0101446. J.M. An and W.E. Pickett, cond-mat/ 0102391; Y. Kong et al., cond-mat/0102499.[5] A. Sharoni, et al., cond-mat/0102325; G. Karapetrov, et al., cond-mat/0102312; H. Schmidt, et al., cond-mat/0102389;[6]: Ch. Walti, et al., cond-mat/0102522[7]: D.C. Larbalestier et al., cond-mat/0102216. M. Kambara et al., Supercond. Sc. Techn. 14, L5-L7, (2001)[8]: P.C. Canfield et al., cond-mat/0102289.Figure captions:Fig 1: Resistance versus temperature characteristics for an MgB 2 film (a) as grown and (b) after annealing at 600º C.Fig 2: Resistance versus temperature characteristic measured at a different position on the annealed sample of fig. 1b. The inset shows the transition to zero resistance on an enlarged scale.0501001502002503000.00.51.01.52.02.53.03.54.0R (Ω)T (K)Figure 1a020406080100R (Ω)T (K)Figure 1b010203040T (K)R (Ω) Figure 2。