Thick Film Superconductors on YSZ Substrates

a r X i v :c o n d -m a t /0509385v 2 [c o n d -m a t .s u p r -c o n ] 19 S e p 2005Interface Spin-Orbit Coupling in a Non-centrosymmetric Thin-Film SuperconductorX.S.Wu and P.W.AdamsDepartment of Physics and AstronomyLouisiana State UniversityBaton Rouge,Louisiana,70803Y.Yang and R.L.McCarley Department of Chemistry and the Center for Biomodular Multi-scale Systems Louisiana State University Baton Rouge,LA,70803(Dated:February 2,2008)We present a detailed study of the effects of interface spin-orbit coupling (ISOC)on the critical field behavior of non-centrosymmetric (NCS),ultra-thin superconducting Be/Au bilayers.Parallel field measurements were made in bilayers with Be thicknesses in the range of d =2−30nm and Au coverages of 0.5nm.Though the Au had no significant effect on the superconducting gap,it produced profound changes in the spin states of the system.In particular,the parallel critical field exceeded the Clogston limit by an order of magnitude in the thinnest films studied.In addition,the parallel critical field unexpectedly scaled as H c ||/∆o ∝1/d suggesting that the spin-orbit coupling energy was proportional to ∆o /d 2.Tilted field measurements showed that contrary to recent theory,the ISOC induces a large in-plane superconducting susceptibility but only a very small transverse susceptibility.PACS numbers:74.20.Rp,74.78.Db,73.40.Jn One of the most fundamental characteristics of a superconductor is the symmetry of its condensate wavefunction.Indeed,this has proven to be a central issue in the description of a number of non-conventional superconductors such as high-T c systems [1]and the ruthenates [2,3].In conventional BCS superconductivity the condensate is time reversal invariant and is formed from Cooper pairs consisting of electrons of opposite momentum and opposite spin [4].In non-conventional superconductors,however,this simple symmetry can be modified by the underlying crystal structure and/or the symmetry of the pairing interaction.A compelling example of the former is the recently discovered heavy fermion superconductor CePt 3Si,whose crystal structure lacks inversion symmetry [5].CePt 3Si exhibits a line node gap structure [6,7,8]which is believed to be,in part,a consequence of strong spin-orbit (SO)coupling in a non-centrosymmetric (NCS)crystal symmetry [5,9,10].This has stimulated renewed interest in the possibility of realizing non-conventional pairing states from the convolution of broken inversion symmetry and spin orbit coupling,neither of which violate time reversal invariance.Recent theoretical work on the problem has suggested that a bilayer configuration,which,by definition,lacks inversion symmetry,consisting of a low atomic mass thin-film superconductor coated with a high atomic mass non-superconducting element such as Au or Pt would be a model system for studying the effects of SO coupling in a NCS superconductor [11,12,13].In the present Letter,we present a study of interface SO coupling in thin Be films coated with 0.5nm of Au via critical magnetic field measurements.Contrary to recent theoretical predictions,we find that the SO induced in-plane superconducting spin susceptibility is significantly larger than the corresponding perpendicular susceptibility.Furthermore,the SO coupling cannot be described in terms of Abrikosov-Gorkov impurity formalism [4]in that it appears to be a function of the superconducting gap.In the experiments described below we use critical field measurements to determine the SO coupling strength in Be/Au films of varying Be thickness.The Maki equation [14,15]is a useful tool for extracting the spin response of the superconductor from the orbital response,particularly when the film is not in the thin-film limit and/or the field is not parallel to the film surface.In general the critical field of a thin film is a function of the superconducting gap∆o ,the film thickness d ,the electron diffusivity D ,and the spin orbit coupling parameter b .The critical field H c is determined by the implicit function [15]:ln T 2 −α+2+ǫ+2α−2γψ 14πk B T(1)whereα±=b ±γ,γ=(b 2−µ2B H 2c )1/2,T c is the critical temperature,andψis the digamma function.ǫis a function of the angle between the plane of the film and the magneticfield,ǫ(θ)=D[2eH c sin(θ)+1∆o≈√3b/∆o b/∆o≥1,(3)where Eq.(2)is the familiar Clogston spin-paramagnetic criticalfield[16,17,18].Note that from Eq.(3)the critical field can be arbitrarily high with increasing b.In contrast,if the Zeeman coupling is neglected then,at anyfinite thickness d<ξ,the parallel criticalfield is limited by the orbital term,2µB H c||3 3d(4)Numerous studies of the spin-paramagnetic transition in ultra-thin Al and Befilms have shown that these two light elements have a very low intrinsic SO scattering rate[19,20,21]and are true spin-singlet superconductors. Consequently,they make ideal candidates for systematic studies of the effects of ISOC induced by impurity coatings [11,22].Not only does this bilayer configuration break inversion symmetry,but one can treat the ISOC as a boundary condition on the spin component of the superconducting wave function.Early measurements of the criticalfield behavior of Alfilms coated with less than0.2nm of Pt revealed that the Pt-induced ISOC can produce significant enhancements of the parallel criticalfield with virtually no effect on the transition temperature[19].Though the temperature and angular dependencies of the Al/Pt criticalfields were in reasonable agreement with the Maki formula, the overall magnitude of H c||was typically∼10−30%higher than could be accounted for by reasonable estimates of b.Recent analysis of the spin states of two-dimensional NCS superconductors,and,in particular,superconducting-normal metal bilayers,predicts that ISOC will introduce an anisotropic spin triplet component into superconducting ground state[12,13].The triplet component is most directly manifest in the spin susceptibility of the superconductor χs.Of course,conventional spin-singlet BSC superconductors haveχs∼0at T=0,but ISOC is expected to liftthe spin degeneracy,and in the strong coupling l:χs∼χn/2,χs⊥∼χn,whereχs is the in-plane superconducting susceptibility andχn is the normal state susceptibility.The Clogston criticalfield given by Eq.(2)is derived by equating the magnetic free energy difference between normal and superconducting states with the condensation energy of the superconducting state.Ifχs=0then Eq.(2)can be generalized,2µB H c=√1−χs/χn.(5)This would imply that the parallel criticalfield of a bilayer,such as the Al/Pt samples of Ref.19,would never be larger than H c||=∆o/µB.However,the criticalfield enhancements observed in those early experiments were significantly greater than this upper limit.Since the late1970’s very little work has been done on SO coupling in thinfilm superconductors,though several fundamental questions remain unanswered.For instance,the Al/Pt measurements were made at a single Al thickness and over a very narrow range of gap values.Clearly,one would like to determine the depth to which the ISOC penetrates into the superconductingfilm and how the spin component of criticalfield behavior scales withfilm thickness and gap magnitude.Another important issue is whether or not the anisotropy in χs is observable in the angular dependence of the criticalfield.Be/Au bilayerfilms of varying Be thickness were prepared by e-beam evaporation in a initial vacuum of∼0.2µTorr. All of the depositions were made onfire polished glass substrates held at84K.First a layer of Befilm with thickness in the range2.−30.0nm was deposited at a rate of0.14nm/s,then a0.5nm Aufilm was deposited at0.01nm/s without breaking the vacuum.Both the Be and Be/Aufilms were found to be very smooth and homogenous,with no evidence of islanding or granularity,see Fig.1.Thefilms were subsequently trimmed in order to eliminate edge effects.Resistive measurements were made in a dilution refrigerator with a base temperature50mK by a standard four-probe lock-in method.Thefilms were aligned with the magneticfield via an in situ mechanical rotator.In the data presented below the transition temperatures were defined by the temperature at which the resistance fell to10% of its normal state value and the criticalfield was determined by the midpoint of the resistive transition.The transition temperature of the homogeneously disordered Be/Aufilms used in this study are plotted as a function of Be thickness in Fig.2.Films with d<2nm are known to display a non-perturbative zero bias anomaly in their tunneling density of states,which is associated with the emergence of the Coulomb gap[23].As can be seen in Fig. 2,this is also the critical thickness below which the zero temperature superconducting phase is lost and the electron diffusivity goes to zero.In order to make use of Eq.(1)it was necessary tofit the thickness dependence of T c and D with an empirical functional form.In particular,the solid lines in the main panel and the inset of Fig.2are the functions:T c(d)=T co tanh[(d−1.35)/1.29)](6)D(d)=D o tanh[d2/23.3],(7) where T co=0.68K and D o∼3 /m.D o was determined fromfilms with d>10nm using the relation1/R= 2e2ν0D o d,where R is the sheet resistance andν0is the density of states per spin of Be.The BCS coherence length for a Befilm with T c∼0.7K isξo∼4µm.For the range of diffusivities plotted in the inset of Fig.2the mean free√path is always l o<1nm and the corresponding Pippard coherence lengths are in the rangeξ=0.85criticalfields of the twofilms.This reflects the fact that it is almost indistinguishable from what one would obtain using the phenomenological Tinkham formula[4,15]which only involves H c||and H c2.In contrast,the dashed line depicts the solution to Eq.(1)assuming an exponentially attenuated SO parameter b=1.85exp(−θ/θo)mV,with a characteristic angleθo=2.5◦.The dashed line captures the dip structure in the data which indicates that the Zeeman component of the criticalfield is angle dependent.The dip structure is consistent with an anisotropic superconducting susceptibility consisting of a large in-plane component(of the order of the normal state susceptibility)and a small transverse component.The sense of this anisotropy is of the opposite sign of that calculated for non-disordered 2D NCS superconductors,where the in-plane component is expected to be half that of the transverse component. Nevertheless,the fact that ISOC induces a preferentially large in-plane susceptibility would also account for earlier reports of anomalously high parallel criticalfields in Al/Pt bilayers[19].In summary,we have used criticalfield measurements to probe the effects of interface spin-orbit coupling on the spin states of superconducting Befilms.Wefind that a∼1monolayer coating of Au on the Be surface produces a large,anisotropic enhancement to the Zeeman component of the criticalfield.The normalized parallel criticalfield H c||/∆o of Be/Au bilayers scales as the inverse of the Be thickness and can exceed the Clogston limit by as much as an order of magnitude.The criticalfield scaling was observed over a wide range of∆o which is inconsistent with the standard impurity scattering model of SO coupling.We believe that the scaling is,in fact,a manifestation of the superconductor’s attempt to reconcile a mixed-spin boundary condition at the Au interface with the intrinsic spin-singlet ground state of Be.Naively,one would expect that the ISOC healing length would be of the order of ξ,but it may be significantly shorter in the presence of disorder.Nevertheless,the anisotropic spin susceptibility is clearly evident in the tiltedfield data.A highfield study of the local tunneling density of states at the Be/Au and the Be/substrate interfaces,respectively,should provide an important local probe of the extent of spin-mixing at the two boundaries.We gratefully acknowledge enlightening discussions with Victor Edelstein,Gianluigi Catelani,Ilya Vekhter,Dana Browne,and David Young.This work was supported by the National Science Foundation under Grant DMR02-04871.[1]C.C.Tsuei and J.R.Kirtley,Rev.Mod.Phys.72,969(2000).[2]A.P.Mackenzie and Y.Maeno,Rev.Mod.Phys.75,657(2003).[3]K.D.Nelson,Z.Q.Mao,Y.Maeno,and Y.Liu,Science306,1151(2004).[4]M.Tinkham,Introduction to Superconductivity(McGraw-Hill,New York,1996).[5]E.Bauer,G.Hilscher,H.Michor,C.Paul,E.W.Scheidt,A.Gribanov,Y.Seropegin,H.Noel,M.Sigrist,and P.Rogl,Phys.Rev.Lett.92,027003(2004).[6]K.Izawa,Y.Kasahara,K.Matsuda,Y.and Behnia,T.Yasuda,R.Settai,and Y.Onuki,Phys.Rev.Lett.94,197002(2005).[7]I.Bonalde,W.Bramer-Escamilla,and E.Bauer,Phys.Rev.Lett.94,207002(2005).[8]D.P.Young,M.Moldovan,X.S.Wu,P.W.Adams,and J.Y.Chan,Phys.Rev.Lett.94,107001(2005).[9]P.A.Frigeri,D.F.Agterberg,A.Koga,and M.Sigrist,Phys.Rev.Lett.92,097001(2004).[10]K.Samokhin,E.Zijlstra,and S.Bose,Phys.Rev.B69,094514(2004).[11]V.M.Edelstein,Phys.Rev.B67,020505(2003).[12]L.P.Gor’kov and E.I.Rashba,Phys.Rev.Lett.8703,037004(2001).[13]S.K.Yip,Phys.Rev.B65,144508(2002).[14]K.Maki,Phys.Rev.148,362(1966).[15]K.Aoi,R.Meservey,and P.M.Tedrow,Phys.Rev.B9,875(1974).[16]A.M.Clogston,Phys.Rev.Lett.9,266(1962).[17]B.S.Chandrasekhar,Appl.Phys.Lett.1,7(1962).[18]The b=0solution of the Maki equation actually represents the supercooling criticalfield of an intrinsically hystereticfirst-order phase transition.[19]P.M.Tedrow and R.Meservey,Phys.Rev.Lett.43,384(1979).[20]P.W.Adams,Phys.Rev.Lett.92,067003(2004).[21]P.W.Adams,P.Herron,and E.I.Meletis,Phys.Rev.B58,R2952(1998).[22]P.M.Tedrow and R.Meservey,Phys.Rev.B25,171(1982).[23]V.Y.Butko,J.F.DiTusa,and P.W.Adams,Phys.Rev.Lett.84,1543(2000).[24]G.Bergmann and C.Horriaresser,Phys.Rev.B31,1161(1985).[25]G.Bergmann,Phys.Rev.B6319,193101(2001).FiguresFIG.1:A)0.1x0.1µm atomic force micrograph of a6nm thick Befilm evaporated onto glass at84K.B)Micrograph of a Befilm coated with0.5nm of Au.FIG.2:Transition temperature of Be/Au bilayers as a function of Be thickness.The Au thickness was0.5nm in each sample. The solid line is a bestfit to the data using the empirical form of Eq.(6).Inset:relative diffusivity of Be/Au bilayers as a function of Be thickness.The solid line is afit to Eq.(7).FIG.3:Normalized parallel criticalfields as a function of Be thickness for Be/Au bilayers(circles),Be/Pb(crossed box),pure Befilms(triangles).The long dashed line represents the theoretical orbitally limited criticalfield given by Eq.(4).The solid line is a linear leastfit to the bilayer data.The horizontal dashed line represents the Clogston criticalfield.FIG.4:Ratio of the criticalfield of Be/Au bilayers and Befilms of equal Be thickness as a function of tilt angle,θ=0 corresponds to parallelfield.triangles:d=7.4nm,circles:d=5.4nm,diamonds:d=2.9nm.The solid lines are a guide to the eye.FIG.5:Ratio of the criticalfield of a5.4nm Be/Au bilayer(T c=0.68K,H c2=0.137T,R=240Ω)and5.4nm Befilm (T c=0.505K,H c2=0.048T,R=162Ω)as a function of tilt angle.Solid line is the solution of Eq.(1)assuming an isotropic SO coupling parameter of b=1.85mV for the Be/Au bilayer and b=0.0132mV for the Befilm.The dashed line is the solution of Eq.(1)assuming that the Be/Au SO parameter is exponentially attenuated with increasing tilt angle.Left inset: Fit of Eq.(1)to the Befilm data.Right inset:Solid line is afit of Eq.(1)to the Be/Au data with a constant b.The dashed line is a somewhat betterfit using an exponentially form b=b o exp(−θ/θo).。

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。

a r X i v :c o n d -m a t /9709005v 1 [c o n d -m a t .s u p r -c o n ] 1 S e p 1997Non-equilibrium Superconductivity and Quasiparticle Dynamics studied by PhotoInduced Activation of Mm-Wave Absorption (PIAMA).B.J.Feenstra a,∗,J.Sch¨u tzmann a ,and D.van der Marel a ,R.P´e rez Pinaya b ,and M.Decroux baMaterials Science Centre,Rijksuniversiteit Groningen,Nijenborgh 4,9747AG Groningen,The NetherlandsbDept.de Physique de la mati`e re condens´e e,Universit´e de Gen`e ve,24quai Ernest-Ansermet,CH-1211Gen`e ve 4,Switzerland(February 1,2008)We present a study of non-equilibrium superconductivity in DyBa 2Cu 3O 7−δusing photo induced activation of mm-wave absorption (PIAMA).We monitor the time evolution of the thin film trans-missivity at 5cm −1subject to pulsed infrared radiation.In addition to a positive bolometric signal we observe a second,faster,decay with a sign opposite to the bolometric signal for T >40K.We at-tribute this to the unusual properties of quasi-particles residing near the nodes of an unconventional superconductor,resulting in a strong enhancement of the recombination time.The occurrence of zero’s in the superconducting gapfor certain values of the momentum ¯h k at the Fermi sur-face of high T c superconductors has a number of intrigu-ing consequences for the dynamical behavior and life-time of the quasi-particles at low temperatures,which has only recently begun to attract the attention of re-searchers in the field.Due to the presence of these zero’s (or nodes)the reduction in the superfluid fraction (ρs )[1,2]and specific heat [3]is proportional to H 1/2,where H is the magnetic field.Also,a strong reduction of the quasi-particle scattering rate (1/τ)below T c [4–6]pro-vides evidence that the dominant scattering mechanism has an electronic signature.In this Letter we present a study of the quasi-particle dynamics using Photo Induced Activation of Mm-wave Absorption (PIAMA).In this pump/probe experiment we use a free electron laser [7](FELIX)which is con-tinuously tunable from 100to 2000cm −1as a pump to create a temporary excited state of a superconductor.FELIX produces macro-pulses with a stepwise off-on-offintensity profile (’on’for 3<t <7µs in Fig.1),consisting of 5000micropulses (1-5ps).The step-response of the complex dielectric constant is monitored at 5cm −1using the combination of a Backward Wave Oscillator (BWO)and a fast waveguide diode detector as a probe to mea-sure the transmission through a superconducting film as a function of time.The mm-wave detector-circuit was selected as a compromise between sensitivity and speed of detection,resulting in an overall time resolution of 1µs.This choice of experimental parameters is optimal for the detection of small changes induced in the dielectric function by the infrared (IR)pulse at,as we will see,the scale of the lifetime of nonequilibrium superconductivity in high T c ’s.We used films of DyBa 2Cu 3O 7−δwhich were prepared by RF sputtering on LaAlO 3substrates.The film thick-ness was 20nm and T c was 88K.Optimal surface quality was obtained by using Dy instead of Y.This substitu-tion does not affect the superconducting properties.A detailed description of the preparation,characterization and the mm-wave dielectric properties of these films hasbeen given elsewhere [8,9].The LaAlO 3substrate supporting the film is plan-parallel,with a thickness D =0.054cm and a refrac-tive index n =4.70.At k/2π≈5cm −1,which is our probe frequency,the dielectric function of the film |ǫ|ranges from 104to 106depending on temperature,while (kd )−2≈3·108.Hence the films are optically thin and (kd )−2≫|ǫ|≫1.In that limit the Fresnel expression for transmission through the film/substrate system is I t =(2−ikdǫ)cos ψ2n−2(1)where ψ=nkD .The effect of increasing the tempera-ture is to transfer spectral weight from the condensate to the quasi-particles,while at the same time reducing the quasi-particle lifetime.The net result is,that both |ǫ′|and ǫ′′are reduced as the temperature increases,and the thin film transmission increases.In the inset of Fig.1the mm-wave transmission through a DyBa 2Cu 3O 7−δfilm of 20nm thickness on a LaAlO 3substrate is displayed for k/2π=5cm −1and for k/2π=4cm −1.The former corresponds to a larger sensitivity to the quasi-particles (represented by ǫ′′)as compared to the latter frequency.A detailed analysis has been given elsewhere [9].Most significant for the identification of a possible bolometric response is the monotonic temperature dependence of the transmission over the entire temperature interval.In Fig.1the photo induced change in transmission (δI t )of the same film is shown between 5and 65K.The probe frequency is 5cm −1.The pump frequency is k/2π=800cm −1,with a power of ≃10mJ/pulse.Here and in Fig.2the curves have been calibrated against vari-ations in the incident power of FELIX.We see that for temperatures lower than 40K,the IR-pulse enhances the transmissivity of the thin film.However,around 40K the situation changes and the transmission after the IR-pulse is reduced instead.δI t is smaller at higher temperatures and becomes undetectable above 75K.The ordinary monotonic behavior seen in the temperature dependence of the unperturbed mm-wave transmission indicates thata simple heating of the sample can not account forthefact thatδI t<0above40K.Thefits shown in Fig.1correspond to a linear combination of a slow(τB)and afast(τR)decay:δI t=i B e−t/τB+i R e−t/τR.The slowcomponent i B has a weak time dependence(τB≫45µs)on the interval displayed in Fig.1and is reduced fromi R/3at5K to zero for T>40K.The prefactor of thefast component(4µs<τR<25µs)changes sign at40K.FIG.1.Change in transmission,δI t for DyBa2Cu3O7−δonLaAlO3,shown for several temperatures.The FIR-pulse en-hances transmission at low temperatures,while it reduces itat temperatures higher than40K.The exponentialfits areshown as the solid lines.Inset,upper right corner:tempera-ture dependence of the unperturbed transmission at4and5cm−1.Inset,lower right corner:Temperature dependence ofthe faster relaxation time,τR.The changes in transmission as a function of pump fre-quency show a rather non-monotonic behavior and havebeen summarized in Fig.2for several temperatures rang-ing from5to60K.Plotted are the maxima(minima)of the positive(negative)peak intensities obtained aftercalibrating against the changes in incident power.Forcomparison we display in the samefigure the absorptioncoefficient in the superconductingfilm A f=1−R f−T f ofthe IR-light,where R f is the reflectivity of the substrate-supportedfilm,and T f is the transmission through thefilm into the substrate.We calculated A f without ad-justable parameters from the experimentally determineda-and c-axis dielectric function of YBaCuO[10,11]andLaAlO3[12]using the Fresnel equations for light of mixedpolarization incident at an angle of45◦on a20nm thick,c-axis oriented YBaCuOfilm on a LaAlO3substrate,identical to the experimental situation.Optical absorp-tion in the substrate occurs at185,427and651cm−1.For thefilm A f has minima at these frequencies and max-ima at290,600and760cm−1,which is due to resonantreflection at the substrate/film interface for frequenciesmatched to the longitudinal phonons of the substrate.FIG.2.NormalizedδI t as a function of frequency,shownfor temperatures ranging from5to60K.Also shown is theabsorptivity within thefilm(solid line).The main conclusion from Fig.2is,thatδI t tracks thelaser power deposited in thefilm,not in the substrate.This demonstrates that PIAMA probes changes in thephysical state of the superconductor,while secondary ef-fects due to substrate heating can be excluded.The amplitude of the slow component,τB,in Fig.1corresponds to an increase in temperature of13and0.2K for the5K and40K curves respectively.A crude es-timate of the increase in temperature based on the inputlaser-power and the specific heat of thefilm/substratesystem gives∆T=9and0.2K respectively.We there-fore attribute the slow response to bolometric heating ofthefilm/substrate system.At higher temperatures thespecific heat is too large,and∆T is insignificant.We ob-served a similar bolometric response for MgO supportedNbN thin superconductingfilms,in which case the fasterdecay was absent within the limitations of the time res-olution of our detector.A more extensive discussion ofthis work is presented elsewhere[13].Let us now consider the faster decay,τR.For suffi-ciently low frequencies(ωτ≪1)the inductive responseis proportional to the condensate amplitude(ǫ′∝ρs),and will be reduced during and following the IR-pulse,so thatδρs<0.Here we are interested in the behaviorof the quasi-particle response,which is represented by thefinite value ofǫ′′.The latter is proportional to the den-sity of quasi-particles and their lifetime(ǫ′′∝ρqpτ).Dueto transfer of spectral weight from the condensate to thequasi-particle peak we expect thatδρqp>0in the non-equilibrium state following the IR-pulse.With PIAMAwe attempt to probe the time-evolution of variations inthe volume density of quasi-particles(δρqp).The highestsensitivity to the latter variations relative to those of thecondensate is obtained for cosψ=0,which is also theexperimental situation in Figs.1and2.In that case the transmission coefficient varies as:2n2ρs −kdǫ′′[1+n2+kdǫ′′]δρqpττR= k,k′g2|M kk′|2Im f k f k′(1+n q)δq−k k′τi= k,k′g2|L kk′|2δq+k k′Imf k(1−f k′)n q+f k′(1−f k)(1+n q)Einstein distribution functions of quasi-particles and phonons respectively,and L kk ′=u k ′v k −v k ′u k .We adopted a d x 2−y 2order parameter with ∆max =25meV.The resulting temperature dependence of τR and τi is displayed in Fig.3.FIG.3.Calculated temperature dependence of the quasi-particle-phonon scattering time (τin ,triangles)and the quasi-particle recombination time (τR ,squares).Most importantly we notice that τR ≫τi at all tem-peratures.The same calculation assuming an isotropic s -wave gap confirms the earlier result that τR and τi are equal for T →T c in s -wave superconductors [21].A small admixture of s-wave symmetry of the type ’d +s ’merely breaks the 4-fold rotation symmetry of the quasi-particle dispersion,without affecting the physical pic-ture.With an admixture of the type ’d +i s ’the en-ergy of the quasi particles near the nodes is increasedto E 2k =(∂k ∆)2k 2t +¯h 2v 2F k 2l +∆2s ,causing a further sup-pression of the available phase space for recombination processes,while |M kk ′|increases near the nodes.The net effect on τR depends on ∂k ∆,v F and ∆s .Finally we discuss our observations in relation to time-scales obtained with other experimental -ing micro-wave experiments the scattering time is found to change from 100fs at 90K to less than 10ps at 40K.With pump/probe experiments using visible light a decay of 0.2ps has been observed,which was associated with the life-time of quasiparticles near the Fermi energy,along with a second slow decay of at least 20ns [22].A re-laxation of the resistivity within a few ns [23]has been at-tributed to non-equilibrium quasiparticle-generation by hot phonons.Based on an analysis of the critical flux-flow velocity Doettinger et al.[24]determined an inelastic scattering time ranging from 10ps at 80K to 0.1µs at 40K.The timescale of several µs reported in this Let-ter is much longer.We attribute this to the fact that the quasi-particle recombination time is always longer than the inelastic scattering time,which is the sum of all electron-electron and electron-phonon scattering pro-cesses,as is demonstrated by the numerical calculation of the two electron-phonon time constants τR and τi pre-sented above.In conclusion,we have observed a non-equilibrium state with a life-time of several µs in DyBa 2Cu 3O 7−δusing photo induced activation of mm-wave absorption (PIAMA).The non-equilibrium state is clearly distinct from bolometric heating of the superconductor.The long time-constant seems to reveal an unusually long quasi-particle recombination time,which can be understood as a consequence of the highly peculiar nature of quasi-particles near the nodes in these materials.Along with other factors,such as the amplitude of the gap,the pres-ence of nodes distinguishes these materials from conven-tional superconductors.Acknowledgements We gratefully acknowledge the as-sistance by the FELIX staff,in particular A.F.G.van der Meer.Furthermore we thank W.N.Hardy,D.I.Khomskii and O.Fisher for their stimulating comments during the preparation of this manuscript and A.Wittlin for fruitfull discussions at the initial stage of this project.。

PROGRESS IN PHOTOVOLTAICS:RESEARCH AND APPLICATIONSProg.Photovolt:Res.Appl.2003;11:319–331(DOI:10.1002/pip.495)Cu(In,Ga)Se 2Thin FilmsGrown with a Cu-Poor/Rich/Poor Sequence:Growth Modeland Structural ConsiderationsJ.Kessler 1*,y C.Chityuttakan 2,J.Lu 1,J.Scho¨ldstro ¨m 1and L.Stolt 11A ˚ngstro ¨m Solar Center,Uppsala University,PO Box 534,SE-75121Uppsala,Sweden 2SPRL,Chulalongkorn University,Bangkok,ThailandThin films of Cu(In,Ga)Se 2are grown by a co-evaporation process in which the In,Ga,and Se fluxes,as well as the substrate temperature,are constant and the only variableis the Cu flux.This Cu flux varies in three steps in such a way that the growing filmevolves from Cu-poor to Cu-rich and then back to Cu-poor.The film growth is mon-itored by the ‘end point detection’method,and film thicknesses of the order of 2 mare deposited in less than 20min.Quality devices (efficiencies above 15%)are pro-duced in our baseline processes for all of the other synthesis steps.The Cu(In,Ga)Se 2layers are studied from a (112)versus (220)(204)orientation and recrystallizationpoint of view.Including the results from a previous study on the influence of the sub-strate temperature to the present X-ray diffraction and scanning as well as tunnelingelectron microscopy data,a five-stage growth model for the films is described.The spe-cific features of these films are that they are weakly (220)(204)oriented and exhibitcrevices in their top fractions.The growth model hypothesizes about the origins ofthese crevices and on how to avoid them.Copyright #2003John Wiley &Sons,Ltd.1INTRODUCTIONT he impressive performance levels reached by cells,mini-modules,and product-size modules based onCu(In,Ga)Se 2thin-film absorbers will be ineffectual for the production of solar energy if the practical producibility issues are not satisfied.For the growth of the Cu(In,Ga)Se 2layer itself,this is at the heart of the debate between co-evaporation from elemental sources and sequential deposition,by sputtering and sele-nization techniques.Process control is a prerequisite to yield,as deposition rate is to throughput at cost.There is a need for a rapid process recipe that combines ease and simplicity of growth with resulting high device quality.Many co-evaporation recipes use changes in the substrate temperature during growth.It is questionable whether this is realistic for large substrates being rapidly processed in large machines.In this paper,all films are grown by elemental co-evaporation at constant substrate temperatures.Although a study as a function of the substrate temperature is presented,the concept is that the ‘base’recipe should be run at a maximum of 500 C.We also impose a maximum deposition time of 20min and use the change in the thermal behavior of theReceived 28November 2002Copyright #2003John Wiley &Sons,Ltd.Revised 4Apirl 2003*Correspondence to:John Kessler,A ˚ngstro ¨m Solar Center,Uppsala University,PO Box 534,SE-75121Uppsala,Sweden.y E-mail:john.kessler@angstrom.uu.seContract/grant sponsors:Foundation for Strategic Environmental Research;Swedish Energy Agency.Research320J.KESSLER ET AL. substrate due to the variations in emissivity in the vicinity of stoechiometry of the Cu(In,Ga)Se2film as a control signal.1,2In this work we have chosen to growfilms at thicknesses at or above2m m,therefore the deposition time could probably be further shortened by simply growing thinner layers.It is expected3that the device per-formance is not significantly hindered until thefilm thickness is substantially less than1Á5m m,and20min is not the minimum reported growth times4,5for device quality layers.In our past work6we have used similar boundary conditions and control concepts for a two-step process where the initial growth is Cu-rich under uniformfluxes,followed by a step containing no Cu vapor where thefilm evolves from Cu-rich to Cu-poor.This transition can be visualized and is referred to as‘end point detec-tion’(EPD).Previously introduced,7and developed in this paper is a similar process in which the initial growth is Cu-poor under uniformfluxes.The Cuflux is then increased,so as to bring thefilm to Cu-rich conditions before the Cuflux is set to zero and,as in the previous process,thefilm evolves back to a Cu-poor state.Others8 have used and reported such recipes previously.We have named the above two processes CURO and CUPRO in reference to the evolution of the Cuflux(respectively Cu-rich-off and Cu-poor-rich-off).The present paper details the CUPRO process and examines some of the structural considerations such as (112)versus(220)(204)orientation and morphology for recipes that are proven to be both tolerant to parameter variations(thus uniform and easily reproducible),and yield high-quality devices(cells above15%without anti-reflective coatings).The features of this CUPRO process are compared with those of the‘Boeing’process9 as well as to those of the‘three-stage’process.10We briefly remind the reader that in the‘Boeing’process,an initial Cu-richfilm growth at lower substrate temperatures($350 C)is followed by Cu-poorflux conditions at higher substrate temperatures($450 C)until the overallfilm composition becomes Cu-poor,whereas the ‘three-stage’process starts by the growth of an(In,Ga)2Se3layer at low substrate temperatures($250–400 C)that is converted to Cu(In,Ga)Se2by exposure tofluxes of Cu and Se at high substrate temperatures (>550 C)until the overall composition becomes Cu-rich.Thefilm is then brought back to Cu-poor composi-tions by exposure tofluxes of In,Ga and Se while sustaining the high substrate temperature.2EXPERIMENTAL2.1Film growthThe vacuum chamber used for the elemental co-evaporation of the Cu(In,Ga)Se2consists of a considerably modified Balzers UMS500P system,achieving base pressures in the order of5Â10À7mbar.For the evapora-tion of the metals,three modified Luxel Radak II sources are used while the selenium source is a quartz crucible placed in a simple coil heater.All sources are positioned so as to point to the middle of the10Â10cm2 molybdenum-coated soda-lime glass(SLG)substrate.This substrate,positioned approximately40cm above the sources,is suspended under a heater box containing a set of IR lamps.By means of a thermocouple‘in contact’with the back surface of the substrate,the temperature T sub is measured and kept constant by regulation of the output power(OP(t))delivered to the IR lamps.It should be remarked that as T sub is representative of a limited area sampled by the tip of the thermocouple,the OP(t)delivered to the IR lamps is governed by the local properties of that limited area.All temperatures are controlled by Eurotherm PID systems and are regulated in the phase-angle-fire mode.In general,a‘recipe’is the evolution,during growth,of afilm’s composition,thickness,and temperature.As the composition of thefilm results from that of the vaporflux,itself resulting from the source temperatures,it is useful tofirst calibrate the system so as to know the relationships between the individual source temperatures T s( C),measured by the control thermocouples,placed beneath the crucibles,and the vaporfluxes incident to the substrateÈs(atoms cmÀ2sÀ1)at the growingfilm surface(i.e.,the T s¼f(Ès)relationships,where S¼Cu, In,Ga,and Se).These relationships are determined with the sources in steady state mode only,where there are fixed correspondances between the measured values of T s and the temperatures of the evaporating surfaces of the melts in the crucibles.For Cu(In,Ga)Se2films the composition is commonly defined by the metal ratios x¼[Ga]/([In]þ[Ga])and y¼[Cu]/([In]þ[Ga])and the assumption that all compositions should lie on the pseudobinary tie line,as long as the growth conditions are in Se excess.Similarly,the vaporflux composition can be defined by the parameters X¼ÈGa/(ÈInþÈGa)and Y¼ÈCu/(ÈInþÈGa),complemented byÈSe. Copyright#2003John Wiley&Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331Cu(In,Ga)Se2THIN-FILM GROWTH321 A‘base’recipe for a CUPRO run is shown in Figure1.This is presented as three time dependencies;thefirst (Figure1a)is that of the measured temperatures of the control thermocouples for the three metal sources,the second(Figure1b)is that of the measured output power level to the substrate heater,and the third(Figure1c)is that of the estimated global composition(value of y(t))of the growingfilm.Various characteristic durations are defined in Figure1(a and b),either relative to the source control(t1¼t1aþt1bþt1c and t2),theflux composition (Y<1or Y>1or Y¼0)or thefilm composition(y<1or y>1).For Figure1(a)the specific values of the temperatures of the substrate and Se source(not shown infigure)arefixed respectively at500and315 C. At of315 C the seleniumflux(ÈSe)is of the order of1–1Á5Â1016atom cmÀ2sÀ1.From the T s¼f(Ès)relation-ships,the ratios of the temperatures of the metal sources are calculated so that x is constant throughout the whole process(here x$0Á25)and so that during the time t1a theflux Y andfilm y compositions are equal to 0Á75.The Cu source temperature is then increased over the time t1b so that the globalflux changes from Cu-poor(Y<1)to Cu-rich(Y>1)conditions where it is maintained during the time t1c until thefilm becomes sufficiently Cu-rich(y>1Á1).At this point t1the Cu source is turned off,the Cuflux rapidly falls to zero and,as in our earlier work,6,7thefilm returns to Cu-poor compositions,where the growth is interrupted when y$0Á9.The amplitudes of the source temperatures are chosen so that the total acquiredfilm thickness is between2and2Á2m m,for total times less than20min.The open triangles in Figure1(c)are calculated from the source temperatures in Figure1(a)under the hypothesis that the source dynamics is negligible(i.e.,that the T Cu¼f(ÈCu)relationship is continuously valid).Especially during t1b this is not true as the dynamic situation of the source leads to a delay between the temperatures measured by the thermocouple and those of the evaporat-ing surface.Previously6,7we have shown that the transition in the OP(t)signal occurs for variations of y(t) between1Á1and0Á9.From Figure1(b)this is used to position the points where y(t)¼0Á9and y(t)¼1Á1,between which the solid lines in Figure1(c)are determined from the expected evolution of the integralfilm composition. The open circles represent an estimation of the evolution of y(t)outside the values‘visualized’by the OP(t) signal,taking into account the dynamics of the Cu source,both on the t1b up-heating and of the non-instanta-neous turn-off at t1.This leads to a delay,as shown in Figure1(c),of the point in time where the maximal value of y is reached.This maximal y value is not obtained at t1but at t1þÁt.In the present example the end of the growth(i.e.,t2the point in time where y$0Á9)as determined by the calculated values of y or as determined by the OP(t)signal is not greatly different.Nevertheless,in practice,6,7it is found that the use of the OP(t)signal to target the terminal y(t2)composition of thefilm(i.e.,the EPD)is much more reliable.This OP(t)signal is also used to determine the time t1at which the power to the Cu source is turned off,by estimating the time where y(t)51Á1.2.2Film analysisStructural analysis offilms grown at incomplete points of,or for variations of,the‘base’recipe shown in Figure1,as well asfilms grown at different substrate temperatures,are studied by X-ray diffraction(XRD). The system employed is a Siemens D5000equipped with a Cu-K source and the measurements are carried out from2 ¼10–90 .The conditions used for the XRD are45kV and40mA.Morphological and composi-tional studies of the samefilms are undertaken by scanning electron microscopy(SEM)equipped with energy-dispersive X-ray spectroscopy(EDS).The SEM system is a LEO1550and the EDS is an EDAX detector with ISIS software.The EDS is performed for acceleration voltages of20kV.The Cu,Ga,and Se are measured by integration of the K lines whereas In is measured from the L line.These EDS measurements are used to cali-brate the sources and to confirm the various values of x and y determined in this work.In order to complement the SEM information,transmission electron microscopy(TEM)is used.The TEM characterization is carried out with a Joel2000FXII operated at200kV.2.3Device structureIn parallel to thefilm analysis,devices are produced from all runs where working devices could be expected.All components of the device other than the Cu(In,Ga)Se2layers are deposited according to the present‘baseline’recipes established in our laboratory.11These can briefly be summarized as:Copyright#2003John Wiley&Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331322J.KESSLER ET AL.Figure1.A‘base’recipe for a CUPRO run where the chosen growth parameters are:T sub¼500 C;x$0Á25;ÈSe$ 1–1Á5Â1016atom cmÀ2sÀ1;y(t1a)¼0Á75;y(t1)>1Á10;y(t2)$0Á90;t1a%7min;t1%13min;t2%17min(from EPD).(a)Temperature(of the control thermocouple)of the metal sources versus time,with Y¼ÈCu/(ÈInþÈGa):ratio of the metalfluxes at the growing surface;(b)measured output power levels to the substrate heater(i.e.,OP(t))versus time,with y¼[Cu]/([In]þ[Ga])globalcomposition of the growingfilm;(c)evolution offilm composition,y¼[Cu]/([In]þ[Ga])versus time:triangles calculated from(a)considering instant-aneous source response;circles estimated from(b)considering actual source inertia;bold lines derived from the OP(t) variations measured in(b)Copyright#2003John Wiley&Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331Cu(In,Ga)Se2THIN-FILM GROWTH3232and1-mm-thick low-iron soda-lime glass(SLG)substrates;*10Â10cm*0Á4-m m-thick DC-sputtered Mo layer(optimized for Na permeability);*the Cu(In,Ga)Se2layer under investigation,subsequently cut into four5Â5cm2pieces;*50-nm-thick(CBD)CdS deposited within hours after the Cu(In,Ga)Se2growth;*70nm of RF-sputtered high-density ZnO;*300nm of RF-sputtered low-Al:ZnO;*Ni/Al/Ni gridfingers respectively50/2000/50nm thick.In general,of the four5Â5cm2pieces from each run,two are processed into32devices each,and the other two are used forfilm analysis.Each device has dimensions of5Â10mm2and the grid coverage is of the order of2Á5%.To date,all devices studied are as-grown,i.e.,without temperature annealing or light soaking.Current–voltage and quantum efficiency(I(V)and QE( ))measurements are performed with calibrated home-built sys-tems.As the spectral match of our solar simulator to AM1Á5is poor in the long wavelength region(above 900nm),the short-circuit current densities are calculated from integration of the QE( )data,whereas the open-circuit voltage andfill factors are determined from the I(V)measurement.The devices thus produced are considered as‘high-quality devices’since cells with total area efficiencies above15%are obtained without the use of additional anti-reflection coating.3RESULTS AND DISCUSSION3.1Effect onfilm orientation:(112)versus(220)(204)It has been shown earlier7that when thefilms are Cu-rich at the beginning of the growth(i.e.,the CURO pro-cess),they are then found to be(112)oriented,with the degree of this orientation increasing as the Cu excess decreases,but maintaining y>1.In contrast to this,films grown from a Cu-poor start(i.e.,the CUPRO process) are found to be(220)(204)oriented.Some authors have shown that for the commonly used‘three-stage’pro-cess the degree of(220)(204)orientation depends upon the Seflux in thefirst stage of the growth,12while others have correlated thefilm orientation to the properties of the Mo back contact,13and at least partially to its impact on the Na content of the Cu(In,Ga)Se2layer.Figure2shows the orientation of differentfilms(A,B,C,D,E,and F)grown by various recipes depicted in Figure2(a)all at T sub¼500 C.The signatures of their(112)and(220)(204)XRD peaks are shown respectively in Figure2(b and c).Films A and B are grown as uniformflux references,respectively at y¼0Á90(the targeted terminal composition)and y¼0Á75(the chosen initial Cu-poor value used in the present CUPRO process). Films C and D are uncompleted layers,whereasfilm E is the result of a completed CUPRO process.Film C represents the state of the growingfilm just prior to the increase in Cu-flux,whereasfilm D is the state just prior to thefilm becoming globally Cu-rich.Film F is given as reference to the CURO process,where the initial growth is only moderately Cu-rich(i.e.,when y$1Á1).Although the plotted XRD spectra contain more infor-mation than the peak intensities,we here limit our use of this data to measuring the z¼I(112)/I(220)(204) ratios,given in Table I.In comparing the results forfilms A and B,it is seen that these Cu-poor uniformfilms are(220)(204)oriented to a degree that increases with the decreasing y value.The evolution of thefilm grown during the CUPRO process can be studied by the comparison offilms C,D,and E.However,the measured differences between the z ratios for thesefilms are not considered significant,as they are within the reprodu-cibility of each experiment.The orientations offilms C,D,and E are all considered to be comparable to that of film A.On the other hand,the difference between these z ratios and that offilm B is considered representative. In particular,in comparingfilms B and C it is seen that by growing a thicker y¼0Á75film,there is an increase in the extent of the(220)(204)orientation.This will be complemented by SEM/TEM cross-sections given here-after in Section3.2.Although thefilms A,E,and F all have approximately the same terminal composition (y$0Á9),films A and E have a similar degree of(220)(204)orientation(z$1Á5),whereasfilm F is highly (112)oriented with z$50.The comparison betweenfilms A and F demonstrates the impact on the crystal orien-tation of a Cu-rich versus a Cu-poor initialfilm growth.Also,as will be shown later in Section3.2,the similar z ratios offilms A and E are not indicative of similar morphology;these twofilms differ considerably from this point of view.Copyright#2003John Wiley&Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331Although the CUPRO process used here can also be considered as being comprised of three deposition pro-cess steps (Cu-poor,Cu-rich,Cu-off),it is not the ‘three-stage’process as defined by others.10,12,13Neverthe-less,it is interesting to compare the proposed criteria for (220)(204)preferred orientation.According to Chaisitsak et al.12the factor dictating the orientation is the ÈSe /(ÈIn þÈGa ),ratio during the first stage,which is Cu-free in the ‘three-stage’process.It is shown that (220)orientation results from high Se overpressures (i.e.,ÈSe /(ÈIn þÈGa )>7Á6).While,according to Contreras et al.13the Mo/SLG substrate,its Nacontent,Figure 2.Six different film growths (A–F),produced from different y (t )evolutions and their resulting XRDcharacterization.(a)Growth ‘recipes’(i.e.,composition versus time)for uniform (A and B),CURO (F),CUPRO (E),and partial CUPRO(C and D)growths;(b)XRD from 2 ¼26–28 for (112)peak evaluation;(c)XRD from 2 ¼44–46 for (220)(204)peak evaluation324J.KESSLER ET AL.Copyright #2003John Wiley &Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331and its temperature during the second stage are shown to result in control of the preferred orientation.In our experiments,the Se overpressure is low—ÈSe /(ÈCu þÈIn þÈGa )is estimated to be of the order of 2during the Cu-poor growth,and of the order of only 1Á2in the Cu-rich growth,and the Mo layer is baseline quality (i.e.,not particularly impermeable to the Na).However,our experiments do corroborate Contreras et al.13in that a Cu-rich growth hinders the attainment of the (220)(204)orientation.This would explain why film F,which has been grown in Cu-rich conditions,is (112)oriented.3.2RecrystallizationSEM is used to examine the morphology of the different films presented in Figure 2.A first comparison is made between the two films A (y ¼0Á90)and B (y ¼0Á75)grown under uniform flux conditions.Shown in Figure 3,the cross-sections of these two films present very a similar morphology,but show film B to be a little thicker than film A.This thickness difference is explained by a combination of the two following facts:(a)the deposi-tion time of film B is 1min longer than that of film A;(b)both films are grown under the same Cu flux,but both Table I.Orientation factors for the films shown in Figure 2Filmz ¼I (112)/I (220)(204)A1Á6B0Á6C1Á7D1Á2E1Á5F 49Á2Figure 3.SEM cross-sections (about 10 tilt)for the films shown in Figure 2(except film F).Top row:films A and B,uniform fluxes at y ¼0Á90and y ¼0Á75.Bottom row:films C–E,evolution of the CUPRO growthCu(In,Ga)Se 2THIN-FILM GROWTH 325Copyright #2003John Wiley &Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331326J.KESSLER ET AL. the In and Gafluxes are higher for the growth offilm B.Bothfilms exhibit a small grain structure near the Mo back contact,while the grain size increases towards the front surface of thefilms.Also shown in Figure3are the intermediate uncompleted layers(C and D)as well as thefinal result(E)of the CUPRO growth process pre-sented in Figure2.Film C is produced under the same growth conditions asfilm B,except that the growth is interrupted at7rather paring the SEM cross-sections of thesefilms C and B,it can be seen that a more‘textured’overgrowth becomes dominant as the thickness increases.It would be consistent with the XRD data to interpret this‘textured’over layer as being increased in the(220)(204)orientation.Film D is the evolution offilm C resulting from the increase of Cu vapor in theflux,but,as previously stated,prior to the moment where the global composition of thefilm becomes Cu-rich.It is most remarkable that the grain size offilm D appears larger,even at the rear of thefilm,than does that offilm C.We believe that recrystallization occurs as a result of the change in the metalflux ratios.Examination of a slightly later point in the growth,when the globalfilm composition has exceeded y¼1(film not shown in Figures2or3),does not result in any sig-nificant difference relative tofilm D.The morphology offilm E,at the end of the CUPRO process,appears to be very similar to that offilm D,except that the total thickness is then of the order of2m m and that crevices are observed in the top fraction of thefilm that has been added in the evolution from D to E.These crevices can be more clearly revealed by means of polished SEM cross-sections,as has been presented earlier.7For increased clarity,thefilms shown in Figure3(exceptfilm A)are further examined by TEM cross-sections.These are shown in Figure4and support what has been already seen in the SEM study.In particular, the evolution fromfilm C tofilm D clearly permits the justification of the term‘recrystallization’.These TEM images also make very evident the morphological differences between thefilms grown by the CUPRO process compared with those grown at constantflux.As for the SEM,it can also be seen that the evolution fromfilm D to film E,apart from the additional thickness,is mostly in the formation of crevices seen in this additional material. At this point one could question whetherfilm D is of device quality or not,possibly by producing afilm in a similar manner,but at a device-relevant thickness(e.g.,at least>1Á5m m).The questions are:why drive thefilm Cu-rich only to bring it back to y$0Á9if this only results in the creviced surface;and does the globally Cu-rich growth(growth stages3and4in Figure1b,where there is existence of Cu x Se)do anything special relative to the finalfilm quality?In the present work,one of the reasons for the complete CUPRO scheme is to enable easy use of the EPD.Although the stopping point required to producefilm D is within the zone where the OP(t)signal evolves,it is considerably more critical to use as an EPD than is the Cu-rich-to-Cu-poor transition.3.3Five-stage growth modelThe present primitive growth model attempts to explain these results.The pretensions of this model are modest and are not more than a‘probable picture’.The objective is to understand the‘base’recipe,considered to cor-respond to T sub¼500 C.Although the control of the CUPRO process occurs in three steps of the Cuflux (ÈCu¼low,ÈCu¼high,ÈCu¼0)or(constant y,increasing y,decreasing y)represented in Figure1(b),we further subdivide,distinguishing y<1from y>1,and examine thefilm growth infive stages,also represented in Figure1(b)as well as Figure5.During thefirst stage of the growth,where both y and Y arefixed at0Á75,a compositionally uniformfilm is grown,initially exhibiting small and close to randomly oriented crystallites.As thefilm grows thicker,the(220) (204)oriented grain growth dominates(probably due to a more rapid growth than that of the(112)orientation), and thefilm becomes increasingly(220)(204)oriented.We believe that the chosen value of y is not critical,and it is observed thatfilms grown uniformly at y¼0Á90behave in the same way as those grown at y¼0Á75,i.e.,film A andfilm B are very similar.During the second stage of the growth,where the global composition evolves from y¼0Á75to y¼1,the top surface of thefilm is grown more Cu-rich than the bulk,and we believe that this Cu gradient results in a Cu diffu-sion that acts as a driving force for the recrystallization of thefilm.This recrystallization occurs without much reorientation as the(220)(204)preferred orientation is maintained(film C versusfilm D).Even assuming that Cu x Se could be locally present at the growing surface,one argument against the postulate the importance of a liquid state(cf.solid–liquid–vapor(SLV)growth14)of this Cu x Se in this second stage is that in our previous work15we have not observed the recrystallization to be dependent on the substrate temperatures,for growths Copyright#2003John Wiley&Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331at 475,500,525and 550 C (i.e.,for temperatures above and below the solid–liquid transition for Cu x Se at 532 C).Moreover,if Cu x Se had been present,we believe that it would have affected the OP(t )signal,but this was not observed.At the end of this second stage,and assuming very rapid Cu diffusion,the film is single-phase (to the detection limit of the XRD,analysis not shown),large-grain (Figures 3and 4),weakly (220)(204)oriented (z $1Á5,Table I),and believed to be uniform and stoichiometric Cu(In,Ga)Se 2.The hypothesis of very rapid Cu diffusion is supported by the previously stated fact that the OP(t )signal is indicative of a Cu-poor surface,i.e.,a surface without Cu x Se segregation,throughout this second stage of the growth.In the latter part of this second stage,the Cu flux is very high (Y >2),and if the Cu diffusion is not at least as fast as the excess Cu accumulation at the surface (relative to Cu(In,Ga)Se 2stoichiometry),segregation of Cu x Se at the surface would be expected.The third stage of the growth is increasingly Cu-rich from y ¼1until the maximum value of y ,where the Cu source is turned off (neglecting the source dynamics).Here,an overgrowth on the previous stoichiometric Cu(In,Ga)Se 2layer occurs,consisting of the expected two-phase system of additional stoichiometric Cu(In,Ga)Se 2with an increasing fraction of Cu x Se as a secondary phase.In this overgrowth,the Cu xSe Figure 4.TEM cross-sections for the films shown in Figure 2(except film A and film F).Top row:films C to B,evolutionof the uniform flux growth at y ¼0Á75.Bottom row:films C–E:evolution of the CUPRO growthCu(In,Ga)Se 2THIN-FILM GROWTH 327Copyright #2003John Wiley &Sons,Ltd.Prog.Photovolt:Res.Appl.2003;11:319–331。

Thick Film Array Chip Resistor■Scope－This specification applies to all sizes of rectangular-type fixed chip resistors with Ruthenium-base as material.■Features－Small size and light weight－Reduction of assembly costs and matching with placement machines －Reliability, high quality －Suitable for IR reflow soldering■Construction■Applications－Entertainment－Computer & Related Products －Communication Equipment －Power Equipment －Measuring InstrumentTypeNumber of ResistorsL (mm)W (mm)H (mm)A (mm)B (mm)C (mm)Y (mm)Weight (g) (1000pcs)CN-21 2 0.80±0.100.60±0.10 0.35±0.100.30±0.100.50±0.100.15±0.10 0.15±0.100.500 CN-41 4 1.40±0.100.60±0.10 0.35±0.100.20±0.100.40±0.100.10±0.07 0.15±0.050.833 CN-42 4 2.00±0.10 1.00±0.10 0.45±0.100.30±0.100.50±0.050.22±0.15 0.22±0.15 2.817 CN-43 4 3.20±0.15 1.60±0.15 0.55±0.100.50±0.150.80±0.050.30±0.15 0.30±0.158.288 CNA42 4 2.00±0.10 1.00±0.10 0.40±0.100.30±0.100.50±0.050.20±0.10 0.25±0.10 3.003 CNA43 4 3.20±0.151.60±0.15 0.55±0.100.50±0.150.80±0.050.30±0.15 0.40±0.1510.115CN-42/43 CN-41■Part Numbering■Derating CurveOperating Voltage=√(P*R) or Max. operating voltage listed above, whichever is lower. Overload Voltage=2.5*√(P*R) or Max. overload voltage listed above, whichever is lower. ■ Viking is capable of manufacturing the optional spec based on customer’s requirement.■Equivalent Circuit Diagram■Soldering ConditionIR Reflow Soldering Wave Soldering (Flow Soldering)(1) Time of IR reflow soldering at maximum temperature point 260°C ：10s (2) Time of wave soldering at maximum temperature point 260°C ：10s (3) Time of soldering iron at maximum temperature point 410°C ：5s■Environmental CharacteristicsRequirementItem±1%±5%JumperTest MethodTemperature Coefficient of Resistance (T.C.R.)As Spec.JIS-C-5201-1 4.8 IEC-60115-1 4.8-55°C~+125°C, 25°C is the reference temperature Short Time Overload ±(1.0%+0.05Ω) ±(2.0%+0.05Ω)<50m ΩJIS-C-5201-1 4.13 IEC-60115-1 4.13RCWV*2.5 or Max. Overload voltage whichever is lower for 5 secondsInsulation Resistance ≥10GJIS-C-5201-1 4.6 IEC-60115-1 4.6Max. Overload voltage for 1 minuteEndurance±(2.0%+0.10Ω) ±(3.0%+0.10Ω)<50m ΩCN-21/41:<100m ΩJIS-C-5201-1 4.25 IEC-60115-1 4.25.170±2°C, RCWV for 1000 hrs with 1.5 hrs “ON” and 0.5 hrs “OFF” Damp Heat with Load ±(2.0%+0.10Ω) ±(3.0%+0.10Ω)<50m ΩJIS-C-5201-1 4.2440±2°C, 90~95% R.H., RCWV for 1000 hrs with 1.5 hrs “ON” and 0.5 hrs “OFF” Dry Heat±(1.0%+0.05Ω) ±(1.5%+0.10Ω)CN-21/41: ±(3.0%+0.10Ω)<50m ΩCN-21/41:<100m ΩJIS-C-5201-1 4.23 IEC-60115-1 2.23.2 at +125/+155°C for 1000 hrsCN-42/43 CNA42/43CN-41CN-21RequirementItem±1%±5%JumperTest MethodBending Strength ±(1.0%+0.05Ω) ±(1.0%+0.05Ω)<50m ΩJIS-C-5201-1 4.33 IEC-60115-1 4.33Bending once for 5 seconds with 3mm Solderability 95% min. coverageJIS-C-5201-1 4.17 IEC-60115-1 4.17 245±5°C for 3 seconds Resistance to Soldering Heat ±(0.5%+0.05Ω) ±(1.0%+0.05Ω)<50m ΩJIS-C-5201-1 4.18 IEC-60115-1 4.18 260±5°C for 10 secondsVoltage Proof No breakdown or flashoverJIS-C-5201-1 4.7 IEC-60115-1 4.71.42 times Max. Operating Voltage for 1 minute LeachingIndividual leaching area ≦5% Total leaching area ≦ 10%JIS-C-5201-1 4.18 IEC-60068-2-58 8.2.1 260±5°C for 30 seconds Rapid Change of Temperature±(0.5%+0.05Ω) ±(1.0%+0.05Ω)<50m ΩJIS-C-5201-1 4.18 IEC-60115-1 4.18-55°C to +125/+155°C, 5 cyclesRCWV(Rated continuous working voltage)=√(P*R) or Max. Operating voltage whichever is lower.■Storage Temperature: 25±3°C; Humidity < 80%RH■Recommend Land PatternTypeA (mm)B (mm)C (mm)I (mm)P(mm)CN-21 0.80 0.90 -- 0.30 0.50 CN-41 1.40 0.90 0.20 0.30 0.40 CN-42 1.80 2.10 0.30 0.50 0.50CN-43 2.85 3.10 0.45 0.80 0.80 CNA42 1.80 2.10 0.30 0.50 0.50CNA43 2.85 3.10 0.45 0.80 0.80【】深圳捷比信－－高品质精密元件供应商ｗｗｗ．ｊｅｐｓｕｎ．ｃｏｍCN Series▓PackagingReel Specifications & Packaging QuantityPaper Tape SpecificationsTypeA(mm)B (mm)W (mm)E (mm)F (mm) P 0 (mm)P 1 (mm)P 2 (mm)ΦD 0 (mm)T (mm)CN-21 0.77±0.05 0.97±0.05 8.0±0.2 1.75±0.1 3.5±0.05 4.0±0.1 2.0±0.05 2.0±0.05 1.50+0.1,-00.50±0.1CN-41 0.77±0.05 1.57±0.05 8.0±0.2 1.75±0.1 3.5±0.05 4.0±0.1 2.0±0.05 2.0±0.05 1.50+0.1,-00.50±0.1CN-42 1.20±0.1 2.20±0.1 8.0±0.2 1.75±0.1 3.5±0.05 4.0±0.1 2.0±0.05 2.0±0.05 1.50+0.1,-00.70±0.1CN-43 1.95±0.1 3.50±0.1 8.0±0.2 1.75±0.1 3.5±0.05 4.0±0.1 4.0±0.05 2.0±0.05 1.50+0.1,-00.85±0.1CNA42 1.20±0.1 2.20±0.1 8.0±0.2 1.75±0.1 3.5±0.05 4.0±0.1 2.0±0.05 2.0±0.05 1.50+0.1,-00.70±0.1CNA43 1.95±0.1 3.50±0.1 8.0±0.2 1.75±0.13.5±0.054.0±0.1 4.0±0.052.0±0.05 1.50+0.1,-00.85±0.1Type Packaging QuantityTape WidthReel Diameter ΦA (mm) ΦB (mm) ΦC (mm) W (mm) T (mm)CN-21 CN-41Paper 10K 8mm7 inch178.5±1.560+1/-013.0±0.2 9.0±0.5 12.5±0.510K 8mm7 inch 178.5±1.5 60+1/-0 13.0±0.2 9.0±0.5 12.5±0.5 20K 8mm 10 inch 254±1.0 100±0.5 13.0±0.2 9.5±0.5 13.5±0.5 CN-42 CNA42Paper 40K 8mm 13 inch 330±1.0 100±0.5 13.0±0.2 9.5±0.5 13.5±0.5 5K 8mm7 inch 178.5±1.5 60+1/-013.0±0.2 9.0±0.5 12.5±0.510K 8mm 10 inch 254±1.0 100±0.5 13.0±0.2 9.5±0.5 13.5±0.5 CN-43 CNA43 Paper 20K 8mm13 inch 330±1.0 100±0.5 13.0±0.2 9.5±0.5 13.5±0.5Top TapeBottom Tape■MarkingNo Marking for CN-21 and CN-41Jumper for all: Letter “0”1% for CN-42/CN-43/CNA42/CNA43: 4 digits marking (non-including E24 series)Example:Resistance 102Ω 2.49KΩ30K1Ω49.9KΩ121KΩmarking 1020 2491 3012 4992 12135% for CN-42/CN-43/CNA42/CNA43: 3 digits marking in E24Example: 101=100Ω 102=1KΩ(1st and 2nd are E24 code and 3rd code is multiplier)E2410 11 12 13 15 1618 20 22 242730333639434751 56 62 68758291 code。

专利名称：Thin film high TC oxide superconductors and vapor deposition methods for making thesame发明人：Praveen Chaudhari,Richard J. Gambino,RogerH. Koch,James A. Lacey,Robert B.Laibowitz,Joseph M. Viggiano申请号：US08/264227申请日：19940623公开号：US05447906A公开日：19950905专利内容由知识产权出版社提供摘要：Superconducting transition metal oxide films are provided which exhibit very high onsets of superconductivity and superconductivity at temperatures in excess of 40°K. These films are produced by vapor deposition processes using pure metal sources for the metals in the superconducting compositions, where the metals include multi-valent nonmagnetic transition metals, rare earth elements and/or rare earth-like elements and alkaline earth elements. The substrate is exposed to oxygen during vapor deposition, and, after formation of the film, there is at least one annealing step in an oxygen ambient and slow cooling over several hours to room temperature. The substrates chosen are not critical as long as they are not adversely reactive with the superconducting oxide film. Transition metals include Cu, Ni, Ti and V, while the rare earth- like elements include Y, Sc and La. The alkaline earth elements include Ca, Ba and Sr.申请人：INTERNATIONAL BUSINESS MACHINES CORPORATION代理人：Daniel P. Morris更多信息请下载全文后查看。

Thick Film Chip Resistor – General PurposeFeatures• Small and light weight• Excellent heat resistance and moisture resistance• Suitable size and packaging for surface mount assembly • RoHS CompliantApplications• For general purpose applications• For laptop and notebook computer, memory module, digital camera and telecommunication equipmentAbsolute Maximum Ratings & CharacteristicsProductNumbermm TolerancePower Rating @70˚CMAX Working Voltage MAXOverload VoltageTCR ppm/℃Resistance RangeRated WorkingTemperature±200 1Ω ~ 9.76Ω±100 10Ω ~ 1M ΩRC2512 6432J: ±5%F: ±1%1W 250V 500V ±2001.02M Ω ~ 10M Ω-55℃~+155℃*JumperProduct NumberJumper RatedCurrentResistanceRated Working Temperature RC2512 4A 50m Ω (Max.)-55℃~+155℃RC2512 Power Derating CurveFor resistors operate in the ambient temperature over 70˚C, loading power ratio will de-rate in accordance with following curve.Soldering ConditionIR Reflow soldering Wave soldering (flow soldering)RC2512 Dimensions (in mm)ProductNumbermm L W H A BAverageWeight RC25126432 6.35 ± 0.203.20± 0.150.55 ± 0.100.60 ± 0.250.50 ± 0.20 40.01 mg Marking(1) ±5% Tolerance (J): 3 digits, the first two digits are significant figures; the third digit is numberof zeros to follow. Letter “R” is as decimal point; Letter “0” for jumper.(2) ±1% Tolerance (F): 4 digits, the first three digits are significant figures; the fourth digit isnumber of zeros. Letter “R” is as decimal point; Letter “0” for jumper.Examples:3 digits marking (±5%)4 digits marking (±1%)683 = 68x103Ω Jumper 6812 = 681x102Ω= 68000 Ω = 68KΩ = 68100 Ω = 68.1KΩ7R5 = 7.5 ΩRC2512 Test and RequirementsRequirement Test Item Test Method Test Condition±1% ±5% JumperTemperature Coefficient of Resistance(T.C.R.) JIS C 5201 4.8IEC 60115-1 4.8-55°C~+155,20°C isthe referencetemperatureWithin the specificationShort Time Overload JIS C 5201 4.13IEC 60115-1 4.132.5 times RCWV or max.overload voltage for 5seconds±(1.0%+0.05Ω) ±(2.0%+0.05Ω) <50mΩInsulation Resistance JIS C 5201 4.6IEC 60115-1 4.6Max. overload voltagefor 1 minute≥10GVoltage Proof JIS C 5201 4.7IEC 60115-1 4.71.42 times RCWV(RMS) for 1 minuteno breakdown or flashoverSubstrate Bending Test JIS C 5201 4.33IEC 60115-1 4.33Bending once with 5seconds for 3 mm±(1.0%+0.05Ω) ±(1.0%+0.05Ω) <50mΩResistance to soldering heat JIS C 5201 4.18IEC 60115 4.18260±5°C for 10 seconds±(0.5%+0.05Ω) ±(1.0%+0.05Ω) <50mΩLeaching JIS C 5201 4.18IEC 60115 4.18260±5°C for 60 seconds no leachingSolderability JIS C 5201 4.17IEC 60115-1 4.17245±5°C for 3 seconds. >95% coverageEndurance at upper category temperature JIS C 5201 4.23IEC 60115-1 2.23.2at +155°C for 1000 hrs ±(1.0%+0.05Ω) ±(1.5%+0.10Ω) <50mΩRapid change of temperature JIS C 5201 4.19IEC 60115-1 4.19-55°C to +155°C, 5cycles±(0.5%+0.05Ω) ±(1.0%+0.05Ω) <50mΩDamp heat with load JIS 5201 4.2440±2°C, 90~95% R.H.or max. working voltagefor 1000 hrswith 1.5hrs “ON” and 0.5hrs “OFF”±(2.0%+0.10Ω) ±(3.0%+0.10Ω) <100mΩEndurance JIS C 5201 4.25IEC 60115-1 4.25.170±2°C, RCWV or Max.working voltage for 1000hrs with 1.5 hrs“ON” and 0.5 hrs “OFF”±(2.0%+0.10Ω) ±(3.0%+0.10Ω) <100mΩNote: RCWV：Rated Continuous Working Voltage.RCWV= √Rated power (W) × Resistance value (R)RC2512 Packing Information:Carrier Tape Dimensions (in mm)Type A B W E F P0 P1 P2 ψD0 ψD0 TRC2512 3.50±0.2 6.70±0.2 12.0±0.3 1.75±0.1 5.5±0.05 4.0±0.1 4.0±0.1 2.0±0.05 1.5+0.1/-0 1.5+0.25/-0Max1.2 Reel Dimensions (in mm)Reel Diameter PCS per Embossed Tape A B C W T7’’ 4,000180+0/-360+1/-013.0±0.213.0±0.515.4±1Carton InformationPCS per Carton Carton Size192,000 400X400X200(inmm)RC2512 How to OrderRC2512 How to contact us:。

Ž.Physica C3151999117–123Micro-Raman study of ultra-thin YBa Cu O r YSZ films237y dM.S.Chen),Z.X.Shen,W.Z.Zhou,S.Y.Xu,C.K.OngDepartment of Physics,National UniÕersity of Singapore,10Kent Ridge Crescent,Singapore119260,SingaporeReceived21January1999;accepted27February1999AbstractŽ.Micro-Raman scattering measurements of ultra-thin YBa Cu O YBCO films of various thicknesses,deposited by237y dŽ.Ž.pulsed laser ablation on the yttrium-stabilized-zirconia YSZ001substrates,were carried out.The frequency of the Ž.Ž.O4-A mode shows a more marked increase with decrease in film thickness than the O2,3-B mode does.The main g1gŽ.Ž. contribution to the intensity of the O2,3-B mode is shown to be from the c-axis oriented grains and that of the O4-A1g gŽ.mode comes from the a-axis oriented grains.Raman evidence for the formation of the BaZrO BZO transitional layer at3Ž.Ž.the film interface was found,and the frequency changes of the O4-A and O2,3-B modes are explained in terms ofg1gŽ.lattice mismatch between YBCO and BZO at the interface.The large frequency increase of the O4-A mode withgŽ.Ž.decreasing film thickness is due to the large mismatch between the Cu2–Cu2separation and the length of one unit cell of BZO,despite the good match between one unit cell of YBCO and three unit cells of BZO for the a-axis oriented grains. q1999Elsevier Science B.V.All rights reserved.PACS:78.30.-j;74.76.-w;68.35.CtKeywords:Raman;High-T thin films;Interface;Strains;Lattice mismatchc1.IntroductionStrong correlation has been established between the microstructure of high-temperature superconduct-Ž.Ž. ing HTSC films and its transition temperature T,cŽ.critical current density j and surface resistancecŽ.Ž. R.The early stage of YBa Cu O YBCO s237y dfilm growth plays an important role in determining the structural and the physical properties of these films.Consequently,it is of great interest,in order to fully understand the growth mechanism of HTSC films and to optimize the growth parameters,to)Corresponding author.Fax:q65-7776126;E-mail: scip7148@.sg study the structural characteristics of HTSC films in the vicinity of the film–substrate interface.Due to its low cost,good high-frequency proper-ties and relatively good chemical stability at highŽ. temperature,yttrium-stabilized-zirconia YSZ is one of the most common substrates for growing YBCO w xfilms1–5.In addition,YSZ has frequently been used as a buffer layer on reactive substrates such as w x w xSi6–8and Al O9.The relative large lattice23mismatch and the chemical reaction between the YBCO film and YSZ result in complicated structural and physical properties of the YBCO films at the interface region.The interfaces were widely studiedŽ.w by transmission electron microscopy TEM2–xŽ.w x4,6,8,9,X-ray diffraction XRD8and atomic0921-4534r99r$-see front matter q1999Elsevier Science B.V.All rights reserved.Ž.PII:S0921-45349900214-2()M.S.Chen et al.r Physica C3151999117–123 118Ž.w xŽ. force microscopy AFM4.A BaZrO BZO layer3of2–6nm in thickness,which results from the chemical reaction between YBCO film and YSZ,is always present between the YBCO film and YSZ w xsubstrate1,3–5or YSZ buffer layer regardless of the growth techniques used to grow the films.The formation of the BZO layer leads to defects such as w x w xdislocation3,microcrack8and misorientation of w xthe films2,3,6.Some impurity phases such as CuO,Ž.Ž. Y BaCuO211phase,YBa Cu O124phase, 25248Y O and BaCuO may also exist in the YBCO 232w xfilms1,3,6,10.Micro-Raman spectroscopy is fast,nondestruc-tive,and sensitive to the local atomic-site coordina-w xtion11–15.Due to the small penetration depth ofŽ. visible light in the superconductors50–100nm w x10,Raman spectroscopy is particularly advanta-geous for studying the progressing structural charac-teristics of YBCO films of various thicknesses w x11,16–18.In this article,we report on Raman scattering from YBCO thin films with thicknesses ofŽ. 16,28,40,80and200nm,grown on the001 surface of YSZ substrates.By properly subtracting the substrate spectrum from the as-recorded one,the true Raman spectrum,which exclusively results from the film,was obtained.We focus on the thicknessŽ.Ž. dependence of the O2,3-B and O4-A modes,1g gthe additional modes and the analysis of the corre-sponding mechanisms and causes.2.ExperimentalŽ.YBCO thin films were deposited on YSZ001Ž. substrates by using the pulsed laser ablation PLA technique,which had been described in detail else-w xwhere19.In this experiment,a series of YBCO thin films with different thickness were fabricated under identical conditions.The parameters for depo-Ž.2 sition were:laser248nm fluence2J r cm,laser pulse frequency5Hz,substrate temperature7108C, oxygen pressure0.21mbar and substrate-to-target distance48mm.The sample thickness was con-trolled by the duration of deposition.After deposi-tion,the chamber was filled with O to1atm,while2the sample was cooled down to4008C and was annealed at this temperature for30min and was further cooled to room temperature.The film thick-nesses measured by AFM were,respectively,200Ž.Ž.Ž.Ž.Ž. sample a1,80a2,40a3,28a4and16a5nm.Micro-Raman measurements were carried out atroom temperature with a SPEX1702r04Ramanspectrometer attached to an Olympus microscopeand equipped with a liquid-nitrogen-cooled CCDdetector.An argon-ion laser with wavelength l s 488nm was used as the excitation source.The instrumental resolution is about0.7cm y1.The fo-cused laser on sample is about1m m in diameter,Ž. and the laser power was kept low enough-6mW to avoid degradation of the film due to overheating of the probed volume.Raman spectra were recorded in the backscattering geometry.3.Results and discussion3.1.Thickness dependence of the raman spectraŽ.Fig.1shows the typical as-recorded z x,x q y z Raman spectra from the series of YBCO r YSZfilmsFig. 1.As-recorded Raman spectra of YBCO thin films withŽ.Ž.Ž.Ž. thicknesses of200sample a1,80a2,40a3,28a4and Ž.Ž.16nm a5obtained at z x,x q y z scattering geometry.The bottom spectrum is that of YSZ substrate obtained for the same scattering geometry.()M.S.Chen et al.r Physica C 3151999117–123119and YSZ substrate.A strong peak at 611cm y 1due to the substrate appears in the as-recorded spectra except for sample a 1which is the thickest.As the Raman peaks due to the substrate become more pronounced with decreasing film thickness,they have to be subtracted from the as-recorded Raman spectra.We chose the strong YSZ peak at 611cm y 1as the reference peak which does not overlap with the intrinsic peaks of the YBCO film and the Raman w x peaks from impurities and defects 10,15,20–28.In general,for YBa Cu O ,five A Raman modes 237y d g were observed near 116,145,340,430and 500cm y 1and they were assigned to the vibrations of Ba,Ž.Ž.ŽŽ.Cu 2,O 2,3out-of-phase namely O 2,3-B 1g .Ž.Ž.ŽŽ.mode ,O 2,3in-phase and O 4namely O 4-A g .w x mode in the c -axis direction,respectively 28.The Raman spectral subtraction was carried out using the software provided by Renishaw.We have tried dif-ferent subtraction scales in order to eliminate prop-erly the 611cm y 1peak of the substrate.In addition,we referred to the spectrum of sample a 1which Ždoes not have Raman peaks of the substrate see Fig..1a 1.It was found that slight variation of the scale has very little influence on the positions of the Raman peaks of the YBCO films and the additional modes.This further supports the reliability of sub-traction even if the YSZ 611cm y 1peak overlaps with those from the impurities and defects with very low concentrations.The Raman spectra obtained af-ter substrate spectra subtraction are displayed in Fig.2a.In order to determine the repeatability of the spectra,we have performed substrate spectrum sub-traction for spectra collected at different locations of the samples.The results for the thinnest sample,sample a 5,are presented in Fig.2b,which clearly show that the peak positions of the processed spectra are reproducible and the sample is homogeneous.3.2.The A and B modes as a function of film g 1g thicknessŽ.For the O 2,3-B mode,the interaction of the 1g phonon state with a broad electronic continuum re-Ž.sults in the asymmetry of the O 2,3-B mode 1g w x called the Fano profile 29.The Raman intensity is given by2´v q q Ž.Ž.I v s I q B v q C1Ž.Ž.021q ´v Ž.Ž.Fig. 2.a Raman spectra of the series of YBCO films after Ž.subtraction of the substrate features.b Raman spectra of the different points for the sample a 5after slight smoothing,showing that the thin film sample is homogeneous and the spectral features are reproducible.Ž.Ž.where ´v s v y v g with v being the phonon v v Ž.frequency and g the phonon line width HWHM .q is a parameter that defines the asymmetry,and the background is a linear term of the form B v q C ,where B and C are adjustable parameters.We deter-mined the frequency and integrated intensity of the Ž.y 1Ž.O 2,3-B mode at about 339cm and the O 4-A 1g g mode at about 500cm y 1by fitting the spectra with()M.S.Chen et al.r Physica C 3151999117–123120Ž.Ž.Ž.Fig. 3.Frequencies of a the O 2,3-B mode and b the 1g Ž.O 4-A mode vs.film thickness.The dashed lines are average g values of three measurements.w x Fano and Lorentz profiles 30,respectively.Fig.3shows the thickness dependence of the frequencies Ž.Ž.of the O 2,3-B mode and the O 4-A mode.1g g With decreasing film thickness,both modes show an Ž.increase in their vibrational frequencies,O 4-A g y 1Ž.mode by 9cm and the O 2,3-B mode by 21g cm y 1.For high-T YBCO single crystals,the frequency c Ž.of the O 4-A mode has been shown to be closely g related to the oxygen content of YBCO ing the empirical relationship between the oxygen Ž.content of YBCO and the frequency of the O 4-Ag w x mode 31:7y d s 0.027v y 6.58,where v is the v v Ž.y 1frequency of the O 4-A mode in unit cm ,the g Ž.oxygen content of the thickest a 1and thinnest Ž.a 5samples would be 6.84and 6.99,respectively.However,our film samples were grown under identi-cal conditions and the oxygen diffusion length along the c -axis direction when annealed is about 70nm w x for YBCO thin films 32,which is greater than the film thickness of the sample a 3,a 4and a 5and the same magnitude as the penetration depth of laser in the films.Therefore,the main contribution to the variation of the frequencies observed in our experi-ments should result from the film thickness,not theoxygen stoichiometry.This indicates that for thin films the correlation between the frequency of the Ž.O 4-A mode and the oxygen deficiency needs to g w x be handled with care 12,33.We suggest that the observed frequency changes with film thickness are reflections of strain at the film interface,which show up more clearly for the thinner samples.In Section 3.3,we explain the reason why strains influence the A mode more than the B mode.g 1g 3.3.Strain in the YBCO–BZO interface region Under the growth conditions used to fabricate the samples,the films are expected to be predominantly c -axis oriented,i.e.,the majority of the YBCO grains which make up the film sample are oriented such that their c -axis is perpendicular to the substrate w x surface 19.Raman spectra have been used as a convenient and non-destructive method to determine the fraction of c -axis orientation in YBCO films,and w x it is in the range of 85–95%for our samples 34.In the backscattering geometry,the contribution to the Ž.Ž.Raman intensity of the O 2,3-B and O 4-A 1ggŽ.Ž.Fig.4.The contribution to the O 2,3-B mode and the O 4-A 1g g mode by the c -and a -axes oriented grains.The shaded area represents the range of c -axis orientation for our samples.It is clear that the main contributions to the B mode come from the 1g c -axis oriented grains and A mode from a -axis oriented grains.g()M.S.Chen et al.r Physica C3151999117–123121modes by the c-and a-axis oriented grains wasw x calculated using a model presented in Ref.35and the results are shown in Fig.4.It is clear that theŽ.Raman signal for the O2,3-B mode mainly re-1gsults from the c-axis oriented grains,whereas the Ž.O4-A mode are mainly due to the a-axis oriented ggrains.In this paragraph,we present an explanation as to Ž.why the O4-A mode shows a larger frequencygshift with film thickness.For YBCO films grown onŽ.YSZ substrates,a BaZrO BZO is always present3w xat the interface1,3–5.Our Raman result also sup-Ž.ports this finding see Section3.4.At the interface, the lattice mismatches between YBCO and BZO are shown in Table1.Because the a-axis and b-axis lengths are approximately equal,the a-and b-axis orientations are not differentiated and all noted as a-axis orientation.Fig.5shows the schematic dia-Ž.Ž.gram for the a c-axis and b a-axis oriented grainsŽwith the BZO layer.For the c-axis orientation Fig. .5a,the in-plane strains induced by the;8%lattice mismatch between YBCO and BZO should haveŽ.little effect on the O2,3-B mode,which involves1gŽ.Ž.mainly the O2–O3oxygen atoms vibrating along the c-axis,e.g.,perpendicular to the interface.ForŽ.the a-axis oriented grains Fig.5b,c r3is often quoted as the relevant matching parameter.However, it does not correspond to any particular atomic posi-w xtions along the c-axis direction37,as shown in Table 1.Instead,we should consider the relative positioning of the atoms of the YBCO and BZO lattices at the interface region.Although thelattice Fig.5.Schematic diagram of the interface between YBCO and Ž.Ž.Ž.BZO for a c-axis and b a-axis orientations.a Shows the upper half of the YBCO unit cell.The corresponding vibration of Ž.Ž.the O2,3-B and the O4-A modes are indicated by arrows in 1g gŽ.Ž.1and2,respectively.mismatches between c-axis of YBCO and three unitŽ.Ž.cells of BZO,and between the Cu1–Cu2and oneŽunit cell of BZO are very small y7.3%,y1.2%,Table1Ž.Lattice mismatch between YBCO and BZO at room temperature RT and7108CŽ.Ž.Lattice constant nm Mismatch%RT7108C RT7108Cc-axis a-axis c-axis a-axis w xYBCO10a0.38220.3848y9.0y9.0y8.7y8.7b0.38910.3918y7.5y7.5y7.0y7.0c 1.1677 1.1837y7.3y6.4Ž.Ž.Cu1–Cu20.41500.4207y1.2y0.2Ž.Ž.Cu2–Cu20.33770.3423y19.5y18.8 w xBZO360.41900.4215The a-and b-axes orientations are not differentiated.Both of them are noted as a-axis orientation.For a-axis orientation,the values are calculated according to one unit cell of YBCO matching with three unit cells of BZO.()M.S.Chen et al.r Physica C3151999117–123 122.respectively,the lattice mismatch between the Ž.Ž.Cu2–Cu2and one unit cell of BZO is large Ž.y19.5%.As a result,the bond length of the bridg-Ž.Ž.Ž. ing oxygen O4shortens and that of Cu2–Cu2Ž. increases.The shortening of the O4bond leads toŽ.the increase in the frequency of the O4-A modegŽ.Fig.3.3.4.Impurity phases and defectsIn Fig.2a,there are also some additional modesŽ.at307,464visible in sample a5,560and630cm y1.We suggest that the464cm y1peak shows the formation of the BZO layer due to the reaction ofw xYBCO with YSZ20.The coexistence of YBCO and BZO Raman spectra in sample a5indicates that the thickness of the BZO layer must be much less than16nm,the thickness of the film.This is consis-tent with results obtained using other techniques which show that the BZO layer is thinner than6nm w x y1 1,3–5.We assign the strong peak at630cm to the impurity phase BaCuO which is an impurity2phase frequently found for YBCO films.The pres-ence of CuO at the interface region is characterized by two peaks at307and630cm y1with similar intensity.The weak peak at560cm y1does not correspond to any known impurity phases.We spec-ulate that it is induced by defects.There is noevidence for the presence of the impurities Y O and23w xY BaCuO21,22which may be expected at the 25interface region to account for the excess yttrium duew xto the formation of the BZO layer3.With an increase in the film thickness,these modes gradually disappear,showing that the impurities and defects exist mainly at the interface region.4.ConclusionsRaman experiments were carried out for YBCOŽ.films on YSZ001substrates with thickness be-tween16–200nm.Raman spectra belonging to the ultra-thin YBCO films were obtained by proper sub-strate spectra subtraction.Our results support the existence of a BZO transitional layer at the film interface.Raman evidence for the formation of CuOand BaCuO were found in the vicinity of the inter-2face.However,we did not observe the Y O or23Y BaCuO phases which are expected to form at the 25interface.The frequency variation with film thickness is explained in terms of the influence of the YBCO r BZO interface.The smaller effect on the Ž.O2,3-B mode was observed and it was attributed 1gŽ.to the relatively small y8%mismatch between the a r b axis of c-axis oriented YBCO grains and theŽ.unit cell of BZO.Despite the small y7.3%mis-match between the three unit cells of BZO and one unit cell of YBCO along the c-axis for the a-axisŽ.Ž. oriented grains,the mismatch between Cu2–Cu2Ž. of YBCO and unit cell of BZO is large y19.5%.Ž.Ž. The larger mismatch shortens the Cu2–O4dis-tance,which in turn is responsible for the increase of Ž.the O4-A mode.gAcknowledgementsThe authors are grateful to Dr.M.E.Huntelaar of Netherlands Energy Research Foundation ECN and Dr.P.Groen of University of Amsterdam,Nether-lands for providing the BaZrO Raman spectra prior3to publication.Referencesw x1M.J.Cima,J.S.Schneider,S.C.Peterson,W.Coblenz,Appl.Ž.Phys.Lett.531988710.w x2V.L.Svetchnikov,V.M.Pan,H.W.Zandbergen,Supercond.Ž.Sci.Technol.61993176.w x3J.G.Wen, C.Traeholt,H.W.Zandebergen,K.Joosse,Ž.E.M.C.M.Reuvekamp,H.Rogalla,Physica C218199329. w x4J.A.Alarco,G.Brorsson,H.Olin,E.Olsson,J.Appl.Phys.Ž.7519943202.w x5G.Brorsson,E.Olsson,Z.G.Lvanov,E.A.Stepantsov,J.A.Alarco,Yu.Boikov,T.Claeson,P.Berastegui,nger,Ž.M.Lofgren,J.Appl.Phys.7519947958.¨w x6 A.L.Vasiliev, E.Olsson,Ju.Boikov,T.Claeson,N.A.Ž.Kiselev,Physica C2531995297.w x7 D.K.Fork,G.A.N.Connell,D.B.Fenner,J.B.Boyce,J.M.Phillips,T.H.Geballe,Science and Technology of Thin Film Superconductors2,Plenum,New York,1990,p.187.w x8 D.-S.Hwang,S.-G.Lee,Y.-K.Park,J.-S.Chun,J.-C.Park,Ž.Physica C2501995375.w xŽ.9O.Eibl,K.Hradil,H.Schmidt,Physica C177199189.w x10 C.Thomsen,M.Cardona,Physical Properties of High Tem-perature Superconductors,World Scientific,Singapore,1989, p.451.()M.S.Chen et al.r Physica C3151999117–123123w x11P.Zhang,T.Haage,H.-U.Habermeier,T.Ruf,M.Cardona,Ž.J.Appl.Phys.8019962935.w x12O.Martınez,J.Jimenez,P.Martın,A.C.Prieto,S.Degoy,´´´Ž.Physica C2701996144.w x13L.F.Cohen,Y.B.Li,G.Gibson,J.MacManus-Driscoll,Mat.Ž.Res.Soc.Symp.Proc.4011996351.w x14O.Martınez,J.Jimenez,P.Martın, D.Chambonnet,S.´´´Ž.Degoy,Mat.Res.Soc.Symp.Proc.4011996405.w x15M.N.Iliev,V.G.Hadjie,V.G.Ivanov,J.Raman Spectrosc.Ž.271996333.w x16M.V.Belousov,N.V.Orekhova,V.Yu.Davydov,S.G.Kon-Ž.nikov,Superconductivity:Phys.Chem.Tech.SPCT6Ž.199382.w x17H.-U.Habermeier,P.X.Zhang,T.Haage,J.Q.Li,Physica C Ž.282–2871997661.w x18P.Zhang,T.Haage,H.-U.Habermeier, A.Kazimirov,T.Ž.Ruf,M.Cardona,J.Alloys Comp.251199770.w x19 B.L.Low,S.Y.Xu, C.K.Ong,X.B.Wang,Z.X.Shen,Ž.Supercond.Sci.Technol.10199741.w x20M.Huntelaar,P.Groen,private communication.w x21H.Rosen,E.M.Engler,T.C.Strand,V.Y.Lee,D.Bethune,Ž.Phys.Rev.B361987726.w x22Z.V.Popovic,C.Thomsen,M.Cardona,R.Liu,G.Stanisic,Ž.W.Konig,Solid State Commun.66198843.¨w x23H.J.Rosen,R.M.MacFarlane,E.M.Engler,V.Y.Lee,R.D.Ž.Jacowitz,Phys.Rev.B3819882460.w xŽ.24 C.Thomsen,Adv.Mater.41992341.w xŽ.25R.J.Hemley,H.K.Mao,Phys.Rev.Lett.5819872340.w x26H.F.Goldstein, D.-S.Kim,P.Y.Yu,L.C.Bourne,Phys.Ž.Rev.B4119907192.w x27 E.T.Heyen,R.Liu,C.Thomsen,R.Kremer,M.Cardona,Ž.Phys.Rev.B41199011058.w x28R.Liu,C.Thomsen,W.Kress,M.Cardona,F.W.de Wette, J.Prade, A.D.Kulkafni,U.Schroder,Phys.Rev.B37¨Ž.1988797.w x29 B.Friedl, C.Thomsen,M.Cardona,Phys.Rev.Lett.65Ž.1990915.w x30M.Iliev,C.Thomsen,V.Hadjiev,M.Cardona,Phys.Rev.B Ž.47199312341.w x31P.V.Huong,J.C.Bruyere, E.Bustarret,P.Grandchamp,`Ž.Solid State Commun.721989191.w x32S.H.Lee,S.C.Bae,J.K.Ku,H.J.Shin,Phys.Rev.B46Ž.19929142.w x33S.Degoy,J.Jimenez,P.Martın,O.Martınez,A.C.Prieto,D.´´´Chambonnet,C.Audry,C.Belouet,J.Perriere,Physica C`Ž.2561996291.w x34M.S.Chen,Z.X.Shen,W.Z.Zhou,S.Y.Xu, C.K.Ong, Supercond.Sci.Technol.w x35N.Dieckmann,R.Kursten,M.Lohndorf,A.Bock,Physica¨¨Ž.C2451995212.w x36 D.Dierickx,I.Houben,pin,F.Delannay,O.Van DerŽ.Biest,J.Mater.Sci.Lett.1519961573.w x37U.Jeschke,R.Schneider,G.Ulmer,G.Linker,Physica C Ž.2431995243.。

a r X i v :c o n d -m a t /9808176v 1 [c o n d -m a t .d i s -n n ] 17 A u g 1998Thickness-Magnetic Field Phase Diagram at the Superconductor-Insulator Transitionin 2DN.Markovi´c ,C.Christiansen and A.M.GoldmanSchool of Physics and Astronomy,University of Minnesota,Minneapolis,MN 55455,USA (May 1,1998)The superconductor-insulator transition in ultrathin films of amorphous Bi was tuned by changing the film thickness,with and without an applied magnetic field.The first experi-mentally obtained phase diagram is mapped as a function of thickness and magnetic field in the T=0limit.A finite size scaling analysis has been carried out to determine the critical exponent product νz,which was found to be 1.2±0.2for the zero field transition,and 1.4±0.2for the finite field tran-sition.Both results are different from the exponents found for the magnetic field tuned transition in the same system,0.7±0.2.PACS numbers:74.76.-w,74.40.+k,74.25.Dw,72.15.RnSuperconductor-insulator (SI)transition in ultrathin films of metals is believed to be a continuous quantum phase transition [1]which can be traversed by changing a parameter such as disorder,film thickness,carrier con-centration or the applied magnetic field [2,3].The scal-ing theory and a phase diagram for a two-dimensional system as a function of disorder and magnetic field was postulated by Fisher et al .[3,4],based on the assumption that this transition can be fully described in terms of a model of interacting bosons,moving in the presence of disorder.The dirty boson problem has been extensively studied by quantum Monte Carlo simulations [5–8],real-space renormalization group calculations [9,10],strong coupling expansion [11]and in other ways [12–14],but there is still some disagreement as to the universality class of the transition.Conflicting experimental evidence suggests that the bosonic model might be relevant [15],but does not give the full picture [16].An alternative model of interacting electrons has also been proposed [17].Experimentally,the thickness tuned transition has been studied in the context of the scaling theory in zero magnetic field [18].In the present work,for the first time,the SI transition was tuned by systematically changing the film thickness in a finite magnetic field.This allows us to map a phase diagram as a function of thickness and magnetic field in the T=0limit and to determine the critical exponents using a finite size scaling analysis at different fields.The results suggest that this transition is similar to the zero field transition,but the exponent is different from that of the magnetic-field tuned transition studied on the same set of films [19].The ultrathin Bi films were evaporated on top of a 10˚A thick layer of amorphous Ge,which was pre-deposited onto a 0.75mm thick single-crystal of SrT iO 3(100).The substrate temperature was kept below 20K during all depositions and all the films were grown in situ under UHV conditions (∼10−10Torr).Under such circum-stances,successive depositions can be carried out with-out contamination to increase the film thickness grad-ually in increments of ∼0.2˚A .Film thicknesses were determined using a previously calibrated quartz crystal monitor.Films prepared in this manner are believed to be homogeneous,since it has been found that they be-come connected at an average thickness on the order of one monolayer [20].Resistance measurements were car-ried out between the depositions using a standard dc four-probe technique with currents up to 50nA.Mag-netic fields up to 12kG perpendicular to the plane of the sample were applied using a superconducting split-coil magnet.The evolution of the temperature dependence of the resistance as the film thickness changes is shown on Fig.1.The thinnest films show an exponential temperature dependence of the resistance at low temperatures,consis-tent with variable range hopping,which crosses over to a logarithmic behavior for thicker films [21].At some critical thickness,d c ,the resistance is independent of temperature,while for even thicker films it decreases rapidly with decreasing temperature,indicating the on-set of superconductivity.The critical thickness can be determined by plotting the resistance as a function of thickness for different temperatures (inset of Fig.1)and identifying the crossing point for which the resistance is temperature independent,or by plotting dR/dT as a function of thickness at the lowest temperatures and find-ing the thickness for which (dR/dT )=0.In the zero temperature quantum critical regime the resistance of a two dimensional system is expected to obey the following scaling law [1,4]:R (δ,T )=R c f (δT −1/νz )(1)Here δ=d −d c is the deviation from the critical thick-ness,R c is the critical resistance at d =d c ,f (x )is a universal scaling function such that f (0)=1,νis the co-herence length exponent,and z is the dynamical critical exponent.We rewrite Eq.1as R (δ,t )=R c f (δt ),where t ≡T −1/νz ,and treat the parameter t (T )as an unknown variable which is determined at each temperature to ob-tain the best collapse of all the data.The exponent νz is 1then found from the temperature dependence of t,which must be a power law in temperature for the procedure to make sense.This scaling procedure does not require detailed knowledge of the functional form of the temper-ature or thickness dependence of the resistance,or prior knowledge of the critical exponents.It is simply based on the data which includes an independent determination of d c.The collapse of the resistance data as a function of δt in zerofield is shown in Fig. 2.The critical expo-nent productνz,determined from the temperature de-pendence of the parameter t(inset of Fig.2),is found to beνz=1.2±0.2.This result is in agreement with the predictions of Ref.[2,3],from which z=1would be expected for a bosonic system with long range Coulomb interactions independent of the dimensionality,andν≥1 in two dimensions for any transition which can be tuned by changing the strength of the disorder[22].A simi-lar scaling behavior has been found in ultrathinfilms of Bi by Liu et al.[18],with the critical exponent product νz≈2.8on the insulating side andνz≈1.4on the su-perconducting side of the transition.The fact thatνz was found to be different on the two sides of the transi-tion raises the question of whether the experiment really probed the quantum critical regime.We believe that the scaling was carried out too deep into the insulating side, forcing the scaling form(Eq.1)onfilms which were in a fundamentally different insulating regime[21].Suchfilms should not be expected to scale together with the super-conductingfilms,hence the discrepancy on the insulating side of the transition.In the present work,the mea-surements were carried out at lower temperatures than previously studied and with more detail in the range of thicknesses close to the transition.We were able to scale both sides of the transition withνz≈1.2,which is close to the value obtained by Liu et al.on the superconduct-ing side of the transition.Our result is also in very good agreement with the renormalization group calculations [9,10,14],and close to that found in Monte Carlo sim-ulations by Cha and Girvin[7],Sørensen et al.[6]and Makivi´c et al.[5].In addition to the above,the magnetoresistance as a function of temperature and magneticfield was measured for eachfilm.By sorting the magnetoresistance data,one can probe the thickness-tuned superconductor-insulator transition in afinite magneticfield,which has not been studied before.The same analysis as described above was carried out for severalfixed magneticfields,rang-ing from0.5kG up to7kG.The normalized resistance data as a function of the scaling variable for six different values of the magneticfield shown on Fig.3all collapse on a single curve,which suggests that the scaling func-tion is indeed universal.The critical exponent product determined from the temperature dependence of the pa-rameter t(inset of Fig.3)is found to beνz=1.4±0.2, apparently independent of the magneticfield.An appliedmagneticfield is generally expected to change the uni-versality class of the transition,since it breaks the time reversal symmetry.Wefind,however,that the critical ex-ponent productνz for the thickness driven SI transition in afinite magneticfield is very close to that obtained for a zero-field transition,given the experimental uncer-tainties.This result is in agreement with Monte Carlo simulations of the(2+1)-dimensional classical XY model with disorder by Cha and Girvin[7],whichfindνz≈1.07 for the zero-field transition andνz≈1.14in afinite mag-neticfield.The critical resistance R c at the transition is non-universal,as it decreases with increasing magnetic field.Furthermore,once a magneticfield is applied and the time-reversal symmetry broken,the thickness-tuned transition in thefield is expected to be in the same uni-versality class as the transition which is tuned by chang-ing the magneticfield at afixedfilm thickness.The magnetic-field tuned transition was studied on the same set offilms used in this study[19],which allows a di-rect comparison of the critical exponents,without hav-ing to worry about differences in the microstructure be-tween different samples.The resistance as a function of temperature forfive selectedfilms from Fig.1was studied in magneticfields up to12kG applied perpen-dicular to the plane of the sample.The critical expo-nent product was determined using the method described above,but with the magneticfield as the tuning parame-ter rather than thefilm thickness.It was found to be νB z B=0.7±0.2,independent of thefilm thickness, which strongly suggests a universality class different from that of the thickness-tuned transition,both in zero-field and in thefield.This result does not agree with the pre-dictions based on the model of interacting bosons in the presence of disorder[3,4].It does,however,agree with what might be expected from a similar model without disorder[8,7].The details of the analysis and this unex-pected value of the critical exponent product,as well as the discussion of its disagreement with previous determi-nations[23],are reported elsewhere[19].The fact that the SI transition was traversed by chang-ing both the thickness and the magneticfield indepen-dently on the same set offilms allows us to determine the phase diagram as a function of thickness and the magneticfield in T=0limit,which is shown in Fig. 4.Thefilms characterized by parameters which lie above the phase boundary are”superconducting”(δR/δT<0 atfinite temperatures),and the ones bellow it are”insu-lating”(δR/δT>0atfinite temperatures).The phase boundary itself follows a power law:d c(B)−d c(0)∝B x c, where x≈1.4.Our results imply that the critical expo-nent productνz depends on whether this phase bound-ary is crossed vertically(changing the thickness at a con-stant magneticfield),in which caseνz≈1.4,or horizon-tally(changing the magneticfield at afixed thickness), in which caseνB z B≈0.7.In other words,relatively 2weak magneticfields which are experimentally accessible to us do not significantly change the universality class of the thickness-tuned transition,but the magnetic-field tuned transition is in a different universality class from the thickness-tuned transition in B=0.In the absence of a detailed theory,we can only speculate on the origins of this surprising result.Thefirst important issue we wish to discuss is the role of thefilm thickness as the control parameter. Adding metal sequentially to a quench-condensedfilm has been shown to decrease the disorder,since the in-creased screening smooths the random potential seen by the electrons.It presumably also increases the carrier concentration,which in the presence of an attractive electron-electron interaction might result in an increased Cooper pair density.Increasing thefilm thickness might therefore be thought of as adding Cooper pairs,which condense at some critical density.In a similar way,an applied mag-neticfield adds vortices,which behave as point parti-cles and also condense at some critical density,making the system insulating.However,this symmetry between charges and vortices is not perfect,since Cooper pairs interact as1/r and vortices interact logarithmically[24]. If the mechanism responsible for the localization in the magnetic-field tuned transition is different from that of the thickness-tuned transition,than having a non-zero magneticfield may not play a major role in the thickness-tuned transition.Also,the correlation length associated with the thickness-tuned transition would then be differ-ent from that associated with the magnetic-field tuned transition.The disorder might be important in one case and not in the other,depending on how these correlation lengths compare to the length scale which characterizes the disorder.A second difference between the thickness-tuned and thefield-tuned transitions may be the nature of disor-der itself.In thefield-tuned transition the geometry of thefilm isfixed,and the disorder does not change.In the disorder-tuned transition,eachfilm in the sequence offilms will have a slightly different microstructure,so that the disorder may have to be averaged over the dif-ferent configurations.It has been suggested recently[25] that the nature of the disorder averaging might play an important role in determining the critical exponents. Another possibility is that the localization transition is enhanced by percolation effects[26]as thefilm thickness is tuned.This approach takes into account localfluc-tuations of the amplitude of the superconducting order parameter,which are routinely neglected in the scaling theory and the numerical simulations.Percolation of is-lands with strong amplitudefluctuations might change the localization exponents obtained from the scaling the-ory[26].The role of percolation has also been empha-sized in recent discussions of low temperature transport in these systems[27].Finally,one cannot exclude the possibility that to ac-cess the quantum critical region these measurements need to be carried out at much lower temperatures or at high frequencies[28].We gratefully acknowledge useful discussions with A. P.Young,S.Sachdev and S.L.Sondhi.This work was supported in part by the National Science Foundation under Grant No.NSF/DMR-9623477.and A.M.Goldman,Phys.Rev.B47,5931(1993),D.B.Haviland,Y.Liu,and A.M.Goldman,Phys.Rev.Lett.62,2180(1989).[19]N.Markovi´c,C.Christiansen,and A.M.Goldman,sub-mitted to Phys.Rev.Lett.[20]M.Strongin,R.S.Thompson,O.F.Kammerer,and J.E.Crow,Phys.Rev.B1,1078(1970).[21]A.M.Mack,N.Markovi´c,C.Christiansen,G.Martinez-Arizala,and A.M.Goldman,submitted to Phys.Rev.B.[22]J.T.Chayes,L.Chayes,D.S.Fisher,and T.Spencer,Phys.Rev.Lett.57,2999(1986).[23]Ali Yazdani and Aharon Kapitulnik,Phys.Rev.Lett.74,3037(1995);A.F.Hebard and M.A.Paalanen,Phys.Rev.Lett.65,927(1990).[24]Under some very strict conditions(see L.V.Keldysh,Pis’ma Zh.Exsp.Teor.Phys.29,716(1979)[JETP Lett.29,659(1979)])charges in thinfilms can interact loga-rithmically.We do not have any reason to believe that those conditions are satisfied here.[25]F.P´a zm´a ndi,R.T.Scalettar,and G.T.Zim´a nyi,Phys.Rev.Lett.79,5130(1997).[26]K.Sheshadri,H.R.Krishnamurthy,Rahul Pandit,andT.V.Ramakrishnan,Phys.Rev.Lett.75,4075(1995).[27]Efrat Shimshoni,Assa Auerbach,and Aharon Kapitul-nik,Phys.Rev.Lett.80,3352(1998).[28]Kedar Damle and Subir Sachdev,Phys.Rev.B56,8714(1997).FIG.1.Resistance per square as a function of temperature for a series of bismuthfilms with thicknesses ranging from 9˚A(top)to15˚A(bottom).Inset:Resistance as a function of thickness for the same set offilms close to the transition at low temperature.Different curves represent different temper-ature,ranging from0.14K to0.40K.FIG.2.Resistance per square as a function of the scaling variable,t|d-d c|,for seventeen different temperature,ranging from0.14K to0.5K.Here t=T−1/νz is treated as an ad-justable parameter to obtain the best collapse of the data. Different symbols represent different temperature.Inset:Fit-ting the temperature dependence of the parameter t to a power law determines the value ofνz.FIG.3.Normalized resistance per square as a function of the scaling variable,t|d−d c|,at different temperature,rang-ing from0.14K to0.5K.Different symbols represent different magneticfields,ranging from0.5kG-7kG.Here t=T−1/νz is treated as an adjustable parameter to obtain the best collapse of the data,and R c is the resistance at d=d c.Inset:Fitting the temperature dependence of the parameter t to a power law determines the value ofνz.FIG.4.The phase diagram in the d-B plane in the T=0 limit.The points on the phase boundary were obtained from disorder driven transitions(triangles)and magneticfield driven transitions(circles).The solid line is a power lawfit.The values of the critical exponent product are shown next to the arrows giving the direction in which the boundary was crossed.Here d c is taken to be the critical thickness in zero field.4103104105106107051015R (Ω)T(K)400050006000700080009000100000.0010.010.11R (Ω)t|d-d c|0.50.60.70.80.910.0010.010.11R /R ct|d-d c|0.10.20.30.40.50.6(d -d c )(Å)B(kG)。