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High-speed preparation of c-axis-oriented YBa2Cu3O7-δ film by laser chemical vapor deposition
Materials Letters 64 (2010) 102–104
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
High-speed preparation of c-axis-oriented YBa2Cu3O7-δ film by laser chemical vapor deposition Pei Zhao, Akihiko Ito, Rong Tu, Takashi Goto ⁎ Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan
a r t i c l e
i n f o
Article history: Received 24 August 2009 Accepted 11 October 2009 Available online 17 October 2009 Keywords: Laser chemical vapor deposition YBCO High deposition rate
a b s t r a c t YBa2Cu3O7-δ (YBCO) films were prepared by laser chemical vapor deposition using Y(DPM)3, Ba(DPM)2/Ba (TMOD)2 and Cu(DPM)2 as precursors with enhancement by a continuous wave Nd:YAG laser. A c-axisoriented YBCO film almost entirely in a single phase was obtained. The YBCO film consisted of rectangular grains about 30 μm in size. The highest deposition rate was about 100 μm h− 1, which was 10–1000 times higher than that of conventional MOCVD. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Since the discovery of high-temperature superconductor YBa2Cu3O7-δ (YBCO) with a high TC of about 93 K in 1987, [1–3] intensive attention aimed at improving its superconductive performance has been focused on the preparation process of YBCO thin film, such as sol–gel, [4] metalorganic deposition using trifluoroacetates (TFA-MOD), [5] multilayer evaporation, [6] thermal evaporation, [7] pulsed laser deposition, [8] sputtering, [9,10] molecular beam deposition [11] and metalorganic chemical vapor deposition (MOCVD) [12]. MOCVD is considered to be a promising process for YBCO film preparation because of its excellent orientation controllability [12–16]. YBCO films with c-axis orientation prepared by MOCVD have showed excellent electrical properties, i.e., TC = 83–93 K and JC = 105–106 A/cm2, [17–32] indicating the great potential of MOCVD YBCO films in practical application. However, the deposition rate (Rdep) of YBCO film prepared by MOCVD is commonly 100 nm h− 1 to several µm h− 1 [14,19,21,23–25,30–32]. In fact, plasma and magnetic-field enhanced MOCVD have been studied to improve the Rdep of YBCO films. Zhao et al. [20,21] applied a plasma enhanced MOCVD to prepare YBCO film at a Rdep of 1.1 µm h− 1, showing a high TC =90 K and JC =3.3×106 A/cm2 (at 77 K). Ma et al. [22,23] prepared YBCO film by high magnetic-field enhanced MOCVD. Although a high TC of 88 K and a JC of about 1.1×105 A/cm2 were obtained, the Rdep was only 0.3 µm h− 1 [22]. We have previously reported a new laser CVD (LCVD) technique to prepare oxide and non-oxide films (i.e., TiO2, [25] yttria stabilized
⁎ Corresponding author. E-mail address: [email protected] (T. Goto). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.027
zirconia (YSZ) [25] and Y2O3 [26]) with significant orientation at a high Rdep. In the present study, we prepared YBCO films by LCVD at high Rdep. 2. Experimental YBCO films were prepared on Al2O3 substrates (10 mm×10 mm× 2.5 mm) by LCVD using Y(DPM)3, Ba(DPM)2/Ba(TMOD)2 and Cu(DPM)2 (DPM; dipivaloy methanate and TMOD; 2,2,6,6-tetramethy1-3,5-octanedionato) as precursors. The Ba precursor was a mixture of Ba(DPM)2 and Ba(TMOD)2 with a molar ratio of 4 to 1, which could suppress the decomposition of Ba(DPM)2 at the temperatures over their eutectic point and vaporize at a constant rate [24]. A schematic of the LCVD apparatus is shown in Fig. 1. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with laser power (PL) from 50 to 200 W was employed. The laser beam was defocused up to 20 mm in diameter to irradiate the whole substrate and was introduced through a quartz window at an incident angle of 30º to the substrate. The Al2O3 substrate was heated on a heating stage at preheating temperature (Tpre) of 673–873 K. The deposition temperature (Tdep) was measured with a thermocouple inserted into a slot 1.5 mm in depth at the back side of the substrate. The flow rates of Ar and O2 gases were 8.3×10− 7 m3 s− 1 and 3.3×10− 6 m3 s− 1, respectively. The composition of the YBCO film was controlled by the vaporization temperature (Tvap) of the Y (TY), Ba (TBa), and Cu (TCu) precursors at the range of TY =468–493 K, TBa =595–623 K and TCu =523–533 K, respectively. The temperature of all the gas lines was maintained at 623 K to prevent the condensation of the precursor during the transportation. The total pressure (Ptot) was held at 1 kPa. The deposition was conducted for 600 s. The distance between the nozzle and the substrate was 28 mm. After deposition, the YBCO films were heat-treated at 823 K for 43.2 ks in a pure O2 atmosphere (100 kPa). The crystal phase was identified by
P. Zhao et al. / Materials Letters 64 (2010) 102–104
103
Fig.1. Schematic diagram of the present LCVD equipment.
X-ray diffraction (XRD; Rigaku RAD – 2C) and the microstructure was observed by scanning electron microscopy (SEM; Hitachi S – 3100H).
Fig.3. Surface and cross-sectional SEM images of YBCO film prepared at Tdep = 1123 K, PL = 130 W, Tpre = 873 K, Ptot = 1 kPa, TY = 473 K, TBa = 600 K, TCu = 528 K (a, c) and that heat-treated at 823 K (b, d).
3. Results and discussion
occurred during heat treatment (Fig. 2), no obvious changes on the surface and the cross-sectional morphologies of the YBCO film were observed (Fig. 3(b), (d)). Generally, the grain size of YBCO film prepared by conventional MOCVD was about 0.5–2 µm [12,14,25,28]. Fig. 4 shows the effect of Tdep on the Rdep in the present study and those reported in the literature [14,19–23,25,28,33–35]. YBCO films prepared by MOCVD at Tdep =923–1023 K, TY =383–403 K, TBa =503– 573 K and TCu =393–403 K, [14,22,23,25,28,33–35] and their Rdep were mainly located at 0.1–1 µm h− 1. Abe et al. [33] prepared YBCO films at different deposition temperatures from 873 to 1053 K, obtaining a relatively high Rdep of 10 µm h− 1 at relatively high vaporization temperature of TY =433 K, TBa =573 K, and TCu =453 K and Tdep =1053 K. The Rdep increased with increasing Tdep as well as Tvap of precursors; however, the Tdep cannot exceed the melting point of YBCO (1273 K), which may limit the increase in the Tvap and eventually the Rdep in conventional MOCVD. In the present study, the highest Rdep was 100 µm h− 1, which is about 10–1000 times higher than those of conventional MOCVD. The high Rdep was owing to the relatively high TY, TBa and TCu which ensure a high
Fig. 2 shows the XRD patterns of the YBCO film prepared at TY =473 K, TBa = 600 K, TCu = 528 K, Tpre = 873 K, PL = 130 W, Ptot = 1 kPa and Tdep =1123 K (Fig. 2(a)), and that heat-treated at 823 K (Fig. 2(b)). YBCO film exhibited a c-axis preferred orientation, and only a small amount of the secondary phase of Y2O3 was identified (Fig. 2 (a)). The asdeposited film showed a tetragonal phase with a c-length of 1.181 nm. According to the relationship between composition and c-length reported by Jorgensen, [13] the δ in YBa2Cu3O7-δ was deduced as being 0.96. The clength after heat treatment decreased to 1.169 nm, suggesting δ =0.18 and a transition from tetragonal to orthorhombic phase. Fig. 3 shows the microstructure of the as-deposited YBCO film and that heat-treated at 823 K. The YBCO film consisted of grains about 30 µm in size (Fig. 3(a) and had a dense cross section (Fig. 3(c)). Although a phase transformation from tetragonal to orthorhombic
Fig. 2. XRD patterns of the YBCO film prepared at Tdep = 1123 K, PL = 130 W, Ptot = 1 kPa, Tpre = 873 K, TY = 473 K, TBa = 600 K, TCu = 528 K (a), and that heat-treated at 823 K (b).
Fig.4. Effect of Tdep on the Rdep in the present study and those reported in the literature.
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P. Zhao et al. / Materials Letters 64 (2010) 102–104
supply rate of three precursor gases and the enhancement of chemical reaction by laser irradiation of the film and the precursor gases. 4. Conclusion YBCO films in an almost single phase were prepared by LCVD. The YBCO films consisted of relatively large, rectangular-shaped grains about 30 µm in size. The crystal phase of YBCO films changed from tetragonal to orthorhombic after heat treatment. The highest Rdep was 100 µm h− 1, suggesting that the present LCVD technique may be advantageous for the preparation of YBCO films in practical applications. Acknowledgement This work was supported in part by the International Superconductivity Technology Center (ISTEC) and by the Global COE program of Materials Integration, Tohoku University. References [1] Müller KA, Bednorz JG. Science 1987;237:1133–9. [2] Wu MK, Ashburn JR, Torng CJ, Hor PH, Meng RL, Gao L, Huang ZJ, Wang YQ, Chu CW. Phys Rev Lett 1987;58:908–10. [3] Larbalestier D, Gurevich A, Feldmann DM, Polyanskii A. Nature 2001;414:368–77. [4] Shibata S, Kitagawa T, Okazaki H, Kimura T. Jpn J Appl Phys 1988;27:L646–8. [5] Honjo T, Nakamura Y, Teranishi R, Fuji H, Shibata J, Izumi T, Shiohara Y. IEEE Trans Appl Supercond 2003;13:2516–9. [6] Bao ZL, Wang FR, Jiang QD, Wang SZ, Ye ZY, Wu K, Li CY, Yin DL. Appl Phys Lett 1987;51:946–7. [7] Berberich P, Tate J, Dietsche W, Kinder H. Appl Phys Lett 1988;53:925–6. [8] Inam A, Hegde MS, Wu XD, Venkatesan T, England P, Miceli PF, Chase EW, Chang CC, Tarascon JM, Wachtman JB. Appl Phys Lett 1988;53:908–10. [9] Enomato Y, Murakami T, Suzuki M, Moriwaki K. Jpn J Appl Phys 1987;26: L1248–50. [10] Char K, Kent AD, Kapitulnik A, Beasley MR, Geballe TH. Appl Phys Lett 1987;51:1370–2.
[11] Kwo J, Hsich TC, Fleming RH, Hong M, Liou SH, Davidson BA, Feldman TC. Phys Rev B 1987;36:4039–42. [12] Berry D, Gaskill DK, Holm RT, Cukauskas EJ, Kaplan R, Henry RL. Appl Phys Lett 1988;52:1743–5. [13] Jorgensen JD, Veal BW, Paulikas AP, Nowicki LJ, Crabtree Gw, Claus H, Kwok WK. Phys Rev B 1990;41:1863–77. [14] Yamane H, Masumoto H, Hirai T, Iwasaki H, Watanabe K, Kobayashi N, Muto Y. Appt Phys Lett 1988;53:1548–50. [15] Zhao J, Dahmen KH, Marcy HO, Tonge LM, Marks TJ, Wessels BW, Kannewunf CR. Appl Phys Lett 1988;53:1750–2. [16] Panson J, Charies RG, Schmidt DN, Szedon JR, Machiko GJ, Braginski AI. Appl Phys Lett 1988;53:1756–8. [17] Watanabe T, Kashima, Suda NN, Mori M, Nagaya S, Miyata S, Ibi A, Yamada Y, Izumi T, Shiohara Y. IEEE Trans Appl Supercond 2007;17:3386–9. [18] Gurvitch M, Fiory AT. Appl Phys Lett 1987;51:1027–9. [19] Chern CS, Zhao J, Li YQ, Norris P, Kear B, Gallois B, Kalman Z. Appl Phys Lett 1991;58:185–7. [20] Zhao J, Li YQ, Chern CS, Lux P, Norris P, Gallois B, Kear B, Cosandey F, Wu XD, Muenchausen RE, Garrison SM. Appl Phys Lett 1991;59:1254–6. [21] Zhao J, Li YQ, Chern CS, Norris P, Gallois B, Kear B, Wessels BW. Appl Phys Lett 1991;58:89–91. [22] Ma YW, Watanabe K, Awaji S, Motokawa M. Jpn J Appl Phys 2000;39:L726–9. [23] Ma YW, Watanabe K, Awaji S, Motokawa M. Jpn J Appl Phys 2001;40:6339–43. [24] Tasaki Y, Yoshizawa S, Koyama K, Fujino Y. IEEE Trans Appl Supercond 1999;9:2367–70. [25] Yamane H, Kurosawa H, Iwasaki H, Masumoto H, Hirai T, Kobayashi N, Muto Y. Jpn J Appl Phys 1988;27:L1275–6. [26] Goto T, Kimura T. Thin Solid Films 2006;515:46–52. [27] Goto T, Banal R, Kimura T. Surf Coat Technol 2007;201:5776–81. [28] Oda S, Zama H, Yamamoto S. IEEE Trans Appl Supercond 1988;5:1801–4. [29] DeSisto WJ, Newman HS, Henry RL, Cestone VC. Appl Phys Lett 1993;62:1682–4. [30] Kawagishi K, Komori K, Fukutomi M, Togano K. Physica C 2003;392:1236–40. [31] Bagarinao KD, Yamasaki H, Nakagawa Y, Obara H, Yamada H. Physica C 2003;392:1229–35. [32] Nie JC, Yamasaki H, Bagarinao KD, Nakagawa Y. IEEE Trans Appl Supercond 2007;17:3459–62. [33] Abe H, Tsuruoka T, Nakamori T. Jpn J Appl Phys 1988;27:L1473–5. [34] Yamane H, Kurosawa H, Hirai T. Chem Lett 1988;6:939–40. [35] Kanehori K, Sughii N, Fukazawa T, Miyauchi K. Thin Solid Films 1989;182:265–9.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
High-speed preparation of c-axis-oriented YBa2Cu3O7-δ film by laser chemical vapor deposition Pei Zhao, Akihiko Ito, Rong Tu, Takashi Goto ⁎ Institute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan
a r t i c l e
i n f o
Article history: Received 24 August 2009 Accepted 11 October 2009 Available online 17 October 2009 Keywords: Laser chemical vapor deposition YBCO High deposition rate
a b s t r a c t YBa2Cu3O7-δ (YBCO) films were prepared by laser chemical vapor deposition using Y(DPM)3, Ba(DPM)2/Ba (TMOD)2 and Cu(DPM)2 as precursors with enhancement by a continuous wave Nd:YAG laser. A c-axisoriented YBCO film almost entirely in a single phase was obtained. The YBCO film consisted of rectangular grains about 30 μm in size. The highest deposition rate was about 100 μm h− 1, which was 10–1000 times higher than that of conventional MOCVD. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Since the discovery of high-temperature superconductor YBa2Cu3O7-δ (YBCO) with a high TC of about 93 K in 1987, [1–3] intensive attention aimed at improving its superconductive performance has been focused on the preparation process of YBCO thin film, such as sol–gel, [4] metalorganic deposition using trifluoroacetates (TFA-MOD), [5] multilayer evaporation, [6] thermal evaporation, [7] pulsed laser deposition, [8] sputtering, [9,10] molecular beam deposition [11] and metalorganic chemical vapor deposition (MOCVD) [12]. MOCVD is considered to be a promising process for YBCO film preparation because of its excellent orientation controllability [12–16]. YBCO films with c-axis orientation prepared by MOCVD have showed excellent electrical properties, i.e., TC = 83–93 K and JC = 105–106 A/cm2, [17–32] indicating the great potential of MOCVD YBCO films in practical application. However, the deposition rate (Rdep) of YBCO film prepared by MOCVD is commonly 100 nm h− 1 to several µm h− 1 [14,19,21,23–25,30–32]. In fact, plasma and magnetic-field enhanced MOCVD have been studied to improve the Rdep of YBCO films. Zhao et al. [20,21] applied a plasma enhanced MOCVD to prepare YBCO film at a Rdep of 1.1 µm h− 1, showing a high TC =90 K and JC =3.3×106 A/cm2 (at 77 K). Ma et al. [22,23] prepared YBCO film by high magnetic-field enhanced MOCVD. Although a high TC of 88 K and a JC of about 1.1×105 A/cm2 were obtained, the Rdep was only 0.3 µm h− 1 [22]. We have previously reported a new laser CVD (LCVD) technique to prepare oxide and non-oxide films (i.e., TiO2, [25] yttria stabilized
⁎ Corresponding author. E-mail address: [email protected] (T. Goto). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.027
zirconia (YSZ) [25] and Y2O3 [26]) with significant orientation at a high Rdep. In the present study, we prepared YBCO films by LCVD at high Rdep. 2. Experimental YBCO films were prepared on Al2O3 substrates (10 mm×10 mm× 2.5 mm) by LCVD using Y(DPM)3, Ba(DPM)2/Ba(TMOD)2 and Cu(DPM)2 (DPM; dipivaloy methanate and TMOD; 2,2,6,6-tetramethy1-3,5-octanedionato) as precursors. The Ba precursor was a mixture of Ba(DPM)2 and Ba(TMOD)2 with a molar ratio of 4 to 1, which could suppress the decomposition of Ba(DPM)2 at the temperatures over their eutectic point and vaporize at a constant rate [24]. A schematic of the LCVD apparatus is shown in Fig. 1. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with laser power (PL) from 50 to 200 W was employed. The laser beam was defocused up to 20 mm in diameter to irradiate the whole substrate and was introduced through a quartz window at an incident angle of 30º to the substrate. The Al2O3 substrate was heated on a heating stage at preheating temperature (Tpre) of 673–873 K. The deposition temperature (Tdep) was measured with a thermocouple inserted into a slot 1.5 mm in depth at the back side of the substrate. The flow rates of Ar and O2 gases were 8.3×10− 7 m3 s− 1 and 3.3×10− 6 m3 s− 1, respectively. The composition of the YBCO film was controlled by the vaporization temperature (Tvap) of the Y (TY), Ba (TBa), and Cu (TCu) precursors at the range of TY =468–493 K, TBa =595–623 K and TCu =523–533 K, respectively. The temperature of all the gas lines was maintained at 623 K to prevent the condensation of the precursor during the transportation. The total pressure (Ptot) was held at 1 kPa. The deposition was conducted for 600 s. The distance between the nozzle and the substrate was 28 mm. After deposition, the YBCO films were heat-treated at 823 K for 43.2 ks in a pure O2 atmosphere (100 kPa). The crystal phase was identified by
P. Zhao et al. / Materials Letters 64 (2010) 102–104
103
Fig.1. Schematic diagram of the present LCVD equipment.
X-ray diffraction (XRD; Rigaku RAD – 2C) and the microstructure was observed by scanning electron microscopy (SEM; Hitachi S – 3100H).
Fig.3. Surface and cross-sectional SEM images of YBCO film prepared at Tdep = 1123 K, PL = 130 W, Tpre = 873 K, Ptot = 1 kPa, TY = 473 K, TBa = 600 K, TCu = 528 K (a, c) and that heat-treated at 823 K (b, d).
3. Results and discussion
occurred during heat treatment (Fig. 2), no obvious changes on the surface and the cross-sectional morphologies of the YBCO film were observed (Fig. 3(b), (d)). Generally, the grain size of YBCO film prepared by conventional MOCVD was about 0.5–2 µm [12,14,25,28]. Fig. 4 shows the effect of Tdep on the Rdep in the present study and those reported in the literature [14,19–23,25,28,33–35]. YBCO films prepared by MOCVD at Tdep =923–1023 K, TY =383–403 K, TBa =503– 573 K and TCu =393–403 K, [14,22,23,25,28,33–35] and their Rdep were mainly located at 0.1–1 µm h− 1. Abe et al. [33] prepared YBCO films at different deposition temperatures from 873 to 1053 K, obtaining a relatively high Rdep of 10 µm h− 1 at relatively high vaporization temperature of TY =433 K, TBa =573 K, and TCu =453 K and Tdep =1053 K. The Rdep increased with increasing Tdep as well as Tvap of precursors; however, the Tdep cannot exceed the melting point of YBCO (1273 K), which may limit the increase in the Tvap and eventually the Rdep in conventional MOCVD. In the present study, the highest Rdep was 100 µm h− 1, which is about 10–1000 times higher than those of conventional MOCVD. The high Rdep was owing to the relatively high TY, TBa and TCu which ensure a high
Fig. 2 shows the XRD patterns of the YBCO film prepared at TY =473 K, TBa = 600 K, TCu = 528 K, Tpre = 873 K, PL = 130 W, Ptot = 1 kPa and Tdep =1123 K (Fig. 2(a)), and that heat-treated at 823 K (Fig. 2(b)). YBCO film exhibited a c-axis preferred orientation, and only a small amount of the secondary phase of Y2O3 was identified (Fig. 2 (a)). The asdeposited film showed a tetragonal phase with a c-length of 1.181 nm. According to the relationship between composition and c-length reported by Jorgensen, [13] the δ in YBa2Cu3O7-δ was deduced as being 0.96. The clength after heat treatment decreased to 1.169 nm, suggesting δ =0.18 and a transition from tetragonal to orthorhombic phase. Fig. 3 shows the microstructure of the as-deposited YBCO film and that heat-treated at 823 K. The YBCO film consisted of grains about 30 µm in size (Fig. 3(a) and had a dense cross section (Fig. 3(c)). Although a phase transformation from tetragonal to orthorhombic
Fig. 2. XRD patterns of the YBCO film prepared at Tdep = 1123 K, PL = 130 W, Ptot = 1 kPa, Tpre = 873 K, TY = 473 K, TBa = 600 K, TCu = 528 K (a), and that heat-treated at 823 K (b).
Fig.4. Effect of Tdep on the Rdep in the present study and those reported in the literature.
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P. Zhao et al. / Materials Letters 64 (2010) 102–104
supply rate of three precursor gases and the enhancement of chemical reaction by laser irradiation of the film and the precursor gases. 4. Conclusion YBCO films in an almost single phase were prepared by LCVD. The YBCO films consisted of relatively large, rectangular-shaped grains about 30 µm in size. The crystal phase of YBCO films changed from tetragonal to orthorhombic after heat treatment. The highest Rdep was 100 µm h− 1, suggesting that the present LCVD technique may be advantageous for the preparation of YBCO films in practical applications. Acknowledgement This work was supported in part by the International Superconductivity Technology Center (ISTEC) and by the Global COE program of Materials Integration, Tohoku University. References [1] Müller KA, Bednorz JG. Science 1987;237:1133–9. [2] Wu MK, Ashburn JR, Torng CJ, Hor PH, Meng RL, Gao L, Huang ZJ, Wang YQ, Chu CW. Phys Rev Lett 1987;58:908–10. [3] Larbalestier D, Gurevich A, Feldmann DM, Polyanskii A. Nature 2001;414:368–77. [4] Shibata S, Kitagawa T, Okazaki H, Kimura T. Jpn J Appl Phys 1988;27:L646–8. [5] Honjo T, Nakamura Y, Teranishi R, Fuji H, Shibata J, Izumi T, Shiohara Y. IEEE Trans Appl Supercond 2003;13:2516–9. [6] Bao ZL, Wang FR, Jiang QD, Wang SZ, Ye ZY, Wu K, Li CY, Yin DL. Appl Phys Lett 1987;51:946–7. [7] Berberich P, Tate J, Dietsche W, Kinder H. Appl Phys Lett 1988;53:925–6. [8] Inam A, Hegde MS, Wu XD, Venkatesan T, England P, Miceli PF, Chase EW, Chang CC, Tarascon JM, Wachtman JB. Appl Phys Lett 1988;53:908–10. [9] Enomato Y, Murakami T, Suzuki M, Moriwaki K. Jpn J Appl Phys 1987;26: L1248–50. [10] Char K, Kent AD, Kapitulnik A, Beasley MR, Geballe TH. Appl Phys Lett 1987;51:1370–2.
[11] Kwo J, Hsich TC, Fleming RH, Hong M, Liou SH, Davidson BA, Feldman TC. Phys Rev B 1987;36:4039–42. [12] Berry D, Gaskill DK, Holm RT, Cukauskas EJ, Kaplan R, Henry RL. Appl Phys Lett 1988;52:1743–5. [13] Jorgensen JD, Veal BW, Paulikas AP, Nowicki LJ, Crabtree Gw, Claus H, Kwok WK. Phys Rev B 1990;41:1863–77. [14] Yamane H, Masumoto H, Hirai T, Iwasaki H, Watanabe K, Kobayashi N, Muto Y. Appt Phys Lett 1988;53:1548–50. [15] Zhao J, Dahmen KH, Marcy HO, Tonge LM, Marks TJ, Wessels BW, Kannewunf CR. Appl Phys Lett 1988;53:1750–2. [16] Panson J, Charies RG, Schmidt DN, Szedon JR, Machiko GJ, Braginski AI. Appl Phys Lett 1988;53:1756–8. [17] Watanabe T, Kashima, Suda NN, Mori M, Nagaya S, Miyata S, Ibi A, Yamada Y, Izumi T, Shiohara Y. IEEE Trans Appl Supercond 2007;17:3386–9. [18] Gurvitch M, Fiory AT. Appl Phys Lett 1987;51:1027–9. [19] Chern CS, Zhao J, Li YQ, Norris P, Kear B, Gallois B, Kalman Z. Appl Phys Lett 1991;58:185–7. [20] Zhao J, Li YQ, Chern CS, Lux P, Norris P, Gallois B, Kear B, Cosandey F, Wu XD, Muenchausen RE, Garrison SM. Appl Phys Lett 1991;59:1254–6. [21] Zhao J, Li YQ, Chern CS, Norris P, Gallois B, Kear B, Wessels BW. Appl Phys Lett 1991;58:89–91. [22] Ma YW, Watanabe K, Awaji S, Motokawa M. Jpn J Appl Phys 2000;39:L726–9. [23] Ma YW, Watanabe K, Awaji S, Motokawa M. Jpn J Appl Phys 2001;40:6339–43. [24] Tasaki Y, Yoshizawa S, Koyama K, Fujino Y. IEEE Trans Appl Supercond 1999;9:2367–70. [25] Yamane H, Kurosawa H, Iwasaki H, Masumoto H, Hirai T, Kobayashi N, Muto Y. Jpn J Appl Phys 1988;27:L1275–6. [26] Goto T, Kimura T. Thin Solid Films 2006;515:46–52. [27] Goto T, Banal R, Kimura T. Surf Coat Technol 2007;201:5776–81. [28] Oda S, Zama H, Yamamoto S. IEEE Trans Appl Supercond 1988;5:1801–4. [29] DeSisto WJ, Newman HS, Henry RL, Cestone VC. Appl Phys Lett 1993;62:1682–4. [30] Kawagishi K, Komori K, Fukutomi M, Togano K. Physica C 2003;392:1236–40. [31] Bagarinao KD, Yamasaki H, Nakagawa Y, Obara H, Yamada H. Physica C 2003;392:1229–35. [32] Nie JC, Yamasaki H, Bagarinao KD, Nakagawa Y. IEEE Trans Appl Supercond 2007;17:3459–62. [33] Abe H, Tsuruoka T, Nakamori T. Jpn J Appl Phys 1988;27:L1473–5. [34] Yamane H, Kurosawa H, Hirai T. Chem Lett 1988;6:939–40. [35] Kanehori K, Sughii N, Fukazawa T, Miyauchi K. Thin Solid Films 1989;182:265–9.