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Preparation of highly (100)-oriented CeO2 films on polycrystalline Al2O3 substrates by laser chemical vapor deposition
Surface & Coatings Technology 204 (2010) 3619–3622
Contents lists available at ScienceDirect
Surface & Coatings Technology 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 / s u r f c o a t
Preparation of highly (100)-oriented CeO2 films on polycrystalline Al2O3 substrates by laser chemical vapor deposition Pei Zhao, Akihiko Ito, Rong Tu, Takashi Goto ⁎ Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
a r t i c l e
i n f o
Article history: Received 2 February 2010 Accepted in revised form 13 April 2010 Available online 18 April 2010 Keywords: Laser chemical vapor deposition CeO2 film High deposition rate
a b s t r a c t CeO2 films were prepared on Al2O3 substrates by laser chemical vapor deposition at different laser power (PL) up to 182 W. The (100)-oriented CeO2 films were prepared at PL = 101–167 W (Tdep = 792–945 K). The texture coefficient (TC) of (200) reflection had a maximum of 6.7 at PL = 113 W (Tdep = 836 K). The (100)oriented CeO2 films consisted of granular grains and showed a columnar cross section. The deposition rates (Rdep) of (100)-oriented CeO2 films showed a maximum of 43 μm h−1 at PL = 152 W (Tdep = 912 K). © 2010 Elsevier B.V. All rights reserved.
1. Introduction Since Al2O3 substrate is superior in corrosion-resistance, dielectric constant and cost effectiveness comparing with MgO, SrTiO3 and LaAlO3 substrates [1,2], Al2O3 is an attractive substrate for the production of YBa2Cu3O7 − δ (YBCO) superconducting films for various microwave devices such as resonators, filters and delay lines [1–3]. C-axis oriented YBCO thin films can be deposited on signal-crystal Al2O3 substrate [2–5]; however, Al2O3 substrate often reacts with Ba and deteriorates the c-axis orientation of YBCO film at elevated temperatures [1]. Therefore, an intermediate buffer layer should be deposited on Al2O3 substrate as diffusion barrier. Ceria (CeO2) film can be a promising candidate for the buffer layer because it has a fluorite structure (a = 5.411 Å) with a lattice mismatch less than 1% between CeO2 (200) and YBCO (110) planes [6,7]. This favors epitaxial growth of YBCO film with almost no distortion on CeO2 layer. Furthermore, a similar thermal expansion of CeO2 (9.5–12.3 × 10−6 K−1) [5] and YBCO (13 × 10−6 K−1) [8] can ensure the formation of crack-free YBCO film on CeO2 layer. Since CeO2 is stable between 298 to 1473 K [9,10], CeO2 can prevent the reaction between the substrate and YBCO film. Many deposition methods to prepare CeO2 films such as pulsed laser deposition (PLD) [11], magnetron sputtering [12,13], electronbeam evaporation [19], and metalorganic chemical vapor deposition (MOCVD) [6,10,15] have been reported. Highly (100)-oriented CeO2 films have been usually obtained on signal-crystal (R-cut sapphire) Al2O3 substrates [6,10–15]. On the other hand, polycrystalline Al2O3 substrate is more commonly available and cost-effective than signal-
⁎ Corresponding author. E-mail address: [email protected] (T. Goto). 0257-8972/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2010.04.037
crystal Al2O3, and therefore it is beneficial to prepare highly (100)oriented CeO2 buffer layer on polycrystalline Al2O3 substrate. We have reported the preparation of oxide and non-oxide films such as TiO2 [16], YSZ [16] and Y2O3 [17] by using laser chemical vapor deposition (LCVD). This LCVD can prepare many kinds of films at a significantly high Rdep with strongly preferred orientation on polycrystalline substrates. In the present study, we have prepared CeO2 films on polycrystalline Al2O3 substrates by LCVD, and mainly investigated the effect of laser power on the orientation, deposition rate, and microstructure of CeO2 films.
2. Experimental CeO2 films were prepared on polycrystalline Al2O3 substrates (10 mm × 10 mm × 2.5 mm) by LCVD using Ce(DPM)4 (DPM; dipivaloymethanate) as precursor. The experimental setup of the LCVD apparatus is shown in Fig. 1. A continuous wave Nd:YAG laser (wavelength: 1064 nm) was employed at laser power output (PL) from 17 to 182 W. 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 substrates were heated on a heating stage at a pre-heating temperature (Tpre) of 673 K. The deposition temperature (Tdep) was measured with a thermocouple inserted at the back side of the substrate. The flow rates of Ar and O2 gases were both 1.7 × 10−6 m3s−1. The vaporization temperature (Tvap) of the Ce precursor was maintained at 523 K. The temperature of all the gas lines was maintained at 573 K to prevent the condensation of precursor during the transportation. The total pressure (Ptot) in the CVD chamber was held at 800 Pa. The deposition was conducted for 600 s. The distance between the nozzle and the substrate was 25 mm.
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P. Zhao et al. / Surface & Coatings Technology 204 (2010) 3619–3622
Fig. 2. XRD patterns of the CeO2 film prepared on Al2O3 substrates at Tvap = 523 K and at different PL of 85 W (Tdep = 767 K) (a), 152 W (Tdep = 912 K) (b) and 182 W (Tdep = 970 K) (c). Fig. 1. The schematic of the LCVD apparatus.
The phase and crystallinity were studied by using X-ray diffraction (XRD; Rigaku RAD-2C; θ–2θ, ω-scan (rocking curve)). The degree of orientation on (200) reflection was calculated by the Harris texture coefficient (TC):
TCðhklÞ = N
Im ðhklÞ = I0 ðhklÞ ; ∑Im ðhklÞ = I0 ðhklÞ
ð1Þ
where Im(hkl) and I0(hkl) are the intensity from the (100) plane measured in the present study and that reported in JCPDS card (No. 43-1002), respectively. (111), (200), (220), (311), (222), (400), (331) and (420) reflections were used for the calculation (N = 8). The microstructure was observed by a field emission scanning electron microscope (FESEM; JEOL JSM-7500F). 3. Results and discussion Fig. 2 shows typical XRD patterns at P L = 17–182 W. The deposition temperatures (Tdep) ranged from 685 to 970 K at PL of 17–182 W. Crystalline CeO2 films were prepared at PL = 17–85 W (Tdep = 685–767 K), where the diffraction peaks were slightly broad (Fig. 2(a)). With increasing PL from 17 to 85 W, the (100) preferred orientation became sharper. At PL = 101–167 W (Tdep = 792–945 K), highly (100)-oriented CeO2 films were prepared (Fig. 2(b)). The orientation changed from (100) to (311) plane at PL = 182 W (Tdep = 970 K) (Fig. 2(c)). Fig. 3 shows the effect of PL on TC (200) of CeO2 films. The TC increased from 1.1 to 3.6 with increasing PL from 17 to 85 W (Tdep from 685 to 767 K). The TC of highly (100)-oriented CeO2 films prepared at PL = 101–167 W (Tdep = 792–945 K) ranged from 5.2 to 6.7, and it declined to 2.2 at PL = 182 W (Tdep = 970 K). Fig. 4 shows the effect of PL on surface and cross-sectional FESEM images of the CeO2 films. At PL = 17–85 W (Tdep = 685–767 K), the CeO2 films showed a granular morphology (Fig. 4(a)). At PL = 101– 167 W (Tdep = 792–945 K), the surface of the (100)-oriented CeO2 films had fine grains 100–200 nm in diameter consisting of granular facets. The cross section showed a columnar growth, corresponding with the highly textured (100) orientation (Fig. 2(b)). The CeO2 film
prepared at PL = 182 W (Tdep = 970 K) had a rough surface (Fig. 4(e)) and showed a dendritic growth. Fig. 5 shows the effects of PL (Tdep) on Rdep of CeO2 films prepared at PL = 101–167 W (Tdep = 792–945 K) comparing with literature data of conventional MOCVD [1,10,15,18,19]. In MOCVD, the Rdep increased with increasing Tdep and commonly less than several μm h−1 [10,15,19]. Their activation energies generally ranged from 15 to 45 kJ mol−1 [10,15,19], indicating a surface chemical reaction limited process [20]. In the present study, the activation energy was about 30 kJ mol−1, closely matching values reported in the literature [10,15,19]. Meanwhile, the Rdep increased 10 to 100 times faster than those reported in literature because the chemical reaction might be activated by laser irradiation. Table 1 gives the comparison on the preparation of CeO2 films on different substrates by MOCVD and LCVD. In the case of MOCVD, the formation of (100)-oriented CeO2 films needs single crystal substrates such as YSZ, MgO, TiO2 and Al2O3 (R-cut) [10,21–23], and high Tdep of 873–1073 K, while their Rdep were usually less than a few μm h−1 [10,21–23]. In the present study, highly (001)-oriented CeO2 films were deposited on polycrystalline Al2O3 substrate. The Tdep of (001)oriented CeO2 films was relatively low (Tdep = 792–945 K) whereas
Fig. 3. TC of the CeO2 films as a function of Tdep.
P. Zhao et al. / Surface & Coatings Technology 204 (2010) 3619–3622
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Fig. 4. Surface and cross-sectional FESEM images of CeO2 films prepared on Al2O3 substrates at Tvap = 523 K and at PL of 85 W (Tdep = 767 K) (a, b), 152 W (Tdep = 912 K) (c, d) and 182 W (Tdep = 970 K) (e, f).
the Rdep (43 μm h−1) was much higher than those of MOCVD [10,21– 23]. High-intensity and specially-oriented energy source of laser irradiation generated plasma around the deposition zone [24]. This plasma formation might have caused the highly-oriented CeO2 films in the present LCVD.
the maximum of 6.7 at PL = 113 W (Tdep = 836 K). The (100)-oriented CeO2 films showed granular grains in surface and columnar cross section. The highest value of Rdep of CeO2 films was 43 μm h−1 at PL = 152 W (Tdep = 912 K).
4. Conclusions
Acknowledgments
Highly (100)-oriented CeO2 films were prepared on Al2O3 substrates by LCVD at different PL. The TC of (200) reflection exhibited
This work was supported in part by the International Superconductivity Technology Center (ISTEC) and by the Global COE program of Materials Integration, Tohoku University.
Table 1 Preparation of CeO2 films by MOCVD and LCVD.
Fig. 5. Effect of Tdep on Rdep of CeO2 films.
CVD
Substrate
Tdep/K
MOCVD MOCVD MOCVD MOCVD MOCVD LCVD
YSZ (100) MgO (100) TiO2 (001) Al2O3 (1ī02) YSZ (100) Al2O3 (random)
673–1073 0.3–0.4 RG 673–1073 0.1–0.9 RG 723–1323 0.7–1.1 RG 973–1173 0.07 GG 723–923 0.04–0.06 GG 685–970 25–43 GG
GG: Granular grains. RG: Rectangular grains.
Rdep/ μm h−1
Morphology Orientation Ref. (100) (100) (100) (100) (100) (100)
[10] [10] [21] [19] [23] Present study
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P. Zhao et al. / Surface & Coatings Technology 204 (2010) 3619–3622
References [1] K. Fröhlich, J. Souc, D. Machajdík, M. Jergel, J. Snauwaert, L. Hellemans, Chem. Vap. Deposition 4 (1998) 216. [2] Y.S. Jiang, T. Kobayashi, T. Goto, IEEE Trans. Appl. Supercond. 9 (1999) 1657. [3] B.F. Cole, G.C. Liang, N. Newman, K. Char, G. Zaharchuk, J.S. Martens, Appl. Phys. Lett. (1992) 1727. [4] M. Maul, B. Schulte, P. Häussler, G. Frank, T. Steinborn, H. Fuess, J. Appl. Phys. 74 (1993) 2942. [5] A.G. Zaitsev, R. Wördenweber, G. Ockenfuβ, R. Kutzner, T. Königs, C. Zuccaro, N. Klein, IEEE Trans. Appl. Supercond. 7 (1997) 1482. [6] Z. Lu, R. Hiskes, S.A. DiCarolis, A. Nel, R.K. Route, R.S. Feigelson, J. Crystal Growth 156 (1995) 227. [7] K. Fröhlich, D. Machajdík, I. Vávra, J. Šouc, A. Rosovfá, A. Figueras, F. Weiss, K.H. Dahmen, J. Alloys Compd. 251 (1997) 284. [8] J.C. Nie, H. Yamasaki, K.D. Bagarinao, Y. Nakagawa, IEEE Trans. Appl. Supercond. 17 (2007) 3459. [9] R.G. Schwab, R.A. Steiner, G. Mages, H.J. Beie, Thin Solid Films 207 (1992) 288. [10] M. Becht, T. Morishita, Chem. Vap. Deposition 2 (1996) 191.
[11] G.L. Skofronick, A.H. Carim, S.R. Folty, R.E. Muenchhausen, J. Mater. Res. 8 (1993) 2785. [12] S. Guo, H. Arwin, S.N. Jacobson, K. Jarrendahl, U. Helmersson, J. Appl. Phys. 77 (1995) 5369. [13] F. Wang, R. Wordenweber, Thin Solid Films 227 (1993) 200. [14] B. Tatar, E.D. Sam, K. Kutlu, M. Ürgen, J. Mater. Sci. 43 (2008) 5102. [15] S. Liang, C.S. Chern, Z.Q. Shi, P. Lu, B.H. Kear, J. Cryst. Growth 151 (1995) 359. [16] T. Goto, T. Kimura, Thin Solid Films 515 (2006) 46. [17] T. Goto, R. Banal, T. Kimura, Surf. Coat. Technol. 201 (2007) 5776. [18] M. Maul, B. Schulte, P. Häussler, G. Frank, T. Steinborn, H. Fuess, H. Adrian, J. Appl. Phys. 74 (15) (1993) 2492. [19] C.Y. Tian, Y. Du, S.W. Chan, J. Vac. Sci. Technol. A 15 (1997) 85. [20] W.A. Bryant, J. Mater. Sci. 12 (1997) 1285. [21] R.L. Nigro, R. Toro, G. Malandrino, I.L. Fragala, Chem. Mater. 15 (2003) 1434. [22] K. Fröhlich, D. Machajdik, L. Hellemans, J. Snauwaert, J. Phys. IV France 9 (1999) Pr8-341. [23] A.C. Wang, J.A. Belot, T.J. Marks, P.R. Markworth, R.P.H. Chang, M.P. Chudzik, C.R. Kannewurf, Physica C 320 (1999) 154. [24] H. Miyazaki, T. Kimura, T. Goto, Jpn. J. Appl. Phys. 42 (2003) L316.
Contents lists available at ScienceDirect
Surface & Coatings Technology 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 / s u r f c o a t
Preparation of highly (100)-oriented CeO2 films on polycrystalline Al2O3 substrates by laser chemical vapor deposition Pei Zhao, Akihiko Ito, Rong Tu, Takashi Goto ⁎ Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan
a r t i c l e
i n f o
Article history: Received 2 February 2010 Accepted in revised form 13 April 2010 Available online 18 April 2010 Keywords: Laser chemical vapor deposition CeO2 film High deposition rate
a b s t r a c t CeO2 films were prepared on Al2O3 substrates by laser chemical vapor deposition at different laser power (PL) up to 182 W. The (100)-oriented CeO2 films were prepared at PL = 101–167 W (Tdep = 792–945 K). The texture coefficient (TC) of (200) reflection had a maximum of 6.7 at PL = 113 W (Tdep = 836 K). The (100)oriented CeO2 films consisted of granular grains and showed a columnar cross section. The deposition rates (Rdep) of (100)-oriented CeO2 films showed a maximum of 43 μm h−1 at PL = 152 W (Tdep = 912 K). © 2010 Elsevier B.V. All rights reserved.
1. Introduction Since Al2O3 substrate is superior in corrosion-resistance, dielectric constant and cost effectiveness comparing with MgO, SrTiO3 and LaAlO3 substrates [1,2], Al2O3 is an attractive substrate for the production of YBa2Cu3O7 − δ (YBCO) superconducting films for various microwave devices such as resonators, filters and delay lines [1–3]. C-axis oriented YBCO thin films can be deposited on signal-crystal Al2O3 substrate [2–5]; however, Al2O3 substrate often reacts with Ba and deteriorates the c-axis orientation of YBCO film at elevated temperatures [1]. Therefore, an intermediate buffer layer should be deposited on Al2O3 substrate as diffusion barrier. Ceria (CeO2) film can be a promising candidate for the buffer layer because it has a fluorite structure (a = 5.411 Å) with a lattice mismatch less than 1% between CeO2 (200) and YBCO (110) planes [6,7]. This favors epitaxial growth of YBCO film with almost no distortion on CeO2 layer. Furthermore, a similar thermal expansion of CeO2 (9.5–12.3 × 10−6 K−1) [5] and YBCO (13 × 10−6 K−1) [8] can ensure the formation of crack-free YBCO film on CeO2 layer. Since CeO2 is stable between 298 to 1473 K [9,10], CeO2 can prevent the reaction between the substrate and YBCO film. Many deposition methods to prepare CeO2 films such as pulsed laser deposition (PLD) [11], magnetron sputtering [12,13], electronbeam evaporation [19], and metalorganic chemical vapor deposition (MOCVD) [6,10,15] have been reported. Highly (100)-oriented CeO2 films have been usually obtained on signal-crystal (R-cut sapphire) Al2O3 substrates [6,10–15]. On the other hand, polycrystalline Al2O3 substrate is more commonly available and cost-effective than signal-
⁎ Corresponding author. E-mail address: [email protected] (T. Goto). 0257-8972/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2010.04.037
crystal Al2O3, and therefore it is beneficial to prepare highly (100)oriented CeO2 buffer layer on polycrystalline Al2O3 substrate. We have reported the preparation of oxide and non-oxide films such as TiO2 [16], YSZ [16] and Y2O3 [17] by using laser chemical vapor deposition (LCVD). This LCVD can prepare many kinds of films at a significantly high Rdep with strongly preferred orientation on polycrystalline substrates. In the present study, we have prepared CeO2 films on polycrystalline Al2O3 substrates by LCVD, and mainly investigated the effect of laser power on the orientation, deposition rate, and microstructure of CeO2 films.
2. Experimental CeO2 films were prepared on polycrystalline Al2O3 substrates (10 mm × 10 mm × 2.5 mm) by LCVD using Ce(DPM)4 (DPM; dipivaloymethanate) as precursor. The experimental setup of the LCVD apparatus is shown in Fig. 1. A continuous wave Nd:YAG laser (wavelength: 1064 nm) was employed at laser power output (PL) from 17 to 182 W. 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 substrates were heated on a heating stage at a pre-heating temperature (Tpre) of 673 K. The deposition temperature (Tdep) was measured with a thermocouple inserted at the back side of the substrate. The flow rates of Ar and O2 gases were both 1.7 × 10−6 m3s−1. The vaporization temperature (Tvap) of the Ce precursor was maintained at 523 K. The temperature of all the gas lines was maintained at 573 K to prevent the condensation of precursor during the transportation. The total pressure (Ptot) in the CVD chamber was held at 800 Pa. The deposition was conducted for 600 s. The distance between the nozzle and the substrate was 25 mm.
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P. Zhao et al. / Surface & Coatings Technology 204 (2010) 3619–3622
Fig. 2. XRD patterns of the CeO2 film prepared on Al2O3 substrates at Tvap = 523 K and at different PL of 85 W (Tdep = 767 K) (a), 152 W (Tdep = 912 K) (b) and 182 W (Tdep = 970 K) (c). Fig. 1. The schematic of the LCVD apparatus.
The phase and crystallinity were studied by using X-ray diffraction (XRD; Rigaku RAD-2C; θ–2θ, ω-scan (rocking curve)). The degree of orientation on (200) reflection was calculated by the Harris texture coefficient (TC):
TCðhklÞ = N
Im ðhklÞ = I0 ðhklÞ ; ∑Im ðhklÞ = I0 ðhklÞ
ð1Þ
where Im(hkl) and I0(hkl) are the intensity from the (100) plane measured in the present study and that reported in JCPDS card (No. 43-1002), respectively. (111), (200), (220), (311), (222), (400), (331) and (420) reflections were used for the calculation (N = 8). The microstructure was observed by a field emission scanning electron microscope (FESEM; JEOL JSM-7500F). 3. Results and discussion Fig. 2 shows typical XRD patterns at P L = 17–182 W. The deposition temperatures (Tdep) ranged from 685 to 970 K at PL of 17–182 W. Crystalline CeO2 films were prepared at PL = 17–85 W (Tdep = 685–767 K), where the diffraction peaks were slightly broad (Fig. 2(a)). With increasing PL from 17 to 85 W, the (100) preferred orientation became sharper. At PL = 101–167 W (Tdep = 792–945 K), highly (100)-oriented CeO2 films were prepared (Fig. 2(b)). The orientation changed from (100) to (311) plane at PL = 182 W (Tdep = 970 K) (Fig. 2(c)). Fig. 3 shows the effect of PL on TC (200) of CeO2 films. The TC increased from 1.1 to 3.6 with increasing PL from 17 to 85 W (Tdep from 685 to 767 K). The TC of highly (100)-oriented CeO2 films prepared at PL = 101–167 W (Tdep = 792–945 K) ranged from 5.2 to 6.7, and it declined to 2.2 at PL = 182 W (Tdep = 970 K). Fig. 4 shows the effect of PL on surface and cross-sectional FESEM images of the CeO2 films. At PL = 17–85 W (Tdep = 685–767 K), the CeO2 films showed a granular morphology (Fig. 4(a)). At PL = 101– 167 W (Tdep = 792–945 K), the surface of the (100)-oriented CeO2 films had fine grains 100–200 nm in diameter consisting of granular facets. The cross section showed a columnar growth, corresponding with the highly textured (100) orientation (Fig. 2(b)). The CeO2 film
prepared at PL = 182 W (Tdep = 970 K) had a rough surface (Fig. 4(e)) and showed a dendritic growth. Fig. 5 shows the effects of PL (Tdep) on Rdep of CeO2 films prepared at PL = 101–167 W (Tdep = 792–945 K) comparing with literature data of conventional MOCVD [1,10,15,18,19]. In MOCVD, the Rdep increased with increasing Tdep and commonly less than several μm h−1 [10,15,19]. Their activation energies generally ranged from 15 to 45 kJ mol−1 [10,15,19], indicating a surface chemical reaction limited process [20]. In the present study, the activation energy was about 30 kJ mol−1, closely matching values reported in the literature [10,15,19]. Meanwhile, the Rdep increased 10 to 100 times faster than those reported in literature because the chemical reaction might be activated by laser irradiation. Table 1 gives the comparison on the preparation of CeO2 films on different substrates by MOCVD and LCVD. In the case of MOCVD, the formation of (100)-oriented CeO2 films needs single crystal substrates such as YSZ, MgO, TiO2 and Al2O3 (R-cut) [10,21–23], and high Tdep of 873–1073 K, while their Rdep were usually less than a few μm h−1 [10,21–23]. In the present study, highly (001)-oriented CeO2 films were deposited on polycrystalline Al2O3 substrate. The Tdep of (001)oriented CeO2 films was relatively low (Tdep = 792–945 K) whereas
Fig. 3. TC of the CeO2 films as a function of Tdep.
P. Zhao et al. / Surface & Coatings Technology 204 (2010) 3619–3622
3621
Fig. 4. Surface and cross-sectional FESEM images of CeO2 films prepared on Al2O3 substrates at Tvap = 523 K and at PL of 85 W (Tdep = 767 K) (a, b), 152 W (Tdep = 912 K) (c, d) and 182 W (Tdep = 970 K) (e, f).
the Rdep (43 μm h−1) was much higher than those of MOCVD [10,21– 23]. High-intensity and specially-oriented energy source of laser irradiation generated plasma around the deposition zone [24]. This plasma formation might have caused the highly-oriented CeO2 films in the present LCVD.
the maximum of 6.7 at PL = 113 W (Tdep = 836 K). The (100)-oriented CeO2 films showed granular grains in surface and columnar cross section. The highest value of Rdep of CeO2 films was 43 μm h−1 at PL = 152 W (Tdep = 912 K).
4. Conclusions
Acknowledgments
Highly (100)-oriented CeO2 films were prepared on Al2O3 substrates by LCVD at different PL. The TC of (200) reflection exhibited
This work was supported in part by the International Superconductivity Technology Center (ISTEC) and by the Global COE program of Materials Integration, Tohoku University.
Table 1 Preparation of CeO2 films by MOCVD and LCVD.
Fig. 5. Effect of Tdep on Rdep of CeO2 films.
CVD
Substrate
Tdep/K
MOCVD MOCVD MOCVD MOCVD MOCVD LCVD
YSZ (100) MgO (100) TiO2 (001) Al2O3 (1ī02) YSZ (100) Al2O3 (random)
673–1073 0.3–0.4 RG 673–1073 0.1–0.9 RG 723–1323 0.7–1.1 RG 973–1173 0.07 GG 723–923 0.04–0.06 GG 685–970 25–43 GG
GG: Granular grains. RG: Rectangular grains.
Rdep/ μm h−1
Morphology Orientation Ref. (100) (100) (100) (100) (100) (100)
[10] [10] [21] [19] [23] Present study
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References [1] K. Fröhlich, J. Souc, D. Machajdík, M. Jergel, J. Snauwaert, L. Hellemans, Chem. Vap. Deposition 4 (1998) 216. [2] Y.S. Jiang, T. Kobayashi, T. Goto, IEEE Trans. Appl. Supercond. 9 (1999) 1657. [3] B.F. Cole, G.C. Liang, N. Newman, K. Char, G. Zaharchuk, J.S. Martens, Appl. Phys. Lett. (1992) 1727. [4] M. Maul, B. Schulte, P. Häussler, G. Frank, T. Steinborn, H. Fuess, J. Appl. Phys. 74 (1993) 2942. [5] A.G. Zaitsev, R. Wördenweber, G. Ockenfuβ, R. Kutzner, T. Königs, C. Zuccaro, N. Klein, IEEE Trans. Appl. Supercond. 7 (1997) 1482. [6] Z. Lu, R. Hiskes, S.A. DiCarolis, A. Nel, R.K. Route, R.S. Feigelson, J. Crystal Growth 156 (1995) 227. [7] K. Fröhlich, D. Machajdík, I. Vávra, J. Šouc, A. Rosovfá, A. Figueras, F. Weiss, K.H. Dahmen, J. Alloys Compd. 251 (1997) 284. [8] J.C. Nie, H. Yamasaki, K.D. Bagarinao, Y. Nakagawa, IEEE Trans. Appl. Supercond. 17 (2007) 3459. [9] R.G. Schwab, R.A. Steiner, G. Mages, H.J. Beie, Thin Solid Films 207 (1992) 288. [10] M. Becht, T. Morishita, Chem. Vap. Deposition 2 (1996) 191.
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