- Email: [email protected]
Behavior of Ag photodoping in sulfide bulk glasses
Journal of Non-Crystalline Solids 352 (2006) 2643–2646 www.elsevier.com/locate/jnoncrysol
Behavior of Ag photodoping in sulfide bulk glasses R. Kitagawa a
a,*
, H. Takebe b, M. Kuwabara
b
Department of Applied Science for Electronics and Materials, Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan b Department of Engineering Sciences for Electronics and Materials, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan Available online 24 May 2006
Abstract The relationship between Ag photodoping behavior and glass structure has been studied using various sulfide bulk glasses. The transmission measurement revealed that the photodoping rate increased with an increase of S concentration in Ge–S glasses and GeS2–SbS2 glasses, while the disappearance of Ag film was not be observed in Ge40S60 and Ga2S3-based glasses, which contain modifier ions. The correlation between photodoping rate and S–S bond content in a host glass was confirmed. From the point of view of the behavior of Ag photodoping, sulfide glasses were classified into two groups: (1) a covalent glasses containing S–S bonds and (2) an ionic glasses containing modified ions. Ó 2006 Elsevier B.V. All rights reserved. PACS: 61.43.Dq; 66.30. h Keywords: Composition; Chalcogenides; Photoinduced effects; Structure
1. Introduction The dissolution of some metals, such as Ag or Cu, into chalcogenide glasses under an illumination of light, called photodoping or photodissolution, is one of the photoinduced phenomena in chalcogenide glasses. This phenomenon has been investigated by many researchers since Kostyshin et al. reported [1]. In most studies, Ag metal is used as a dopant and the kinetics of photodoping has been studied. Several models have been proposed from the results of chalcogenide glass thin film [2]. However, these models are based on the structure model of a bulk glass although glass structures and properties are different between bulk and thin film because of their preparation methods [3]. Recently, several optical devices, such as waveguide [4] and one-dimensional photonic crystal [5], were prepared using photodoping. However, the design and preparation *
Corresponding author. Tel.: +81 92 583 7529; fax: +81 92 575 7529. E-mail address: [email protected] (R. Kitagawa).
0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.03.047
of these applications using photodoping is still difficult because the relationship between glass structure and photodoping behavior is unknown. In the present paper, the effect of glass-composition and -structure were studied using several sulfide bulk glasses which have well known glass structure. The classification of glass structure regarding photodoping behavior was also shown. 2. Experimental Sulfide glasses of various systems, such as Ge–S, Ge–Sb–S, La2S3–Ga2S3 and BaS–Ga2S3, were prepared by a conventional melt-quenching method. The glass preparation process has been described elsewhere [6,7]. Ag films with a thickness of 25 nm were deposited on a polished glass plate with a thickness of 0.5 mm by a vacuum evaporation. These samples were illuminated using UV light at 365 nm with an intensity of 0.7 mW/cm2. The illumination was carried out from the Ag film side of the sample in the dark at room temperature. In this study, the disappearance
time of the Ag film on a glass plate was determined by a saturation point of the change of transmittance at 800 nm under an illumination time. It is reported that the photodoping rate by an illumination of a longer wavelength than the absorption edge of a host glass is negligible small [8]. Therefore, the light at a wavelength of 800 nm was employed to avoid photodoping during the transmittance measurement. The photodoping rate was calculated by the ratio of Ag thickness (nm) and Ag disappearance time (min). The disappearance of Ag film was also confirmed by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. Glass structures of the prepared glass samples were characterized by Raman spectroscopy using an Ar+ ion laser at 514.5 nm. The laser intensity was controlled less than 1 mW to avoid sample damage. 3. Results
1.0
(a)
0.8 0.6 0.4 0.2 0.0 0.8
(b) 0.6 0.4 0.2 0.0
Fig. 1 shows the changes of optical transmittance at 800 nm of Ag/Ge–S and Ag/Ga2S3-based glasses under an illumination of UV light. The transmittances of Ag/Ge–S samples increased with an increase of illumination time because of Ag photodoping. However, the change of the transmittance was not confirmed in Ag/Ge40S60 within 17 h. In Ag/Ga2S3-based glass samples, the transmittance remained constant. From the results of SEM observation near the Ag film of samples after an illumination for 24 h, the disappearance of Ag film was confirmed in Ag/Ge–S samples except Ag/Ge40S60. XRD analysis also revealed that the diffraction patterns of Ag/Ge–S samples showed halo-pattern after an illumination for 24 h, while Ag phase was confirmed on the surface of Ag/Ge40S60 and Ag/Ga2S3-based glass samples. Fig. 2(a) shows the compositional dependences of photodoping rate in Ag/Ge–S samples. Photodoping rate increased with an increase of S content in Ge–S glasses.
70
Ge15S85
50 40 30 20
30La2S3S-70Ga2S3 Ge40S60
10
90
Fig. 2(b) shows the compositional dependences of the relative Raman intensity of the peak at 475 cm 1 in Ge–S glasses, which is assigned to the stretching A1 mode of S–S bond [9]. The peak intensity at 475 cm 1 was normalized by the peak intensity of A1 mode GeS4 tetrahedra at 342 cm 1. It is reported that the glass structure of Ge100 xSx consists of GeS4 tetrahedron, S–S bond and S8 ring depending on S concentration [9]. In S-rich glasses (x > 67), the relative amount of S–S bond increases with an increase of S concentration. From Fig. 2(a) and (b), it is found that Ag photodoping rate is closely related to S–S bond content in a host glass. To investigate the effect of glass network unit on Ag photodoping behavior, the compositional dependence of photodoping rate in Ge–Sb–S glasses was studied. Fig. 3
400
Ag/(100-y)GeS2-ySbS2
0.5
0.4
0.3
0.2
Ag/(100-y)GeS2-ySbS1.5
0.1
65BaS-35Ga2S3
200
80
Ge33S67
Ge38S62
0
70
Fig. 2. The composition dependences of (a) Ag photodoping rate and (b) relative Raman intensity of S–S bond peak at 475 cm 1 in Ge–S glasses.
60
0
60
S (at%)
Photodoping rate (nm/min)
Transmittance at 800 nm (%)
Photodoping rate (nm/min)
R. Kitagawa et al. / Journal of Non-Crystalline Solids 352 (2006) 2643–2646
I475 cm-1 /I342 cm-1
2644
600
800
1000
Time (min) Fig. 1. Changes of optical transmittance at 800 nm under an illumination of UV lamp.
0
20
40
60
80
y (mol%) Fig. 3. The composition dependences of Ag photodoping rate in Ge–Sb–S glasses.
R. Kitagawa et al. / Journal of Non-Crystalline Solids 352 (2006) 2643–2646
2645
Fig. 4. Schematic drawings of the classified two-dimensional glass structures regarding Ag photodoping behavior. (a) A covalent glass structure containing S–S bond, and (b) an ionic glass structure containing modifier cations.
shows the compositional dependence of Ag photodoping rate in Ag/Ge–Sb–S samples. The glass network of Ge–Sb–S glass system consists of a mixture of GeS4 tetrahedron and SbS3 pyramid [10]. In GeS2–SbS1.5 glass system, the glass network consists of stoichiometric component, i.e., GeS4 tetrahedron and SbS3 pyramid, while S–S bond also exist in GeS2–SbS2 glass [10]. As shown in Fig. 3, Ag photodoping rate increased with y content in Ag/GeS2–SbS2 samples. On the other hand, the compositional dependence of photodoping rate in Ag/GeS2– SbS1.5 remained stable compared with Ag/GeS2–SbS2 samples. From this result, it is considered that the effect of S–S content is dominant on photodoping rate rather than that of glass network former. 4. Discussion Kluge explained that photodoping phenomenon is a kind of a solid state reaction as an intercalation of an amorphous solid [11]. He also suggested that the host matrix has to provide empty interatomic volumes for an additional accommodation of the guest ions which are related to regions of occurring van der Waals bonding. From the result of Fig. 1, Ag photodoping was not confirmed in Ge40S60 and Ga2S3-based glasses on the illumination condition employed in this study. From the point of view of glass structure, it is known that these glasses have the network modifier ions, such as Ge2+ and La3+ [9,12]. On the other hand, S-rich Ge–S and GeS2–SbS2 glasses, which exhibited Ag photodoping, contain S–S bonds. In Fig. 2(a) and (b), the photodoping rate was related to S–S bond content in a host glass compared with network former unit. In the case of the evaporated Ge–S glass thin films [13], the dissolution of Ag film is confirmed in Ge100 xSx (x < 60) glass and the compositional dependence of photodoping rate has a minimum around the stoichiometric composition GeS2. The difference of photodoping behavior between the thin film and the bulk is attributed to the difference of a glass structure. It is known that the
glass structure of the evaporated glass thin film contains homopolar bonds, i.e., S–S and Ge–Ge [3], which leads to a higher electrical conductivity compared with the bulk glass [14]. Therefore, it is considered that the homopolar bonds in a host glass play an important role for the migration of Ag ions. As shown in Fig. 2(a), the gradient of photodoping rate changed around Ge20S80 in Ag/Ge–S. It is considered that the enhancement of photodoping rate is attributed to S8 ring, which is formed over S content of 80 at.% in Ge–S glasses [9], because the interatomic volumes increase in a host glass. These results support the intercalation reaction mechanism. It could be said that S–S bond play role as a channel of a migration of Ag ion. In fact, Extended X-ray absorption fine structure (EXAFS) analysis revealed that the silver occupy sites covalently bonded to neighboring chalcogen atoms in Ag photodoped glasses [15,16]. Fig. 4 shows the classified glass structure regarding Ag photodoping behavior. In the beginning of photodoping process, Ag ions, which are ionized by an illumination of light [17], migrates inside glass through S–S bond region as a channel. The region formed by S–S bond show a high covalent and S–S bond is broken by Ag ions due to an illumination of light. Finally, Ag–S bond is formed [15,16]. In the case of a glass structure containing modifier cations (see Fig. 4(b)), such as Ge40S60 and Ga2S3-based glasses, these modifier cations are connected to sulfur ions strongly because the ionicities of these ions are higher than that of Ag ion. This situation makes the incursion of Ag ions toward glass network difficult. Therefore, Ag photodoping could not be observed in this glass structure. 5. Conclusions In this study, we investigated the effect of glass-composition and -structure on Ag photodoping behavior using various sulfide bulk glasses which have well known glass structures. The transmission measurement revealed that the behavior of Ag photodoping depends on glass-system
2646
R. Kitagawa et al. / Journal of Non-Crystalline Solids 352 (2006) 2643–2646
and -composition. In S-rich Ge–S and GeS2–SbS2 glasses, the photodoping rate increases as S concentration increased, while Ag photodoping was not observed in Ge40S60 and Ga2S3-based glasses which contain modifier ions. Raman spectroscopy revealed that photodoping rate correlates with S–S bond concentration and sulfur molecular type in a host glass. Our experimental results are explained by an intercalation model. From the point of Ag photodoping behavior, sulfide glasses can be classified into a covalent glasses containing S–S bonds (active glass) and ionic glasses containing modifier ions (inert glass). References [1] M.T. Kostyshin, E.V. Mikhailovskaya, P.F. Romanenko, Sov. Phys. Solid State 8 (1966) 451. [2] A.V. Kolobov, S.R. Elliott, Adv. Phys. 40 (1991) 625. [3] K. Tanaka, Y. Kasanuki, A. Odajima, Thin Solid Films 117 (1984) 251. [4] R.M. Bryce, H.T. Nguyen, P. Nakeeran, R.G. DeCorby, P.K. Dwivedi, C.J. Haugen, S.O. Kasap, J. Vac. Sci. Technol. A 22 (2004) 1044.
[5] H. Lee, T. Yao, J. Vac. Sci. Technol. B 20 (2002) 2017. [6] H. Takebe, K. Morinaga, Proceeding of 2nd International Conference on Processing Materials for Properties, in: M. Mishra, C. Yamaguchi (Eds.), The minerals, Metals & Materials Society, 2000, p. 205. [7] D.W. Hewak, J.A. Medeiros Net, B. Samson, R.S. Brown, K.P. Jedrzejewski, J. Wang, E. Taylor, R.I. Laming, G. Wylangowski, D.N. Payne, IEEE Photo. Technol. Lett. 6 (1994) 609. [8] D. Goldschmidt, P.S. Rudman, J. Non-Cryst. Solids 22 (1976) 229. [9] H. Takebe, H. Maeda, K. Morinaga, J. Non-Cryst. Solids 291 (2001) 14. [10] H. Takebe, T. Hirakawa, T. Ichiki, K. Morinaga, J. Ceram. Soc. Jpn. 111 (2003) 572. [11] G. Kluge, Phys. Stat. Sol. (a) 101 (1987) 105. [12] S. Benazeth, M.H. Tulier, A.M. Loireau-Lozac’h, H. Dexpert, P. Lagarde, J. Flahaut, J. Non-Cryst. Solids 110 (1989) 89. [13] T. Kawaguchi, S. Maruno, J. Appl. Phys. 71 (1992) 2195. [14] I. Watanabe, T. Maeda, T. Shimizu, J. Non-Cryst. Solids 37 (1980) 335. [15] J.M. Oldale, J. Rennie, S.R. Elliott, Thin Solid Films 164 (1988) 467. [16] A.T. Steel, G.N. Greaves, A.P. Firth, A.E. Owen, J. Non-Cryst. Solids 107 (1989) 155. [17] S.R. Elliott, J. Non-Cryst. Solids 130 (1991) 85.
Behavior of Ag photodoping in sulfide bulk glasses R. Kitagawa a
a,*
, H. Takebe b, M. Kuwabara
b
Department of Applied Science for Electronics and Materials, Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan b Department of Engineering Sciences for Electronics and Materials, Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan Available online 24 May 2006
Abstract The relationship between Ag photodoping behavior and glass structure has been studied using various sulfide bulk glasses. The transmission measurement revealed that the photodoping rate increased with an increase of S concentration in Ge–S glasses and GeS2–SbS2 glasses, while the disappearance of Ag film was not be observed in Ge40S60 and Ga2S3-based glasses, which contain modifier ions. The correlation between photodoping rate and S–S bond content in a host glass was confirmed. From the point of view of the behavior of Ag photodoping, sulfide glasses were classified into two groups: (1) a covalent glasses containing S–S bonds and (2) an ionic glasses containing modified ions. Ó 2006 Elsevier B.V. All rights reserved. PACS: 61.43.Dq; 66.30. h Keywords: Composition; Chalcogenides; Photoinduced effects; Structure
1. Introduction The dissolution of some metals, such as Ag or Cu, into chalcogenide glasses under an illumination of light, called photodoping or photodissolution, is one of the photoinduced phenomena in chalcogenide glasses. This phenomenon has been investigated by many researchers since Kostyshin et al. reported [1]. In most studies, Ag metal is used as a dopant and the kinetics of photodoping has been studied. Several models have been proposed from the results of chalcogenide glass thin film [2]. However, these models are based on the structure model of a bulk glass although glass structures and properties are different between bulk and thin film because of their preparation methods [3]. Recently, several optical devices, such as waveguide [4] and one-dimensional photonic crystal [5], were prepared using photodoping. However, the design and preparation *
Corresponding author. Tel.: +81 92 583 7529; fax: +81 92 575 7529. E-mail address: [email protected] (R. Kitagawa).
0022-3093/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.03.047
of these applications using photodoping is still difficult because the relationship between glass structure and photodoping behavior is unknown. In the present paper, the effect of glass-composition and -structure were studied using several sulfide bulk glasses which have well known glass structure. The classification of glass structure regarding photodoping behavior was also shown. 2. Experimental Sulfide glasses of various systems, such as Ge–S, Ge–Sb–S, La2S3–Ga2S3 and BaS–Ga2S3, were prepared by a conventional melt-quenching method. The glass preparation process has been described elsewhere [6,7]. Ag films with a thickness of 25 nm were deposited on a polished glass plate with a thickness of 0.5 mm by a vacuum evaporation. These samples were illuminated using UV light at 365 nm with an intensity of 0.7 mW/cm2. The illumination was carried out from the Ag film side of the sample in the dark at room temperature. In this study, the disappearance
time of the Ag film on a glass plate was determined by a saturation point of the change of transmittance at 800 nm under an illumination time. It is reported that the photodoping rate by an illumination of a longer wavelength than the absorption edge of a host glass is negligible small [8]. Therefore, the light at a wavelength of 800 nm was employed to avoid photodoping during the transmittance measurement. The photodoping rate was calculated by the ratio of Ag thickness (nm) and Ag disappearance time (min). The disappearance of Ag film was also confirmed by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. Glass structures of the prepared glass samples were characterized by Raman spectroscopy using an Ar+ ion laser at 514.5 nm. The laser intensity was controlled less than 1 mW to avoid sample damage. 3. Results
1.0
(a)
0.8 0.6 0.4 0.2 0.0 0.8
(b) 0.6 0.4 0.2 0.0
Fig. 1 shows the changes of optical transmittance at 800 nm of Ag/Ge–S and Ag/Ga2S3-based glasses under an illumination of UV light. The transmittances of Ag/Ge–S samples increased with an increase of illumination time because of Ag photodoping. However, the change of the transmittance was not confirmed in Ag/Ge40S60 within 17 h. In Ag/Ga2S3-based glass samples, the transmittance remained constant. From the results of SEM observation near the Ag film of samples after an illumination for 24 h, the disappearance of Ag film was confirmed in Ag/Ge–S samples except Ag/Ge40S60. XRD analysis also revealed that the diffraction patterns of Ag/Ge–S samples showed halo-pattern after an illumination for 24 h, while Ag phase was confirmed on the surface of Ag/Ge40S60 and Ag/Ga2S3-based glass samples. Fig. 2(a) shows the compositional dependences of photodoping rate in Ag/Ge–S samples. Photodoping rate increased with an increase of S content in Ge–S glasses.
70
Ge15S85
50 40 30 20
30La2S3S-70Ga2S3 Ge40S60
10
90
Fig. 2(b) shows the compositional dependences of the relative Raman intensity of the peak at 475 cm 1 in Ge–S glasses, which is assigned to the stretching A1 mode of S–S bond [9]. The peak intensity at 475 cm 1 was normalized by the peak intensity of A1 mode GeS4 tetrahedra at 342 cm 1. It is reported that the glass structure of Ge100 xSx consists of GeS4 tetrahedron, S–S bond and S8 ring depending on S concentration [9]. In S-rich glasses (x > 67), the relative amount of S–S bond increases with an increase of S concentration. From Fig. 2(a) and (b), it is found that Ag photodoping rate is closely related to S–S bond content in a host glass. To investigate the effect of glass network unit on Ag photodoping behavior, the compositional dependence of photodoping rate in Ge–Sb–S glasses was studied. Fig. 3
400
Ag/(100-y)GeS2-ySbS2
0.5
0.4
0.3
0.2
Ag/(100-y)GeS2-ySbS1.5
0.1
65BaS-35Ga2S3
200
80
Ge33S67
Ge38S62
0
70
Fig. 2. The composition dependences of (a) Ag photodoping rate and (b) relative Raman intensity of S–S bond peak at 475 cm 1 in Ge–S glasses.
60
0
60
S (at%)
Photodoping rate (nm/min)
Transmittance at 800 nm (%)
Photodoping rate (nm/min)
R. Kitagawa et al. / Journal of Non-Crystalline Solids 352 (2006) 2643–2646
I475 cm-1 /I342 cm-1
2644
600
800
1000
Time (min) Fig. 1. Changes of optical transmittance at 800 nm under an illumination of UV lamp.
0
20
40
60
80
y (mol%) Fig. 3. The composition dependences of Ag photodoping rate in Ge–Sb–S glasses.
R. Kitagawa et al. / Journal of Non-Crystalline Solids 352 (2006) 2643–2646
2645
Fig. 4. Schematic drawings of the classified two-dimensional glass structures regarding Ag photodoping behavior. (a) A covalent glass structure containing S–S bond, and (b) an ionic glass structure containing modifier cations.
shows the compositional dependence of Ag photodoping rate in Ag/Ge–Sb–S samples. The glass network of Ge–Sb–S glass system consists of a mixture of GeS4 tetrahedron and SbS3 pyramid [10]. In GeS2–SbS1.5 glass system, the glass network consists of stoichiometric component, i.e., GeS4 tetrahedron and SbS3 pyramid, while S–S bond also exist in GeS2–SbS2 glass [10]. As shown in Fig. 3, Ag photodoping rate increased with y content in Ag/GeS2–SbS2 samples. On the other hand, the compositional dependence of photodoping rate in Ag/GeS2– SbS1.5 remained stable compared with Ag/GeS2–SbS2 samples. From this result, it is considered that the effect of S–S content is dominant on photodoping rate rather than that of glass network former. 4. Discussion Kluge explained that photodoping phenomenon is a kind of a solid state reaction as an intercalation of an amorphous solid [11]. He also suggested that the host matrix has to provide empty interatomic volumes for an additional accommodation of the guest ions which are related to regions of occurring van der Waals bonding. From the result of Fig. 1, Ag photodoping was not confirmed in Ge40S60 and Ga2S3-based glasses on the illumination condition employed in this study. From the point of view of glass structure, it is known that these glasses have the network modifier ions, such as Ge2+ and La3+ [9,12]. On the other hand, S-rich Ge–S and GeS2–SbS2 glasses, which exhibited Ag photodoping, contain S–S bonds. In Fig. 2(a) and (b), the photodoping rate was related to S–S bond content in a host glass compared with network former unit. In the case of the evaporated Ge–S glass thin films [13], the dissolution of Ag film is confirmed in Ge100 xSx (x < 60) glass and the compositional dependence of photodoping rate has a minimum around the stoichiometric composition GeS2. The difference of photodoping behavior between the thin film and the bulk is attributed to the difference of a glass structure. It is known that the
glass structure of the evaporated glass thin film contains homopolar bonds, i.e., S–S and Ge–Ge [3], which leads to a higher electrical conductivity compared with the bulk glass [14]. Therefore, it is considered that the homopolar bonds in a host glass play an important role for the migration of Ag ions. As shown in Fig. 2(a), the gradient of photodoping rate changed around Ge20S80 in Ag/Ge–S. It is considered that the enhancement of photodoping rate is attributed to S8 ring, which is formed over S content of 80 at.% in Ge–S glasses [9], because the interatomic volumes increase in a host glass. These results support the intercalation reaction mechanism. It could be said that S–S bond play role as a channel of a migration of Ag ion. In fact, Extended X-ray absorption fine structure (EXAFS) analysis revealed that the silver occupy sites covalently bonded to neighboring chalcogen atoms in Ag photodoped glasses [15,16]. Fig. 4 shows the classified glass structure regarding Ag photodoping behavior. In the beginning of photodoping process, Ag ions, which are ionized by an illumination of light [17], migrates inside glass through S–S bond region as a channel. The region formed by S–S bond show a high covalent and S–S bond is broken by Ag ions due to an illumination of light. Finally, Ag–S bond is formed [15,16]. In the case of a glass structure containing modifier cations (see Fig. 4(b)), such as Ge40S60 and Ga2S3-based glasses, these modifier cations are connected to sulfur ions strongly because the ionicities of these ions are higher than that of Ag ion. This situation makes the incursion of Ag ions toward glass network difficult. Therefore, Ag photodoping could not be observed in this glass structure. 5. Conclusions In this study, we investigated the effect of glass-composition and -structure on Ag photodoping behavior using various sulfide bulk glasses which have well known glass structures. The transmission measurement revealed that the behavior of Ag photodoping depends on glass-system
2646
R. Kitagawa et al. / Journal of Non-Crystalline Solids 352 (2006) 2643–2646
and -composition. In S-rich Ge–S and GeS2–SbS2 glasses, the photodoping rate increases as S concentration increased, while Ag photodoping was not observed in Ge40S60 and Ga2S3-based glasses which contain modifier ions. Raman spectroscopy revealed that photodoping rate correlates with S–S bond concentration and sulfur molecular type in a host glass. Our experimental results are explained by an intercalation model. From the point of Ag photodoping behavior, sulfide glasses can be classified into a covalent glasses containing S–S bonds (active glass) and ionic glasses containing modifier ions (inert glass). References [1] M.T. Kostyshin, E.V. Mikhailovskaya, P.F. Romanenko, Sov. Phys. Solid State 8 (1966) 451. [2] A.V. Kolobov, S.R. Elliott, Adv. Phys. 40 (1991) 625. [3] K. Tanaka, Y. Kasanuki, A. Odajima, Thin Solid Films 117 (1984) 251. [4] R.M. Bryce, H.T. Nguyen, P. Nakeeran, R.G. DeCorby, P.K. Dwivedi, C.J. Haugen, S.O. Kasap, J. Vac. Sci. Technol. A 22 (2004) 1044.
[5] H. Lee, T. Yao, J. Vac. Sci. Technol. B 20 (2002) 2017. [6] H. Takebe, K. Morinaga, Proceeding of 2nd International Conference on Processing Materials for Properties, in: M. Mishra, C. Yamaguchi (Eds.), The minerals, Metals & Materials Society, 2000, p. 205. [7] D.W. Hewak, J.A. Medeiros Net, B. Samson, R.S. Brown, K.P. Jedrzejewski, J. Wang, E. Taylor, R.I. Laming, G. Wylangowski, D.N. Payne, IEEE Photo. Technol. Lett. 6 (1994) 609. [8] D. Goldschmidt, P.S. Rudman, J. Non-Cryst. Solids 22 (1976) 229. [9] H. Takebe, H. Maeda, K. Morinaga, J. Non-Cryst. Solids 291 (2001) 14. [10] H. Takebe, T. Hirakawa, T. Ichiki, K. Morinaga, J. Ceram. Soc. Jpn. 111 (2003) 572. [11] G. Kluge, Phys. Stat. Sol. (a) 101 (1987) 105. [12] S. Benazeth, M.H. Tulier, A.M. Loireau-Lozac’h, H. Dexpert, P. Lagarde, J. Flahaut, J. Non-Cryst. Solids 110 (1989) 89. [13] T. Kawaguchi, S. Maruno, J. Appl. Phys. 71 (1992) 2195. [14] I. Watanabe, T. Maeda, T. Shimizu, J. Non-Cryst. Solids 37 (1980) 335. [15] J.M. Oldale, J. Rennie, S.R. Elliott, Thin Solid Films 164 (1988) 467. [16] A.T. Steel, G.N. Greaves, A.P. Firth, A.E. Owen, J. Non-Cryst. Solids 107 (1989) 155. [17] S.R. Elliott, J. Non-Cryst. Solids 130 (1991) 85.