- Email: [email protected]
Phase separation of Na2O–SiO2 films prepared by sputtering
Journal of Non-Crystalline Solids 349 (2004) 337–340 www.elsevier.com/locate/jnoncrysol
Phase separation of Na2O–SiO2 films prepared by sputtering Futoshi Utsuno *, Hisashi Mori, Hiroyuki Inoue, Itaru Yasui Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1 Meguro-ku, Tokyo 153-8505, Japan Available online 2 November 2004
Abstract While the phenomena of phase separation in bulk glass have been well examined, those of amorphous thin films have not been fully detailed. From the viewpoint of new applications, the control of phase separation in thin films is very interesting. To investigate phase separation phenomena of amorphous films, Na2O–SiO2 films with various thicknesses were prepared by sputtering and the annealed films examined by SEM. Though a thin film with a thickness in 120 nm did not show phase separation in the vicinity of the surface, it was found that a clear binodal structure was observed in the film after HF etching. The microstructure and behavior of phase separation in the films was different from that found in bulk glass with the same Na2O–SiO2 composition. XPS results revealed that the compositions of Na/Si were inhomogeneous along the thickness, which explained the structural difference of the phase separation. Ó 2004 Elsevier B.V. All rights reserved. PACS: 64.75.+g; 64.70.Ja; 68.37.Hk; 68.55.Jk
1. Introduction There have been many studies done on the mechanisms of phase separation and the morphologies of phase-separated glasses [1]. Initially, phase separation in glass was used and studied mostly in bulk glass; though recently, the uses of phase separation in thin film have been suggested as being useful to make new nanoscale textured thin films for electronic devices or to modify surfaces of materials [2–11]. Phase separation in film form has been studied for films prepared by the sol-gel method. For example, Nakanishi and Soga reported spinodal phase separation in a silica sol-gel system containing polyacrylic acid [2]. Films in Na2O–B2O3–SiO2, TiO2–SiO2 and MgO–B2O3–SiO2 glass systems have been prepared by the sol-gel process and separated into
*
Corresponding author. Tel.: +81 3 5452 6307; fax: +81 3 5452 6308. E-mail address: [email protected] (F. Utsuno). 0022-3093/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2004.08.205
two phases [3–11]. However, the morphology of glassglass phase separation has not been observed clearly in the films. While Bates et al. reported that Li2O–SiO2– P2O5 thin films prepared by the sputtering method were phase-separated, their claim relied on just two observations; the presence of color and an impedance spectrum [12]. In the present work, we prepared thin films of Na2O– SiO2 glass by sputtering to investigate phase separation in thin films. We choose this glass system because of its simplicity of composition and the ease of comparing it with bulk; also, because phase separation in an Na2O– SiO2 system has been well studied, and a metastable immiscibility region has been reported in this system [1,13,14]. The synthesis by sputtering of a glass film containing sodium has scarcely been studied, so it is interesting to prepare such a film in this glass system. The surface morphologies of the annealed films after etching were observed by a scanning electron microscope (SEM), and the depth profile of the sodium content of the film was measured by X-ray photoelectron spectroscopy (XPS).
338
F. Utsuno et al. / Journal of Non-Crystalline Solids 349 (2004) 337–340
2. Experimental The films were prepared by conventional rf planar magnetron sputtering using powder targets: a silica holder with a diameter 50 mm. The powder targets were prepared by the following method; starting materials of Na2CO3 and SiO2 were mixed and then melted at 1550 °C in a platinum crucible, the melt was quenched between two stainless plates, and a powder of diameter 2 mm or less was obtained by crushing the obtained glass. Sputter deposition was carried out at a gas pressure of 1 Pa in a mixture of argon and oxygen (Ar:O2 = 1:1) with an rf power of 100 W. Silica glass substrates were water-cooled during sputtering. The films thickness was measured with a surface profilometer (Dektak3, Veeco). The films were heated to cause phase separation at temperatures in the range from 500 to 650 °C for 10 h. X-ray diffraction (Rint-2500V, Rigaku) measurements with a thin film attachment were performed to confirm these films had not crystallized. High resolution SEM (S-4500, Hitachi) was used to observe phase separation; samples for SEM observation were prepared as follows. Coatings were etched with a 5% solution of hydrofluoric acid (HF) in a range from 1 to 180 s, and then washed with ion-exchange water. Pt–Pd films were deposited on the surface of samples. To measure the rate of etching by the HF solution, samples with part of the film masked by wax was etched by the HF solution for 60, 120 and 180 s. After clearing the wax from the film, the vertical displacement between the etched and non-etched areas was measured by the surface profilometer, and the etching rate was estimated to be about 0.7 nm/s. We then obtained in-depth profiles of the distribution of sodium in thin films by XPS (Quantum 2000, Ulvac-Phi); utilizing a differentially pumped Ar-ion gun operating at 2 keV energy, and the samples were thus etched intermittently.
Fig. 1. SEM micrographs of glasses with compositions of 6Na2O– 94SiO2, 12Na2O–88SiO2 and 18Na2O–82SiO2 after heating at 620 °C for 10 h and etching for 60 s with a 5% solution of HF.
3. Results The morphologies of bulk samples with compositions of 6Na2O–94SiO2, 12Na2O–88SiO2 and 18Na2O– 82SiO2 were observed to compare them with the morphologies of films, (Fig. 1). Amorphous transparent films with thicknesses in the range from 30 to 700 nm were deposited on the SiO2 glass substrates by using targets with compositions of 12Na2O–88SiO2 and 18Na2O– 82SiO2. After the 12Na2O–88SiO2 film with a thickness of 700 nm heated at 620 °C for 10 h was etched by HF solution for various times, the morphologies of the surface were observed by SEM. Although no change of the morphologies was observed in the specimen etched for less than 60 s, a binodal structure was observed in the film etched for 60 s, as shown in Fig. 2. The phase-separated film was transparent in appearance. To investigate
the effect of the heat treatment temperature, 12Na2O– 88SiO2 films were heated within the range from 500 to 650 °C. While no decomposition was observed at 550 °C or less, droplets of the same-size as those in Fig. 2 were observed in the films heated at 600, 620 and 650 °C. Although the droplets could not be observed clearly in the film heated for 3 h at 620 °C, droplets were formed by the heat-treatment for 5 h or more but their growth was hardly observable. Since it was considered that the morphologies depended on the thickness of the films as influenced by the surface, films of various thicknesses were prepared. In the case of a film with a thickness of 30 nm, no morphology change was observed even when the film was etched by HF solution for a long time (180 s). In the film with a thickness of 60 nm, a
F. Utsuno et al. / Journal of Non-Crystalline Solids 349 (2004) 337–340
binodal-like structure was observed after etching for 120 or 150 s, as shown in Fig. 3. In a film of 120 nm or more, morphology similar to that in Fig. 2 was observed after etching for 60 s. A spinodal-like structure was observed after etching for 120 s in a film prepared using a target with a composition of 18Na2O–82SiO2, as seen in Fig. 4. Fig. 5 shows the XPS profiles of sodium distributions in the 12Na2O–88SiO2 films before and after heat treatment. The bottom of the as-deposited film was considered to be located at the point of 70 min sputtering time as shown by the black arrow in Fig. 5, and for the film heated at 620 °C for 10 h the bottom was considered to be located at 60 min, as shown by the gray arrow in the figure. In the as-deposited film, a large amount of Na+ ions existed at the interface between the film and
Fig. 4. SEM micrograph of the annealed film with a thickness of 230 nm, which was prepared by using the target with the composition of 18Na2O–82SiO2 after heating at 620 °C for 10 h and after etching for 120 s with a 5% solution of HF.
Si-2p
Intensity
Fig. 2. SEM micrograph of the annealed film with a thickness of 700 nm that was prepared using a target with a composition of 12Na2O–88SiO2 after heating heated at 620 °C for 10 h after etching for 60 s with a 5% solution of HF.
339
Na-1s
0
20
40 60 Ar sputter time /min
80
100
Fig. 5. Depth profiles of XPS spectra for a 12Na2O–88SiO2film with no heat treatment (black line) and heat treatment at 620 °C for 10 h (dotted line). The arrows indicate the estimated interface between the film and the substrate.
the substrate, while no Na+ ions were observed in the vicinity of the surface. On the other hand, in the film heated at 620 °C for 10 h, the sodium concentration on the surface was higher than that in the middle of the film. The interface between the film and the substrate was not clear because of the sodium diffusion to the substrate caused by the heat treatment.
4. Discussion
Fig. 3. SEM micrograph of the annealed film with a thickness of 60 nm, which was prepared by using a target with the composition of 12Na2O–88SiO2 after heating at 620 °C for 10 h and after etching for 120 s with a 5% solution of HF.
The droplets obtained in films prepared by using a target with a composition of 12Na2O–88SiO2 consisted of the Na2O rich phase because this phase is etched easier by the HF solution than the SiO2 rich phase; this because the morphology agreed well with that of 6Na2O–94SiO2 bulk glass, as shown in Fig. 1 [17]. An
340
F. Utsuno et al. / Journal of Non-Crystalline Solids 349 (2004) 337–340
interconnected structure was observed in the film sputtered with a target of 18Na2O–82SiO2. Contrarily, glass with a composition of 12Na2O–88SiO2, which was prepared by a melt method, develops an interconnected structure after heating at 650 °C [1]. Therefore, it is considered that the sodium concentration of the film is lower than that of the target by comparing with the morphologies of the bulk. It has been reported that when using oxide targets including alkali ions, the alkali composition of the film deposited by sputtering was lower than that of the target, due to the diffusion of alkali in the surface of the target during sputtering [12,15,16]. The low sodium concentration in the film is also due to the Na2O diffusion to the substrate caused by the heat treatment, as shown in the results of the XPS measurements in Fig. 5 [18]. It is also assumed that the distribution of sodium in the as-deposited film in Fig. 5 causes the emission of sodium atoms by bombardment of oxygen negative ions and/or argon recoil atoms generated by sputtering [19]. It is thought that the sodium distribution in the film corresponds to the various morphologies; no decomposition was observed from the surface to about 20 nm in depth, but soluble droplets were readily formed at about 40 nm in depth as estimated by the etching rate. Although droplets were observed in film of 60 nm or more thickness, decomposition was not observed in film with a thickness of 30 nm. In fact, the sodium concentration of the latter film was much lower than that of the former, as revealed by XPS measurements. Though it is necessary to have some degree of sodium concentration, so that the film may decompose, the extraction of alkali ions by the bombardment of oxygen negative ions and/or the sodium diffusion in the target during sputtering as mentioned above caused a decrease in the low sodium content in the very thin film. It is thus difficult to prepare a film with the intended composition in the Na2O–SiO2 system by sputtering without sodium distribution in its depth. To avoid the effects of oxygen negative ions and argon recoil atoms, the substrate was set vertically for the target. The film was deposited on the substrate and the sodium distribution depth was measured by XPS. A higher sodium concentration was detected at the surface of the as-deposited film; strongly suggestive that the low sodium concentration in the surface in that film is caused by oxygen negative ions and argon recoil atoms.
5. Conclusion Spinodal and binodal decompositions were observed in thin sodium-silicate films prepared by sputtering. Decomposition can be clearly observed in films with a thickness of 60 nm. The sodium distribution of the asdeposited film was detected by XPS measurements and the sodium concentration of the film was lower than that of the target used in the sputtering. This is suggested as being due to the diffusion of sodium in the target and the bombardment of oxygen negative ions and argon recoil atoms. The morphology of the decomposed film is strongly influenced by the distribution and the concentration of sodium in the as-deposited film. References [1] O.V. Mazurin, E.A. Porai-Koshits (Eds.), Phase Separation in Glass, North-Holland, Amsterdam, 1984. [2] K. Nakanishi, N. Soga, J. Non-Cryst. Solids 139 (1992) 1. [3] K. Makita, Y. Akamatsu, A. Takamatsu, S. Yamazaki, Y. Abe, J. Sol–Gel Sci. Tech. 14 (1999) 175. [4] N. Pellegri, D.J.C. Dawnay, E.M. Yeatman, J. Sol–Gel Sci. Technol. 2 (1994) 519. [5] H.G. Chung, J.W. Lee, H.J. Lee, J.H. Moon, H.M. Jang, J. NonCryst. Solids 261 (2000) 79. [6] N. Tohge, T. Minami, Chem. Express 3 (8) (1988) 455. [7] N. Tohge, T. Minami, J. Non-Cryst. Solids 112 (1989) 432. [8] O. Martins, R.M. Almeida, J. Sol–Gel Sci. Technol. 19 (2000) 651. [9] S.P. Mukherjee, W.H. Lowdermilk, J. Non-Cryst. Solids 48 (1982) 177. [10] A. Karthikeyan, R.M. Almeida, J. Mater. Res. 16 (6) (2001) 1626. [11] K. Kajihara, K. Nakanishi, K. Tanaka, K. Hirao, N. Soga, J. Am. Ceram. Soc. 81 (10) (1998) 2670. [12] J.B. Bates, N.J. Dudney, C.F. Luck, B.C. Sales, R.A. Zuhr, J.D. Robertson, J. Am. Ceram. Soc. 76 (4) (1993) 929. [13] L.D. Pye, L. Ploetz, L. Manfredo, J. Non-Cryst. Solids 14 (1974) 310. [14] B. Roy, H. Jain, S.K. Saha, D. Chakravorty, J. Am. Ceram. Soc. 81 (9) (1998) 2360. [15] H. Kinoshita, T. Sei, T. Tsuchiya, J. Ceram. Soc. Jpn. 100 (10) (1992) 1245. [16] N.J. Dudney, J.B. Bates, J.D. Robertson, J. Vac. Sci. Technol. A 11 (2) (1993) 377. [17] T. Harada, F. Utsuno, I. Yasui, J. Ceram. Soc. Jpn. 112 (5) (2004) S1240. [18] J.B. Bates, N.J. Dudney, G.R. Gruzalski, R.A. Zuhr, A. Choudhury, C.F. Luck, J.D. Robertson, Solid State Ionics 53–56 (1992) 647. [19] K. Ishibashi, K. Hirata, N. Hosokawa, J. Vac. Sci. Technol. A 10 (4) (1992) 1718.
Phase separation of Na2O–SiO2 films prepared by sputtering Futoshi Utsuno *, Hisashi Mori, Hiroyuki Inoue, Itaru Yasui Institute of Industrial Science, The University of Tokyo, Komaba 4-6-1 Meguro-ku, Tokyo 153-8505, Japan Available online 2 November 2004
Abstract While the phenomena of phase separation in bulk glass have been well examined, those of amorphous thin films have not been fully detailed. From the viewpoint of new applications, the control of phase separation in thin films is very interesting. To investigate phase separation phenomena of amorphous films, Na2O–SiO2 films with various thicknesses were prepared by sputtering and the annealed films examined by SEM. Though a thin film with a thickness in 120 nm did not show phase separation in the vicinity of the surface, it was found that a clear binodal structure was observed in the film after HF etching. The microstructure and behavior of phase separation in the films was different from that found in bulk glass with the same Na2O–SiO2 composition. XPS results revealed that the compositions of Na/Si were inhomogeneous along the thickness, which explained the structural difference of the phase separation. Ó 2004 Elsevier B.V. All rights reserved. PACS: 64.75.+g; 64.70.Ja; 68.37.Hk; 68.55.Jk
1. Introduction There have been many studies done on the mechanisms of phase separation and the morphologies of phase-separated glasses [1]. Initially, phase separation in glass was used and studied mostly in bulk glass; though recently, the uses of phase separation in thin film have been suggested as being useful to make new nanoscale textured thin films for electronic devices or to modify surfaces of materials [2–11]. Phase separation in film form has been studied for films prepared by the sol-gel method. For example, Nakanishi and Soga reported spinodal phase separation in a silica sol-gel system containing polyacrylic acid [2]. Films in Na2O–B2O3–SiO2, TiO2–SiO2 and MgO–B2O3–SiO2 glass systems have been prepared by the sol-gel process and separated into
*
Corresponding author. Tel.: +81 3 5452 6307; fax: +81 3 5452 6308. E-mail address: [email protected] (F. Utsuno). 0022-3093/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2004.08.205
two phases [3–11]. However, the morphology of glassglass phase separation has not been observed clearly in the films. While Bates et al. reported that Li2O–SiO2– P2O5 thin films prepared by the sputtering method were phase-separated, their claim relied on just two observations; the presence of color and an impedance spectrum [12]. In the present work, we prepared thin films of Na2O– SiO2 glass by sputtering to investigate phase separation in thin films. We choose this glass system because of its simplicity of composition and the ease of comparing it with bulk; also, because phase separation in an Na2O– SiO2 system has been well studied, and a metastable immiscibility region has been reported in this system [1,13,14]. The synthesis by sputtering of a glass film containing sodium has scarcely been studied, so it is interesting to prepare such a film in this glass system. The surface morphologies of the annealed films after etching were observed by a scanning electron microscope (SEM), and the depth profile of the sodium content of the film was measured by X-ray photoelectron spectroscopy (XPS).
338
F. Utsuno et al. / Journal of Non-Crystalline Solids 349 (2004) 337–340
2. Experimental The films were prepared by conventional rf planar magnetron sputtering using powder targets: a silica holder with a diameter 50 mm. The powder targets were prepared by the following method; starting materials of Na2CO3 and SiO2 were mixed and then melted at 1550 °C in a platinum crucible, the melt was quenched between two stainless plates, and a powder of diameter 2 mm or less was obtained by crushing the obtained glass. Sputter deposition was carried out at a gas pressure of 1 Pa in a mixture of argon and oxygen (Ar:O2 = 1:1) with an rf power of 100 W. Silica glass substrates were water-cooled during sputtering. The films thickness was measured with a surface profilometer (Dektak3, Veeco). The films were heated to cause phase separation at temperatures in the range from 500 to 650 °C for 10 h. X-ray diffraction (Rint-2500V, Rigaku) measurements with a thin film attachment were performed to confirm these films had not crystallized. High resolution SEM (S-4500, Hitachi) was used to observe phase separation; samples for SEM observation were prepared as follows. Coatings were etched with a 5% solution of hydrofluoric acid (HF) in a range from 1 to 180 s, and then washed with ion-exchange water. Pt–Pd films were deposited on the surface of samples. To measure the rate of etching by the HF solution, samples with part of the film masked by wax was etched by the HF solution for 60, 120 and 180 s. After clearing the wax from the film, the vertical displacement between the etched and non-etched areas was measured by the surface profilometer, and the etching rate was estimated to be about 0.7 nm/s. We then obtained in-depth profiles of the distribution of sodium in thin films by XPS (Quantum 2000, Ulvac-Phi); utilizing a differentially pumped Ar-ion gun operating at 2 keV energy, and the samples were thus etched intermittently.
Fig. 1. SEM micrographs of glasses with compositions of 6Na2O– 94SiO2, 12Na2O–88SiO2 and 18Na2O–82SiO2 after heating at 620 °C for 10 h and etching for 60 s with a 5% solution of HF.
3. Results The morphologies of bulk samples with compositions of 6Na2O–94SiO2, 12Na2O–88SiO2 and 18Na2O– 82SiO2 were observed to compare them with the morphologies of films, (Fig. 1). Amorphous transparent films with thicknesses in the range from 30 to 700 nm were deposited on the SiO2 glass substrates by using targets with compositions of 12Na2O–88SiO2 and 18Na2O– 82SiO2. After the 12Na2O–88SiO2 film with a thickness of 700 nm heated at 620 °C for 10 h was etched by HF solution for various times, the morphologies of the surface were observed by SEM. Although no change of the morphologies was observed in the specimen etched for less than 60 s, a binodal structure was observed in the film etched for 60 s, as shown in Fig. 2. The phase-separated film was transparent in appearance. To investigate
the effect of the heat treatment temperature, 12Na2O– 88SiO2 films were heated within the range from 500 to 650 °C. While no decomposition was observed at 550 °C or less, droplets of the same-size as those in Fig. 2 were observed in the films heated at 600, 620 and 650 °C. Although the droplets could not be observed clearly in the film heated for 3 h at 620 °C, droplets were formed by the heat-treatment for 5 h or more but their growth was hardly observable. Since it was considered that the morphologies depended on the thickness of the films as influenced by the surface, films of various thicknesses were prepared. In the case of a film with a thickness of 30 nm, no morphology change was observed even when the film was etched by HF solution for a long time (180 s). In the film with a thickness of 60 nm, a
F. Utsuno et al. / Journal of Non-Crystalline Solids 349 (2004) 337–340
binodal-like structure was observed after etching for 120 or 150 s, as shown in Fig. 3. In a film of 120 nm or more, morphology similar to that in Fig. 2 was observed after etching for 60 s. A spinodal-like structure was observed after etching for 120 s in a film prepared using a target with a composition of 18Na2O–82SiO2, as seen in Fig. 4. Fig. 5 shows the XPS profiles of sodium distributions in the 12Na2O–88SiO2 films before and after heat treatment. The bottom of the as-deposited film was considered to be located at the point of 70 min sputtering time as shown by the black arrow in Fig. 5, and for the film heated at 620 °C for 10 h the bottom was considered to be located at 60 min, as shown by the gray arrow in the figure. In the as-deposited film, a large amount of Na+ ions existed at the interface between the film and
Fig. 4. SEM micrograph of the annealed film with a thickness of 230 nm, which was prepared by using the target with the composition of 18Na2O–82SiO2 after heating at 620 °C for 10 h and after etching for 120 s with a 5% solution of HF.
Si-2p
Intensity
Fig. 2. SEM micrograph of the annealed film with a thickness of 700 nm that was prepared using a target with a composition of 12Na2O–88SiO2 after heating heated at 620 °C for 10 h after etching for 60 s with a 5% solution of HF.
339
Na-1s
0
20
40 60 Ar sputter time /min
80
100
Fig. 5. Depth profiles of XPS spectra for a 12Na2O–88SiO2film with no heat treatment (black line) and heat treatment at 620 °C for 10 h (dotted line). The arrows indicate the estimated interface between the film and the substrate.
the substrate, while no Na+ ions were observed in the vicinity of the surface. On the other hand, in the film heated at 620 °C for 10 h, the sodium concentration on the surface was higher than that in the middle of the film. The interface between the film and the substrate was not clear because of the sodium diffusion to the substrate caused by the heat treatment.
4. Discussion
Fig. 3. SEM micrograph of the annealed film with a thickness of 60 nm, which was prepared by using a target with the composition of 12Na2O–88SiO2 after heating at 620 °C for 10 h and after etching for 120 s with a 5% solution of HF.
The droplets obtained in films prepared by using a target with a composition of 12Na2O–88SiO2 consisted of the Na2O rich phase because this phase is etched easier by the HF solution than the SiO2 rich phase; this because the morphology agreed well with that of 6Na2O–94SiO2 bulk glass, as shown in Fig. 1 [17]. An
340
F. Utsuno et al. / Journal of Non-Crystalline Solids 349 (2004) 337–340
interconnected structure was observed in the film sputtered with a target of 18Na2O–82SiO2. Contrarily, glass with a composition of 12Na2O–88SiO2, which was prepared by a melt method, develops an interconnected structure after heating at 650 °C [1]. Therefore, it is considered that the sodium concentration of the film is lower than that of the target by comparing with the morphologies of the bulk. It has been reported that when using oxide targets including alkali ions, the alkali composition of the film deposited by sputtering was lower than that of the target, due to the diffusion of alkali in the surface of the target during sputtering [12,15,16]. The low sodium concentration in the film is also due to the Na2O diffusion to the substrate caused by the heat treatment, as shown in the results of the XPS measurements in Fig. 5 [18]. It is also assumed that the distribution of sodium in the as-deposited film in Fig. 5 causes the emission of sodium atoms by bombardment of oxygen negative ions and/or argon recoil atoms generated by sputtering [19]. It is thought that the sodium distribution in the film corresponds to the various morphologies; no decomposition was observed from the surface to about 20 nm in depth, but soluble droplets were readily formed at about 40 nm in depth as estimated by the etching rate. Although droplets were observed in film of 60 nm or more thickness, decomposition was not observed in film with a thickness of 30 nm. In fact, the sodium concentration of the latter film was much lower than that of the former, as revealed by XPS measurements. Though it is necessary to have some degree of sodium concentration, so that the film may decompose, the extraction of alkali ions by the bombardment of oxygen negative ions and/or the sodium diffusion in the target during sputtering as mentioned above caused a decrease in the low sodium content in the very thin film. It is thus difficult to prepare a film with the intended composition in the Na2O–SiO2 system by sputtering without sodium distribution in its depth. To avoid the effects of oxygen negative ions and argon recoil atoms, the substrate was set vertically for the target. The film was deposited on the substrate and the sodium distribution depth was measured by XPS. A higher sodium concentration was detected at the surface of the as-deposited film; strongly suggestive that the low sodium concentration in the surface in that film is caused by oxygen negative ions and argon recoil atoms.
5. Conclusion Spinodal and binodal decompositions were observed in thin sodium-silicate films prepared by sputtering. Decomposition can be clearly observed in films with a thickness of 60 nm. The sodium distribution of the asdeposited film was detected by XPS measurements and the sodium concentration of the film was lower than that of the target used in the sputtering. This is suggested as being due to the diffusion of sodium in the target and the bombardment of oxygen negative ions and argon recoil atoms. The morphology of the decomposed film is strongly influenced by the distribution and the concentration of sodium in the as-deposited film. References [1] O.V. Mazurin, E.A. Porai-Koshits (Eds.), Phase Separation in Glass, North-Holland, Amsterdam, 1984. [2] K. Nakanishi, N. Soga, J. Non-Cryst. Solids 139 (1992) 1. [3] K. Makita, Y. Akamatsu, A. Takamatsu, S. Yamazaki, Y. Abe, J. Sol–Gel Sci. Tech. 14 (1999) 175. [4] N. Pellegri, D.J.C. Dawnay, E.M. Yeatman, J. Sol–Gel Sci. Technol. 2 (1994) 519. [5] H.G. Chung, J.W. Lee, H.J. Lee, J.H. Moon, H.M. Jang, J. NonCryst. Solids 261 (2000) 79. [6] N. Tohge, T. Minami, Chem. Express 3 (8) (1988) 455. [7] N. Tohge, T. Minami, J. Non-Cryst. Solids 112 (1989) 432. [8] O. Martins, R.M. Almeida, J. Sol–Gel Sci. Technol. 19 (2000) 651. [9] S.P. Mukherjee, W.H. Lowdermilk, J. Non-Cryst. Solids 48 (1982) 177. [10] A. Karthikeyan, R.M. Almeida, J. Mater. Res. 16 (6) (2001) 1626. [11] K. Kajihara, K. Nakanishi, K. Tanaka, K. Hirao, N. Soga, J. Am. Ceram. Soc. 81 (10) (1998) 2670. [12] J.B. Bates, N.J. Dudney, C.F. Luck, B.C. Sales, R.A. Zuhr, J.D. Robertson, J. Am. Ceram. Soc. 76 (4) (1993) 929. [13] L.D. Pye, L. Ploetz, L. Manfredo, J. Non-Cryst. Solids 14 (1974) 310. [14] B. Roy, H. Jain, S.K. Saha, D. Chakravorty, J. Am. Ceram. Soc. 81 (9) (1998) 2360. [15] H. Kinoshita, T. Sei, T. Tsuchiya, J. Ceram. Soc. Jpn. 100 (10) (1992) 1245. [16] N.J. Dudney, J.B. Bates, J.D. Robertson, J. Vac. Sci. Technol. A 11 (2) (1993) 377. [17] T. Harada, F. Utsuno, I. Yasui, J. Ceram. Soc. Jpn. 112 (5) (2004) S1240. [18] J.B. Bates, N.J. Dudney, G.R. Gruzalski, R.A. Zuhr, A. Choudhury, C.F. Luck, J.D. Robertson, Solid State Ionics 53–56 (1992) 647. [19] K. Ishibashi, K. Hirata, N. Hosokawa, J. Vac. Sci. Technol. A 10 (4) (1992) 1718.