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Preparation of micro-porous Si particles from Mg2Si powder
Materials Letters 98 (2013) 157–160
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation of micro-porous Si particles from Mg2Si powder Takahiro Yamada a,n, Hiroshi Itahara b, Hisanori Yamane a a b
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan Toyota Central Research and Development Laboratories Inc., Nagakute, Aichi 480-1192, Japan
a r t i c l e i n f o
abstract
Article history: Received 21 December 2012 Accepted 10 February 2013 Available online 18 February 2013
Polycrystalline Si powder consisting of micro-porous particles was prepared by heating Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa. The porous Si particles were composed of primary Si crystals ranging in size from 100 nm to 5 mm with pores less than 10 mm in size. Porous Si particles with similar morphology were also prepared at 700 1C for 50 Pa and 500 Pa for 10 h. The formation of the porous Si particles was attributed to Mg evaporation from Mg2Si particles, followed by crystallization of Si. & 2013 Elsevier B.V. All rights reserved.
Keywords: Porous materials Powder processing Microstructure Silicon
1. Introduction Porous silicon (Si) is a promising material for optoelectronic and sensing devices, anodes of Li-ion batteries, and catalytic support [1–9]. Their performance depends on the sizes and morphologies of the Si crystals and pores (including the pore wall), as well as on the specific surface area. Porous Si with variously-sized (nano-, meso-, and micro-sized) pores has been prepared by electrochemical anodization [2,3,10] or by wet-chemical etching in hydrofluoric acid (HF) solution [7]. Recently, Bao et al. have converted silica diatom frustules into the micro-porous Si replicas by heating at 650 1C for 2.5 h in Mg vapor, followed by washing with HCl solution and subsequently with HF solution [11]. Morito et al. have succeeded in preparing a porous Si bulk composed of particles with a size of a few micrometers by evaporation of Na from a mixture of NaSi and Si powders at 800–900 1C for 24 h in an Ar-filled container with a temperature gradient [12]. The purpose of the present study was to develop a method for the preparation of porous Si particles using Mg2Si as a source material. Because the melting point of Mg2Si (1085 1C) is close to the boiling point of Mg metal (1097 1C), the casting of Mg2Si has been carried out under a positive pressure of an inert gas to prevent the vaporization of Mg [13,14]. On the other hand, the decomposition of Mg2Si below the melting temperature under a reduced pressure has been mentioned in a few reports on the preparation of Mg2Si thin film [15,16]. To our knowledge, however, there has been no report on the decomposition products of Mg2Si and their morphology. We attempted to prepare porous Si particles from Mg2Si by Mg vaporization. The morphology and
n
Corresponding author. Tel./fax: þ 81 22 217 5813. E-mail address: [email protected] (T. Yamada).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.02.022
yield of the porous Si particles prepared at 550–700 1C and at 50 Pa, 500 Pa, and 10 kPa for 10 and 40 h were investigated.
2. Experimental procedure Commercially available Mg2Si powder (Kojundo Chemical Lab. Co Ltd., 99%, o400 mm) was used as a source material. The size of Mg2Si particles in the powder was between 5 and 400 mm and the median particle size was approximately 100 mm. About 200 mg of Mg2Si powder was loaded into a sintered BN crucible (Showa Denko, 99.5%, an inner diameter of 6 mm, a depth of 13 mm) in air. The crucible was placed at the upper position in a stainlesssteel container (SUS316, an inner diameter of 11 mm, a length of 400 mm) in an Ar gas-filled glove box (MBraun, O2, H2O o1 ppm). The container was then placed in an electric furnace and connected to a vacuum line (See supplementary material, Fig. S1). One end of the container which protruded from the furnace was cooled with a fan. The sample was heated at 550–700 1C for 10 and 40 h with an electric furnace under pressures of 50 Pa, 500 Pa, and 10 kPa, followed by cooling in the furnace. After cooling, the crucible was taken out of the container. The sample was immersed in a 0.5 mol/L HCl solution, washed with distilled water, and subsequently dried at 353 K in air. The crystalline phases of the samples were identified by X-ray diffraction (XRD, Rigaku, RINT2200). The morphology of the samples was observed with a scanning electron microscope (SEM, Philips, ESEM XL30), and elemental analysis of the samples was carried out with an energy-dispersive X-ray analyzer (EDX, EDAX) attached to the SEM. Transmission electron microscopic (TEM) images and selected-area electron diffraction (SAD) patterns of the specimens were obtained with a 200 kV electron
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T. Yamada et al. / Materials Letters 98 (2013) 157–160
microscope (JEM-2000EX, JEOL Ltd.). The yield of Si was evaluated from the mass loss of the sample in the crucible after heating.
3. Results and discussion Light-brown powder was prepared by heating blue-gray Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa. Mg was condensed at the inner part of the container cooled with a fan. Fig. 1 shows the XRD pattern of the source Mg2Si powder and the obtained powders. In the XRD patterns of the as-prepared sample (Fig. 1b), strong diffraction peaks are seen to be associated with Si
Fig. 1. Powder X-ray diffraction (XRD) patterns of the source Mg2Si powder (a) and the sample prepared by heating the Mg2Si powder at 600 1C and 500 Pa for 40 h (b), followed by washing with HCl solution (c).
and the small broad peaks at 431 and 621 correspond to MgO, not to Mg. However, no MgO peaks are observed in the XRD pattern of the sample after washing with HCl solution (Fig. 1c). The yield of Si, defined as the molar ratio of Si/(Si þMg2Si), resulting from the decomposition of Mg2Si at 600 1C and 500 Pa for 40 h was determined to be 1.0. SEM images of the sample prepared from Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa are shown in Fig. 2. The size ( o400 mm) and shape of the as-prepared particles are similar to those of the particles of the source Mg2Si powder. However, pores of less than 10 mm in diameter are observed on the surface of the particles (Fig. 2a). After washing with HCl solution, the powder is seen to be composed of porous Si particles less than 50 mm in size (Fig. 2b). On the surface of the Si particles, primary Si crystals ranging in size from 100 nm to 5 mm and open spaces can be observed (Fig. 2c and d). Fig. 3 shows the TEM image and SAD pattern of the crushed porous Si particles, dispersed on holey carbon film. The size of the Si crystals in the TEM image is 200–500 nm. The diffraction spot of the Si crystals are sharp, indicating high crystallinity of the Si crystals, while there is no ring and spots of MgO and Mg2Si. The characteristic X-rays of Si, Mg and O from the surface of the particles in the as-prepared sample were observed in the EDX spectrum. O was also detected from the surface of the source Mg2Si particles. On the other hand, Si was only detected inside the crushed particles and at both surface and inside of the porous Si particles washed with HCl solution. MgO on the surface of the as-prepared particles was probably derived from the oxidized surface of the source Mg2Si particles. According to the Mg–Si binary phase diagram [17], the melting temperature of Mg2Si is 1085 1C, and the eutectic temperature between Mg2Si and Si is 946 1C. Since the size and shape of the asprepared porous Si particles were similar to those of the source Mg2Si particles, the formation of the porous Si particles was attributed to Mg evaporation from Mg2Si particles, followed by crystallization of Si at 600 1C and 500 Pa. The porosity of the porous
100 µm
100 µm
10 µm
1 µm
Fig. 2. Scanning electron microscopic (SEM) images of the porous Si particles prepared at 600 1C and 500 Pa for 40 h; as prepared particles (a) and particles after washing with HCl solution at different magnifications (b, c, d).
T. Yamada et al. / Materials Letters 98 (2013) 157–160
159
Si (400) Si (200)
Si (442)
Si (311) Si (331)
200 nm Fig. 3. Transmission electron microscopic image (a) and selected area diffraction pattern (b) of the crushed porous Si particles prepared at 600 1C and 500 Pa for 40 h after washing with HCl solution. Forbidden reflections of Si (200) are present due to double diffraction.
100 µm
The effects of the heating temperature and pressure on the yield of Si were investigated at a heating-time of 10 h. The yields of Si showed a positive correlation with temperature and a negative one with the pressure in the container, as shown in Table 1. The yield of 1.0 was obtained by heating at 700 1C and at 50, 500 Pa for 10 h. The morphology of these porous Si particles were similar to that prepared at 600 1C and 500 Pa for 40 h (See supplementary material, Fig. S2). It indicates that the rapid and efficient preparation of the porous Si particles was realized at low-pressure and high-temperature conditions. Further investigation is necessary to find the best conditions for the synthesis of the porous Si particles.
4. Conclusions
10 µm Fig. 4. SEM images taken of the inside of a particle in the sample prepared by heating Mg2Si at 600 1C and 500 Pa for 10 h with a high-magnification (main image) and a low-magnification (inset). The particle was embedded in resin and planed for the SEM observation. Table 1 Yields of the porous Si particles prepared by decomposition of Mg2Si at various temperatures and pressures for the heating time of 10 h. Temperature, (1C)
700 600 550
Si powder consisting of micro-porous particles was prepared by heating Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa. The porous particles were composed of primary Si crystals ranging from 100 nm to 5 mm in size and openings less than 10 mm in size. MgO derived from the oxidized surface of the source Mg2Si particles was present on the as-prepared surface of the porous Si particles and was removed by reaction with HCl solution. The porous Si particles were formed by Mg evaporation from Mg2Si particles and by crystallization of Si during heating under a reduced pressure. The porosity of the particles was estimated to be 69%.
Yields (50 Pa)
(500 Pa)
(10 kPa)
1.0 0.7 0.4
1.0 0.5 0.2
0.2 0.0 0.0
Si particles was estimated to be 69%, assuming that they were formed from Mg2Si particles by Mg evaporation without any particle-size change. In order to clarify the process of the porous Si particles formation, the preparation at 600 1C and 500 Pa for 10 h was carried out. The product was a mixture of Mg2Si and Si, and the yield of Si in the sample was 0.5. An obtained particle buried in resin was planed to observe the cross section by SEM (Fig. 4). The contrast observed in the SEM image and EDX analysis revealed that the outer porous part of the particle was Si, while the inner dense part was Mg2Si. These results demonstrate that porous Si structure was formed from the surface of Mg2Si particle by Mg evaporation.
Acknowledgments This work was supported in part by a Grant-in-Aid (23550222) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013. 02.022.
References [1] Canham LT. Appl Phys Lett 1990;57:1046–9. [2] Canham LT. Properties of porous silicon. London: Institution of Electrical Engineers; 1997.
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T. Yamada et al. / Materials Letters 98 (2013) 157–160
[3] Sallow MJ. Porous silicon in practice: preparation, characterization and applications. Weinheim: Wiley-VCH; 2011. [4] Chan CK, Peng HL, Liu G, Mcllwrath K, Zhang XF, Huggins RA, et al. Nat Nanotechnol 2008;3:31–5. [5] Kim H, Han B, Choo J, Cho J. Angew Chem 2008;120:10305–8. [6] Gao P, Fu J, Yang J, Lv R, Wang J, Nuli Y, et al. Phys Chem Chem Phys 2009;11:11101–5. [7] Zhao Y, Liu X, Li H, Zhai T, Zhou H. Chem Commun 2012;48:5079–81. [8] Polisski S, Goller B, Wilson K, Kovalev D, Zaikowskii V, Lapkin A. J Catal 2010;271:59–66. [9] Mizsei J. Thin Solid Films 2007;515:8310–5. [10] Uhlir A. Bell Syst Tech J 1956;35:333–47. [11] Bao Z, Weatherspoon MR, Shian S, Cai Y, Graham PD, Allan SM, et al. Nature 2007;446:172–5.
[12] Morito H, Yamada T, Ikeda T, Yamane H. J Alloys Compd 2009;480:723–6. [13] Noda Y, Kon H, Fukukawa Y, Otsuka N, Nishida IA, Masumoto K. Mater Trans JIM 1992;33:845–50. [14] Yoshinaga M, Iida T, Noda M, Endo T, Takanashi Y. Thin Solid Films 2004;461:86–9. [15] Wang X, Wang Y, Zou J, Zhang T, Mei Z, Guo Y, et al. Chin Phys B 2009;18:3079–83. [16] Xiao Q, Xie Q, Zhao K, Yu Z. Adv Mater Res 2010;129–131:290–4. [17] Okamoto H, Subramanian PR, Kacprzak L. 2nd ed.Binary alloy phase diagrams, vol. 1–2. Metals Park: American Society for Metals; 1990 p. 2547–9.
Contents lists available at SciVerse ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation of micro-porous Si particles from Mg2Si powder Takahiro Yamada a,n, Hiroshi Itahara b, Hisanori Yamane a a b
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan Toyota Central Research and Development Laboratories Inc., Nagakute, Aichi 480-1192, Japan
a r t i c l e i n f o
abstract
Article history: Received 21 December 2012 Accepted 10 February 2013 Available online 18 February 2013
Polycrystalline Si powder consisting of micro-porous particles was prepared by heating Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa. The porous Si particles were composed of primary Si crystals ranging in size from 100 nm to 5 mm with pores less than 10 mm in size. Porous Si particles with similar morphology were also prepared at 700 1C for 50 Pa and 500 Pa for 10 h. The formation of the porous Si particles was attributed to Mg evaporation from Mg2Si particles, followed by crystallization of Si. & 2013 Elsevier B.V. All rights reserved.
Keywords: Porous materials Powder processing Microstructure Silicon
1. Introduction Porous silicon (Si) is a promising material for optoelectronic and sensing devices, anodes of Li-ion batteries, and catalytic support [1–9]. Their performance depends on the sizes and morphologies of the Si crystals and pores (including the pore wall), as well as on the specific surface area. Porous Si with variously-sized (nano-, meso-, and micro-sized) pores has been prepared by electrochemical anodization [2,3,10] or by wet-chemical etching in hydrofluoric acid (HF) solution [7]. Recently, Bao et al. have converted silica diatom frustules into the micro-porous Si replicas by heating at 650 1C for 2.5 h in Mg vapor, followed by washing with HCl solution and subsequently with HF solution [11]. Morito et al. have succeeded in preparing a porous Si bulk composed of particles with a size of a few micrometers by evaporation of Na from a mixture of NaSi and Si powders at 800–900 1C for 24 h in an Ar-filled container with a temperature gradient [12]. The purpose of the present study was to develop a method for the preparation of porous Si particles using Mg2Si as a source material. Because the melting point of Mg2Si (1085 1C) is close to the boiling point of Mg metal (1097 1C), the casting of Mg2Si has been carried out under a positive pressure of an inert gas to prevent the vaporization of Mg [13,14]. On the other hand, the decomposition of Mg2Si below the melting temperature under a reduced pressure has been mentioned in a few reports on the preparation of Mg2Si thin film [15,16]. To our knowledge, however, there has been no report on the decomposition products of Mg2Si and their morphology. We attempted to prepare porous Si particles from Mg2Si by Mg vaporization. The morphology and
n
Corresponding author. Tel./fax: þ 81 22 217 5813. E-mail address: [email protected] (T. Yamada).
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.02.022
yield of the porous Si particles prepared at 550–700 1C and at 50 Pa, 500 Pa, and 10 kPa for 10 and 40 h were investigated.
2. Experimental procedure Commercially available Mg2Si powder (Kojundo Chemical Lab. Co Ltd., 99%, o400 mm) was used as a source material. The size of Mg2Si particles in the powder was between 5 and 400 mm and the median particle size was approximately 100 mm. About 200 mg of Mg2Si powder was loaded into a sintered BN crucible (Showa Denko, 99.5%, an inner diameter of 6 mm, a depth of 13 mm) in air. The crucible was placed at the upper position in a stainlesssteel container (SUS316, an inner diameter of 11 mm, a length of 400 mm) in an Ar gas-filled glove box (MBraun, O2, H2O o1 ppm). The container was then placed in an electric furnace and connected to a vacuum line (See supplementary material, Fig. S1). One end of the container which protruded from the furnace was cooled with a fan. The sample was heated at 550–700 1C for 10 and 40 h with an electric furnace under pressures of 50 Pa, 500 Pa, and 10 kPa, followed by cooling in the furnace. After cooling, the crucible was taken out of the container. The sample was immersed in a 0.5 mol/L HCl solution, washed with distilled water, and subsequently dried at 353 K in air. The crystalline phases of the samples were identified by X-ray diffraction (XRD, Rigaku, RINT2200). The morphology of the samples was observed with a scanning electron microscope (SEM, Philips, ESEM XL30), and elemental analysis of the samples was carried out with an energy-dispersive X-ray analyzer (EDX, EDAX) attached to the SEM. Transmission electron microscopic (TEM) images and selected-area electron diffraction (SAD) patterns of the specimens were obtained with a 200 kV electron
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T. Yamada et al. / Materials Letters 98 (2013) 157–160
microscope (JEM-2000EX, JEOL Ltd.). The yield of Si was evaluated from the mass loss of the sample in the crucible after heating.
3. Results and discussion Light-brown powder was prepared by heating blue-gray Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa. Mg was condensed at the inner part of the container cooled with a fan. Fig. 1 shows the XRD pattern of the source Mg2Si powder and the obtained powders. In the XRD patterns of the as-prepared sample (Fig. 1b), strong diffraction peaks are seen to be associated with Si
Fig. 1. Powder X-ray diffraction (XRD) patterns of the source Mg2Si powder (a) and the sample prepared by heating the Mg2Si powder at 600 1C and 500 Pa for 40 h (b), followed by washing with HCl solution (c).
and the small broad peaks at 431 and 621 correspond to MgO, not to Mg. However, no MgO peaks are observed in the XRD pattern of the sample after washing with HCl solution (Fig. 1c). The yield of Si, defined as the molar ratio of Si/(Si þMg2Si), resulting from the decomposition of Mg2Si at 600 1C and 500 Pa for 40 h was determined to be 1.0. SEM images of the sample prepared from Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa are shown in Fig. 2. The size ( o400 mm) and shape of the as-prepared particles are similar to those of the particles of the source Mg2Si powder. However, pores of less than 10 mm in diameter are observed on the surface of the particles (Fig. 2a). After washing with HCl solution, the powder is seen to be composed of porous Si particles less than 50 mm in size (Fig. 2b). On the surface of the Si particles, primary Si crystals ranging in size from 100 nm to 5 mm and open spaces can be observed (Fig. 2c and d). Fig. 3 shows the TEM image and SAD pattern of the crushed porous Si particles, dispersed on holey carbon film. The size of the Si crystals in the TEM image is 200–500 nm. The diffraction spot of the Si crystals are sharp, indicating high crystallinity of the Si crystals, while there is no ring and spots of MgO and Mg2Si. The characteristic X-rays of Si, Mg and O from the surface of the particles in the as-prepared sample were observed in the EDX spectrum. O was also detected from the surface of the source Mg2Si particles. On the other hand, Si was only detected inside the crushed particles and at both surface and inside of the porous Si particles washed with HCl solution. MgO on the surface of the as-prepared particles was probably derived from the oxidized surface of the source Mg2Si particles. According to the Mg–Si binary phase diagram [17], the melting temperature of Mg2Si is 1085 1C, and the eutectic temperature between Mg2Si and Si is 946 1C. Since the size and shape of the asprepared porous Si particles were similar to those of the source Mg2Si particles, the formation of the porous Si particles was attributed to Mg evaporation from Mg2Si particles, followed by crystallization of Si at 600 1C and 500 Pa. The porosity of the porous
100 µm
100 µm
10 µm
1 µm
Fig. 2. Scanning electron microscopic (SEM) images of the porous Si particles prepared at 600 1C and 500 Pa for 40 h; as prepared particles (a) and particles after washing with HCl solution at different magnifications (b, c, d).
T. Yamada et al. / Materials Letters 98 (2013) 157–160
159
Si (400) Si (200)
Si (442)
Si (311) Si (331)
200 nm Fig. 3. Transmission electron microscopic image (a) and selected area diffraction pattern (b) of the crushed porous Si particles prepared at 600 1C and 500 Pa for 40 h after washing with HCl solution. Forbidden reflections of Si (200) are present due to double diffraction.
100 µm
The effects of the heating temperature and pressure on the yield of Si were investigated at a heating-time of 10 h. The yields of Si showed a positive correlation with temperature and a negative one with the pressure in the container, as shown in Table 1. The yield of 1.0 was obtained by heating at 700 1C and at 50, 500 Pa for 10 h. The morphology of these porous Si particles were similar to that prepared at 600 1C and 500 Pa for 40 h (See supplementary material, Fig. S2). It indicates that the rapid and efficient preparation of the porous Si particles was realized at low-pressure and high-temperature conditions. Further investigation is necessary to find the best conditions for the synthesis of the porous Si particles.
4. Conclusions
10 µm Fig. 4. SEM images taken of the inside of a particle in the sample prepared by heating Mg2Si at 600 1C and 500 Pa for 10 h with a high-magnification (main image) and a low-magnification (inset). The particle was embedded in resin and planed for the SEM observation. Table 1 Yields of the porous Si particles prepared by decomposition of Mg2Si at various temperatures and pressures for the heating time of 10 h. Temperature, (1C)
700 600 550
Si powder consisting of micro-porous particles was prepared by heating Mg2Si powder at 600 1C for 40 h under a pressure of 500 Pa. The porous particles were composed of primary Si crystals ranging from 100 nm to 5 mm in size and openings less than 10 mm in size. MgO derived from the oxidized surface of the source Mg2Si particles was present on the as-prepared surface of the porous Si particles and was removed by reaction with HCl solution. The porous Si particles were formed by Mg evaporation from Mg2Si particles and by crystallization of Si during heating under a reduced pressure. The porosity of the particles was estimated to be 69%.
Yields (50 Pa)
(500 Pa)
(10 kPa)
1.0 0.7 0.4
1.0 0.5 0.2
0.2 0.0 0.0
Si particles was estimated to be 69%, assuming that they were formed from Mg2Si particles by Mg evaporation without any particle-size change. In order to clarify the process of the porous Si particles formation, the preparation at 600 1C and 500 Pa for 10 h was carried out. The product was a mixture of Mg2Si and Si, and the yield of Si in the sample was 0.5. An obtained particle buried in resin was planed to observe the cross section by SEM (Fig. 4). The contrast observed in the SEM image and EDX analysis revealed that the outer porous part of the particle was Si, while the inner dense part was Mg2Si. These results demonstrate that porous Si structure was formed from the surface of Mg2Si particle by Mg evaporation.
Acknowledgments This work was supported in part by a Grant-in-Aid (23550222) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
Appendix A. Supporting information Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013. 02.022.
References [1] Canham LT. Appl Phys Lett 1990;57:1046–9. [2] Canham LT. Properties of porous silicon. London: Institution of Electrical Engineers; 1997.
160
T. Yamada et al. / Materials Letters 98 (2013) 157–160
[3] Sallow MJ. Porous silicon in practice: preparation, characterization and applications. Weinheim: Wiley-VCH; 2011. [4] Chan CK, Peng HL, Liu G, Mcllwrath K, Zhang XF, Huggins RA, et al. Nat Nanotechnol 2008;3:31–5. [5] Kim H, Han B, Choo J, Cho J. Angew Chem 2008;120:10305–8. [6] Gao P, Fu J, Yang J, Lv R, Wang J, Nuli Y, et al. Phys Chem Chem Phys 2009;11:11101–5. [7] Zhao Y, Liu X, Li H, Zhai T, Zhou H. Chem Commun 2012;48:5079–81. [8] Polisski S, Goller B, Wilson K, Kovalev D, Zaikowskii V, Lapkin A. J Catal 2010;271:59–66. [9] Mizsei J. Thin Solid Films 2007;515:8310–5. [10] Uhlir A. Bell Syst Tech J 1956;35:333–47. [11] Bao Z, Weatherspoon MR, Shian S, Cai Y, Graham PD, Allan SM, et al. Nature 2007;446:172–5.
[12] Morito H, Yamada T, Ikeda T, Yamane H. J Alloys Compd 2009;480:723–6. [13] Noda Y, Kon H, Fukukawa Y, Otsuka N, Nishida IA, Masumoto K. Mater Trans JIM 1992;33:845–50. [14] Yoshinaga M, Iida T, Noda M, Endo T, Takanashi Y. Thin Solid Films 2004;461:86–9. [15] Wang X, Wang Y, Zou J, Zhang T, Mei Z, Guo Y, et al. Chin Phys B 2009;18:3079–83. [16] Xiao Q, Xie Q, Zhao K, Yu Z. Adv Mater Res 2010;129–131:290–4. [17] Okamoto H, Subramanian PR, Kacprzak L. 2nd ed.Binary alloy phase diagrams, vol. 1–2. Metals Park: American Society for Metals; 1990 p. 2547–9.