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Simultaneous phase and morphology controllable synthesis of copper selenide films by microwave-assisted nonaqueous approach
Solid State Sciences 16 (2013) 125e129
Contents lists available at SciVerse ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Simultaneous phase and morphology controllable synthesis of copper selenide films by microwave-assisted nonaqueous approach Jing Li a, Wenjun Fa a, *, Yasi Li b, Hongxiao Zhao a, Yuanhao Gao a, Zhi Zheng a, * a
Key Laboratory for Micro-Nano Energy Storage and Conversion Materials of Henan Province, Institute of Surface Micro and Nano Materials, Xuchang University, Henan, Xuchang 461000, PR China b College of Chemistry and Chemical Engineering, Xuchang University, Xuchang 461000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 April 2012 Received in revised form 31 October 2012 Accepted 1 November 2012 Available online 9 November 2012
Copper selenide films with different phase and morphology were synthesized on copper substrate through controlling reaction solvent by microwave-assisted nonaqueous approach. The films were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The result showed that the pure films could be obtained using cyclohexyl alcohol or benzyl alcohol as solvent. The cubic Cu2xSe dendrites were synthesized in cyclohexyl alcohol reaction system and hexagonal CuSe flaky crystals were obtained with benzyl alcohol as solvent. Ó 2012 Elsevier Masson SAS. All rights reserved.
Keywords: Copper selenide Film Controllable synthesis Microwave-assisted approach
1. Introduction As an important p-type semiconductor, copper selenide has been attracting increasing attention due to its fascinating properties and wide applications in solar cells [1], gas sensors [2], fast ionic conductors [3], thermoelectric converters [4], etc. As is well-known, copper selenide exists in a wide range of stoichiometric compositions (CuSe, Cu2Se, CuSe2, Cu3Se2, Cu5Se4, Cu7Se4, etc.) and nonstoichiometric compositions (Cu2xSe) [5e9]. There are several crystal structures (monoclinic, cubic, tetragonal, hexagonal, etc [10]) corresponding to these compositions. Many researches were focused on the synthesis methods such as solvothermal method [11], electrochemical technology [12,13], colloidal synthesis [14], solution phase reaction [15], chemical bath deposition [16,17] and pulsed laser deposition [18]. Recently, it is recognized that the size and shape of the semiconductor nanocrystals play important roles on their properties. However, the micro-morphology of the copper selenide has not been well studied yet in the literature. Zhang et al. [19] reported the controlled synthesis of CuSe with hexagonal nanoplates/ nanowires or only hexagonal nanoplates through a green paraffinacetate method in which the phase, composition and morphology of the final films could be controlled by adjusting the reaction parameters, especially the effective Cu/Se ratio of the reactants. * Corresponding authors. Tel./fax: þ86 374 296 8783. E-mail addresses: [email protected] (W.J. Fa), [email protected] (Z. Zheng). 1293-2558/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.solidstatesciences.2012.11.002
In the previous experiments, we have successfully fabricated hierarchically ordered dendritic Cu2xSe crystalline via a solvothermal routes by using alcohol as the solvent [20]. However, solvothermal process needs high pressure, high temperature and long reaction time. Compared with traditional heating, microwave heating is simple, rapid, uniform, efficient, economical and eco-friendly [21e23]. Herein, we report a microwave-assisted nonaqueous route for the synthesis of two kinds of copper selenide films on copper foil with different phases and morphologies. It is found that the morphologies and phases of the resulting films can be controlled by adjustment of several reaction parameters, such as solvent, temperature and irradiation time. 2. Experimental 2.1. Preparation All the reagents and solvents in analytical purity were purchased and used without further purification. A piece of copper foil, 1.0 0.5 cm2 (thickness: 0.2 mm), was used as substrate, which was ultrasonic rinsed well in diluted hydrochloric acid solution and ethanol in sequence to remove the impurity adhering to the surface of copper foil. The reaction was equipped with magnetic stirring. The exposure time and temperature were programmed. The automatic temperature-control system allowed continuous monitoring and controlling of the internal temperature of the reaction system
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J. Li et al. / Solid State Sciences 16 (2013) 125e129
Table 1 The reaction parameters for the different samples. Solvent
Quantity Temperature/ Irradiation The phase time/min and morphology of selenium C of the samples powder/g
Absolute ethanol Isopropyl alcohol Cyclohexyl alcohol Benzyl alcohol
0.015
80
40
No products
0.015
83
40
No products
0.015
160
10
Cubic Cu2xSe dendrites
0.015
150
10
Hexagonal CuSe flaky crystals
(1 C). The preset profile (desired time and temperature) was followed automatically by continuously adjusting the applied microwave power. As a typical preparation procedure, a piece of copper foil and 0.015 g elemental selenium powder was placed in a 50 mL three-neck round-bottom flask, and then 25 mL cyclohexyl alcohol was added. The reaction system was stirred at room temperature for 10 min, then heated to 160 C and maintained for 10 min under microwave irradiation. When the reaction mixture was cooled to room temperature, the foil was washed with absolute ethanol, and finally dried in vacuum for further characterization. Other solvents, such as benzyl alcohol, absolute ethanol and isopropyl alcohol, were also used instead of cyclohexyl alcohol while other parameters kept constant. 2.2. Characterization The as-prepared films were characterized by powder X-ray diffraction (XRD) on a Bruker D8 Advance X-ray diffractometer with Ni-filtered Cu Ka radiation at 40 kV and 40 mA. Data were recorded
at a 2q scan rate of 0.1 s step1 in the 2q range 20e90 . The morphologies of the resulting films were performed with a scanning electron microscope (SEM, ZEISS EVO LS15) at an accelerating voltage of 15 kV. 3. Results and discussion 3.1. Growth of copper selenide films in different reaction solvents When other parameters were unaltered, the final phase of copper selenide was determined by the experimental solvents. Table 1 lists the experimental parameters and the resulting samples. SEM images and the corresponding XRD patterns of films were shown in Fig. 1. Dendritic nanostructures were obtained under microwave irradiation for 10 min at 160 C in cyclohexyl alcohol (Fig. 1a). The corresponding XRD pattern of dendrites is matched well with the (111), (220) and (311) crystal planes of the cubic Cu2xSe (JCPDS No. 72-7490). The peaks marked with an asterisk (*) are assigned to the substrate copper foil (cubic copper, JCPDS No. 03-1005). When the solvent was substituted with benzyl alcohol, flaky crystals were obtained under microwave irradiation for 10 min at 150 C (Fig. 1c), whose morphologies were obviously different from dendrites. The corresponding XRD patterns confirmed the formation of a new crystal phase apart from the firstly generated Cu2xSe nanodendrites. These diffraction peaks (100), (101), (102) and (110) crystal planes can be well indexed to the hexagonal CuSe (JCPDS No. 34-171) (Fig. 1d). Compared with the Cu2xSe and CuSe films synthesized in cyclohexyl alcohol and benzyl alcohol, there were no products obtained in absolute ethanol and isopropyl alcohol solvothermal system even though the microwave irradiation time was prolonged to 40 min. The possible reason is that the boiling point of these alcohols is too low to activate the reaction.
Fig. 1. SEM micrographs and the corresponding XRD patterns of films in different reaction solvent a, b) cyclohexyl alcohol as solvent; c, d) benzyl alcohol as solvent.
J. Li et al. / Solid State Sciences 16 (2013) 125e129
127
Fig. 2. SEM micrographs and XRD patterns of the Cu2xSe films obtained at different reaction temperature in cyclohexyl alcohol reaction system. a) T ¼ 140 C; b) T ¼ 160 C.
3.2. The influence of the reaction temperature on the films The reaction temperature was controlled under the boiling point of the corresponding solvent. So the highest temperature was controlled at 160 C and 206 C when cyclohexyl alcohol and benzyl alcohol as the reaction medium, respectively. Fig. 2 shows SEM images and XRD patterns of the films formed at different reaction temperature in cyclohexyl alcohol reaction system. The cubic Cu2xSe could be obtained when the temperature increased from
140 C to 160 C. However, the growth of dendrites was not enough at the lower temperature (Fig. 2a). When the temperature increased to 160 C, which was a boiling temperature of cyclohexyl alcohol, the entirely dendrites were distributing the whole foil (Fig. 2b). The corresponding XRD patterns of dendrites were matched well with the cubic Cu2xSe (JCPDS No. 72-7490) (Fig. 2c). The (111), (220) and (311) diffraction peaks corresponding to the sample obtained at 160 C was stronger than that of films obtained at lower reaction temperature. These observations suggested that
Fig. 3. SEM micrographs and XRD patterns of the CuSe films obtained at different reaction temperature in benzyl alcohol reaction system. a) T ¼ 150 C; b) T ¼ 160 C.
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J. Li et al. / Solid State Sciences 16 (2013) 125e129
Fig. 4. SEM micrographs of the Cu2xSe films obtained in cyclohexyl alcohol with different microwave irradiation time. a: 5 min; b: 10 min; c: 15 min; d: 20 min.
a comparatively high temperature was favorable for the formation of the Cu2xSe dendrites in cyclohexyl alcohol reaction system. Fig. 3 shows SEM morphologies and XRD patterns of the films formed at different reaction temperature in benzyl alcohol reaction system. The flaky crystals were obtained at lower temperature of 150 C (Fig. 3a). The regular and smooth edges of flaky crystals were destroyed when the reaction temperature increased to 160 C (Fig. 3b). At the same time, the impure diffractive peaks were observed from the XRD patterns in the film obtained at higher reaction temperature (Fig. 3c). The results indicated that a comparatively low temperature was appropriate for the formation the CuSe flaky crystals in benzyl alcohol.
3.3. The influence of the irradiation time under microwave on the films In order to understand the influence of irradiation time under microwave on the crystal growth behavior, a series of timedependent experiments were performed. Figs. 4 and 5 showed the SEM images and XRD patterns of the films obtained in cyclohexyl alcohol at 160 C under microwave irradiation for 5 min, 10 min, 15 min and 20 min, respectively. When the reaction was carried out for 5 min, only a small quantity of dendrites appeared and the corresponding XRD diffraction intensity of Cu2xSe was weak, which indicated the irradiation time was not adequate (Fig. 4a). When the reaction time was prolonged to 10 min, the films were entirely dendrites (Fig. 4b). Further prolonging the reaction time to 15 min, the dendrites with more flower-like microstructures appeared (Fig. 4c). When the reaction time reached 20 min, flaky crystals were observed coexisting in the dendrites (Fig. 4d). A few diffraction peaks of CuSe also appeared in the XRD patterns (Fig. 5). So, 10 min was the most appropriate reaction time for the growth of Cu2xSe dendrites. 4. Conclusion
Fig. 5. XRD patterns of the Cu2xSe films obtained in cyclohexyl alcohol with different microwave irradiation time.
In summary, we have successfully prepared two kinds of different stoichiometric copper selenides with different phases and morphologies though controlling the reaction medium. Microwave-assisted nonaqueous approach is a simple, rapid, economical and efficient method. The Cu2xSe dendrites were synthesized when cyclohexyl alcohol as reaction solvent and CuSe flaky crystals were obtained when benzyl alcohol as reaction solvent. The reaction temperature and irradiation time under microwave also have a significant effect on the morphologies and the phases of the films. The higher temperature is favorable for the formation of the Cu2xSe dendrites in cyclohexyl alcohol. However,
J. Li et al. / Solid State Sciences 16 (2013) 125e129
the lower temperature is suitable for the formation of CuSe flaky crystals in benzyl alcohol. The optimized irradiation time for both copper selenides is 10 min. Acknowledgments We thank the Foundation of National Natural Science of China (21007053, 61106125, and 51102204), the Natural Science Foundation of Henan Province (122300410267) and the Education Department of Henan Province (2011A150025, 2012IRTSTHN021, 2012GGJS-174) for their financial support of this research. References [1] S.B. Ambade, R.S. Mane, S.S. Kale, S.H. Sonawane, A.V. Shaikh, S.H. Han, Appl. Surf. Sci. 253 (2006) 2123e2126. [2] J. Xu, W.X. Zhang, Z.H. Yang, S.X. Ding, C.Y. Zeng, L.L. Chen, Q. Wang, S.H. Yang, Adv. Funct. Mater. 19 (2009) 1759e1766. [3] S.A. Danilkin, J. Alloy. Compd. 467 (2009) 509e513. [4] Y. Zhang, C.G. Hu, C.H. Zheng, Y. Xi, B.Y. Wan, J. Phys. Chem. C 114 (2010) 14849e14853. [5] Z.M. Du, C.P. Guo, M. Tao, C.R. Li, Int. J. Mater. Res. 99 (2008) 294e300.
129
[6] X.B. Cao, C. Zhao, X.M. Lan, G.J. Gao, W.H. Qian, Y. Guo, J. Phys. Chem. C 111 (2007) 6658e6662. [7] M. Lakshmi, K. Bindu, S. Bini, K.P. Vijayakumar, C.S. Kartha, T. Abe, Y. Kashiwaba, Thin Solid Films 386 (2001) 127e132. [8] T. Ohtani, M. Shohno, J. Solid State Chem. 177 (2004) 3886e3890. [9] Y.J. Yang, L.Y. He, Russ. J. Electrochem. 41 (2005) 1241e1243. [10] P. Kumar, K. Singh, Struct. Chem. 22 (2011) 103e110. [11] F. Lin, G.Q. Bian, Z.X. Lei, Z.J. Lu, J. Dai, Solid State Sci. 11 (2009) 972e975. [12] Q.T. Wang, Mater. Lett. 63 (2009) 1493e1495. [13] R. Yu, T. Ren, K.J. Sun, Z.C. Feng, G.N. Li, C. Li, J. Phys. Chem. C 113 (2009) 10833e10837. [14] J. Choi, N. Kang, H.Y. Yang, H.J. Kim, S.U. Son, Chem. Mater. 22 (2010) 3586e3588. [15] T.P. Vinod, X. Jin, J. Kim, Mater. Res. Bull. 46 (2011) 340e344. [16] V.M. Garcia, P.K. Nair, M.T.S. Nair, J. Cryst. Growth 203 (1999) 113e124. [17] M. Lakshmi, K. Bindu, S. Bini, K.P. Vijayakumar, C.S. Kartha, T. Abe, Y. Kashiwaba, Thin Solid Films 370 (2000) 89e95. [18] M.Z. Xue, Y.N. Zhou, B. Zhang, L. Yu, H. Zhang, Z.W. Fu, J. Electrochem. Soc. 153 (2006) A2262eA2268. [19] A.Y. Zhang, Q.A. Ma, Z.G. Wang, M.K. Lu, P. Yang, G.J. Zhou, Mater. Chem. Phys. 124 (2010) 916e921. [20] D.P. Li, Z. Zheng, Y. Lei, S.X. Ge, Y.D. Zhang, Y.G. Zhang, K.W. Wong, F.L. Yang, W.M. Lau, CrystEngComm 12 (2010) 1856e1861. [21] S.X. Ge, L.Z. Zhang, H.M. Jia, Z. Zheng, J. Mater. Res. 24 (2009) 2268e2275. [22] H.D. Xie, D.Z. Shen, X.Q. Wang, G.Q. Shen, Mater. Chem. Phys. 110 (2008) 332e336. [23] S.X. Ge, Z.Y. Shui, Z. Zheng, L.Z. Zhang, Opt. Mater. 33 (2011) 1174e1178.
Contents lists available at SciVerse ScienceDirect
Solid State Sciences journal homepage: www.elsevier.com/locate/ssscie
Simultaneous phase and morphology controllable synthesis of copper selenide films by microwave-assisted nonaqueous approach Jing Li a, Wenjun Fa a, *, Yasi Li b, Hongxiao Zhao a, Yuanhao Gao a, Zhi Zheng a, * a
Key Laboratory for Micro-Nano Energy Storage and Conversion Materials of Henan Province, Institute of Surface Micro and Nano Materials, Xuchang University, Henan, Xuchang 461000, PR China b College of Chemistry and Chemical Engineering, Xuchang University, Xuchang 461000, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 April 2012 Received in revised form 31 October 2012 Accepted 1 November 2012 Available online 9 November 2012
Copper selenide films with different phase and morphology were synthesized on copper substrate through controlling reaction solvent by microwave-assisted nonaqueous approach. The films were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The result showed that the pure films could be obtained using cyclohexyl alcohol or benzyl alcohol as solvent. The cubic Cu2xSe dendrites were synthesized in cyclohexyl alcohol reaction system and hexagonal CuSe flaky crystals were obtained with benzyl alcohol as solvent. Ó 2012 Elsevier Masson SAS. All rights reserved.
Keywords: Copper selenide Film Controllable synthesis Microwave-assisted approach
1. Introduction As an important p-type semiconductor, copper selenide has been attracting increasing attention due to its fascinating properties and wide applications in solar cells [1], gas sensors [2], fast ionic conductors [3], thermoelectric converters [4], etc. As is well-known, copper selenide exists in a wide range of stoichiometric compositions (CuSe, Cu2Se, CuSe2, Cu3Se2, Cu5Se4, Cu7Se4, etc.) and nonstoichiometric compositions (Cu2xSe) [5e9]. There are several crystal structures (monoclinic, cubic, tetragonal, hexagonal, etc [10]) corresponding to these compositions. Many researches were focused on the synthesis methods such as solvothermal method [11], electrochemical technology [12,13], colloidal synthesis [14], solution phase reaction [15], chemical bath deposition [16,17] and pulsed laser deposition [18]. Recently, it is recognized that the size and shape of the semiconductor nanocrystals play important roles on their properties. However, the micro-morphology of the copper selenide has not been well studied yet in the literature. Zhang et al. [19] reported the controlled synthesis of CuSe with hexagonal nanoplates/ nanowires or only hexagonal nanoplates through a green paraffinacetate method in which the phase, composition and morphology of the final films could be controlled by adjusting the reaction parameters, especially the effective Cu/Se ratio of the reactants. * Corresponding authors. Tel./fax: þ86 374 296 8783. E-mail addresses: [email protected] (W.J. Fa), [email protected] (Z. Zheng). 1293-2558/$ e see front matter Ó 2012 Elsevier Masson SAS. All rights reserved. http://dx.doi.org/10.1016/j.solidstatesciences.2012.11.002
In the previous experiments, we have successfully fabricated hierarchically ordered dendritic Cu2xSe crystalline via a solvothermal routes by using alcohol as the solvent [20]. However, solvothermal process needs high pressure, high temperature and long reaction time. Compared with traditional heating, microwave heating is simple, rapid, uniform, efficient, economical and eco-friendly [21e23]. Herein, we report a microwave-assisted nonaqueous route for the synthesis of two kinds of copper selenide films on copper foil with different phases and morphologies. It is found that the morphologies and phases of the resulting films can be controlled by adjustment of several reaction parameters, such as solvent, temperature and irradiation time. 2. Experimental 2.1. Preparation All the reagents and solvents in analytical purity were purchased and used without further purification. A piece of copper foil, 1.0 0.5 cm2 (thickness: 0.2 mm), was used as substrate, which was ultrasonic rinsed well in diluted hydrochloric acid solution and ethanol in sequence to remove the impurity adhering to the surface of copper foil. The reaction was equipped with magnetic stirring. The exposure time and temperature were programmed. The automatic temperature-control system allowed continuous monitoring and controlling of the internal temperature of the reaction system
126
J. Li et al. / Solid State Sciences 16 (2013) 125e129
Table 1 The reaction parameters for the different samples. Solvent
Quantity Temperature/ Irradiation The phase time/min and morphology of selenium C of the samples powder/g
Absolute ethanol Isopropyl alcohol Cyclohexyl alcohol Benzyl alcohol
0.015
80
40
No products
0.015
83
40
No products
0.015
160
10
Cubic Cu2xSe dendrites
0.015
150
10
Hexagonal CuSe flaky crystals
(1 C). The preset profile (desired time and temperature) was followed automatically by continuously adjusting the applied microwave power. As a typical preparation procedure, a piece of copper foil and 0.015 g elemental selenium powder was placed in a 50 mL three-neck round-bottom flask, and then 25 mL cyclohexyl alcohol was added. The reaction system was stirred at room temperature for 10 min, then heated to 160 C and maintained for 10 min under microwave irradiation. When the reaction mixture was cooled to room temperature, the foil was washed with absolute ethanol, and finally dried in vacuum for further characterization. Other solvents, such as benzyl alcohol, absolute ethanol and isopropyl alcohol, were also used instead of cyclohexyl alcohol while other parameters kept constant. 2.2. Characterization The as-prepared films were characterized by powder X-ray diffraction (XRD) on a Bruker D8 Advance X-ray diffractometer with Ni-filtered Cu Ka radiation at 40 kV and 40 mA. Data were recorded
at a 2q scan rate of 0.1 s step1 in the 2q range 20e90 . The morphologies of the resulting films were performed with a scanning electron microscope (SEM, ZEISS EVO LS15) at an accelerating voltage of 15 kV. 3. Results and discussion 3.1. Growth of copper selenide films in different reaction solvents When other parameters were unaltered, the final phase of copper selenide was determined by the experimental solvents. Table 1 lists the experimental parameters and the resulting samples. SEM images and the corresponding XRD patterns of films were shown in Fig. 1. Dendritic nanostructures were obtained under microwave irradiation for 10 min at 160 C in cyclohexyl alcohol (Fig. 1a). The corresponding XRD pattern of dendrites is matched well with the (111), (220) and (311) crystal planes of the cubic Cu2xSe (JCPDS No. 72-7490). The peaks marked with an asterisk (*) are assigned to the substrate copper foil (cubic copper, JCPDS No. 03-1005). When the solvent was substituted with benzyl alcohol, flaky crystals were obtained under microwave irradiation for 10 min at 150 C (Fig. 1c), whose morphologies were obviously different from dendrites. The corresponding XRD patterns confirmed the formation of a new crystal phase apart from the firstly generated Cu2xSe nanodendrites. These diffraction peaks (100), (101), (102) and (110) crystal planes can be well indexed to the hexagonal CuSe (JCPDS No. 34-171) (Fig. 1d). Compared with the Cu2xSe and CuSe films synthesized in cyclohexyl alcohol and benzyl alcohol, there were no products obtained in absolute ethanol and isopropyl alcohol solvothermal system even though the microwave irradiation time was prolonged to 40 min. The possible reason is that the boiling point of these alcohols is too low to activate the reaction.
Fig. 1. SEM micrographs and the corresponding XRD patterns of films in different reaction solvent a, b) cyclohexyl alcohol as solvent; c, d) benzyl alcohol as solvent.
J. Li et al. / Solid State Sciences 16 (2013) 125e129
127
Fig. 2. SEM micrographs and XRD patterns of the Cu2xSe films obtained at different reaction temperature in cyclohexyl alcohol reaction system. a) T ¼ 140 C; b) T ¼ 160 C.
3.2. The influence of the reaction temperature on the films The reaction temperature was controlled under the boiling point of the corresponding solvent. So the highest temperature was controlled at 160 C and 206 C when cyclohexyl alcohol and benzyl alcohol as the reaction medium, respectively. Fig. 2 shows SEM images and XRD patterns of the films formed at different reaction temperature in cyclohexyl alcohol reaction system. The cubic Cu2xSe could be obtained when the temperature increased from
140 C to 160 C. However, the growth of dendrites was not enough at the lower temperature (Fig. 2a). When the temperature increased to 160 C, which was a boiling temperature of cyclohexyl alcohol, the entirely dendrites were distributing the whole foil (Fig. 2b). The corresponding XRD patterns of dendrites were matched well with the cubic Cu2xSe (JCPDS No. 72-7490) (Fig. 2c). The (111), (220) and (311) diffraction peaks corresponding to the sample obtained at 160 C was stronger than that of films obtained at lower reaction temperature. These observations suggested that
Fig. 3. SEM micrographs and XRD patterns of the CuSe films obtained at different reaction temperature in benzyl alcohol reaction system. a) T ¼ 150 C; b) T ¼ 160 C.
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J. Li et al. / Solid State Sciences 16 (2013) 125e129
Fig. 4. SEM micrographs of the Cu2xSe films obtained in cyclohexyl alcohol with different microwave irradiation time. a: 5 min; b: 10 min; c: 15 min; d: 20 min.
a comparatively high temperature was favorable for the formation of the Cu2xSe dendrites in cyclohexyl alcohol reaction system. Fig. 3 shows SEM morphologies and XRD patterns of the films formed at different reaction temperature in benzyl alcohol reaction system. The flaky crystals were obtained at lower temperature of 150 C (Fig. 3a). The regular and smooth edges of flaky crystals were destroyed when the reaction temperature increased to 160 C (Fig. 3b). At the same time, the impure diffractive peaks were observed from the XRD patterns in the film obtained at higher reaction temperature (Fig. 3c). The results indicated that a comparatively low temperature was appropriate for the formation the CuSe flaky crystals in benzyl alcohol.
3.3. The influence of the irradiation time under microwave on the films In order to understand the influence of irradiation time under microwave on the crystal growth behavior, a series of timedependent experiments were performed. Figs. 4 and 5 showed the SEM images and XRD patterns of the films obtained in cyclohexyl alcohol at 160 C under microwave irradiation for 5 min, 10 min, 15 min and 20 min, respectively. When the reaction was carried out for 5 min, only a small quantity of dendrites appeared and the corresponding XRD diffraction intensity of Cu2xSe was weak, which indicated the irradiation time was not adequate (Fig. 4a). When the reaction time was prolonged to 10 min, the films were entirely dendrites (Fig. 4b). Further prolonging the reaction time to 15 min, the dendrites with more flower-like microstructures appeared (Fig. 4c). When the reaction time reached 20 min, flaky crystals were observed coexisting in the dendrites (Fig. 4d). A few diffraction peaks of CuSe also appeared in the XRD patterns (Fig. 5). So, 10 min was the most appropriate reaction time for the growth of Cu2xSe dendrites. 4. Conclusion
Fig. 5. XRD patterns of the Cu2xSe films obtained in cyclohexyl alcohol with different microwave irradiation time.
In summary, we have successfully prepared two kinds of different stoichiometric copper selenides with different phases and morphologies though controlling the reaction medium. Microwave-assisted nonaqueous approach is a simple, rapid, economical and efficient method. The Cu2xSe dendrites were synthesized when cyclohexyl alcohol as reaction solvent and CuSe flaky crystals were obtained when benzyl alcohol as reaction solvent. The reaction temperature and irradiation time under microwave also have a significant effect on the morphologies and the phases of the films. The higher temperature is favorable for the formation of the Cu2xSe dendrites in cyclohexyl alcohol. However,
J. Li et al. / Solid State Sciences 16 (2013) 125e129
the lower temperature is suitable for the formation of CuSe flaky crystals in benzyl alcohol. The optimized irradiation time for both copper selenides is 10 min. Acknowledgments We thank the Foundation of National Natural Science of China (21007053, 61106125, and 51102204), the Natural Science Foundation of Henan Province (122300410267) and the Education Department of Henan Province (2011A150025, 2012IRTSTHN021, 2012GGJS-174) for their financial support of this research. References [1] S.B. Ambade, R.S. Mane, S.S. Kale, S.H. Sonawane, A.V. Shaikh, S.H. Han, Appl. Surf. Sci. 253 (2006) 2123e2126. [2] J. Xu, W.X. Zhang, Z.H. Yang, S.X. Ding, C.Y. Zeng, L.L. Chen, Q. Wang, S.H. Yang, Adv. Funct. Mater. 19 (2009) 1759e1766. [3] S.A. Danilkin, J. Alloy. Compd. 467 (2009) 509e513. [4] Y. Zhang, C.G. Hu, C.H. Zheng, Y. Xi, B.Y. Wan, J. Phys. Chem. C 114 (2010) 14849e14853. [5] Z.M. Du, C.P. Guo, M. Tao, C.R. Li, Int. J. Mater. Res. 99 (2008) 294e300.
129
[6] X.B. Cao, C. Zhao, X.M. Lan, G.J. Gao, W.H. Qian, Y. Guo, J. Phys. Chem. C 111 (2007) 6658e6662. [7] M. Lakshmi, K. Bindu, S. Bini, K.P. Vijayakumar, C.S. Kartha, T. Abe, Y. Kashiwaba, Thin Solid Films 386 (2001) 127e132. [8] T. Ohtani, M. Shohno, J. Solid State Chem. 177 (2004) 3886e3890. [9] Y.J. Yang, L.Y. He, Russ. J. Electrochem. 41 (2005) 1241e1243. [10] P. Kumar, K. Singh, Struct. Chem. 22 (2011) 103e110. [11] F. Lin, G.Q. Bian, Z.X. Lei, Z.J. Lu, J. Dai, Solid State Sci. 11 (2009) 972e975. [12] Q.T. Wang, Mater. Lett. 63 (2009) 1493e1495. [13] R. Yu, T. Ren, K.J. Sun, Z.C. Feng, G.N. Li, C. Li, J. Phys. Chem. C 113 (2009) 10833e10837. [14] J. Choi, N. Kang, H.Y. Yang, H.J. Kim, S.U. Son, Chem. Mater. 22 (2010) 3586e3588. [15] T.P. Vinod, X. Jin, J. Kim, Mater. Res. Bull. 46 (2011) 340e344. [16] V.M. Garcia, P.K. Nair, M.T.S. Nair, J. Cryst. Growth 203 (1999) 113e124. [17] M. Lakshmi, K. Bindu, S. Bini, K.P. Vijayakumar, C.S. Kartha, T. Abe, Y. Kashiwaba, Thin Solid Films 370 (2000) 89e95. [18] M.Z. Xue, Y.N. Zhou, B. Zhang, L. Yu, H. Zhang, Z.W. Fu, J. Electrochem. Soc. 153 (2006) A2262eA2268. [19] A.Y. Zhang, Q.A. Ma, Z.G. Wang, M.K. Lu, P. Yang, G.J. Zhou, Mater. Chem. Phys. 124 (2010) 916e921. [20] D.P. Li, Z. Zheng, Y. Lei, S.X. Ge, Y.D. Zhang, Y.G. Zhang, K.W. Wong, F.L. Yang, W.M. Lau, CrystEngComm 12 (2010) 1856e1861. [21] S.X. Ge, L.Z. Zhang, H.M. Jia, Z. Zheng, J. Mater. Res. 24 (2009) 2268e2275. [22] H.D. Xie, D.Z. Shen, X.Q. Wang, G.Q. Shen, Mater. Chem. Phys. 110 (2008) 332e336. [23] S.X. Ge, Z.Y. Shui, Z. Zheng, L.Z. Zhang, Opt. Mater. 33 (2011) 1174e1178.