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Solution-phase synthesis of rose-like CuO
Materials Letters 63 (2009) 1840–1843
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Solution-phase synthesis of rose-like CuO Yuanlie Yu a,b, Junyan Zhang a,⁎ a b
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China
a r t i c l e
i n f o
Article history: Received 12 February 2009 Accepted 26 May 2009 Available online 31 May 2009 Keywords: Rose-like Nanoarchitectures Band gap
a b s t r a c t Rose-like nanoarchitectures CuO have been prepared by a mild solution-phase route without the utility of templates, additives or external magnetic field. The CuO nanoparticles exhibit a perfect rose flower structure which are composed of nanosheets in size of several micrometers in length and width and 30–40 nm in thickness. The corresponding band gap was estimated to be 2.65 eV. It is expected that the novel copper compound particles may offer some potential applications in catalysis, electrochemistry, and sensors. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Cupric oxide (CuO) as an important P-type transition-metal semiconductor with a narrow band gap, has received much attention for their various applications. Recently, CuO not only has been used as field emission materials, catalyst, gas-sensing, high temperature superconductors and giant magneto-resistance materials [1–17], but also has been explored to be as a promising electrode material for solar cells [4–6,14]. For the properties of semiconductors depending on their size, shape and crystalline structure, the control of the shape and size of the semiconductors has become more important [18], and lots of well-defined CuO nanostructures have been prepared by a series of solution and vapor phase process, such as nanoparticles [19], nanoribbons [20,21], nanosheets [22], nanoneedles [23,24], nanorings [21], nanowhiskers [24], nanowires [25], nanorod [10,25,26], nanotubes [10], and nanoleves [8]. Compared with the sample 0-dimensional, 1-dimensional and 2-dimensional CuO structures, recently, researchers have focused on the complex 3-dimensional architectures due to the potential applications of the complex and hierarchical nano/microstructures [27–30]. Hollow dandelionlike CuO microspheres [31], nanoellipsoids [22], nanofluid [25], peanut-shaped nanoribbon bundle [32], chrysanthemum-like architectures [24], honeycomb-like [33], flower-like [33,34], and hollow microspheres CuO/Cu2O composite [18] have been obtained by different synthesis methods. Moreover, it is a challenge to control the construction of the hierarchical nanostructured materials and it still lacks great knowledge about assembling the hierarchical structures with low-dimensional nanosized units [34].
In this work, we report a facile and mild solution-phase approach without the use of templates, organic surfactants and external magnetic field, to synthesize well-defined rose-like CuO nanostructures. The advantages of the approach synthesized rose-like particles are their mild temperature, low cost, and easy control. The UV–vis spectra show that the band gap of the CuO nanoparticles is about 2.65 eV. It is expect that the novel copper compound particles may offer some exciting opportunities for some potential applications in catalysis, electrochemistry, and sensors. 2. Experimental 2.1. Synthesis All the reagents used in the experiments were analytically pure, and were used without further purification. A typical synthesis of copper compound micro/nanostructures was performed as follows: an aqueous solution was prepared in a 50 mL beaker by mixing analytically pure 8.4 g KOH, 1 g (NH4)2S2O8, and 30 mL water. When the aqueous solution was baked by water-base to 40 °C, 0.5 g Cu powders (≥99.5%, 200 mesh) were immersed in the solution quickly. Then the mixture was heated for 20 min. When stirring strongly, the initial temperature slowly rises reaching up to about 76 °C 15 min later in the heated procedure. When the reaction ended, the powders were rinsed with distilled water several times and were put into a furnace at 250 °C for 1 h in air, followed by cooling down to room temperature gradually. 2.2. Characterization
⁎ Corresponding author. Tel./fax: +86 931 4968295. E-mail address: [email protected] (J. Zhang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.05.061
The composition and structure of the as-prepared sample were examined by the X-ray powder diffraction (XRD, Philips X'Pert-MRD),
Y. Yu, J. Zhang / Materials Letters 63 (2009) 1840–1843
1841
Fig. 1. FE-SEM image of the rose-like structure: (a) a detailed obverse view on an individual rose-like structure, (b) a detailed side view on an individual rose-like structure, (c) a piece of petal and (d) side view of petals composed of rose-like CuO particles.
high-resolution transmission electron microscopy (HRTEM, JEM 2010), selected-area electron diffraction (SAED), and field emission electron microscopy (FE-SEM, JSM-6701F). The UV–vis absorption spectra were recorded on a SPECORD 50 spectrophotometer in the wavelength range of 200–600 nm.
3. Results and discussion Fig. 1 shows FE-SEM images of the rose-like CuO nanostructures. The panoramic FE-SEM image of an individual CuO particle (shown in Fig. 1a) exhibits a perfect rose flower structure, which are composed of
Fig. 2. (a) XRD patterns of the as-obtained products taken from the reaction at 76 °C 20 min; (b) TEM image of the rose-like structures and the inset is the SAED pattern of nanosheet formed the rose-like structure and (c) corresponding HRTEM image of this nanosheet.
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Y. Yu, J. Zhang / Materials Letters 63 (2009) 1840–1843
can be demonstrated that the as-obtained products are monoclinicphase CuO. UV–vis absorption measurement has been studied extensively, because it is one of the most important methods to investigate the energy structures and optical properties of semiconductor nanocrystals [22]. Fig. 3a shows the UV–vis absorption spectrum of samples which are dispersed in absolute ethanol. There is a broad absorption peak with broader shoulders at about 270–340 nm and weak absorption peak at about 355–375 nm. The absorption edge energy (Eg) can be determined by the following equation: n=2
αhm = Aðhm− EgÞ
where α is the absorption coefficient, ν is the frequency of photons, A is a constant, Eg is the band gap energy and n depends on the nature of the transition (n = 1 for direct transitions) [25]. As shown in Fig. 3b, we have plotted (αhν)2 as a function of (hν − Eg) to estimate the Eg for direct transition. According to the extrapolated values (the point of intersection of the straight lines and the x axis) of linear section, the band gap Eg is estimated to be 2.65 eV and 3.25 eV (compared to the XRD pattern and other works, we think 2.65 eV is the band gap of the as-obtained products [8,22]). Compared with that of the bulk (1.85 eV) [35], the value blue-shifts by 0.80 eV due to quantum size effect [33]. 4. Conclusion
Fig. 3. (a) UV–vis absorption spectrum of sample dispersed in absolute ethanol and (b) (αE)2 vs E curves of the products.
many interconnected wide nanosheets. The diameter of the CuO micro-flower is about 4 μm. Fig. 1b shows a detailed side view on the individual rose-like CuO particle, which clearly shows that the sample unfolds a layered structure like a rose flower. Fig. 1c shows a typical image of a piece of leaves forming the rose-like structures, which clearly shows that the width of nanopetals is about 1.2 μm and the length is about 2.2 μm and the thickness is in average of 30–40 nm at a higher magnification (shown in Fig. 1d). The composition of the as-prepared sample was examined by XRD. The typical XRD patterns of the samples are shown in Fig. 2a. In the XRD patterns, there are three kinds of peaks that appeared, which belong to CuO, Cu2O and Cu, respectively. Compared with the standard diffraction peaks from JPCDS card no. 02-1040, the peaks [− 110], [002], [111], [− 202], [020], [202], [−113], [−311] and [− 220] can be indexed to monoclinic-phase CuO. The diffraction peaks marked with a star (☆) and a rhombus (♦) are attributed to Cu and Cu2O (JCPDS card no. 77-0199), respectively. The reason that the peaks of Cu and Cu2O appeared is that the Cu powders were superfluous in the solution and some of them were not completely reacted. Compared with standard diffraction patterns, there are no other characteristic peaks observed belonging to impurities. By the analysis of XRD, it can be demonstrated that the as-obtained particles are mostly CuO and a small quantity of Cu2O. For detailed structure observations, the products were further characterized by TEM, shown in Fig. 2b and c. Fig. 2b represents the morphology of rose-like CuO micro/nanostructures, which reveals that the CuO flower is composed of wide nanosheets. The inset in Fig. 2b shows the corresponding electron diffraction pattern taken from a piece of nanopetal, which markedly indicates the rose-like structure is a single-crystal. Fig. 2c shows a typical HRTEM image of the CuO micro/nano rose-like structure. The HRTEM image shows that the regular spacing of the clear lattice planes is 0.252 nm, which corresponds well to (002) planes of monoclinic-phase CuO. On the basis of HRTEM and SAED analysis, it
In summary, we have succeeded in constructing well-defined roselike micro/nano CuO structures by a simple strategy. The rose-like structures are composed of nanosheets in size of several micrometers in length and width and 30–40 nm in thickness. The advantages of the approach synthesizing rose-like particles for the final practical applications are their mild temperature, low cost, and easy control. In our work, UV–vis spectra were employed to estimate the optical property and the band gap of CuO nanoparticles is determined to be 2.65 eV. It is expect that the novel copper compound particles may offer some exciting opportunities for some potential applications in catalysis, electrochemistry, and sensors. Acknowledgments The authors are grateful to the National Natural Science Foundation of China (Grant No. 50572108) and “Hundreds Talent Program” of the Chinese Academy of Sciences for financial support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
Yu H, Yu JG, Liu SG, Mann S. Chem Mater 2007;19:4327–34. Wen XG, Xie YT, Choi CL, Wan KC, Li XY, Yang SH. Langmuir 2005;21:4729–37. Hsieh CT, Chen JM, Lin HH, Shih HC. Appl Phys Lett 2003;82:3316–8. Xu YY, Chen DR, Jiao XL. J Phys Chem B 2005;109:13561–6. Xu JS, Xue DF. J Phys Chem B 2005;109:17157–61. Song XY, Yu HY, Sun SX. J Colloid Interface Sci 2005;289:588–91. Lee SH, Her YS, Matijevic E. J Colloid Interface Sci 1997;186:193–202. Liangy ZH, Zhu YJ. Chem Lett 2004;33:1314–5. Yang R, Gao L. Chem Lett 2004;33:1194–5. Cao MH, Hu CW, Wang YH, Guo YH, Guo CX, Wang EB. Chem Commun 2003;15: 1884–5. Jiang XC, Herricks T, Xia YN. Nano Lett 2002;2:1333–8. Du GH, Van Tendeloo G. Chem Phys Lett 2004;393:64–9. Chang Y, Zeng HC. Cryst Growth Des 2004;4:397–402. Lu CH, Qi LM, Yang JH, Zhang DY, Wu NZ, Ma JM. J Phys Chem B 2004;108:17825–31. Liu Y, Chu Y, Li MY, Dong LH. J Mater Chem 2006;16:192–8. Musa AO, Akomolafe T, Carter MJ. Sol Energy Mater Sol Cells 1998;51:305–16. Zheng XG, Xu CN, Tomokiyo Y, Tanaka E, Yamada H, Soejima Y. Phys Rev Lett 2000;85:5170–3. Alivisatos AP. Science 1996:271933–7. Zhong ZY, Ng V, Luo ZH, Teh SP, Teo J, Gedanken A. Langmuir 2007;23:5971–7. Hou HY, Xie Y, Li Q. Cryst Growth Des 2005;5:201–5. Wang XQ, Xi GG, Xiong SL, Liu YK, Xi BJ, Yu WC, et al. Cryst Growth Des 2007;7: 930–4.
Y. Yu, J. Zhang / Materials Letters 63 (2009) 1840–1843 [22] Liu JP, Huang XT, Li YY, Sulieman KM, He X, Sun FG. Cryst Growth Des 2006;6: 1690–6. [23] Liu YL, Liao L, Li JC, Pan CX. J Phys Chem C 2007;111:5050–6. [24] Zhang WX, Wen XG, Yang SH. Inorg Chem 2003;42:5005–14. [25] Kaur M, Muthe KP, Despande SK, Choudhury S, Singh JB, Verma N. J Cryst Growth 2006;289:670–5. [26] Wang WZ, Zhan YJ, Wang GH. Chem Commun 2001:727–8. [27] Yonezawa T, Onoue S, Kimizuka N. Adv Mater 2001;13:140–2. [28] Ewers TD, Sra AK, Norris BC, Cable RE, Cheng CH, Shantz DF, et al. Chem Mater 2005;17:514–20.
[29] [30] [31] [32] [33] [34] [35]
1843
Chen XY, Wang X, Wang ZH, Yang XG, Qian YT. Cryst Growth Des 2005;5:347–50. Zhang J, Sun LD, Yin JL, Su HL, Liao CS, Yan CH. Chem Mater 2002;14:4172–7. Liu B, Zeng HC. J Am Chem Soc 2004;126:8124–5. Zhang LZ, Yu JC, Xu AW, Li Q, Kwong KW, Yu SH. J Cryst Growth 2004;266:545–51. Liu Y, Chu Y, Zhuo YJ, Li MY, Li LL, Dong LH. Cryst Growth Des 2007;7:467–70. Xu YY, Chen DR, Jiao XL, Xue KY. Mater Res Bull 2007;42:1723–31. Santra K, Sarkar CK, Mukherjee MK, Cosh B. Thin Solid Films 1992;213:226–9.
Contents lists available at ScienceDirect
Materials Letters j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / m a t l e t
Solution-phase synthesis of rose-like CuO Yuanlie Yu a,b, Junyan Zhang a,⁎ a b
State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China Graduate School of the Chinese Academy of Sciences, Beijing 100039, PR China
a r t i c l e
i n f o
Article history: Received 12 February 2009 Accepted 26 May 2009 Available online 31 May 2009 Keywords: Rose-like Nanoarchitectures Band gap
a b s t r a c t Rose-like nanoarchitectures CuO have been prepared by a mild solution-phase route without the utility of templates, additives or external magnetic field. The CuO nanoparticles exhibit a perfect rose flower structure which are composed of nanosheets in size of several micrometers in length and width and 30–40 nm in thickness. The corresponding band gap was estimated to be 2.65 eV. It is expected that the novel copper compound particles may offer some potential applications in catalysis, electrochemistry, and sensors. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Cupric oxide (CuO) as an important P-type transition-metal semiconductor with a narrow band gap, has received much attention for their various applications. Recently, CuO not only has been used as field emission materials, catalyst, gas-sensing, high temperature superconductors and giant magneto-resistance materials [1–17], but also has been explored to be as a promising electrode material for solar cells [4–6,14]. For the properties of semiconductors depending on their size, shape and crystalline structure, the control of the shape and size of the semiconductors has become more important [18], and lots of well-defined CuO nanostructures have been prepared by a series of solution and vapor phase process, such as nanoparticles [19], nanoribbons [20,21], nanosheets [22], nanoneedles [23,24], nanorings [21], nanowhiskers [24], nanowires [25], nanorod [10,25,26], nanotubes [10], and nanoleves [8]. Compared with the sample 0-dimensional, 1-dimensional and 2-dimensional CuO structures, recently, researchers have focused on the complex 3-dimensional architectures due to the potential applications of the complex and hierarchical nano/microstructures [27–30]. Hollow dandelionlike CuO microspheres [31], nanoellipsoids [22], nanofluid [25], peanut-shaped nanoribbon bundle [32], chrysanthemum-like architectures [24], honeycomb-like [33], flower-like [33,34], and hollow microspheres CuO/Cu2O composite [18] have been obtained by different synthesis methods. Moreover, it is a challenge to control the construction of the hierarchical nanostructured materials and it still lacks great knowledge about assembling the hierarchical structures with low-dimensional nanosized units [34].
In this work, we report a facile and mild solution-phase approach without the use of templates, organic surfactants and external magnetic field, to synthesize well-defined rose-like CuO nanostructures. The advantages of the approach synthesized rose-like particles are their mild temperature, low cost, and easy control. The UV–vis spectra show that the band gap of the CuO nanoparticles is about 2.65 eV. It is expect that the novel copper compound particles may offer some exciting opportunities for some potential applications in catalysis, electrochemistry, and sensors. 2. Experimental 2.1. Synthesis All the reagents used in the experiments were analytically pure, and were used without further purification. A typical synthesis of copper compound micro/nanostructures was performed as follows: an aqueous solution was prepared in a 50 mL beaker by mixing analytically pure 8.4 g KOH, 1 g (NH4)2S2O8, and 30 mL water. When the aqueous solution was baked by water-base to 40 °C, 0.5 g Cu powders (≥99.5%, 200 mesh) were immersed in the solution quickly. Then the mixture was heated for 20 min. When stirring strongly, the initial temperature slowly rises reaching up to about 76 °C 15 min later in the heated procedure. When the reaction ended, the powders were rinsed with distilled water several times and were put into a furnace at 250 °C for 1 h in air, followed by cooling down to room temperature gradually. 2.2. Characterization
⁎ Corresponding author. Tel./fax: +86 931 4968295. E-mail address: [email protected] (J. Zhang). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.05.061
The composition and structure of the as-prepared sample were examined by the X-ray powder diffraction (XRD, Philips X'Pert-MRD),
Y. Yu, J. Zhang / Materials Letters 63 (2009) 1840–1843
1841
Fig. 1. FE-SEM image of the rose-like structure: (a) a detailed obverse view on an individual rose-like structure, (b) a detailed side view on an individual rose-like structure, (c) a piece of petal and (d) side view of petals composed of rose-like CuO particles.
high-resolution transmission electron microscopy (HRTEM, JEM 2010), selected-area electron diffraction (SAED), and field emission electron microscopy (FE-SEM, JSM-6701F). The UV–vis absorption spectra were recorded on a SPECORD 50 spectrophotometer in the wavelength range of 200–600 nm.
3. Results and discussion Fig. 1 shows FE-SEM images of the rose-like CuO nanostructures. The panoramic FE-SEM image of an individual CuO particle (shown in Fig. 1a) exhibits a perfect rose flower structure, which are composed of
Fig. 2. (a) XRD patterns of the as-obtained products taken from the reaction at 76 °C 20 min; (b) TEM image of the rose-like structures and the inset is the SAED pattern of nanosheet formed the rose-like structure and (c) corresponding HRTEM image of this nanosheet.
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Y. Yu, J. Zhang / Materials Letters 63 (2009) 1840–1843
can be demonstrated that the as-obtained products are monoclinicphase CuO. UV–vis absorption measurement has been studied extensively, because it is one of the most important methods to investigate the energy structures and optical properties of semiconductor nanocrystals [22]. Fig. 3a shows the UV–vis absorption spectrum of samples which are dispersed in absolute ethanol. There is a broad absorption peak with broader shoulders at about 270–340 nm and weak absorption peak at about 355–375 nm. The absorption edge energy (Eg) can be determined by the following equation: n=2
αhm = Aðhm− EgÞ
where α is the absorption coefficient, ν is the frequency of photons, A is a constant, Eg is the band gap energy and n depends on the nature of the transition (n = 1 for direct transitions) [25]. As shown in Fig. 3b, we have plotted (αhν)2 as a function of (hν − Eg) to estimate the Eg for direct transition. According to the extrapolated values (the point of intersection of the straight lines and the x axis) of linear section, the band gap Eg is estimated to be 2.65 eV and 3.25 eV (compared to the XRD pattern and other works, we think 2.65 eV is the band gap of the as-obtained products [8,22]). Compared with that of the bulk (1.85 eV) [35], the value blue-shifts by 0.80 eV due to quantum size effect [33]. 4. Conclusion
Fig. 3. (a) UV–vis absorption spectrum of sample dispersed in absolute ethanol and (b) (αE)2 vs E curves of the products.
many interconnected wide nanosheets. The diameter of the CuO micro-flower is about 4 μm. Fig. 1b shows a detailed side view on the individual rose-like CuO particle, which clearly shows that the sample unfolds a layered structure like a rose flower. Fig. 1c shows a typical image of a piece of leaves forming the rose-like structures, which clearly shows that the width of nanopetals is about 1.2 μm and the length is about 2.2 μm and the thickness is in average of 30–40 nm at a higher magnification (shown in Fig. 1d). The composition of the as-prepared sample was examined by XRD. The typical XRD patterns of the samples are shown in Fig. 2a. In the XRD patterns, there are three kinds of peaks that appeared, which belong to CuO, Cu2O and Cu, respectively. Compared with the standard diffraction peaks from JPCDS card no. 02-1040, the peaks [− 110], [002], [111], [− 202], [020], [202], [−113], [−311] and [− 220] can be indexed to monoclinic-phase CuO. The diffraction peaks marked with a star (☆) and a rhombus (♦) are attributed to Cu and Cu2O (JCPDS card no. 77-0199), respectively. The reason that the peaks of Cu and Cu2O appeared is that the Cu powders were superfluous in the solution and some of them were not completely reacted. Compared with standard diffraction patterns, there are no other characteristic peaks observed belonging to impurities. By the analysis of XRD, it can be demonstrated that the as-obtained particles are mostly CuO and a small quantity of Cu2O. For detailed structure observations, the products were further characterized by TEM, shown in Fig. 2b and c. Fig. 2b represents the morphology of rose-like CuO micro/nanostructures, which reveals that the CuO flower is composed of wide nanosheets. The inset in Fig. 2b shows the corresponding electron diffraction pattern taken from a piece of nanopetal, which markedly indicates the rose-like structure is a single-crystal. Fig. 2c shows a typical HRTEM image of the CuO micro/nano rose-like structure. The HRTEM image shows that the regular spacing of the clear lattice planes is 0.252 nm, which corresponds well to (002) planes of monoclinic-phase CuO. On the basis of HRTEM and SAED analysis, it
In summary, we have succeeded in constructing well-defined roselike micro/nano CuO structures by a simple strategy. The rose-like structures are composed of nanosheets in size of several micrometers in length and width and 30–40 nm in thickness. The advantages of the approach synthesizing rose-like particles for the final practical applications are their mild temperature, low cost, and easy control. In our work, UV–vis spectra were employed to estimate the optical property and the band gap of CuO nanoparticles is determined to be 2.65 eV. It is expect that the novel copper compound particles may offer some exciting opportunities for some potential applications in catalysis, electrochemistry, and sensors. Acknowledgments The authors are grateful to the National Natural Science Foundation of China (Grant No. 50572108) and “Hundreds Talent Program” of the Chinese Academy of Sciences for financial support. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
Yu H, Yu JG, Liu SG, Mann S. Chem Mater 2007;19:4327–34. Wen XG, Xie YT, Choi CL, Wan KC, Li XY, Yang SH. Langmuir 2005;21:4729–37. Hsieh CT, Chen JM, Lin HH, Shih HC. Appl Phys Lett 2003;82:3316–8. Xu YY, Chen DR, Jiao XL. J Phys Chem B 2005;109:13561–6. Xu JS, Xue DF. J Phys Chem B 2005;109:17157–61. Song XY, Yu HY, Sun SX. J Colloid Interface Sci 2005;289:588–91. Lee SH, Her YS, Matijevic E. J Colloid Interface Sci 1997;186:193–202. Liangy ZH, Zhu YJ. Chem Lett 2004;33:1314–5. Yang R, Gao L. Chem Lett 2004;33:1194–5. Cao MH, Hu CW, Wang YH, Guo YH, Guo CX, Wang EB. Chem Commun 2003;15: 1884–5. Jiang XC, Herricks T, Xia YN. Nano Lett 2002;2:1333–8. Du GH, Van Tendeloo G. Chem Phys Lett 2004;393:64–9. Chang Y, Zeng HC. Cryst Growth Des 2004;4:397–402. Lu CH, Qi LM, Yang JH, Zhang DY, Wu NZ, Ma JM. J Phys Chem B 2004;108:17825–31. Liu Y, Chu Y, Li MY, Dong LH. J Mater Chem 2006;16:192–8. Musa AO, Akomolafe T, Carter MJ. Sol Energy Mater Sol Cells 1998;51:305–16. Zheng XG, Xu CN, Tomokiyo Y, Tanaka E, Yamada H, Soejima Y. Phys Rev Lett 2000;85:5170–3. Alivisatos AP. Science 1996:271933–7. Zhong ZY, Ng V, Luo ZH, Teh SP, Teo J, Gedanken A. Langmuir 2007;23:5971–7. Hou HY, Xie Y, Li Q. Cryst Growth Des 2005;5:201–5. Wang XQ, Xi GG, Xiong SL, Liu YK, Xi BJ, Yu WC, et al. Cryst Growth Des 2007;7: 930–4.
Y. Yu, J. Zhang / Materials Letters 63 (2009) 1840–1843 [22] Liu JP, Huang XT, Li YY, Sulieman KM, He X, Sun FG. Cryst Growth Des 2006;6: 1690–6. [23] Liu YL, Liao L, Li JC, Pan CX. J Phys Chem C 2007;111:5050–6. [24] Zhang WX, Wen XG, Yang SH. Inorg Chem 2003;42:5005–14. [25] Kaur M, Muthe KP, Despande SK, Choudhury S, Singh JB, Verma N. J Cryst Growth 2006;289:670–5. [26] Wang WZ, Zhan YJ, Wang GH. Chem Commun 2001:727–8. [27] Yonezawa T, Onoue S, Kimizuka N. Adv Mater 2001;13:140–2. [28] Ewers TD, Sra AK, Norris BC, Cable RE, Cheng CH, Shantz DF, et al. Chem Mater 2005;17:514–20.
[29] [30] [31] [32] [33] [34] [35]
1843
Chen XY, Wang X, Wang ZH, Yang XG, Qian YT. Cryst Growth Des 2005;5:347–50. Zhang J, Sun LD, Yin JL, Su HL, Liao CS, Yan CH. Chem Mater 2002;14:4172–7. Liu B, Zeng HC. J Am Chem Soc 2004;126:8124–5. Zhang LZ, Yu JC, Xu AW, Li Q, Kwong KW, Yu SH. J Cryst Growth 2004;266:545–51. Liu Y, Chu Y, Zhuo YJ, Li MY, Li LL, Dong LH. Cryst Growth Des 2007;7:467–70. Xu YY, Chen DR, Jiao XL, Xue KY. Mater Res Bull 2007;42:1723–31. Santra K, Sarkar CK, Mukherjee MK, Cosh B. Thin Solid Films 1992;213:226–9.