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Controllable hydrothermal synthesis of Cu2S nanowires on the copper substrate
Materials Letters 64 (2010) 252–254
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 ev i e r. c o m / l o c a t e / m a t l e t
Controllable hydrothermal synthesis of Cu2S nanowires on the copper substrate Xuelian Yu a,b,⁎, Xiaoqiang An c a b c
School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China Motorola (China) Electronics Ltd., No. 10, 4th Avenue, TEDA, Tianjin 300457, P. R. China Department of Fire Protection Engineering, Chinese People's Armed Police Academy, Langfang, Hebei 065000, PR China
a r t i c l e
i n f o
Article history: Received 25 September 2009 Accepted 22 October 2009 Available online 27 October 2009 Keywords: Crystal growth Nanomaterials Copper sulfide Hydrothermal reaction Optical property
a b s t r a c t In this paper, a simple solution-based method has been applied to fabricate metal chalcogenide nanostructures. Abundant Cu2S nanowires on Cu substrates are successfully prepared through the in-situ hydrothermal reaction between sulfur powder and Cu foil. It is observed that the addition of hydrazine and cetyltrimethylammonium bromide plays an important role in the growth of Cu2S nanowires. A rolling-up mechanism of metal chalcogenide film is used to illustrate the growth of these nanostructures. UV–vis spectrum of Cu2S nanowires reveals obvious absorption below the wavelength of 900 nm. The calculated band gap of Cu2S nanowires (1.5 eV) shows obvious blue shift because of the quantum size effect. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Transition metal chalcogenide semiconductors have attracted extraordinary research interest owing to their potential application in catalyst, solar cell, field emission, photoluminescence and optoelectronic devices [1]. Among them, Cu2S is an excellent p-type semiconductor material with a direct band gap of 1.2 eV. It shows promising applications in solar cells, transistor for panel display, electronic and optoelectronic chips [2,3]. Various Cu2S nanostructures have been obtained by various methods, such as nanoparticles, nanodisks, nanowires, nanobelts, and dendrites [4–8]. However, most of them are in a powder form. The growth of onedimensional (1-D) nanostructures on substrates is considered to be a definitive step toward the fabrication of advanced nanodevices [9]. Hence, much attention has been paid to the reaction around substrate surface, in order to fabricate 1-D metal chalcogenide nanostructures. For example, Yu et al fabricated oriented nickel sulfide nanowires on Ni foil via a hydrothermal method [10]. They also obtained PbTe nanowires on Pb foil through a rolling-up process [11]. Oriented Cu2S nanowires have also been fabricated by a gas–solid reaction of Cu foil [12,13]. However, solution-based synthesis of copper chalcogenide is more attractive because of its controllability, low cost and high yield [14]. Recently, Zhang et al fabricated 1-D CuTe nanostructures on copper substrate [15]. The in-situ synthesis of 1-D Cu2S nanostructures on substrate has not been reported. In this paper, abundant Cu2S nanowires have been successfully fabricated on Cu substrate by the hydrothermal reaction ⁎ Corresponding author. School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China. Tel.: +86 0316 2067260. E-mail address: [email protected] (X. Yu). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.051
between sulfur powder and copper foil. The possible growth mechanism and optical property are well discussed. 2. Experimental In a typical procedure, a piece of copper foil (Thickness: 0.2 mm; 2 ⁎ 2 cm), 1 mmol sulfur powder, 1 mL hydrazine and 1 mmol cetyltrimethylammonium bromide (CTAB) were placed in an autoclave.
Fig. 1. XRD pattern of the Cu2S nanostructures on copper substrate.
X. Yu, X. An / Materials Letters 64 (2010) 252–254
253
Fig. 2. (a) SEM image of the Cu2S nanowires on Cu foil; (b) TEM image of the Cu2S nanowires.
Then 25 mL distilled water was added. The autoclave was maintained at 180 °C for 12 h and cooled to room temperature naturally. The copper foil was taken out, washed with ethanol and dried in air for the characterization. The structure of the product was characterized by X-ray powder diffraction (XRD, Philips X'pert PRO). Scanning electron microscopy (SEM, KYKY-2800) and transmission electron microscopy (TEM, Hitachi H-800) were used to characterize the morphology of the products. The optical property was studied by the UV–vis absorption spectrum (U-3101, Hitachi). 3. Results and discussion Fig. 1 shows the XRD pattern of the collected product. The strong peaks around 43, 50 and 75° are all ascribed to the copper substrate. All the other peaks can be indexed to hexagonal β-Cu2S (JCPDS card File No. 46-1195). Thus, the formation of Cu2S on the copper substrate is well deduced. Fig. 2a is the SEM image of the product in the presence of 1 mmol CTAB. As can be seen clearly, the surface of copper foil is well covered by abundant of straight nanowires. These nanowires were ultrasonic treated with ethanol and further characterized by TEM. In Fig. 2b, the
Cu2S nanowires have a large aspect ratio and the average diameter is about 110 nm. The inset in Fig. 2b is the SAED pattern of Cu2S nanowire, which can be well indexed to hexagonal β-Cu2S. The polycrystalline nature of them can be easily deduced. To investigate the growth mechanism of nanowires, the influence of experimental conditions to the product is researched. It indicates that hydrazine is essential for the formation of Cu2S nanowires. As can be seen from Fig. 3a, no obvious 1-D nanostructure is obtained in the absence of hydrazine. In addition, CTAB shows a promotive effect to the growth of Cu2S nanowires. In Fig. 3b, only networked Cu2S nanostructures are collected in the hydrazine solution without CTAB. While with the addition of 1 mL hydrazine and 2 mmol CTAB, abundant Cu2S nanowires with higher aspect ratio are achieved (Fig. 3c). Moreover, CuTe nanowires can also be in-situ fabricated using similar situation, which indicates the applicability of this method in the synthesis of other metal chalcogenide materials. A rolling-up mechanism was used to explain the growth of metal telluride nanostructures in previous reports. The formation of a thin layer of metal telluride in the initial stage was supposed. This mechanism might also be applied to illustrate the growth of Cu2S nanowires in our experiments. As can be seen from the above results, hydrazine played an important role in this process, because no Cu2S
Fig. 3. SEM images of the copper chalcogenide on Cu foil under different conditions. (a) 1 mmol S, 1 mmol CTAB; (b) 1 mmol S, 1 mL hydrazine; (c) 1 mmol S, 2 mmol CTAB and 1 mL hydrazine; (d) CuTe nanowires in the presence of 1 mmol Te powder.
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X. Yu, X. An / Materials Letters 64 (2010) 252–254
Fig. 4. (a) Intermediate nanosheets obtained in the reaction; (b) UV–vis spectrum of the Cu2S nanowires.
nanowires were obtained in the absence of hydrazine. As the literature report [16], it was believed that hydrazine promoted the formation of Cu2S film through forming a complex between copper foil and hydrazine in our work. In addition, CTAB acted as a selective etchant to aid the rolling up of the in-situ formed film, into 1-D nanostructures [17]. The porous film in Fig. 3b and intermediate nanosheets in Fig. 4a well proved our hypothesis. Fig. 4b shows the UV–vis spectrum of the prepared Cu2S nanowires, which reveals obvious absorption below the wavelength of 900 nm. Cu2S nanowires show an absorption edge at about 830 nm. Thus, the calculated band gap of Cu2S nanowires is about 1.5 eV. This value shows obvious blue shift compared to that of bulk phase (1022 nm, 1.21 eV), and a little larger than that of Cu2S nanocrystals [18]. It is believed that this shift is a result of the quantum size effect [19,20]. 4. Conclusion In summary, abundant Cu2S nanowires on Cu substrate were prepared through the in-situ hydrothermal reaction between sulfur powder and Cu foil, in the presence of hydrazine and CTAB. A rollingup mechanism is used to illustrate the growth of these nanostructures. Hydrazine and CTAB are both essential in the formation of Cu2S nanowires.
Acknowledgement This work was supported by the China Postdoctoral Science Foundation via Grant No. 20090450089.
References [1] Hu Y, Zheng Z, Jia H, Tang Y, Zhang L. J Phys Chem, C 2008;112:13037–42. [2] Peng M, Ma L, Zhang Y, Tan M, Wang J, Yu Y. Mater Res Bull 2009;44:1834–41. [3] Soga T. Nanostructured Materials for Solar Energy Conversion. Amsterdam: Elsevier; 2006. [4] Li S, Wang H, Xu W, Si H, Tao X, Lou S, et al. J Colloid Interface Sci 2009;330:483–7. [5] Chen Y, Chen L, Wu L. Chem Eur J 2008;14:11069–75. [6] Wang S, Yang S. Adv Mater Opt Electron 2000;10:39–45. [7] Li Z, Yan H, Ding Y, Xiong Y, Xie Y. Dalton Trans 2006;149:149–51. [8] Gorai S, Ganguli D, Chaudhuri S. Mater Lett 2005;59:826–8. [9] Liu Y, Mao J, Jiang P, Xu Z, Yuan H, Xiao D. Cryst Eng Comm 2009; ASAP Articles. [10] Zhang L, Yu JC, Mo M, Wu L, Li Q, Kwong KW. J Am Chem Soc 2004;126:8116–7. [11] Zhang L, Yu JC, Mo M, Wu L, Kwong KW, Li Q. Small 2005;1:349–54. [12] Wang S, Yang S, Dai ZR, Wang ZL. Phys Chem Chem Phys 2001;3:3750–3. [13] Lim Y, Ok YW, Tark SJ, Kang Y, Kim D. Curr Appl Phys 2009;9:890–3. [14] Zhang X, Guo Y, Liu W. Mater Lett 2009;63:982–4. [15] Zhang L, Ai Z, Jia F, Liu L, Hu X, Yu JC. Chem Eur J 2006;12:4185–90. [16] Yuan M, Mitzi DB. Dalton Trans 2009:6078–88. [17] Lv S, Suo H, Zhao X, Wang C, Zhou T, Jing S, et al. J Alloy Compd 2009;479:L43–6. [18] Wu Y, Wadia C, Ma W, Sadtler B, Alivisatos AP. Nano lette 2008;8:2551–5. [19] Zhang P, Gao L. J Mater Chem 2003;13:2007–10. [20] Ding Y, Liu X, Guo R. Mater Res Bull 2008;43:748–58.
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 ev i e r. c o m / l o c a t e / m a t l e t
Controllable hydrothermal synthesis of Cu2S nanowires on the copper substrate Xuelian Yu a,b,⁎, Xiaoqiang An c a b c
School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China Motorola (China) Electronics Ltd., No. 10, 4th Avenue, TEDA, Tianjin 300457, P. R. China Department of Fire Protection Engineering, Chinese People's Armed Police Academy, Langfang, Hebei 065000, PR China
a r t i c l e
i n f o
Article history: Received 25 September 2009 Accepted 22 October 2009 Available online 27 October 2009 Keywords: Crystal growth Nanomaterials Copper sulfide Hydrothermal reaction Optical property
a b s t r a c t In this paper, a simple solution-based method has been applied to fabricate metal chalcogenide nanostructures. Abundant Cu2S nanowires on Cu substrates are successfully prepared through the in-situ hydrothermal reaction between sulfur powder and Cu foil. It is observed that the addition of hydrazine and cetyltrimethylammonium bromide plays an important role in the growth of Cu2S nanowires. A rolling-up mechanism of metal chalcogenide film is used to illustrate the growth of these nanostructures. UV–vis spectrum of Cu2S nanowires reveals obvious absorption below the wavelength of 900 nm. The calculated band gap of Cu2S nanowires (1.5 eV) shows obvious blue shift because of the quantum size effect. © 2009 Elsevier B.V. All rights reserved.
1. Introduction Transition metal chalcogenide semiconductors have attracted extraordinary research interest owing to their potential application in catalyst, solar cell, field emission, photoluminescence and optoelectronic devices [1]. Among them, Cu2S is an excellent p-type semiconductor material with a direct band gap of 1.2 eV. It shows promising applications in solar cells, transistor for panel display, electronic and optoelectronic chips [2,3]. Various Cu2S nanostructures have been obtained by various methods, such as nanoparticles, nanodisks, nanowires, nanobelts, and dendrites [4–8]. However, most of them are in a powder form. The growth of onedimensional (1-D) nanostructures on substrates is considered to be a definitive step toward the fabrication of advanced nanodevices [9]. Hence, much attention has been paid to the reaction around substrate surface, in order to fabricate 1-D metal chalcogenide nanostructures. For example, Yu et al fabricated oriented nickel sulfide nanowires on Ni foil via a hydrothermal method [10]. They also obtained PbTe nanowires on Pb foil through a rolling-up process [11]. Oriented Cu2S nanowires have also been fabricated by a gas–solid reaction of Cu foil [12,13]. However, solution-based synthesis of copper chalcogenide is more attractive because of its controllability, low cost and high yield [14]. Recently, Zhang et al fabricated 1-D CuTe nanostructures on copper substrate [15]. The in-situ synthesis of 1-D Cu2S nanostructures on substrate has not been reported. In this paper, abundant Cu2S nanowires have been successfully fabricated on Cu substrate by the hydrothermal reaction ⁎ Corresponding author. School of Materials Science and Engineering, Tianjin University, Tianjin 300072, PR China. Tel.: +86 0316 2067260. E-mail address: [email protected] (X. Yu). 0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2009.10.051
between sulfur powder and copper foil. The possible growth mechanism and optical property are well discussed. 2. Experimental In a typical procedure, a piece of copper foil (Thickness: 0.2 mm; 2 ⁎ 2 cm), 1 mmol sulfur powder, 1 mL hydrazine and 1 mmol cetyltrimethylammonium bromide (CTAB) were placed in an autoclave.
Fig. 1. XRD pattern of the Cu2S nanostructures on copper substrate.
X. Yu, X. An / Materials Letters 64 (2010) 252–254
253
Fig. 2. (a) SEM image of the Cu2S nanowires on Cu foil; (b) TEM image of the Cu2S nanowires.
Then 25 mL distilled water was added. The autoclave was maintained at 180 °C for 12 h and cooled to room temperature naturally. The copper foil was taken out, washed with ethanol and dried in air for the characterization. The structure of the product was characterized by X-ray powder diffraction (XRD, Philips X'pert PRO). Scanning electron microscopy (SEM, KYKY-2800) and transmission electron microscopy (TEM, Hitachi H-800) were used to characterize the morphology of the products. The optical property was studied by the UV–vis absorption spectrum (U-3101, Hitachi). 3. Results and discussion Fig. 1 shows the XRD pattern of the collected product. The strong peaks around 43, 50 and 75° are all ascribed to the copper substrate. All the other peaks can be indexed to hexagonal β-Cu2S (JCPDS card File No. 46-1195). Thus, the formation of Cu2S on the copper substrate is well deduced. Fig. 2a is the SEM image of the product in the presence of 1 mmol CTAB. As can be seen clearly, the surface of copper foil is well covered by abundant of straight nanowires. These nanowires were ultrasonic treated with ethanol and further characterized by TEM. In Fig. 2b, the
Cu2S nanowires have a large aspect ratio and the average diameter is about 110 nm. The inset in Fig. 2b is the SAED pattern of Cu2S nanowire, which can be well indexed to hexagonal β-Cu2S. The polycrystalline nature of them can be easily deduced. To investigate the growth mechanism of nanowires, the influence of experimental conditions to the product is researched. It indicates that hydrazine is essential for the formation of Cu2S nanowires. As can be seen from Fig. 3a, no obvious 1-D nanostructure is obtained in the absence of hydrazine. In addition, CTAB shows a promotive effect to the growth of Cu2S nanowires. In Fig. 3b, only networked Cu2S nanostructures are collected in the hydrazine solution without CTAB. While with the addition of 1 mL hydrazine and 2 mmol CTAB, abundant Cu2S nanowires with higher aspect ratio are achieved (Fig. 3c). Moreover, CuTe nanowires can also be in-situ fabricated using similar situation, which indicates the applicability of this method in the synthesis of other metal chalcogenide materials. A rolling-up mechanism was used to explain the growth of metal telluride nanostructures in previous reports. The formation of a thin layer of metal telluride in the initial stage was supposed. This mechanism might also be applied to illustrate the growth of Cu2S nanowires in our experiments. As can be seen from the above results, hydrazine played an important role in this process, because no Cu2S
Fig. 3. SEM images of the copper chalcogenide on Cu foil under different conditions. (a) 1 mmol S, 1 mmol CTAB; (b) 1 mmol S, 1 mL hydrazine; (c) 1 mmol S, 2 mmol CTAB and 1 mL hydrazine; (d) CuTe nanowires in the presence of 1 mmol Te powder.
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X. Yu, X. An / Materials Letters 64 (2010) 252–254
Fig. 4. (a) Intermediate nanosheets obtained in the reaction; (b) UV–vis spectrum of the Cu2S nanowires.
nanowires were obtained in the absence of hydrazine. As the literature report [16], it was believed that hydrazine promoted the formation of Cu2S film through forming a complex between copper foil and hydrazine in our work. In addition, CTAB acted as a selective etchant to aid the rolling up of the in-situ formed film, into 1-D nanostructures [17]. The porous film in Fig. 3b and intermediate nanosheets in Fig. 4a well proved our hypothesis. Fig. 4b shows the UV–vis spectrum of the prepared Cu2S nanowires, which reveals obvious absorption below the wavelength of 900 nm. Cu2S nanowires show an absorption edge at about 830 nm. Thus, the calculated band gap of Cu2S nanowires is about 1.5 eV. This value shows obvious blue shift compared to that of bulk phase (1022 nm, 1.21 eV), and a little larger than that of Cu2S nanocrystals [18]. It is believed that this shift is a result of the quantum size effect [19,20]. 4. Conclusion In summary, abundant Cu2S nanowires on Cu substrate were prepared through the in-situ hydrothermal reaction between sulfur powder and Cu foil, in the presence of hydrazine and CTAB. A rollingup mechanism is used to illustrate the growth of these nanostructures. Hydrazine and CTAB are both essential in the formation of Cu2S nanowires.
Acknowledgement This work was supported by the China Postdoctoral Science Foundation via Grant No. 20090450089.
References [1] Hu Y, Zheng Z, Jia H, Tang Y, Zhang L. J Phys Chem, C 2008;112:13037–42. [2] Peng M, Ma L, Zhang Y, Tan M, Wang J, Yu Y. Mater Res Bull 2009;44:1834–41. [3] Soga T. Nanostructured Materials for Solar Energy Conversion. Amsterdam: Elsevier; 2006. [4] Li S, Wang H, Xu W, Si H, Tao X, Lou S, et al. J Colloid Interface Sci 2009;330:483–7. [5] Chen Y, Chen L, Wu L. Chem Eur J 2008;14:11069–75. [6] Wang S, Yang S. Adv Mater Opt Electron 2000;10:39–45. [7] Li Z, Yan H, Ding Y, Xiong Y, Xie Y. Dalton Trans 2006;149:149–51. [8] Gorai S, Ganguli D, Chaudhuri S. Mater Lett 2005;59:826–8. [9] Liu Y, Mao J, Jiang P, Xu Z, Yuan H, Xiao D. Cryst Eng Comm 2009; ASAP Articles. [10] Zhang L, Yu JC, Mo M, Wu L, Li Q, Kwong KW. J Am Chem Soc 2004;126:8116–7. [11] Zhang L, Yu JC, Mo M, Wu L, Kwong KW, Li Q. Small 2005;1:349–54. [12] Wang S, Yang S, Dai ZR, Wang ZL. Phys Chem Chem Phys 2001;3:3750–3. [13] Lim Y, Ok YW, Tark SJ, Kang Y, Kim D. Curr Appl Phys 2009;9:890–3. [14] Zhang X, Guo Y, Liu W. Mater Lett 2009;63:982–4. [15] Zhang L, Ai Z, Jia F, Liu L, Hu X, Yu JC. Chem Eur J 2006;12:4185–90. [16] Yuan M, Mitzi DB. Dalton Trans 2009:6078–88. [17] Lv S, Suo H, Zhao X, Wang C, Zhou T, Jing S, et al. J Alloy Compd 2009;479:L43–6. [18] Wu Y, Wadia C, Ma W, Sadtler B, Alivisatos AP. Nano lette 2008;8:2551–5. [19] Zhang P, Gao L. J Mater Chem 2003;13:2007–10. [20] Ding Y, Liu X, Guo R. Mater Res Bull 2008;43:748–58.