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Catalyst-free synthesis of honeycomb-like and straight ZnO nanowires
Journal of Alloys and Compounds 494 (2010) 468–471
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Catalyst-free synthesis of honeycomb-like and straight ZnO nanowires Yinxiao Du ∗ , Qing-Xin Yuan Department of Mathematics and Physics, ZhengZhou Institute of Aeronautical Industry Management, Zhengzhou 450015, PR China
a r t i c l e
i n f o
Article history: Received 12 January 2010 Accepted 14 January 2010 Available online 25 January 2010 Keywords: Nanostructured materials Semiconductors Optical property
a b s t r a c t Honeycomb-like ZnO nanowire arrays and straight nanowires were directly grown on the carbon-coated Si substrates without the aid of any metal catalysts, revealing an interesting growth behavior. It is found that one-dimensional (1D) nanostructures can easily grow on the carbon surface at different temperature region mainly due to the large difference in interface energy between the ZnO and C surface. Both the honeycomb-like nanowire arrays and straight nanowires exhibit excellent ultraviolet (UV) quality and common defect-related green emissions are almost not detected, indicating their perfect crystalline nature. © 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
As an important n-type semiconductor with wide bandgap (Eg = 3.37 eV at 300 K), ZnO possesses many unique optical, acoustic and electric properties, and thus has been attracted immense research interests [1,2]. In recent years, ZnO nanowires have attracted considerable attentions due to their potential applications in field emission, waveguides, nanogenerators, nanopiezotronics nanosensors, nanolasers, UV detectors, and optical switches [3–9]. Up to now, the methods for the fabrication of ZnO nanowires mainly include solution route or catalytically activated vapor (VLS) growth route. Though large-scale and costeffective ZnO nanowires can easily be produced by the solution route such as hydrothermal/solvothermal process [10,11], the assynthesized nanowires have so many O vacancies and surface defects that the optical and electric properties of the ZnO nanowires are not desired. The VLS growth has been proven to be powerful due to the controllability of both the position and size via the metal catalysts and the as-synthesized ZnO nanowires usually exhibit good optical performance [12,13]. Nevertheless, the metal catalysts pose serious concerns since they may be incorporated into nanowires creating deep-level traps [14]. In this paper, we developed a catalyst-free method to fabricate the honeycomb-like ZnO nanowire arrays and straight nanowires on the amorphous carboncoated (1 0 0) Si substrates. Moreover, we investigated the effects of pre-deposited carbon layer and the deposition temperature on the structure, growth process and photoluminescence (PL) property of the ZnO nanostructures.
Commercial ZnO powders were used as the source for the growth of ZnO nanowires, and were loaded in an alumina boat and placed in the center zone of a tube furnace. Amorphous carbon-coated Si (1 0 0) substrates were produced by magnetic filed filtered ion deposition and were used for the nucleation and growth of ZnO nanostructures. The thickness of the carbon layer is about 100 nm. In the experiments, the ZnO powders were heated to 1300 ◦ C with heating rate of 15 ◦ C/min and were kept at the peak temperature for an hour. In the whole growth process, Ar was used as carrier gas with flow rate of 30 sccm to facilitate the ZnO growth. After the furnace was cooled to room temperature, some products were found to deposit in the region with local temperature of 800–900 ◦ C. Powder X-ray diffraction (XRD) data of the nanowires were collected on a MACM18XHF diffractometer (Cu K␣ radiation, = 1.5418 Å). Morphologies and lattice
∗ Corresponding author. Tel.: +86 371 68252171; fax: +86 371 68252171. E-mail address: [email protected] (Y. Du). 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.01.084
Fig. 1. XRD patterns of the products deposited on (a) the carbon-coated Si substrate at 800 ◦ C, (b) the carbon-coated Si substrate at 850 ◦ C, (c) the uncoated Si substrate at 800 ◦ C, and (d) the uncoated Si substrate at 850 ◦ C.
Y. Du, Q.-X. Yuan / Journal of Alloys and Compounds 494 (2010) 468–471 fringes of the nanowires were characterized by field-emission scanning electron microscopy (SEM; FEI XL30 S-FEG), and transmission electron microscopy (TEM; Philips CM200). The PL property of ZnO nanostructures was performed at room temperature by using 325 line of He–Cd laser as the excitation source.
3. Results and discussion Fig. 1a shows the XRD pattern of the product deposited in the region with the temperature of 800 ◦ C. The diffraction peaks of the product can be assigned to (1 0 0), (0 0 2), (1 0 1), (1 0 2) lines of hexagonal ZnO (JCPDS No. 361451), respectively. The overwhelming (0 0 2) peak indicates that the preferred growth direction of the
469
ZnO product is along the c-axis. The corresponding SEM images observed from different angle are shown in Fig. 2a–c. Fig. 2a is a plane-view image of the deposited product, clearly exhibiting that oriented honeycomb-like ZnO nanowire arrays are grown on the surface of Si substrate. Fig. 2b and c shows the tilted view images of the aligned ZnO nanowires with different magnification, respectively, showing that the length of nanowires has a little variation. The ZnO nanowire is a little bending and thus forms honeycomb-like nanowire arrays (Fig. 2c). The TEM images (Fig. 2d and e) further reveal the feature of the nanowires configuration. The nanowires are of smooth surface and uniform diameter of 80 nm along the growth direction, though these nanowires are a little
Fig. 2. (a–c) SEM of the products observed from different angles. (d) TEM image of the ZnO nanowires deposited at 800 ◦ C. (e) TEM image of an individual ZnO nanowire. The inset is corresponding fast Fourier transformation (FFT) pattern. (f) HRTEM image of the single nanowire.
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Y. Du, Q.-X. Yuan / Journal of Alloys and Compounds 494 (2010) 468–471
Fig. 3. SEM images of ZnO deposited on (a and b) the carbon-coated Si substrate at 850 ◦ C, (c) the uncoated Si substrate at 800 ◦ C, and (d) the uncoated Si substrate at 850 ◦ C.
bending (Fig. 2e). HRTEM image of a single nanowire recorded along [2 1¯ 1¯ 0] (Fig. 2f) and the corresponding fast Fourier transformation (inset of Fig. 2e) reveals that the ZnO nanowires are highly crystalline. The measured spacing of the lattice fringes corresponds to the (0 0 1) lattice plane of hexagonal ZnO, indicating the [0 0 0 1] growth direction of the nanowires. The effect of deposition temperature on the growth of 1D ZnO is also investigated. At deposition temperature of 850 ◦ C, straight nanowires can be obtained (Fig. 3a and b). These nanowires with smooth surface are straight along the growth direction and the
average diameter and length are about 100 nm and 6 m, respectively. The corresponding XRD pattern (Fig. 1b) indicates that these straight nanowires also are hexagonal ZnO. However, the preferred orientation of ZnO product is not obviously along the c-axis, which is different from that of honeycomb-like ZnO nanowire arrays. In order to investigate the role of amorphous layer in the ZnO nanowires growth, we place uncoated (1 0 0) Si substrates on the same deposition-temperature regions. It is found that the morphology of deposited ZnO products is completely different from the products deposited on the carbon surface. Large-scale ZnO micro-
Fig. 4. Photoluminescence spectra of ZnO products deposited on (a) the carbon-coated Si substrate at 800 ◦ C, (b) the carbon-coated Si substrate at 850 ◦ C, (c) the uncoated Si substrate at 800 ◦ C, and (d) the uncoated Si substrate at 850 ◦ C.
Y. Du, Q.-X. Yuan / Journal of Alloys and Compounds 494 (2010) 468–471
combs and microwires deposit in the temperature region of 800 ◦ C (Figs. 1c and 3c). Meanwhile, irregular microparticles with hexagonal structure are observed on the temperature region of 850 ◦ C, as shown in Figs. 1d and 3d. Based on the experimental observations, it is demonstrated that the carbon plays an important role in the 1D growth of ZnO. Recently, Yang et al. [15] had reported the synthesis of 1D agave-like ZnO on the amorphous carbon. We have found similar results: If the thickness of the carbon is too thin (e.g. 20 nm), agave-like ZnO is also produced (the morphology is not shown here). If the thickness of the carbon is increase to 100 nm, honeycomb-like nanowire arrays and straight nanowires are obtained. We deduce that thickness of carbon layer is the main reason for the difference in our and Yang’s work. Yang et al. demonstrated that immiscibility of zinc oxide–carbon (ZnO–C) system is key factor for the 1D growth of ZnO [15]. We deduce that the explanation can illuminate the results in this work. ZnO first covers the surface of the amorphous carbon and thus forms ZnO clusters. When the size of ZnO cluster reaches critical nucleus, the nucleation of ZnO will happen. ZnO nuclei cannot gradually grow large by trapping and diffusing on the carbon surface due to large interface energy between the ZnO nuclei and carbon. To minimize the interface energy, the orienting one-dimensional growth of ZnO nuclei could occur on the amorphous carbon surface, as the growth model is thermodynamically favorable [15]. So, ZnO nanowires can easily be fabricated on the carbon surface, which is accordance with vapor–solid (VS) process. Moreover, deposition temperature plays another important role in the ZnO nanowire growth. The radial growth rate of ZnO nuclei will vary at different temperature, which leads to difference in the morphology and size of the final products on the carbon layer. The PL properties of these ZnO nanostructures are investigated, and presented some novel features. Fig. 4a and b shows the PL spectra of the nanowires deposited at 800 and 850 ◦ C, respectively. It is found that only strong UV emission peak centered at 381.2 and 381.7 nm can be observed in the honeycomb-like nanowire arrays and straight nanowires, respectively. The common green emissions which is related to point defects including oxygen vacancy (VO ), zinc vacancy (VZn ), oxygen interstitial (Oi ) and zinc vacancy (VZn ) are not detected, indicating perfect crystal quality of the ZnO nanowires grown on the carbon surface. However, the ZnO products obtained on the carbon-uncoated Si substrates have poor PL quality. It is clearly seen that the products deposited at 800 and 850 ◦ C exhibit obvious green emission centered at 515.1 and 520.3 nm, respectively, reveals that large amount of point defects exist in the products (Fig. 4a and b). It is demonstrated that the 1D ZnO nanostructures are of perfect PL properties. Moreover, we observe that obvious blue shift of UV emission from 392.9 to 381.2 nm as the size of the sample decreases. The reduction of
471
bandgap induced by tensile stress was the main reason for the interesting blue shift [16]. 4. Conclusions 1D ZnO nanostructures were directly grown on the amorphous carbon-coated (1 0 0) Si substrates without using any metal catalysts. Honeycomb-like ZnO nanowire arrays and straight nanowires are obtained in the temperature region of 800 and 850 ◦ C, respectively. Based on the experimental observation and analysis, it is deduced that the immiscibility of ZnO–C system should be responsible for 1D growth of ZnO by providing a thermodynamic driving force and creating the energetically favorable situation for the 1D growth of ZnO nuclei. The PL spectra of the two samples grown on the carbon surface exhibit perfect UV emission quality and the defect-related green emission is almost not detected, indicating carbon layer is contributed to increase high-quality nature of the as-synthesized 1D ZnO nanostructures. Acknowledgement This work was financially supported by the Aeronautical Science Foundation of China (no. 2008ZF55006) and the Natural Science Foundation of Henan Provincial Educational Department (no. 2008A140013). References [1] Z.K. Tang, G.K.L. Wong, P. Yu, M. Kawasaki, A. Ohtomo, H. Koinuma, Y. Seqawa, Appl. Phys. Lett. 72 (1998) 3270–3272. [2] Y.F. Hu, Y.F. Gao, S. Singamaneni, W. Tsukruk, Z.L. Wang, Nano Lett. 9 (2009) 2661–2665. [3] J.H. Lee, M.H. Hon, Y.W. Chung, I.C. Leu, J. Am. Ceram. Soc. 92 (2009) 2192–2196. [4] J.C. Johnson, H.Q. Yan, P.D. Yang, R.J. Saykally, J. Phys. Chem. B 107 (2003) 8816–8828. [5] L. Liao, H.B. Lu, J.C. Li, C. Liu, D.J. Fu, Y.L. Liu, Appl. Phys. Lett. 91 (2007) 173110. [6] H.Y. Li, S. Rule, R. Khedoe, A.F. Koenderink, D. Vanmaekelbergh, Nano Lett. 9 (2009) 3515–3520. [7] A. Umar, B.K. Kim, J.J. Kim, Y.B. Hahn, Nanotechnology 18 (2007) 175606. [8] X.D. Wang, J.H. Song, Z.L. Wang, Science 316 (2007) 102–105. [9] Z.L. Wang, Mater. Today 10 (2007) 20–28. [10] H.D. Yu, Z.P. Zhang, M.Y. Han, X.T. Hao, F.R. Zhu, J. Am. Chem. Soc. 127 (2005) 2378–2379. [11] L.E. Greene, M. Law, J. Goldberger, F. Kim, J.C. Johnson, Y. Zhang, R.J. Saykally, P.D. Yang, Angew. Chem. Int. Ed. 42 (2003) 3031–3034. [12] P.D. Yang, H.Q. Yan, S. Mao, R. Russo, J. Johnson, R. Saykally, N. Morris, J. Pham, R.R. He, H.J. Choi, Adv. Funct. Mater. 12 (2002) 323–331. [13] M.H. Huang, S. Mao, H. Feick, H.Q. Yan, Y.Y. Wu, H. Kind, E. Weber, R. Russo, P.D. Yang, Science 292 (2001) 1897–1899. [14] S. Braun, H.G. Grimmeiss, J. Appl. Phys. 45 (1974) 2658–2661. [15] Y.H. Yang, B. Wang, G.W. Yang, Cryst. Growth Des. 7 (2007) 1242–1245. [16] D. Stichtenoth, C. Ronning, T. Niermann, L. Wischmeier, T. Voss, C.J. Chien, P.C. Chang, J.G. Lu, Nanotechnology 18 (2007) 435701.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom
Catalyst-free synthesis of honeycomb-like and straight ZnO nanowires Yinxiao Du ∗ , Qing-Xin Yuan Department of Mathematics and Physics, ZhengZhou Institute of Aeronautical Industry Management, Zhengzhou 450015, PR China
a r t i c l e
i n f o
Article history: Received 12 January 2010 Accepted 14 January 2010 Available online 25 January 2010 Keywords: Nanostructured materials Semiconductors Optical property
a b s t r a c t Honeycomb-like ZnO nanowire arrays and straight nanowires were directly grown on the carbon-coated Si substrates without the aid of any metal catalysts, revealing an interesting growth behavior. It is found that one-dimensional (1D) nanostructures can easily grow on the carbon surface at different temperature region mainly due to the large difference in interface energy between the ZnO and C surface. Both the honeycomb-like nanowire arrays and straight nanowires exhibit excellent ultraviolet (UV) quality and common defect-related green emissions are almost not detected, indicating their perfect crystalline nature. © 2010 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
As an important n-type semiconductor with wide bandgap (Eg = 3.37 eV at 300 K), ZnO possesses many unique optical, acoustic and electric properties, and thus has been attracted immense research interests [1,2]. In recent years, ZnO nanowires have attracted considerable attentions due to their potential applications in field emission, waveguides, nanogenerators, nanopiezotronics nanosensors, nanolasers, UV detectors, and optical switches [3–9]. Up to now, the methods for the fabrication of ZnO nanowires mainly include solution route or catalytically activated vapor (VLS) growth route. Though large-scale and costeffective ZnO nanowires can easily be produced by the solution route such as hydrothermal/solvothermal process [10,11], the assynthesized nanowires have so many O vacancies and surface defects that the optical and electric properties of the ZnO nanowires are not desired. The VLS growth has been proven to be powerful due to the controllability of both the position and size via the metal catalysts and the as-synthesized ZnO nanowires usually exhibit good optical performance [12,13]. Nevertheless, the metal catalysts pose serious concerns since they may be incorporated into nanowires creating deep-level traps [14]. In this paper, we developed a catalyst-free method to fabricate the honeycomb-like ZnO nanowire arrays and straight nanowires on the amorphous carboncoated (1 0 0) Si substrates. Moreover, we investigated the effects of pre-deposited carbon layer and the deposition temperature on the structure, growth process and photoluminescence (PL) property of the ZnO nanostructures.
Commercial ZnO powders were used as the source for the growth of ZnO nanowires, and were loaded in an alumina boat and placed in the center zone of a tube furnace. Amorphous carbon-coated Si (1 0 0) substrates were produced by magnetic filed filtered ion deposition and were used for the nucleation and growth of ZnO nanostructures. The thickness of the carbon layer is about 100 nm. In the experiments, the ZnO powders were heated to 1300 ◦ C with heating rate of 15 ◦ C/min and were kept at the peak temperature for an hour. In the whole growth process, Ar was used as carrier gas with flow rate of 30 sccm to facilitate the ZnO growth. After the furnace was cooled to room temperature, some products were found to deposit in the region with local temperature of 800–900 ◦ C. Powder X-ray diffraction (XRD) data of the nanowires were collected on a MACM18XHF diffractometer (Cu K␣ radiation, = 1.5418 Å). Morphologies and lattice
∗ Corresponding author. Tel.: +86 371 68252171; fax: +86 371 68252171. E-mail address: [email protected] (Y. Du). 0925-8388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2010.01.084
Fig. 1. XRD patterns of the products deposited on (a) the carbon-coated Si substrate at 800 ◦ C, (b) the carbon-coated Si substrate at 850 ◦ C, (c) the uncoated Si substrate at 800 ◦ C, and (d) the uncoated Si substrate at 850 ◦ C.
Y. Du, Q.-X. Yuan / Journal of Alloys and Compounds 494 (2010) 468–471 fringes of the nanowires were characterized by field-emission scanning electron microscopy (SEM; FEI XL30 S-FEG), and transmission electron microscopy (TEM; Philips CM200). The PL property of ZnO nanostructures was performed at room temperature by using 325 line of He–Cd laser as the excitation source.
3. Results and discussion Fig. 1a shows the XRD pattern of the product deposited in the region with the temperature of 800 ◦ C. The diffraction peaks of the product can be assigned to (1 0 0), (0 0 2), (1 0 1), (1 0 2) lines of hexagonal ZnO (JCPDS No. 361451), respectively. The overwhelming (0 0 2) peak indicates that the preferred growth direction of the
469
ZnO product is along the c-axis. The corresponding SEM images observed from different angle are shown in Fig. 2a–c. Fig. 2a is a plane-view image of the deposited product, clearly exhibiting that oriented honeycomb-like ZnO nanowire arrays are grown on the surface of Si substrate. Fig. 2b and c shows the tilted view images of the aligned ZnO nanowires with different magnification, respectively, showing that the length of nanowires has a little variation. The ZnO nanowire is a little bending and thus forms honeycomb-like nanowire arrays (Fig. 2c). The TEM images (Fig. 2d and e) further reveal the feature of the nanowires configuration. The nanowires are of smooth surface and uniform diameter of 80 nm along the growth direction, though these nanowires are a little
Fig. 2. (a–c) SEM of the products observed from different angles. (d) TEM image of the ZnO nanowires deposited at 800 ◦ C. (e) TEM image of an individual ZnO nanowire. The inset is corresponding fast Fourier transformation (FFT) pattern. (f) HRTEM image of the single nanowire.
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Y. Du, Q.-X. Yuan / Journal of Alloys and Compounds 494 (2010) 468–471
Fig. 3. SEM images of ZnO deposited on (a and b) the carbon-coated Si substrate at 850 ◦ C, (c) the uncoated Si substrate at 800 ◦ C, and (d) the uncoated Si substrate at 850 ◦ C.
bending (Fig. 2e). HRTEM image of a single nanowire recorded along [2 1¯ 1¯ 0] (Fig. 2f) and the corresponding fast Fourier transformation (inset of Fig. 2e) reveals that the ZnO nanowires are highly crystalline. The measured spacing of the lattice fringes corresponds to the (0 0 1) lattice plane of hexagonal ZnO, indicating the [0 0 0 1] growth direction of the nanowires. The effect of deposition temperature on the growth of 1D ZnO is also investigated. At deposition temperature of 850 ◦ C, straight nanowires can be obtained (Fig. 3a and b). These nanowires with smooth surface are straight along the growth direction and the
average diameter and length are about 100 nm and 6 m, respectively. The corresponding XRD pattern (Fig. 1b) indicates that these straight nanowires also are hexagonal ZnO. However, the preferred orientation of ZnO product is not obviously along the c-axis, which is different from that of honeycomb-like ZnO nanowire arrays. In order to investigate the role of amorphous layer in the ZnO nanowires growth, we place uncoated (1 0 0) Si substrates on the same deposition-temperature regions. It is found that the morphology of deposited ZnO products is completely different from the products deposited on the carbon surface. Large-scale ZnO micro-
Fig. 4. Photoluminescence spectra of ZnO products deposited on (a) the carbon-coated Si substrate at 800 ◦ C, (b) the carbon-coated Si substrate at 850 ◦ C, (c) the uncoated Si substrate at 800 ◦ C, and (d) the uncoated Si substrate at 850 ◦ C.
Y. Du, Q.-X. Yuan / Journal of Alloys and Compounds 494 (2010) 468–471
combs and microwires deposit in the temperature region of 800 ◦ C (Figs. 1c and 3c). Meanwhile, irregular microparticles with hexagonal structure are observed on the temperature region of 850 ◦ C, as shown in Figs. 1d and 3d. Based on the experimental observations, it is demonstrated that the carbon plays an important role in the 1D growth of ZnO. Recently, Yang et al. [15] had reported the synthesis of 1D agave-like ZnO on the amorphous carbon. We have found similar results: If the thickness of the carbon is too thin (e.g. 20 nm), agave-like ZnO is also produced (the morphology is not shown here). If the thickness of the carbon is increase to 100 nm, honeycomb-like nanowire arrays and straight nanowires are obtained. We deduce that thickness of carbon layer is the main reason for the difference in our and Yang’s work. Yang et al. demonstrated that immiscibility of zinc oxide–carbon (ZnO–C) system is key factor for the 1D growth of ZnO [15]. We deduce that the explanation can illuminate the results in this work. ZnO first covers the surface of the amorphous carbon and thus forms ZnO clusters. When the size of ZnO cluster reaches critical nucleus, the nucleation of ZnO will happen. ZnO nuclei cannot gradually grow large by trapping and diffusing on the carbon surface due to large interface energy between the ZnO nuclei and carbon. To minimize the interface energy, the orienting one-dimensional growth of ZnO nuclei could occur on the amorphous carbon surface, as the growth model is thermodynamically favorable [15]. So, ZnO nanowires can easily be fabricated on the carbon surface, which is accordance with vapor–solid (VS) process. Moreover, deposition temperature plays another important role in the ZnO nanowire growth. The radial growth rate of ZnO nuclei will vary at different temperature, which leads to difference in the morphology and size of the final products on the carbon layer. The PL properties of these ZnO nanostructures are investigated, and presented some novel features. Fig. 4a and b shows the PL spectra of the nanowires deposited at 800 and 850 ◦ C, respectively. It is found that only strong UV emission peak centered at 381.2 and 381.7 nm can be observed in the honeycomb-like nanowire arrays and straight nanowires, respectively. The common green emissions which is related to point defects including oxygen vacancy (VO ), zinc vacancy (VZn ), oxygen interstitial (Oi ) and zinc vacancy (VZn ) are not detected, indicating perfect crystal quality of the ZnO nanowires grown on the carbon surface. However, the ZnO products obtained on the carbon-uncoated Si substrates have poor PL quality. It is clearly seen that the products deposited at 800 and 850 ◦ C exhibit obvious green emission centered at 515.1 and 520.3 nm, respectively, reveals that large amount of point defects exist in the products (Fig. 4a and b). It is demonstrated that the 1D ZnO nanostructures are of perfect PL properties. Moreover, we observe that obvious blue shift of UV emission from 392.9 to 381.2 nm as the size of the sample decreases. The reduction of
471
bandgap induced by tensile stress was the main reason for the interesting blue shift [16]. 4. Conclusions 1D ZnO nanostructures were directly grown on the amorphous carbon-coated (1 0 0) Si substrates without using any metal catalysts. Honeycomb-like ZnO nanowire arrays and straight nanowires are obtained in the temperature region of 800 and 850 ◦ C, respectively. Based on the experimental observation and analysis, it is deduced that the immiscibility of ZnO–C system should be responsible for 1D growth of ZnO by providing a thermodynamic driving force and creating the energetically favorable situation for the 1D growth of ZnO nuclei. The PL spectra of the two samples grown on the carbon surface exhibit perfect UV emission quality and the defect-related green emission is almost not detected, indicating carbon layer is contributed to increase high-quality nature of the as-synthesized 1D ZnO nanostructures. Acknowledgement This work was financially supported by the Aeronautical Science Foundation of China (no. 2008ZF55006) and the Natural Science Foundation of Henan Provincial Educational Department (no. 2008A140013). References [1] Z.K. Tang, G.K.L. Wong, P. Yu, M. Kawasaki, A. Ohtomo, H. Koinuma, Y. Seqawa, Appl. Phys. Lett. 72 (1998) 3270–3272. [2] Y.F. Hu, Y.F. Gao, S. Singamaneni, W. Tsukruk, Z.L. Wang, Nano Lett. 9 (2009) 2661–2665. [3] J.H. Lee, M.H. Hon, Y.W. Chung, I.C. Leu, J. Am. Ceram. Soc. 92 (2009) 2192–2196. [4] J.C. Johnson, H.Q. Yan, P.D. Yang, R.J. Saykally, J. Phys. Chem. B 107 (2003) 8816–8828. [5] L. Liao, H.B. Lu, J.C. Li, C. Liu, D.J. Fu, Y.L. Liu, Appl. Phys. Lett. 91 (2007) 173110. [6] H.Y. Li, S. Rule, R. Khedoe, A.F. Koenderink, D. Vanmaekelbergh, Nano Lett. 9 (2009) 3515–3520. [7] A. Umar, B.K. Kim, J.J. Kim, Y.B. Hahn, Nanotechnology 18 (2007) 175606. [8] X.D. Wang, J.H. Song, Z.L. Wang, Science 316 (2007) 102–105. [9] Z.L. Wang, Mater. Today 10 (2007) 20–28. [10] H.D. Yu, Z.P. Zhang, M.Y. Han, X.T. Hao, F.R. Zhu, J. Am. Chem. Soc. 127 (2005) 2378–2379. [11] L.E. Greene, M. Law, J. Goldberger, F. Kim, J.C. Johnson, Y. Zhang, R.J. Saykally, P.D. Yang, Angew. Chem. Int. Ed. 42 (2003) 3031–3034. [12] P.D. Yang, H.Q. Yan, S. Mao, R. Russo, J. Johnson, R. Saykally, N. Morris, J. Pham, R.R. He, H.J. Choi, Adv. Funct. Mater. 12 (2002) 323–331. [13] M.H. Huang, S. Mao, H. Feick, H.Q. Yan, Y.Y. Wu, H. Kind, E. Weber, R. Russo, P.D. Yang, Science 292 (2001) 1897–1899. [14] S. Braun, H.G. Grimmeiss, J. Appl. Phys. 45 (1974) 2658–2661. [15] Y.H. Yang, B. Wang, G.W. Yang, Cryst. Growth Des. 7 (2007) 1242–1245. [16] D. Stichtenoth, C. Ronning, T. Niermann, L. Wischmeier, T. Voss, C.J. Chien, P.C. Chang, J.G. Lu, Nanotechnology 18 (2007) 435701.