Liquid phase morphology control of ZnO crystals was realized with simple aqueous solution system. ZnO nanowires were successfully fabricated at 50°C. They were over 50？μm in length and about 100？nm in width. Aspect ratio was estimated to be over 500. They had no branches and were obtained without aggregations. Curved nano-wires clearly indicated high flexibility and high mechanical strength. Additionally, ellipse particles, hexagonal rods and particles were fabricated in the solutions. Morphology, crystal growth speed, and preferred growth faces were well-controlled by precise adjustment of growth conditions. 1. Introduction Metal oxides have been used for electronic devices, optoelectronic device, and so forth. They will further expand beyond the present borders of research area. Especially, expectations for metal oxide nanostructures have increased recently for future applications. Syntheses of novel metal oxide nanostructures and development of their applications are under intense investigation [1–8]. Special issues [9], reviews [10–13], and books [14] on applications of metal oxide nanostructures have received a great response. ZnO has attracted much attention as varistors [15], piezoelectric devices [16], electroacoustic transducers [17], and highly transparent conducting windows for solar cells, displays [18], vacuum fluorescent displays (VFDs) [19], field emission displays (FEDs) [20], electroluminescent displays (ELDs) [21], UV light-emitting diodes (LEDs), laser diodes [22], and gas sensors [23, 24], dye-sensitized solar cells [25–29], and molecular sensors [30]. Novel ZnO nanostructures are eagerly anticipated for the applications [31–34]. ZnO nanowires especially are required for luminescent devices, dye-sensitized solar cells and high sensitive sensors. The nanowires have high electrical conductivity along the longer direction. They have large surface area due to high aspect ratio of the shape. High flexibility and high mechanical strength are required to apply for the devices. Recently, several ZnO nano-/microstructures were prepared in the solutions [34–39]. Patterning of them was realized on self-assembled monolayers (SAMs) [35]. Hydrophobic surface of SAMs accelerated deposition of ZnO nanostructures rather than hydrophilic silanol group surfaces [35]. These studies contributed development of future ZnO devices. In this study, ZnO nanowires were developed in aqueous solutions. Anisotropic crystal growth of ZnO was well-controlled by precise adjustment of solution conditions. Additionally, ellipse particles, hexagonal rods, and particles
References
[1]
L. Tang, M. Salamon, and M. R. D. Guire, “Cerium oxide thin films on solid oxide fuel cell anodes,” Science of Advanced Materials, vol. 2, no. 1, pp. 79–89, 2010.
[2]
D. Chu, Y.-P. Zeng, D. Jiang, and Y. Masuda, “Room temperature ferromagnetism in transition metal doped TiO2 nanowires,” Science of Advanced Materials, vol. 1, no. 3, pp. 227–229, 2009.
[3]
T. Kawai, H. Takahashi, Y. Matsushima, T. Ogata, and H. Unuma, “Evaluation of photocatalytic activity of TiO2 thin films by spin-trap ESR spectroscopy,” Science of Advanced Materials, vol. 2, no. 1, pp. 74–78, 2010.
[4]
Y. Masuda, T. Ohji, and K. Kato, “Multineedle TiO2 nanostructures, self-assembled surface coatings, and their novel properties,” Crystal Growth and Design, vol. 10, no. 2, pp. 913–922, 2010.
[5]
Y. Masudaa and K. Katoa, “Tin oxide coating on polytetrafluoroethylene films in aqueous solutions,” Polymers for Advanced Technologies, vol. 21, no. 3, pp. 211–215, 2010.
[6]
M. Inada, K. Mizue, N. Enomoto, and J. Hojo, “Thermal stability of rutile TiO2 with high specific surface area synthesized by self-hydrolysis process,” Science of Advanced Materials, vol. 2, no. 1, pp. 102–106, 2010.
[7]
Y. Tokunaga, H. Uchiyama, Y. Oaki, and H. Imai, “Specific photocatalytic performance of nanostructured rutile-type Tio2: selective oxidation of thiazin dye with a bundled architecture consisting of oriented nanoneedles,” Science of Advanced Materials, vol. 2, no. 1, pp. 69–73, 2010.
[8]
Y. Masuda, Y. Jinbo, and K. Koumoto, “Room temperature CVD of TiO2 thin films and their electronic properties,” Science of Advanced Materials, vol. 1, no. 2, p. 138, 2009.
[9]
Y. Masuda, “A special issue on applications of metal oxide nanostructures,” Science of Advanced Materials, vol. 2, no. 1, pp. 1–2, 2010.
[10]
Y. Masuda, “Liquid phase patterning of ceramics,” Journal of the Ceramic Society of Japan, vol. 115, no. 1338, pp. 101–109, 2007.
[11]
Y. Masuda, Y. F. Gao, P. X. Zhu, et al., “Site-selective deposition of ceramic thin films using self-assembled monolayers,” Journal of the Ceramic Society of Japan, vol. 112, no. 5, p. 1495, 2004.
[12]
A. D. Handoko and G. K. L. Goh, “One-dimensional perovskite nanostructures,” Science of Advanced Materials, vol. 2, no. 1, p. 16, 2010.
[13]
G. Neri, “Non-conventional sol-gel routes to nanosized metal oxides for gas sensing: from materials to applications,” Science of Advanced Materials, vol. 2, no. 1, pp. 3–15, 2010.
[14]
A. Umar and Y.-B. Hahn, Metal Oxide Nanostructures and Their Applications, American Scientific Publishers, Calif, USA, 2009.
[15]
Y. Lin, Z. Zhang, Z. Tang, F. Yuan, and J. Li, “Characterisation of ZnO-based varistors prepared from nanometre precursor powders,” Advanced Materials for Optics and Electronics, vol. 9, no. 5, pp. 205–209, 1999.
[16]
G. Agarwal and R. F. Speyer, “Current change method of reducing gas sensing using ZnO varistors,” Journal of the Electrochemical Society, vol. 145, no. 8, pp. 2920–2925, 1998.
[17]
F. Quaranta, A. Valentini, F. R. Rizzi, and G. Casamassima, “Dual-ion-beam sputter deposition of ZnO films,” Journal of Applied Physics, vol. 74, no. 1, pp. 244–248, 1993.
[18]
T. Pauporté and D. Lincot, “Electrodeposition of semiconductors for optoelectronic devices: results on zinc oxide,” Electrochimica Acta, vol. 45, no. 20, pp. 3345–3353, 2000.
[19]
S. Ruan, “Color picture element tube for large-screen display,” in Proceedings of the SPIE, vol. 262, p. 2892, 1996.
[20]
Y. Nakanishi, A. Miyake, H. Kominami, T. Aoki, Y. Hatanaka, and G. Shimaoka, “Preparation of ZnO thin films for high-resolution field emission display by electron beam evaporation,” Applied Surface Science, vol. 142, no. 1–4, pp. 233–236, 1999.
[21]
L. Yi, Y. Hou, H. Zhao et al., “Photo- and electro-luminescence properties of ZnO: Zn thin film,” Displays, vol. 21, no. 4, pp. 147–149, 2000.
[22]
R. F. Service, “Will UV lasers beat the blues?” Science, vol. 276, no. 5314, p. 895, 1997.
[23]
H. Gong, J. Q. Hu, J. H. Wang, C. H. Ong, and F. R. Zhu, “Nano-crystalline Cu-doped ZnO thin film gas sensor for CO,” Sensors and Actuators, B: Chemical, vol. 115, no. 1, pp. 247–251, 2006.
[24]
W. J. Moon, J. H. Yu, and G. M. Choi, “The CO and H-2 gas selectivity of CuO-doped SnO2-ZnO composite gas sensor,” Sensors and Actuators, B: Chemical, vol. 87, no. 3, pp. 464–470, 2002.
[25]
M. Law, L. E. Greene, J. C. Johnson, R. Saykally, and P. Yang, “Nanowire dye-sensitized solar cells,” Nature Materials, vol. 4, no. 6, pp. 455–459, 2005.
[26]
J. B. Baxter and E. S. Aydil, “Nanowire-based dye-sensitized solar cells,” Applied Physics Letters, vol. 86, no. 5, Article ID 053114, pp. 1–3, 2005.
[27]
R. Katoh, A. Furube, K. Hara et al., “Efficiencies of electron injection from excited sensitizer dyes to nanocrystalline ZnO films as studied by near-IR optical absorption of injected electrons,” Journal of Physical Chemistry B, vol. 106, no. 50, pp. 12957–12964, 2002.
[28]
S. Karuppuchamy, K. Nonomura, T. Yoshida, T. Sugiura, and H. Minoura, “Cathodic electrodeposition of oxide semiconductor thin films and their application to dye-sensitized solar cells,” Solid State Ionics, vol. 151, no. 1–4, pp. 19–27, 2002.
[29]
K. Keis, C. Bauer, G. Boschloo et al., “Nanostructured ZnO electrodes for dye-sensitized solar cell applications,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 148, no. 1–3, pp. 57–64, 2002.
[30]
H. Tokudome, Y. Yamada, S. Sonezaki et al., “Photoelectrochemical deoxyribonucleic acid sensing on a nanostructured TiO2 electrode,” Applied Physics Letters, vol. 87, no. 21, Article ID 213901, pp. 1–3, 2005.
[31]
R. Wahab, Y.-S. Kim, D. S. Lee, J.-M. Seo, and H.-S. Shin, “Controlled synthesis of zinc oxide nanoneedles and their transformation to microflowers,” Science of Advanced Materials, vol. 2, no. 1, pp. 35–42, 2010.
[32]
S. K. Mohanta, D. C. Kim, B. H. Kong, H. K. Cho, W. Liu, and S. Tripathy, “Optical properties of ZnO nanorods and hybrid structures grown on p-type GaN/sapphire and silicon-on-insulator substrates,” Science of Advanced Materials, vol. 2, no. 1, pp. 64–68, 2010.
[33]
D. W. Chu, Y. Masuda, T. Ohji, and K. Kato, “Formation and photocatalytic application of ZnO nanotubes using aqueous solution,” Langmuir, vol. 26, no. 4, pp. 2811–2815, 2010.
[34]
X. L. Hu, Y. Masuda, T. Ohji, and K. Kato, “Micropatterning of ZnO nanoarrays by forced hydrolysis of anhydrous zinc acetate,” Langmuir, vol. 24, no. 14, pp. 7614–7617, 2008.
[35]
Y. Masuda, N. Kinoshita, F. Sato, and K. Koumoto, “Site-selective deposition and morphology control of UV- and visible-light-emitting ZnO crystals,” Crystal Growth and Design, vol. 6, no. 1, pp. 75–78, 2006.
[36]
Y. Masuda, N. Kinoshita, and K. Koumoto, “Hexagonal symmetry radial whiskers of ZNO crystallized in aqueous solution,” Journal of Nanoscience and Nanotechnology, vol. 9, no. 1, pp. 522–526, 2009.
[37]
Y. Masuda and K. Kato, “Morphology control of zinc oxide particles at low temperature,” Crystal Growth and Design, vol. 8, no. 8, pp. 2633–2637, 2008.
[38]
Y. Masuda and K. Kato, “High c-axis oriented stand-alone ZnO self-assembled film,” Crystal Growth and Design, vol. 8, no. 1, pp. 275–279, 2008.
[39]
Y. Masuda and K. Kato, “Rapid growth of thick particulate film of crystalline ZnO in an aqueous solution,” Thin Solid Films, vol. 516, no. 9, pp. 2474–2477, 2008.
[40]
Y. Masuda, T. Sugiyama, H. Lin, W. S. Seo, and K. Koumoto, “Selective deposition and micropatterning of titanium dioxide thin film on self-assembled monolayers,” Thin Solid Films, vol. 382, no. 1-2, pp. 153–157, 2001.
[41]
Y. Masuda, Y. Jinbo, T. Yonezawa, and K. Koumoto, “Templated site-selective deposition of titanium dioxide on self-assembled monolayers,” Chemistry of Materials, vol. 14, no. 3, pp. 1236–1241, 2002.
[42]
Y. Masuda, T. Sugiyama, and K. Koumoto, “Micropatterning of anatase TiO2 thin films from an aqueous solution by a site-selective immersion method,” Journal of Materials Chemistry, vol. 12, no. 9, pp. 2643–2647, 2002.
[43]
Y. Masuda, S. Ieda, and K. Koumoto, “Site-selective deposition of anatase TiO2 in an aqueous solution using a seed layer,” Langmuir, vol. 19, no. 10, pp. 4415–4419, 2003.
[44]
Y. Masuda, N. Saito, R. Hoffmann, M. R. de Guire, and K. Koumoto, “Nano/micro-patterning of anatase TiO2 thin film from an aqueous solution by site-selective elimination method,” Science and Technology of Advanced Materials, vol. 4, no. 5, pp. 461–467, 2003.
[45]
Y. Masuda and K. Kato, “Aqueous synthesis of ZnO rod arrays for molecular sensor,” Crystal Growth and Design, vol. 9, no. 7, pp. 3083–3088, 2009.
