H Hou et al. /Solid State Sciences 7(2005)45-51 (SDBS) and sodium dodecyl sulfate (SDS), cannot come be formed under the synergic effect of structure-directing into being the epitaxial whiskers, indicating that CTAB plays agent of CTAB and the dehydration of Zn(Oh)2 under the an undeniable and irreplaceable role. It has been found that pH=8 in hydrothermal growth conditions. It is expected the optimal molar ratio of zinc(If) acetate dihydrate to CTAb that the novel tubular whiskers may offer exciting oppor- (2: 1)favors the growth of Zno epitaxial whiskers tunities for potential applications in catalysis, microsized Under the effect of structure-directing agent CTAB, the waveguides or optical fibers. The novel epitaxial whiskers direction of stable connection of anionic coordination poly- may offer exciting opportunities for homozygote in photo- hedrons [Zn-O4] is the determinant to epitaxial whiskers electronic devices. In addition, we believe that this simple under the condition of pH=8 in hydrothermal growth con- process can also be applied to synthesize other tubular and ditions. Because of the crystal ZnO characteristic, the link- epitaxial whiskers for functional materials. Further research ing mode between ZnO particles is the same as that of the is still under progress in our laboratory growth unit in the interface, which be connected along the direction of stable connection of the anionic coordination polyhedrons, i.e., along the fastest growth direction of the Acknowledgements corresponding crystal [29, 30]. The connection schematic di- agram of ZnO epitaxial whiskers was shown in Fig 9(c, d) Financial support from the National Natural Science Fig 9(c)exhibits the connection view of connection between Foundation of China and the Chinese Ministry of Educa- the positive c (0001)and negative polar faces c(0001). tion is gratefully acknowledged The symmetrical characteristic of the geometric distribution of the epitaxial whiskers is corresponding to the symmetry of the crystal structure. Zn-O4 tetrahedrons connection onReferences positive and negative polar faces along c-axis, as shown in Fig. 9(d), reveals the connection direction of growth unit [1 C.M. Lieber, Solid State Commun. 107(1998)607. The ID ZnO epitaxial whiskers can only be formed under [2] V Srikant, D.R. Clarke, J Appl. Phys. 83(1998)5447 the synergic effect of structure-directing agent of CTAB and B ]L Guo, Y.L. Ji, H.B. Xu, P. Simon, Z.Y. Wu, J. Amer. Chem. Soc. 124 the direction of stable connection of anionic coordination polyhedrons [Zn-O4]- under the ph=8 in hydrothermal [4J. Zhang, L D. Sun, J. L. Yin, H.L. Sun, C S. Liao, C H. Yan, Chem. Mater.14(2002)4172 growth conditions 5 T. Yoshida, H. Naito, M. Okuda, S Ehara, T. Takagi, O. Kusumoto, n the process of tubular and epitaxial Zno whiskers, sin- H. Kado, K. Yokoyama, T. Tohda, Appl. Phys. Lett. 64(1994) gle whisker's unique growth direction is explained by the favorable energy along a specific growth direction [31, 32] [6]JQ. Hu, Q. Li, N.B. Wong, C.S. Lee, S.T. Lee, Chem. Mater. 14 The hexagonal prismatic morphology and the facet outlook (2002)1216 of the whiskers are caused by the different growth rates of [7 C.X. Xu, X.W. Sun, Jpn J Appl. Phys. 1(42)(2003)4949 [8] H. Najafov, Y. Fukada, S. Ohshio, S. lida, H Saitoh, Jpn. J, Appl the crystalline faces [ 6] hys.1(42)(2003)3490 [9]WJ.Li, E.W. Shi, W.Z. Zhong, w.Z. Yin, J Cryst Growth 203(1999 4. Conclusions 10J. Zhang, L D Sun, C.S. Liao, C.H. Yan, Chem. Commun.(Cam- bridge)(2002)262 [11]YJ, Xing, Z.H. Xi, Z.Q. Xue, X.D. Zhang, J.H. Song, R.M. Wang, In summary, the synthesis of Zno tubular and epitaxial J. Xu, Y Song, S L Zhang, D.P. Yu, Appl. Phys. Lett. 83(2003)1689 whiskers have been described via a simple mild hydrother [12]JQ. Hu, Y Bando, Appl. Phys. Lett. 82(2003)1401 mal method The sample of tubular whiskers has fairly uni- [13]JJ.Wu, S.C. Liu, C.T. Wu, K.H. Chen, L.C. Chen, Appl. Phys form diameters of around 4 um and the length of up to Let.81(2002)1312 20 um. The hollow cavity of tubular Zno whisker has the [14]H. Saitoh, M. Satoh, S. Ohshio, J. Ceram. Soc. Jpn. 110(2002) same regular prismatic hexagon with the individual whisker [15]AJ. Strauss, Phys. Rev. Lett. 16(1966)1193 Its photoluminescence spectrum exhibits a strong shoulder [16]C K. Xu, G.D. Xu, Y.K. Liu, G.H. Wang, Solid State Commun. 122 emission band located at 400 and 408 nm and a weak and (2002)175 large scale of epitaxial whiskers with smooth and syme a [17) U. Koch, A Fojtik, H. Weller, A.Henglein, Chem. Phys.Lett.122 broad emission band centered at 533 nm. The sample of [18]S Monticone, R. Tufen, A.V. Kanaev, J Phys. Chem. B 102(1998) rically hexagonal shapes and well-knit structure has fairly uniform diameters of around 4 um and the length of about [19]B D Yao, H.Z. Shi, H.J. Bi, L D Zhang, J Phys. Condens Mater. 12 10 um. Its photoluminescence spectrum exhibits a strong (2000)6265 shoulder emission band located at 411 and 447 nm. The 20]K. Vanheusden, W.L. Warren, C H. Seager, D.R. Tallant, J.A. Voigt, ID Zno tubular whiskers can only be formed with the co- B.E. Ganade, J. Appl. Phys. 79(1996)7983 21]YLi, G.S. Cheng, L D Zhang, J Mater. Res 15(2000)2305 operation of structure-directing agent of CTAB and the hy- [22]PD Yang, H.Q.Yan,S.Mao,R.Russo,J.Johnson,R.Sayka dration of Zn(NH3)4- under the pH= 10 in hydrothermal N. Morris, J. Pham, R.R. He, H.J. Choi, Adv. Funct Mat. 12(20 growth conditions. The ID ZnO epitaxial whiskers can only50 H. Hou et al. / Solid State Sciences 7 (2005) 45–51 (SDBS) and sodium dodecyl sulfate (SDS), cannot come into being the epitaxial whiskers, indicating that CTAB plays an undeniable and irreplaceable role. It has been found that the optimal molar ratio of zinc(II) acetate dihydrate to CTAB (2:1) favors the growth of ZnO epitaxial whiskers. Under the effect of structure-directing agent CTAB, the direction of stable connection of anionic coordination poly￾hedrons [Zn–O4] 6− is the determinant to epitaxial whiskers under the condition of pH = 8 in hydrothermal growth con￾ditions. Because of the crystal ZnO characteristic, the link￾ing mode between ZnO particles is the same as that of the growth unit in the interface, which be connected along the direction of stable connection of the anionic coordination polyhedrons, i.e., along the fastest growth direction of the corresponding crystal [29,30]. The connection schematic di￾agram of ZnO epitaxial whiskers was shown in Fig. 9(c,d). Fig. 9(c) exhibits the connection view of connection between the positive c (0001) and negative polar faces c (0001). The symmetrical characteristic of the geometric distribution of the epitaxial whiskers is corresponding to the symmetry of the crystal structure. Zn–O4 tetrahedrons connection on positive and negative polar faces along c-axis, as shown in Fig. 9(d), reveals the connection direction of growth unit. The 1D ZnO epitaxial whiskers can only be formed under the synergic effect of structure-directing agent of CTAB and the direction of stable connection of anionic coordination polyhedrons [Zn–O4] 6− under the pH = 8 in hydrothermal growth conditions. In the process of tubular and epitaxial ZnO whiskers, sin￾gle whisker’s unique growth direction is explained by the favorable energy along a specific growth direction [31,32]. The hexagonal prismatic morphology and the facet outlook of the whiskers are caused by the different growth rates of the crystalline faces [6]. 4. Conclusions In summary, the synthesis of ZnO tubular and epitaxial whiskers have been described via a simple mild hydrother￾mal method. The sample of tubular whiskers has fairly uni￾form diameters of around 4 µm and the length of up to 20 µm. The hollow cavity of tubular ZnO whisker has the same regular prismatic hexagon with the individual whisker. Its photoluminescence spectrum exhibits a strong shoulder emission band located at 400 and 408 nm, and a weak and broad emission band centered at 533 nm. The sample of a large scale of epitaxial whiskers with smooth and symmet￾rically hexagonal shapes and well-knit structure has fairly uniform diameters of around 4 µm and the length of about 10 µm. Its photoluminescence spectrum exhibits a strong shoulder emission band located at 411 and 447 nm. The 1D ZnO tubular whiskers can only be formed with the co￾operation of structure-directing agent of CTAB and the hy￾dration of Zn(NH3)4 2+ under the pH = 10 in hydrothermal growth conditions. The 1D ZnO epitaxial whiskers can only be formed under the synergic effect of structure-directing agent of CTAB and the dehydration of Zn(OH)2 under the pH = 8 in hydrothermal growth conditions. It is expected that the novel tubular whiskers may offer exciting oppor￾tunities for potential applications in catalysis, microsized waveguides or optical fibers. The novel epitaxial whiskers may offer exciting opportunities for homozygote in photo￾electronic devices. In addition, we believe that this simple process can also be applied to synthesize other tubular and epitaxial whiskers for functional materials. Further research is still under progress in our laboratory. Acknowledgements Financial support from the National Natural Science Foundation of China and the Chinese Ministry of Educa￾tion is gratefully acknowledged. References [1] C.M. Lieber, Solid State Commun. 107 (1998) 607. [2] V. Srikant, D.R. Clarke, J. Appl. Phys. 83 (1998) 5447. [3] L. Guo, Y.L. Ji, H.B. Xu, P. Simon, Z.Y. Wu, J. Amer. Chem. Soc. 124 (2002) 14,864. [4] J. Zhang, L.D. Sun, J.L. Yin, H.L. Sun, C.S. Liao, C.H. Yan, Chem. Mater. 14 (2002) 4172. [5] T. Yoshida, H. Naito, M. Okuda, S. Ehara, T. Takagi, O. Kusumoto, H. Kado, K. Yokoyama, T. Tohda, Appl. Phys. Lett. 64 (1994) 3243. [6] J.Q. Hu, Q. Li, N.B. Wong, C.S. Lee, S.T. Lee, Chem. Mater. 14 (2002) 1216. [7] C.X. Xu, X.W. Sun, Jpn. J. Appl. Phys. 1 (42) (2003) 4949. [8] H. Najafov, Y. Fukada, S. Ohshio, S. Iida, H. Saitoh, Jpn. J. Appl. Phys. 1 (42) (2003) 3490. [9] W.J. Li, E.W. Shi, W.Z. Zhong, W.Z. Yin, J. Cryst. Growth 203 (1999) 186. [10] J. Zhang, L.D. Sun, C.S. Liao, C.H. Yan, Chem. Commun. (Cam￾bridge) (2002) 262. [11] Y.J. Xing, Z.H. Xi, Z.Q. Xue, X.D. Zhang, J.H. Song, R.M. Wang, J. Xu, Y. Song, S.L. Zhang, D.P. Yu, Appl. Phys. Lett. 83 (2003) 1689. [12] J.Q. Hu, Y. Bando, Appl. Phys. Lett. 82 (2003) 1401. [13] J.J. Wu, S.C. Liu, C.T. Wu, K.H. Chen, L.C. Chen, Appl. Phys. Lett. 81 (2002) 1312. [14] H. Saitoh, M. Satoh, S. Ohshio, J. Ceram. Soc. Jpn. 110 (2002) 693. [15] A.J. Strausse, Phys. Rev. Lett. 16 (1966) 1193. [16] C.K. Xu, G.D. Xu, Y.K. Liu, G.H. Wang, Solid State Commun. 122 (2002) 175. [17] U. Koch, A. Fojtik, H. Weller, A. Henglein, Chem. Phys. Lett. 122 (1985) 507. [18] S. Monticone, R. Tufen, A.V. Kanaev, J. Phys. Chem. B 102 (1998) 2854. [19] B.D. Yao, H.Z. Shi, H.J. Bi, L.D. Zhang, J. Phys.: Condens. Mater. 12 (2000) 6265. [20] K. Vanheusden, W.L. Warren, C.H. Seager, D.R. Tallant, J.A. Voigt, B.E. Ganade, J. Appl. Phys. 79 (1996) 7983. [21] Y. Li, G.S. Cheng, L.D. Zhang, J. Mater. Res. 15 (2000) 2305. [22] 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. Mat. 12 (2002) 323