that affected the flow of Zn vapor and influenced both nucleus den- [21 H. Kim, B.K. Ju, Y-H. Lee, J.Jang. M -H. Oh, J. Electrochem. Soc. 147(2000) sity and stoichiometry of the Zno nanostructures. A relatively 4705. weak UV band and a strong broad bluish-green band were ob Y Cui, C.M. Lieber, Science 291(2001)85 served in the PL spectrum, indicating that the as-prepared Zno [5] w l Park, G -C Yi, M. Kim, s.J. Pen Adv. Mater.15(2003)526 anostructures had many surface defects related to oxygen vacan-[6X. Xu, G.R. Brandes, Appl. Phys. Lett. 74(1999)2549 ies. The turn-on fields of the Zno nanowhiskers, nanotips and L. Zhu, Xu, Y xiu, D W. Hess, C.P. Wong, Electron Mater. 35(2006)195 well-aligned nanorods were 4.5, 5.8 and 6.1 V/um, respectively Electrochem. Soc. The well-aligned nanorods exhibited a high stability in field emis- [9 M.K. Patra, K Manzoor, M. Manoth, S.R. Vadera, N Kumar. J Lumin 128(2008) sion and achieved current density of 20.5 HA/cm at an 110)Yx Chen, M. Lewis, WL Zhou, I Cryst. Growth 282(2005)85 electric field of 8.46 V/um after cont us operation for 6 h [111 Y. Chen, ]. Li, Y. Han, x Yang. Dai, ]. Cryst. Growth 245(2002)163. [12]RS. Wagner, W.C. Ellis, AppL. [13 C Li, G Fang. Q Fu, F Su, G. Li, x Wu, x Zhao, Cryst. Growth 292(2006)19 The authors thank the National Science Council of the Republic [16] S.P. Turano, J. Ready, J. Electron. Mater. 35(2006)192 of China for financially supporting this work under Contract No. 101 B.D. Yao, Y. Chan,N Wang. Appl. Phys. Lett 81 2002)757 SsC96-2221E-151-021 19 M-T. Chen, 1-M. Ti Zhao, M. Zhang P. R. Liu, XY. Zhang, LM. Cao, D.Y. Dai, H. Chen, Y.F. Xu, References [1] H.S. Uh, S.S. Park, J Electrochem. Soc. 150(2003)H12. bertson, Carbon 37(1999)759 [23]S.-H. Yang, M. Yokoyama, Jpn. AppL Phys, Part 1 36(1997)5275.that affected the flow of Zn vapor and influenced both nucleus den￾sity and stoichiometry of the ZnO nanostructures. A relatively weak UV band and a strong broad bluish-green band were ob￾served in the PL spectrum, indicating that the as-prepared ZnO nanostructures had many surface defects related to oxygen vacan￾cies. The turn-on fields of the ZnO nanowhiskers, nanotips and well-aligned nanorods were 4.5, 5.8 and 6.1 V/lm, respectively. The well-aligned nanorods exhibited a high stability in field emis￾sion and achieved an emission current density of 20.5 lA/cm2 at an electric field of 8.46 V/lm after continuous operation for 6 h. Acknowledgements The authors thank the National Science Council of the Republic of China for financially supporting this work under Contract No. NSC 96-2221-E-151-021. References [1] H.S. Uh, S.S. Park, J. Electrochem. Soc. 150 (2003) H12. [2] H. Kim, B.-K. Ju, Y.-H. Lee, J. Jang, M.-H. Oh, J. Electrochem. Soc. 147 (2000) 4705. [3] S. Iijima, Nature 354 (1991) 56. [4] Y. Cui, C.M. Lieber, Science 291 (2001) 851. [5] W.I. Park, G.-C. Yi, M. Kim, S.J. Pennycook, Adv. Mater. 15 (2003) 526. [6] X. Xu, G.R. Brandes, Appl. Phys. Lett. 74 (1999) 2549. [7] L. Zhu, J. Xu, Y. Xiu, D.W. Hess, C.P. Wong, J. Electron. Mater. 35 (2006) 195. [8] F.M. Kolb, H. Hofmeister, R. Scholz, M. Zacharias, U. Gösele, D.D. Ma, S.-T. Lee, J. Electrochem. Soc. 151 (2004) G472. [9] M.K. Patra, K. Manzoor, M. Manoth, S.R. Vadera, N. Kumar, J. Lumin. 128 (2008) 267. [10] Y.X. Chen, M. Lewis, W.L. Zhou, J. Cryst. Growth 282 (2005) 85. [11] Y. Chen, J. Li, Y. Han, X. Yang, J. Dai, J. Cryst. Growth 245 (2002) 163. [12] R.S. Wagner, W.C. Ellis, Appl. Phys. Lett. 4 (1964) 89. [13] C. Li, G. Fang, Q. Fu, F. Su, G. Li, X. Wu, X. Zhao, J. Cryst. Growth 292 (2006) 19. [14] H. Guo, J. Zhou, Z. Lin, Electrochem. Commun. 10 (2008) 146. [15] M. Guo, P. Diao, S. Cai, J. Solid State Chem. 178 (2005) 1864. [16] S.P. Turano, J. Ready, J. Electron. Mater. 35 (2006) 192. [17] B.D. Yao, Y.F. Chan, N. Wang, Appl. Phys. Lett. 81 (2002) 757. [18] B.H. Kong, H.K. Cho, J. Cryst. Growth 289 (2006) 370. [19] M.-T. Chen, J.-M. Ting, Thin Solid Films 494 (2006) 250. [20] J.H. Zhao, M. Zhang, P.R. Liu, X.Y. Zhang, L.M. Cao, D.Y. Dai, H. Chen, Y.F. Xu, W.K. Wang, J. Mater. Res. 14 (1999) 2888. [21] A. Khan, M.E. Kordesch, Physica E 30 (2005) 51. [22] J. Robertson, Carbon 37 (1999) 759. [23] S.-H. Yang, M. Yokoyama, Jpn. J. Appl. Phys., Part 1 36 (1997) 5275. e184 S.-H. Yang et al. / Current Applied Physics 9 (2009) e180–e184