[01] Anju Singh, Department of Physics, Rungta College of Engineering and Technology (RCET), Bhilai, Chhattisgarh, India. [02] H. L. Vishwakarma, Department of Physics, (VEC), Lakhanpur, Sarguja University, Ambikapur, Chhattisgarh, India.

In this paper, undoped and cobalt doped Zinc Oxide (ZnO) nanorods were achieved by a simple chemical precipitation method at room temperature in the presence of Poly Vinyl Pyrrolidone (PVP) as a capping agent. Zinc acetate (Zn (CH₃COO) ₂.2H₂O) and cobalt acetate (Co (CH₃COO) ₂.4H₂O) were taken as precursors. The effect of doping concentration ranging from 0 to 2 wt% on structural, morphological and optical properties have been studied by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Ultraviolet visible (UV-Vis) spectrophotometer. Crystallite sizes have been calculated by Debye Scherrer formula whose values are decreasing with increase in cobalt content up to 2%. The average particle size of doped nanorods is about 60 nm which is greater than that of pure ZnO (about 43 nm). It has been seen that the growth orientation of the prepared ZnO nanorods were (101). The XRD analysis also ensures that ZnO has a hexagonal (wurtzite) crystal structure. The Scanning Electron Microscope (SEM) image confirmed the size and shape of these nanorods. The absorption peaks for undoped and 1 to 2% cobalt doped ZnO nanorods samples have been observed around 355 nm, 330 nm and 380 nm by UV-Vis spectrophotometer. The doped ZnO nanorods exhibited a blue shifted band gap. The energy band gap have been obtained from the Taucs plot was found increasing up to 1% and then decreasing up to 2% of cobalt doping.

ZnO Nanorods, Optical Band Gap, Wurtzite, XRD, SEM, Absorption Peak

[01] D. Appell, Nanotschnology: wired for success, Nature.,419 553 (2002). [02] L. Samuelson, Self-forming nanoscale devices, Mater. Today, 6, 22 (2003). [03] X FDuan, Y Huang, J F Wang and C MLieber,Indium phosphide nanowires as building blocks for nanoscale electronic and optoelectronic devices, Nature.,409 ,66 (2001). [04] Y Cui, Q Wei, H Park and C M Lieber, Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species, Science., 293,1289 (2001). [05] Y N Xia, P D Yang, Y G Sun, Y YWu, B Mayers, B Gates, Y D Yin, F Kim and H Q Yan, One-dimensional nanostructures: synthesis, characterization and applications, Adv.Mater.,15, 353 (2003). [06] Z LWang, Characterizing the structure and properties of individual wire-like nanoentities, Adv. Mater., 12, 1295 (2000). [07] J Hu, T W Odom and C MLieber, Chemistry and physics in one dimension: synthesis and properties of nanowires and nanotubes, Acc.Chem.Res., 32, 435 (1999). [08] M. H. Huang, Y. Wu, H. Feick, N. Tran, E.Weber and P. Yang 13, Catalytic growth of Zinc Oxidenanowires by vapor transport, Adv. Mater. b, Vol.13, pp. 113-116 (2001). [09] Z.-M Liao, K.- J Liu, J.- M Zhang, J. Xu, and D.-P Yu, Effect of surface states on electron transport in individual ZnO nanowires, Phys. Lett. A., Vol.367, pp. 207-210 (2007). [10] Q. H. Li, T.Gao, Y. G. Wang and T. H. Wang, Adsorption and desorption of oxygen probed from ZnO nanowire films by photocurrent measurements, Appl. Phys. Lett..,Vol.86, pp. 123117 (2005). [11] H. Kind, H. Q. Yan, B.Messer, M.Law andP. D. Yang, Nanowire ultravioletphotodetectors and optical switche, Adv. Mater., Vol.14, pp. 158–160 (2002). [12] C. Soci, A.Zhang, B. Xiang, S. A. Dayeh, D. P. R.Aplin, J.Park, X. Y.Bao, Y. H. Lo,and D.Wang, ZnO nanowire UV photodetectors with high internal gain, NanoLett. , Vol.7, pp. 1003-1009 (2007). [13] N. H. Alvi, M. Riaz, G.Tzamalis,O.Nur and M.Willander, Fabrication andcharacterization of high-brightness light emitting diodes based on n-ZnOnanorodsgrown by a low-temperature chemical method on p-4H-SiC and p-GaN, Semicond.Sci. Technol., Vol.25, pp. 065004 (2010). [14] J.Liu, Y. H. Ahn, J.-Y Park,K. H. Koh and S. Lee, ,Hybrid light-emitting diodes based on flexible sheets of mass-produced ZnO nanowires, Nanotechnol.,Vol.20, pp.4452063 (2009). [15] M. Law, L. E. Green, J. C. Jhonson, R.Saykally andP.Yang, Nanowire dye-sensitized solar cells, Nature Mater., Vol.4, pp. 455-495 (2005). [16] M. Law, L. E. Greene, A.Radenovic, T.Kuykendall, J.Liphardt and P.Yang, ZnOAl2O3 and ZnO-TiO2 core-shell nanowire dye-sensitized solar cells, J. Phys. Chem. B.,Vol.110, pp. 22652-22663 (2006). [17] K. S Yeong, M. K H.and J. T. L Thong, The effects of gas exposure and UVillumination on field emission from individual ZnO nanowires, Nanotechnol., Vol.18, pp. 185608 (2007). [18] S.Xu, Y.Qin, C.Xu, Y.Wei, R.Yang and Z. L Wang, Self-powered nanowire devices, Nat. Nanotechnol., Vol.5, pp. 366-373 (2010). [19] D. J Gargas, M. Eugenia, T. Molares and P Yang, Imaging single ZnO vertical nanowire laser cavities using UV-laser scanning confocal microscopy, J. Am. Chem.Soc.,Vol.131, No.6, pp. 2125-2127 (2009). doi:10.1021/ja8092339. [20] K Keem, H Kim, G T Kim, J S Lee, B Min, K Cho, M Y Sung and S Kim, Photocurrent in ZnO nanowires grown from Au electrodes, Appl. Phys. Lett., 84, 4376 (2004). [21] M S Arnold, PAvouris, Z W Pan and Z L Wang , Field effect transistors based on single semiconducting oxide nanobelts, J.Phys.Chem.B.,107, 659 (2003). [22] M H Huang, S Mao, H Feick, H Q Yan, Y Y Wu, H Kind, E Weber, R Russo and P D Yang, Room temperature ultraviolet nanowire, nanolasers Science.,292, 1897 (2001). [23] C J Lee, T J Lee, S C Lyu, Y Zhang, H Ruh and H J Lee, Field emission from well aligned zinc oxide nanowires grown at low temperature, Appl. Phys.Lett., 81, 3648 (2002). [24] W I Park, Y H Jun, S W Jung and G C Yi,Excitonic emission observed in ZnOsingle crystal nanorods, Appl.Phys.Lett.,82,964 (2003). [25] P. K. Giri, S. Dhara and R. Chakra borty, Effect of ZnO seed layer on the catalytic growth of vertically aligned ZnOnanorod arrays, Mater. Chem. Phys.,Vol.122, pp. 18-22 (2010). [26] C. Li, G. Fang, J. Li, L. Ai, B. Dong and X. Zhao, Effect of seed layer on structural properties of ZnOnanorod arrays grown by vapor-phase transport, J. Phys. Chem. C., Vol.112, pp. 990-995 (2008). [27] B. D. Yao, Y. F. Chan and N.Wang, Formation of ZnO nanostructures by a simple way of thermal evaporation, Appl. Phys. Lett.,Vol.81, pp. 757-759 (2002). [28] H. Yuan and Y. Zhang, Preparation of well-aligned ZnO whiskers on glass substrate by atmospheric MOCVD, J. Cryst. Growth, Vol.263, pp. 119–124 (2004). [29] W. I. Park, D. H.Kim, S. W. Jung and G. C. Yi,Metalorganicvapor-phase epitaxial growth of vertically well-aligned ZnOnanorods, Appl. Phys. Lett., Vol.80, pp. 4232–4234 (2002). [30] D. C. Kim, B. H. Kong, and H. K Cho, Synthesis and growth mechanism of catalyst free ZnOnanorods with enhanced aspect ratio by high flow additional carrier gas at low temperature, J. Phys. D: Appl. Phys.,Vol.42, pp. 065406 (2009). [31] Y. WHeo, V.Varadarajan, M.Kaufman, K.Kim, D. P. Norton, F.Ren, andP. H. Fleming, Site-specific growth of ZnOnanorods using catalysis-driven molecular-beam epitaxy, Appl. Phys. Lett., Vol.81, pp. 3046–3048 (2002). [32] M.Breedon, C.Rix and K.Kalantar-zadeh,Seeded growth of ZnOnanorods from NaOH solutions, Mater. Lett., Vol.63, pp. 249–251 (2009). [33] M. A. Verges, A. Mifsud and C. J. Serna, Formation of rodlike zinc-oxide microcrystals in homogeneous solutions, J. Chem. Soc., Faraday Trans., Vol.86, pp. 959-963 (1990). [34] N. H. Alvi, M. Riaz, G.Tzamalis, O.Nur and M.Willander, Fabrication and characterization of high-brightness light emitting diodes based on n-ZnOnanorods grown by a low-temperature chemical method on p-4H-SiC and p-GaN, Semicond. Sci. Technol., Vol.25, pp. 065004 (2010). [35] Y.Tak andK.Yong Controlled growth of well-aligned ZnOnanorod array using a novel solution method, J. Phys. Chem. B, Vol.109, pp. 19263-19269 (2005). [36] C.Pacholski, A.Kornowski and H. Weller, Self-assembly ofZnO: from nanodots to nanorods, Angew. Chem. Int. Ed.,Vol.41, pp. 1188-1191 (2002). [37] J. Songand S.Lim, Effect of seedlayer on the growth of ZnOnanorods, J. Phys. Chem. C,Vol.111, pp. 596-600 (2007). [38] J. J. Wu, H. I. Wen, C. H. Tseng and S. C. Liu, Well-aligned ZnOnanorods via hydrogen treatment of ZnO films, Adv. Funct. Mater. Lett., Vol.14, pp. 806–810 (2004). [39] X. Huang, G. Li, B. Cao, M. Wang and C. Hao, J.Phys. Chem. C, 113, 4381 (2009). [40] G. Murugadoss,J. Lumin., 132, 2043 (2012). [41] K.M.K. Srivatsa, D. Chhikara and M. Senthil Kumar, .J. Mater. Sci. Technol., 27, 701 (2011). [42] W.Y. Zhou, Y. Zhou and S.Q. Tang, Mater. Lett., 59, 3115 (2005). [43] H. Tokudome and M. Miyauchi, Chem. Lett., 33, 1108 (2004). [44] J.H. Park, S. Kim and A.J. Bard, Nano Lett., 6, 24 (2006). [45] M.G. Ou, B. Mutelet, M. Martini, R. Bazzi, S. Roux,G. Ledoux, O. Tillement and P. Perriat, J. ColloidInterf. Sci. 333, 684, (2009). [46] G. Campet, M. Jakani, J. P. Doumerc, J.Claverie, P. Hagenmuller, Photoconduction mechanisms in titanium and rare earth n-typesemiconducting electrodes with pyrochlore and perovskite structures, Solid State Communications, 42(2), 93-6 (1982). [47] W.Choi, A. Termin, M. Hoffmann, The role of metal ion dopants in quantum-sized TiO2: correlation between photoreactivity and charge carrier recombination dynamics,The Journal of Physical Chemistry, 98(51), 13669-79 (1994). [48] T. Umebayashi, T. Yamaki, H. Itoh, K. Asai, Analysis of electronic structures of 3d transition metal-doped TiO2 based on band calculations, Journal of Physics and Chemistry of Solids,63(10), 1909-20 (2002). [49] R.Wang,J. H. Xin, Y. Yang,H.Liu, L. Xu, J. Hu, The characteristics and photocatalytic activities of silver doped ZnOnanocrystallites, Applied Surface Science,227(1-4), 312-7 (2004). [50] C. J. Cong, J. H. Hong, Q. Y.Liu, L.Liao, K. L. Zhang, Synthesis, structure and ferromagnetic properties of Ni-doped ZnO nanoparticles, Solid State Communications,138(10-11), 511-5 (2006). [51] K. G. Kanade, B. B Kale, J.- O. Baeg,S. M. Lee, C. W Lee, S.-J Moon, H. Chang,Self-assembled aligned Cu doped ZnO nanoparticles for photocatalytic hydrogen production under visible light irradiation, Materials Chemistry and Physics ,102(1), 98-104 (2007). [52] N. Volbers, H.Zhou, C.Knies, D. Pfisterer, J. Sann, D. M.Hofmann, B. K. Meyer, Synthesis and characterization of ZnO:Co²⁺ nanoparticles, Applied Physics A: Materials Science & Processing.,88(1), 153-5 (2007). [53] L .Li, W. Wang, H. Liu, X. Liu, Q .Song andS.Ren, First principles calculations of electronic band structure and optical properties of Cr-doped ZnO, The Journal ofPhysical Chemistry C ,113(19), 8460-4 (2009). [54] N. Samaele, P.Amornpitoksuk andS.Suwanboon, Morphology and optical properties of ZnO particles modified by diblock copolymer, Materials Letters, 64(4), 500-2 (2010). [55] J. Zhou, F. Zhao, Y. Wang, Y. Zhang, and L. Yang, Size-controlled synthesis of ZnO nanoparticles and their photoluminescence properties,Journal of Luminescence, vol. 122-123, no. 1-2, pp. 195–197 (2007). [56] Z. M. Khoshhesab, M. Sarfaraz, and M. A. Asadabad,Preparation of ZnO nanostructures by chemical precipitation method, Synthesis and Reactivity in Inorganic,Metal-Organic and Nano-Metal Chemistry,vol. 41, no. 7, pp. 814–819 (2011). [57] X.H. Huang, Z.Y. Zhan, X. Wang, Z. Zhang, G.Z. Xing, D.L. Guo, D.P. Leusink, L.X. Zheng and T. Wu, Appl. Phys. Lett., 97, 203112 (2010). [58] R.D. Shannon, Acta Crystallogr. Sect. A,32 (Sep1) 751–767 (1976). [59] A.S. Ahmed, M.M. Shafeeq, M.L. Singla, S. Tabassum, A.H. Naqvi, A. Azam,J.Lumin., 1,131 (2010). [60] J. Tauc, Amorphous and Liquid Semiconductors, Plenum Press, New York, p. 171 (1974). [61] T. Takagahara, K. Takeda, Phys. Rev. B, 46, 15578(1992). [62] S. Suwanboon, T. Ratana, W.T. Ratana, Walailak, J. Sci. Technol.,4 (1),111(2007). [63] G. Murugadoss, Synthesis and Characterization of Transition Metals Doped ZnO Nanorods, J. Mater. Sci. Technol., 28(7), 587-593(2012). [64] S. Udayakumar, V.Renuka and K.Kavitha,Structural, optical and thermal studies of cobalt doped hexagonal ZnO by simple chemical precipitation method,J. Chem. Pharm. Res.,4(2),1271-1280 (2012).