Effect of Cobalt Doping on Physical Properties of ZnO Nanoparticles

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1 CPUH-Reearch Journal: 06, (), 47-5 ISSN (nline): Effect of Cobalt oping on Phyical Propertie of Zn Nanoparticle Neha Sharma, Shaveta Thakur, Ruchita Sharma and Jitender Kumar * epartment of Phyic, Arni Univerity, Kangra (Himachal Pradeh) epartment of Phyic, Career Point Univerity, Hamirpur (HP) INIA jiten.arni@gmail.com (Received 5 Aug, 05; Accepted 0 Sept, 05; Publihed 0 Mar, 06) ABSTRACT: Nanocrytal of undoped and Cobalt doped Zinc xide nanoparticle (Zn -x Co x, where x = 0, 0. and 0.M) were yntheized by imple olution route. Crytalline phae, optical aborption and band gap of Cobalt doped Zn nanoparticle/thin film were tudied by X-ray diffraction and UV viible pectrophotometer. XR reult revealed that the ample product wa crytalline with a hexagonal wurtzite phae. The particle ize wa determined by Scherrer method and W-H analyi. In cae of Scherrer method and W-H anayli, the particle ize of cobalt doped Zn nanoparticle decreae with increae in concentration of cobalt (0, 0. and 0.M) but the particle ize of different concentration (0, 0. and 0.M) of cobalt doped Zn by uing W-H analyi i greater than the particle ize determined by uing Scherrer method. The W-H analyi wa ued to tudy the individual contribution of crytallite ize and lattice train on the peak broadening of Co doped Zn nanoparticle. Nanocrytalline Zn thin film were prepared by a pin coating technique. The tronget aborption peak appear at around 50nm, which i blue hifted from the aborption edge of bulk Zn (65nm). The band gap value of prepared cobalt doped Zn NP increae with increae in concentration of cobalt doping. ptical tudie indicated that nanoparticle had a good tranmittance ( 60%) and the band gap increaed from.ev to.5ev upon Cobalt doping at temperature 500 o C. Keyword: Nanocrytal; oping XR and Zinc xide. INTRUCTIN: Nanotructured material have received much attention becaue of their novel propertie, which differ from thoe of bulk material. Control of dimenion and morphology of material ha aroued the interet of reearcher in the deign of functional device due to the optical and electronic propertie of nanometer and micrometer ized material, which determine their application can be adapted by varying their ize and hape []. Nanocience and nanotechnology involve tudying and working with matter on an ultra mall cale from ub nanometer to everal hundred nanometer. Thee nanoize material have propertie that are often ignificantly different from their counterpart with ordinary ize []. Nanotructured Zn material have received broad attention due to their ditinguihed performance in electronic, optic and photonic. Zn ha a direct wide band gap (.4eV) at room temperature, which i n-type emiconductor, ued in optoelectronic device becaue of it high optical tranparency. In ome cae, it i preferred to be ued in n-type doping []. In ambient condition, Zn ha a table hexagonal wurtzite tructure with lattice pacing a=0.5nm and c= 0.5 nm and compoed of a number of alternating plane with tetrahedrally coordinated - and Zn + ion. Zn i known a an important emiconductor which ha been tudied extenively in the pat few year due to it fundamental and technological importance. Thi emiconductor ha everal favorable propertie: good tranparency, high electron mobility, wide band gap, large exciton binding energy and excellent chemical tability and ugget a great many poible practical application uch a in electronic, field emiion device, ga enor and varitor [4]. Particle ize and optical propertie play important role in thee application, which have driven reearcher to focu on the ynthei of nanocrytalline Zn in recent year. Keeping in view the extenive ue of Zn, variou type of ynthei technique have been formulated over the year. Variou chemical method have been developed to prepare nanoparticle of different material of interet. Mot of the Zn crytal have been yntheized by vapour depoition method [5], ol-gel method [6] and a thermal method [7]. Solution route i a promiing alternative ynthetic method becaue of the low proce temperature and eay to control the particle ize. In the preent work undoped Zn and Cobalt doped Zn nanoparticle were yntheized by uing imple olution route, which i robut and reliable to control the hape and ize of particle without requiring the expenive and complex equipment. 47

2 [(CPUH-Reearch Journal: 06, (), 47-5) Effect of Cobalt oping on Phyical Propertie of Zn Nanoparticle] A perfect crytal would extend infinitely in all direction therefore; no crytal are perfect due to their finite ize. Thi deviation from perfect crytallinity lead to a broadening of the diffraction peak. The two main propertie extracted from peak width analyi are the crytallite ize and lattice Strain. Crytallite ize i a meaure of the ize of coherently diffracting domain. The crytallite ize of the particle i not generally the ame a the particle ize due to the formation of polycrytalline aggregate [8]. Lattice train i a meaure of ditribution of lattice contant ariing from crytal imperfection, uch a lattice dilocation. Crytallite ize and lattice train affect the Bragg peak in different way. Both thee effect increae the peak width and intenity and hift the θ peak poition accordingly. The peak width derived from crytallite ize varie a /Coθ, wherea train varie a tanθ. Thi difference in behavior a a function of θ enable to dicriminate between the ize and train effect on peak broadening. The Bragg width contribution from crytallite ize i inverely proportional to the crytallite ize [9]. In thi work, a comparative evaluation of the mean particle ize of the undoped and cobalt doped Zn NP obtained from powder XR procedure i reported and the band gap meaurement are obtained from optical tudie. The train due to lattice deformation aociated with the Zn NP heated at 500 o C wa etimated by Williamon-hall analyi (W-H). MATERIAL NA METHS: Sample ynthei and geometric characterization: The ynthei of Zn nanoparticle wa carried out by imple olution route. The tarting material, Zn(CH C).H and Co(N ).6H olution were prepared a follow: Solution-A: M Zn(CH C).H wa diolved in the olution containing 80 ml ditilled water and 0 ml ethanol and Solution-B: ifferent concentration of Co (N ).6H wa mixed with 80 ml of deionized water and 0ml of ethanol. Mixing thee olution ha reulted into olution C. The experiment wa performed at room temperature. Then ammonia olution wa added into the olution drop by drop. The initial olution contain milky colored precipitate of Zinc acetate at low concentration of ammonia. Separately, a buffer olution wa prepared by diolving appropriate amount of odium hydroxide. The buffer olution wa then added drop wie to the vigorouly tirred olution C until the precipitation occur. Then put the olution at contant temperature for hour. The precipitate wa filtered and wahed with ditilled water. The precipitate wa dried at 500 C for hour in muffle furnace. Then grind the dry particle. The cobalt nitrate/ baic zinc acetate dehydrate precipitate wa decompoed in cobalt doped zinc oxide. Preparation of Co doped Zn thin film uing Spin Coater: The depoition of doped zinc oxide by pin coating technique ha een increaed reearch activity over the pat everal year a the need for high quality zinc oxide thin film ha increaed. Spin coating i ued for the application of thin film and for thi were ued a ubtrate. A typical proce involve depoiting a mall puddle of a Fluid rein onto the center of a ubtrate and then pinning the ubtrate at high peed (typically around 000 rpm). After preparing Zn colloidal olution, thin film were depoited. We ued well cleaned gla lide 75 x 5mm quare inch lide of thickne.5mm a the ubtrate. Prior to proceing, each gla lide wa wahed equentially in acetone and ditilled water. The gla lide were then dried. Thi enure that there i no contamination on the gla urface that could potentially interfere with depoition of Zn thin film. The ubtrate i ecure properly on to the pin coater, and with the aid of yringe, mall amount of colloidal olution carefully dipered on to the ubtrate. The pin coater i immediately pun at the rate of 000rpm for 0 ec. The crytal tructure and the particle ize of the thin film were identified uing an X-ray diffractometer (XR Model: 8 Focu). A UV-50 UV vi pectrophotometer (SHIMAZU, Japan) with an integrating phere wa ued to directly record diffue reflectance pectra of the pure and Cobalt doped Zn. RESULTS AN ISCUSSIN: XR Analyi: The XR pattern of the prepared ample are hown in Figure. It i clearly een that the FWHM of the reflection peak decreae after adding the dopant cation, indicating growth of the crytalline or change in the crytal train. There i alo a negligible hift in peak, and their FWHM obviouly decreaed for the ample that were doped with different concentration of Co compared to the un-doped Zn-NP. Thi hift alo correpond to the train of the compound and replacement of ome Zn cation with Cobalt in each compound. By replacing Co with Zinc in the lattice, the train changed a hown in the peak hift. Wurtzite lattice parameter uch a the value of d, the ditance between adjacent plane in the Miller indice (hkl), lattice contant a, b, and c, interplaner angle {the angle between the plane (h k l ), of pacing d and the plane (h k l ) of pacing d }, and unit cell volume were calculated from the Lattice Geometry equation preented below [0]. The lattice parameter of the powder heated at 48

3 [(CPUH-Reearch Journal: 06, (), 47-5) Effect of Cobalt oping on Phyical Propertie of Zn Nanoparticle] C with different concentration (0, 0. and 0.M) = are ummarized in Table. a d = 4 h hk k h l h kk ( hk hk ) ll a c () a a ( h k hk l )( h k hk a c V a c () Table : The tructure parameter of un-doped and Co-doped Zn NP heated at C Compound theta hkl d(å) Structure Pure Zn Zn 0. 8 Zn (00) (00) (00) (00) (00) (00) Lattice parameter(nm) a = 0.5 a = 0.5 a = 0.5 V(nm ) l Co () Figure : The XR pattern of Pure Zn -NP and Co doped Zn- NP heated at C. (a) Pure Zn- NP, (b) Co (0.M) - doped Zn- NP, (c) Co (0.M) -doped Zn NP; the XR pattern how that the ample product are crytalline with a hexagonal Wurtzite phae. Particle ize and train:. Scherrer method: XR can be utilized to evaluate peak broadening with crytallite ize and lattice train due to dilocation. The crytalline ize of the undoped Zn and Cobalt doped Zn with different concentration were determined by the X-ray line broadening method uing the Scherrer equation = ( k / co ), where i the crytalline ize in nanometer, k i a contant equal to 0.94, i the peak width at half maximum intenity, i the wavelength of radiation (for CuK α tion =.54056A 0 ) and i the peak poition. ebye Scherrer formula i given a k = (4) co Co = k (5). Williamon-Hall method: The W-H method doe not follow a / co dependency a in the Scherrer equation but intead varie with tan. Thi fundamental difference allow for a eparation of reflection broadening when both micro tructural caue mall crytallite ize and micro train- occur together. The different approache preented in the following aume that ize and train broadening are additive component of the total integral breadth of a Bragg peak []. Addition of the Scherrer equation and є = / tan reult in following equation: (6) k hkl (4 Єtan ) co (7) Rearranging Eq. (7) give: 49

4 [(CPUH-Reearch Journal: 06, (), 47-5) Effect of Cobalt oping on Phyical Propertie of Zn Nanoparticle] k hkl co (4 Єin ) (8) Compound Method Scherrer W-H Analyi (nm) (nm) Zn Zn 0.8 Zn Figure : The W-H analyi of Co-doped Zn NP heated at C (a) Undoped Zn NP (b) Co (0.M) - doped Zn NP (c) Co (0.M) - doped Zn NP. The correponding Williamon-Hall plot howed that line broadening wa eential iotropic (Figure ). Thi indicate that the diffracting domain were iotropic and there wa alo a microtrain contribution. The Particle ize of Undoped and Cobalt Zn nanoparticle wa determined by uing two method: Scherrer method and W-H analyi. The W-H analyi wa ued to tudy the individual contribution of crytallite ize and lattice train on the peak broadening of Co doped Zn nanoparticle. From Table, it i clear that in cae of Scherrer method and W-H anayli, the particle ize of cobalt doped Zn nanoparticle decreae with increae in concentration of cobalt but the particle ize of different concentration of cobalt doped Zn by uing W-H analyi i greater than the particle ize determined by uing Scherrer method. PTICAL STUIES: The optical aborption pectra of undoped and cobalt doped Zn (Zn -x Co x, where x= 0, 0. and 0.M) thin film by UV-Vi pectrophotometer in the range nm were preented. From figure, it can be een that the aborption peak of prepared undoped and cobalt doped thin film appear at 55nm which i fairly blue hifted from the aborption edge of the bulk Zn. The tranmittance quickly decreae below 50 nm due to aborption of light caued by the excitation of electron from the valence band to conduction band of Zn. The aborption edge hifted toward longer wavelength (i.e red hift) with the increae of cobalt doped concentration. The energy band gap i determined by uing the relationhip α =A (hv-e g ) n (0) Where hv = photonic energy, α = aborption coefficient (α = 4πK/; k i the aborption index or aborbance, λ i the wavelength in nm), E g = Energy band gap, A = contant, n = / for allowed direct band gap. Exponent n depend upon on the type of tranition and it may have value /,, / and correponding to the allowed direct, allowed indirect, forbidden direct and forbidden indirect tranition repectively Table : Variation of band gap with increae in concentration of Co doped Zn heated at C. Compound Band gap (ev) Aborption Edge(nm) Pure Zn.50 4 Zn Zn Table : Geometric parameter of pure and Co doped Zn NP at 500 o C 50

5 [(CPUH-Reearch Journal: 06, (), 47-5) Effect of Cobalt oping on Phyical Propertie of Zn Nanoparticle] CNCLUSIN: Nanocrytal of undoped and cobalt doped Zn NP (Zn -x Co x ) were uccefully yntheized by uing imple olution route. The crytalline tructure, optical propertie and band gap were determined by XR and UV-viible pectrophotometer. XR analyi how that the prepared ample are in hexagonal wurtzite phae. The particle ize can be determined by Scherrer formula, and Williamon Hall analyi. The average ize of Co doped Zn NP decreae a the concentration of cobalt doping increae. Thi difference i proportional to train value and how that the role of train i important; therefore, it hould be conidered in the calculation of crytalline ize. Thu, uing the Scherrer method without conidering train may yield inaccurate reult. Nanocrytalline Zn thin film were prepared by a pin coating technique. The tronget aborption peak appear at around 50 nm, which i blue hifted from the aborption edge of bulk Zn (65nm).The band gap value of prepared cobalt doped Zn NP increae with increae in concentration of cobalt doping. ACKNWLEGEMENTS: Author are thankful to r. Atul Khanna from Guru Nanak ev Univerity, Amritar for technical upport in carrying XR tudy. Figure : ptical aborption pectra of cobalt doped Zn nanoparticle with different concentration of Co i.e (a) Undoped Zn (b) Co(0.)- doped Zn- NP, (d) Co(0.)-doped Zn NP at C. From figure, it can be een that excitonic aborption peak of a prepared undoped and with different concentration of cobalt doped Zinc oxide become narrow a the concentration i increae. The harp exitionic peak in the aborption pectra at 500 o C i indicative of the mall ize ditribution of nanocrytal in the ample and broadening of peak at different concentration clearly indicate the increae in ize of nanocrytal with the increae of concentration of Co. It can be oberved clearly from table that the aborbance decreae a the concentration increae at 500 o C. In Cobalt doped Zn, an aborption band localized between 00 nm and 50 nm at 500 o C. The tronget aborption peak appear at around 50nm, which i blue hifted from the aborption edge of bulk Zn (65nm). The band gap value of prepared undoped and cobalt doped Zn NP increae with increae in concentration of cobalt doping. REFERENCES:. Ju-Nam, Y et al. (008) Sci Total Environ. 400(- ), Zhong Lin Wang, (004) Journal of Phyic: Condened Matter. 6 R89- R858.. T. Kataoka, Y. Yamazaki, Y. Sakamoto, A. Fujimori, F.-H. Chang, H. J. Lin, et.al. (00) Appl. Phy. Lett. 96, S. Hingorani, V. Pillai, P. kumar, M. S. Muntai,.. Shah, (99) Mater. Re. Bull. 8, M.R. Vaezi, S.K. Sadrnezhaad, (007)Mater. e. 8, A. Bandyopadhyay, S. Modak, S. Acharya, A.K. eb, P.K. Chakarabarti, (00) Solid State Sci., H. Bai, X. Liu, (00) Mater. Lett. 64, K. Ramakanth, Baic of iffraction and It Application, I.K. International Publihing Houe Pvt. Ltd., New elhi, (007). 9. V.K. Pecharky, P.Y. zawali, Fundamental of Powder iffraction and Structural Characterization of Material, Springer, New York, (00). 0. B.. Culity, Element of X-ray iffraction, Addion-Weley Publihing Company Inc., California, (956).. M. Birkholz, Thin Film Analyi by X-ray Scattering. Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim (006). 5