Photonic crystals in biology - NanoTR-VI

PP mPP vs.P =P,PP (1)P andPoster Session, Thursday, June 17Theme F686 - N1123Influence of Annealing Conditions on Optical Properties of ZnO Thin Films111111UDerya BaharUP P*, Göknil BabürP P, Sinan DikenP P, Tuba Aye TermeliP P, Banu ErdoanP P, Sava SönmezoluPPand Güven ÇankayaP1PDepartment of Physics, Faculty of Arts and Science, Gaziosmanpaa University, Tokat 60250, TurkeyAbstract-ZnO thin films were deposited on soda lime glass substrates by sol–gel spin-coating technique. The optical properties of ZnO thin filmsare investigated for different annealing temperatures. The optical band gaps of thin film are found to vary with annealing temperatures. Theobtained films are also transparent in the UV- visible region1Zinc oxide (ZnO) as a wide-band-gap semiconductor hasattracted much attention in current semiconductor research,due to its superior optical properties. In addition, ZnO is aversatile semiconductor material, which has attracted attentionfor its wide range of applications, such as thin films, solarcells, luminescent, electrical and acoustic devices andchemical sensors [1-2].In this paper, we report the investigation of ZnO thin filmsprepared by sol-gel spin coating process using zinc acetate(ZnAc). The optical characterization is investigated fordifferent annealing temperatures using Perkin Elmer Lambda35 UV-VIS Spectrometer at room temperature.Transmittance (%)100806040200200 400 600 800 1000 1200Wavelenght (nm)200 C 0300 C 0400 C 0500 C 0Figure 1. UV–VIS spectra of the ZnO thin film for varioustemperatures.In order to prepare a ZnO solution, first, 3.35gr zinc acetate(Zn(CHR3RCOO)R2R·2HR2RO, Merck), used as a precursor, wasdissolved in 50 ml ethanol [CR2RHR6RO, Merck] and stirred for 50min at 60 P PC in a magnetic mixture. Then, 5 ml glacial aceticacide [CR2RHR4ROR2R, Merck] and 1.5 ml hydrochloride acid (HCl,Merck) were added in the solution, and the final solution wassubjected to the magnetic mixture for 2 h. Here, glacial aceticacid and hydrochloride acid were used as an inhibitor to slowdown the zinc acetate fast hydrolysis. Prior to the coatingprocess, the glass was washed with water, ultrasonicallycleaned in ethanol for 20 min, and in acetone for 20 min,respectively. The deposition was carried out at a spinningspeed of 3000 rpm for 30 s. The spin coating procedure was0 0 0continuously repeated five times at 200P PC, 300P PC, 400P PC and0500P PC annealing temperatures on glass substrate.Fig. 1 shows the UV–VIS spectra ZnO thin films fordifferent annealing temperatures in wavelength range 300–1100nm. The transmission of the thin films of zinc oxidedecreases with the increase in annealing temperature. This canbe linked with the increase in the grain size, and indicating itshigh surface roughness and inhomogeneity [3].(h v) 2 (eV/m) 220161284200 C 0 , E g= 3.84 eV300 C 0 , E g= 3.74 eV400 C 0 , E g= 3.67 eV500 C 0 , E g = 3.58 eV02.4 2.8 3.2 3.6 4Photon energy (eV)Figure 2. UV–VIS spectra of the ZnO thin film for varioustemperatures.The optical band gap of the film was calculated by thefollowing relation [4]:(hv) = A (hv - ERgR) P7where A is an energy-independent constant between 10P8 -110PP, Eg is the optical band gap and r is a constant, whichdetermines type of optical transition, r = 1/2, 2, 3/2 or 3 forallowed direct, allowed indirect, forbidden direct andforbidden indirect electronic transitions, respectively [4]. The1/rr(hv)P hv curves were plotted for different r values andthe best fit was obtained for r = ½. The film at variousannealing temperatures shows a direct allowed transition. Theoptical band gap was determined by extrapolating the linear2portion of the plots to (hv)P 0. The optical band gaps of thethin film were found to be 3.84, 3.74, 3.67 and 3.58 eV at 200 °C,300 °C, 400 °C and 500 °C annealing temperature, respectively.The thicknesses of ZnO film were also determined fromtransmittance measurements in Fig.1 and found to be 1361, 692,939 and 660 nm, respectively. The optical band gap decreaseswith the increasing annealing temperatures. The decrease inthe optical band gap is attributed to the lowering of theinteratomic spacing, which may be associated with a decreasein the amplitude of atomic oscillations around theirequilibrium positions [5].In summary, the analysis of the transmission spectra showsthat ZnO thin films are transparent in the UV-visible regionirrespective of the annealing temperatures. This work waspartially supported by the Scientific Research Commission ofGaziosmanpaa University (Project No: 2009/29).*Corresponding author: HTbhr_dry@hotmail.comT[1] Y. Chen, D.M. Bagnall, Z. Zhu, T. Sekiuchi, K. Park, K. Hiraga,T. Tao, S. Koyama, M.Y. Shen, T. Goto, J. Cryst. Growth 181 (1997)165.[2] S. Saito, M. Miyayama, K. Koumoto, H. Yanagida, J. Am. Ceram.Soc. 68 (1985) 40–43[3] K. Liu, X. Wu, B. Wang, Q. Liu, Mater. Res. Bull. 37 (2002)2255.[4] J. Tauc, Mater. Res. Bull. 5 (1970) 721.[5] S. Sönmezolu, G. Çankaya,P PN. Serin, T. Serin, Int. Conf. onNanomaterials and Nanosystems, 10-13 August 2009, p. 129.6th Nanoscience and Nanotechnology Conference, zmir, 2010 619