Photonic crystals in biology - NanoTR-VI

PP mPP vs.P vs.P =P (1)P andPoster Session, Thursday, June 17Theme F686 - N1123The Coating Layers Dependence of Optical Properties of ZnO Thin Films111111UTuba Aye TermeliUP P*, Banu ErdoanP P, Derya BaharP P, Göknil BabürP P, Sinan DikenP P, Sava SönmezoluP Pand Güven ÇankayaP1PDepartment of Physics, Faculty of Arts and Science, Gaziosmanpaa University, Tokat 60250, TurkeyAbstract-We have prepared ZnO thin films using sol–gel spin-coating technique, and investigated the optical properties of these thin films fordifferent coating thickness.The film thickness increased with increasing coating layers, on the contrary, the optical band gaps of thin filmdecreased with increasing coating layers. This difference is attributed to the containing its high grain size, and inhomogeneity. Furthermore, theobtained films are transparent over %70-80 in the UV- visible region.1ZnO thin films now attract significant attention due to theirwide range of electrical and optical properties. They havepotential application in electronics, optoelectronics andinformation technology devices including displays, solar cellsand 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 coating thickness using Perkin Elmer Lambda 35UV-VIS Spectrometer at room temperature.Transmittance (%)100806040203 layers5 layers7 layers9 layers12 layers0200 400 600 800 1000 1200Wavelenght (nm)Figure 1. UV–VIS spectra of the ZnO thin film for various coatinglayers.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 at 3000 rpm for 30 s. The spin coating procedure wasrepeated for 3 layers, 5 layers, 7 layers, 9 layers and 12 layerscoating thickness at the same temperature (400 ºC), respectively.Figure 1 shows the UV–VIS spectra ZnO thin films fordifferent coating layers in wavelength range 300–1100nm. Thetransmission of the thin films of zinc oxide decreases with theincrease in coating thickness, except 12 layers. This can belinked with containing its high grain size, and inhomogeneity [3].(Alfahv) 2 (eV/m) 214121086423 layers5 layers7 layers9 layers12 layers02 2.4 2.8 3.2 3.6 4Photon energy (eV)1/rFigure 2. The plot of (Alfahv)P hv of the ZnO thin film forvarious spinning speeds.The optical band gap of the film was calculated by thefollowing relation [4]:r(Alfahv) = 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/r(Alfahv)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 (Alfahv)P 0. The optical band gaps ofthe thin film were found to be 3.57, 3.55, 3.43, 3.71 and 3.63 eV0at 400P PC in different coating layers, respectively. The thicknessesof ZnO film were also determined from transmittancemeasurements in Figure1 and found to be, 117, 294, 560, 975 and815 nm, respectively. It has shown that there is irregularrelation between optical band gap and coating layers.In summary, the film thickness increased with increasing coatinglayers, on the contrary, the optical band gaps of thin film decreasedwith increasing coating layers. This work was partially supportedby the Scientific Research Commission of GaziosmanpaaUniversity (Project No: 2009/29).*Corresponding author: HTt.aysedonmezoglu@hotmail.comTH[1] S. Bandyopadhyay, G.K. Paul, S.K. Sen, Sol. Energy Mater. Sol.Cells 71 (2002) 103.[2] Y. Natsume, H. Sakata, Thin Solid Films 372 (2000) 30.[3] S. Fujihara, C. Sasaki, T. Kimura, Appl. Surf. Sci. 180 (2001)341.[4] J. Tauc, Mater. Res. Bull. 5 (1970) 721.6th Nanoscience and Nanotechnology Conference, zmir, 2010 624