Photonic crystals in biology - NanoTR-VI

PP mPP vs.P =P,PP (1)P andPoster Session, Thursday, June 17Theme F686 - N1123The Effect of Film Thickness on the Optical Properties of ZnO Thin Films111111UBanu ErdoanUP P*, Derya BaharP P, Göknil BabürP P, Sinan DikenP P, Aye Tuba TermeliP 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 opticalproperties of ZnO thinfilms are investigated for different film thickness. It showed that the optical band gaps of thin filmdecreased with increasing film thickness, onthe contrary, transmission of thin films increased with increasing film thickness.1Zinc oxide (ZnO) is one of the most important group II–VIsemiconductor materials. ZnO is one of the most promisingmaterials for the fabrication of the next generation ofoptoelectronic devices in the UV region and optical or displaydevices. As a matter of fact, simultaneous occurrence of bothhigh optical transmittance in the visble range, and lowresistivity make ZnO an important material in the manufactureof heat mirrors used in gas stoves, conducting coatings inaircrafts glasses to avoid surface icing, and thin filmelectrodes in amorphous silicon solar cell [1]. ZnO is also usedto fabricate piezoelectric micro-force sensor chip[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 film thickness using Perkin Elmer Lambda 35 UV-VIS Spectrometer at room temperature.Transmittance (%)100806040205 layer10 layer15 layer20 layer0200 400 600 800 1000 1200Wavelenght (nm)Figure1. UV–VIS spectra of the ZnO thin film for different filmthicknessIn 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 wasrepeated for 5 layers, 10 layers, 15 layers and 20 layers on glasssubstrate at 300 ºC temperature.Figure 1 shows the UV–VIS spectra ZnO thin films fordifferent film thickness in wavelength range 300–1100nm.The transmission of thin films increases with increased thefilm thickness. The diffrerence related to the grain boundariesare observed as the film grows thicker. [3].(hv) 2 (eV/m) 2543215 layer, E g= 3.66 eV10 layer, E g= 3.59 eV15 layer, E g= 3.63 eV20 layer, E g = 3.64 eV02 2.4 2.8 3.2 3.6 4Photon energy (eV)2Figure2. The plot of (hv)P P vs. hv of the ZnO thin film for differentfilm thickness.The optical band gap of the film was calculated by thefollowing relation [4]:r(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/r(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 3.66, 3.59, 3.63 and 3.64 eV at 300 ºCannealing temperature. The thicknesses of ZnO film were alsodetermined from transmittance measurements in Figure1 andfound to be 302, 308, 385 and 695 nm, respectively. The opticalband gap decreases with the increasing film thickness.In summary, the analysis of the transmission spectrashows that ZnO thin films are transparent in the UV-visibleregion irrespective of the film thickness. This work waspartially supported by the Scientific Research Commission ofGaziosmanpaa University (Project No: 2009/29).*Corresponding author: bnrdgn@gmail.com[1] M. Suchea, S. Chiritoulakis, K. Moschovis, N. Katsarakis, G.Kiriakidis, Thin Solid Films 515 (2006) 551.[2] S.S. Lee, R.M. White, Sens. Actuators A 71 (1998) 153–157.[3]. C.J. Brinker, G.W. Scherer, Sol–Gel Science: The Physics andChemistry of Sol Gel Processing, Academic Press, New York, 1975,p. 87.[4] . Tauc, Mater. Res. Bull. 5 (1970) 7216th Nanoscience and Nanotechnology Conference, zmir, 2010 621