Photonic crystals in biology - NanoTR-VI

Poster Session, Thursday, June 17Theme F686 - N1123Optical Properties of Fullerene C60 Thin Films Annealed at Different Temperatures in Air and Argon AtmospheresHüseyin Özgener 1 , Hasan Aydın 2 , Salih Okur 2*1 Izmir Institute of Technology, Faculty of Science, Department of Chemistry, Gulbahce Koyu Kampusu, 35430, Urla, Izmir,Turkey2 Izmir Institute of Technology, Faculty of Science, Department of Physics, Gulbahce Koyu Kampusu, 35430, Urla, Izmir,TurkeyAbstract- This study focuses on optical properties of fullerene (C60) thin films at different annealing temperatures in Air and Aratmospheres with a thickness of 65nm deposited on quartz substrate by thermal evaporation method. Schimazdu UV-2550 PCUV-visible recording spectrometer has been used for optical measurements. Our experimantal results show that optical bandedge exhibit stable in Ar environment with increasing annealing temperatures up to 400 0 C. On the other hand it degrades at theannealing temperatures above 280 0 C (melting point of C60) in air atmosphere. These results might be important for solar cellapplications made of C60 nanoparticles.C60 thin films, which show significant deviceperformance and optical properties, are mostly used inelectronic devices such as light emitting diodes [1], solarcells [2] and field effect transistors [3]. That’s why, there isan increasing interest in these materials over the last decades.In this study, we have investigated C60 thin films atdifferent annealing temperatures in atmosphere and argon gasconditions with thicknesses of 65 nm deposited on quartzsubstrates by thermal evaporation method (Nanovak). Duringthe deposition the vacuum chamber was about 8x10 -6 Torr.Optical Reflectance (R) and Transmittance (T) data havebeen obtained at normal incidense using a Shimadzu 2550UV-visible spectrometer. R and T measurements have beendone after annealing at 100 o C, 300 o C and 400 o C for 60minutes in air and argon atmospheres. The thickness of C60thin films were measured with a Dektak profilometer fromVeeco.Fig.1 shows the Transmittances and Reflectances of theannealed C60 thin films. Both transmittance and reflectanceare varying with increasing annealing temperatures in airatmosphere except the films annealed at relatively lowtemperatures below melting point of C60 e.g. at 25 0 C and100 0 C. The spectral features of C60 are visible in the UVregion below 400nm.Transmittance(%)10080604020Annealed atT 25 0 CT 100 o CT 300 0 CT 400 0 CR 25 0 CR 100 0 CR 300 0 CR 400 0 C(a)0200 300 400 500 600Wavelenght(nm)151050Reflectance(%)Transmittance(%)10080604020Annealed atT 250 CT 100 0 CT 300 0 CT 400 0 C(b)R 25 0 CR 100 0 CR 300 0 CR 400 0 C0200 300 400 500 600Wavelenght(nm)Annealed atFigure.1. Transmittance and Reflectance of C60 thin film annealed at 25,100, 300, 400 O C for 60 minutes in air atmosphere (a), and argon gas (b).Transmittance and Reflectance of C60 thin filmannnealed at 25, 100, 300, 400 0 C for 60 minutes in argongas are shown Fig.1(b). Both transmittance and reflectanceshow similiar behaviours at increasing annealingtemperatures in argon compared to air atmosphere.Figure.3.AFM Topography of C60 thin film annealed at 25 0 C (a) , 400 0 C (b)in air atmosphere and 400 0 C in argon gas (c).AFM Topographies given in Fig 2 show that C60 thin filmsurface annealed at 400 0 C in argon gas does not change so151050Reflectance(%)much, while the annealed films in air become very roughwith large aggregates after annealing at 400 0 C.The optical band gap can be expressed [4],where E g is the optical band gap, hυ is the incident photonenergy and α is the absorption coefficient shown as following[5],,where t is the thickness, T is the transmission and R is thereflectance.(.E) 2 x 10 12 (cm -1 eV) 21.2 10 4 Annealed at (a)1 10 4300 0 C25 o C 100 0 C8000400 0 C60004000200000 1 2 3 4 5 6E(eV)(.E) 2 x 10 12 (cm -1 eV) 26 10 4 Annealed at (b)25 o C100 0 C400 0 C300 0 C55 10 44 10 43 10 42 10 41 10 400 1 2 3 4 6E(eV)Figure.3. The change of optical band gap with annealing temperature atdifferent annealing temperatures in (a) air atmosphere and (b) argon gas.The (αhν) 2 versus energy plots of C60 thin films at differentannealing temperatures are shown in Fig.3. It is seen that thepeaks in the absorption band edges disappear with increasingannealing temperatures in air atmosphere. However the peaksin that of C60 thin films do not change with increasingtemperatures in argon gas. The absorption features startaround 1.56 eV corresponds to the so called onset energy gap(Q-band) while the absorption starting around 3.52 eVcorresponds to the fundamental energy gap (B- band or Soretband) [6] at room temperature. The results show that bothonset and fundamental energy gaps are changed withannealing process above the melting point up to 400 0 C in air,but there is little or no change for that annealed in Aratmosphere.As a summary, our experimantal results show that opticalband edge look stable in Ar environment with increasingannealing temperatures up to 400 0 C. On the other hand itdegrades at the annealing temperatures above 2800 C(melting point of C60) in air atmosphere. These results mightbe important for solar cell applications made of C60.*Corresponding author: salihokur@iyte.edu.tr,[1] Z. H. Huang, W. M. Su, and X. T. Zeng SIMTech technical reports(STR_V8_N4_02_STG), Volume 8 Number 4 Oct-Dec 2007[2] Nobuaki Kojima, Yusuke Sugiura, Masafumi Yamaguchi, Solar Energy Materials &Solar Cells 90 (2006) 3394–33983[3]Mihai Irimia-Vladu, Nenad Marjanovic, Marius Bodea, Gerardo Hernandez-Sosa,Alberto Montaigne Ramil, Reinhard Schwödiauer, Siegfried Bauer, Niyazi SerdarSariciftci, Frank Nüesch Organic Electronics 10 (2009) 408–415[4] E.A. Davis, N.F. Mott, Philos. Mag. 22 (1970) 903[5] T.S. Moss, Semiconductor Optoelectronics, Butterworths, London,1973.[6] M. M. El-Nahass, F.S. Bahabri and R. Al-Harbi, Egypt. J. Sol., 24, 1, (2001)6th Nanoscience and Nanotechnology Conference, zmir, 2010 634