THE EFFECT OF SPIN COATING RATE ON MICROSTRUCTURES OF CUPROUS OXIDE THIN FILM PREPARED BY SOL-GEL TECHNIQUE DEWI SURIYANI BT CHE HALIN School of Material Engineering Perlis University of Malaysia MALAYSIA A PhD Student Physics Program Faculty of Science and Technology National University of Malaysia MALAYSIA

OUTLINE INTRODUCTION EXPERIMENTAL RESULT AND DISCUSSIONS CONCLUSIONS ACKNOWLEDGEMENT

INTRODUCTION Copper forms two well known oxides; (1) Cu2O (2) CuO Cu2O - an interesting p-type semiconductor. - direct energy gap of 2.0-2.2 eV. - promising material in solar energy applications. - nontoxic and low cost to produce. - cubic structure with a lattice parameter of 4.27 Å.

Cu2O leads to become a promising material in solar energy applications. Various methods were used to prepared Cu2O thin films; Sputtering Thermal oxidation Electrodeposition Vacuum evaporation Sol-gel process

Sol-gel spin coating requires considerably; Less equipment Low cost production Simple Effective way of making thin films with varying its thickness by just controlling parameters.

EXPERIMENTAL Copper (II) acetate Isopropyl alcohol Mixed continuously Add small amount of glucopone Stirring using magnetic bar for 24 hours Filtered using 0.45 μm filter Spin coating Annealing (350 ˚C) Cuprous oxide films Diethanolamine (DEA) Dried in oven Repeated for 2 layers of coating 5% H2 95% N2

CHARACTERIZATION Microstructure of films X-ray diffractometer Scanning electron microscopy Morphology of films Ultraviolet-visible spectroscopy Optical properties X-ray photoelectron spectrometer Chemical state of films

X-RAY DIFFRACTOMETER a crystalline cubic Cu2O film with two peaks, (111) and (200). mineral cuprite,Cu2O (JCPDs card no. 01-075-1531).

SCANNING ELECTRON MICROSCOPY b c 2000 rpm, 61 nm 4000 rpm, 49 nm 6000 rpm, 40 nm All films exhibit a smooth continuous film. The films were in orderly form consisting fine grains of rounded shape.

The average thickness of the films measured using the scanning electron microscopy are 108 nm, 64 nm and 62 nm for spinning rates of 2000, 4000 and 6000 rpm, respectively. The lower the spinning rate, the thicker the film.

X-RAY PHOTOELECTRON SPECTROMETER 1000 800 600 400 200 0 Binding energy (eV) Intensity (cps) C KLL Cu 2p O KLL O 1s Cu LMN C 1s Cu 3s Cu 3p Cu 2p1/2 = 932.4 eV

The survey scan shows the presence of copper, oxygen and a small carbon peaks. The Cu 2p1/2 peak binding energy of 932.4eV shows excellent agreement with the value of 932.4-932.5 eV quoted in the literature. No other phases detected by XPS which is in good agreement with the GAXRD pattern.

ULTRAVIOLET-VISIBLE SPECTROSCOPY High absorbance Low spinning rate Thickest film High spinning rate Thinnest film Low absorbance

The optical band gap increased with spinning rate. Table 1. The relationship between optical properties, spin rate and grain size of cuprous oxide films prepared by sol-gel technique. Spinning rate (r.p.m) Grain size (nm) Thickness Optical band gap (eV) 2000 61 108 2.08 4000 52 64 2.16 6000 45 58 2.20 The optical band gap increased with spinning rate. The increasing in grain size of film with decreasing of spinning rate will also contribute to the reduction in optical transparency through optical scattering.

CONCLUSIONS Cuprous oxide films have successfully been deposited on indium tin oxide (ITO) substrates by a sol-gel spin coating technique using copper (II) acetate. The lower spin rate was able to produce a thicker film compared to the film obtained at higher spin rate. The thickest film (108 nm) with high absorbance is potentially suitable for a photoelectrochemical solar cell application.

ACKNOWLEDGEMENT The authors gratefully acknowledge the financial support by MOSTI, through Science Fund grant No. 03-01-02-SF0211. Perlis University of Malaysia (UniMAP) for the PhD scholarship (Feb 2006-August 2009)

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