STUDYING STRUCTURAL, OPTICAL, ELECTRICAL, AND SENSING PROPERTIES OF NANOCRYSTALLINE SnO2: Cu FILMS PREPARED BY SOL-GEL METHOD FOR CO GAS SENSOR APPLICATION AT LOW TEMPERATURE

Nanocrystalline SnO2 and SnO2:Cu thin films derived from SnCl2 center dot 2H(2)O precursors have been prepared on glass substrates using sol-gel dip-coating technique. The deposited film was 300 +/- 20 nm thick and the films were annealed in air at 500 degrees C for 1 h. Structural, optical and sensing properties of the films were studied under different preparation conditions, such as Cu-doping concentration of 2%, 4% and 6 wt.%. X-ray diffraction studies show the polycrystalline nature with tetragonal rutile structure of SnO2 and Cu:SnO2 thin films. The films have highly preferred orientation along (110). The crystallite size of the prepared samples reduced with increasing Cu-doping concentrations and the addition of Cu as dopants changed the structural properties of the thin films. Surface morphology was determined through scanning electron microscopy and atomic force microscopy. Results show that the particle size decreased as doping concentration increased. The films have moderate optical transmission (up to 82.4% at 800 nm), and the transmittance, absorption coefficient and energy gap at different Cu-doping concentration were measured and calculated. Results show that Cu-doping decreased the transmittance and energy gap whereas it increased the absorption coefficient. Two peaks were noted with Cu-doping concentration of 06wt.%; the first peak was positioned exactly at 320 nm ultraviolet emission and the second was positioned at 430-480 nm. Moreover, emission bands were noticed in the photoluminescence spectra of Cu:SnO2. The electrical properties of SnO2 films include DC electrical conductivity, showing that the films have two activation energies, namely, E-a1 and E-a2, which increase as Cu-doping concentration increases. Cudoped nanocrystalline SnO2 gas-sensing material has better sensitivity to CO gas compared with pure SnO2.