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

Abstract

Nanocrystalline SnO2 and SnO2:Cu thin films derived from SnCl[Formula: see text]H2O precursors have been prepared on glass substrates using sol–gel dip-coating technique. The deposited film was [Formula: see text][Formula: see text]nm thick and the films were annealed in air at 500[Formula: see text]C for 1[Formula: see text]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[Formula: see text]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[Formula: see text]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 0–6[Formula: see text]wt.%; the first peak was positioned exactly at 320[Formula: see text]nm ultraviolet emission and the second was positioned at 430–480[Formula: see text]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, [Formula: see text] and [Formula: see text], which increase as Cu-doping concentration increases. Cudoped nanocrystalline SnO2 gas-sensing material has better sensitivity to CO gas compared with pure SnO2.