Synthesis and Characterization of PbS:Cd, Cu, Co Nano composites Prepared by Pulsed Laser Deposition For Gas Sensor Applications

Abstract

ture: Name: Dr. Ammar A. Habeeb Title: Assist. Professor Head of the Physics Department Address: College of Science, University of Diyala Date: / / 2022 Abstract In this work , lead sulfide PbS thin films deposited on a glass substrate were mixed with (30, 50, and 70%) of cadmium, copper, and cobalt at room temperature. by use a pulsed laser deposition (PLD) technique, The laser energy was 600 mJ, and wave length 1064 nm. The number of laser pulses was fixedly set to 100 pulses for each ablation . The effect of mixing ratios on the structural and optical properties of PbS films were studied. Using X-ray diffraction method, the structures of (PbS, PbS:Cd, PbS:Cu, and PbS:Co) thin films were investigated. X-ray analysis of the structure showed that it is polycrystalline and that the film's crystal system is the cubic system. also shows that the high intensity appeared at (2θ˚ =53.48886 and 69.14403) and that the dominant trend of growth is (2 2 2) and (3 3 1), respectively and that the crystal size of the Pure PbS sample is (17.74 nm) and that the size of the crystal grows with the mixed ratio of (Cd, Cu, and Co). The surface morphology of pure and mixed thin films deposited on a glass substrate by laser induced plasma technique at room temperature was examined by Field Emission Scanning Electron Microscope (FESEM). FESEM micrographs for pure lead sulphide (PbS) and mixed (PbS: Cd, Cu, and Co) films deposited on glass substrates at various ratios it was noticed that the mixing of Cd ,Cu and Co exhibits some changes in the PbS surface morphology in which the surface was found to be densely packed with crystallite. For pure PbS thin film, it was observed that the film was dense, smooth, non-homogeneous with pinholes. Also, it was noted that the grains have a mixture of nano cauliflower and spherical-like shapes with different sizes. In addition, it was noted that PbS thin film formed was highly agglomerated. FESEM micrographs of PbS thin film deposited with 30% of Cd,Cu,Co showed large clusters of spherical or semispherical shaped grains on some parts of the images indicating an irregular growth rate of the grains. The images exhibited a dense compact of the grains covering the entire surface without any defects like cracks or pinholes. While the mixing ratios (50% and 70%) it was clearly observed that the mix ratio of cadmium increased the loss of the grain their sharp-edged nature and becomes smaller in size. AFM measurements, which demonstrate that the films created using the PLD process, have In every instance, a dense surface for the thin films was achieved. The stacked grains made up the thin films. From result of optical measurement by UV-ViS spectrophotometer showed that the thin films of (PbS, PbS:Cd, PbS:Cu, and PbS:Co) exhibit direct transit energy gap transitions. The absorbance of the films rises with the rising mixing ratio. The optical constants have been determined, including the absorption coefficient (α). As the mixing ratio is increased, the energy gap narrows. Hall effect measurement showed that all the samples of (PbS , PbS:Cd , PbS:Cu and PbS:Co) were p- type conduction. The gas sensor measurements showed that the resistivity of p- type gas sensor increases and return decreases by NO2 Oxidization gas and decreases by high operation temperature . The sensitivity of all the samples decreased with increasing of mixing ratio because decreases the surface area with increase the grain size and the best sensor for NO2 gas was the sample with a percentage of X = 30% Cu with a sensitivity of 355% at 150 oC