Josephine Liew Ying Chyi

OPTICAL BAND GAP AND CONDUCTIVITY MEASUREMENTS OF POLYPYRROLE-CHITOSAN COMPOSITE THIN FILMS

Electrical conductivity and optical properties of polypyrrole-chitosan (PPy-CHI) conducting polymer composites have been investigated to determine the optical transition characteristics and energy band gap of composite films. The two electrode method and I–V characteristic technique were used to measure the conductivity of the PPy-CHI thin films, and the optical band gap was obtained from their ultraviolet absorption edges. Depending upon experimental parameter, the optical band gap (Eg) was found within 1.30–2.32 eV as estimated from optical absorption data. The band gap of the composite films decreased as the CHI content increased. The room temperature electrical conductivity of PPy-CHI thin films was found in the range of 5.84 × 10−7–15.25 × 10−7 S·cm−1 depending on the chitosan content. The thermogravimetry analysis (TGA) showed that the CHI can improve the thermal stability of PPy-CHI composite films.

Synthesis of BaTiO 3 Nanoparticles via Hydrothermal Method

In this work, BaTiO3 nanoparticles were synthesized through hydrothermal method. The powder obtained from the hydrothermal process (as-synthesized powder) was calcined at 1000 °C. The phase formation and morphology of the as-synthesized and calcined powders were studied using X-ray diffraction (XRD), thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyzer, and transmission electron microscope (TEM). The XRD data showed that the as-synthesized powder is partially amorphous. Upon calcining the powder at 1000 °C, highly crystalline BaTiO3 with tetragonal structure was obtained. As shown by TGA and DSC analysis, the precursor powder was completely transformed into BaTiO3 at 1000 °C. The presence of BaCO3 as an impurity phase in the powder is due to the lack of Ba2+ / Ti3+/4+. Transmission electron microscope images showed that the particle size of the as-synthesized powder increased after calcination due to crystal growth. In addition, nanocubes with the average size of around 11.66 nm were obtained as a result of the calcination compared to the ellipsoid like particles of the as-synthesized powder.

Synthesis, Structural and Optical Properties of Cerium Oxide Nanoparticles Prepared by Thermal Treatment Method

A sample thermal treatment technique was utilised to synthesis cerium dioxide (CeO2) nanoparticles, using cerium (111) nitrate as a precursor, Polyvinylpyrrolidone as a capping agent, and deionized water as a solvent. The product underwent calcination treatment of 500, 550, 600, and 650 1C to crystallize the nanoparticles and to remove organic compounds. It was verified by XRD that by varying the calcination temperature, the cubic fluorite structure of CeO2 nanoparticles with pure products was achieved. Furthermore, the crystal sizes of the CeO2 nanoparticles were assessed to be 4 nm for the lowest calcination temperature and 23 nm for the highest calcination temperature. The FESEM micrographs of the CeO2 nanoparticles revealed a structure of CeO2 nanospherical that exhibited a tendency to amalgamate at higher calcination temperatures. The optical characteristics that were evaluated with the help of a UV-Vis spectrophotometer indicated a decrease in the band gap energy with an increase in calcination temperature as a result of the increase in the crystal sizes.

Optical Characterization of Zinc Selenide Compound Prepared through Hydrothermal Method

ZnSe which show a potential application in electronic devices such as photovoltaic devices, light emitting devices and photodetector have been synthesized through a hydrothermal method using ZnCl2 and Se powder as the source. In a typical synthesis, Zn2+ and Se2- ion have been prepared separately and charged into a Teflon-lined stainless steel autoclave. The hydrothermal reaction was conducted at 180 °C for 32 hours. Structural properties of ZnSe are studied by X-ray diffraction (XRD) while the optical properties of ZnSe compound are characterized through ultraviolet–visible spectroscopy (UV-Vis). From the XRD result, pure ZnSe with main XRD peak at 2θ = 27.29°, 45.30°, 53.62°, 65.88°, 72.68° has been observed. The result have been supported by the optical results where absoprtion peak at 460 nm with optical band gap energy (Eg) at 2.5 eV.

Synthesis and Electrical Studies of Quaternary Chalcogenide Semiconductor Cu2ZnSnSe4

Quaternary chalcogenide semiconductor has attracted much attention as absorber-layer materials in solar cells. The absorber-layer material, Cu2ZnSnSe4 (CZTSe) which is a p-type semiconductor that has high absorption coefficient, had been synthesized by using solvothermal method. The variation of concentrations of the Copper (II) Chloride dihydrate have brought some effects towards producing the stoichiometry and non-stoichiometry copper zinc tin selenide that may lead to the improvement of efficiency of solar cells. The synthesized reaction was conducted at 250°C for 24 hours. Properties of the samples have been characterized by X-ray diffraction (XRD) to determine the crystal structure of the sample and X-ray Fluorescence (XRF) to determine the elemental composition of the sample. The electrical properties such as resistance and conductivity have been studied through Van der Pauw configuration. The CZTSe has been successfully synthesized at concentrations of 0.15 M with no impurities phases existed.