Advanced Materials Research Vol. 832

Abstract: A novel self-prepared Aerosol-Assisted Chemical Vapor Deposition (AACVD) system was developed to deposit the amorphous carbon (a-C) thin films for the carbon-based solar cell applications. The nitrogen doping was applied towards the a-C thin films at deposition temperature of 600°C and 650°C. The samples gave the photoresponse characteristic for the electrical measurement by using the solar simulator system in under illumination condition. FESEM images signify the nanostructured sized a-C:N (<100nm) and EDX spectrum clarify the presence of N content in the N doped a-C. Solar cell efficiency was also obtained with the value of 0.001648% for 650°C and 0.000124% for 600°C when the a-C:N were deposited on p-Si substrate. The presence of the rectifying curves at the a-C:N/p-Si junction indicates the hetero-junction behavior between the p-n structure and thus proves the successful doping of N doped a-C using the AACVD technique.

Abstract: Pure amorphous Carbon (a-C) thin films had been deposited by Aerosol-Assisted CVD (AACVD) onto glass substrate in Argon atmosphere. The camphor oil was chosen as the carbon precursor to prepare the a-C thin films with the deposition time of 15 minutes, 30 minutes, 45 minutes, 60 minutes and 75 minutes. The electrical, optical and structural properties of the deposited a-C were discussed by using the current-voltage solar simulator system, UV-Vis-Nir spectrophotometer and Raman spectroscope respectively. For the electrical characterization, the samples showed the photoresponse performance when being illuminated under AM 1.5 illuminations: 100 mW/cm², 25°C. Transmittance value for the a-C thin films was also considered high ~80% and the structural analysis by using Raman spectroscope exhibit two main peaks known as the D-peak and G-peak which is typical for the a-C.

Abstract: Poly (vinylideneflouride)/nanomagnesium oxide (PVDF/MgO) nanocomposites with MgO loading percentage of 7% were annealed with various annealing temperatures ranging from 70oC to 170oC. The PVDF/MgO(7%) thin films were fabricated using spin coating technique with MIM structure. The dielectric constant of PVDF/MgO(7%) was studied over a wide range of annealing temperatures with rapid removal from the oven once the annealing was utilized. The nanocomposites thin films annealed at temperature of 70oC (AN70) shows an improvement in the dielectric constant of 23 at 10³ Hz compared to unannealed sample (UN), which was 21 at the same frequency. However, as the annealing temperatures were increased from 90oC (AN90) to 170o C (AN170), the dielectric constant of PVDF/MgO(7%) were found to decrease from 16 to 7 respectively, which were lower than the UN thin films. AN70 also produced low value of tangent loss at low frequency˼˰˸̱̈́̾˰δ˹˰̴̷̹̹̳̱̹̾̈́̾˰̸̱̈́̈́˼˰̵̷̱̱̼̹̾̾̾˰̱̈́˰temperatures 70oC is favourable temperature used to improve the dielectric constant of PVDF/MgO(7%).

Abstract: The different morphology of 250 nm PVDF-TrFE (70:30 mol%) thin films were observed in relation to its ferroelectricity. The annealing temperatures were varied from solvent evaporation (T_s), Curies transition (T_c), up to melting temperature (T_m). It was found that the annealing process promoted the development of elongated crystallite structure also known as ferroelectric crystal, which significantly improved the ferroelectric properties of PVDF-TrFE (70:30 mol%) thin films. However, the presence of nanoscale separations on the thin film annealed over T_m (AN160) suggested high possibility of defects, and hence a reduction in ferroelectric properties of thin films.

Abstract: The surface charge and average size of ZnO was studied with a function of pH and time. The interactions between ZnO and Suwannee River humic acid (SRHA) were further investigated under a range of environmentally relevant conditions with the pH_PZC as a point of reference. The anionic charge carried by aquatic humic substances plays a major part in the aggregation and disaggregation of metal oxide nanoparticles. At low concentrations of SRHA (<0.05 mg="" l="" the="" positively="" charged="" zno="" aggregates="" were="" rapidly="" adsorbed="" below="" ph="" sub="">PZC. With similar SRHA concentrations, at pH=pH_PZC, SRHA was able to control the suspension behavior of the ZnO and promoted partial disaggregation in small volumes. This was more distinguishable as SRHA form a surface coating on the nanoparticles and enhances stability via electrostatic stabilization mechanism which induces the disaggregation behavior in the ZnO nanoparticles and hence, decreases the aggregate size.

Abstract: This paper will present on preparation and characterizations of hybrid nanoTiO₂/ZnO using sol-gel spin coating techniques. The study involved of modification band-gap energy of Titanium Dioxide (TiO₂) at different precursor molecular concentration of Zinc oxide (ZnO). The FESEM (Field emission scanning electron microscope) morphological characterize shows TiO₂ and ZnO particle produced at nanoscale size. The compositional of both particles confirmed using EDAX (Energy Disperse Analyzer X-ray) analysis. The XRD (X-Ray diffraction) characterize measured the structural properties of anatase and rutile for TiO₂ as well as zincite for ZnO. By increasing ZnO molecular concentration, the crystallite size, d were decreased until the optimum sample, ratio of 4 TiO₂ : 1 ZnO, with value of 23.71 nm. For UV-VIS (Ultra-Violet/Visible Spectroscopy) measurement, we found the optical band-gap increased with increasing ZnO molecular concentration. The optical band-gap for optimum sample was 3.38 e.V represented this study has successfully improved the optical band-gap of TiO₂.

Abstract: Cotton coated titanium dioxide, TiO₂ was prepared by using immersion method. Three samples with different concentration which are 0.2 M, 0.5 M and 0.6 M of TiO₂ solution with fixed value of temperature and time immersion has been used in this project. Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and Ultraviolet/Visible (UV-Vis) Spectrophotometer have been used to determine the properties of samples. The surface morphology of the cotton, crystalline phase of TiO₂ particles deposited on the cotton fiber and the amount of the TiO₂ particles dispersed in the water has been investigated. The existence of TiO₂ on the cotton fiber was identified by using SEM and XRD where the immersion method that has been used in this project contributed to the agglomerated TiO₂ particles on the surface of cotton fiber. None of the samples showed the formation of anatase crystalline phase of TiO₂ particle and UV-Vis showed the released of TiO₂ in the water was higher in the first immersion and decreased exponentially for the second, third and fourth immersion.

Abstract: In this work, the effect of NH₄F concentration on the formation, dimensions and photoelectrochemical response of titania nanotubes produced by anodisation of Ti in ethylene glycol has been investigated. The results showed that a minimum amount of 0.25 wt.% NH₄F is needed for the formation of uniform and ordered nanotubes in viscous ethylene glycol. Self-organized nanotubes can be synthesized in the concentration range of 0.250.7 wt.%; with a higher fluoride concentration leads to severe etching of the tube tops resulting in a grassy-like appearance. Varying the concentration of NH₄F has no effect on the tube diameter and wall thickness. However, nanotubes length increases gradually by increasing the NH₄F concentration with preferred growth along the c-axis. Thermal annealing at 500 °C transforms the amorphous nature of as-formed nanotubes into pure anatase phase. Photoelectrochemical response of nanotubes was tested with linear sweep photovoltammetry. It was found that microstructures, crystallinity and geometry of the nanotubes are important factors influencing the photoresponse.

Abstract: ZnO thin films with typical c-axis (0 0 2) orientation were successfully deposited on glass substrates by two-step deposition method; mist-atomization and solution-immersion. The samples were annealed at selected temperature range of 350-500 ᵒC. The prepared samples then analyzed by Raman spectroscopy and photoluminescence (PL) spectroscopy. The optical properties of the samples were studied. The results of different annealing temperatures are also compared to investigate the optical and physical properties of each sample. Photoluminescence (PL) spectra showed low intensity in UV emission and high intensity in the visible emission, which indicates a good surface morphology of the ZnO nanorod. The Raman intensity changes in all sample were also tested.

Abstract: Flower-shaped ZnO nanocrystals have been synthesized by a two-step solution based deposition method; mist-atomizer and solution-immersion on seeded glass substrate. The samples are annealed at different temperature in the range of 350 to 500 ᵒC. The structural properties of the samples were studied. Field emission scanning electron microscopy (FESEM) micrograph and atomic force microscopy (AFM) images for the ZnO thin films were obtained. Morphological changes due to various annealing temperature are discussed as changes observed in the ZnO crystals. FESEM image of the surface of the ZnO reveal the flowerlike vertical nanorods with hexagonal crossection. The samples with higher roughness analyzed from AFM images indicate that the sample have larger grain. AFM results are found in good agreement and supported the FESEM results.