Advanced Materials Research Vol. 501

Abstract: In this work, the effect of water content from < 1 to 100 vol% on the electrochemical anodization of titanium in ethylene glycol-based electrolyte was investigated. The samples were characterized using X-ray diffraction (XRD) and their dimensional change was monitored by field emission scanning electron microscopy (FE-SEM). It was found that the microstructure and morphology of TiO2 varies dramatically with the water content. Nanotubes become less ordered with increasing water content up to 50 vol%. At 75 vol% water, only porous structure could be observed. Most importantly, at fixed applied voltage, smoother but relatively longer tubes can be grown with lower water content. Varying water content has no effect on the crystalline phase of the resulted nanotubes. However, the intensity of anatase (101) peak increases with increasing water content, indicating better crystallinity of samples. Nanotubes obtained in 50 vol% water exhibit the highest photoresponse when tested using linear sweep photovoltammetry due to enhanced microstructure and crystallinity.

Abstract: Silicon self-assembled nanodots have been fabricated on corning (7059) and quartz glass substrates using a magnetron sputtering method at different experimental conditions, including the deposition time, RF power and substrate temperature. It was observed that, as the deposition time increases, PL intensities increased with deposition time. However, the full width at half maximum of individual spectra was observed to decrease with time. This occurs because the nature of PL is such that an improvement in the number of carriers (electron and holes) results in enhanced PL intensities. An increase in the deposition time allows more silicon attached to substrate and forming the nanodots, thus increasing the number of atoms as well as carriers. The effect of RF power was indicated by increasing trends in PL intensities. Higher deposition power appeared to increase the ratio of Si atomic concentration and, hence, an increasing number of silicon nanodots. On the other hand, the results showed that, the PL intensity decreased as the substrate temperatures were increased caused by an activated non-radiative recombination process and decrease of crystal quality. It was also observed that the peak of PL wavelength centered at 693 nm or 1.78eV energy bandgap did not differ much from those peaks obtained by varying the RF power and substrate temperature. The suggested that deposition time up to 5 min, RF power of 200 W and substrate temperature of 400°C as optimum conditions for the growth of dome-shaped silicon nanodots, with sizes between 40-80 nm. Generally the shifts in PL intensities are attributed to the structural changes which occurs during the growth processes

Abstract: Inverted bulk heterojunction organic solar cells based on vertically aligned dye-coated ZnO nanorods arrays were fabricated. The dye, Eosin-Y was wrapped on ZnO nanorods arrays with dye coating concentration ranging from 0.05 mM to 0.3 mM at room temperature for 1 h. The effects of Eosin-Y solution concentration on the performance of inverted bulk heterojunction organic solar cells based on a blend of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEHPPV) as donor and (6,6)-phenyl-C61 butyric acid methyl ester (PCBM) as acceptor with a structure of fluorine-doped tin oxide (FTO)/Eosin-Y coated ZnO nanorod arrays/MEHPPV:PCBM/Ag were investigated. Length, diameter and morphology of ZnO nanorods arrays were characterized. The optical properties of the Eosin-Y coated ZnO nanorod arrays were investigated and the organic solar cells were characterized by current–voltage measurements under 100 mW/cm2 simulated AM 1.5 G sunlight. It was found that current density, Jsc increased from 0.00134 mA/ cm2 to 0.0162 mA/ cm2 with increase in concentration of Eosin-Y from 0.05 mM to 0.3 mM. Solar cell with 0.3 mM Eosin-Y gave the highest power conversion efficiency, which is 7.15×10-4 %. Short circuit current density was 0.0162 mA/ cm2 and the corresponding open circuit voltage was 0.17 V.

Abstract: In this work, layer structured silicon suboxide/gold/silicon suboxide (SiOx/Au/SiOx) films were prepared by using plasma enhanced chemical vapor deposition assisted with hot wire evaporation technique. Post rapid thermal annealing (RTA) process was done on the as-prepared films for 100, 500 and 700s at constant temperature of 800oC in vacuum ambient. Effects of RTA process on the structural and morphological properties of films were studied using FE-SEM, depth profiling and XRD measurement. While, surface plasmon resonance (SPR) phenomenon exhibited by Au particles was investigated via the optical absorption spectra. SPR signals can be exhibited by sample annealed for longer time duration. Individual Au islands tend to form the spherical shape as a whole. Diffusion of Au particles towards the surface of SiOx film is temperature dependent and crystallite size of Au enlarges with the rapid thermal annealing time.

Abstract: In this study, current-voltage (I-V) measurements at room temperature (RT) of platinum (Pt) metal contact combine with n-Al0.08In0.08Ga0.84N thin film which grown epitaxially by molecular beam epitaxy (MBE) technique on sapphire substrate to form Schottky diode have been characterized. Schottky barrier heights of diode related with the high work function metal of Pt electrode was measured and investigated. Pt metal was fabricated using RF-sputtering technique. The effect of annealing temperature ranged from 300 °C to 600 °C on the structural and electrical properties has been studied. The results revealed that in spite of the various annealing temperature used there is no change in XRD diffraction peak observed in Pt contact. Furthermore, at 400 °C the best surface morphology was obtained and the value of SBH and ideality factor (n) was 0.76 eV and, 1.03 respectively. This concludes that at this annealing temperature Pt metal exhibited optimum (I-V) rectifying characteristics of Pt/Al0.08In0.08Ga0.84N Schottky diode.

Abstract: Zinc selenide based materials are suitable for fabrication of light emitting diodes operating in the blue-green light. In fabrication of zinc selenide films, electrodeposition method appears to be the simplest and low-cost technique. In this work, the application of ethylenediamine tetraacetic acid (EDTA) in electrodeposition of zinc selenide was investigated to evaluate its effect on the optical and electronic properties of the films. It was found that the presence of EDTA stabilized the cathodic over potential during deposition. The zinc selenide deposits consist of small grain size deposits which contribute to enhance the photoelectrochemical performance. Besides that, the zinc selenide films produced in the presence of EDTA also shows high photoluminescence intensity due to minimized surface defects on the glass substrate. The film shows photoluminescence peak at the blue region of wavelength due to its quantum confinement effect. The optical property of zinc selenide film was measured using ultraviolet-visible spectrophotometer. The band gap of zinc selenide is 2.65 eV with direct transition.

Abstract: Thin films nanoparticles TbxY3-xFe5O12 (x=0.0, 1.0, 2.0) were prepared by the sol-gel process followed by annealing process at various annealing temperatures of 700° C, 800° C and 900° C in air for 2 h. The results obtained from X-ray diffractometer (XRD) show that the films annealed below 900°C exhibit peaks of garnet mixed with small amounts of YFeO3 and Fe2O3. Pure garnet phase has been detected in the films annealed at 900°C. Before annealing the films show amorphous structures. The particles sizes measurement using the field emission scanning electron microscope (FE-SEM) showed that the particles sizes increased as the annealing temperature increased. The magnetic properties were measured at room temperature using the vibrating sample magnetometer (VSM). The saturation magnetization (M_s) of the films also increased with the annealing temperature. However, different behavior of coercivity (H_c) has been observed as the annealing temperature was increased.

Abstract: κ-Carrageenan is an anionic polymer extracted from marine red algae. In order to increase conductivity of the κ-carrageenan, carboxymethyl κ-carrageenan was synthesized by the reaction of κ-carrageenan with monochloroacetic acid. A polymer electrolyte comprising κ-carrageenan and carboxymethyl κ-carrageenan was prepared by solution-casting technique. The films were characterized by Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR) to investigate the presence of the complexes. Electrochemical Impedance Spectroscopy was conducted to obtain ionic conductivity. Ionic conductivity was found to increase with the addition of carboxymethyl group on carrageenan. The conductivity achieved for κ-carrageenan and carboxymethyl κ-carrageenan were 5.34×10-7 S cm−1 and 2.02×10−4 S cm-1, respectively.

Abstract: Cuprous oxide (Cu₂O) thin films were formed onto indium tin oxide (ITO) coated glass substrate by sol-gel spin coating technique using different additives namely polyethylene glycol and ethylene glycol. It was found that the organic additives added had an important influenced on the formation mechanism of Cu₂O films and lead to different microstructures and optical properties. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ultraviolet-visible spectroscopy (UV-Vis). Based on the FESEM micrographs the grain size of film prepared by polyethylene glycol has smaller grain of about 83 nm with irregular shape. The highest optical absorbance film was obtained by the addition of polyethylene glycol which improved optical properties due to fine crystalline grain and thus decreases the scattering. The prepared cuprous oxide thin films were used as working electrodes for photovoltaic cell of ITO/Cu₂O/PVC-LiClO₄/graphite and tested using current-voltage characteristic under light illumination and also in the dark.

Abstract: Two types of polar solvent materials; namely glycerol and ethylene glycol (EG) were used in this study as dopants for PEDOT:PSS. The 2 to 10% of doped PEDOT:PSS were synthesized using sol-gel technique and were spin-coated onto glass substrate. The optical, conductivity and morphological characteristics of the doped PEDOT:PSS thin films were measured via UV-VIS spectrometer, two-point probes technique and AFM measurement, respectively. All films show direct band gap behavior and compared to the pristine thin film, the doped PEDOT:PSS show higher transparency in visible range. Furthermore, the conductivity of glycerol and EG doped PEDOT:PSS thin films were also improved due to the changes in molecule alignment and interchain interaction in the thin films.