Papers by Author: Muhamad Mat Salleh

Abstract: Localized surface plasmon resonance (LSPR) peak wavelength of nanostructures metallic materials, such as gold and silver, is very sensitive to the dielectric environment of the materials; hence widely used as sensors to detect various types of chemicals. In this study, high - yield gold nanoplates ca. 63% have been grown on the quartz substrate using the seed - mediated growth method. The grown gold nanoplates exhibit variety of shapes such as triangular, hexagonal, truncated hexagonal and flat rod. The LSPR spectrum of Au nanoplates sample has two absorption bands; centring at 543 nm and 710 nm, which are associated with transverse SPR (t-SPR) and longitudinal SPR (l-SPR) respectively. The intensities and peaks position of these two bands were found to linearly change with the concentration of boric acid solutions.

Abstract: Composite of TiO₂ nanowire and Cu₂O nanocube has been prepared. TiO₂ nanowire with ~240nm in thickness and 20 nm in length were synthesized by using liquid phase deposition(LPD) method at 50°C for 4h on ITO substrate. The anatase phase of TiO₂ nanowire was obtained by annealing the samples at 400°C for 1hin air. The Cu₂O nanocubes were prepared by the reduction of Cu²⁺ions with ascorbic acid in the present of trisodium citrate and sodium dodecilsulfat (SDS) surfactant under an alkaline condition. The SDS addition was added with various concentrations namely 10 mM, 18 mM, and 26 mM during the Cu₂O preparation for spin-coated onto TiO₂ nanowire at 3000 rpm for 30s. An optical property of TiO₂ Nanowire - Cu₂O Nanocube has been characterized by UV-Vis spectroscopy.The original TiO₂ nanowire has single absorption peak at 318 nm, but it was shifted to 321 nm as Cu₂O/SDS addition. A new peak at 440 nm was as the Cu₂O nanocube absorption spectra. The Cu₂O nanocube addition to the TiO₂ nanostructure film caused increase in the optical absorption of the system in the region 400 – 800 nm. We also studied the absorption properties of the hybrid system when Cu₂O nanocube preparation under SDS condition. It was that found the increase in the SDS concentration has caused the optical absorption of the hybrid in this region decreased. This is believed due to the decrease of Cu₂O nanocube size as the SDS concentration increase. This could be due to change in the TiO₂ nanowire-Cu₂O nanocube hybrid-structure. This cooperate may find use in photoelectrochemical application.

Abstract: The effect of laser dye (Fluorol 7GA) content on the optoelectronic properties of Poly ( 9,9'-di-n-octylfluorenyl-2.7-diyl) conjugated polymer (PFO) based OLEDs has been investigated. The PFO/Fluorol 7GA hybrids with weight ratios between 0.1 and 5 wt. % were prepared using the solution blending method. The blends were deposited on ITO (Indium Tin Oxide) substrate using spin-coating technique. Thin layer of aluminum was deposited on top of the films to act as electrode. Absorption and photoluminescence techniques were used to investigate the energy transfer in the blend. The device performance was investigated in terms of electroluminescence, luminance, luminance efficiency and color measurements. The Förster energy transfer occurred in the blends as evidence from optical spectroscopy and average distance between donor and acceptor molecules. The optimum ratio was 0.5 wt. % where highest enhancement in OLEDs performance was observed. These were attributed to the synchronize effect of efficient energy transfer from PFO to Fluorol 7GA and carrier trapping processes.

Abstract: Room temperature fluorescence gas sensor was developed based on TiO₂ nanoparticles coated with porphyrin dye thin films. The porphyrin dye used for this experiment were Iron (III) meso-tetraphenylporphine chloride (IMTPPCl) and Manganase (III) 5,10,15,20 tetra (4-pyridyl)-21H, 23H porphine chloride tetrakis (metachloride). The sensing sensitivity was due to the changes of the emission spectra produce by the thin film when expose to the organic vapors from volatile organic compounds; ethanol, acetone and 2-propanol. Both thin films show good response toward volatile organic vapors. However, TiO₂ nanoparticles with porphyrin; IMTPPCl thin film shows pronounced interaction, marked fluorescence spectra and more selective property, hence useful for chemical identification purpose.

Abstract: This paper reports an attempt to develop an optical sensor system to detect Bisphenol A (BPA) in water based on plasmonic property of Gold Nanoparticles (GNPs). Spherical GNPs of the average size of ca. 31±7 nm were grown on quartz substrate using seed mediated growth. An optical sensor system was setup, comprises a tungsten lamp light source, a duplex fiber optic probe, a spectrometer and a sensor chamber. Detection of BPA was done by comparing the Localized Surface Plasmon Resonance (LSPR) spectra of the GNPs film immersed in the deionised water and in BPA solutions by varying the concentration of BPA solutions from 58 mg/L to 0.003 ng/L. The LSPR spectra of GNPs sample were very sensitive to the presence of BPA where the shifted of their peaks position and the changed of their intensities are increases with the concentration of the BPA solutions.

Abstract: The effects of reactant concentration on the growth of ZnO nanostructures and the photovoltaic performance of inverted 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 FTO/ZnO nanostructures/MEHPPV:PCBM/Ag utilizing ZnO nanostructures as electron collecting layer and silver as a hole collecting electrode were investigated. The ZnO preparation consisted of ZnO nanoparticles seed layer coating and followed by ZnO nanostructures growth in equimolar aqueous solution of zinc nitrate hexahydrate (0.02-0.08 M) and hexamethylenetetramine (0.02-0.08 M). ZnO nanorods having diameter of 50-70 nm and with length up to 120 nm were obtained at reactant concentration of 0.04 M. The ZnO nanorods started to merge with each other and formed irregular nanostructures vertically on the substrates at higher reactant concentrations of 0.06 M and 0.08 M. The solar cell with ZnO nanorods prepared at reactant concentration of 0.04 M provided the largest interface area between polymer active layer and ZnO, resulting in the highest power conversion efficiency of 0.053 % with short circuit current density of 0.43 mA/cm², open circuit voltage of 0.42 V and fill factor of 29 %.

Abstract: Inverted type bulk heterojunction organic solar cell based on ZnO nanorod arrays have been used to overcome the degradation problem of conjugated polymer and low work function electrode. ZnO nanorods and Eosin-Y are widely used to increase the charge mobility and light absorbance, respectively. The effects of Eosin-Y coating temperature (30 – 50 oC) on the performance of 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 (PC61BM) as acceptor with a structure of fluorine-doped tin oxide (FTO)/Eosin-Y coated ZnO nanorod arrays/MEHPPV:PCBM/Ag were investigated. By using FTO as a substrate, sol-gel and spin coating method was used to deposit ZnO seed layer on FTO surface. The ZnO nanorods were then grown on the ZnO seed layer by chemical bath deposition method and coated with dye by immersing the substrates into Eosin-Y solution at different temperatures. The result shows that absorption of Eosin-Y coated ZnO nanorods increased with dye coating temperature. The optimum power conversion efficiency of η = 1.24 × 10-2 % was achieved at dye coating temperature 50 oC under 100 mW/cm2 simulated AM 1.5 G sunlight.

Abstract: This paper reports a study on plasmonic properties of gold nanoparticles to detect the presence of formaldehyde solution in water. Gold nanoparticles were grown on substrates by the seed mediated growth method. A sensor system was setup, comprises a light source, a dual arm fibre optic probe, a spectrometer and sensor chamber. The detection of formaldehyde was done by comparing the Localized Surface Plasmon Resonance (LSPR) spectra of gold nanoparticles samples immersed in the deionised water and formaldehyde solution. It was observed that the peak position LSPR spectra of nanogold samples and their intensity were change by the presence formaldehyde. The difference between resonance peak intensity of LSPR spectra gold nanoparticles sample in formaldehyde solution and water can be used as sensing sensitivity parameter of the sensor. It was found that the sensing sensitivity is increase with the size of nanoparticles until it reach the optimum particles size.

Abstract: Electronic nose is a device that attempts to mimic the living being smell system for detection of particular gases or volatile compounds. This paper reports the development of an optical electronic nose using Fe (III) based metalloporphyrins Langmuir-Blodgett thin films as sensing elements for discriminating four volatiles, 2-propanol, acetone, cyclohexane and ethanol. A multilayer feed forward neural network was developed to classify the input vectors from these two sensors. After the network being trained 100 times and introduced to blind samples, it was found that there are three fault decision for propanol, two for acetone, five for cyclohexane and one four ethanol, during 50 times being recognized to the samples.

Abstract: This paper reports on the effect of growth temperatures on optical properties of monodisperse CdSe QDs synthesized via wet chemical method. The growth temperature was varied from 260 – 310 °C while growth period was fixed at 60 s. The resulting colloidal was in strong quantum confinement regime and having yield as high as 53%. As the growth temperature increased, the monodispersed CdSe QDs with diameter in the range of 3-7 nm were obtained. Both absorption and PL spectra of the QDs revealed a strong red-shift with the increment of growth temperature. Thus, the size of QDs was enlarged with increment of the wavelength from both the spectra. Consequently, the energy gap of resulting QDs can be tuned by tuning the size of QDs. More importantly, the narrow widths of the PL emissions with different colors make these colloidal to be a potential candidate for different optical and optoelectronic devices.