Papers by Author: U. Hashim

Abstract: Chitosan (CS) is an interesting polysaccharide biopolymer that widely used in the fields of agriculture, horticulture, industry, biomedicine and chemical sensor due to its numerous advantage like non-toxic nature, excellent film forming ability, good mechanical strength, high permeability and cost effectiveness. The chitosan solution (0.05 %) was prepared by dissolving 0.05g chitosan (Sigma corp) in 10 ml of acetic acid (2mol/L). after the is the preparation of preparation of chitosan: A very small amount of chitosan were taken and dissolved in distilled water. The solution was then ultrasonicated for 90 minutes to obtain a homogenized solution. The spectra shows featureless absorption in the 400-800 nm and a sharp absorption peak at 250 nm regions which are similar to the spectra of chitosan in the previous research. The UV-vis spectra of chitosan in at different concentration. The spectra show featureless absorption in the 400-800 nm. A sharp absorption peak at approximately 300 nm. The observed absorption peak in chitosan solution depends on the solution concentration. When the chitosan concentration was less, the peak was not that clearly seen compared to the concentration of 0.05.

Abstract: At a macro scale level, mixing is generally achieved by a turbulent flow, which makes possible of segregating the fluid in small domains, thereby leading to an increase in the contact surface and decrease in the mixing path. At low Reynolds number, the viscous effects dominate inertial effects and a completely laminar flow occurs. In the laminar flow system, fluid streams flow parallel to each other and the velocity at any location within the fluid stream is variant with pressure when boundary conditions are constant and due to the change in surface area–to-volume tension and diffusion, do not simply scale linearly from large to small devices. This makes the use of microfluidic as a mixing device difficult. Thus, the study posed to bridge this gap by created geometrically enhanced Micromixer for homogenous mixing.

Abstract: An in-expensive way of fabricating PDMS microfluidic using room temperature curing process is presented which can be used for both laboratory and commercial scale. The microfluidic was designed using AutoCAD for master mold preparation and subsequently created with SU8 for rapid prototyping process; the micro mixer and the whole mixer were fabricated in less than without using costly fabrication steps. The device profiles were observed for structural integrity and evaluation by dropping two food coloring dyes through the two inlets and collecting the sample at outlet. Flow rate and mixing efficiency were quantitatively measured by analyzing the recorded flow profiles and values of the image collected from the high powered microscope at inlet and outlet locations is fully obtained and will be presented in our next publication

Abstract: In the current research we have studied the structural, morphological, optical and ultraviolet (UV) light sensing properties of ZnO thin film. The film was prepared by sol-gel technique and deposited on glass substrate by spin coating method. The structural analysis was performed by X-ray diffractometer (XRD) while the surface morphology and optical properties of the deposited thin film were monitored using field emission scanning electron microscope and UV-VIS spectrophotometer. The FESEM image displayed the homogenous coverage of ZnO nanoparticles over the surface of glass substrate. The deposited thin film shows an average transmittance value of more than 90%, in the visible light spectrum. The calculated value for optical band-gap was 3.26 eV. Refractive indices and dielectric constants were calculated by utilizing the bandgap value by considering different relations. Current to voltage characterization was conducted by using Kiethley sourcemeter connected with ultraviolet (UV) light illuminated LED’s. The excellent photo to dark current (Iph/Id) ratio (5.49) and rapid rise and decay time (15 s and 6 s) and the measured responsivity (1 A/W) suggest that the deposited ZnO thin film can be used for ultraviolet (UV) light sensing application.

Abstract: The cleaning process of the silicon wafer becomes one of the most important procedures in semiconductor fabrication. It is acknowledged to remove the contamination on the wafer surface as well as to promote an acceptable surface roughness, prior to performing various deposition methods. The wafer cleaning process which based on hot alkaline and acidic solutions is known as the RCA cleaning. The RCA is still the most important wafer cleaning method used in wafer fabrication industry. In this paper, the effects of various cleaning procedure to the silicon wafer surface roughness are measured using AFM. Subsequently, an optimum cleaning recipe is discussed and proposed.

Abstract: The electrical performances of silicon dioxide-based Interdigitated electrodes (IDEs) as biosensor were developed. The IDEs was made up by two individually addressable Interdigitated comb-like finger structure have frequently been suggested as a biosensor which promises higher sensitivity compared to conventional parallel electrodes. The purpose of this paper was to investigate the capacitance test and impedance test to taken with various pH solution to observe the response of the sensor with different pH values. Purchased pH buffer solutions which varied from pH2 to pH10 are dropped on the microelectrode and the effect on it is investigated for the application in pH measurement. This research has proven that increase in pH value from acidic to alkaline is proportional with capacitance. The measured values of capacitance with respect to each pH concentrations applied during the measurements were repeatable and reproducible.

Abstract: In this work, we demonstrated a method to fabricate and characterize poly-silicon nanowires for biosensing application using conventional photolithography and etching process. Nanowires Mask must be first designed using AutoCAD, before patterning onto chrome mask. Chrome mask was used for better photo masking and to transfer structure onto poly-silicon layer. The poly-silicon nanowires process flow were developed which includes all the fabrication process such as growth, deposition, lithography and etching process. In order to prove the effectiveness of the fabricated devices as a biologically sensor (Biosensor), the poly-silicon nanowires is modified chemically to allow the integration with biological element. The drain (I_d) was found to increase after the DNA immobilization and hybridization. These results demonstrate that the in-house fabricated poly-silison nanobiosensor is capable as a platform for label-free biosensing. The morphological characterizations were carried out using a Scanning Electron Microscope (SEM) and Atomic Force Microscope (AFM). Besides that, the electrical measurement of the poly-silicon biosensor were carried out using a KEITHLEY 6487 picoampmeter/voltage source.

Abstract: Iron (Fe) doped ZnO nanorods were synthesized on glass substrate using a sol-gel hydrothermal growth method by adopting various concentration ratios of 0.8 at% Fe, 1 at% Fe and 3 at% Fe respectively. The X-ray diffraction (XRD) analysis show that all the grown ZnO nanorods have a hexagonal wurtzite structure and are preferentially oriented along the c-axis perpendicular to the substrate surface. At 3 at% Fe-doping, the crystalline quality and the preferential orientation of ZnO nanorods are improved and below 3 at% Fe-doping concentration crystalline quality and the preferential orientation of ZnO nanorods is weakened in turn. The surface morphology analysis of the samples show that the ZnO nanorods are grown vertically to the substrate surface and highly interconnected. Such interconnected network will facilitates the electron transport along the nanorods axis. Current-voltage and current-time characterization under the exposure of UV light ON/OFF sates with exhibited excellent current gain of 1.12 and good response/recovery time of 30 and 10 s showed that the fabricated device can be used for UV sensing applications.

Abstract: Cu₂Zn_1-xCd_xSnS₄ pentrary alloys nanostructures have been grown on glass substrate using sol-gel technique. The concentration of Cd has showed obvious effect for structural properties. X-ray diffraction (XRD) measurements have proved nanoscale nature of the utilized alloys. The stiffness has been calculated using specific model of bulk modulus as a function of Cd concentration. The obtained results give good comparison with the experimental and theoretical data.

Abstract: Pentrary alloys of Cu₂Zn_1-xCd_xSnS₄ nanostructures have been grown on glass substrate using sol-gel technique. The concentration of Cd has showed obvious effect for characterization study. Field emission-scanning electron microscope (FE-SEM) and atomic force microscope (AFM) have provide nanostructures of the utilized alloys. Those alloys give good impression about increasing the grain size with Cd concentration increasing, that lead to increasing the surface coarse.