Papers by Author: Mohamad Rusop

Abstract: We have reviewed humidity sensors based on the Zinc oxide (ZnO) humidity sensor. There are only a few papers reviewing on the ZnO humidity sensor. The characteristics, structures, advantages, and fabrication methods of ZnO have been studied to understand the suitability of the ZnO to be applied at different kind of condition such as for extreme environment, low level humidity detection, and very high humidity level circumstances. The electrical and physical properties of ZnO humidity sensors such as sensitivity, response time, stability, uniformity, and crystallinity have also been discussed in this review. ZnO nanostructures have been widely used for humidity sensors because of its’ good stability, high sensitivity for humidity-sensing, low cost, and has a wide band gap. Sol-gel preparation method is commonly used to for ZnO humidity sensor fabrication since it can produce a film with high uniformity, simple process and low cost. Keywords: Humidity Sensor, Metal Oxide, Semiconducting Type, Ceramic Type, Humidity-Sensing, Band Gap, Sol-Gel Preparation Method.

Abstract: Fabrication and performance of metal-semiconductor-metal (MSM)–type intrinsic zinc oxide-coated, aluminium-doped ZnO nanorod array-based ultraviolet photoconductive sensors were reported and discussed. The Al-doped ZnO nanorod arrays were prepared using sonicated sol-gel immersion method. The coating process of intrinsic ZnO onto Al-doped ZnO nanorod arrays was performed using radio-frequency (RF) magnetron sputtering at different deposition times varying from 0 to 10 min. We observed that responsivity of the sensors decreased with increasing intrinsic ZnO deposition time, decreasing from 4.81 A/W without coating to 1.37 A/W after 10 min of coating. Interestingly, the sensitivity of the sensors improved with intrinsic ZnO coating, having a maximum value of 19.0 after 1 min coating.

Abstract: In this work, seeded porous silicon (PSi) was used as a substrate in the growth of ZnO nanostructures. PSi was prepared by electrochemical etching method. ZnO thin films as seeded were deposited via sol-gel spin coating method. ZnO nanostructures were grown on seeded PSi using hydrothermal immersion method. In order to study the effect of post-heat treatment on the substrate, post annealing temperature were varied in the range of 300 to 700 °C. The FESEM results shows ZnO thin film composed of nanoparticles were distributed over the PSi surface. Based on AFM characterization, the smoothest surface was produced at post annealing temperature of 500 °C. There are two different peaks appeared in PL characterization. The peak in near-UV range is belonging to ZnO thin films while a broad peak in visible range can be attributed to ZnO defects and PSi surface. In addition, FESEM, XRD and PL were used to characterize the ZnO nanostructures. The FESEM results revealed ZnO nano-flower were successfully grown on seeded PSi. Hexagonal wurtzite of ZnO with dominated by the plane (100), (002), and (101) was found by XRD characterization. Two different peaks in UV range and visible range can be attributed to ZnO nano-flower and various defects of ZnO, respectively.

Abstract: In this study, ZnO nanostructures were synthesized on porous silicon (PSi) substrate using hydrothermal immersion method. Different post-annealing temperatures were varied from 300°C to 600°C. Surface morphology was studied by field emission scanning electron microscopy. It shows that a better shape was produce at annealing temperatures of 500°C. Structural studies of ZnO nanostructure were implemented using X-ray diffraction grating. The result shows post-annealing can influence the crystallinty of ZnO. Photoluminescence spectra were used to study the optical properties of ZnO nanostructure. The result shows that peak corresponds to ZnO nanostructures are appeared in UV range. Besides, broad peaks are also appeared in visible range which is attributed to structural defects and PSi substrate.

Abstract: We have reviewed humidity sensors based on the Zinc oxide (ZnO) humidity sensor. There are only a few papers reviewing on the ZnO humidity sensor. The characteristics, structures, advantages, and fabrication methods of ZnO have been studied to understand the suitability of the ZnO to be applied at different kind of condition such as for extreme environment, low level humidity detection, and very high humidity level circumstances. The electrical and physical properties of ZnO humidity sensors such as sensitivity, response time, stability, uniformity, and crystallinity have also been discussed in this review. ZnO nanostructures have been widely used for humidity sensors because of its’ good stability, high sensitivity for humidity-sensing, low cost, and has a wide band gap. Sol-gel preparation method is commonly used to for ZnO humidity sensor fabrication since it can produce a film with high uniformity, simple process and low cost. Keywords: Humidity Sensor, Metal Oxide, Semiconducting Type, Ceramic Type, Humidity-Sensing, Band Gap, Sol-Gel Preparation Method.

Abstract: In this paper, the nanostructured Sn-doped ZnO thin films were prepared by Spin coating technique on glass substrates at various Sn doping of 0, 1, 1.5, 1, 2.0 and 3 at.%. The structural, optical and electrical properties were characterized by field emission scanning electron microscopy (FESEM), X-Ray Diffraction (XRD), UV-Vis-NIR and I-V measurement, respectively. The surface morphology reveals that the average particle size of nanostructured Sn-doped ZnO thin films decreased as the Sn concentrations increased. The results show all films are transparent in the visible region with average transmittance above 88%. Meanwhile, the resistivity of Sn-soped ZnO thin films was decreased when the Sn concentrations increased. Among all of Sn-doped ZnO thin films, the thin films doped with 2 at.% shows the optimum properties of average resistivity and transmittance were 7.7 x 10² Ω.Cm and 96%, respectively.

Abstract: The surfaces of Al-doped ZnO nanorods thin films were coated with platinum (Pt) by five different thicknesses; 5 nm, 10 nm, 15 nm, 20 nm and 25 nm. The resistivity decreases while the conductivity increases, proving the trend in current-voltage measurement. The transmittance spectra show diverse result. Meanwhile the 5 nm coating sample shows highest absorbance characteristic among others. This absorption coefficient was calculated from transmittance obtained by UV-vis spectra, indicating that they have high UV absorbance properties at wavelengths below 400 nm. Absorption rate might be due to the thickness of Pt that allows the penetration of UV for more oxygen absorption.

Abstract: Aluminium (Al)-doped zinc oxide (ZnO) nanorod arrays have been synthesized on a glass substrate, where the seed layer is Al-doped ZnO thin film as well, using the sonicated sol–gel immersion method. The nanorods structure was synthesized by preparing a solution 0.0026 M of zinc nitrate hexahydrate (Zn (NO₃)₂·6H₂O, 98%, Systerm) as a precursor, 0.1 M hexamethylenetetramine (HMT, C₆H₁₂N₄, 99%, Aldrich) as a stabilizer and 0.001M aluminum nitrate nonahydrate (Al (NO₃)₃∙9H₂O, 98%, Analar) as a dopant, dissolved in deionized (DI) water. The resistivity is 7626.72 Ωcm and the conductivity is 1.31 x 10^-4 Scm^-1. The peak of UV emission of the sample is at 380 nm.

Abstract: Centella asiatica (C. Asiatica) contains asiatic acid as one of bioactive constituent that has the commercial medicinal value such as anticancer and also possess wound healing property. The ball milling process was carried out at 0.5, 4 and 8 hours. The effects of ball milling at different times were characterized using particles size analysis (Photon Correlation Spectroscopy) and Fourier Transform infra red (FTIR) Spectroscopy. The surface morphology was characterized by Field-Emission Scanning Electron Microscope (FESEM). As a result, smallest particles size by mean 279.5 nm was produced at a longest milling time (8 hr) and FTIR spectra shows there is no obvious change in the structure of C. asiatica nanopowders as compared to the micropowders. Centella asiatica nanopowders shows good extraction yield of asiatic acid with 5.5 μg/ml of yield but poor inhibition of DPPH as compared to micropowders.

Abstract: The polymer matrix of poly (metyl methacrylate) (PMMA) has been introduced with the titanium dioxide (TiO₂) nanopowder to study the effects of the TiO₂ size on the properties of the nanocomposites. The particle size is playing an important role in determining the properties of the nanocomposite. The decrease the filler size has increase the thermal decomposition of the nanocomposites due to the higher amount of the filler between the polymer chains. The results of X-ray diffraction (XRD) and Energy Dispersive X-Ray Spectrometry (EDS) also were discussed in this paper.