Papers by Author: M.H. Mamat

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: Tin-doped Zinc Oxide (Sn-doped ZnO) thin films were prepared using zinc acetate dehydrate as a starting material by sol-gel immersion method. The doping concentrations were varied at 0 at.%, 1.0 at.%, 2.0 at.% and 3.0 at.%. The synthesized samples were characterized by Field Emission Scanning Electron Microscopy (FESEM).

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: 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: Nanograins zinc oxide (ZnO) with c-axis preferred orientation was deposited on glass substrates by RF magnetron sputtering. It was performed with a ZnO target with 99.999% purity at RF power of 200 W. The deposition was carried out in argon and oxygen ambient at the ratio flow-rates of 10 and 5 sccm respectively, with total deposition time of 1 hour. The films were grown atgrowth temperatures were specified at RT, 100, 200, 300, 400 and 500°C. The effects of the growth temperature on the ZnO structural property was investigated by x-ray diffraction (XRD). The best ZnO crystalline quality obtained at growth temperature, T_G of 300°C was further characterized by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM).

Abstract: Nickel (Ni)-doped zinc oxide (ZnO) layers were deposited simultaneously by radio frequency (RF) magnetron sputtering from a Ni and ZnO target. A Ni seed layer was used as catalyst prior to the deposition of Ni-doped ZnO. The Ni seed layer was grown with 15 sccm of Ar flow rate while the Ni-doped ZnO was grown with mixture of Ar:O₂ at 25:5 sccm gas flow rate ratio. The deposition pressure is 5 mTorr for both Ni seed layer and Ni-doped ZnO layer. This paper studies the influence of deposition temperature to the Ni seed layer and Ni-doped ZnO layer at temperature range from room temperature (RT) until 500°C with an increment of every 100°C. The sample was characterized using field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD) and UV visible spectroscopy (UV-vis) to determine the structural, crystallinity and optical properties of the deposited layer. FESEM surface analysis shows that uniformity of the nanocolumns is improved when deposition temperature is increased. The transmittance of the deposited nanocolumns was improved when temperatures are increased to 500°C.

Abstract: Nanocolumnar zinc oxide (ZnO) was deposited on glass substrates by RF magnetron sputtering.It was performed with a ZnO target at RF power of 200 W. The deposition wascarried out in argon and oxygen ambient at the ratio of 10 and 5 sccmrespectively, with total deposition time of 1 hour. The growth temperature wasfixed at 500°C and deposition pressure specified at 3, 5 and 10 mTorr. It wasobserved that the morphological and photoluminescence properties of ZnOstrongly dependent on the deposition pressure. The ZnO mean grain area was inverselyrelated with the surface roughness. The best morphological andphotoluminescence properties was found to be associated with ZnO grown at 10mTorr. Smooth ZnO surface and lowest defects related emission in PL wasobtained for the respective sample.

Abstract: Nanocolumnar ZnO was successfully deposited on glass substrate by RF magnetron sputtering. It was performed with a ZnO target with 99.999% purity at RF power of 200 W. The growth temperature was specified at 500°C, with total deposition time of 1 hour. The effects of oxygen gas composition during sputtering process was investigated. Argon to oxygen ratio was varied at Ar10:Ox5, Ar8:Ox7 and Ar5:x10 sccm. Optical characterization on samples indicated that the transmittance though visible range is higher than 80%. Based on morphological property obtained, higher oxygen content exhibited better uniformity and surface roughness. This is due to the reduction of oxygen vacancies in the ZnO layer.

Abstract: Nickel (Ni) / indium tin oxide (ITO) nanostructures were deposited on glass and silicon (111) substrates by RF magnetron sputtering using a nickel target and ITO (In-Sn, 90%-10%) targets. The post-deposition annealing has been performed for Ni/ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties on ITO films was studied. We found the appearance of (411) and (622) peaks in addition to (400) and (222) major peaks, which indicates an improvement of the film crystallinity at high annealing temperature of 650°C. The samples show higher transmittance of more than 90% at 460 nm after annealing. In addition, increasing the annealing temperatures also improve the film electrical properties. The resistivity decreases to 6.67×10^-6 Ωcm when annealed at 500°C as opposed to 6.75×10^-5 Ωcm in as-deposited film.