Papers by Author: Mohamad Deraman

Abstract: Interest in research of supercapacitor has been in increasing trend because of high demand of supercapacitor application as energy storage device in both systems that require low and high power-energy usage. For supercapacitor using porous carbon electrodes, the energy storage mechanism involves the electrolyte ions in electrodes pores and electronic charges in electrodes to form electric double layers at the electrode-electrolyte interface without undergoes any chemical reaction. The specific surface area of porous electrodes, which affect the performance of supercapacitor, have been widely investigated by many researchers using the nitrogen adsorption-desorption measurement. However, despite its simplicity the X-ray diffraction method is rarely found being used to determine the specific surface area of porous electrodes. Therefore, in the present paper, we propose a new equation which expressed the specific surface area of electrodes as a function the electrode structural parameters obtained from the X-ray diffraction data, and duration of activation time employed during the electrode preparation. This equation is found to produce a satisfactory result and is expected to be beneficial for studying supercapacitor electrode materials.

Abstract: In this study, Ohmic contact were fabricated on AlGaAs HEMTs structure. A good metal-semiconductor interface are essentially for achieving lower specific contact resistance. An AlGaAs epi wafer was supply by the vendor. AlGaAs substrate was cleaned using wet chemical etching. Electrodes were fabricated through a sequenced of lithography, cleaning, sputtering and lift-off processes. The electrodes were made with metal layers of Ge, Au and Ni. Parameters such as metal thickness, annealing temperatures (from 300°C to 400°C) and annealing time were varies during fabrication process. Electrical characterizations after annealing are carried out using transmission line method (TLM) to obtain the specific contact resistance. Annealing temperature between 340°C to 360°C produced contact resistance below 5 x 10ˉ³Ω/cm^-2.

Abstract: Green Monoliths (GMs) of self-adhesive carbon grain from fibers of oil palm empty fruit bunches were prepared by compression pressure at 1.43 × 107, 1.91 × 107 and 2.39 × 107 kg/m2, respectively. Activated carbon monoliths ACM-A, ACM-B and ACM-C prepared by CO2 activation from these GMs, respectively, were used as electrodes in supercapacitor cells which employed stainless steel 316L current collector and H2SO4 electrolyte. Evaluation of the electrochemical properties showed that ACM-A, ACM-B and ACM-C cells had specific capacitance of 30, 9 and 5 F/g, total ESR of 3.21, 4.95 and 7.33 Ω, specific power (maximum) of 173.41, 107.58 and 33.82 W/kg, and specific energy (maximum) of 0.67, 0.15 and 0.09 Wh/kg. These properties are directly associated with the surface area of the ACMs, i.e. 419, 336 and 302 m2/g for the ACM-A, ACM-B and ACM-C, respectively, indicating a direct effect of compression pressure on the physical and electrochemical properties of ACMs electrodes.