Muhammad M. Ramli

The effect of softbaking temperature on SU-8 photoresist performance

One of the steps required during the fabrication of SU-8 mold for soft lithography is softbaking, which is conducted after the deposition of the photoresist. The purpose of softbaking is to stabilize the resist film and eliminate any remaining solvent through evaporation. This ensures that the resist surface is non-sticking, hence avoiding debris when transferring the patterns later. In this paper, we investigate the effects of softbaking temperature on the polymerization of SU-8 photoresist. The significance of this work is to optimize the fabrication process involved in producing SU-8 mold structures with thickness of 30 μm. This project involves a series of experiments covering softbaking temperatures ranging from 45° to 115° C. Experiments results show that softbaking temperature of 85°C results in completely stick and crack free structures. By this, a huge improvement obtained if compared to the result of processing at the standard soft bake temperature of 95°C. The soft bake temperature should not be taken lightly while optimizing SU-8 processing because it has a big influence on the material properties and the lithographic performance of the resist.

The Effect of Different Reduction Methods on Conductivity of Reduced-Graphene Oxide (r-GO)

Large quantity of graphene oxide (GO) was prepared by Modified Hummer’s method, in which graphite was treated with a mixture of sulphuric acid, potassium permanganate and hydrogen peroxide. A chemically reduced graphene oxide (r-GO) was prepared using sodium borohydride (NaBH4), followed by thermal treatment and thermal treatment of chemically reduce using NaBH4. The electrical resistance of r-GO was measured using Keithley sourcemeter. The results revealed that r-GO show lower resistance on thermal reduction which is 2.39 kΩ compared to chemical reduction and thermal of NaBH4 reduction which is 2.18 MΩ and 3.16 kΩ respectively. It can be concluded that thermal reduction is the best method to produce high conductivity r-GO film.

Fabrication of multi-walled carbon nanotubes hydrogen sensor on plastic

Vacuum filtration method was applied to build optically homogeneous film of palladium (Pd) nanoparticles dispersed multi-walled carbon nanotubes (MWCNTs) networks on plastic substrate. Measurement of the sheet resistance as a function of MWCNTs concentration showed a transition from 2D percolation to 3D conduction behaviour when the concentration of MWCNTs exceeded 0.015 mg/ml. The electrical response to H2 gas exposure was investigated at room temperature.

Hybrid TiO2-Gigantochloa Albociliata Charcoal in Dye Sensitized Solar Cell

The Dye Sensitized Solar cell (DSSC) is an alternative to the silicon solar cell because it is low cost and easy to fabricate. In previous work, Remazol Orange (RO) was used as a dye sensitizer in DSSC but the efficiency is still low, 0.13%. In order to increase the device performance, TiO2 thin film as the working electrode is hybridized with high conducting and absorption material which is bamboo charcoal powder (BCP). It is founded that the nanoparticle size of TiO2-BCP composite was smaller compared to pristine TiO2. The ratio of TiO2 and BCP did not give any significant effect towards the particle size. The efficiency of RO DSSC was highly improved by 84.6% at higher carbonization temperature, 1100 °C compared to 500 °C during pyrolysis process due to its capability in absorbing more dye as it has larger specific area.

Remazol orange dye sensitized solar cell

Water based Remazol Orange was utilized as the dye sensitizer for dye sensitized solar cell. The annealing temperature of TiO2 working electrode was set at 450 °C. The performance of the device was investigated between dye concentrations of 0.25 mM and 2.5 mM at three different immersion times (3, 12 and 24 hours). The adsorption peak of the dye sensitizer was evaluated using UV-Vis-Nir and the device performance was tested using solar cell simulator. The results show that the performance was increased at higher dye concentration and longer immersion time. The best device performance was obtained at 0.2% for dye concentration of 2.5 mM immersed at 24 hours.

Fabrication and electrical characterization of graphene oxide as transducing channel for biosensor application

In this paper, we present the fabrication and electrical characterization of field-effect transistor-based sensor with integrated graphene oxide (GO) on channel between source and drain. We aim to demonstrate the optimum condition in electrical performance for field-effect transistor-based biosensor device. Graphene oxide prepared by using modified hummers method was deposited on the channel with different amount to act as amplification layer on the FET. The structural properties of GO were examined using photoluminescence (PL). A 3D surface profilometer were used to observe the surface morphology of GO-FET. Multi-graphene layer on the FET channel result in increasing the current flow in the device and make it more sensitive to be used as biosensor.

Wearable gas sensor utilising dye-functionalized single-walled carbon nanotubes

The suspension of single-walled carbon nanotubes (SWCNTs) that was functionalized by organic dye, was used as a sensing material. The Golden orange dye (Color Index : 40215) was used as the dispersion agent in order to establish a stable suspension of SWCNTs in water. The ratio of dye and deionized water (DI water) mixture is 1:1. Uniform thin film of SWCNTs was produced using vacuum filtration method where uniform thin film of SWCNTs network was formed. In this project, plastic was used as a substrate. The device was then being exposed to NO2 gas at three different temperatures which is room temperature, 200 °C and 300 °C.

Structural and Morphological Investigation for Water-Processed Graphene Oxide/Single-Walled Carbon Nanotubes Hybrids

New group of materials derived from hybridization of single walled carbon nanotubes (SWCNTs) and graphene oxide (GO) which resulting novel three dimensional (3D) materials generates an outstanding properties compared to corresponding SWCNTs and GO/Graphene. In this paper, we describe a simple approach using water processing method to develop integrated rGO/GO-SWCNT hybrids with different hybrid ratios. The hybrid ratios were varied into three divided ratio and the results were compared between pristine SWCNTs and GO in order to investigate the structural density and morphology of these carbonaceous materials. With an optimized ratio of rGO/GO-SWCNT, the hybrid shows a well-organized hybrid film structures with less defects density sites. The optimized mixture ratio emphasized the important of both rGO and SWCNTs in the hybrid structures. Morphological structural and defects density degrees were examined by Field Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy.

Incorporation of polydimethylsiloxane with reduced graphene oxide and zinc oxide for tensile and electrical properties

Polydimethylsiloxane (PDMS) is an organosilicon polymer that is commonly used to incorporate with other fillers. PDMS in high viscous liquid form is mechanically stirred with reduced graphene oxide (rGO) and mixed with zinc oxide (ZnO) with specific ratio, thus rendering into two types of samples. The mechanical and electrical properties of both samples are characterized. The result shows that PDMS sample with 50 mg rGO has the highest tensile strength with the value of 9.1 MPa. For electrical properties, sample with the lowest resistance is PDMS with 50 mg rGO and ZnO with the value of l.67×l05 Ω. This experiment shows the significant role of conductive fillers like rGO and ZnO incorporated in polymeric material such as PDMS to improve its electrical properties.Polydimethylsiloxane (PDMS) is an organosilicon polymer that is commonly used to incorporate with other fillers. PDMS in high viscous liquid form is mechanically stirred with reduced graphene oxide (rGO) and mixed with zinc oxide (ZnO) with specific ratio, thus rendering into two types of samples. The mechanical and electrical properties of both samples are characterized. The result shows that PDMS sample with 50 mg rGO has the highest tensile strength with the value of 9.1 MPa. For electrical properties, sample with the lowest resistance is PDMS with 50 mg rGO and ZnO with the value of l.67×l05 Ω. This experiment shows the significant role of conductive fillers like rGO and ZnO incorporated in polymeric material such as PDMS to improve its electrical properties.

Emission rate and internal quantum efficiency enhancement in different geometrical shapes of GaN LED

This work is based on the development of light emitting diode (LED) using different geometry of top surface on GaN p-n junction structure. Three types of LED chips are designed with different top surface to differ whether p-type layer or p contact plays an important role in improving its efficiency. The voltage applied ranges from 0V to 4V. Current-voltage characteristic for all three samples are obtained and analyzed. The results show that dome shaped of p-type layer operating at 4V increases the emission rate and internal quantum efficiency up to 70%, which is two times higher than basic cylindrically LED chip. Moreover, this new design effectively solved the higher forward voltage problem of the usual curve surface of p-contact GaN LED.