Browsing by Author "Fatin Bazilah Fauzi"

Until now, producing homogeneous chemical vapour deposited graphene with zero defects remains a challenge. The research on chemical aspects has been extensively explored either through experiments or computational studies. Given that it is a mass-transport limited process for atmospheric-pressure CVD (APCVD), the gas-phase dynamics and interfacial phenomena at the gas-solid interface (i.e., the boundary layer) is a crucial controlling factors. In this research, the importance of CVD fluid dynamics aspect was emphasised through fundamental studies at both gas-phase and gas-solid phase. As a preliminary study, an extensive review of available APCVD literature provided information on the relationship of graphene quality and its corresponding growth parameter. From these parameters, Reynolds number was calculated with the consideration that it is a ternary gas mixture. This was then compiled into a CH4-H2-Ar ternary plot which predicts the quality of graphene and Reynolds number at all gas compositions. Higher Reynolds number was found to be promising for high-quality graphene deposit which could be obtained at the gas composition range of ≤1% of CH4, ≤10% of H2, and ≥90% of Ar. Following this, a customised homogenous gas with properties similar to mixture of CH4, H2 and Ar was used in our computational fluid dynamics (CFD) of APCVD graphene. The in-depth details on gas-phase dynamics, interfacial phenomena, particularly the boundary layer and mass transport during the deposition process, were studied. Conditions, where gravity parameter is vital or could be safely neglected in CFD, was also determined. CFD model also allowed a close-up view of the boundary layer at the gas-solid interface. This was found to provide the most reasonable estimation of boundary-layer thickness formed on top of substrate for a bounded flow system like in a CVD. Higher Reynolds number formed thinner boundary layer. Consecutively, the relationship between the deposited graphene quality with Reynolds number, boundary-layer thickness and mass transport were explored. Calculated mass transport coefficient shows a good correlation to graphene thickness but not it's defect density which suggests that graphene defects are more dependent on factors other than fluid dynamics. At the highest Reynolds number of 84, few-layer graphene with monolayer ratio, I2D/IG of ∼0.67 and defect ratio, ID/IG of ∼0.45 was obtained. Wherein the quality of graphene improves when the ID/IG decreased by 90% and I2D/IG increased by 60%. Based on the experimental and computational studies, transport process was shown to have a vital role in the APCVD graphene growth.

Memristor has become one of the alternatives to replace the current memory technologies. Instead of titanium dioxide (TiO2), many researches have been done to explore the compatibility of others transition metal oxide (TMO) by using various deposition methods. Recently, the compatibility of zinc oxide (ZnO) to be used as the active layer of memristor has been widely explored. Meanwhile, the usage of organic materials in electronic device has shown a rapid growth as the size demand of devices is increasingly smaller and faster. Future electronics industry depends on the development of organic base semiconductor devices due to their advantages. In this study, the metal-insulator-metal (MIM) of Au/ZnO-Cu2O-CuO/Cu and Au/ZnO/ITO/PET memristor were fabricated using dilute electrodeposition of zinc (Zn) and subsequent thermal oxidation methods at 773 K and 423 K respectively. The 15 s deposition gives the thinnest thin film, 80.67 nm for ZnO-Cu2O-CuO on Cu and 68.10 nm for ZnO on ITO coated PET. The deposited thin film was characterized via X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). On Cu substrate, the XRD result indicates that Zn was oxidized to ZnO and has a wurzite structure. Meanwhile, Cu substrate also was oxidized to Cu2O and CuO. There was formation of needle like structure observed through FESEM after thermal oxidation method. While on ITO coated PET substrate, Zn was oxidized to wurzite ZnO as shown in XRD result with nodule structure of ZnO after the thermal oxidation method. Both Au/ZnO-Cu2O-CuO/Cu and Au/ZnO/ITO/PET sandwich memristive behavior were identified by the pinched hysteresis loop obtained from the I-V measurement. The high resistance state, HRS over low resistance state, LRS ratio of 1.110 and 1.067 respectively were obtained. Empirical study on thermodynamics of ZnO, Cu2O, CuO and diffusivity of Zn2+ and O2- in ZnO shows that zinc vacancy was formed in ZnO layer, thus giving rise to its memristive behavior. The synthesized Au/ZnO-Cu2O-CuO/Cu and Au/ZnO/ITO/PET memristor show potential application in the production of a non-complex and low cost memristor. A flexible Au/ZnO/ITO coated PET memristor produces a comparable result to the Au/ZnO-Cu2O-CuO/Cu memristor and other previous studies on memristor. The flexible memristor is applicable to be fabricated using dilute electrodeposition at room temperature with low thermal oxidation process.