Hafizal Yahaya

High electron mobility and low carrier concentration of hydrothermally grown ZnO thin films on seeded a-plane sapphire at low temperature

Hydrothermal zinc oxide (ZnO) thick films were successfully grown on the chemical vapor deposition (CVD)-grown thick ZnO seed layers on a-plane sapphire substrates using the aqueous solution of zinc nitrate dehydrate (Zn(NO3)2). The use of the CVD ZnO seed layers with the flat surfaces seems to be a key technique for obtaining thick films instead of vertically aligned nanostructures as reported in many literatures. All the hydrothermal ZnO layers showed the large grains with hexagonal end facets and were highly oriented towards the c-axis direction. Photoluminescence (PL) spectra of the hydrothermal layers were composed of the ultraviolet (UV) emission (370 to 380 nm) and the visible emission (481 to 491 nm), and the intensity ratio of the former emission (IUV) to the latter emission (IVIS) changed, depending on both the molarity of the solution and temperature. It is surprising that all the Hall mobilities for the hydrothermal ZnO layers were significantly larger than those for their corresponding CVD seed films. It was also found that, for the hydrothermal films grown at 70°C to 90°C, the molarity dependences of IUV/IVIS resembled those of mobilities, implying that the mobility in the film is affected by the structural defects. The highest mobility of 166 cm2/Vs was achieved on the hydrothermal film with the carrier concentration of 1.65 × 1017 cm−3 grown from the aqueous solution of 40 mM at 70°C.

Semiconductor nanopores formed by chemical vapor deposition of heteroepitaxial SiC films on SOI(100) substrates

The authors investigated the formation of nanometer-scale pore (nanopore) arrays by chemical vapor deposition (CVD) of heteroepitaxial SiC films on Si(100) membranes prepared by anisotropic etching of silicon on insulator substrates from the back-side surfaces. SiC heteroepitaxial films with thicknesses of ∼10 nm were grown by pulse jet CVD of CH3SiH3 gas. During the SiC growth, inverted pyramidal pits with {111} facets grew into the Si membranes due to the surface diffusion of Si atoms outward from the bulk Si. Nanopores were formed at the tips of the inverted pyramidal pits. The pore sizes were found to be dependent on the existence of the buried oxide layers under the Si membranes. It is suggested that maintaining the {111} facets during the SiC growth on the Si membrane is essential for smaller size (∼nm) pore formation.

Enhancing Ride Comfort of Quarter Car Semi-active Suspension System Through State-Feedback Controller

The objective of this study is to simulate the road disturbance toward suspension in quarter car system. Suspension consists of the system of springs, shock absorbers, and linkages that connects a vehicle to its wheel and allows relative motion between the car body and the wheel. This paper shows the mathematical modeling in order to design the quarter car suspension system using Simulink and MATLAB software. The work shows the effect of suspension travel in quarter car system toward road profile by using state-feedback controller. The state-feedback controller’s purpose is to decrease the continuous damping in suspension system. The inconsistency condition of the road is the main element that affects the ride comfort which is in this paper represented by different heights of road profile. In suspension principles, the road wheels and vehicle body produce vertical forces which are rotational motions. Therefore, state-feedback controller must be able to reduce body deflection caused by road disturbance to achieve the ride comfort of driver and passengers. The results show that the proposed controller is capable of reducing the vibration of suspension after experiencing the bumps with different heights.

Graphene Nanoplatelets (GnP)-PVA Based Passive Saturable Absorber

A passive Q-switched pulsed laser at 1.5 m region incorporating graphene nanoplatelets (GnPs) embedded in Polyvinyl Alcohol (PVA) is demonstrated. A surfactant is used to aid the dispersion of the GnPs before it is mixed with PVA to develop a GnPs-PVA film based SA. The SA is integrated into the laser cavity by attaching a cut of the GnPs-PVA film in between two fiber ferrule of the laser ring cavity.The proposed GnPs-PVA film based passive Q–switched laser was able to operate as the input pump power was increased from 39 mW up to a maximum of 148 mW before diminishing. The laser obtained operated with a central wavelength of 1530.76 nm. Repetition rates were obtained at 33 kHz to 91.5 kHz, throughout the tunable input pump power with the shortest pulse width of 2.42 s. Maximum attainable peak power and pulse energy of 1.2 mW and 5.9 nJ, respectively, was recorded, accompanied by a signal to noise ratio (SNR) of 28 dB.

The Thermal Instability Analysis of Functionally Graded Carbon Nanotube Composite Plates Using Finite Element Method

In recent years carbon nanotube (CNT) has been combined with polymers to take advantage of the extremely high strength and stiffness of the CNT. This paper reports a study on the thermal instability of carbon nanotube reinforced composites (CNTRC) plate subjected to uniform temperature rise. Finite element method (FEM) formulation was developed based on the first order shear deformation theory. The extended rule of mixture was used to determine the effective properties of the CNTRC plate. The CNTRC plate was functionally graded in its thickness direction. The results of the thermal instability were validated using past results and several parametric studies were then conducted using the developed formulation. The parametric studies showed that the critical temperature of the CNTRC was increased with the increase of the CNT volume fraction and the FG-4 configuration gave the highest critical temperature.

Position-controlled formation of Si nanopores by chemical vapor deposition of SiC/SOI(100)

We investigated the position-controlled nanopore formation in the surface of thin Si layer of a Silicon on Insulator (SOI) substrate by utilizing chemical vapor deposition (CVD). The Si membrane was obtained by anisotropic etching of the handle wafer. The SiC film growth was carried out from the backside surface by utilizing CH3SiH3 pulse jet CVD at the substrate temperature of 900 °C. Square pits with the sizes of ≤0.5 μm were observed on the Si membrane while no pit was formed on the top Si layer. This result indicates that the position of the nanopores on the top Si layer can be controlled without using SiO2 masks on the front side surface.

Fabrication of nanopores utilizing SiC/Si(001) heteroepitaxial growth on SOI substrates: Nanopore density control

We have investigated the nanopore formation utilizing SiC/Si (001) heteroepitaxial growth. Inverse pyramidal pits were produced by {111} faceted on the top of Si layer of Silicon on Insulator (001) substrate after SiC growth by using CH3SiH3 pulse jet chemical vapor deposition. Randomly distributed nanopores with the size of ~10 nm were obtained after dipped into BHF solution for etching the buried oxide layer through the top of the pit. It was found that the densities of the pits and the nanopores strongly depend on the initial SiC nucleation density which can be controlled by the pulse frequency and number of CH3SiH3 pulse jets.