Influence of InxGa1−xAs Underlying Layer on the Structural of the In0.5Ga0.5As Quantum Dots Grown by MOCVD

The single layer In0.5Ga0.5As quantum dots (QDs) were grown on a thin InxGa1−xAs underlying layer by metal-organic chemical vapour deposition (MOCVD) via Stranski-Krastanow growth mode. The effect of different indium composition in the In − xGa1−xAs underlying layer was investigated using atomic force microscopy (AFM). AFM images show that the QDs structures were formed on the surface. The dots formation onthe surface changes with different composition of InxGa1−xAs underlying layer. Increasing indium composition in the underlying layer resulted to formation of higher density and smaller size dots. Several large dots were also formed on the surface. Growing of underlying layer reduces the lattice mismatch between In0.5Ga0.5As and GaAs, and decreases the critical thickness of the dots. This strongly influences the dots nucleation on the surface. Growth of quantum dots using underlying layer is one way to modify dot formation in order to achieve uniform QDs of right size and high density, which are essential for QDs device applications

Synthesis and analysis of silicon nanowire below Si-Au eutectic temperatures using very high frequency plasma enhanced chemical vapor deposition

Silicon nanowires (SiNWs) were synthesized from pure silane precursor gas and Au nanoparticles catalyst at below Au-Si eutectic temperature. The SiNWs were grown onto Si (1 1 1) substrates using very high frequency plasma enhanced chemical vapor deposition via a vapor-solid-solid mechanism at temperatures ranging from 363 to 230 degrees C. The morphology of the synthesized SiNWs was characterized by means of field emission scanning electron microscope equipped with energy dispersive X-ray, high resolution transmission electron microscopy, X-ray diffraction technique and Raman spectroscope. Results demonstrated that the SiNWs can be grown at the temperature as low as 250 degrees C. In addition, it was revealed that the grown wires were silicon-crystallized

Response of FBG-bonded plastic plate at different locations of applied stress

Fiber Bragg Grating sensing (FBG) has been intensively studied in the application of smart structures because of its immense advantages offered over those of the conventional sensors. In these researches unique characteristics of FBG, like its high sensitive resonance frequency spectrum and its resonant behavior were reported when FBG was coated by a ring-shaped material and used as an underwater acoustic sensor. In this study, the response of a FBG-bonded plastic plate at different locations of applied stress is demonstrated. The sensing element utilized for this purpose is a 10 mm FBG sensor bonded onto the surface of a plastic plate. Results of reflection spectrum showed that the output power increased randomly when the location of applied stress approached the location of FBG. This was assured from the increment of the area of reflection spectrum. The random increase in the output voltage was attributed to the insufficient stiffness of the plastic ruler, suggesting the implement of graphene plate instead of plastic ruler and increasing the grating length of FBG. The results showed an increase in the output power as detected by the photodiode. Consequently, a clear correlation between the optical and electrical outputs was observed

Signal refinement: principal component analysis and wavelet transform of visual evoked response

This study presents an analysis on Visual Evoked Potentials (VEPs) recorded mainly from the occipital area of the brain. Accumulation of segmented windows (time locked averaging), Coiflet wavelet decomposition with dyadic filter bank and Principle Component Analysis (PCA) of three stages were utilized in order to decompose the recorded VEPs signal, to improve the Signal to Noise Ratio (SNR) and to reveal statistical information. The results shown that the wavelet transformation offer a significant SNR improvement at around four times compared to PCA as long as the shape of the original signal is retained. These techniques show significant advantages of decomposing the EEG signals into its details frequency bands

Feature Extraction of Visual Evoked Potentials Using Wavelet Transform and Singular Value Decomposition

Introduction: Brain visual evoked potential (VEP) signals are commonly known to be accompanied by high levels of background noise typically from the spontaneous background brain activity of electroencephalography (EEG) signals. Material and Methods: A model based on dyadic filter bank, discrete wavelet transform (DWT), and singular value decomposition (SVD) was developed to analyze the raw data of visual evoked potentials and extract time-locked signals with external visual stimulation. A bio-amplifier (iERG 100P) and data acquisition system (OMB-DAQ-3000) were utilized to record EEG raw data from the human scalp. MATLAB Data Acquisition Toolbox, Wavelet Toolbox, and Simulink model were employed to analyze EEG signals and extract VEP responses. Results: Results were verified in Simulink environment for the real recorded EEG data. The proposed model allowed precise decomposition and classification of VEP signals through the combined operation of DWT and SVD. DWT was successfully used for the decomposition of VEP signals to different frequencies followed by SVD for feature extraction and classification. Conclusion: The visual and quantitative results indicated that the impact of the proposed technique of combining DWT and SVD was promising. Combining the two techniques led to a two-fold increase in the impact of peak signal to noise ratio of all the tested signals compared to using each technique individually

Metod pengajaran guru bagi meningkatkan kemahiran menyelesaikan masalah dalam fizik

Antara tujuan utama kurikulum fizik ialah untuk membangunkan kemahiran menyelesaikan masalah di kalangan pelajar tetapi ianya merupakan suatu tugasan yang kompleks dan kritikal dalam pembelajaran pelajar. Namun begitu hingga kini, ia masih terus diusahakan dan terus menjadi agenda utama dalam bidang pendidikan. Kajian-kajian lepas menunjukkan tahap kemahiran menyelesaikan masalah Fizik dalam kalangan pelajar di Malaysia adalah masih lemah. Walau bagaimanapun, pelbagai inisiatif dan usaha telah dilaksanakan untuk meningkatkan kemahiran menyelesaikan masalah ini. Salah satu elemen yang dapat membantu pelajar dalam meningkatkan kemahiran ini ialah metod pengajaran guru. Oleh itu, kertas konsep ini akan membincangkan beberapa metod pengajaran guru dalam subek Fizik bagi membantu untuk meningkatkan kemahiran menyelesaikan masalah dalam kalangan pelajar

Fabrication parameters dependent morphology variation of silicon thin film

Achieving two dimensional quantum structure of silicon with welldefined tuneable morphology is an outstanding issue. We present the preliminary results on fabrication parameters dependent silicon thin film production using VHF-PECVD method. Five samples are prepared on Si(100) substrate with gold (Au) catalyst by adjusting different parameters such as deposition time, temperature and the flow of precursor gas. The samples morphology are analysed using FESEM. The results reveal that the silicon thin film appear to be smooth and crystal-like after an enormous amount of hydrogen is inserted together with the precursor gas (silane) during the deposition process. More interestingly, the films exhibit silicon nanowires as the deposition time is increased up to 1 hour. This morphological transformation is attributed to the vapour-liquid-solid (VLS) mechanism related to the deposition process. Our results may contribute towards the development of nanosilicon based optoelectronics

A redox mediated UME biosensor using immobilized chromobacterium violaceum strain R1 for rapid biochemical oxygen demand measurement

An effective ferricyanide-mediated microbial biochemical oxygen demand (BOD) biosensor was constructed and used for BOD determination in a water system. This BOD sensor uses ultramicroelectrode (UME) technology in which the tip of the sensor consists of a two-electrode system (10-µm Pt working electrode and Pt counter electrode). Because of their small size, UMEs have relatively large diffusion layers and small overall currents enabling rapid achievement of useful steady-state conditions with very high scan rates. Living Chromobacterium violaceum R1 cells (isolated from pineapple industry wastewater) were immobilized on the surface of the UME working electrode using a calcium alginate gel and further enclosure by a layer of polyamide membrane. Glucose-glutamic acid (GGA) solution was used as the standard solution. The amperometric measurement was optimized at +450 mV operating potential and 30 mM ferricyanide in a 0.1 M phosphate buffer (pH 7.0) at 26 °C. The sensor exhibited a linear response ranging from 20 to 225 mg O2 L-1 BOD5 for standard GGA solution and 25 to 230 mg O2 L-1 BOD5 for OECD synthetic wastewater with a response time of 30 min. Repeatability and reproducibility of the biosensor were within the limits set by the APHA; i.e., less than 15.4%. The rapid BOD estimation of the biosensor is applicable for measuring samples with a high content of fast and easily assimilated compounds. When used to estimate the BOD of various wastewaters, the developed biosensor provided values comparable to those obtained using the conventional BOD5 method

Pengukuran ketulenan emas menggunakan kaedah ujian tanpa musnah: suatu ulasan perbandingan

Penentuan ketulenan jongkong emas dengan kaedah ujian tanpa musnah adalah perkara yang paling mencabar dalam industri emas terutama jika jongkong emas dipalsukan dengan cara meletakkan tungsten di dalamnya. Instrumen yang sedia ada mempunyai keterbatasan untuk menentukan ketulenan jongkong emas dan sukar untuk mengesan tungsten di dalamnya kerana tungsten mempunyai ketumpatan yang hampir sama dengan emas. Kajian ini mengemukakan keterbatasan instrumen kaedah ujian tanpa musnah seperti densimeter, alat timbangan, sinar-x pendarfluor dan ultrasonik. Dalam kajian ini menemui kesukaran untuk mengenal pasti emas palsu menggunakan instrumen kaedah ujian tanpa musnah seperti ultrasonik dan x-ray fluorescence (XRF) kerana instrumen ini mempunyai batasan. Setakat ini tiada lagi kajian yang berkaitan pemalsuan jongkong emas kerana harganya yang mahal untuk dijadikan sebagai sampel kajian. Masalah jongkong emas palsu dapat diselesaikan jika ketepatan instrumen yang digunakan untuk mengukur ketumpatan dapat ditingkatkan lagi sehingga 0.01 g/ml. Ini kerana perbezaan antara ketumpatan emas dan tungsten adalah 0.05 g/ml. Pemalsuan emas dengan mencampurkan tungsten akan dapat dikesan jika ada instrumen yang mempunyai ketepatan sekurang-kurangnya 0.01 g/ml. Manakala instrumen lain seperti XRF digunakan untuk mengesahkan ketulenan emas di bahagian permukaan sahaja. Oleh itu, bagi pengujian yang lebih menyeluruh masalah jongkong emas palsu ini perlu diselesaikan dengan menggabungkan kedua-dua kaedah ini

Recent progress on CVD growth of graphene from a liquid carbon precursor

Graphene has become a remarkable highlight of advanced material research because of its far superior properties compared to other materials. Chemical vapor deposition (CVD) has emerged as an essential method for scalable production and large area graphene for various applications. Various carbon precursors have been reported for graphene production as they can dramatically impact the graphene growth yield. In the early years of graphene CVD growth, hydrocarbon gases such as methane and acetylene have become favorable carbon precursors because of their stability at elevated temperature and controllable growth. However, hydrocarbon gases are known as explosives and toxic, therefore require a growth system with a high degree of safety and handling precautions. With the limitations mentioned above, liquid carbon source may change the graphene growth landscape as it is relatively inexpensive, nonexplosive compared to the conventional gaseous precursor. This article aims to review a detailed synthesis of large-area graphene using liquid carbon precursors via the CVD technique. Challenges and future perspectives are highlights