Theoretical Analysis of Diffraction Efficiency of Photocarrier Grating

The diffraction efficiency of the photocarrier grating (PCG) has been theoretically analyzed. Firstly, the model of the PCG has been set up, and the distribution of the carrier concentration has been studied. Secondly, the change in refractive index produced by the photocarriers has been estimated. Finally, a rigorous coupled-wave analysis has been employed to investigate the diffraction efficiency of the PCG. The results show that when the angle between the two excitation lasers increases, the change of the refractive index decreases, leading to a weak grating. The optimal incident angle of the probe laser is dependent on the angle between the two excitation lasers, and the relation between these two angles for the higher diffraction efficiency of the +1st forward-diffracted wave has been found. In terms of diffraction efficiency, the optimal parameters have been estimated, and the feasibility of the PCG to be a forward-diffracted component has been confirmed.     

An approach for obtaining the structural diversity of multi-walled carbon nanotubes on Ni/Al catalyst with low Ni content

A mass of multi-walled carbon nanotubes were fabricated on Ni/Al catalyst with low Ni content (2.5 wt.%) by chemical vapor deposition in the temperature range of 773–923 K and characterized with respect to their structure. The tubular and the bamboo-shaped structure occurred in the 773–873 K and 873–923 K temperature ranges, respectively. In order to figure out the reasons for the observed structural instabilities, the effects of reduction and reaction temperature on the catalyst particle sizes and the carbon nanotube dimensions (lengths and diameters) were investigated in detail using statistical measurements based on transmission electron microscope observations. The reduction and reaction temperatures have strong influences on the catalyst particle sizes and the carbon nanotube diameters. The influence of reaction temperatures on the carbon nanotube length is feeble. Furthermore, mechanisms of the structure formation are discussed as well as open questions are addressed.     

Improved ant colony optimization algorithms for determining project critical paths

In project management, a project can be represented as a network in two ways; namely, activity-on-arc (AoA) and activity-on-node (AoN). Two recent papers have shown that ant colony optimization (ACO) could find critical path(s) in projects represented as AoA networks. This paper points out that the number and placement of logical dummy activities associated with AoA-based networks can pose serious problems. To get around the problems, an ACO technique based on AoN networks is then proposed. For comparison, the two existing AoA-based ACO algorithms were reproduced and modified into AoN-based algorithms. Moreover, the proposed ACO algorithm was applied to AoA networks as well. All six algorithms were tested with several benchmark problems. The test results strongly indicate that AoN-based ACO algorithms are more effective and efficient in finding critical paths than AoA-based algorithms.     

Review of Polymer‐Based Nanodielectric Exploration and Film Scale‐Up for Advanced Capacitors

The uprising demands for electrical power and electrification requires advanced dielectric functionalities including high capacitance density, high energy density, high current handling capability, high voltage, high temperature, high thermal conductivity, light weight, and environmental reliability. Nanodielectric engineering emerges and attracts extensive efforts from many countries as a result. Unlike prior reviews focusing on lab scale nanocomposite study, this review focuses on recent innovations in polymer‐based nanodielectric design on a large scale and their film scale‐up efforts for advanced capacitors. The unconventional polymer‐nanofiller engineering and their process in the last two decades are discussed. The nanofunctionalized polymers on a molecular level for high dielectric constants and high dielectric strength are briefly described. The challenge associated with film scale‐up and retention of nanodielectric properties are then pointed out to be crucial toward a transfer of dielectric and capacitor technology. Several important attempts at scaling up dielectric films and capacitors recently supported by the US government and industry are reviewed. An alternative strategic approach to achieving high performance polymer films is introduced by leveraging 2D surface coating on commercially mature large‐scale polymer films. Future pathways for high quality scalable dielectric films exhibiting desirable dielectric properties and feasibility for capacitor manufacturing are suggested.     

Photoconductivity measurements in optical fibre preforms

The AC photoconductivity and the photodielectric shift in UV-illuminated germano-silicate preforms and optical fibres has been measured using a noncontact microwave resonator technique at 2.9 GHz. The highest photoconductivity measured was 1.5*10/sup -6/ ( Omega cm)/sup -1/ and the largest measured photodielectric shift corresponded to an increase of the refractive index of 1.6*10/sup -2/. A permanently induced increase of the refractive index, 6.1*10/sup -3/, was also observed. The dark DC conductivity was measured to be 10/sup -15/ ( Omega cm)/sup -1/.<>     

Some silicon-based heterostructures for optical applications

In this paper, we will present our recent research on the growth and characterization of some Si-based heterostructures for optical and photonic devices. The heterostructures to be discussed are ZnO nanorods on Si, SiO₂, and other substrates such as SiN and sapphire. We will also consider strained Si_1−xGe_x/Si heterostructures for Si optoelectronics. The performance and functionality extension of Si technology for photonic applications due to the development of such heterostructures will be presented. We will focus on the results of structural and optical characterization in relation to device properties. The structural characterization includes x-ray diffraction for assessment of the crystallinity and stress in the films and secondary ion mass spectrometry for chemical analysis. The optical properties and electronic structure were investigated by using photoluminescence. The device application of these thin film structures includes detectors, lasers, and light emitting devices. Some of the Si-based heterostructures to be presented include devices emitting and detecting up to the blue-green and violet wave lengths.     

Phase Equilibria of BaO-R2O3-CuO z Systems (R = Y and Lanthanides) under CO2-free Conditions

For applications ranging from phase equilibria to the processing of second-generation high T _c superconductor-coated-conductors, phase diagrams constructed under carbonate-free conditions are needed. Subsolidus phase equilibria of BaO-R₂O₃-CuO _z (R = Ho) have been investigated at (810°C), 21 kPa (875°C) and 0.1 MPa (850 and 930°C) by applying controlled atmosphere methods to minimize the presence of carbonate and CO₂ and H₂O contamination. Under carbonate-free conditions, most of these phase diagrams are different from those reported in the literature. In this paper, we also review and compare the phase diagrams of ten BaO-R₂O₃-CuO _z systems (R = Nd, Sm, Eu, Gd, Dy, Y, Ho, Er, Tm and Yb) that were previously determined in this laboratory under Among these diagrams, a distinct trend of phase formation and tie-line relationships is observed.     

Efficient Decoding for Generalized Quasi-Orthogonal Space–Time Block Codes

Space–time coding can achieve transmit diversity and power gain over spatially uncoded systems without sacrificing bandwidth. There are various approaches in coding structures, including space–time block codes. A class of space–time block codes namely quasi-orthogonal space–time block codes can achieve the full rate, but the conventional decoders of these codes experience interference terms resulting from neighboring signals during signal detection. The presence of the interference terms causes an increase in the decoder complexity and a decrease in the performance gain. In this article, we propose a modification to the conventional coding/decoding scheme that will improve performance, reduce decoding complexity, and improve robustness against channel estimation errors as well.     

CMOS compatible dual metal gate integration with successful Vth adjustment on high-k HfTaON by high-temperature metal intermixing

In this paper, we report for the first time a novel dual metal gate (MG) integration process for gate-first CMOS platform by utilizing the intermixing (InM) of laminated ultra-thin metal layers during high-temperature annealing at 1000 °C. In this process, an ultra-thin (2 nm) TaN film is first deposited on gate dielectric as a buffer layer. Preferable laminated metal stacks for NMOS and PMOS are then formed on a same wafer through a selective wet-etching process in which the gate dielectric is protected by the TaN buffer layer. Dual work function for CMOS can finally be achieved by the intermixing of the laminated metal films during the S/D activation annealing. To demonstrate this process, prototype metal stacks of TaN/Tb/TaN (NMOS) and TaN/Ti/HfN (PMOS) has been integrated on a single wafer, with WF of 4.15 and 4.72 eV achieved, respectively. Threshold voltage (V_th) adjustment and transistor characteristics on high-k HfTaON dielectric are also studied.