MEMS On/off and x2 Optical Switch with Integrated Fiber Alignment Capability

An on/off free space optical switch is described in this paper. The device consists of intersecting cantilevers and is electrostatically actuated. A fiber is put onto the cantilevers and by controlling the position of the flber through actuation, switching operation can be achieved. The device is also suitable for inpackage fiber alignment application, where the cantilevers can be used as passive or active fiber alignment microstructure

Influence of crystal structure on charge carrier effective masses in BiFeO3_3

Ferroelectric-based photovoltaics have shown great promise as a source of renewable energy, thanks to their in-built charge separation capability, yet their efficiency is often limited by low charge carrier mobilities. In this work, we compare the photovoltaic prospects of various phases of the multiferroic material BiFeO$_3$ by evaluating their charge carrier effective masses using first-principles simulations. We identify a tetragonal phase with the promising combination of a large spontaneous polarisation and relatively light charge carriers. From a systematic study of the octahedral distortions present in BiFeO$_3$, we explain the relationship between structure and effective masses in terms of the changes to the orbital character and overlap at the band edges that result from changes in the geometry. The findings in this study provide some design principles to engineer desired effective masses in BiFeO$_3$ and similar materials through manipulation of their crystal structures in experimentally accessible ways.Comment: 12 pages, 10 figure

Effect Of Deposition Temperature And Type Of Substrates On Structural, Surface Morphology And Optical Properties Of Rf Magnetron Sputtered Ccto Thin Film

Calcium copper titanate (CCTO) thin film with high dielectric permittivity (ε), low tangent loss (tan δ) and have high temperature phase stability up to 300 °C is very importance for several advanced microelectronic applications. The electrical and optical properties are depended on the structural and surface morphology of CCTO thin film. This project aims to study effect of deposition temperature and type of substrates (ITO, FTO and glass) on the structural, surface morphology and optical properties of sputtered CCTO thin film. Firstly, CCTO thin films were deposited on different type of substrates (ITO, FTO and glass) at deposition temperatures of 100, 150, 200 and 250 °C by RF magnetron sputtering in Argon atmosphere. The structural, surface morphology and optical properties of the deposited CCTO thin film have been studied by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX) and ultraviolet-visible (UV-vis) spectrophotometer. XRD analysis showed CCTO thin films on ITO and FTO substrates have a highest intensity peak at (022) while CCTO thin film on glass substrates showed almost amorphous in structure. Besides, crystallinity of CCTO thin film on ITO and FTO increased with increase of deposition temperature. FESEM only able to reveal the crystallite size of CCTO thin film on ITO substrates and the crystallite size is increased with increase of deposition temperature. AFM analysis showed the blank FTO substrates with 6 times rougher than blank ITO and glass substrates caused the CCTO thin film on it have significant higher in surface roughness and pore size. This is due to CCTO thin film are highly dependent on the surface feature of substrate. Increase of deposition temperature have increased the surface roughness (Ra) and pore size respectively. In addition, Tauc plot method was used to estimate the optical energy band gap of the deposited CCTO thin film. Optical energy band gap of the CCTO were decreased from 3.50 eV to 3.14 eV (ITO), 3.52 eV to 3.10 eV (FTO) and 3.58 eV to 3.10 eV (glass) as deposition temperature increased from 100 °C to 250 °C. Therefore, favourable CCTO thin film properties can be possibly obtained for particular application by controlling deposition temperature and using different type of substrates

Theory and Simulation of ZrO2/SrTiO3 Multilayer Structures

High ionic conductivity of nano-layered heteroepitaxial oxide systems reported in recent literature has been attributed to high interfacial mobility of anions, although this interpretation has remained controversial. My work aims to understand the mechanism of ionic motion in such heterostructures by simulating the atomic structure at the interfaces, specifically for a multilayer system of Y2O3-stabilised ZrO2 (YSZ) and SrTiO3. By probing the energy landscape with a genetic algorithm in which the interatomic potentials were modelled with simple classical pair potentials, possible low energy lattice structures of pure ZrO2 layers in perfectly coherent epitaxy with SrTiO3 layers were explored. These configurations were identified and their energies were evaluated with more accuracy based on density functional theory (DFT). My expectation, based on indirect evidence from published high-resolution transmission electron microscopy, was that the ZrO2 layer has an epitaxial fluorite structure. However, I found that the fluorite ZrO2 structure is completely unstable as an epitaxial layer between layers of SrTiO3. Instead, anatase-, columbite-, rutile- and pyrite-like ZrO2 phases were found to be more stable structures in epitaxy, with the anatase-like epitaxy being the most stable configuration over a wide range of chemical potential of the components. Even with inclusion of Y2O3 doping, the fluorite epitaxial structure could not be stabilised. The genetic algorithm suggested a completely different phase stabilised by the presence of vacancies, whose cation lattice might resemble that of a fluorite or a perovskite. DFT calculations predicted this structure to be even more stable than an anatase YSZ/SrTiO3 structure. Molecular dynamics (MD) simulations of this configuration revealed some relatively low barriers for lateral anion diffusion; nevertheless, the activation energy for anion diffusion within the YSZ layer was predicted to be much higher than that of bulk YSZ. The results of this work therefore indicate that ionic conductivity of an ultra thin YSZ film in epitaxy with SrTiO3 would be suppressed, in contradiction to some of the literature

5D building information modelling – a practicability review

Quality, time and cost are the three most important elements in any construction project. Building information that comes timely and accurately in multiple dimensions will facilitate a refined decision making process which can improve the construction quality, time and cost. 5 dimensional Building Information Modelling or 5D BIM is an emerging trend in the construction industry that integrates all the major information starting from the initial design to the final construction stage. After that, the integrated information is arranged and communicated through Virtual Design and Construction (VDC). This research is to gauge the practicability of 5D BIM with an action research type pilot study by the means of hands-on modelling of a conceptual bungalow design based on one of the most popular BIM tools. A bungalow is selected as a study subject to simulate the major stages of 5D BIM digital workflow. The whole process starts with developing drawings (2D) into digital model (3D), and is followed by the incorporation of time (4D) and cost (5D). Observations are focused on the major factors that will affect the practicability of 5D BIM, including the modelling effort, inter-operability, information output and limitations. This research concludes that 5D BIM certainly has high level practicability which further differentiates BIM from Computer Aided Design (CAD). The integration of information not only enhanced the efficiency and accuracy of process in all stages, but also enabled decision makers to have a sophisticated interpretation of information which is almost impossible with the conventional 2D CAD workflow. Although it is possible to incorporate more than 5 dimensions of information, it is foreseeable that excessive information may escalate the complexity unfavourably for BIM implementation. 5D BIM has achieved a significant level of practicability; further research should be conducted to streamline implementation. Once 5D BIM is matured and widely accepted, it is foreseeable that additional BIM dimensions of information will be incorporated into sophisticated digital building model to achieve specific project outcomes

Necessity and challenges of nature conservation

Nature conservation is the preservation of resources that are produced naturally for example wild animals and plants, ecosystem and biodiversity especially from the effects of human activities for example exploitation and industrialization. Nature conservation is necessary in protecting the biodiversity for example to prevent animal species from endangering or extinct, protection for natural ecosystem and human’s freshwater sources for drinking purposes. Moreover, nature conservation is important in maintaining a long-life natural environment as well as an environment that is sustainable towards development. However, nature conservation is not an easy task as it requires a lot of manpower as well as money. Therefore, nature conservation is challenging as well. The challenges of nature conservation include human’s overpopulation, global warming and overharvesting. Human’s overpopulation is one of the most challenging factors that influences the practice of nature conservation