GAS SENSOR APPLICATIONS WITH PHOTONIC CRYSTAL FIBER AND CARBON DIOXIDE SENSOR DESIGN
It’s very important to control and monitor gases that are produced by industrial applications in different values and kinds because they can cause environmental pollution and health problems. Photonic Crystal Fiber (PCF), which is a different kind of optical fiber, is a new alternative for gas sensors due to their small sample volumes, low transmission losses and high flexibility properties. PCF’s are silica-glass fibers, made by periodic sequence of hollows along the fiber. By filling these hollows with optical liquids or gases very sensitive sensors can be made. In this project, we aimed to design a sensitive sensor by filling the hollows with proper gases and liquids in the solid core PCF. For these applications ethanol, methanol, toluene vapors and carbon dioxide was used. And to observe carbon dioxide’s effects ionic liquid (EMIMBF4), which carbon dioxide can dissolve in, was filled then the experiments were repeated. It was observed that the transmission of light in PCF changed depending on the refractive index of the gas that was filled. With this change, it was understood that there were another gas besides the usual containments of air. Our system could measure the absorbtion peak of toluen so it can be used as a toluen dedector and when ionic liquid filled the fiber, two steps that occur in the spectra of corbon dioxide so it can also be used as a carbon dioxide dedector. The system was customized as a carbon doxide sensor in a cost-efficient and portable way. Our system can be specialized and easiliy used with right light source, which is efficient to see the absorbtion peaks, and proper liquids to dedect intended gas. Making a carbon dioxide sensor by filling PCF with ionic liquid was never attempted before. Also the lack of carbon dioxide sensor studies supports the originality of our project. That’s why we think our project will contribute very importancies to the existing literature.
Determining Crystal Orientation via Reflection High Energy Electron Diffraction
1 Purpose of the Research Nanocrystal thin films exhibit many useful properties, including electrochromicity and superconductivity. When synthesised via Molecular Beam Epitaxy (MBE), selection of substrate, specifically knowledge of crystal orientation, is critical. Reflection High Energy Electron Diffraction (RHEED) is an in situ crystal characterisation method highly compatible with MBE. This study explores a new method of RHEED analysis to determine crystal orientation. 2 Procedure/Theoretical Framework RHEED characterization is the incidence of a beam of high-energy electrons at a low angle with respect to the sample surface. Electrons diffract, and interfere to form patterns on the detector. Traditionally, studies of RHEED analyse one static image as a representation of the surface structure, or observations of RHEED patterns over time. The approach to RHEED analysis in this study exploits changes in RHEED patterns given a rotating substrate. Having specific rotational symmetries along different axes, crystal structures can be differentiated by determining rotational symmetry through RHEED. Electrons scatter upon incidence with crystal planes within the crystal to form Kikuchi lines on the RHEED detector (Fig. 2). The orientation of crystal with respect to incident electron beam affects the Kikuchi line patterns. If the crystal is rotated, crystal planes change orientation, and electrons would diffract from crystal planes in different directions. As such, as the crystal is rotated, the Kikuchi lines move. When the degree of rotation of the crystal corresponds to the rotational symmetry of the crystal (Fig. 1), the Kikuchi lines return to their original position. As crystals with different crystal plane orientations exhibit different orders of symmetries, analyzing the Kikuchi line patterns of the crystal at different degrees of rotation can reveal the rotational symmetry and consequently crystal plane orientation of a crystal. 3 Data/Experimental Testing In order to assess the practical viability of the proposed method, experiments were conducted on SrTiO3 (001), (110), and (111). SrTiO3 exists as a typical perovskite structure (Fig. 3), often used in the synthesis of superconductors via MBE. 3.1 Methodology RHEED images of each sample were taken at 0◦, 60◦, 90◦ and 180◦. Curves were fit to each Kikuchi line observed in the image (Fig. 4). These Kikuchi line approximations are compared by superimposing the curves traced and qualitatively assessing the degree of similarity between the Kikuchi lines of 2 images, to verify the order of symmetry and crystal orientation of the crystal. In the images of the superimposed Kikuchi lines illustrated in Fig. 5, there is similarity between the Kikuchi lines when only when the sample has been rotated by an angle corresponding its degree of symmetry. 4 Conclusions This study offers a method to determine the crystal orientation of thin film through determining the degree of rotational symmetry of the sample, by observation of Kikuchi lines in the RHEED pattern as the sample is rotated. Experimental data was analyzed qualitatively to verify the viability of this theoretical method in practice. This method could be extended to analyze the symmetry of other crystal structures. As it does not require information on the machine settings or usage of complex functions to produce a reliable output, this method is fast and straightforward, opening doors to more streamlined RHEED analysis.