الفهرس 
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Abstract
A lot of attention has recently been paid to semiconductor nanowires (SCNWs) due to their crucial role in physiochemical science and their high potential for important applications in advanced devices such as solar cells, light-emitting diodes, transistors, and bio / chemical sensors. Vertical-aligned silicon nanowires SiNWs platform is considered a strong candidate for advanced devices due to their high volume-to-surface ratio as well as the high aspect ratio resulting from the vertical structure. The CMOS functionality of such a system allows for cheap commercial production of nano-photonic integrated circuits. Nanowire diameter is typically on the order of several nanometers and is equivalent to the length of Debye, which often results in a much greater resistance than its thin film. In this thesis, we design a vertically aligned SiNWs gas sensor optimized to detect carbon monoxide (CO) and ammonia (NH3) gas at the mid-infrared (MIR) range. SiNWs with a diameter of only 200 nanometers are grown on Si wafers. According to Liao et al, thin nanotubes have significantly better sensing efficiency than thick nanotubes when detecting C2H5OH and H2S (100 ppm) in water. Besides, (MIR) gas sensing is very useful and user-friendly; as gasses are detected directly as they pass through the active sensing area of the sensor without human interaction with hazardous gases. Finite difference time-domain (FDTD) simulations are conducted to check the results and to hold a correlation between the FDTD and the experimental results. This work aims to construct and characterize an optical gas sensor, based on a layer of silicon nanowires coated with a metal oxide (e.g: TiO2, RGO) as the sensing material. The metal oxide will be utilized to demonstrate a high-selectivity for the detection of different harmful gases. The optical source will be a laser in the infrared spectral range (1.5-3 μm). This proto-type design is expected to enable the detection and quantification of various atmospheric gases simultaneously in the same air mass. In this work, we demonstrate a laser-based method for the direct reduction of graphene oxide (GO) thin films at room temperature. Raman spectroscopy and SEM were used to characterize the structure and surface morphology of the synthesized samples, respectively. The characteristic broad peaks at 1360 cm−1 and 1608 cm−1, corresponding to the reduced GO lattice bands D and G, respectively were observed in the Raman spectra of all samples, and their relative intensities are found to be influenced by the laser power and the exposure time. To our knowledge the lowest irradiation time and laser power recorded till now was 5 min. and 20 mW respectively, to get RGO film, so we focus on two parameters in this study: I)irradiation time, and II) laser power, and their influence on the quality of the thin film. In this thesis, we will discuss the latest results on the development and use of an easy and fast laser scripted reduced graphene oxide (LSRG) technique that is compatible with large-area flexible opto-electronics. This procedure does not require the use of expensive equipment, chemicals or high-temperature annealing devices. The combination of these unique characteristics associated with the proposed method suggests that it may be used for the processing of RGO thin films for large-volume applications in plastic electronics.