Master Theses & Projects (FEAS)

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Browsing Master Theses & Projects (FEAS) by Subject "Ablation"

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    Investigation of selective optical properties of Si/SiO2 nanostructures generated by pulsed laser ablation as-deposited and post-treated
    (2020-05-01) Moghareh Abed, Meisam; Kiani, Amirkianoosh
    Silicon and its derivatives like SiO2 are essential materials for industrial applications such as semiconductors, optoelectronics, and telecommunication. Optical properties of a large group of silicon/silica nanofibrous thin films are studied. A picosecond pulse laser was employed for indirect deposition of ablated silicon on glass substrates. Prominent parameters such as laser power, repetition rate, pulse duration, and scanning speed were changed to vary the structural and compositional properties of synthesized nanofibrous thin films. Transmission and specular reflection measurements along with material characterization techniques, Raman, FTIR XPS, and XRD were employed for better interpretation of the results. Three studies are included in this research. First, exploration of the effect of manufacturing parameters as frequency, power, pulse duration and scanning speed on optical properties of samples generated. By and large, an increase in the values for repetition rate and scanning speed produces a corresponding increase in optical data intensity, while an increase in power and pulse duration leads to a drop in the spectra. The results show that the degree of oxidation and the inherent porous structure is driving the light interaction in thin samples, as indicated by the changes in intensity or spectrum shape. The second study looks into the influence of post heat treatment on the optical properties of samples prepared by frequency variation. Samples were heated up to 400°C and 1000°C and cooled down to room temperature for measurements. The inverse relationship of annealing temperatures on Vis-range reflection spectra to increase and decrease the intensity was confirmed. These improvements are attributed to crystalline and amorphous lattice structures and elemental composition. The third study focuses on the emission of a heated sample, to 200°C and 350°C while data is collected at the elevated temperatures. Results show the emission amplifying effect of nanofibrous structure and its density as well as oxidation level at NIR (Near Infra-Red) range reflection.