الفهرس 
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Abstract
Quantum dot nanocrystalline silicon (Si-nc) is recently attracting the interest of researchers in order to upgrade solar cells. New structural forms are still needed to improve its optoelectronic properties. Herewith, the fabrication of Si-nc from two types of silicon namely; p-type Si and pntype Si wafers is reported. In this study Si nanocrystals were fabricated by Liquid Phase Pulsed Laser Ablation (LP-PLA) of silicon wafers immersed in double distilled water or ethyl alcohol. In this technique short duration laser pulses were focused onto the surface of the solid target embedded inside the liquid. Such focused laser provides high power beam that instantaneously ablate the solid into a plume of the target material under extreme conditions of temperature and pressure. The species in the plume, as atoms, ions, and clusters, traveling with high kinetic energy, under such typical non-equilibrium conditions, are confined and vigorously interact within the high density domain providing new structures of the ablated solid in the form of nano-particles. One can clearly indicate that LP-PLA has become a successful material fabrication technique,allowing versatile design through choosing suitable solid targets and confining liquids. LP-PLA gained intensive attention for its ability to form more complex, better size distribution nanostructures and offered a way to study the dynamical processes among laser-solid-liquid binteractions. The technique of LP-PLA has many distinct advantages that could be summarized as: Chemically simple and clean synthesis of products without poisonous reagents; ii. Low cost experimental setup with easily controlled parameters; iii. Extreme confined conditions due to the focused nanosecond laser pulse that favoring formation of new structure. In the present study, p-type and pn-type of mono-crystalline CZ-silicon wafers were used as targets immersed in 3 ml of either distilled water or ethyl alcohol (95%). Two nanosecond pulsed lasers were employed to irradiate the Si samples, namely UV Nitrogen laser and Nd:YAG laser. The UV Nitrogen laser provides pulses of wavelength 𝜆 = 332 ± 2 nm, pulse duration 𝜏 = 15 ± 2 nanosecond and focused power density up to 25 ± 5 GW/cm2. The Nd:YAG laser deliver 7 ± 1 nanosecond pulses of wavelengths 𝜆 = 1064 ± 2 nm and second harmonic pulses of wavelength λ =532 nm, repetition rate of 10 Hz and focused power densities up to 48.985 ± 0.005 GW/cm 2. characterizations of the deposited Si Nanocrystals were done by Transmission Electron Microscopy namely, High Resolution Transmission Electron Microscopy, selected Area Electron Diffraction measurements to identify the crystalline structure of the formed Nano-Particles. Scanning Electron Microscope was used to study the morphology of the Si samples after the LPPLA process. The technique of Energy Dispersive X-rays was applied to determine the elemental composition of the Si samples accuracy. The optical properties were determined by measuring the absorption spectra for the formed Si-nc by UV-visible spectrometer and consequently also the transmission spectra were determined. Photoluminescence spectroscopy using Ar laser lines for excitation were also measured, providing the same emission wavelength. The morphology results were analyzed for the structural properties Si-nc samples concerning Nanocrystal size, shape, size distribution, crystal type and orientation. The Optical Properties were also speculated and most important indicated absorption spectrum blue shift for the pn-Si-nc prepared by LP-PLA method in water using the UV Nitrogen laser.It was found that the particle density and the nanocrystals sizes are dependent to the laser fluencies while the Si-nc structures kept perfect crystalline structure [111] irrespective of the laser properties and fluencies. It was also noticed that the liquid type affected the mean size of Si nanoparticles. The optical absorption and optical luminescence spectra were found to change a function in the laser beam properties. The LP type affect the formed nano-Si properties that will be speculated in details in Chapter III.