چكيده به لاتين
Silicon nanomaterials are being increasingly used for optoelectronic devices as well as biomedical applications due to excellent biocompatibility, unique electronic, optical and mechanical properties. In recent years, observation of size tunable visible to near IR emissions from quantum confined silicon nanoparticles (Si NPs) has stimulated worldwide interest in obtaining efficient nanoparticle Si-based light emitting devices for low cost applications. Thus, it is of great scientific effort to study the optical properties of Si NPs for potential application in optoelectronics and biological fields. Especially, control of oxide related surface characteristics is one of the main remaining challenges having important effects on the optical properties of Si NPs, which should be investigated further.
In this thesis, our goal is to analyse the role of effective parameters in the laser ablation process in liquids to produce colloidal Si NPs with different size distributions and surface characteristics which can result in different photoluminescence (PL) properties. For this purpose, the colloidal Si NPs in water and ethanol have been prepared by the nanosecond pulsed laser ablation processes under different experimental conditions. As a main change in the laser parameters, the ablation processing has been performed by irradiating the silicon wafer with collinear double laser beams consisting of a low intensity pre-pulse and second main pulse delayed for some specific times i.e. 5, 10, 15 and 20 ns. Our results indicate that the double-pulse laser ablation (DPLA) of silicon leads to a higher rate of production of colloidal Si NPs with size distributions less than 10 nm and different surface characteristics compared to the more common single-pulse processing under the same experimental conditions. For colloidal Si NPs in water, the experimental results show that the DPLA can synthesize Si NP colloids with greater PL intensities at the visible spectral range of 550-650 nm through the direct oxide related surface engineering of the nanoparticles. A detailed analysis of the PL emissions using the stochastic quantum confinement model explained that there is a competition between the mechanisms of quantum confinement and surface effects in the emission properties of Si NPs. For the colloidal Si NPs in ethanol prepared by the DPLA at diffrrent delay times, luminescence spectra with similar PL behaviors but different intensities have been observed at the spectral range of 300–600 nm. A detailed analysis of the PL emissions explained that the excitation-dependent luminescence spectra of the colloids are associated with the Raman scattering of pure ethanol which is enhanced due to the presence of Si NPs with different hydroxyl related surface characteristics. In this case, with drying out ethanol and preparation of the Si NP thin films, PL spectra with emission maxima at the wavelength range of the 350-550 nm have been observed due to the quantum confinement effect.