چكيده به لاتين
In recent decades, laser ablation has been considered by researchers. The reason for the importance of the laser processor can be its many applications. Among these applications, we can mention the machining, the coating layer and the production of nanoparticles.
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 analysis 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 have been prepared by the Nd: YAG nanosecond pulsed laser ablation processes under different experimental conditions. As a major change in the parameters affecting the materialization process, these ablation processes are carried out in the presence of an external electrical DC field.
The sample is Silicon (99.99% purity, p-type), which is exposed to radiation from Nd: YAG laser beam with pulse duration of 10 ns and 10Hz repetition rate. Furthermore, in each case, the target was irradiated by laser beam with 21000 pulses for a total time of 35min. The radiation was carried out at two conditions, with and without the electric field perpendicular to the laser beam path. The optical absorption of the SiNP colloids was measured by a UV-visible-near infrared (UV–vis–NIR) spectrophotometer (Perkin-Elmer, lamda 25). The photoluminescence measurements of the SiNP colloidal solutions were performed at room temperature on a fluorophotometer (Varian Cary Eclipse Fluorescence Spectrophotometer). The optical properties of the colloids were investigated just after laser ablation process. Field Emission Scanning Electron Microscopy (FESEM) together with image processing technique were used to evaluate the results. The results show that the external electric field can significantly influence the concentration of nanoparticles in water. The experimental results show that the ablation process in the presence of an external electric field produces colloids with relatively intense radiation in the indigo - violet region of the visible spectrum.
