Browsing by Subject "Metals."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Open Access Plasmonics from metal nanoparticles for solar cell applications(Bilkent University, 2013) Günendi, Mehmet CanIn today’s economy, need for development in energy is essential. Solar energy is safe, and at the same time is one of the cleanest, cheapest choices of energy alternative to fossil fuels. In this perspective, using the sun light effectively is in fundamental importance. One of the problems, because of the indirect band gap of the material Si, is small energy conversion ratios of various solar cell structures and limited absorption of red light. Because of the material properties, Si cells cannot absorb red light, which contributes great amount of the sun light. One of the recent developed techniques to use red light is using metal nanoparticles (MNP) embedded in a semiconductor medium as sub-wavelength antennas or MNP scatterers, hence increasing the effective path length of light in the cell. Absorption and scattering are mostly in plasmon resonances. Shifting the plasmon resonance peaks is possible by changing various parameters of the system like the size of the MNPs. In this work, Finite-Difference Time-Domain (FDTD) method is used to analyze various systems worked. Mainly the MEEP package, developed at MIT, is used to simulate systems and other codes, related to analytical work, have also used to compare results. The plasmon resonances of various sizes of Ag MNPs embedded in different mediums at different positions are analyzed. Critical parameters like particle size, shape, dielectric medium, film thickness are discussed for improved solar cell applications.Item Open Access Synthesization of noble metal nanoparticles by pulsed laser ablation method in liquids and thin film applications(Bilkent University, 2012) Vural, Hüseyin AvniPulsed Laser Ablation in Liquid (PLAL) is promising, alternative, easy, fast and free of agent method for synthesization of nanoparticles (NPs). Various kinds of NPs can be synthesized easily by PLAL, such as base metals, noble metals, semiconductors, nanoalloys, magnetic and core–shell nanostructures. Additionally, crystallized NPs can be easily obtained in one-step procedure by PLAL without subsequent heat-treatments. Synthesization of gold (Au), silver (Ag) and platinum (Pt) NPs with PLAL using Nd: YLF laser (Q-Switched Laser, 527 nm wavelength, 16 W average power, 110 ns pulse duration, and 16 mJ pulse energy for 1 kHz) in different liquid environments is reported. Firstly, Ag, Au and Pt NPs have been synthesized with pulsed Nd: YLF laser in deionized water. Secondly, these NPs have been synthesized in methanol under similar conditions. Colloidal NP solutions are then characterized with Transmission Electron Microscopy, Scanning Electron Microscopy, X-Ray Photoelectron Spectrophotometer, X-Ray Diffractometer and UV-Vis Photospectrometer analysis techniques.In the second part, applications of noble metal nanoparticles have been investigated. Firstly, Au and Ag NPs have been synthesized in Polyvinylpyrolidone solution in order to prepare nanofibrous composites. The Au and Ag NPs embedded in nanofibrous composites then characterized with UV-Vis Photospectrometer and Transmission Electron Microscopy. In addition, AuNPs have been synthesized with varying energies of laser (9,2 mJ, 12 mJ and 16 mJ for 1kHz) in order to understand the role of laser energy on PLAL. Finally, thin-film applications also presented: Pulsed Laser Deposition by PLAL and simple spin-coating deposition with AuNPs synthesized in methanol.