Photoluminescence properties of Si nanocrystals embedded in SiO2 matrix

Seyhan, Ayşe
This thesis examines the luminescence properties of nanoscale silicon (Si) by using spectroscopic techniques. Since the development of new optical devices requires understanding light emission mechanism optical spectroscopy has become more important tool in the analysis of these structures. In this thesis, Si nanocrystals embedded in SiO2 matrix will be studied. Photoluminescence (PL) and Time-resolved photoluminescence spectroscopy (TRPL) have been used to detect the light emission in UV-Vis-NIR range. Experiments have been performed in the temperature range 10-300 K. PL is sensitive to impurities and defects that affect materials quality and device performance. In this context, the role of defects in limiting the luminescence of Si nanocrystals and the removal of these defects by hydrogen passivation has been investigated. v TRPL was employed to determine the time evolution of photoluminescence as function of temperature. The decay time of the PL spectra was determined by a stretched exponential function and perfectly fitted to an expression based on three excitonic levels. Carrier lifetimes associated with these three levels were determined and compared with literature. Additionally, temporal variation of PL from free-standing Si nanoparticles is studied under a strong laser illumination. The observed bleaching behavior (time dependent emission intensity), which is reversible, have discussed in terms of exciton trapping at the interface between nanocrystal and the surrounding oxide layer. The results of this thesis will provide new insight on the understanding of light emission mechanism of Si nanocrytals.


Density functional theory investigation of TiO2 anatase nanosheets
Sayın, Ceren Sibel; Toffoli, Hande; Department of Physics (2009)
In this thesis, the electronic properties of nanosheets derived from TiO2 anatase structure which acts as a photocatalyst, are investigated using the density functional theory. We examine bulk constrained properties of the nanosheets derived from the (001) surface and obtain their optimized geometries. We investigate properties of lepidocrocite-type TiO2 nanosheets and nanotubes of different sizes formed by rolling the lepidocrocite nanosheets. We show that the stability and the band gaps of the considered ...
Imaging solar cells using terahertz waves
Kayra, Seda; Altan, Hakan; Department of Physics (2011)
In this thesis, Terahertz Time-Domain spectroscopy (THz-TDS) was used in order to measure the electrical properties of silicon solar cells. The advantage of THz-TDS is that it allows us to measure the electrical properties without electrical contacts. In order to perform these measurements, a reflection based system was constructed and the changes in the peak amplitude in the time-domain under a, 450mW 808 nm continuous wave laser source were measured. The solar cell that was used in this thesis was manufac...
Adsorption of gold atoms on anatase TiO2 (100)-1x1 surface
Vural, Kıvılcım Başak; Ellialtıoğlu, Süleyman Şinasi; Department of Physics (2009)
In this work the electronic and structural properties of anatase TiO2 (100) surface and gold adsorption have been investigated by using the first-principles calculations based on density functional theory (DFT). TiO2 is a wide band-gap material and to this effects it finds numerous applications in technology such as, cleaning of water, self-cleaning, coating, solar cells and so on. Primarily, the relation between the surface energy of the anatase (100)-1x1 phase and the TiO2-layers is examined. After an app...
The controlled drift detector as an x-ray imaging device for diffraction enhanced imaging
Özkan, Çiğdem; Serin, Meltem; Department of Physics (2009)
Diffraction Enhanced Imaging (DEI) is an X-ray imaging technique providing specific information about the molecular structure of a tissue by means of coherently scattered photons. A Controlled Drift Detector (CDD) is a novel 2D silicon imager developed to be used in X-ray imaging techniques. In this work a final (complete and detailed) analysis of DEI data taken with the CDD in the ELETTRA synchrotron light source facility in Trieste (Italy) in 2005, is presented and the applicability of both this new techn...
Photoluminescence spectroscopy in the study of growth of CdSxSe1-x nanocrystals in glass
Allahverdi, C; Yukselici, MH; Turan, Raşit; Seyhan, A (IOP Publishing, 2004-08-01)
Growth of CdS0.08Se0.92 nanocrystals embedded in glass is studied through the combinative analysis of optical absorption and photoluminescence (PL) spectroscopy at room temperature. The quantum confinement effect is observed in these structures. Average nanocrystal radii are found to be in the range of 2.3-4.2 nm with the help of a quantized state effective mass theory. Photoluminescence spectra are studied by means of the model of Ravindran et al (1999 Nanostruct. Mater. 11 603). The difference between the...
Citation Formats
A. Seyhan, “Photoluminescence properties of Si nanocrystals embedded in SiO2 matrix,” Ph.D. - Doctoral Program, Middle East Technical University, 2010.