Electron microscopic imaging of an ion beam mixed SiO 2/Si interface correlated with photo- and cathodoluminescence

Energy filtered transmission electron microscopy (EFTEM), scanning transmission electron microscopy (STEM) imaging, and electron energy loss spectroscopy (EELS) of a thin 28 nm SiO 2 layer on Si substrate implanted by Si + ions with an energy of 12 keV are reported. The maximum concentration of implanted Si + ions is located near the SiO 2-Si interface region leading there to an ion beam mixed gradual SiO X (2 ≥ x > 0) buffer region, which is even extended into the Si substrate by atomic collisions (knocking-off and knocking-on processes) during ion implantation. Thus, the width of this SiO X buffer layer amounts to about 30 nm extended from 10 to 40 nm depth. The SiO X profile is demonstrated by the above given electron microscopic and spectroscopic methods. Thermal annealing leads to partial phase separation from SiO X1 to SiO X2 with x 2 > x 1 and silicon precipitates (partially nc-Si) changing the photo- (PL) and cathodoluminescence (CL) spectra especially in the near IR-region, probably, due to the formation of Si nanoclusters and associated quantum confinement effects. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Nonlinear optical properties of nano structures

Nonlinear optical properties of nanoscale semiconductors had been a topic of intense research in recent years in attempts to realize all-optical communication systems. These semiconductor nanoclusters, in the range of 1-100nm are hosted in a dielectric material and are considered as a particular example of Conditional Artificial Dielectric (CAD). It has been reported that the dielectric properties of such materials will be greatly changed by light intensity. Two main paths to realize nano semiconductor clusters are reported in this dissertation. The Pulsed Laser Deposition (PLD) technique is first described. Here we were investigating the effect of surface modification of nano silicon clusters by incorporating various gases (142, Ar, He) during the deposition process. Linear and nonlinear optical properties of these passivated Si nanoclusters were obtained. Ion Implantation is another successful method to obtain nano semiconductor clusters. In order to ftirther enhance the nonlinear optical properties of these clusters, we incorporated them in optically confining structures, such as three-dimensional photonic crystals. The latter part of the dissertation is devoted to three-dimensional periodic structures made of silica spheres (opal) which were implanted with Si, Ge and Er. Linear and nonlinear optical properties of these novel materials have been measured and assessed

Optical and surface enhanced Raman scattering properties of Au nanoparticles embedded in and located on a carbonaceous matrix

Au nanoparticles (NPs) on the surface and embedded in a matrix have been the subject of studies dealing with a variety of spectroscopic and sensing applications. Here, we report on low energy Ar ion induced evolution of the morphology of a thin Au film on a polyethylene terephthalate (PET) substrate along with thermodynamic interpretations, and corresponding unique surface plasmon resonance (SPR) and photoluminescence (PL) properties. These properties are linked to the variation of surface nanostructures and the surface enhanced Raman scattering (SERS) effect of methyl orange (MO) dye molecules adsorbed on the surface. Ion induced thermal spike and sputtering resulted in dewetting of the film with subsequent formation of spherical NPs. This was followed by embedding of the NPs in the modified PET due to the thermodynamic driving forces involved. The surface and interface morphologies were studied using atomic force microscopy and cross-sectional transmission electron microscopy. X-ray photoelectron spectroscopy was used to study the chemical changes in the system upon irradiation. The optical properties were studied by diffuse reflectance UV-Vis spectroscopy and PL using a 325 nm He-Cd laser. The red shift of the SPR absorption and the blue shift of the PL emission have been correlated with the surface morphology. The blue PL emission bands at around 3.0 eV are in good agreement with the literature with respect to the morphological changes and the blue shift is attributed to compressive strain on the embedded Au NPs. Enhancement of the SERS signals is observed and found to be correlated with the SPR response of the Au nanostructures. The SERS analyses indicate that MO molecules may be adsorbed with different orientations on these surfaces i.e. Au NPs located on the surface or embedded in the modified PET. These polymeric substrates modified by NPs can have a potential application in solid-state light emitting devices and can be applied in SERS based sensors for the detection of organic compounds

Properties of Si quantum dots

The fundamental properties of matter in confined particles change dramatically due to quantum effects. In this work, we have explored the optical properties of silicon quantum dots (Si-QDs) embedded in Si3N4; and the role of crystallinity on the optical properties and formation of Si-QDs in Al2O3. This work examined the role of (1) annealing temperature and the composition of the film, (2) Al doping of the host Si3N4 film, (3) doping Si-QDs and (4) Al and P passivation of Si-QDs on the PL intensity of Si-QDs embedded in Si3N4. Photoluminescence (PL), time-resolved photoluminescence (TRPL), X-ray absorption near edge spectroscopy (XANES), X-ray excited optical luminescence (XEOL), elastic recoil detection (ERD), positron annihilation spectroscopy (PAS) and Fourier-Transform infrared (FTIR) spectroscopy measurements were used for characterization. We have found that the luminescence originated from both quantum confinement effects and defects. H, Al and P passivation was found to increase the PL intensity of Si-QDs in Si3N4 while impurities such as Cr3+ and oxygen vacancies dominate the PL spectra for Si-QDs in Al2O3

Investigating the Influence of Interface and Vacancy Defects on the Growth of Silicon Quantum Dots in SiO2

The effects of interface and vacancy defects on silicon quantum dot (Si-QD) growth are investigated using measurements of Time Resolved Photoluminescence (TRPL), Photoluminescence (PL) Spectroscopy and Electron Paramagnetic Resonance (EPR). Thermally grown SiO2 thin films (280nm) were irradiated with high energy (400keV – 1MeV) silicon ions in order to introduce defects into the Si-QD growth layer of SiO2. A noticeable increase in PL emission intensity is seen with the highest energy pre-implanted sample over a single implant sample. TRPL results show increased radiative lifetimes for the lower energy (400keV) pre-implant while little or no difference is seen in TRPL results between the single implant and the higher energy implanted samples. The origin of increased PL emission intensity and a trend towards shorter radiative lifetimes with increased implant energy in TRPL measurements are believed to be due to defect-mediated Si-QD growth in high energy pre-implanted samples