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Hu Hailong Thesis-Photoluminescence of Metallic ..

There is an existing concept to modify this method by using photoluminescence instead of electroluminescence.

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Porous silicon photoluminescence in the presence of gaseous ..

In sections three and four, experimental methods and results are presented for the systems described in the previous chapters. The apparatus is described for the measurement of transmission, absorptivity, photoluminescence, photo-product spectra and current-voltage characteristics. The photoluminescence of silicon, Ruthenium dye cells and photosynthesis is found to be consistent with predictions based on the optical absorptivity and induced photocurrent, or photo-product spectra. A novel concept introduced by this thesis is the use of the photo-product spectra to estimate the emissivity and absorptivity used in the Generalized Planck equation. Solar conversion efficiency predictions based on this equation are applied to these three conversion systems and are found to be consistent with the experimental performance. Specifically, the maximum allowed chemical potentials for the silicon solar cell are found to be 0.6-0.65 eV, while those for photosynthesis and the dye sensitized cell are found to be near 1.3 eV. The porous silicon solar cell and phototube photodiode results highlight the finding that the chemical potentials predicted from the analysis of photoluminescence are generally much higher than for the actual device. This is due to the converter configuration and kinetic properties such as resistivity. In the case of the vacuum photodiode, the configuration of the converter allows for heat and light to simultaneously be converted to work. Although this has been predicted using photoluminescence based models, this thesis presents the first clear demonstration of a synergistic effect in a "hot" electron device. In hopes of utilizing this effect in a photochemical system, experiments were conducted using the same metal oxide (Ag2O) as was used as the phototube photodiode absorber. It is found, however, that although the oxide powder reacts at low temperatures, the action of light does not conclusively change the reaction thermodynamics or kinetics.

Thesis/Dissertation: Photoluminescence and Raman spectroscopy of photoelectrochemical ..

Silicon is an indirect band gap material and therefore its luminescent properties are poor. For very small dimensions however, as in a nanocrystal of a few nano meter diameter, luminescence becomes strong and blue shifted due quantum confinement. The topic of this thesis is Photoluminescence spectroscopy (PL) and the spatial and size distribution of silicon nanocrystals. A main object was to correlate size with their light emitting properties which would be subject to quantum confinement. The nanocrystals were produced by ion implantation of 28Si+ ions in thermally grown silicon dioxide which was followed by annealing at 1100◦C in nitrogen atmosphere. As a first approach three different oversaturations of silicon atoms in SiO2 were investigated. The size of the nanocrystals and there distance to each other were characterised with an atomic force microscope (AFM). The effects of the different oversaturations were studied with AFM as well as with PL. Additionally, the samples were etched with hydro fluoric acid in order to remove the oxide matrix such that individual

The Size Distribution and Photoluminescence Spectroscopy ..

The photoluminescence spectra are collected by a micro-PL system from single isolated Au nanostructures fabricated by electron-beam lithography (EBL).

With this thesis, the details of the measurement concept are to be developed, the photoluminescence based inspection method shall be implemented into the inspection setup and the inspection results of both methods shall be correlated.

This thesis reports the behavior of electrons and holes in photoexcited TiO2 powder under high vacuum conditions. We studied the effect of UV irradiation and different adsorbates, electron acceptors and electron donor molecules, on the perturbation of the band structure of TiO2. The electron-hole recombination rate in electronically excited TiO2 is influenced by band bending at the TiO2 surface and was studied by photoluminescence (PL) spectroscopy. In addition, we also employed infrared spectroscopy to qualitatively estimate the surface condition and to quantitatively estimate the amount of adsorbates on the surface.
It was found that continuous UV irradiation at 3.88 eV on an n-type TiO2 surface enhances the photoluminescence emission at ~529 nm (2.34 eV) as UV-induced surface potential causes upward bent bands to flatten. In addition, the adsorption of electron donor molecules such as CO and NH3 caused downward band bending in TiO2 and upon their adsorption/desorption, the PL intensity responded reversibly, showing reversible band bending. On the other hand, adsorption of an electron acceptor molecule such as O2 induces upward band bending and does not respond completely reversibly upon desorption.
We measured the kinetics of transport of adsorbed molecules to and from the outer surface of the TiO2 powder, in a depth of ~ 20 nm, compared to the molecular transport kinetics in the interior of a 95,000 nm thick porous TiO2 material. Here, we employed NH3 and CO as representatives of slow and fast diffusing molecules, respectively. Adsorption of NH3 at the outer surface of the TiO2 powder occurs quickly while its distribution in the powder was found to be retarded. In contrast, adsorption of CO molecule shows that the surface coverage in the first ~ 20 nm of the TiO2 powder lags behind the surface coverage in the bulk due to the fast diffusion into the interior of the powder. In addition, we found that adsorption/desorption of CO showed a hysteresis effect when viewed by the two spatially sensitive surface spectroscopies.
This thesis presents a new method for measuring charge transport between TiO2 particles using an optical method, photoluminescence spectroscopy. We found that long continuous UV irradiation of the TiO2 powder caused photoexcited electrons to percolate deep into the powder inducing changes in the surface photovoltage and band flattening as detected by PL enhancement. The main finding was that in the dark after charging by illumination, the negative charge tends to return back to the surface partially restoring upward band bending as detected by the PL intensity decrease. It was found that the relaxation of the negative charge at 140 K is a very slow process, on a minute time scale. The slow process was assign to either electron hopping from a TiO2 surface site to a surface site or from a TiO2 nanocrystallite to a nanocrystallite in the TiO2 bed. This electron hopping process is temperature-dependent with an activation energy of 15 meV. We used the rate of the discharging process to estimate the electron mobility (~ 10-10 m2 V-1 s-1) at room temperature. Further, we studied the effect of single wall carbon nanotubes and gold nanoparticles on charge transport between TiO2 particles. We found that carbon nanotubes act as electron acceptor molecules but do not affect charge transport between TiO2 particles. In contrast to that, ~ 3 nm gold nanoparticles supported on TiO2 nanpoarticls act as strong electron acceptors significantly suppressing PL intensity and the buildup of surface photovoltage as measured by PL intensity change.

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Sintered diamond compacts have been examined by the technique of photoluminescence ..

Chapter 4 deals with the photoluminescence properties of undoped and In doped Si-rich Si-Ge alloys. We identify the alloy luminescence features on the basis of the temperature dependence, time dependence and pump power dependence of the luminescence intensities. We present results for the band gap shift and free exciton binding energy for each sample examined. In addition, we present a model for the observed broadening of bound exciton luminescence. Finally, we present observations which suggest that excitons bind to local fluctuations in alloy composition at low temperatures. This is the first investigation of the photoluminescence properties of Si-rich Si-Ge alloy semiconductors.

Chapter 4 deals with the photoluminescence properties of undoped and In doped Si-rich Si-Ge alloys. We identify the alloy luminescence features on the basis of the temperature dependence, time dependence and pump power dependence of the luminescence intensities. We present results for the band gap shift and free exciton binding energy for each sample examined. In addition, we present a model for the observed broadening of bound exciton luminescence. Finally, we present observations which suggest that excitons bind to local fluctuations in alloy composition at low temperatures. This is the first investigation of the photoluminescence properties of Si-rich Si-Ge alloy semiconductors.

Thesis On Photoluminescence essay on happiness essays about maya angelou 2011 ap world history comparison essay would you disagree with this
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    “Photoluminescence Studies of Amorphous Boron Carbide and Tungsten Diselenide Thin Films” Masters Thesis

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Photoluminescence studies of sintered diamond …

The nitrogen vacancy (NV) center in diamond has in recent years emerged as one of the most promising systems for quantum information processing and sensing applications. In this presentation, I will talk about my work done during the past few years on producing diamond thin membranes and developing methodology for fabricating photonic devices on thin membranes. Also, I will talk about scalable fabrication of photonic devices from commercially available bulk diamonds. Optical and spin characteristics of these resultant devices will be discussed. In particular, we are able to enhance the zero-phonon line emission of a single nitrogen vacancy center using a photonic crystal cavity and improve the broadband photoluminescence collection efficiency through a bullseye circular grating.

Photoluminescence studies of sintered diamond ..

This thesis concerns the study of ultrafast phenomena in semiconductor physics. At the heart of this research is the construction of a colliding-pulse mode-locked (CPM) ring-dye laser. This laser outputs ultrashort optical pulses at a high repetition rate. With a CPM laser, ultrafast semiconductor phenomena may be optically probed. In addition, using this laser to drive photoconductive circuit elements (PCEs), ultrafast electrical pulses can be generated and sampled, allowing novel high-speed devices to be electronically probed. For the measurement of ultrafast time-resolved photoluminescence (PL) a new pump/probe technique called photoluminescence excitation correlation spectroscopy (PECS) was used. The technique itself was investigated both theoretically and experimentally; it was applied to a variety of GaAs samples of interest in the development of high-speed devices.Chapter 2 discusses the construction and alignment of the CPM laser, and the autocorrelator used to measure the ultrashort pulses. Although the laser can be run with pulse widths of In Chapter 3, the PECS method is investigated both experimentally and theoretically. PECS is a pulse-probe technique that measures the cross-correlation of photo-excited populations. PECS is theoretically investigated using a rate equation model for a simple three-level system consisting of an electron and hole band and a single trap level. The model is examined in the limits of radiative band-to-band dominated recombination, and capture-dominated recombination. In the former limit, no PECS signal is observed. However, in the latter limit, the PECS signal from the band-to-band PL measures the cross-correlation of the excited electron-hole population, and, thus, the electron and hole lifetimes. PECS is experimentally investigated using a case study of PL in semi-insulating (SI) GaAs and In-GaAs. At 77 K, the PECS signal behaves as in the simple model, and an electron-hole lifetime in the range 200 ps is measured. This is much less than the expected radiative lifetime, and therefore the recombination in SI GaAs is capture-dominated. At 5 K, the behavior is more complicated, because of an acceptor, which is un-ionized at 5 K. PECS for the PL band-to-band decay, shows two decay modes: the fast decay (about 100 ps) is due to the saturable decay associated with the acceptor and the slow decay (about 1 ns) is due to bulk capture. The acceptor-related PL also shows complicated behavior: A fast decay is associated with the band-to-acceptor transition, and the donor-acceptor PL saturates, producing a PECS signal that is negative and decays slowly.In Chapter 4, PECS is used to investigate the large band-to-band PL contrast observed near dislocations in In-alloyed GaAs. It is found that the PL intensity contrast between a bright and dark area correlates with the ratio of the lifetimes measured using PECS in these areas. Thus, the PL intensity contrast is due to the difference in the carrier lifetimes in the different regions. The differences in the behavior of the lifetimes in the bright and dark regions with temperature suggest that the lifetime-governing defects in the two regions are different. Moreover, the defects are deep, and from the shortness of the lifetimes, neither defect is EL2. These results agree with earlier research, which indicated that defects are gettered and generated at these dislocations. The effects of surface recombination on the PL intensity and lifetimes in In-alloyed GaAs are important to the investigations of this chapter. These are investigated in Appendix E, where it is shown that both PL intensity and PECS-measured carrier lifetimes are greatly affected by surface properties and by laser dose and surface preparation. This is thought to be due to the creation of defects, which affects the surface recombination directly, and bends the electronic bands at the surface to affect the surface recombination indirectly. These effects are reduced by minimizing the exposure to the laser and by using a recently developed Na2S surface passivation layer.In Chapter 5, the carrier lifetime of damaged GaAs is correlated to the cross-correlation of the PCEs fabricated on the same material. Implantation of 200 keV H+ ions at doses in the range of 1011 - 1014 cm-2 is used to damage the GaAs. The carrier lifetimes are inversely proportional to the dose for doses > 1012 cm-2, and do not indicate a saturation of the damage within the range investigated. For the highest dose of 1014 cm-2, a lifetime of 0.6 ± 0.2 ps was measured at 77 K. The PCE cross-correlation decreases less quickly than the lifetime, indicating that some effect other than the lifetime is governing the cross-correlation response speed.Finally, two of the appendices present independent research that is worthy of note. Appendix C presents an attempt to grow HgTe on CdTe using a novel low-temperature Hg-rich melt liquid-phase epitaxial (LPE) growth technique, which involves an in situ cleave. Appendix D presents a program that models the behavior of ultrafast voltage pulses on a dispersive waveguide, which includes a lumped device.

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