Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2016. / The synthesis of water soluble CdTe, CdTe/CdSe and CdTe/CdSe/ZnSe nanoparticles (NPs) and their optical, cytotoxicity as well as imaging properties are presented. The synthesis was carried out under ambient conditions in the absence of an inert environment and involved the use of potassium tellurite (K2TeO3) and sodium selenosulphate (Na2SeSO4) as a stable tellurium and selenium precursor respectively, while mercaptopropanoic acid (MPA) was used as capping agents. In this method, the CdTe NPs were prepared by the addition of tellurium source solution to MPA-cadmium complex solution at different pH while keeping other parameters constant. The formation of the shell (CdSe) and multi shell (CdSe/ZnSe) were achieved by adding desired precursors to the growing CdTe core NPs at one hour interval. The temporal evolution of the optical properties and stability of the growing nanocrystals was monitored in detail by varying the refluxing time, pH and storing the NPs under ambient condition for several days. The as-prepared NPs were characterised using UV-Vis absorption and photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The formation of the shells was indicated by an immediate change in the colour of the reaction solutions after the addition of the desired precursor and the shift in the absorption wavelength towards red-region. The optical analyses showed an enhancement in the fluorescent intensity after the addition of the shell solution accompanied by red-shifting of the absorption and emission maximum. The stability study revealed an increase in the emission intensity as the ageing days increased. The stability study of the NPs in air at room temperature show highly improved stability of the core-shell NPs than the core. The TEM analysis showed that the materials are small, monodispersed, spherical and highly crystalline. The cytotoxicity of the NPs was investigated on LM 8 and KM-Luc/ GFP cell line using an MTT protocol at different concentrations. The cell viability show significant improvement after the shell formation with CdTe/CdSe/ZnSe core multi shell NPs having the highest cell viability at higher concentration (60 μg/mL). Furthermore a decrease in cytotoxicity is revealed with increase in reaction time, thus NPs prepared at longer (7 h) reaction time showed lower cytotoxicity compared with those prepared at shorter (0.5 h) reaction time. The confocal laser microscope image of the cells after the addition of the as-synthesised NPs confirmed the transfection of the NPs by KM-Luc/GFP cell line, indicating that the NPs have been endocytosis. This study demonstrates the great potential of the as-synthesised core-multi shell nanoparticles for biological and any applications that require efficiency, high fluorescence intensity and stability.

No description available.

<p>In this project we have used Fourier transform infrared spectroscopy to study the photoresponse of two different types of quantum dot-in-a-well infrared photodetectors (DWELL QDIPs). The basic task was to compare the photoresponse of these two detectors, and to study the influence of external resonant laser pumping on the photoresponse. Series of measurements were done at 77K. In the first measurements we investigated the photoresponse for different applied voltages at 77K. </p><p>In a second run of experiments, we used a 1064 nm infrared semiconductor laser to resonantly </p><p>pump the fundamental transition of the quantum dots. The results show that by using this </p><p>additional illumination the photoresponse was dramatically increased by creating additional </p><p>charge carriers in the quantum dots. This could be used to increase the sensitivity of infrared </p><p>detectors based on QDs.</p>

Herein, a program of research is detailed related to transport through the Si metal oxide semiconductor (MOS) quantum dots fabricated in a process flow compatible with modern ULSI (ultra large scale integrated circuit). Silicon quantum dots were fabricated by placing split gates within a MOSFET structure. Quantum dots of several sizes and geometries were fabricated by this process for the purpose of investigating the effects of size and shape on quantized transport through the dots. The transport properties of the different quantum dot sizes and shapes were investigated at low temperatures, and compared to normal MOSFETs fabricated by the same technology. Equilibrium measurements with the device biased in the regime from the onset of weak inversion to just past the onset of strong inversion revealed strongly oscillatory behavior in the tunneling conductance. The conductance peaks appear to map an energy level spectrum in the dot as the inversion and depletion gates are separately swept. Symmetric devices, biased both symmetrically and asymmetrically, show two groups of "branches" which evolve with different slopes in the V[subscript Inv]-V[subscript Depl] plane. An asymmetric device studied shows three groups of branches. In addition, a fine structure is observed in the conductance peak behavior of two devices. This apparent energy level structure is compared to the body of literature on the so-called artificial atoms, as well as self-consistent three dimensional quantum mechanical solutions for the energy levels in the same dot structure, which qualitatively agree with the overall slope of the observed data. However, the calculations reveal only the multiple sets of slopes when asymmetrically biased. These multiple slopes are postulated to arise due to the splitting of the degenerate states of the symmetric structure as the bias makes the structure increasingly asymmetric. Finally, a simplified model is presented which shows how slight asymmetry in the dot confining potential can give rise to both a fine structure and multiple slopes in the branches, and several alternative mechanisms are presented to explain the origin of the fine structure observed. / Graduation date: 2000

Over the past years, semiconductor quantum crystallite or micro-crystals of Si and Ge have received considerable attention for both fundamental and technological reasons. Quantum size effect and visible photoluminescence have been observed in nanometer-sized Si or Ge quantum crystallites. It has two practical applications. one is to prove to be optical semiconductor devices¡Fthe other is to turn into nano-crystal memories. The material Ge is considered a promising material for optical device fabrication. It has been found that Ge quantum dots embedded in Si matrices exhibit photoluminescence (PL) originating from the spatially indirect no-phonon recombination between holes confined within the Ge dots and electrons from the conduction band of the Si. For nano-crystal memories employing discrete charge traps as storage elements have exhibited great potential in device performance, power consumption, and technology scalability, thus recently attracting much research attention as promising candidates to replace the conventional DRAM or Flash memories. In the thesis, we will discuss the material properties of SiNGe and SiCNGe films, such as FTIR, AES, Raman Scattering spectrum analysis. The write/erase and retention characteristics of the nano-crystal are presented through current¡Vvoltage (I¡VV) and capacitance¡Vvoltage (C¡VV) measurements.

Thesis (M.S.)--Missouri University of Science and Technology, 2009. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed December 23, 2009) Includes bibliographical references (p. 39-44).

Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

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In this project we have used Fourier transform infrared spectroscopy to study the photoresponse of two different types of quantum dot-in-a-well infrared photodetectors (DWELL QDIPs). The basic task was to compare the photoresponse of these two detectors, and to study the influence of external resonant laser pumping on the photoresponse. Series of measurements were done at 77K. In the first measurements we investigated the photoresponse for different applied voltages at 77K. In a second run of experiments, we used a 1064 nm infrared semiconductor laser to resonantly pump the fundamental transition of the quantum dots. The results show that by using this additional illumination the photoresponse was dramatically increased by creating additional charge carriers in the quantum dots. This could be used to increase the sensitivity of infrared detectors based on QDs.