Dissertations / Theses on the topic 'Cadmium selenide'
To see the other types of publications on this topic, follow the link: Cadmium selenide.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Cadmium selenide.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Nguyen, Nu Hoai Vi School of Chemical Engineering & Industrial Chemistry UNSW. "Photocatalytic reduction of cadmium and selenium ions and the deposition of cadmium selenide." Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2005. http://handle.unsw.edu.au/1959.4/20849.
Full textAbstract:
Titanium dioxide (TiO2) photocatalysis, which can oxidise or reduce organic and inorganic pollutants, is a developing technology for water and wastewater treatment. The current work investigates the photocatalytic reduction of cadmium and selenium species as the presence of these elements in water are of environmental concern. Although TiO2 has been widely used for the photocatalytic process, its light absorption is limited to the UV region of the solar spectrum. Hence, the current project also explores the possibility to deposit cadmium selenide (CdSe) onto TiO2 to extend the photoresponse to the visible region. This study demonstrated that cadmium (Cd(II)) could be reduced to its metallic form by photocatalysis. The choice of hole scavengers and reaction pH are of importance in determining whether the photocatalytic reduction reaction will occur. It is also essential that both Cd(II) and organic additives are adsorbed on the surface of TiO2. A mechanism for cadmium photoreduction in the presence of formate as the hole scavenger was proposed. The current investigation elucidated the mechanism for the photoreduction of selenite (Se(IV)). Selenite was found to be photoreduced to its elemental form (Se(0)) as films, by direct photoreduction of Se(IV), and as discrete particles, by the reaction between Se(IV) and selenide (Se(2-)) ions. The Se(2-) ions are believed to have been generated from the 6 electron photoreduction of Se(IV) and/or the further photoreduction of the Se(0) deposits. Photocatalytic reduction reactions of Se(IV) and selenate (Se(VI)) using different commercial TiO2 materials was also studied. The current work also successfully deposited CdSe by photocatalysis using Se-TiO2 obtained from the photoreduction of Se(IV) and Se(VI). The mechanism for CdSe deposition was clarified and attributed to the reaction of Cd(II) present in the system and the Se(2-) released from the reduction of Se(0) upon further illumination. The Se??TiO2 photocatalysts obtained from the photoreduction of different selenium precursors (Se(IV) and Se(VI)) resulted in the dominance of different morphologies of the CdSe particles. This suggests a new approach to manipulate the properties of CdSe during its formation, and hence control over electrical and optical properties of this semiconductor.
2
Roy, Santanu. "Spectroscopic study of defects in cadmium selenide quantum dots (QDS) and cadmium selenide nanorods (NRS)." Diss., Kansas State University, 2013. http://hdl.handle.net/2097/16118.
Full textAbstract:
Doctor of PhilosophyDepartment of Chemistry
Viktor Chikan
Ever depleting sources of fossil fuel has triggered more research in the field of alternate sources of energy. Over the past few years, CdSe nanoparticles have emerged as a material with a great potential for optoelectronic applications because of its easy exciton generation and charge separation. Electronic properties of CdSe nanoparticles are highly dependent on their size, shape and electronic environment. The main focus of this research is to explore the effect of different electronic environments on various spectroscopic properties of CdSe nanoparticles and link this to solar cell performance. To attain that goal, CdSe quantum dots (QDs) and nanorods (NRs) have been synthesized and either doped with metal dopants or embedded in polymer matrices. Electronic properties of these nanocomposites have been studied using several spectroscopic techniques such as absorption, photoluminescence, time-resolved photoluminescence, confocal microscopy and wide field microscopy. Indium and tin are the two metal dopants that have been used in the past to study the effect of doping on conductivity of CdSe QDs. Based on the photoluminescence quenching experiments, photoluminescence of both indium and tin doped samples suggest that they behave as n-type semiconductors. A comparison between theoretical and experimental data suggests that energy levels of indium doped and tin doped QDs are 280 meV and 100 meV lower than that of the lowest level of conduction band respectively. CdSe nanorods embedded in two different polymer matrices have been investigated using wide field fluorescence microscopy and confocal microscopy. The data reveals significant enhancement in bandedge luminescence of NRs in the vicinity of a conjugated polymer such as P3HT. Photoactive charge transfer from polymers to the surface traps of NRs may account for the observed behavior. Further study shows anti-correlation between bandedge and trap state emission of CdSe NRs. A recombination model has been proposed to explain the results. The origin of traps is also investigated and plausible explanations are drawn from the acquired data.
3
Varanasi, Mohan R. "Geometries of small cadmium selenide (CdSe) clusters." Virtual Press, 2006. http://liblink.bsu.edu/uhtbin/catkey/1349770.
Full textAbstract:
The sizes, shapes, relaxed atomic positions, eigenvalues, and total energies are calculated for selected ultra-small CdSe clusters using SIESTA, a software package for electronic structure calculations and molecular dynamics simulations of molecules and solids. The properties of these bare clusters with small numbers of constituent atoms are studied using density functional theory (DFT) for energy calculations and the conjugate gradient approximation as well as simulated annealing type of molecular dynamics techniques in relaxing the structure to find the lowest energy configurations.The ab-initio norm-conserving pseudopotentials, the exchange-correlation approximation, and parameters used in the computations by Siesta software is verified using FHI98PP, a package used to generate and test the ab-initio norm-conserving pseudopotentials. The initial position of the atomic co-ordinates is determined using ancillary software written in Matlab.Department of Physics and Astronomy
4
Sacra, Ann. "Stark spectroscopy of cadmium Selenide (CdSe) nanocrystallites." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/9892.
Full text
5
Leatherdale, Catherine A. (Catherine Anne) 1972. "Photophysics of cadmium selenide quantum dot solids." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8828.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2000.Includes bibliographical references.
Semiconductor quantum dots or nanocrystals have size dependent optical and electronic properties that arise from quantum confinement. While the quantum size effect is reasonably well understood, the effect of abrupt interface between the nanocrystal and its dielectric environment is not. In this thesis we study how the dielectric environment affects the quantum dot electronic structure, the optical absorption ~ross-section, charge separation, and transport in cadmium selenide colloidal quantum dots. The electronic states and optical absorption cross-section are found to be less sensitive to changes in the dielectric environment than predicted from theory unless screening from the ligand shell is taken into account. The absolute absorption cross section is measured as a function of quantum dot size; excellent agreement with theory is obtained for absorption far above the band edge. Three-dimensional close packed solids of quantum dots are predicted to act as model artificial solids. Optical absorption measurements indicate that the electronic states of CdSe quantum dots separated by 11 angstroms or more are essentially uncoupled. Photoconductivity measurements suggest that photoexcited quantum confined excitons are ionized by the applied field with a rate that depends on both the size and surface passivation of the quantum dots. The charge generation efficiency decreases with increasing temperature as non-radiative and radiative recombination pathways increasingly compete with charge separation. A simple tunneling model for the initial charge separation step is presented that qualitatively reproduces both the size and surface dependence of the photoconductivity as a function of applied electric field. Finally, we report observations of amplified spontaneous emission from quantum dot solids. The stimulated emission is tunable with quantum dot size and does not sensitively depend upon surface passivation. These measurements demonstrate the feasibility of nanocrystal quantum dot lasers and amplifiers.
by Catherine A. Leatherdale.
Ph.D.
6
Nirmal, Manoj. "Photophysics of cadmium selenide (CdSe) semiconductor nanocrystals." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10715.
Full text
7
Stewart, Helen. "Studies into the growth and doping of zinc selenide and zinc cadmium selenide." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/734.
Full text
8
Philipp, Dean. "Structural and optical properties of small cadmium selenide nanocyrstallites." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38098.
Full text
9
Sih, Bryan Christian. "Gold and cadmium selenide (CdSe) nanoparticles capped with oligothiophenes." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31523.
Full textAbstract:
The preparation and characterization of hybrid materials composed of oligothiophene-capped Au and CdSe nanoparticles with novel chemical, structural, electronic and optical properties are reported. α-Phosphino-oligothiophenes (12-15 and 23) and thiol-substituted oligothiophenes (26, 29, 32) were prepared by metal-catalyzed coupling reactions and studied using absorption and emission spectroscopy, and cyclic voltammetry. These functionalized oligothiophenes were used to passivate the surface of Au (16-19) and CdSe (CdSe-26, CdSe-29, CdSe-32) nanoparticles. Oligothiophene-capped Au nanoparticles were prepared directly by reducing a Au salt in the presence of the phosphino-oligothiophene. Attachment to the Au nanoparticles has little effect on the electronic structure of the oligothiophene as determined from the absorption spectra. On the other hand, the oligothiophenes appear to affect the electronic structure of the Au nanoparticle, as observed via a red-shift in the surface plasmon absorption. Electrochemical oxidation of the phosphino-terthiophene capped Au nanoparticles lead to crosslinking where the nanoparticles are linked both structurally and electronically by observed increases in conjugation, conductivity and plasmon coupling relative to the unlinked particles. The oligothiophene bridge linking the Au nanoparticles is shown to facilitate plasmon coupling between adjacent nanoparticles. The crosslinked material also demonstrates tunable conductivity where the conductivity in the material can be increased by oxidative doping of the π-conjugated bridge. Oligothiophene-capped CdSe nanoparticles were prepared through an exchange reaction between thiol-substituted oligothiophenes and trioctylphosphine oxide-capped CdSe nanoparticles. Attachment of the oligothiophenes to the CdSe nanoparticle has little effect on the electronic structure of the oligothiophene as determined from the absorption spectra. However, the optical properties are significantly affected where the oligothiophene emission is quenched after attachment to the CdSe surface due to either an energy or electron transfer mechanism. Depending on the number of oligothiophenes attached to the CdSe surface, the optical properties of the CdSe nanoparticles are affected differently. An excess number of thiols act as hole traps leading to quenching of the nanoparticle emission. Attempts to electrochemically crosslink these oligothiophene-capped CdSe nanoparticles were unsuccessful possibly due to the intrinsic resistivity in the particles.[See Thesis for Diagrams]Science, Faculty of
Chemistry, Department of
Graduate
10
Oduor, A. O. "Electronic transport properties in evaporated cadmium selenide thin films." Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388869.
Full text
11
Sheridan, Liam A. "Alternative cadmium source precursors for the growth of cadmium sulphide and cadmium selenide by metal-organic chemical vapour deposition." Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339511.
Full text
12
Beukes, Stewart Eva-Panduleni. "EPR studies of electron transfer in cadmium selenide sensitised titania." Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=232399.
Full textAbstract:
Research into renewable energy sources is crucially increasing to counteract the ever more concerning impact of non-renewable sources. Theoretically, Quantum Dot Solar Cells (QDSCs) can achieve much greater efficiencies than current, commercial solar cells, but its expansion is still in its very early stages of scientific study and development. In this project TiO2, one of the most efficient and cost-effective photocatalysts, is coupled with Cadmium Selenide (CdSe) Quantum Dots (QD) in a study of interfacial charge transfers. Thus far, in other studies, CdSe QDs have shown some of the most promising results of QDSCs. EPR spectroscopy has been used here to study charge transfer processes in CdSe quantum dot (QD) sensitised titania. Visible light excitation of QDs directly adsorbed onto titania surfaces causes electron transfer to the titania, producing characteristic EPR signals of trapped electrons in the titania. Under ultraviolet excitation the trapped electron signals seen in titania alone are suppressed in the presence of directly adsorbed quantum dots, as is the formation of superoxide in the presence of oxygen. These observations suggest that reverse electron transfer from the titania to the QDs can also occur. No visible light excited electron transfer occurs in the case of QDs attached to the titania surface via bi-linker molecules, but under ultraviolet excitation a similar suppression of electron trapping in the titania phase is seen. These results show that the nature of the interface between the QDs and the titania phase is crucially important in the electron transfer processes in both directions. The study also looks at the pitfalls of synthesis techniques used for making the CdSe QDs as well as the method of attaching it to the TiO2. Ionic deposition, which generally resulted in the best photocurrents in other studies, was discovered early on this project produced very impure samples. Direct Adsorption produces low titania surface coverage, which can potentially be improved. Whereas the lack of discussion in literature of clear purification methods in synthesis techniques for attaching QDs via a bi-linker molecule, through ligand exchange, causes a significant drawback in the study of such systems.
13
Perera, Jayalath Pathirannehelage Dimuthu Nuwan. "Photocatalytic Properties of Zinc Selenide/Cadmium Sulfide Core-shell Nanoparticles." Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1370994697.
Full text
14
Diederich, Geoffrey M. "Synthesis of Zinc Telluride/Cadmium Selenide/Cadmium Sulfide Quantum Dot Heterostructures for use in Biological Applications." Bowling Green State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1342542873.
Full text
15
Vu, Nhan Trung. "Characterisation of cadmium selenide material for high speed photoconductive switching systems." Thesis, University of Brighton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310102.
Full text
16
Cooke, Sharon A. "Alternative chalcogen sources for the growth of cadmium sulfide and cadmium selenide by metal organic chemical vapour deposition." Thesis, University of Reading, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284186.
Full text
17
Mikulec, Frederic Victor 1971. "Semiconductor nanocrystal colloids : manganese doped cadmium selenide, (core)shell composites for biological labeling, and highly fluorescent cadmium telluride." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9358.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 1999.Includes bibliographical references.
This thesis describes the characterization and applications of nanometer sized semiconductor (or quantum dot) colloids produced by chemical means. The nanocrystals are synthesized by pyrolysis of organometallic precursors in the coordinating solvent trioctylphosphine oxide (TOPO). The important developments that have contributed to this method are discussed. Manganese doped CdSe nanocrystals are synthesized using a manganese and selenium containing organometallic compound. Chemical etching and electron paramagnetic resonance (EPR) experiments reveal that most of the dopant atoms lie near the surface within the inorganic lattice. Results from fluorescence line narrowing (FLN) and photoluminescence excitation (PLE) spectroscopies show that doped nanocrystals behave as if they were undoped nanocrystals in an external magnetic field. The nanocrystal surface is initially passivated by dative organic ligands. Better passivation and optical properties are achieved by growth of a large band gap semiconductor shell that provides both a physical and an energetic barrier between the exciton and the surface. (CdSe)ZnS (core)shell are prepared with control over both core and shell sizes. The composite nanocrystals are characterized by absorption, emission, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), and wide angle X-ray scattering (W AXS). The maximum quantum yield is achieved when the core is protected from oxidation by a complete shell; thicker shells show no further increase in quantum yield values, due to defects caused by the large lattice mismatch. Exchange of surface TOPO ligands for mercaptocarboxylic acids produces (core)shell nanocrystals that, when treated with base, are soluble in water and remain fluorescent. Established protocols are used to link these water-soluble nanocrystals to the biomolecules avidin or biotin, producing useful fluorescent labels. Stable phosphine tellurides are prepared using hexapropylphosphorus triamide (HPPT). This precursor is used to prepare CdTe nanocrystals that display room temperature quantum yields up to 70%. The CdTe growth is investigated by absorption and emission spectroscopy. CdTe nanocrystals are characterized by TEM and WAXS.
by Frederic Victor Mikulec.
Ph.D.
18
Jeedigunta, Sathyaharish. "Development of cadmium selenide as an absorber layer for tandem solar cells." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000279.
Full text
19
Weaver, Joseph Edison. "PATTERNING OF CADMIUM SELENIDE QUANTUM DOT NANOCRYSTALS FOR USE WITH PHOTOVOLTAIC APPLICATIONS." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/976.
Full textAbstract:
In this thesis, cadmium selenide (CdSe) quantum dots (QDs) are synthesized and characterized for patterning applications as well as for photovoltaic devices. The QDs were patterned and embedded into various polymers to form fluorescent composites. Their photophysical properties were investigated in detail. Through template assisted deposition the QDs-polymer composites were patterned into fluorescent nanorods. CdSe QDs were combined with multi-wall carbon nanotubes (CNTs) using a synthesized organic perylene derivative dye (N,N'-di(ethanethiol)-perylene-3,4,9,10-tetracarboxyl diimide) (ETPTCDI) as a link between QDs and CNTs. Upon testing, the QDs-ETPTCDI-CNTs nanocomposite displayed photoactive properties. Photophysical quenching studies of QD-ETPTCDI-CNTs provided better understanding of the electron-hole transfer of each component in the nanocomposite. The nanocomposite material was patterned onto microelectrode devices for photocurrent measurements under an AM1.5 solar simulated light source. These nanocomposites can be used as photovoltaic devices. The preliminary characterization studies of the device show excellent photoresponse under AM1.5 solar simulated light. The band gap alignment of each component of the nanocomposite and the charge transfer kinetics are the key to efficient electron-hole transfer. Optimization of the semiconducting material's interface can potentially make these nanocomposites a system for photovoltaic-based devices.
20
Beer, Michael P. "A study of volatile precursors for the growth of cadmium sulphide and cadmium selenide by Metal Organic Vapour Deposition." Thesis, University of Reading, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303986.
Full text
21
Kagan, Cherie R. 1969. "The electronic and optical properties of close packed cadmium selenide quantum dot solids." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10603.
Full text
22
Yang, Zhiqiang. "Preparation of palladium, palladium sulfide, cadmium selenide nanoparticles and magnesium oxychloride, magnesium hydroxide nanorods." Diss., Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/891.
Full text
23
Chévere-Trinidad, Néstor Luis. "Part A: Nanoscale semiconductors through electrodeposition Part B: Mechanistic studies of the copper-catalyzed reactions /." Amherst, Mass. : University of Massachusetts Amherst, 2009. http://scholarworks.umass.edu/dissertations/AAI3349714/.
Full text
24
Langford, Richard Mark. "Growth and characterisation of cadmium selenide thin films applicable to a liquid crystal light valve." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266074.
Full text
25
Norris, David J. (David James). "Measurement and assignment of the size-dependent optical spectrum in cadmium selenide (CdSe) quantum dots." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11129.
Full text
26
Carlson, Jill A. "Synthetic and Photochemical Study of Ruthenium Polypyridine Solar Dyes Coupled to Cadmium Selenide Quantum Dots." Ohio University Honors Tutorial College / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ouhonors1338682734.
Full text
27
Vakkalanka, Sridevi A. "Development of window layer for high efficiency high bandgap cadmium selenide solar cell for 4-terminal tandem solar cell applications." [Tampa, Fla] : University of South Florida, 2006. http://purl.fcla.edu/usf/dc/et/SFE0001761.
Full text
28
Yildiz, Ibrahim. "Luminescent Probes and Photochromic Switches Based on Semiconductor Quantum Dots." Scholarly Repository, 2008. http://scholarlyrepository.miami.edu/oa_dissertations/103.
Full textAbstract:
A new strategy was developed to switch the luminescence of semiconductor quantum dots with chemical stimulations. It is based on the photoinduced transfer of either energy from CdSe-ZnS core-shell quantum dots to [1,3]oxazine ligands or electrons from the organic to the inorganic components. Upon addition of base or acid, energy or electron transfer pathways respectively become operative, leading to changes in the luminescence of the nanoparticles. These changes are fully reversible and can be exploited to probe the pH of aqueous solutions from 3 up to 11 and this design can lead to the development of pH-sensitive luminescent probes for biomedical applications based on the semiconductor quantum dots. Secondly, an operating principle to transduce the supramolecular association of complementary receptor-substrate pairs into an enhancement in the luminescence of sensitive quantum dots was identified. This system is based on the electrostatic adsorption of cationic quenchers on the surface of anionic quantum dots. The adsorbed quenchers efficiently suppress the emission character of the associated nanoparticles on the basis of photoinduced electron transfer. In the presence of target receptors able to bind the quenchers and prevent electron transfer, however, the luminescence of the quantum dots is restored. Thus, complementary receptor-substrate pairs can be identified with luminescence measurements relying on this system and this protocol can be adapted to signal protein-ligand interactions. Thirdly, a photochromic spiropyran with dithiolane appendage to adsorb on the surface of cadmium sulfide system was designed. The properties of the resulting photochrome-nanoparticle assemblies vary significantly with the experimental conditions selected for the preparation of the inorganic component. Finally, photochromic materials based on the photoinduced transfer of electrons from CdSe-ZnS core-shell quantum dots to bipyridinium dications were developed.
29
Heath, Travis Justin. "Studies on the Preparation and Luminescence Properties of Cadmium Selenide Quantum Dots, Their Immobilization, and Applications." Digital Commons @ East Tennessee State University, 2010. https://dc.etsu.edu/etd/1750.
Full textAbstract:
Quantum dots are semiconductive particles whose properties are highly influenced by the presence of at least one electron. Cadmium selenide quantum dots were synthesized via colloidal synthesis. Contrary to previous preparations, more focus was placed on the temperature rather than the duration of time at which they form. A series of colored solutions were obtained because the excited quantum dots of various sizes emitted specific wavelengths of light. The emission spectra showed that the temperature-dependent quantum dots were successfully synthesized. The quantum dots were also immobilized on various surfaces, and the luminescence properties were examined. The quantum dots that were immobilized in sol-gels through chemiluminescence (CL) analyses were found to be stable and were able to maintain their luminescence properties with extensive uses and long-term storage. Linear calibration curves were obtained for concentrations of hydrogen peroxide from 1.75 x 10-4 M to 1.75 x 10-2 M in TCPO-CL.
30
Dabbousi, Bashir O. (Bashir Osama). "Fabrication and characterization of hybrid organic/inorganic electroluminescent devices based on cadmium selenide nanocrystallites (quantum dots)." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10434.
Full text
31
Norhashim, Nurhakimah. "Temperature dependent photoluminescence of erbium doped YAG, zinc nitride and manganese-doped cadmium selenide optical materials." Thesis, University of Surrey, 2017. http://epubs.surrey.ac.uk/814013/.
Full textAbstract:
Temperature dependent studies of a selection of materials including erbium-doped yttrium aluminum garnet (Er:YAG), zinc nitride nanocrystals(NCs) and manganese-doped cadmium selenide (CdMnSe) NCS have been undertaken in order to determine their fundamental optical properties. The study is based upon the measurement of their photoluminescence (PL) and PL transient decay transient over the temperature range of 300K to 5K. For the Er:YAG samples, two different sample types are studied as a function of erbium concentration that are a fast-cooled (mono-phase) and a slow-cooled (bi-phasic) polycrystalline material. Due to the presence of emission upconversion in these materials the emission dependence on excitation power is also studied. It is found that for high Er concentrations (40-50%) energy transfer upconversion (ETU) occurs that may be of use for assisting population inversion at the 4I11/2 level for the laser 3µm emission. Generally it is confirmed that the single phase and bi-phasic materials possess slightly different optical properties and that the material production must therefore be carefully controlled in order to realize optimized materials for optical applications. Zinc nitride NC materials are studied for the first time with four samples representing a range of NC diameters characterized. These materials were highly susceptible to oxidation which presented a significant challenge in their handling and study. Strong emission was observed across the visible spectral region though the origin of this it was found probably included trap state emission and for the smallest NC samples organic ligand emission. The PL was found to shifting to higher energies as the size of the NC is decreased as expected due to increased quantum confinement and in line with the Brus equation. Two of the samples (8.9nm and 2.7nm diameter NCs) display a temperature dependence of the optical properties in line that seen in other semiconductor NCs such as PbS. The other samples displayed anomalous behavior that could be due to ligand emission (2.5nm NC sample) or higher energy trap states caused by localized oxidation (3.8nm NCs). A study of temperature dependent optical properties of CdMnSe NCs was focused around the role of NC shape and type. Core only, core/shell and dot-in-rod samples were studied and all found to display a blue shift as temperature is reduced from 300K to ~5K of between ~24meV to 58meV. The core only NCs display a different luminescent behavior to that of the core-shell and dot-in-a-rod samples. The PL is related to the recombination of confined excitons within the NC, together with a contribution from what are most probably trap states located at the surface of the NC. In these samples no contribution from the Mn2+ ion is found suggesting that the dopant ions are not fully incorporated into the NC but may reside on the surface.
32
Meerbach, Christian, Cong Wu, Steven C. Erwin, Zhiya Dang, Anatol Prudnikau, and Vladimir Lesnyak. "Halide-Assisted Synthesis of Cadmium Chalcogenide Nanoplatelets." American Chemical Association, 2019. https://tud.qucosa.de/id/qucosa%3A74323.
Full textAbstract:
Atomically flat colloidal semiconductor CdSe nanoplatelets (NPLs) with precisely controlled thickness possess a range of unique optoelectronic properties. Here, we study the growth of CdSe, CdTe, and CdS NPLs with the aim of synthesizing thicker NPLs in order to extend their optical activity further into the lower energy/larger wavelength range. We employ cadmium halides, which lead to faster reaction kinetics as confirmed by control experiments with cadmium hydroxide as a Cd-precursor. Addition of halides in all cases led to the formation of thicker NPL species, as compared with the corresponding syntheses without these additives. Analysis of a recent theoretical model of the platelet growth mechanism confirms an earlier suggestion that reducing both the reaction enthalpy and the surface energy of CdSe, by replacing acetate ligands with chloride ions, should indeed lead to thicker NPLs as observed. We noticed a formation of Cd0-metal nanoparticles in the first stage of the synthesis by preparing the Cd-precursor, which is another key finding of our work. We assume that these particles can serve as an active cadmium source facilitating the growth of the NPLs. The resulting 6 ML CdSe NPLs exhibited bright photoluminescence with quantum yield of up to 50%, exceptionally narrow spectrum centered at 582 nm with full width at half-maximum of approx. 11 nm, and small Stokes shift of 2 nm. Moreover, we demonstrated the synthesis of heterostructured core/shell CdSe/CdS NPLs based on 6 ML CdSe platelets, which also exhibited bright fluorescence. This work shows the possibility to overcome energetic barrier limiting the size (thickness) control by using appropriate promoters of the growth of CdSe, CdTe, and CdS 2D structures.
33
Herz, Erik. "Colloidal Semiconductor Nanocrystals: A Study of the Syntheses of and Capping Structures for CdSe." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/10147.
Full textAbstract:
Luminescent quantum dots (QDs) or rods are semiconductor nano-particles that may be used for a wide array of applications such as in electro-optical devices, spectral bar coding, tagging and light filtering. In the case under investigation, the nano-particles are cadmium-selenide (CdSe), though they can be made from cadmium-sulfide, cadmium-telluride or a number of other II-VI and III-V material combinations. The CdSe quantum dots emit visible light at a repeatable wavelength when excited by an ultraviolet source. The synthesis of colloidal quantum dot nanoparticles is usually an organo-metallic precursor, high temperature, solvent based, airless chemical procedure that begins with the raw materials CdO, a high boiling point ligand, and a Se-trioctylphosphine conjugate. This investigation explores the means to produce quantum dots by this method and to activate the surface or modify the reaction chemistry with such molecules as trioctylphosphine oxide, stearic acid, dodecylamine, phenyl sulfone, aminophenyl sulfone, 4,4'dichlorodiphenyl sulfone, 4,4'difluorodiphenyl sulfone, sulfanilamide and zinc sulfide during the production to allow for further applications of quantum dots involving new chemistries of the outer surface. Overall, the project has been an interesting and successful one, producing a piece of equipment, a lot of ideas, and many dots with varied capping structures that have been purified, characterized, and stored in such a way that they are ready for immediate use in future projects.Master of Science
34
Дрозденко, Д. О., Maksym Mykolaiovych Ivashchenko, Максим Николаевич Иващенко, Максим Миколайович Іващенко, Volodymyr Volodymyrovych Kosiak, Владимир Владимирович Косяк, Володимир Володимирович Косяк, Nadiia Mykolaivna Opanasiuk, Надежда Николаевна Опанасюк, and Надія Миколаївна Опанасюк. "Структурні та оптичні властивості плівок селеніду кадмію." Thesis, Видавництво СумДУ, 2010. http://essuir.sumdu.edu.ua/handle/123456789/4113.
Full textAbstract:
В результаті досліджень встановлені фізико-технологічні режими
осадження плівок CdSe з оптимальними, для використання в якості
поглинаючих шарів тандемних гетероперехідних сонячних
перетворювачів, параметрами.
При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/4113
35
Moore, Christopher S. "Study of Immobilizing Cadmium Selenide Quantum Dots in Selected Polymers for Application in Peroxyoxalate Chemiluminescence Flow Injection Analysis." Digital Commons @ East Tennessee State University, 2013. https://dc.etsu.edu/etd/1151.
Full textAbstract:
Two batches of CdSe QDs with different sizes were synthesized for immobilizing in polyisoprene (PI), polymethylmethacrylate (PMMA), and low-density polyethylene (LDPE). The combinations of QDs and polymer substrates were evaluated for their analytical fit-for-use in applicable immunoassays. Hydrogen peroxide standards were injected into the flow injection analyzer (FIA) constructed to simulate enzyme-generated hydrogen peroxide reacting with bis-(2,4,6-trichlorophenyl) oxalate.
Linear correlations between hydrogen peroxide and chemilumenscent intensities yielded regression values greater than 0.9750 for hydrogen peroxide concentrations between 1.0 x 10-4 M and 1.0 x 10-1 M. The developed technique’s LOD was approximately 10 ppm. Variability of the prepared QD-polymer products was as low as 3.2% throughout all preparations.Stability of the preparations was tested during a 30-day period that displayed up to a four-fold increase in the first 10 days. The preparations were decently robust to the FIA system demonstrating up to a 15.20% intensity loss after twenty repetitive injections.
36
Hiramatsu, Hiroki. "Systematic investigations on the assembly and properties of multicomponent nanostructures comprised of gold, silver, cadmium selenide, and silica nanoparticles /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
Full text
37
Hancock, Jared M. "Formation and Analysis of Zinc Oxide Nanoparticles and Zinc Oxide Hexagonal Prisms and Optical Analysis of Cadmium Selenide Nanoparticles." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3867.
Full textAbstract:
In this dissertation, methods to synthesize ZnO are reported. First, zinc oxide nanoparticles were synthesized with small amounts of transition metal ions to create materials called dilute magnetic semiconductors (DMS). We employed a low temperature sol-gel method that produces ZnO nanoparticles of reproducible size and incorporates cobalt, nickel, and manganese ions into the nanoparticles. Conditions were controlled such that a range of amounts of Co, Ni, and Mn were incorporated. The incorporation was tracked by color changes in the white ZnO powder to blue for Co, green for Ni and yellow for Mn. XRD measurements showed the nanoparticles were on the order of 10 nm in diameter and had a wurtzite structure. Magnetic measurements showed a change from diamagnetic to paramagnetic behavior with increasing concentration of metal dopants. Second, formation of ZnO single crystal hexagonal prisms from a sol-gel method is presented. The method required water, zinc acetate, and ethanolamine to create a gel of zinc hydroxide and zinc hydroxide acetate, which upon heating formed single crystal hexagonal prisms. Characterization of the gel was done by XRD as well as XRD high temperature chamber (HTK) to determine the role of temperature in prism formation. SEM images showed hexagonal prisms were of uniform size (0.5 × 2 µm.) TEM and electron diffraction images showed a change from randomly oriented particles to an ordered single crystal after heating. Water and the acetate salt of zinc proved to be critical to prism formation. Lastly, we report absorption and fluorescence properties of synthesized oligothiophenes and oligothiophene-ruthenium complexes that are bound to CdSe nanoparticles. Their ability to act as sensitizers and charge transfer junctions was tested. It was found that fluorescence of CdSe nanoparticles was quenched when they were bound to the oligothiophenes, and that the fluorescence of the oligothiophenes was also quenched. The fluorescence lifetimes of the quenched species were shortened.
38
Gonsalves, Peter Robert. "THE DESIGN AND FABRICATION OF A MICROFLUIDIC REACTOR FOR SYNTHESIS OF CADMIUM SELENIDE QUANTUM DOTS USING SILICON AND GLASS SUBSTRATES." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/720.
Full textAbstract:
A microfluidic reactor for synthesizing cadmium selenide (CdSe) quantum dots (QDs) was synthesized out of a silicon wafer and Pyrex glass. Microfabrication techniques were used to etch channels into the silicon wafer. Holes were wet-drilled into the Pyrex glass using a diamond-tip drill bit. The Pyrex wafer was anodically bonded to the etched silicon wafer to enclose the microfluidic reactor. Conditions for anodic bonding were created by exposing the stacked substrates to 300V at ~350oC under 5.46N of force. A syringe containing a room temperature CdSe solution was interfaced to the microfluidic reactor by using Poly (dimethylsiloxane) (PDMS) as an interface. The reactor was placed on a hot plate at 225oC, creating thermodynamic conditions for the QD chemical reaction to occur within the etched channels. Tygon® tubing transported solutions in and out of the microfluidic reactor. The CdSe solution was injected into the reactor by a syringe pump at an injection rate of 5 mL/hr, with a channel length of 2.5 cm. While in the microfluidic channels, QD residence time of approximately 30 seconds was sufficient enough for nucleation and growth of QDs to occur. The QD size was characterized by fluorescence full-width-half-maximum (FWHM), which is directly proportional to size distribution. The FWHM of the QDs synthesized was 38 nm, with a peak wavelength of 492 nm. By controlling combinations of pump rate and channel length, a range of QD sizes was able to be consistently synthesized through the microfluidic reactor with significant repeatability and reproducibility.
39
Lafferty, William Henry. "DEVELOPMENT OF A HIGH PRECISION QUANTUM DOT SYNTHESIS METHOD UTILIZING A MICROFLUIDIC REACTOR AND IN-LINE FLUORESCENCE FLOW CELL." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1317.
Full textAbstract:
Quantum dots show great potential for use as spectral converters in solar cells, lighting applications, and biological imaging. These applications require precise control of quantum dot size to maximize performance. The quality, size, and fluorescence of quantum dots depend on parameters that are difficult to control using traditional batch synthesis processes. An alternative, high precision process was developed for the synthesis of cadmium-selenide quantum dots using a microfluidic reactor and fluorescence flow cell. The process required creating separate cadmium and selenium precursors that were then mixed in a nitrogen environment at 17°C. Using an NE-300® syringe pump, the solution was pumped through a microfluidic reactor submerged in a 240°C oil bath. The reactor then fed through a water quench bath at 25°C to terminate the nucleation and growth reaction. The fluorescence profiles of the quantum dot solutions were then characterized with an in-line fluorescence flow cell used in conjunction with an Ocean Optics® USB4000® spectrometer and a ThorLabs® LED UV light source. Flow rates through the reactor were varied from 0.05ml/min to 2ml/min. A central peak wavelength was registered in the fluorescence profiles for each flow rate. Monodisperse Cd-Se quantum dot solutions were synthesized across a broad spectrum of wavelengths ranging from 490nm to 620nm. An empirical relationship between flow rate and center wavelength was determined.
40
Nadarajah, Athavan. "Fundamental Properties of Functional Zinc Oxide Nanowires Obtained by Electrochemical Method and Their Device Applications." PDXScholar, 2012. https://pdxscholar.library.pdx.edu/open_access_etds/633.
Full textAbstract:
We report on the fundamental properties and device applications of semiconductor nanoparticles. ZnO nanowires and CdSe quantum dots were used, prepared, characterized, and assembled into novel light-emitting diodes and solar cells. ZnO nanowire films were grown electrochemically using aqueous soluble chloride-based electrolytes as precursors at temperatures below 90° C. Dopants were added to the electrolyte in the form of chloride compounds, which are AlCl3, CoCl2, CuCl2, and MnCl2. The optical, magnetic, and structural properties of undoped and transition-metal-ion doped ZnO nanowires were explored. Our results indicate that the as-grown nanowire structures have considerable internal strain, resulting in clearly visible lattice distortions in bright and dark-field transmission electron micrographs. Photo and electroluminescence studies indicate that the strain-induced defects strongly dominate any dopant-related effects. However, annealing at moderate temperature as well as laser annealing induces strain relaxation and leads to dopant activation. Hence, the optical and electrical properties of the nanowires significantly improve, allowing these nanowires to become feasible for use in the fabrication of solar cell and LED devices. In addition, the magnetic impurities incorporated into our ZnO nanowires show superparamagnetic behavior at room-temperature, while Al-doped and undoped ZnO nanowires show no magnetic behavior. The electroluminescence (EL) is achieved from a vertical hybrid p-n junction LED arrangement consisting of a hole-conducting polymer and n-type ZnO nanowires, our group was the first to report this vertical nanowire-based LED in Könenkamp et al., 2004 [12]. The observed EL spectra show an ultraviolet excitonic emission peak and a broad defect-related emission band in the visible range. After annealing at 380° C, the defect related EL peak exhibits a characteristic shift to higher wavelengths, where the magnitude of the shift is dependent on the dopant type. Aluminum incorporation exhibited the most improved exciton related-emission, leading to the emergence of a narrow excitonic luminescence peak around 390 nm, which is close to the bandgap of ZnO. The comparison of spectra obtained from temperature-dependent photoluminescence (PL) measurements, before and after thermal annealing, also indicates that the optical activity of impurities changes noticeably upon annealing. The internal quantum efficiency for PL is measured to be as high as 16 percent for Al-doped samples annealed at 380° C. The PL measurements also show that the excitonic luminescence is preferentially guided, while the defect related emission is more isotropically emitted. The nanostructured heterojunction solar cell is designed such that thin CdSe quantum dot films are embedded between a ZnO nanowire film and a hole-conducting polymer layer. This arrangement allows for enhanced light absorption and an efficient collection of photogenerated carriers. Here, we present a detailed analysis of the pyridine solution and 1,2- ethanedithiol ligand exchange processes of the quantum dots, deposition processes of this quantum dot layer, the conformality of this layer on deeply nanostructured samples, and the effect of a surfactant-aided thermal annealing process. Annealing creates a structural conversion of the quantum dot layers into an extremely thin continuous poly-crystalline film, with typical grain diameters of 30-50 nm. This transition is accompanied by a loss of quantum confinement and a significant improvement of the charge transport in the CdSe layer. The combination of the solution and ligand exchange of CdSe quantum dots, as well as the deposition and optimized annealing processes of this quantum dot layer, resulted in solar cells with an open-circuit voltage up to 0.6 V, a short circuit current of ~15 mA/cm2, an external quantum efficiency of 70 percent, and an energy conversion efficiency of 3.4 percent. This 3.4 percent efficiency is presently one of the best efficiencies obtained for this type of device.
41
Chanda, Sheetal Kumar. "Copper doped window layer for CdSe solar cells." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002794.
Full text
42
Schmall, Nicholas Edward. "Fabrication of Binary Quantum Solids From Colloidal Semiconductor Quantum Dots." Bowling Green State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1245257669.
Full text
43
Gutmann, Sebastian. "Electronic Structure Characterization of Nanocrystalline Surfaces and Interfaces with Photoemission Spectroscopy." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3137.
Full textAbstract:
In this study, photoemission spectroscopy (PES) was used to investigate the electronic properties of nanocrystalline titanium dioxide (TiO2), zinc oxide (ZnO), and cadmium selenide (CdSe). Electrospray deposition technique enabled the preparation of thin films in vacuum from a dispersion prepared outside the vacuum chamber. This method also allowed the step-wise formation of interfaces and the monitoring of the evolution of the electronic structure with intermittent PES characterization. The work function of nanocrystalline TiO2 and ZnO was measured with ultraviolet photoemission spectroscopy (UPS) and low-intensity x-ray photoemission spectroscopy (LIXPS). Measurements on environmentally contaminated surfaces revealed an instantaneous and permanent work function decrease of 0.3-0.5 eV upon exposure to ultraviolet radiation during a UPS measurement. The work function reduction is likely to be related to the formation of a surface dipole caused by the photo-chemical hydroxylation of surface defects. This phenomenon was further investigated with regard to its influence on the electronic structure of the indium tin oxide (ITO)/TiO2 interface found in dye-sensitized solar cells. The experiments suggest that UV radiation can cause a small but significant change of the charge injection barriers at the interface. The determined band line-ups revealed electron injection barriers of ~0.3-0.5 eV, while UV radiation caused an increase of about 0.15 eV. This might have the potential to further impede electron transfer to the ITO electrode and affect the performance of solar cell device. Another type of photovoltaic cell using nanocrystalline material is a heterojunction bulk solar cell. Conversion efficiencies of such devices are currently only about 3% due to the inefficient charge separation at interfaces formed by blending organic and inorganic material. An approach to improve efficiencies in such devices is the use of covalently bonded conductive polymer/inorganic hybrid nanocrystals. In this study a prototypical model system was investigated with PES with the aim to develop a measurement protocol that allows the determination of electronic properties for such hybrid materials. The comparison of the relative core-level binding energies of the organics-functionalized CdSe nanocrystal compared to the ligand-free CdSe nanocrystal and the arylselenophosphate ligand material enabled the determination of the electronic structure at the interface. Core-level measurements support the hypothesis that the Se functionality of the organic ligand coordinates to the Cd sites on the nanopthesis surface.
44
Alves, Leticia Rodrigues. "Biochemical and structural alterations induced by selenium under cadmium stress in tomato plants /." Jaboticabal, 2019. http://hdl.handle.net/11449/183154.
Full textAbstract:
Orientador: Priscila Lupino GratãoResumo: As plantas estão expostas a adversidades no ambiente que as circundam, como a contaminação por cádmio (Cd). Este metal pesado tem aumentado na atmosfera devido a atividades humanas. As plantas podem absorver o Cd, causando sérias alterações estruturais, fisiológicas e bioquímicas. As plantas desenvolveram sistemas de defesa complexos, incluindo mecanismos não enzimáticos e enzimáticos para evitar uma cascata de oxidação descontrolada causada pelo estresse oxidativo. Alguns elementos, como o selênio (Se), se utilizados em concentração adequadas, podem induzir uma melhora no sistema antioxidante, no crescimento e nos atributos fotossintéticos. Ainda é pouco conhecido o papel do Se nas respostas das plantas ao estresse. O objetivo deste trabalho foi obter novas informações sobre o papel do selenato e selenito no sistema de desintoxicação das plantas, incluindo a avaliação da nutrição mineral, atividade de enzimas antioxidantes e conteúdo de compostos não enzimáticos, pigmentos, alterações estruturais e o papel do Se na modulação do etileno, com o uso de mutantes hormonais como ferramenta. Nossos dados indicam que o Se é uma estratégia interessante para melhorar o metabolismo da planta sob condições normais ou estressantes. O selênio pode induzir aumento da ação do metabolismo de defesa antioxidante, provavelmente devido a alterações na sinalização do etileno. Além disso, em condições normais, o Se induz alterações estruturais nas células, o que pode contribuir para o desenvolvim... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Cadmium (Cd) contamination is a worldwide concern and one of the most severe causes of abiotic stress in plants, triggering losses in crop production and contamination risks to human health. This heavy metal increased in atmosphere due to human activities. Plants can uptake Cd, causing serious changes in structural, physiological and biochemical processes. Plants developed a complex defence systems including non-enzymatic and enzymatic mechanism to avoid oxidative stress and prevent an uncontrolled oxidation cascade. Some elements, such as selenium (Se), if used in adequate concentration, may induce an improvement in antioxidant system, growth and photosynthetic attributes. It is still unknown the mechanisms of Se in stress responses. The aim of this work was get new insights about the role of selenate and selenite-mediated detoxification strategies, including the evaluation of mineral nutrition, the activity of antioxidant enzymes and non enzymatic compounds, pigments, structural alterations and the role of Se in modulate ethylene, with the use of hormonal mutants as a tool. Our data indicates that Se is an interesting strategy to improve plant metabolism under normal or Cd stressful-condition. Selenium may induce enhancement in antioxidant defence metabolism, probably due to alterations in ethylene signalling. Moreover, under normal condition Se induce structural alterations in cells, which may contribute to plant development. Thus, the information available in this work is... (Complete abstract click electronic access below)
Doutor
45
Issac, Abey. "Photoluminescence Intermittency of Semiconductor Quantum Dots in Dielectric Environments." Doctoral thesis, Universitätsbibliothek Chemnitz, 2006. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200601267.
Full textAbstract:
The experimental studies presented in this thesis deal with the photoluminescence intermittency of semiconductor quantum dots in different dielectric environments. Detailed analysis of intermittency statistics from single capped CdSe/ZnS, uncapped CdSe and water dispersed CdSe/ZnS QDs in different matrices provide experimental evidence for the model of photoionization with a charge ejected into the surrounding matrix as the source of PL intermittency phenomenon. The distribution of the dark state lifetimes can be described by a power law over a wide range while that of bright state can be described by a power law at shorter times followed by an exponential decay. The lifetimes of the bright and dark states are influenced by the dielectric properties of the surrounding environment. Our experimental results show that the lifetime of the dark state increases with the dielectric constant of the matrix. This is very clear from the linear correlation between αoff and f (ε). We propose a self-trapping model to explain the increase of dark state lifetimes with the dielectric constant of the matrix. A charge will be more stabilized in a medium with high dielectric constant. An energetically more favourable state for an electron in a high dielectric medium decreases the return probability which eventually increases the duration of the off-time. Moreover, the self-trapping model establishes a general model for distribution of states in a matrix. We like to mention, that in the case of bright states, a qualitative observation is the cross over of the on-time power law behavior to an exponential one. The power law part of the decay is nearly matrix independent while the exponential decay, which limits the maximum on-time, strongly depends on dielectric properties of the environment. The exponential part of the on-time probability decays much faster in a high dielectric medium and there exists a linear relation between the time constant of the exponential decay and f (ε). Theoretical background has been provided for the observed results using the recently published DCET model which correlates PL intermittency of QDs with properties of the environment. This supports our previous conjecture of a general model for matrix controlled blinking process. The disagreement between experimentally observed dependence of αoff and f (ε) for different matrices with that of the static tunnelling model proposed by Verberk is due to the fact that the tunneling model considers only an electron transfer between a QD and spatially distributed trap states in vacuum. These states are already stabilized states. It does not assume any medium in between. Therefore, matrix dependent blinking kinetics can not be explained quantitatively by tunneling model even though tunneling between a QD and spatially distributed trap states gives a power law distribution for the blinking kinetics. DCET is a more general (dynamic) model. The bright and dark state parabolas contain QD, charge and the matrix. Therefore, this model could in principle explain matrix dependent blinking kinetics in a better way, for example, the energy difference between the minima of the bright and dark state parabolas (-ΔG0) is defined by the stabilization energy of the system provided by the matrix. However, due to lack of the relevant intrinsic parameters we did not compare this relationship and dependence qualitativelyBetrachtet man die Fluoreszenz einzelner Farbstoffmoleküle oder Halbleiternanokristalle bei kontinuierlicher Anregung, so stellt man fest, dass die im Zeitverlauf beobachtete Intensität einer stochastischen Variation unterliegt, d. h. dass das Chromophor zwischen emittierenden und nicht emittierenden Zuständen, auch Hell- und Dunkelzuständen genannt, hin- und herschaltet. Dieses als Blinken bekannte Phänomen ist physikalisch wie auch technologisch herausfordernd, lässt es doch einerseits die Realisierbarkeit einer Reihe von quantenoptischen Anwendungen, so z. B. auf dem Gebiet der Quantenkryptographie, dem Quantum Computing oder der optischen Schaltungstechnik auf Basis einzelner Quantenobjekte, in naher Zukunft möglich erscheinen. Andererseits setzt es gewissen Anwendungen, die auf die permanente Sichtbarkeit des Chromophors aufbauen, Grenzen, so zum Beispiel der Verwendung als Lumineszenzmarker in der medizinischen Diagnostik. Weiterhin ist festzustellen, dass das Blinken kritisch von den äußeren Bedingungen und von den Umgebungsparametern abhängt. Aus diesen und anderen Gründen ist ein fundamentales Verständnis der physikalischen Ursachen und der Wechselwirkungsprozesse unerlässlich. Die Forschung dazu steckt noch in den Kinderschuhen. Basierend auf umfangreiche Messungen der Fluoreszenzzeitreihen einzelner Nanokristalle aus CdSe und CdSe/ZnS in verschiedenen Umgebungen, zeigt diese Dissertation exemplarisch den Einfluss der Dielektrizitätsparameter auf das Blinken. Zur Erklärung des Sachverhalts wird ein so genanntes Self-Trapping-Modell zu Rate gezogen. Demnach kommt es zu einer Ionisation des Quantenobjekts und anschließender Ladungstrennung, woraufhin die abgetrennte Ladung für eine gewisse Zeit in der Umgebung lokalisiert bleibt. Die Dauer der Lokalisierung und damit der emittierenden und nicht emittierenden Perioden hängt von der dielektrischen Funktion des umgebenden Materials ab. Dies ist als direkter Nachweis für den photoinduzierten Ladungstransfer als Ursache des Fluoreszenzblinkens zu deuten. Die Arbeit demonstriert, dass die experimentellen Zeitreihen die charakteristischen Merkmale eines diffusionsgesteuerten Ladungstransferprozesses besitzen und nimmt dabei den gegenwärtigen wissenschaftlichen Diskurs über geeignete theoretische Modelle des Fluoreszenzblinkens auf
46
Dickerson, Bryan Douglas. "Organometallic Synthesis Kinetics of CdSe Quantum Dots." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/27322.
Full textAbstract:
CdSe quantum dots produced by organometallic synthesis are useful as tunable emitters for photonic devices and as multi-colored protein markers for biomedical imaging, applications requiring bright and narrow emission. A diffusion-limited model helped monitor growth rates via photoluminescence and absorbance spectroscopy, in order to characterize synthesis kinetics in stearic acid, dodecylamine, and in trioctylphosphine oxide. The nucleation rate increased with Se concentration, while the growth rate followed the Cd concentration.
Emission peak widths, emission redshift rates, nanocrystal growth rates, and reactant concentrations all decreased to a minimum when emission reached the critical wavelength, at a reaction completion time, tc. The temperature dependence of 1/tc and of redshift rates followed Arrhenius behavior governed by activation energies, which were tailored by the choice of solvent. Synthesis in solvents, such as stearic acid, with lower activation energies produced faster initial nanocrystal growth and longer critical wavelengths. The highest photoluminescence quantum yield was generally at wavelengths shorter than the critical wavelength, when moderate growth rates enabled surface reconstruction while precursors were still available.Ph. D.
47
Lambert, Darcy Erin. "Nanostructured Extremely Thin Absorber (ETA) Hybrid Solar Cell Fabrication, Optimization, and Characterization." PDXScholar, 2011. https://pdxscholar.library.pdx.edu/open_access_etds/637.
Full textAbstract:
Traditional sources of electrical energy are finite and can produce significant pollution. Solar cells produce clean energy from incident sunlight, and will be an important part of our energy future. A new nanostructured extremely thin absorber solar cell with 0.98% power conversion efficiency and maximum external quantum efficiency of 61% at 650 nm has been fabricated and characterized. This solar cell is composed of a fluorine-doped tin oxide base layer, n-type aluminum doped zinc oxide nanowires, a cadmium selenide absorber layer, poly(3-hexylthiophene) as a p-type layer, and thermally evaporated gold as a back contact. Zinc oxide nanowire electrodeposition has been investigated for different electrical environments, and the role of a zinc oxide thin film layer has been established. Cadmium selenide nanoparticles have been produced and optimized in-house and compared to commercially produced nanoparticles. Argon plasma cleaning has been investigated as a method to improve electronic behavior at cadmium selenide interfaces. The thermal anneal process for cadmium selenide nanoparticles has been studied, and a laser anneal process has been investigated. It has been found that the most efficient solar cells in this study are produced with a zinc oxide thin film, zinc oxide nanowires grown under constant -1V bias between the substrate material and the anode, cadmium selenide nanoparticles purchased commercially and annealed for 24 hours in the presence of cadmium chloride, and high molecular weight poly(3-hexylthiophene) spin-coated in a nitrogen environment.
48
Geszke-Moritz, Malgorzata. "Synthesis of stable and non-cadmium containing quantum dots conjugated with folic acid for imaging of cancer cells." Thesis, Vandoeuvre-les-Nancy, INPL, 2011. http://www.theses.fr/2011INPL066N/document.
Full textAbstract:
Les Quantum Dots (QDs) sont des particules cristallines de semi-conducteur ou du métal de forme sphérique et de dimension nanométrique. L'intérêt majeur des QDs réside dans leur grande adaptabilité à de nombreuses applications biologiques.Le but de mon travail était de développer une nouvelle classe de QDs de faible toxicité afin de les utiliser pour la bio-imagerie des cellules cancéreuses. Pour cela, il est nécessaire de préparer des sondes hydrosolubles, photostables, biocompatibles, de luminescence élevée et possédant une faible toxicité. La synthèse des cœurs de type ZnS and ZnSe dopés au manganèse ou au cuivre et stabilisés par l’acide 3-mercapropropionique ou par le 1-thioglycérol a été réalisée par la voie hydrothermale. Les techniques analytiques de caractérisation utilisées sont la spectroscopie UV-visible, la spectroscopie de fluorescence, la diffraction des rayons X (XRD), la spectroscopie photoélectronique de rayon X (XPS), la microscopie électronique à transmission (TEM), la diffusion dynamique de la lumière DLS, la spectroscopie infra-rouge (IR), et la résonance paraélectronique (RPE). La toxicité des QDs a été déterminée sur des cellules cancéreuses. Les différents test de cytotoxicité (MTT, XTT et ferrous oxidation-xylenol orange) ont été réalisés. Finalement, les QDs de type ZnS:Mn conjugués à l’acide folique ont été utilisés pour la bio-imagerie des cellules cancéreuses par le biais d’une excitation biphotoniqueSemiconductor QDs are tiny light-emitting crystals, and are emerging as a new class of fluorescent labels for medicine and biology. The aim of this work was to develop a new class of non-toxic QDs probes with essential attributes such as water dispersibility, photostability, biocompatibility, high luminescence and possible excitation with low-energy visible light, using simple processing method. Such nanoprobes could be used for bio-imaging of cancer cells. In the performed studies, I focused on ZnS and ZnSe QDs as they are cadmium-free and might be excited biphotonically.The synthesis protocols of ZnS and ZnSe QDs doped with two ions such as Mn or Cu and stabilized by 3-mercaptopropionic acid or 1-thioglycerol were established, followed by NCs characterization (diameter, surface charge, photophysical properties, …) using analytical techniques such as spectrophotometry UV-vis, fluorimetry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), dynamic light scattering (DLS), infra-red analysis (FT-IR), thin layer chromatography (TLC) and electron paramagnetic resonance (EPR). The cytotoxicity of synthesized bare and conjugated NPs was evaluated on cancer cell lines using MTT, XTT and ferrous oxidation-xylenol orange assay.Finally, chosen well fluorescent and weakly toxic types of as-prepared and characterized QDs were used for bio-imaging of cancer cells. In these experiments, FA-functionalized NCs were excited biphotonically. The performed experiments showed the potential of QDs as cancer cells fluorescent markers and that they accumulate around the cell nuclei
49
Lima, Leonardo Warzea. "Selenium and sulfur : mitigation in plant stresses /." Jaboticabal, 2016. http://hdl.handle.net/11449/138897.
Full textAbstract:
Orientador: Priscila Lupino GratãoCoorientador: André Rodrigues dos Reis
Banca: Tiago Tezotto
Banca: Tiago Santana Balbuena
Abstract: Plants do not have specific defense mechanisms to counteract the diverse range of abiotic stresses and pollutants into the environment, and its survival depends on the flexibility and adaptability of its own natural defense mechanisms. Furthermore, the maintenance of cellular homeostasis depends on several interlinked and complex mechanisms, while the cellular defense system does not follow a specific pattern of action and may differ due to various factors such as plant species, exposure time to the stress, plant developmental stage, different organs and tissues analyzed. In the light of these considerations, this dissertation aimed to highlight and investigate the role of Sulfur and Selenium against different plant stresses, through the enzymatic and non-enzymatic plant responses and other related defense mechanisms. In the first chapter the author characterize the general biochemical mechanisms of the antioxidant cell defense, specifically the reactive oxygen species (EROs) formation and its chemical singularities and the induced oxidative stress, the enzymatic antioxidant defense system, specifically the superoxide dismutase (SOD) and Catalase (CAT) enzymes, the non-enzymatic mechanisms against the stress, including the Ascorbate-Glutathione cycle, the GSH (reduced glutathione), the phytochelatins and also proline formation. The plant nutritional status during the stress is crucial in order to maintain a proper defense response. In view of this, the chapter two is a publis... (Complete abstract click electronic access below)
Resumo: As plantas não possuem mecanismos de defesa específicos para combater a diversidade de estresses abióticos e poluentes do ambiente, e sua sobrevivência depende da flexibilidade e adaptação dos seus próprios mecanismos de defesa naturais. Além disso, a manutenção da homeostase celular depende de vários mecanismos interligados e complexos, enquanto o sistema de defesa celular não segue um padrão específico de ação e pode ainda variar devido a vários fatores tais como a espécie do vegetal, o tempo de exposição ao estresse, o estágio de desenvolvimento da planta e também nos diferentes órgãos e tecidos analisados. Com base nessas considerações, esta dissertação teve como objetivo destacar e investigar o papel do Enxofre (S) e do Selênio (Se) contra diferentes estresses nas plantas, através das respostas enzimáticas, não enzimáticas e também outros mecanismos de defesa relacionados. No primeiro capítulo, o autor caracteriza os mecanismos bioquímicos gerais da defesa celular antioxidante, especificamente a formação das espécies reativas de oxigênio (EROs) e suas singularidades químicas e o estresse oxidativo induzido, o sistema de defesa antioxidante enzimático, especificamente as enzimas Superóxido Dismutase (SOD) e a Catalase (CAT), os mecanismos não-enzimáticas contra o estresse, incluindo o ciclo Aascorbato-Glutationa, a GSH (glutationa reduzida), as fitoquelatinas e também a formação de prolina. O estado nutricional da planta durante o estresse é crucial a fim de manter uma re... (Resumo completo, clicar acesso eletrônico abaixo)
Mestre
50
Іващенко, Максим Миколайович, Максим Николаевич Иващенко, and Maksym Mykolaiovych Ivashchenko. "Структурні, оптичні та електрофізичні властивості плівок CdSe та ZnSe і гетеропереходів на їх основі." Thesis, Вид-во СумДУ, 2014. http://essuir.sumdu.edu.ua/handle/123456789/36704.
Full textAbstract:
Дисертаційна робота присвячена дослідженню морфології поверхні, структурно-фазового стану, оптичних і електрофізичних властивостей плівок CdSe і ZnSe та гетеропереходів (ГП) на їх основі, отриманих методом термічного випаровування у квазізамкненому об’ємі, моделюванню основних експлуатаційних характеристик сонячних елементів (СЕ) на основі ГП p–ZnTe/n– CdSe і n–ZnSe/n–CdSe, визначенню їх оптимальних фізичних та конструкційних параметрів. У роботі проведено комплексне дослідження морфології поверхні, структурних та субструктурних особливостей плівок CdSe та ZnSe залежно від фізико–технологічних умов їх конденсації. Досліджено зв’язок оптичних та електрофізичних властивостей селенідів з їх структурно-фазовим станом. Установлені режими отримання структурно досконалих плівок, придатних для використання у приладобудуванні. Наведено результати дослідження процесів відбиття, поглинання світла та генерації електронно-діркових пар у СЕ на основі ГП р–ZnTe/n–CdSe і n–ZnSe/n–CdSe. Подаються результати розрахунку оптичних втрат, пов’язаних із поглинанням та відбиттям світла у допоміжних шарах багатошарової структури скло/p-СuO/p-ZnTe/n-CdSe, яка може бути використана як СЕ. В умовах освітлення АМ-1,5 розраховано темнові і світлові ВАХ СЕ та залежності квантового виходу від довжини хвилі випромінювання залежно від таких параметрів моделювання, як товщина базового та віконного шарів, температура експлуатації. У результаті моделювання були встановлені оптимальні конструкційні параметри фотоперетворювачів, що забезпечують максимальний ККД СЕ. З урахуванням результатів моделювання експериментально були отримані гетеросистеми p–ZnTe/n–CdSe та досліджені їх морфологія, структурні, субструктурні та електрофізичні властивості, визначений механізм струмопроходження у ГП.
При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/36704Диссертационная работа посвящена исследованию морфологии поверхности, структурно-фазового состояния, оптических и электрофизических свойств пленок CdSe и ZnSe и гетеропереходов (ГП) на их основе, полученных методом термического испарения в квазизамкнутом объеме, моделированию основных эксплуатационных характеристик солнечных элементов (СЭ) на основе ГП p– ZnTe/n–CdSe и n–ZnSe/n–CdSe, определению их оптимальных физических и конструктивных параметров. В работе проведено комплексное исследование морфологии поверхности, структурных и субструктурных особенностей пленок CdSe и ZnSe в зависимости от физико-технологических условий их конденсации. Исследована связь оптических и электрофизических свойств селенидов с их структурно-фазовым состоянием. В результате установлены режимы получения структурно совершенных пленок селенидов, пригодных для использования в приборостроении. Приведены результаты исследования процессов отражения, поглощения света и генерации электронно-дырочных пар в СЭ на основе ГП р–ZnTe/n–CdSe и n–ZnSe/n–CdSe. Представлены результаты расчета оптических потерь, связанных с поглощением и отражением света во вспомогательных слоях многослойной структуры стекло/p-СuO/p-ZnTe/n-CdSe, которая может быть использована как СЭ. В условиях освещения АМ-1,5 рассчитаны темновые и световые ВАХ СЭ и зависимости квантового выхода от длины волны излучения в зависимости от таких параметров моделирования, как толщина базового и оконного слоев, температура эксплуатации. В результате моделирования были установлены оптимальные конструкционные параметры фотопреобразователей, обеспечивающих максимальный КПД СЭ. С учетом результатов моделирования экспериментально были получены гетеросистемы p-ZnTe/n-CdSe и исследованы их морфология, структурные, субструктурные и электрофизические свойства, определен механизм токопрохождения в ГП. При цитировании документа, используйте ссылку http://essuir.sumdu.edu.ua/handle/123456789/36704
This thesis is devoted to investigation of the surface morphology, structure–phase state, optical and electro-physical properties of CdSe and ZnSe films and hetero–junctions (HJ) on their base obtained be close–spaced vacuum sublimation (CSVS) technique, modeling the general working characteristics of p–ZnTe/n–CdSe and n–ZnSe/n–CdSe HJs, determination their optimal physical and constructional parameters. In this work was carried out a complex investigation of the surface morphology, structural and sub–structural features of CdSe and ZnSe films depend on their physical and technological condensation conditions. Was researched a connection between optical (electro–physical) selenides properties and their structure–phase state. Were estimated regimes obtaining the structurally ideal films suitable for usage in device– making branch. At first it was carried out an investigation of Raman scattering spectra of ZnSe polycrystalline films obtained at different substrate temperatures by CSVS method. On spectra were observed peaks which were interpreted as TO and LO modes and their phonon replicas. A shift of 1LO–phonon replica in a red-spectral range compare to it’s position in a bulk material says about the films tension due to thermal deformations. A presence of a high–order numbers of LO-modes confirms our conclusion of structural investigation about the high films quality.thermal deformations. A presence of a high–order numbers of LO-modes confirms our conclusion of structural investigation about the high films quality. Presented results of investigation the light’s reflectance and absorbance processes, electron–hole pairs generation in SC based on р–ZnTe/n–CdSe and n– ZnSe/n–CdSe HJs. It was carried out a measurement of optical losses connected to the light’s absorption and reflection in auxially layers of multi–layered glass/p–CuO/p– ZnTe/n–CdSe structure, which may be used as SC. At AM-1.5 lighting condition were measured dark and light IV–curves and “quantum efficiency–wavelength” dependencies depend on the next modeling parameters: base and window layer’s thickness, working temperature. As a result of a modeling procedure were estimated optimal construction parameters of photo–convertors which ensure the maximal efficiency of SC. With taking into account resylts of the modeling, were experimentally obtained p–ZnTe/n–CdSe hetero–systems and were investigated their morphology, structural, sub-structural and electro–physical properties and determined their currenttransition mechanism in HJ. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/36704