The synthesis, characterization and amphiphilic self-assembly of polymer brush functionalized nanoparticles (PBNPs) using a block copolymer template is described herein. To study the effect of polymer brush composition on self-assembly, four samples were created using a mixture of PS-b-PAA (polystyrene-block-polyacrylic acid) and PMMA-b-PAA (poly(methyl methacrylate)-block-polyacrylic acid) diblock copolymers to create PBNPs with a CdS quantum dot (QD) core and different ratios of PS and PMMA in the coronal brush. Static light scattering showed that despite differences in brush composition, the PBNPs formed nanoparticles of similar aggregation number and chain density but showed evidence of asymmetric structure in a common solvent for both blocks at higher PS contents. After subsequent hydrolysis of the hydrophobic PMMA to hydrophilic poly(methacrylic acid) (PMAA), these amphiphilic particles were then self-assembled in THF/H2O solution in which it was determined that increasing the hydrophobic content of the brush composition, the initial nanoparticle concentration (c0) or the added salt content (RNaCl), would cause the assembly of low curvature assemblies. Compilation of this data allowed for the construction of phase diagrams for PBNP systems based on brush composition and c0 at different salt contents. Lastly, PS-b-PAA-b-PMMA triblock copolymers with variable PMMA chain length were assembled into PBNPs around a CdS QD core using a block copolymer template approach. Light scattering showed these particles also had similar aggregation number and chain density despite the difference in PMMA chain length. After hydrolysis of PMMA to PMAA these particles were then self-assembled in THF/H2O mixtures to determine the role of PMAA block length on the produced morphological structures. The resulting assemblies suggest that chain length played a minimal role in their self-assembly / Graduate / 2018-09-15

Submitted by Heitor Rapela Medeiros (heitor.rapela@ufpe.br) on 2015-03-03T18:07:38Z No. of bitstreams: 2 DISSERTAÇÃO DE ANTONIO_VERSÃO_FINAL.pdf: 2621194 bytes, checksum: 63f0412f30f9e4e90794017db0616113 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-03T18:07:38Z (GMT). No. of bitstreams: 2 DISSERTAÇÃO DE ANTONIO_VERSÃO_FINAL.pdf: 2621194 bytes, checksum: 63f0412f30f9e4e90794017db0616113 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-02-28 / CAPES / Os Quantum dots (QDs) ou ponto quânticos vem sendo cada vez mais aplicados na área de diagnóstico por fluorescência como uma alternativa mais estável em comparação com os corantes orgânicos usualmente aplicados. Em comparação a estes, os QDs têm características ópticas peculiares que os dão vantagens como: resistência ao fotoescurecimento, possuírem um estreito espectro de emissão e uma larga banda de absorção. Uma vez recobertos, estas nanoestruturas podem ser bioconjugadas a alvos biológicos ou mesmo a anticorpos tornando-se fluoroimunoensaios com grande especificidade. Este foi o objetivo deste manuscrito, onde CdS/Cd(OH)2 - emissão no verde - tendo como agente estabilizante o polifosfato de sódio ([(NaPO3)]n) e CdTe sintetizados com telúrio metálico, Cd(ClO4)2, ácido mercaptosuccínico (AMS) - emissão no laranja - e ácido mercaptopropiônico (AMP) - emissão no verde - como agentes estabilizantes, foram bioconjugados por formação de bases de Shiff e por adsorção a anticorpos do sistema sanguíneo ABO e, posteriormente, usados na marcação simples (A e B) e dupla (AB) de eritrócitos previamente fenotipados sendo o tipo O foi usado como controle negativo. Os QDs foram caracterizados opticamente através de espectroscopias de absorção e emissão e estruturalmente através de técnicas de microscopias eletrônica de transmissão, pela qual pode ser confirmada a sua cristalinidade, e também a difração de raio-X, revelando diâmetros médios de ~3 nm para o QD-AMS, ~2 nm para o QD-AMP e ~7,5 nm para o CdS/Cd(OH)2. Através da Citometria de Fluxo, os sistemas QDs-anitocorpos demonstraram especificidade obtendo-se valores de 28,4% para os bioconjugados com CdS/Cd(OH)2-anti-A, 70,64% para o tipo A com o sistema CdTe/CdS-anti-A em FL2 (canal laranja), 37,73% para o tipo B com o sistema CdTe/CdS-anti-B em FL1 (canal verde) e 58,24% de dupla marcação detectada em ambos os canais. Os resultados dos QDs CdS/Cd(OH)2, QD-AMS e QD-AMP bioconjugados a anticorpos do sistema ABO mostram especificidade da técnica e abrem a possibilidade de determinação de fenótipos fracos desse sistema. Além disso, serve de modelo para a bioconjugação com outros anticorpos e consequentemente, para o diagnóstico de várias doenças.

Single spins confined in semiconductor quantum dots - artificial atoms in the solid-state - are attractive candidates for quantum mechanical bits, the fundamental units and building blocks of a quantum computer. The ability to address quantum dot spins optically allows us to initialise and manipulate the state of the quantum bit. Gaining information on the qubit, for example by reading out its state, not only requires state-selective optical excitation, but also access to the single photons scattered in response by the quantum dot. Further, for a distributed computer architecture where nodes of few quantum bits are interlinked via optical communication channels photonic quantum bits are required to faithfully transmit the quantum information. In this thesis we advocate resonant excitation of quantum dot transitions and collection of the resonance fluorescence to address two outstanding challenges: generating dephasing-free single photons for use as flying quantum bits and single-shot spin readout. To this end we investigate the spectral and first-order coherence properties of quantum dot resonance fluorescence. In particular, we directly observe highly coherent scattering in the low Rabi frequency limit which has remained unexplored for solid-state single photon emitters so far. At the same time, interactions with the semiconductor environment are revealed and quantified through their optical signatures: exciton-phonon coupling, nuclear spin dynamics and local electric field fluctuations signal a departure from the ideal atom-like behaviour. Taking advantage of the laser-like coherence of single phase-locked quantum dot photons in the Heitler regime, we demonstrate near-ideal two-photon quantum interference. This benchmark measurement is a precursor for the photonic entanglement of distant quantum dot spins in a quantum optical network, and the results here predict a high fidelity operation. Finally, moving to tunnel-coupled quantum dot molecules we show that the overlap of carrier wave functions in two closely spaced quantum dots forms new spin-selective optical transitions not available in single quantum dots. Then, the presence or absence of scattered photons reveals the electron spin. Intermittency in the quantum dot resonance fluorescence allowed us, for the first time, to observe spin quantum jumps in real-time. Both achievements - highly coherent photons and spin readout - provide the missing link to attempt creation of a small-scale quantum network now.

Indiana University-Purdue University of Indianapolis (IUPUI) / A Near-field Scanning Optical Microscope (NSOM) is used to study the resonant energy transfer between different size CdSe/ZnS quantum dots (QDs). The NSOM system is used to bring the small QDs which are 6 nm in diameter close to 8 nm diameter QDs which are embed with PMMA on a cover glass. The PMMA is used to prevent the 8 nm QDs from aggregation, which allows us to locate one dot on the cover slide and have the potential to get the interaction of two individual dots. A systematic methodology is used to localize a single QD on the cover glass and align the small and large QDs. Since the ground energy state of the small QDs match the excitation energy level of the large QDs. When the small dots get excited, part of the energy transfers to the large QDs. As the separation between small and large QDs is changed in near-field range (20-50nm), the transition probability is observed, indicating that the FRET level changes as a function of separation between small and large QDs. Possible future improvements are also discussed.

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published_or_final_version / Physics / Master / Master of Philosophy

<p>In this thesis time-resolved photoluminescence spectroscopyis presented as a powerful tool to study the carrier dynamicsin various self-assembled quantum dot (QD) structures, whichare potentially attractive for device applications.</p><p>The experiments reveal the impact of proton irradiation onInGaAs QDs and comparable quantum wells. Nonradiativerecombination at defects–an important material parameterand“measure”of the structure optical quality–is found to play a much less important role for the QD samples.The superior radiation hardness can be explained as a result ofthe three-dimensional carrier confinement in QDs. Comparisonsbetween the structures show a decrease of photoluminescenceintensity for quantum wells but a slight increase for QDsirradiated at low to intermediate doses. This somewhatunexpected characteristic is described by an enhanced carriertransfer into the dots via the defects introduced in thematerial by the protons.</p><p>In a different structure carrier dynamics in spatiallyaligned of InAs QDs are investigated. Alignment along lines isachieved by misfit dislocations deliberately introduced in thesubstrate. Photoluminescence spectra of the dots exhibit muchsmaller inhomogeneous broadening than for the reference sampleas a result of an improved QD uniformity. Samples with varyingbuffer layer thicknesses were grown to study the influence ofdislocation related traps on the observed fastphotoluminescence decay. It is found that the fast carriertrapping is predominantly caused by point defects close to theQDs or at the QD/barrier interfaces.</p><p>Additional numerical simulations confirm the roles of thetwo independently acting traps in nonradiativerecombination.</p>

Thesis (DTech (Chemistry))--Cape Peninsula University of Technology, 2015. / Researchers around the world are now focusing on inculcating green chemistry principles in all level of research especially in nanotechnology to make these processes environmental friendly. Nanoparticles synthesized using green chemistry principles has several advantages such as simplicity, cost effectiveness, compatibility for biomedical and pharmaceutical applications and large scale production for commercial purpose. Based on this background, this thesis present the design, synthesis, characterization and applications of various CdSe based core-shell and core-multi shell quantum dots (QDs), quantum dots-polymer nanocomposites, silver nanoparticles (Ag-NPs) and silver nanocomposites via completely green methods. Various QDs like CdSe/CdS/ZnS and CdSe/ZnS, and there polymer nanocomposites were successfully synthesized and characterized. The high quality of the as-synthesized nanoparticles was confirmed using absorption and photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). Detailed optical and morphological characterization showed that the CdSe/CdS/ZnS core-multi shell QDs were small, monodispersed with high fluorescent intensity and narrow emission width. The CdSe/CdS/ZnS core multi-shell QDs were dispersed in epoxy polymer matrix to obtain fluorescent epoxy nanocomposite. The brillouin spectroscopy analysis revealed that the presence of QDs inside polymer composite reduces the acoustic frequency of the polymer. Highly fluorescent CdSe/ZnS core-shell QDs was also synthesized and dispersed in PMMA polymer matrix to prepare bright yellow emitting nanocomposite film. The as-synthesized QDs also undergone surface exchange to convert the organically soluble nanomaterial to water soluble. After the ligand exchange, the morphology and above all the fluorescence property of the quantum dots remained intact. In another approach, HDA-capped CdSe nanoparticles were synthesized in the absence of an inert gas followed by dispersion in polymer polycaprolactone to produce orange light emitting electrospun polymer nanocomposite nanofibre.