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The study of the immune system has provided insight in the mechanism of protection induced by vaccination; primarily that most clinically protective vaccines are potent in generating neutralizing antibody responses. However, vaccination fails to protect against a wide range of acquired chronic infections caused by viruses, such as HIV, HBV and HCV. One of the major reasons for weak responses to therapeutic vaccine is the impaired function of effector T cells resulting from viral persistence. Although IL-2 can potently increase effect function of viral specific T cells, systemic administration of IL-2 induces organ pathology and expansion of Treg cells. In this study, we have now developed a novel vaccine delivery system IL-2-nanoAPC delivering antigen-MHC complexes (pMHC), co-stimulatory molecules and IL-2 to antigen specific T cells. NanoAPC are derived from the endoplasmic reticulum (ER) membranes of human B cell line 721.221 engineered with selected HLA allele and IL-2 as the ER retention proteins. The IL-2-nanoAPC interacted with antigen specific T cells, induced immune synapses and expression of high affinity IL-2 receptor and enhanced effector function of antigen specific T cells, but did not affect bystander T cells and Foxp3+ Treg cells. Together with pMHC, co-stimulatory molecules, the selective delivery of IL-2 not only increased the CD4 and CD8 T cell responses to viral antigens but also enhanced TCR proximal signalling and suppressed expression of PD1 molecules on IFNγ producing effector CD8 T cells. We also found that the co-induction of T helper responses by IL-2-nanoAPC in a mixed culture could increase CD8 T cell responses to viral antigen. The IL-2-nanoAPC effectively induced responses of CD4 and CD8 T cells from chronic HBV patients. The results demonstrate that selective delivery of IL-2, together with pMHC and co-stimulatory molecules, by nanoAPC to antigen specific T cells has potential to recover anti-viral immune responses in chronic HBV patients.

Low-dimensional semiconductor structures, such as one-dimensional nanowires (NWs) and zerodimensional quantum dots (QDs), are materials with novel fundamental physical properties and a great potential for a wide range of nanoscale device applications. Here, especially promising are direct bandgap II-VI and III-V compounds and related alloys with a broad selection of compositions and band structures. For examples, NWs based on dilute nitride alloys, i.e. GaNAs and GaNP, provide both an optical active medium and well-shaped cavity and, therefore, can be used in a variety of advanced optoelectronic devices including intermediate band solar cells and efficient light-emitters. Self-assembled InAs QDs formed in the GaAs matrix are proposed as building blocks for entangled photon sources for quantum cryptography and quantum information processing as well as for spin light emitting devices. ZnO NWs can be utilized in a variety of applications including efficient UV lasers and gas sensors. In order to fully explore advantages of nanostructured materials, their electronic properties and lattice structure need to be comprehensively characterized and fully understood, which is not yet achieved in the case of aforementioned material systems. The research work presented this thesis addresses a selection of open issues via comprehensive optical characterization of individual nanostructures using micro-Raman ( -Raman) and micro-photoluminescence ( -PL) spectroscopies. In paper 1 we study polarization properties of individual GaNP and GaP/GaNP core/shell NWs using polarization resolved μ-PL spectroscopy. Near band-edge emission in these structures is found to be strongly polarized (up to 60% at 150K) in the orthogonal direction to the NW axis, in spite of their zinc blende (ZB) structure. This polarization response, which is unusual for ZB NWs, is attributed to the local strain in the vicinity of the N-related centers participating in the radiative recombination and to their preferential alignment along the growth direction, presumably caused by the presence of planar defects. Our findings therefore show that defect engineering via alloying with nitrogen provides an additional degree of freedom to control the polarization anisotropy of III-V nanowires, advantageous for their applications as a nanoscale source of polarized light. Structural and optical properties of novel coaxial GaAs/Ga(N)As NWs grown on Si substrates, were evaluated in papers 2-4. In paper 2 we show by using -Raman spectroscopy that, though nitrogen incorporation shortens a phonon correlation length, the GaNAs shell with [N]<0.6% has a low degree of alloy disorder and weak residual strain. Additionally, Raman scattering by the GaAs-like and GaNlike phonons is found to be enhanced when the excitation energy approaches the E+ transition energy. This effect was attributed the involvement of intermediate states that were created by N-related clusters in proximity to the E+ subband. Recombination processes in these structures were studied in paper 3 by means of μ-PL, μ-PL excitation (μ-PLE), and time-resolved PL spectroscopies. At low temperatures, the alloy disorder is found to localize photo-excited carriers leading to predominance of localized exciton (LE) transitions in the PL spectra. Some of the local fluctuations in N composition are suggested to create three-dimensional confining potentials equivalent to that for QDs, based on the observation of sharp PL lines within the LE contour. In paper 4 we show that the formation of these QD-like confinement potentials is somewhat facilitated in spatial regions of the NWs with a high density of structural defects, based on correlative spatially-resolved structural and optical studies. It is also concluded the principal axis of these QD-like local potentials is mainly oriented along the growth direction and emit light that is linearly polarized in the direction orthogonal to the NW axis. At room temperature, the PL emission is found to be dominated by recombination of free carriers/excitons and their lifetime is governed by non-radiative recombination via surface states. The surface recombination is found to become less severe upon N incorporation due to N-induced modification of the surface states, possibly due to partial surface nitridation. All these findings suggest that the GaNAs/GaAs hetero-structures with the onedimensional geometry are promising for fabrication of novel optoelectronic devices on foreign substrates (e.g. Si). Fine-structure splitting (FSS) of excitons in semiconductor nanostructures has significant implications in photon entanglement, relevant to quantum information technology and spintronics. In paper 5 we study FSS in various laterally-arranged single quantum molecular structures (QMSs), including double QDs (DQDs), quantum rings (QRs), and QD-clusters (QCs), by means of polarization resolved μ-PL spectroscopy. It is found that FSS strongly depends on the geometric arrangements of the QMSs, which can effectively tune the degree of asymmetry in the lateral confinement potential of the excitons and can reduce FSS even in a strained QD system to a limit similar to strain-free QDs. Fabrication of nanostructured ZnO-based devices involves, as a compulsory step, deposition of thin metallic layers. In paper 6 we investigate impact of metallization by Ni on structural quality of ZnO NWs by means of Raman spectroscopy. We show that Ni coating of ZnO NWs causes passivation of surface states responsible for the enhanced intensity of the A1(LO) in the bare ZnO NWs. From the resonant Raman studies, strong enhancement of the multiline Raman signal involving A1(LO) in the ZnO/Ni NWs is revealed and is attributed to the combined effects of the Fröhlich interaction and plasmonic coupling. The latter effect is also suggested to allow detection of carbon-related species absorbed at the surface of a single ZnO/Ni NW, promising for utilizing such structures as efficient nano-sized gas sensors.

This thesis systematically investigates the nano handling and measurement techniques for biological cells in culture and studies the techniques to realize innovative and multi-functional applications in biomedicine. Among them, the technique based on AFM is able to visualize and quantify the dynamics of organic cells in culture on the nano scale. Especially, the cellular shear adhesion force on the various locations of biological cells was firstly accurately measured in the research of the cell-substrate interaction in terms of biophysical perspective. The innovative findings are conductive to study the cell-cell adhesion, the cell-matrix adhesion which is related to the cell morphology structure, function, deformation ability and adhesion of cells and better understand the cellular dynamic behaviors. Herein, a new liquid-AFM probe unit and an increment PID control algorithm were implemented suitable for scanning the cell samples under the air conditions and the liquid environments. The influence between the surface of sample and the probe, and the damage of probe during the sample scanning were reduced. The proposed system is useful for the nano handling and measurement of living cells. Besides, Besides, to overcome the limitations of liquid-AFMs, the multiple optical tweezers were developed to integrate with the liquid-AFM. The technique based on laser interference is able to characterize the optical trap stiffness and the escape velocity, especially to realize the capture and sorting of multiple cells by a polarization-controlled periodic laser interference. It can trap and move hundreds of cells without physical contact, and has broad application prospects in cytology. Herein, a new experimental method integrated with the positioning analysis in the Z direction was used to improve the fluid force method for the calibration and characterize the mechanical forces exerted on optical traps and living cells. Moreover, a sensitive and highly efficient polarization-controlled three-beam interference set-up was developed for the capture and sorting of multiple cells. By controlling the polarization angles of the beams, various intensity distributions and different sizes of dots were obtained. Subsequently, we have experimentally observed multiple optical tweezers and the sorting of cells with different polarization angles, which are in accordance with the theoretical analysis.

Si la microscopie de fluorescence est la plus couramment utilisée pour détecter des nano-objets individuels, les méthodes d’absorption permettent de s’affranchir de la photostabilité imparfaite des objets luminescents et d’accéder à d’autres objets en ne se limitant pas aux espèces luminescentes. Au cours de ce travail de thèse, nous avons cherché à pousser les limites des méthodes basées sur l’absorption existantes en termes de sensibilité et de caractère quantitatif. La microscopie photothermique hétérodyne permet de détecter une grande variété de nano-objets absorbants sur fond noir. Nous présentons une nouvelle implémentation de cette technique permettant d’exalter la réponse photothermique de nanoparticules d’or individuelles autour de la transition de phase du milieu les entourant. Un gain d’un facteur 10 a été obtenu par rapport à un milieu classique. Afin de déterminer l’absorption de petits nano-objets à fort rapport d’aspect, comme les nanotubes de carbone, la détection directe est en revanche plus quantitative. En développant une méthode d’absorption à modulation spatiale optimisée, nous avons déterminé pour la première fois la valeur de la section efficace d’absorption de nanotubes de carbone (6,5) de manière absolue. Finalement, nous avons mis au point un protocole de préparation et de tri en longueur de nanotubes de carbone ultracourts. Les longueurs obtenues ont été caractérisées par spectroscopie, microscopies optique et à force atomique. Dans le futur, ces nanotubes pourront être utilisés comme sondes biologiques détectées par le dispositif photothermique. Les nanotubes possèdent en effet des résonances optiques dans le proche infrarouge correspondant à la plage de transparence des tissus biologiques. / Absorption methods can overcome the limited photostability of luminescent nano-objects and allow for detection of non-luminescent ones, making it a desirable alternative to commonly used fluorescence microscopy for single particle detection. During this project, we optimized the sensitivity of existing absorption based methods and developed their use for quantitative applications. Photothermal heterodyne microscopy is a highly sensitive, “background-free” detection method that can be applied to a large variety of individual absorbing nano-objects. We implement a new version of this technique that enhances the photothermal response of single gold nanoparticles by using a phase transition in their surrounding environment. Compared to a standard medium, we demonstrate a 10 fold enhancement of the signal to noise ratio. On the other hand, for measurement of the absorption cross section of small, and high aspect ratio nano-objects, such as carbon nanotubes, direct detection is more quantitative. In pursuit of this goal, we developed an optimized modulated absorption method and used it to directly measure the absolute absorption cross section of (6,5) carbon nanotubes for the first time. Finally, we set up a protocol to prepare ultrashort carbon nanotubes and sort them by length. As they exhibit strong optical resonances in the near infrared corresponding to a transparency window in biological tissues, they will be useful as photothermally detected biological probes. These nanotubes were characterized spectroscopically, and by optical and atomic force microscopy.

Thesis advisor: Cyril P. Opeil / Thermoelectric (TE) materials are of broad interest for alternate energy applications, specifically waste heat applications, as well as solid-state refrigeration. The efficiency of TE materials can be improved through either the enhancement of the Seebeck coefficient and electrical conductivity, or through the reduction of the thermal conductivity, k, specifically the lattice portion of thermal conductivity, klatt. Nanostructuring has been proven to reduce klatt and therefore increase efficiency. The inability to accurately model the lattice and electronic contributions to k makes optimizing the reduction of klatt difficult. This work demonstrates that the lattice and electronic contributions to k in nanostructured materials can be directly measured experimentally by separating the contributions using magnetic field. We use this technique along with other characterization techniques to determine the effects of doping Ce, Sm, and Ho into Bi88Sb12. Along with enhancing the efficiency of the material, TE devices must be thermally stable in the temperature range of operation. Therefore we also study the effects of temperature cycling, annealing, oxidation, and diffusion barriers on TE devices. These studies are accomplished through both homemade and commercially available measurement equipment. / Thesis (PhD) — Boston College, 2013. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Thesis advisor: Michael J. Naughton / Geometrically generalized analytical expressions for device transport are derived from first principles for a photovoltaic junction. Subsequently, conventional planar and unconventional coaxial and hemispherical photovoltaic architectures are applied to detail the device physics of the junction based on their respective geometry. For the conventional planar cell, the one-dimensional transport equations governing carrier dynamics are recovered. For the unconventional coaxial and hemispherical junction designs, new multi-dimensional transport equations are revealed. Physical effects such as carrier generation and recombination are compared for each cell architecture, providing insight as to how non-planar junctions may potentially enable greater energy conversion efficiencies. Numerical simulations are performed for arrays of vertically aligned, nanostructured coaxial and hemispherical amorphous silicon solar cells and results are compared to those from simulations performed for the standard planar junction. Results indicate that fundamental physical changes in the spatial dependence of the energy band profile across the intrinsic region of an amorphous silicon p-i-n junction manifest as an increase in recombination current for non-planar photovoltaic architectures. Despite an increase in recombination current, however, the coaxial architecture still appears to be able to surpass the efficiency predicted for the planar geometry, due to the geometry of the junction leading to a decoupling of optics and electronics. / Thesis (PhD) — Boston College, 2012. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Photonic crystals (PhCs) are periodically structured electromagnetic media, generally characterised by not permitting light of defined ranges of frequency to propagate through the structure. These disallowed ranges of frequency are known as photonic band gaps. The intentional introduction of defects into the crystal gives rise to localized electromagnetic states that provide a mechanism for the control of the propagation of photons through PhCs. In the case of one dimensional (1-D) PhCs, the introduction of a single defect into a finite PhC results in the formation of a resonant cavity structure, a so-called microcavity. The ease of fabrication and scope for integration make 1-D PhCs good candidates for the future applications of PhCs in light transmission systems and, as such, these structures are the focus of the research reported here. The aim of this thesis is to report a practical study of passive 1-D PhC devices and thereby extend the base of measurements that support and extend the results of theory and simulation. Various types of 1-D PhC structures have been fabricated using electron beam lithography and inductively coupled plasma technologies in a clean-room environment. The fabricated structures in effect demonstrate a first or primitive level of integration of 1-D PhCs with another optical device, namely a ridge waveguide. Measurements were performed by butt-coupling from a single mode fibre taper of the transmission characteristics of the resulting integrated waveguides, whilst a Side-band measurement method for very high resolution (0.2pm) microcavity characterisation was invented during the measurement process. A multiple wavelength transmission optical filter transmitting at the telecommunication wavelengths of 1310nm and 1550nm, and which could be used in a WDM system was demonstrated. The effect of introducing mode matching structures to minimize II the scattering loss and boost the quality factor value was investigated. Optimum positioning of the tapers produced a significant enhancement of Q. Finally, a narrow pass band filter constructed from coupled cavities was fabricated and characterised. A quasi-flat transmission peak with a pass band width of just 4nm was observed.

The nitrogen-vacancy (NV) centre in diamond has proven to be an excellent tool to probe electro-magnetic fields and temperature. It has a number of unique features: High sensitivity and resolution, long coherence and lifetimes, the ability to operate from cryogenic temperatures to hundreds of Kelvin, chemical inertness and addressability via optics and microwaves. Recent progress includes the detection of NMR and spectroscopy of single proteins on a diamond surface and in-vivo temperature measurements. However, while the NV centre in bulk diamond has received a lot of attention, the nitrogen-vacancy in nanodiamond has not been investigated extensively due its widely seen inferior properties. It is only very recently that problems with the stability of photoluminescence and short coherence times have been overcome. The NV centre in nanodiamond is thus increasingly seen as an interesting tool for research requiring nanoscale sensors, e.g. in cells. The findings of this thesis facilitate applications of the NV centre in nanodiamond and demonstrate its high potential for future research. Most notably, the nuclear host spin, which is intrinsic to the point defect, can be used to enhance sensitivity and resolution of measurements. In addition, the sensitivity can be improved by time-tagging the emission from the NV centre. Furthermore, the graphite layer covering nanodiamonds can be removed by annealing. This does not have negative effects on the spin properties of the hosted NV centres but enables functionalisation of the surface and therefore advanced in-vivo measurements. Finally, the capabilities of the NV centre in nanodiamond in investigating the formation of magnetic domains are demonstrated at low temperatures. These results enable and motivate the use of the NV centre in nanodiamond for future research, most especially in biological systems.

Dissertação (Mestrado em Engenharia Mecânica) - Centro Universitário FEI, São Bernardo do Campo, 2018