Nano-sized semiconductors, known as quantum dots (QDs), are one of the hottest research areas in recent years. The energy gaps of QDs change with their diameters, giving them size-dependent optical properties. By controlling reaction conditions, people are able to make QDs that can emit in certain wavelength ranges. So far, QDs have shown great potential in telecommunication, bio-imaging, single-photon laser source, etc. This thesis starts with Chapter 1, which first introduces the finding of QDs and why they have such special properties. The quantum confinement and energy gap are discussed, followed by the absorption and emission of QDs. Moreover, the synthesis methods and mechanism involved are reviewed in brief. Chapter 2 presents the synthesis of lead-based core, core-shell and core-shell-shell QDs and previous work by other people. A few techniques including transmission electron microscopy (TEM), UV-absorption, photoluminescence (PL) measurement, and X-ray photoelectron spectroscopy (XPS) were used and shown in this chapter. Core-shell and core-shell-shell QDs are shown to present excellent stability over 20 months. The ZnS shell was proved by energy-dependent XPS and TEM measurements. A detailed discussion on quantum yield (QY) is given in Chapter 3. Absolute and relative QY measurements and some standard dyes are discussed. After that, Chapter 4 shows systematic QY measurements on lead-based core and core-shell QDs. For each type of QDs, at least two batches are selected with their emission spectra presented as well. It is revealed by collected data that they have excitation-dependent QYs. The QY drops as the excitation light increases in energy (higher wavelength), which is due to non-radiative decays from higher excited states or the Auger effects. QY of PbS and PbSe QDs can be as high as 50%. Eventually, the conclusion and future work are included in Chapter 5. All experimental work is described in detail in the experimental section. / Graduate

Le statut ganglionnaire a la valeur pronostique la plus importante chez les patientes atteintes d’un cancer du sein, le taux de survie étant corrélé au nombre de ganglions envahis. Dans le traitement des cancers du sein opérables d'une taille inférieure à 3 cm, la technique du ganglion sentinelle (GS) remplace le curage ganglionnaire de stadification. Toutefois, cette technique nécessite l’emploi simultané de radioisotopes et de colorants physiologiques présentant divers effets secondaires. Ainsi, notre stratégie a été de tester, sur modèle pré-clinique de nouveaux traceurs fluorescents, les Quantum Dots (QDs), pour la technique du GS. Une étude sur la détection in vivo du ganglion axillaire (GA) par spectrofluorimétrie fibrée après injection sous-cutanée (s.c.) de QDs émettant dans le rouge a été réalisée et leur quantification ex vivo a été effectuée par spectrofluorimétrie jusqu’à 24 h. Ce travail a montré l’accumulation rapide et sélective des QDs dans le GA chez la souris. Une étude sur la localisation in vivo de 2 ganglions régionaux par imagerie de fluorescence a été réalisée suite à l’administration s.c. de QDs émettant dans le proche infrarouge (PIR) ainsi qu’une étude de biodistribution ex vivo par spectrométrie de masse (ICP-MS). Les résultats obtenus ont montré que l’imagerie de fluorescence pouvait être utilisée après injection de QDs pour localiser et suivre leur accumulation dans les ganglions superficiels chez la souris saine. Pour se rapprocher de la clinique, le repérage in vivo du GS axillaire a été investi sur modèle tumoral murin de cancer du sein par imagerie de fluorescence après administration s.c. de QDs émettant dans le PIR. Deux techniques de détection des métastases ganglionnaires ont été utilisées puis comparées : l’histologie conventionnelle et la RT-PCR. Tous les GS axillaires ont été détectés in vivo par imagerie, sauf un GS qui était complètement envahi par les cellules tumorales et la meilleure incidence de métastases ganglionnaire a été observée avec la RT-PCR. Ainsi, les QDs pourraient être utilisés comme substitut des marqueurs actuellement employés dans la technique du GS pour les cancers du sein. / Lymph node (LN) status is the most important prognostic factor in breast cancer patients and a determinant predictor of recurrence and survival. In the treatment of operable breast cancers with a size inferior of 3 cm, the sentinel lymph node biopsy (SLNB) substitutes the axillary LN dissection. However, this technique requires the simultaneous use of a radiocolloid and a physiologic dye, which present several secondary effects. Thus, our strategy was to test in preclinical model the new fluorescent markers, Quantum Dots (QDs) for SLNB. A study on in vivo axillary LN (ALN) mapping by light induced fluorescence was performed after subcutaneous (s.c.) injection of red-emitting QDs and their ex vivo quantification was realized by spectrofluorimetry for up to 24 h. We showed a fast and selective accumulation of QDs in ALN in healthy mice. An in vivo study on localization of 2 regional LNs by fluorescence imaging was carried out after the s.c. administration of near-infrared (NIR) emitting QDs along with ex vivo biodistribution study by mass spectroscopy (ICP-MS). Obtained results shown that fluorescence imaging can be used after QDs injection to map and follow their accumulation in superficial LNs in healthy mice. To approach the human clinic in a best possible way, sentinel ALN mapping was investigated after s.c. delivery of NIR emitting QDs in murine breast cancer model by fluorescence imaging. Two techniques for LN metastasis detection were used and compared: conventional histology and RT-PCR. All sentinel ALNs were located in vivo by imaging except one ALNs which was completely invaded by cancer cells and best incidence of LN metastasis was registered by RT-PCR (60 %). Thus, QDs could be used as a substitute for the markers currently employed in SLNB in breast cancers.

Quantum photonic technologies have many exciting applications including secure commu- nication, quantum enhanced measurement and quantum computing. Linear optical quantum computing (LOQC) is a technology of particular interest - especially given that recent progress in on-chip waveguide technology removes the requirement for complex and costly bulk optics setups and state-of-the-art detectors have detection efficiencies of over 90%. Arguably the largest remaining technological hurdle for LOQC is the development of a suitable photon source. A suitable source would produce single, indistinguishable photons deterministically. Additionally, it would be beneficial if the generated photons were entangled, as this can significantly reduce the degree of multiplexing needed to implement LOQC. Quantum dots are a suitable candidate system for these photon sources as they exhibit bright single photon emission and can act as the interface between light and a trapped spin qubit. These properties have resulted in proposals to generate multi-photon entangled states suitable for use in LOQC. This thesis presents some of the progress we have made towards the creation of a suitable photon source. After introducing the background material, we demonstrate pulsed resonant excitation using a single-electron-charged quantum dot. Deterministic excitation is demonstrated by performing Rabi oscillations and Ramsey interference in the excitonic population. We also investigate Ramsey interference in a Faraday geometry magnetic field and observe a variety of beats and oscillations in the interferograms. We develop a model to explain our results and conclude that controlling the phase between the two Ramsey interference pulses allows a degree of control over the state of the trapped spin. We then also demonstrate the coherent optical manipulation of a trapped spin in a Voigt geometry magnetic field. Once we have presented the manipulation of the excitonic state and the state of the trapped spin, we proceed to investigate the properties of the light produced by the resonant excitation of a quantum dot. Hong Ou Mandel interference experiments allow us to probe the indistinguishability of the photons resulting from the resonant excitation of the negative trion transition. Repeating the measurement using light generated from a similar system (this time with a trapped hole rather than a trapped electron) that is embedded in a micropillar cavity, we find that the cavity enhancement of the transition results is higher indistinguishabilities. We make use of this bright source of indistinguishable photons to perform an on-chip quantum enhanced measurement and observe the phase superresolution associated with N00N states. In the final experimental chapter, we propose and implement a scheme to generate multi- qubit single photon states. We show that by repeatedly driving a micropillar-cavity-enhanced Raman transition of a single-hole-charged quantum dot in a Voigt geometry magnetic field it is possible to coherently superpose a photon across multiple time bins. The scheme is conceptually similar to proposed schemes for producing multi-photon entangled states. Lastly, we propose a scheme that makes use of the capabilities shown in the three experimental chapters to overcome several of the experimental difficulties associated with generating multi-photon entangled states.

We introduce the concept of dot product representations of graphs, giving some motivations as well as surveying the previously known results. We extend these representations to more general fields, looking at the complex numbers, rational numbers, and finite fields. Finally, we study the behavior of dot product representations in field extensions.

The purpose of this thesis is to fabricate the In0.75Ga0.25As quantum dot (QD) lasers, and analyze the optical properties of laser devices to be applied to optical fiber communication systems. In laser materials, we grew 12-layer In0.75Ga0.25As QD strcutures by molecular-beam epitaxy (MBE) with S-K mode on GaAs substrate, which contains the cladding layer material Al0.5Ga0.5As (C433) Al0.25Ga0.75As (C486) and Al0.2Ga0.8As (C485) of the three structures, the emission wavelength of about 1.3£gm. In the waveguide design, the design of 2.2£gm ridge width waveguide, the purpose is to enable the single transmission mode in the waveguide, so that smaller dispersion losses. Using ridge waveguide and cleaved mirror as the formation of Fabry-Perot cavity laser. In the quantum dot laser characteristic, C485 in the cavity length is 3000£gm of threshold current is 80mA with a slope efficiency of 41.88mW/A, the main emission Peak at 1201nm, the second Peak at 1197nm, the third Peak at 1182nm ; however C486 cavity length is 3300£gm of threshold current is 120mA with a slope efficiency of 27.44mW/A, the main emission Peak at 1215nm, the second Peak at 1205nm. C485 of the threshold current density is 1212 A/cm2, C486 of the threshold current density is 1454 A/cm2.

This work involves the development of a new technique that integrates Diffusing Colloidal Probe Microscopy (DCPM) and luminescence to simultaneously measure multiple particle-wall interactions. DCPM can be used to map potential energy profiles of multiple particle-surface interactions simultaneously and accurately. Colloidal semiconductor quantum dots were used for spectral multiplexing to enable monitoring of multiple analytes at the same time. DCPM combines Total Internal Reflection Microscopy (TIRM) and Video Microscopy to simultaneously measure multiple particle-surface interactions with nanometer resolution in particle-surface separation. By acquiring the scattered intensity emitted by the particles, the separation distance can be calculated and subsequently the forces of interactions between the particle and the surface. This work demonstrates the use of luminescence instead of scattering as the mode of detection in DCPM. The luminescence is provided by quantum dots which are incorporated into polystyrene microspheres. The unique optical properties of quantum dots enable the creation of an optically multiplexed system where microspheres are tagged by quantum dots of different emission wavelengths. Scattering in DCPM may result in erroneous calculation of the potential energy profiles because of particle polydispersity. Since scattering is dependent on particle size, luminescence is introduced into the system and some interesting results are obtained. These results illustrate that the effect of particle polydispersity is significantly reduced when luminescence is used as the mode of detection. This combined with the DCPM system’s sensitivity would enable the monitoring of multiple functionalized particlesurface interactions simultaneously and accurately.

ABSTRACT Recently, there has been an increasing interest in the fabrication and theory of self-assembled quantum dots (SAQD). Self-assembled quantum dots are of great interest because of good optical properties and device applications such as quantum dot lasers and memory device. The main merit of laser based on quantum dot is both the low threshold current density and low temperature sensitivite. We can grow the ZnSe quantum dot on GaAs substrate. The maximum value of dots density is 1.3¡Ñ109cm-2 at 16.7 of ¢¾/¢º ratio. The dots densities are increasing by the flow rate of DEZn and H2Se. When the ¢¾/¢º ratio are lager than 16.7 or smaller than 7.5 will lead to quantum dots increasing. The blue shift is from 8 nm to 15 nm by quantum confinement. The high quality of ZnS0.81Se0.19 epilayers on GaP substrate are grown with DEZn, H2Se, H2S and H2 fixed at 2.4 sccm, 10 sccm, 10 sccm and 1 slm respectively, and prepared at 340¢J and 50 min. High quality ZnS0.81Se0.19:N epilayer which was lattice-matched to GaP substrate has been prepared. The FWHM of X-ray diffraction was 720.2 arcsec. Its R-value was 5.20%. Then we grow ZnSe quantum dots / ZnS0.81Se0.19/GaP. The largest density of quantum dots is 1.1¡Ñ109 cm-2 at 30 s growth time.

Abstract We have applied PID and IFVP techniques to modify semiconductor bandgap in quantum well and quantum dot to achieve quantum well intermixing (QWI) and quantum dot intermixing (QDI). In quantum well intermixing experiment, we combine inductively coupled plasma reactive ion etching (ICP-RIE) and sputtering 300nm SiO2 to induce defects. And then, after high temperature annealing by RTA, we observed the results by using PL measurement. The samples used in this study were grown by molecular beam epitaxy(MBE) and consists of triple In0.53Ga0.47As/In0.53Ga0.26Al0.21As quantum wells. We used Ar+ bombardment on samples by ICP-RIE for 5 minutes, and then sputtered a 300nm SiO2 capping layer upon the samples. Finally the sample was annealed at 800¢J for 1 minutes. After the process, we got 150nm blue-shift (1575~1425nm) by measurement PL spectrum and applied XRD fitting to simulate 140nm blue-shift (1580~1440nm).On the same process step, we increased ICP-RIE bombardment time to 7 minutes thus we observed largest 269nm blue-shift from PL spectrum. InAs/In0.52Al0.48As,In0.95Al0.05As/In0.52Al0.48As,and In0.95Ga0.05As/In0.52Al0.48As quantum dot structures were grown by MBE. In0.95Ga0.05As/In0.52Al0.48As quantum dot structure has larger blue-shift by sputtering 300nm SiO2 and annealing at high temperature by RTA. We got 282nm blue-shift annealing at 800¢J for In0.95Ga0.05As/In0.52Al0.48As quantum dot structure. Furthermore, we got largest 366nm blue-shift when we etched the thickness of capping layer and annealed at 800¢J.

The purpose of this thesis is to fabricate the quantum dot waveguide and measure electro-optic (EO) modulation characteristics. We focus on the refractive index change (£Gn), phase retardation, and electro-optic coefficients for quantum dot samples. The £fg=1.3£gm InGaAs quantum dot structures were grown on n+ GaAs substrates by MBE. We design a series of 2.2£gm straight and slope 7¢X single mode waveguide, and use the cleavage surface method to produce Fabry-Perot cavity. In fabrication process, we first defined the device pattern by using photo-lithography technique. Second, we etched ridge waveguide by using dry etching or multi-step wet etching method. Finally, we used the etching solution HBr:HCl:H2O2:H2O=5:4:1:70 to smooth the sidewall and reduce the scattering loss. We analyzed the quantum dot EO properties by measuring phase retardation of Fabry-Perot resonance at different bias. From measuring the Fabry-Perot resonance at£f=1515nm TE-polarization, the linear electro-optic (LEO) and quadratic electro-optic (QEO) coefficients of C311 sample are 7.26¡Ñ10-12m/v and 1.14¡Ñ10-18m2/v2 , respectively. And the LEO and QEO coefficients of C251 sample are 2.99¡Ñ10-11m/v and 4.10¡Ñ10-17m2/v2, respectively. By coupling £f=1515nm TM-polarized light, we found the main influence of C251 sample is Kerr effect, and the QEO coefficient is 3.52¡Ñ10-17m2/v2. Both electro-optic coefficients are significantly larger than those measured in quantum wells and bulk GaAs. These results are applicable to QD-based low drive voltage and small size modulators.

Texte remanié de: Th.--Anthropol. sociale et ethnol.--Paris--EHESS, 1993. Titre de soutenance : La dot dans l'Inde d'aujourd'hui, un problème de société ? Une étude de cas au Maharashtra. / Contient un choix de documents. Bibliogr. p. 247-268. Index.