The modern InGaN technology demonstrates high efficiencies only in the blue spectral region and low current operation modes. The growth of InGaN quantum wells (QWs) on nonbasal crystallographic planes (NBP) has potential to deliver high-power blue and green light emitting diodes and lasers. The emission properties of these QWs are largely determined by the localization of carriers in the minima of spatially inhomogeneous band potential, which affects the recombination dynamics, spectral characteristics of the emission, its optical polarization and carrier transport. Understanding it is crucial for increasing the efficiency of NBP structures to their theoretical limit. In this thesis, the influence of carrier localization on the critical aspects of light emission has been investigated in semipolar  and nonpolar  InGaN QWs. For this purpose, novel multimode scanning near-field optical microscopy configurations have been developed, allowing mapping of the spectrally-, time-, and polarization-resolved emission. In the nonpolar QW structures the sub-micrometer band gap fluctuations could be assigned to the selective incorporation of indium on different slopes of the undulations, while in the smoother semipolar QWs – to the nonuniformity of QW growth. The nanoscale band potential fluctuations and the carrier localization were found to increase with increasing indium percentage in the InGaN alloy. In spite to the large depth of the potential minima, the localized valence band states were found to retain properties of the corresponding bands. The reduced carrier transfer between localization sites has been suggested as a reason for the long recombination times in the green-emitting semipolar QWs. Sharp increase of the radiative lifetimes has been assigned to the effect of nanoscale electric fields resulting from nonplanar QW interfaces. Lastly, the ambipolar carrier diffusion has been measured, revealing ~100 nm diffusion length and high anisotropy. / <p>QC 20170919</p>

Les hétérostructures hybrides organique-inorganique présentent des propriétés intéressantes, notamment pour des applications dans le domaine de l’électronique et de la spintronique. Notre intérêt s’est porté particulièrement sur la réalisation d’hétérostructures de type Métal/Monocouche organique/Semiconducteur, dont l’étape de reprise de top-contact métallique reste actuellement un verrou majeur à la réalisation de telles jonctions. L’expérience de l’équipe sur des hétérostructures de type MOS (Métal/Oxyde/Semiconducteur), ainsi que les différentes techniques de surface et de transport disponibles au laboratoire, sont appliquées ici à l’étude de ces hétérostructures hybrides. En particulier, la Microscopie à Emission d’Electrons Balistiques (BEEM) permet d’étudier localement les propriétés électroniques des hétérostructures, avec une résolution spatiale nanométrique. A partir du système Au/GaAs(001) bien connu au laboratoire, nous avons intercalé une monocouche d’alcanethiols à l’interface, pour former des hétérostructures de type Au/Alcanethiols/GaAs(001), entièrement préparées sous ultra-vide. Lors du dépôt d’or à température ambiante, les images BEEM ont révélé des interfaces hétérogènes, avec des zones où le peigne moléculaire est court-circuité ou non par le métal. Une analyse quantitative en spectroscopie BEEM des zones non court-circuitées a mis en évidence des signatures particulières, avec une première contribution associée au passage tunnel des électrons à travers le peigne moléculaire, et une seconde contribution, à plus haute énergie, révélant l’existence de nouveaux canaux de conduction associés à l’existence d’états inoccupés dans la monocouche organique. Les effets de l’épaisseur du métal déposé, de la longueur de chaîne des molécules organiques, ainsi que du groupe terminal de la chaîne organique, ont été discutés. Afin d’améliorer le dépôt du contact métallique, un dispositif expérimental original a permis de déposer l’or sur le substrat refroidi, sur lequel une couche tampon de Xénon est condensée (méthode BLAG : Buffer Layer Assisted Growth). L’analyse BEEM de ces hétérostructures a révélé ici des interfaces homogènes, sans pénétration du métal. Des signatures spectroscopiques similaires aux zones non court-circuitées précédentes ont été mises en évidence. Une étude complète de ces hétérostructures préparées par la méthode BLAG a été réalisée via des mesures de transport à l’échelle macroscopique (J(V) et C(V)), ainsi que des mesures de photoémission par rayonnement synchrotron. Ces mesures ont confirmé le caractère reproductible des jonctions formées, avec des hauteurs de barrière en accord avec celles déterminées par BEEM. / In molecular electronics and spintronics, top-contact metal electrode deposition on organic molecular monolayer (OML)/semiconductor hybrid heterostructures is still a critical issue, leading to metal penetration through the molecules and monolayer’s damage. The experimental set-ups available in the lab and the team’s experience in inorganic-inorganic heterostructures are here applied to hybrid organic-inorganic heterostructures. In particular, the Ballistic Electron Emission Microscopy (BEEM), a technique derived from Scanning Tunneling Microscopy (STM), allows to study electronic properties of such heterostructures, at a nanometer scale. Starting from the well-known Au/GaAs(001) Schottky contact, we here intercalate an alkanethiols monolayer, in order to obtain Au/Alkanethiols/GaAs(001) heterostructures, fully grown in ultra-high vacuum environment. In the case of room-temperature metal deposition, BEEM imaging reveals domains which are short-circuited or not by the metal. A quantitative analysis of non-short-circuited interfaces is realized by BEEM in spectroscopy mode. Particular fingerprints are obtained, with a first component related to electron tunnel transport through the monolayer, and a second component, at higher energy, related to first unoccupied states of the molecular layer reachable for electrons. The effects of metal thickness, molecular chain length and terminal group are discussed. In order to minimize the degree of gold penetration, an alternative top-contact deposition method is used, based on buffer-layer assisted growth (BLAG). BEEM studies on these heterostructures reveal homogeneous interfaces without metal penetration, and similar spectroscopic fingerprints. Complementary studies at macroscopic scale (J(V) and C(V) transport measurements and photoemission by synchrotron radiation) confirm the reproducible character of the junctions with barrier height values similar to the ones obtained by BEEM.

This work presents the first demonstration of a semiconductor based plasmonic near-field superlens, utilizing highly doped GaAs to generate infrared optical images with a spatial resolution beyond the difraction limit. Being easily transferable to other semiconductor materials, the concept described in this thesis can be exploited to realize spectrally adjustable superlenses in a wide spectral range. The idea of superlensing has been introduced theoretically in 2000, followed by numerous publications including experimental studies. The effect initiated great interest in optics, since in contrast to difraction limited conventional optical microscopy it enables subwavelength resolved imaging by reconstructing the evanescent waves emerging from an object. With techniques like scanning near-field optical microscopy (SNOM) and stimulated emission depletion (STED) being already successfully established to overcome the conventional restrictions, the concept of superlensing provides a novel, different route towards high resolution. Superlensing is a resonant phenomenon, relying either on the excitation of surface plasmons in metallic systems or on phonon resonances in dielectric structures. In this respect a superlens based on doped semiconductor benefits from the potential to be controlled in its operational wavelength by shifting the plasma frequency through adjustment of the free carrier concentration. For a proof of principle demonstration, we investigate a superlens consisting of a highly n-doped GaAs layer (n = 4 x 10^18 cm-3) sandwiched between two intrinsic layers. Recording near-field images of subwavelength sized gold stripes through the trilayer structure by means of SNOM in combination with a free-electron laser, we observe both enhanced signal and improved spatial resolution at radiation wavelengths close to l = 22 µm, which is in excellent agreement with simulations based on the Drude-Lorentz model of free electrons. Here, comparative investigations of a purely intrinsic reference sample confirm that the effect is mediated by the charge carriers within the doped layer. Furthermore, slightly differently doped samples provide indications for the expected spectral shift of the resonance. According to our calculations, the wavelength range to be exploited by n-GaAs based superlenses reaches far into the terahertz region, whereas other semiconductor materials are required to explore the near infrared.

Near-field optical microscopy has attracted remarkable attention, as it is the only technique that allows the investigation of local optical properties with a resolution far below the diffraction limit. Especially, the scattering-type near-field optical microscopy allows the nondestructive examination of surfaces without restrictions to the applicable wavelengths. However, its usability is limited by the availability of appropriate light sources. In the context of this work, this limit was overcome by the development of a scattering-type near-field microscope that uses a widely tunable free-electron laser as primary light source. In the theoretical part, it is shown that an optical near-field contrast can be expected when materials with different dielectric functions are combined. It is derived that these differences yield different scattering cross-sections for the coupled system of the probe and the sample. Those cross-sections define the strength of the near-field signal that can be measured for different materials. Hence, an optical contrast can be expected, when different scattering cross-sections are probed. This principle also applies to vertically stacked or even buried materials, as shown in this thesis experimentally for two sample systems. In the first example, the different dielectric functions were obtained by locally changing the carrier concentration in silicon by the implantation of boron. It is shown that the concentration of free charge-carriers can be deduced from the near-field contrast between implanted and pure silicon. For this purpose, two different experimental approaches were used, a non-interferometric one by using variable wavelengths and an interferometric one with a fixed wavelength. As those techniques yield complementary information, they can be used to quantitatively determine the effective carrier concentration. Both approaches yield consistent results for the carrier concentration, which excellently agrees with predictions from literature. While the structures of the first system were in the micrometer regime, the capability to probe buried nanostructures is demonstrated at a sample of indium arsenide quantum dots. Those dots are covered by a thick layer of gallium arsenide. For the first time ever, it is shown experimentally that transitions between electron states in single quantum dots can be investigated by near-field microscopy. By monitoring the near-field response of these quantum dots while scanning the wavelength of the incident light beam, it was possible to obtain characteristic near-field signatures of single dots. Near-field contrasts up to 30 % could be measured for resonant excitation of electrons in the conduction band of the indium arsenide dots. / Die optische Nahfeldmikroskopie hat viel Beachtung auf sich gezogen, da sie die einzige Technologie ist, welche die Untersuchung lokaler optischer Eigenschaften mit Auflösungen unterhalb der Beugungsgrenze ermöglicht. Speziell die streuende Nahfeldmikroskopie erlaubt die zerstörungsfreie Untersuchung von Oberflächen ohne Einschränkung der verwendbaren Wellenlängen. Die Nutzung ist jedoch durch das Vorhandensein entsprechender Lichtquellen beschränkt. Im Rahmen dieser Arbeit wurde diese Beschränkung durch Entwicklung eines streuenden Nahfeldmikroskops überwunden, das einen weit stimmbaren Freie-Elektronen-Laser als primäre Lichtquelle benutzt. Im theoretischen Teil wird gezeigt, dass ein optischer Kontrast erwartet werden kann, wenn Materialien mit unterschiedlichen Dielektrizitätskonstanten kombiniert werden. Es wird hergeleitet, dass diese Unterschiede in unterschiedlichen Streuquerschnitten für das gekoppelte System aus Messkopf und Probe resultieren. Diese Streuquerschnitte definieren die Stärke des Nahfeldsignals, welches auf unterschiedlichen Materialien gemessen werden kann. Ein optischer Kontrast kann also erwartet werden, wenn unterschiedliche Streuquerschnitte untersucht werden. Dass dieses Prinzip auch auf übereinander geschichtete oder sogar verborgene Strukturen angewendet werden kann, wird in dieser Doktorarbeit an zwei Probensystemen experimentell gezeigt. Im ersten Beispiel wurden die unterschiedlichen Dielektrizitätskonstanten durch örtliches Ändern der Ladungsträgerdichte in Silizium durch Bor-Implantation erreicht. Es wird gezeigt, dass die Dichte der freien Ladungsträger an Hand des optischen Kontrastes zwischen implantiertem und reinem Silizium ermittelt werden kann. Zu diesem Zweck wurden zwei unterschiedliche Ansätze verwendet, ein nicht-interferometrischer mittels variabler Wellenlängen und ein interferometrischer mit einer konstanten Wellenlänge. Weil diese Techniken gegensätzliche Informationen liefern, können sie genutzt werden, um die effektive Ladungsträgerdichte quantitativ zu bestimmen. Beide Ansätze lieferten konsistente Resultate für die Trägerdichte, welche sehr gut mit den Vorhersagen der Literatur übereinstimmt. Während die Strukturen im ersten Beispiel im Mikrometer-Bereich lagen, wird die Möglichkeit, verborgene Nanostrukturen zu untersuchen, an Hand einer Probe mit Indiumarsenid Quantenpunkten demonstriert. Diese sind von einer dicken Schicht Galliumarsenid bedeckt. Zum ersten Mal wird experimentell gezeigt, dass Übergänge zwischen Elektronenzuständen in einzelnen Quantenpunkten mit Nahfeldmikroskopie untersucht werden können. Durch die Messung der Nahfeld-Antwort der Quantenpunkte unter Änderung der Wellenlänge des eingestrahlten Lichtes war es möglich, charakteristische Nahfeld-Signaturen der einzelnen Quantenpunkte zu erhalten. Nahfeld-Kontraste bis zu 30 Prozent konnten für die resonante Anregung der Elektronen im Leitungsband der Indiumarsenid Punkte beobachtet werden.

Indiana University-Purdue University Indianapolis (IUPUI) / The details of Polarization Modulation Near-Field Scanning Optical Microscopy (PM-NSOM) are presented. How to properly calibrate and align the system is also introduced. A measurement of Muscovite crystal is used to display the capabilities of the setup. Measurements of supported Lβʹ 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers are presented, emphasizing how it was tooled in exploiting the anisotropic nature of the acyl chains. A discussion of how the effective retardance (ΔS = 2π( n_e-n_o )t/λ) and the direction of the projection of the acyl chains (θ) are measured simultaneously is given, (where t is the thickness of the bilayer and λ is the wavelength of light used). It is shown from ΔS the birefringence (ne-no) of the bilayer is determined, by assuming the acyl chain tilt with respect to the membrane's normal to be ϕ ≈ 32. Time varying experiments show lateral diffusions of ~ 2 x 10-12 cm2/s. Temperature controlled PM-NSOM is shown to be a viable way to determine the main phase transition temperature (Tm) for going from the gel Lβʹ to liquid disorder Lα state of supported DPPC bilayers. A change of ΔS ~ (3.8 +/- 0.3 mrad) at the main phase transition temperature Tm (≈41^o C) is observed. This agrees well with previous values of (ne-no) and translates to an assumed <ϕ> ~ 32^o when T < Tm and 0^o when T > Tm. Evidence of supper heating and supper cooling will be presented, along with a discussion of the fluctuations that occur around Tm. Finally it is shown how physical parameters such as the polarizability are extracted from the data. Values of the transverse (αt) and longitudinal (αl) polarizabilites of the acyl chains are shown to be, αt = 44.2 Å3 and αl = 94.4 Å3, which correspond well with the theoretical values of a single palmitic acid (C16) αt = 25.14 Å3 and αl = 45.8 Å3.

Micro– and subsequently nano–scale fabrication techniques have reshaped our world more drastically than almost any other development of the last half-century. Spurred by the invention of the transistor at Bell Labs in 1947, monolithic integrated circuits—or microchips in the colloquial lexicon—were developed in ’59, kickstarting the modern digital age as we know it. More recently, the maturation of classical computing technology and significant advancements in materials science have led to a boom of interest in and progress by the quantum sector on both computation and communication fronts. The explosive growth currently underway in the field of quantum information science (QIS) marks the dawning of a new age, which will undoubtedly transform our world in ways we have yet to imagine. This dissertation seeks to leverage advanced nanofabrication approaches, atomically thin materials, and state of the art microscopy techniques to develop room-temperature single photon sources for QIS applications. A basic overview of 2D materials is provided in Chapter 1. Particular emphasis is placed on the optical properties of tungsten diselenide (WSe2), which is followed by a brief discussion of quantum emitters in 2D and other material systems. Chapter 2 describes the scanning near-field optical microscopy (SNOM) technique we use to investigate the photoluminescence (PL) response of strained WSe₂ with resolution well below the classical diffraction limit. The third chapter is dedicated to the various fabrication methods explored and developed to produce the plasmonic substrates necessary for near-field optical studies. The first section focuses on the creation of extremely flat metallic surfaces, while the second deals with extremely sharp metallic stressors. These two platforms enable the investigations of nanobubbles—touched upon in Chapter 2—and nanowrinkles, which are the subject of discussion in Chapter 4. The strain confinement provided by these wrinkles leads to highly localized quantum dot-like states that exhibit excitation power saturation at room temperature. Together, these studies lay the groundwork for achieving high-temperature quantum emission in atomically thin semiconducting van der Waals materials.

La microscopie de grille à balayage (SGM pour Scanning GateMicroscopy), développée à la fin des années 1990, est devenue un outilpuissant pour étudier les propriétés électroniques locales dans lesnano-dispositifs semi-conducteurs. La SGM est basée sur la techniqueAFM, mais la pointe métallique est utilisée comme une grille mobilecouplée capacitivement au dispositif, et les propriétés de transportélectronique sont étudiées sous l'influence de cette grille,fournissant des informations spatiales à haute résolution. Cette thèsedécrit d'abord le remplacement de la détection optique de notresystème AFM par une détection piézo-électrique utilisant un diapason àquartz, puis les résultats de mesures SGM sur divers nano-dispositifs,qui sont tous fabriqués à partir d'hétérostructures InGaAs / InAlAscontenant un gaz d'électrons bi-dimensionnel (2DEG) de grande mobilitésitué à quelques dizaines de nanomètres sous la surface. Sur unesimple constriction, nous étudions l'interaction pointe-échantillonavec deux approches: la force électrostatique et l'effet capacitif.Sur une boite quantique, nous étudions les phénomènes de blocage deCoulomb lorsque la pointe est utilisée comme une grille pour modulerla charge à l'intérieur de la boite. Dans un travail sur le paradoxede Braess, avec l'aide de simulations numériques, nous découvrons uneffet paradoxal en modulant la largeur du canal central dans undispositif mésoscopique en forme de double anneau, en analogie avec leparadoxe qui se produit dans un réseau classique. Par une étudedétaillée de l'évolution de la conductance, nous découvrons enfinplusieurs pièges de charge dans les images SGM, et proposons un modèlepour interpréter le changement de conductance en présence de pièges decharge. Nous développons alors une méthode pour imager directement lespièges de charge par des mesures de transconductance avec unemodulation de la tension sur la pointe. / Scanning gate microscopy (SGM), developed in the late 1990's, has become a powerful tool to investigate the local electronic properties in semiconductor nano devices. SGM is based on the AFM technique but the metallic tip is used as a movable gate capacitively coupled to the device, and the electron transport property is studied on influence of this gate, providing spatial information with high resolution. This thesis presents the update of the force detection mode of our AFM system from optical method to force sensing by a quartz tuning fork, and the SGM measurement results on various nano devices, all of which are fabricated from InGaAs/InAlAs heterostructures containing a high mobility 2DEG located a few tens of nanometers below the surface. On a 2DEG constriction, we investigate the tip-sample interaction with two approaches: the capacitive force and the gate effect. On a quantum dot, we study the Coulomb blockade phenomena where the tip is used as a gate to modulate the charging/discharging inside the dot. In a work on Braess paradox, with the help of numerical simulations, we discover a Braess paradox effect by modulating a channel width in a ‘double-ring' shaped mesoscopic device in analogy with the one that occurs in a classical network. By a detailed study of the conductance changes, we discover several charge traps from the SGM map, and propose a model to interpret the conductance change with the presence of charge traps. We develop a method to directly image the charge traps by transconductance measurements with a voltage modulation on the tip.

Para o desenvolvimento da nanociência atual há forte demanda por equipamentos capazes de caracterizar sistemas em escalas da ordem nanométrica. Este contexto impulsionou o desenvolvimento de microscópios ópticos de varredura em campopróximo (Scanning Near-field Optical Microscope SNOM). Diferentemente da microscopia óptica tradicional, os SNOMs detectam a radiação eletromagnética evanescente e, conseqüentemente, a resolução não é limitada pelo critério de Rayleigh. No Laboratório de Materiais Magnéticos IFUSP desenvolvemos um SNOM sensível a efeitos Kerr magnetoópticos (MO-SNOM). Dessa maneira, associamos a alta resolução da técnica à alta sensibilidade dos efeitos magnetoópticos. Trata-se se uma área relativamente pouco explorada e carente de resultados sistemáticos na literatura. Utilizando o MO-SNOM, caracterizamos partículas microestruturadas de Co70.4Fe4.6Si15B10 amorfo com dimensões de 16x16x0.08 microm3 e 4x4x0.08 microm3. Os resultados compreendem dezenas de imagens de susceptibilidade magnetoóptica diferencial com resolução melhor que 200 nm e curvas de histerese local. Em primeira análise, a demonstração de resultados sistemáticos ajuda a estabelecer a técnica. O comportamento magnético das partículas, estudadas sob várias condições de campo aplicado, se mostrou determinado basicamente pela anisotropia de forma. As curvas de histerese local mostraram comportamentos intrinsecamente locais e motivaram uma interessante discussão sobre os parâmetros de caracterização magnética convencionais. As medidas realizadas indicam que o efeito Kerr magnetoótico transversal em campopróximo é similar ao campo-distante. Os resultados são fortemente sustentados por medidas de microscopia magnetoóptica de campo-distante, simulações micromagnéticas e medidas de microscopia de força magnética. Medidas complementares revelam o potencial do MO-SNOM para caracterizações de objetos extensos quanto a potenciais de pinning. Além disso, medidas em filmes finos de NiFe/FeMn acoplados por exchange-bias evidenciam a alta sensibilidade do MO-SNOM, estimada de DM ~ 2 x 10-12 emu. / To support nanosciences evolution, there is a strong demand for developing new instrumentation devoted to nano-scale characterization. In this context, the development of the Scanning Near-field Optical Microscope (SNOM) took place. In contrast to traditional optical microscopes, SNOM deals with evanescent electromagnetic radiation and, consequently, the resolution is no longer limited by the Rayleigh criterion. At Laboratório de Materiais Magnéticos (LMM) IFUSP a SNOM devoted to magneto-optical Kerr effect measurements (MO-SNOM) has been developed. The MOSNOM associates the high resolution of the near-field technique to the high sensibility of the magneto-optical Kerr effect. Near-field magneto-optical microscopy is not yet wellestablished and there is a lack of systematic results in the literature. Using the MO-SNOM, amorphous Co70.4Fe4.6Si15B10 particles with 16x16x0.08 microm3 and 4x4x0.08 microm3 dimensions were studied. With resolution better than 200 nm, several magneto-optical differential susceptibility images and local hysteresis loops were obtained. The systematic results uphold the establishment of this new technique. Under the different applied field conditions, the magnetic behavior of the particles was found to be determined by shape anisotropy. Local hysteresis loops presented shapes intrinsic of local field induced process. The unusual hystesesis loops motivated interesting discussion about the conventional magnetic parameters. The MO-SNOM measurements indicate that the near-field transverse magneto-optical Kerr effect is similar to the far-field case. The results are highly supported by far-field magneto-optical microscopy, micromagnetic simulations and magnetic force microscopy measurements. Complementary measurements indicate the MO-SNOM potential to extensive magnetic surface characterization related to pinning potential distribution. Furthermore, measurements on the exchange-bias coupled NiFe/FeMn thin films make evident the MO-SNOM high sensitivity, estimated to be DeltaM ~ 2 x 10-12 emu.

In dieser Arbeit werden erstmals die nichtlinearen optischen Eigenschaften einzelner Halbleiterquantenpunkte mit Femtosekunden-Zeitauflösung untersucht und dargestellt. Insbesondere die Besetzungs- und Polarisationsdynamik eines einzelnen Halbleiterquantenpunkts wird diskutiert. Zur Durchführung der Experimente wird eine neuartige Messmethode entwickelt und eingesetzt: die Femtosekunden-Nahfeldspektroskopie. Die Kombination aus fs-Anrege-Abtast-Spektroskopie und optischer Nahfeldspektroskopie ermöglicht es, die nichtlinearen optischen Eigenschaften eines einzelnen Quantenpunkts mit hoher räumlicher, temporaler und spektraler Auflösung bei Temperaturen von 10 K bis 300 K zu untersuchen. Das zu diesem Zweck weiter entwickelte optische Nahfeldmikroskop bietet eine hohe räumliche Auflösung von bis zu 150 nm. Die Einführung einer neuartigen optischen Abstandsregelkontrolle sichert identische experimentelle Bedingungen über zahlreiche Stunden, ohne daß mechanische Wechselwirkungen zwischen den untersuchten Strukturen und dem apparativen Aufbau die Ergebnisse negativ beeinflussen. Durch die Kombination dieses Nahfeldmikroskops mit einem klassischen fs-Anrege-Abtast-Aufbau können die nichtlineare optische Eigenschaften einzelner Quantenpunkte mit einer Zeitauflösung von bis zu 150 fs untersucht werden. Zur Charakterisierung der Mehrfachquantenfilmprobe werden die linearen optischen Eigenschaften einzelner Interface Quantenpunkte mit Hilfe der stationären Methoden der Photolumineszenzspektroskopie und Photolumineszenz-Autokorrelationsspektroskopie untersucht und analysiert. Dadurch bietet sich die Möglichkeit der gezielten Untersuchung der räumlichen Statistik lokalisierter Zustände. Einblick in die räumliche Unordnung des zugrundeliegenden Potentialverlaufs kann gewonnen werden. In PL-Emission wird der Übergang von homogen verbreiterten Emissionslinien dicker Quantenfilme in ein inhomogen verbreitertes Emissionsspektrum bei gleichzeitiger Beobachtung spektral scharfer Emissionslinien einzelner lokalisierter Exzitonenresonanzen mit Abnahme der Filmdicke beobachtet. In PL-Autokorrelationsexperimenten wird ein zweites ausgeprägtes Korrelationsmaximum beobachtet. Dieses wird einem angeregten lokalisierten und optisch aktiven Zustand zugeschrieben. Die beobachtete Energiedifferenz zwischen Exzitonengrundzustand und dem beobachteten angeregten Zustand ermöglicht eine Abschätzung des Dipolmoment zu 40-50D und der Ausdehnung von Quantenpunkte von ca. 50nm. Zeitaufgelöste Untersuchungen an interface Quantenpunkten werden mit einer spektralen Auflösung von 60 µeV in Reflexionsgeometrie durchgeführt. Diese gestatten zum einen die Bestimmung der Lebensdauer und Dipolmomente lokalisierter Exzitonenzustände. Zum anderen ist eine nahezu vollständige Rekonstruktion der Polarisationsdynamik nach optischer Anregung möglich. Grossen Einfluss auf die spektrale Form der detektierten Reflektivitätsänderung besitzt die Tiefe unter der ein Quantenpunkt unter der Oberfläche vergraben ist. Diese Tiefenabhängigkeit wird in dieser Arbeit genauer untersucht und analysiert. Weiterhin wird erstmals die Polarisationsdynamik in einem einzelnen Quantenpunkt mit fs-Zeitauflösung untersucht und analysiert. Wird die durch den Abtastimpuls getriebene Polarisation nicht durch Wechselwirkung mit einem zweiten Impuls gestört, wird eine exponentielle zeitliche Abnahme der Polarisation mit der durch die homogenen Linienbreite bestimmten Dephasierungszeit ermittelt. Vielteilchenwechselwirkung nach nichtresonanter Anregung mit einem Anregeimpuls führt zur Änderung der Polarisationsdynamik lokalisierter Zustände und zur Beobachtung nichtverschwindender Reflektivitätsänderungen zu negativen Verzögerungszeiten. Als dominanter Mechanismus der in den zeitaufgelösten Experimenten vorherrschenden Vielteilchenwechselwirkung wird ein anregungsinduziertes Dephasieren nachgewiesen. / In this thesis the first study of nonlinear optical properties of single Quantum Dots with femtosecond time resolution is presented. Especially the population and polarization dynamics in a single semiconductor quantum dot will be discussed. To achieve this goal a new experimental technology is developed, giving the possibility to investigate the temporal dynamics of a single quantum dot within a temperature range between 10 and 300 K. Hereby the combination of a standard pump-probe setup with a near-field microscope for variable temperatures allows highest temporal, spectral and spatial resolution of up to 100 fs, 60 ueV and 150 nm respectively. The introduction of a new optical distance control enables the investigation of nonlinear optical properties of a single quantum dot in reflection geometry without any restrictions due to masking or stress effects. In first experiments the linear optical properties of single interface Quantum Dots in the multiple quantum well structure is characterized and analyzed via PL- and PL-autocorrelation spectroscopy. Knowledge of the spatial statistics of localized states can be gained. Insight into correlation of the underlying disorder potential is achieved. By investigating different quantum wells the crossover from a homogeneous broadened emission spectra of thick quantum films to an inhomogeneous broadened emission spectra is observed accompanied by the occurrence of sharp emission peaks from localized excitons. In PL-Autocorrelation experiments a second pronounced correlation maximum is observed. This correlation maximum can be explained by a localized excited and optical active resonance in a single quantum dot. The energy difference between the localized ground state and the first excited state of about 3 meV allows a rough estimate of underlying dipole moments to 40-50 D and the extent of isolated quantum dots to 50 nm. Time resolved experiments on interface quantum dots are performed with a spectral resolution of 60 µeV in reflection geometry, allowing on one hand the determination of population life times and dipole moments of localized exciton states. On the other hand a nearly complete reconstruction of the polarization dynamics is possible. Large influence on spectral shape of the reflectivity change is given by the distance between interface quantum dots and the sample surface. This burying depth dependence will discussed and analyzed in detail within this thesis. Moreover polarization dynamics in a single quantum dot is investigated with fs-resolution. If the polarization driven by the probe pulse is not disturbed by a second light pulse, an exponential decay of the polarization amplitude with an decay time determined by the homogeneous line width is observed. Many body interaction after excitation by a non-resonant pump-pulse causes changes in the polarization dynamics of localized states at negative delay times. As prominent mechanism of many-body interactions governing the experiments an excitation induced dephasing will be determined.

The light-matter interaction in the near-field of high-Q resonators in SOI and SiN platforms is studied. The interactions of high-Q traveling-wave resonators with both resonant and non-resonant nanoparticles are studied and different applications based on this enhanced interactions in near-field such as high-resolution imaging of mode profile of high-Q resonators, label-free sensing, optical trapping, and SERS sensing are investigated. A near-field imaging system for the investigation of the near-field phenomena in the near-field of high-Q resonators is realized. A new technique for high-resolution imaging of the optical modes in high-Q resonators based on the near-field perturbation is developed that enables to achieve a very high resolution (< 10 nm) near-field image. The prospect of the high Q resonators on SOI platform for highly multiplexed label-free sensing and the effect of different phenomena such as the analyte drift and diffusion and the binding kinetics are studied. Also, the possibility of enhancing nanoparticle binding to the sensor surface using optical trapping is investigated and the dynamic of a nanoparticle in the high-Q resonator optical trap is studied. Furthermore, the interaction between a resonant nanoparticle with a high-Q microdisk resonator and its application for SERS sensing is studied. A model for interaction of resonant nanoparticles with high-Q resonators is developed and the optimal parameters for the design of coupled microdisk resonator and a plasmonic nanoparticle are calculated. The possible of resonant plasmonic nanoparticle trapping and alignment in an SiN microdisk resonator optical trap is also shown.