Stuttgart, Univ., Diss., 2006.

Dortmund, Universiẗat, Diss., 2001.

Among several hundred impurities and defects that can occur in diamond, the nitrogenvacancy (NV) center is one of the most interesting for quantum technologies at room temperature. Several properties make it an excellent platform for many applications, from nanosensor to quantum information processing. This thesis presents the first explorations of NV-based technologies in our laboratory, investigating three sets of studies aimed at learning the know-how of this field of research and developing the necessary infrastructure to explore them in future quantum technologies. The first set of studies focus on magnetometry and how to improve NV-based magnetic sensing. We show that, using engineered ensembles of NV centers in ultrapure synthetic diamonds, one can build a relatively simple apparatus to do magnetic imaging of relatively large areas while determining the full vector field with high spatial resolution and very good sensitivity. We also show that these measurements can be used to reconstruct the current density distribution of nearby sources, opening exciting possibilities to study two-dimensional materials. Another set of studies involve spin coherence of an ensemble of NV centers. For that, we developed a method based on a CCD camera and an imaging protocol that allows implementing pulse sequences like Rabi, Ramsey and Hahn echo, performing Electron Spin Resonance (ESR) spectroscopy over extended areas. Using this method we extract parameters from our sample, including measurements for T1, T2 and T*2. The method was also used to observe Electron Spin Echo Envelope Modulation (ESEEM), due to hyperfine interaction with nearby 15N nucleus, resulting in improved frequency sensitivity. The third set of studies explore how to use femtosecond lasers to produce NV centers in diamond and investigated the nonlinear index of refraction (n2) of the diamond (type IIa) in a broad spectral region, from the infrared (1500 nm) to the ultraviolet (260 nm). / Entre várias centenas de impurezas e defeitos que podem ocorrer no diamante, o centro Nitrogênio-Vacância (NV) é um dos mais interessantes para tecnologias quânticas em temperatura ambiente. Diversas propriedades fazem dele uma excelente plataforma para muitas aplicações, desde nanosensores até o processamento de informações quânticas. Esta tese apresenta a primeira exploração de tecnologias baseadas em NV no nosso laboratório, investigando três conjuntos de estudos com objetivo de aprender o know-how desta área de pesquisa e desenvolver a infra-estrutura necessária para explorá-los em futuras tecnologias quânticas. O primeiro conjunto de estudos enfoca a magnetometria e como melhorar o sensores magnético baseado em centros NV. Mostramos que um aparato relativamente simples pode ser usado para produzir imagens magnéticas do campo vetorial, usando ensembles de centros NV em diamantes sintéticos ultrapuros. Também mostramos que essas medidas podem ser usadas para reconstruir a distribuição de densidade de corrente de fontes próximas, abrindo possibilidades interessantes para o estudo de materiais bidimensionais. Outro conjunto de estudos envolve a coerência de spin de um ensemble de centros NV. Para isso, desenvolvemos um método baseado em uma câmera CCD e um protocolo de imagem que permite implementar sequências de pulsos como Rabi, Ramsey e eco Hahn, realizando espectroscopia de ressonância de spin eletrônico (ESR) sobre áreas estendidas. Usando esse método, extraímos parâmetros de nossa amostra, incluindo medidas para T1, T2 e T*2. O método também foi usado para observar o efeito ESEEM (Envelope de Modulação de Eco de Spin Eletrônico), devido à interação hiperfina com o núcleo próximo de 15N, resultando numa melhor sensibilidade de freqüência. Finalmente, o terceiro conjunto de estudos explorou como usar lasers de femtossegundos para produzir centros NV em diamante e investigou o índice de refração não-linear (n2) do diamante (tipo IIa) em uma ampla região espectral, desde o infravermelho (1500 nm) até o ultravioleta (260 nm).

Universiẗat, Diss., 2000--Dortmund. / Dateiformat: PDF.

Universiẗat, Diss., 1990--Paderborn.

University, Diss., 2001--Dortmund.

In this thesis I will discuss the development, construction and testing of a sub-Kelvin Q-band electron paramagnetic resonance (EPR) spectrometer and optically detected magnetic resonance (ODMR) of wide bandgap semiconductors at Q-band. The sub-Kelvin EPR spectrometer was developed to be integrated into a standard commercial system. Characterisation of the cryogenics and microwave components of the spectrometer will be discussed as well as the design and adaptations made to enable EPR experiments to be performed below 1 K. A waveguide thermal break design, previously only used in detectors for the cosmic microwave background radiation, was optimised using ANSYS High frequency structure simulator (HFSS) to operate at Q-band and was built and tested in this spectrometer. The sub-Kelvin EPR spectra of Cr3+ in Al2O3 and [Cr12O9(OH)3(O2CCMe3)15] were obtained. The resonant cavity of the spectrometer was also successfully tested at room temperature, with a pulsed microwave bridge, paving the way for further development of the system to enable sub-Kelvin pulsed EPR. A home-built Q-band ODMR spectrometer was used to investigate the wide band gap semiconductors ZnO and InGaN/GaN multiple quantum wells (MQWs). The ZnO was a natural crystal, and used to characterise the spectrometer. ODMR from a green c-plane InGaN/GaN MQW was studied to probe the method of carrier localisation in the QW. It was shown qualitatively that the ODMR results support current theories for carrier localisation mechanisms, but the noise on these measurements needs to be reduced to provide quantitative support.

In dieser Arbeit werden drei verschiedene kohlenstoffbasierte Materialsysteme behandelt: (i) Organische Halbleiter und kleine Moleküle, in Kombination mit Fullerenen für Anwendungen in der organischen Photovoltaik (OPV), (ii) Halbleitende Einzelwand-Kohlenstoffnanoröhren und (iii) Siliziumkarbid (SiC), dessen Defekte erst seit kurzem als Kandidaten für Quantenapplikationen gehandelt werden. Alle Systeme wurden mit optisch detektierter Magnetresonanzspektroskopie (ODMR) untersucht. Im OPV-Kapitel, die intrinsischen Parameter und Orientierungen von Exzitonen mit hohem Spin wurden für die Materialsysteme P3HT, PTB7 und DIP untersucht. Speziell der Einfluss von Ordnung diesen organischen Systemen wurde diskutiert. Der zweite Teil des Kapitels beschäftigt sich mit Triplettgeneration mittels Elektronenrücktransfer im leistungsfähigen Materialsystem PTB7:PC71BM. Das Kohlenstoffnanoröhren-Kapitel zeigt zuert den ersten zweifelsfreien Nachweis von Triplettexzitonen in halbleitenden (6,5) Einzelwandkohlenstoffnanoröhren (SWNT), mittels ODMR-Spektroskopie. Ein Modell für die Anregungskinetik, die intrinsischen Parameter des Exzitons und Abhängigkeit von der Orientierung der Röhren wurden diskutiert. Der letzte Teil der Arbeit gilt Spinzentren in Siliziumkarbid. Nach einer kurzen Einführung in das Materialsystem wird die Spinmultiplizität für die V2 und V3 Siliziumfehlstellen, sowie eines Frenkelpaars und eines noch nicht zugeordneten Defekts (UD) in 6H SiC, weiterhin für die V2 Fehlstelle und das Frenkelpaar in 4H SiC, durchgängig zu S=3/2 festgestellt. Das spinpolarisierte Befüllen der 3/2-Zustände des Grundzustands der Siliziumfehlstellen erlaubt stimulierte Mikrowellenemission. Ausserdem wurde für UD und Frenkelpaar in 6H SiC eine große Temperaturabhängigkeit der Nullfeldparameter festgestellt, während die Siliziumfehlstellen temperaturunabhängig sind. Anwendung des UD und Frenkelpaars als Temperatursensor, und der Vakanzen als Vektormagnetometer wurden diskutiert. / In this work, three different material systems comprising carbon were researched: (i) Organic polymers and small molecules, in conjunction with fullerene molecules for applications in organic photovoltaics (OPV), (ii) single walled semiconducting carbon nanotubes and (iii) silicon carbide (SiC), whose defect color centers are recently in the limelight as candidates for quantum applications. All systems were analyzed using the optically detected magnetic resonance (ODMR) spectroscopy. In the OPV chapter, first the intrinsic parameters and orientations of high spin excitons were analyzed in the materials P3HT, PTB7 and DIP. Specifically the influence of ordering in these organic systems was adressed. The second part of the OPV chapter is concerned with triplet generation by electron back transfer in the high-efficiency OPV material combination PTB7:PC71BM. The carbon nanotube chapter first shows the way to the first unambiguous proof of the existence of triplet excitons in semiconducting (6,5) single-walled carbon nanotubes (SWNT) by ODMR spectroscopy. A model for exciton kinetics, and also orientation and intrinsic parameters were propoesed. The last part of this work is devoted to spin centers in silicon carbide (SiC). After a brief introduction, the spin multiplicity of the V2 and V3 silicon vacancies, and also of a Frenkel pair and an unassigned defect UD in 6H SiC, and of the V2 vacancy and the Frenkel pair in 4H SiC, was shown to be S=3/2. The spin polarized pumping of the 3/2 manifold of the quartet ground state of the silicon vacancies allows stimulated microwave emission. Furthermore, in 6H SiC, the UD and Frenkel pair were shown to have a large dependence of their intrinsic zero field interaction parameters on the temperature, while the vacancies are temperature independent. The application of the UD and Frenkel pair as temperature sensor, and of the vacancies as a vector magnetic field sensor is discussed.

No description available.

Universiẗat- Gesamthochsch., Diss.--Paderborn, 1997.