Thesis--Oulun yliopisto, 1992. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Techn. Universiẗat, Diss., 2003--Dresden.

The concept of "aggregation-induced emission" (AIE) effect has induced a great deal of attention these days. Now, exploration of new AIE-active molecular system and multiple high technique applications for AIE materials are the two research hotspots. Cyanostilbene, as a classical structural unit in photoelectric functional materials, also exhibited this unique luminescence behavior. The research background was illustrated in Chapter 1, which mainly introduced the development of this subject. In this project, Chapter 2 and Chapter 3 presented two classes of functionalized AIE-active molecules based on cyanostilbene moiety, and their applications were investigated, while Chapter 4 demonstrated a series of donor-acceptor (D-A) molecules with highly emissive unit, and their photophysical properties were studied.;In Chapter 2, four different donor-substituted cyanostilbene-based dipyrrins were synthesized and characterized. The investigation of photophysical properties confirms that these molecules are AIE-active, which should be attributed to the cyanostilbene moiety. The introduction of different donor groups showed little impact on their luminescence. Furthermore, the emission properties of these molecules were found to be sensitive to Zn2+, that is, addition of Zn2+ enormously enhanced its fluorescence in THF. The titration experiments proved they showed good selectivity and sensitivity for Zn2+ detection with relatively low limit of detection. Job's curve and spectral studies of their corresponding zinc complex indicated that the ratio for dipyrrins and Zn2+ is 2:1, which suggested the formation of zinc complex by chelation-enhanced fluorescence (CHEF) effect should be the reason of the enhanced fluorescence. By combining dipyrrin with typical AIE-active moiety tetraphenylethylene (TPE), an AIE-active TPE-based dipyrrin was prepared. The studies of its fluorogenic Zn2+ detection confirmed that the CHEF effect together with AIE effect are responsible for the intense fluorescence, indicating the potential application as a Zn2+ detector in aqueous media.;In Chapter 3, the cyanostilbene backbone was functionalized with a terpyridine unit to construct four terpyridine-based cyanostilbene molecules with different donor substitutents. The investigation of their photophysical properties confirms that they are AIEE-active. With the effect of different electron-donating groups, their solid-state fluorescence color was adjusted from blue to orange-red successfully. According to the calculation results of their frontier molecular orbitals, terpyridine has little impacts on their luminescence, but would influence their solid-state emission obviously owing to its large steric hindrance. This class of molecules displayed higher luminescence efficiency in solid state than in their dissolved state. The twisted molecular conformation in single crystal, which effectively avoids close π-π stacking, was assumed to be responsible for the high luminescence efficiency in solid state. This kind of molecules show distinct switched fluorescence by stimuli of acid/base vapors, and this phenomenon derives from the protonation effect of nitrogen atoms in the terpyridine unit. Moreover, three of these molecules exhibit good electroluminescence properties. Especially, the crystal of non-donor substituted molecule show amplified spontaneous emission (ASE) properties, indicating this blue-emissive material can be used in multiple areas such as chemical sensor, organic light emitting diodes (OLEDs) and organic laser media.

Thesis advisor: Hong Ding / High temperature superconductivity has been one of the most challenging problems in condensed matter physics since its discovery. This dissertation presents systematic studies on electronic structures of single layer high temperature supconductor Bi2Sr2CuO6+[delta] by angle-resolved photoemission spectroscopy. A high binding energy band anomaly is observed in PbxBi2−xSr2CuO6+[delta]. Comparing with LDA calculation, the band is highly remonetized by a factor of 3, the incoherent part coexists and forms a band anomaly as a non-dispersive dive structure. Systematic studies are performed on Bi2+xSr2−xCuO6+[delta] with a wide doping range, revealing a linear doping nature of Bi substitution. An unusual Coulomb gap is observed in the heavily substituted samples. Our results reveal the dual role of off-plane chemical substitution in high-TC cuprates and elucidate the nature of the quantum electronic nature due to strong correlation and disorder. High resolution ARPES on LaxBi2Sr2−xCuO6+[delta] observes a large gap and a small gap coexisting at antinodal region below TC. The small gap is d-wave like and attributed to superconductivity, while the large gap is attributed to a CDW order. A strong short-ranged correlation between the small and large gap magnitude suggesting that superconductivity and charge ordering are driven by similar physical mechanism. / Thesis (PhD) — Boston College, 2008. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Mn5Ge3 suscite de l'intérêt pour des applications dans le domaine de l'électronique de spin car il a une température de Curie élevée (≈300 K) et il peut croître épitaxialement sur des substrats Ge(111) permettant ainsi d'injecter directement dans le semi-conducteur Ge un courant polarisé en spin.Nous avons étudié par photoémission résolue en angle et en spin (ARPES, SARPES), utilisant le rayonnement synchrotron, des films minces de Mn5Ge3(001), obtenus par croissance sur la surface reconstruites Ge(111)-c(2x8).Les résultats ARPES, obtenus dans les plans GALM et GAHK, sont en accord avec des simulations faites sur la base de calculs de structure de bandes faisant appel à la théorie de la fonctionnelle de la densité.Les mesures SARPES faites en plusieurs points du plan GALM sont aussi bien reproduites par ces simulations.D'une façon globale, nos résultats apportent une validation remarquable de la description des propriétés électroniques de Mn5Ge3 par le modèle de bandes. Seule l'intensité spectrale au niveau de Fermi n'est pas bien expliquée par la simulation. Cette différence est attribuée à la nature tridimensionnelle de l'échantillon et à des effets de corrélation. / Mn5Ge3 attracts strong interest for spintronics applications because it has a high Curie-temperature (≈300 K) and it can be grown epitaxially on Ge(111) substrates, permitting direct injection of a spin-polarized current into the Ge semiconductor.Mn5Ge3(001) thin films grown on Ge(111)-c(2x8) reconstructed surface were studied by angle- and spin- resolved photoemission (ARPES, SARPES) using synchrotron radiation. ARPES results, obtained in the GALM and GAHK planes, are in agreement with simulations done with the help of band structure calculations based on the density functional theory, taking into account lifetime broadening and broadening caused by correlation effects.SARPES measurements done at several k-points of the GALM plane are also well acounted for by these simulations.Overall our results provide a remarkable validation of the band structure model for a proper description of the electronic properties of Mn5Ge3. Only the spectral intensity at the Fermi level is not well explained by the simulation. This departure is attributed to the 3D nature of the sample and to correlation effects.

Thesis (Ph. D.)--University of Oregon, 2003. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 166-167). Also available for download via the World Wide Web; free to University of Oregon users.

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1990. / Includes bibliographical references (leaves 118-122) / Microfiche. / xv, 122 leaves, bound ill. 29 cm

Universiẗat, Diss., 1999--Osnabrück.

abstract: The electronic states of semiconductor interfaces have significant importance for semiconductor device performance, especially due to the continuing miniaturization of device technology. The application of ultra high vacuum (UHV) enables the preparation and characterization of fresh and cleaned interfaces. In a UHV environment, photoemission spectroscopy (PES) provides a non-destructive method to measure the electronic band structure, which is a crucial component of interface properties. In this dissertation, three semiconductor interfaces were studies to understand different effects on electronic states. The interfaces studied were freshly grown or pre-treated under UHV. Then in-situ PES measurements, including x-ray photoemission spectroscopy (XPS) and ultra-violet photoemission spectroscopy (UPS), were conducted to obtain electronic states information. First, the CdTe/InSb (100) heterointerface was employed as a model interface for II-VI and III-V heterojunctions. It was suggested that an interface layer formed, which consisted of In-Te bonding. The non-octal bonding between In and Te atoms has donor-like behavior, which was proposed to result in an electron accumulation layer in InSb. A type-I heterointerface was observed. Second, Cu/ZnO interfaces were studied to understand the interface bonding and the role of polarization on ZnO interfaces. It was shown that on O-face ZnO (0001) and PEALD ZnO, copper contacts had ohmic behavior. However, on Zn-face ZnO (0001), a 0.3 eV Schottky barrier height was observed. The lower than expected barrier heights were attributed to oxygen vacancies introduced by Cu-O bonding during interface formation. In addition, it is suggested that the different barrier heights on two sides of ZnO (0001) are caused by the different behavior for the ZnO (0001) faces. Last, a pulse mode deposition method was applied for P-doped diamond growth on (100) diamond surfaces. Pretreatment effects were studied. It is suggested that an O/H plasma treatment or a short period of H-plasma and CH4/H2 plasma could yield a higher growth rate. PES measurements were conducted on H-terminated intrinsic diamond surface and P-doped/intrinsic diamond (100) interfaces. It was suggested that electronic states near the valence band maximum caused Fermi level pinning effects, independent of the diamond doping. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2018

Ce travail de thèse a pour objet l'étude de la famille des supraconducteurs à base de fer, composés découverts en 2008 et présentant un diagramme de phase très riche dans lequel se trouve de la supraconductivité, du magnétisme, ainsi que d'autres ordres électroniques tel que la nématicité électronique. Ceci offre la possibilité de fortes interactions et/ou compétitions entre ces divers types d'ordres électroniques, et l'étude de ces composés vise à mieux comprendre la nature et le lien entre ces différents ordres. Ceci devrait permettre de mieux comprendre de façon générale les comportements collectifs des électrons corrélés dans les solides cristallins. Les supraconducteurs à base de fer sont en général des métaux et présentent un caractère multi-orbital,ce qui donne des degrés de liberté supplémentaires aux électrons. Dans cette thèse,nous avons étudié certains de ces matériaux par photoémission résolue en angle (ARPES),technique permettant de sonder leur structure électronique et d'estimer la force et la nature des corrélations électroniques dans chaque orbitale. Nous nous sommes intéressés à des phases non supraconductrices afin d'avoir une vision plus globale des supraconducteurs au fer. La première partie de cette thèse se concentre sur le composé FeSe. L'intérêt pour ce composé vient de l'émergence d'un nouveau type d'ordre électronique : la nématicité, où les électrons brisent spontanément la symétrie de rotation, ce qui rend les propriétés électroniques anisotropes.Grâce à l'ARPES, nous avons pu suivre l'évolution des différentes orbitales dxz, dyz et dxy,présentes au niveau de Fermi, à travers la transition structurale pour caractériser l'anisotropie de la structure électronique. Pour interpréter ces évolutions, nous avons collaboré au niveau théorique avec le groupe de Lara Benfatto de l'université de Rome. Nous avons élaboré un modèle où les fluctuations de spins, bien présentes dans FeSe même s'il n'y a pas d'ordre magnétique, sont capables de modifier la surface de Fermi. Ceci rend compte des modifications que nous observons par ARPES dans la phase nématique si on suppose que ces fluctuations deviennent anisotropes. La deuxième partie de cette thèse se penche sur les pnictures de la forme AM ₂ As ₂ (A = Ba, Sr, Ca, M = Fe, Co). Cette famille présente plusieurs cas où la nature du magnétisme est différente de celui que l'on trouve à proximité de la phase supraconductrice. Dans les composés à base de fer, il peut se produire une transition vers une phase "collapsée" qui a pour effet de supprimer les moments magnétiques locaux portés par les fers. Nous avons cherché à comprendre comment les propriétés électroniques sont affectées par cette transition. Dans les composés à base de cobalt, des fluctuations ferromagnétiques apparaissent dans les plans CoAs, et CaCo ₂ As ₂ s'ordonne magnétiquement à 72K. C'est un magnétisme plutôt itinérant, assez différent de celui des phases au fer, et nous avons voulu observer cette transition et l'évolution des corrélations dans cette limite. Durant cette étude nous avons été amené à nous poser des questions sur la façon dont l'ARPES, qui est une technique de surface, peut visualiser l'évolution des structures électroniques, notamment la tridimensionnalité, entre les différents composés où la distance entre les plans CoAs varie fortement suivant la nature de A. / This thesis focuses on the study of the family of iron-based superconductors,compounds discovered in 2008 and displaying a rich phase diagram where there is superconductivity, magnetism and also other electronic orders such as electronic nematicity. This offers the possibility for strong interactions and/or competitions between those various electronic orders,and the study of these compounds aim for a better understanding of the nature and the link between these orders. This should allow generally a better understanding of the collective behavior of correlated electrons in crystalline solids. These compounds are generally metals and havea multi-orbital nature, giving extra degrees of freedom to the electrons. During this PhD, westudied some of these materials using Angle Resolved Photoelectron Spectroscopy (ARPES),a technique allowing to probe their electronic structure and estimate the nature and strength of electronic correlations in each orbital. We focused on phases that are not superconducting,in order to have a more global view of iron-based superconductors. The first part of this PhD focuses on FeSe. The interest for this compound comes from the emergence of a new sort of electronic order : the nematicity, where the electrons break spontaneously the rotational symmetry, making the electronic properties anisotropic. Thanks to ARPES, we were able to follow the evolution of the various orbitals dxz, dyz and dxy, existing at the Fermi level, through the structural transition in order to characterize the electronic structure anisotropy. To interpret these evolutions, we collaborated with the theory group of Lara Benfatto from the Roma uni-versity. We elaborated a model where spin fluctuations, which exist in FeSe although there isno magnetic order, are able to modify the Fermi surface. This reflects the modifications that we observe by ARPES in the nematic phase if we suppose these fluctuations become anisotropic.The second part of this PhD focuses on the pnictides with the form AM ₂ As ₂ (A = Ba, Sr, Ca,M = Fe;Co). This family displays several cases where the magnetism is different from that found near the superconducting phases. In the iron-based compounds, there is a transition towards a collapsed phase where the magnetism is suppressed. We have tried to understand how the electronic properties are affected by this transition. In the cobalt-based compounds,ferromagnetic fluctuations appear within the CoAs planes, and CaCo ₂ As ₂ orders at 72K. This magnetism is itinerant, quite different from that found in the iron-based compounds, and we wanted to observe this transition and the evolution of the correlations in this limit. During this study we have come to question ourselves about the way ARPES, which is a surface technique,can visualize the evolution of the electronic structure, notably its three dimensionality, among the different compounds where the distance between CoAs layers strongly changes depending on the nature of A.