Orientador: Mario Antonio Bica de Moraes / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-11T18:58:49Z (GMT). No. of bitstreams: 1 Rouxinol_FranciscoPauloMarques_D.pdf: 6433084 bytes, checksum: 84d703ca8da3620b077c3b1335c59965 (MD5) Previous issue date: 2008 / Resumo: Técnicas de condensação de vapor são úteis na preparação de ligas magnéticas cujos componentes têm pouca, o mesmo nenhuma, solubilidade em condições de equilíbrio Neste trabalho, uma dessas técnicas ¿ sputtering ¿ foi empregada para fabricar ligas metaestáveis de GdXCr1-X, cujas propriedades magnéticas foram investigadas em função da concentração de Gd, x. Difratometria de raios-X de baixo ângulo (GAXRD) e espectroscopia de retroespalhamento Rutherford foram utilizados para determinar a estrutura do filme e sua composição elementar, respectivamente. As análises de GAXRD mostraram que a estrutura da fase de Gd, é hcp quando x ³ 0,88; e amorfa quando 0,16 £ 0,76. Uma estrutura bcc , para a fase de Cr, foi observada nos difratogramas quando x < 0,16, e amorfa quando x ³ 0,16 Para investigar as propriedades magnéticas utilizamos um magnetometro SQUID e m PPMS. O primeiro foi utilizado para as medidas de momento magnético em função do campo estático e temperatura. O PPMS foi tilizado nas investigações de susceptibilidade-AC em função da freqüência de oscilação do campo, temperatura e campo estático. A complexa natureza magnética dos filmes de Gd-Cr foi observada através das isotermas MxH, que não apresentaram saturação em baixas temperaturas, nem comportamento linear em altas temperaturas. Pela análise dos dados magnéticos, observamos que as amostras admitem um comportamento ferromagnético para x ³ 0,5 e paramagnético para as outras concentrações de Gd. A temperatura de Curie (TC) apresenta um aumento monotônico de 170 para 290 K quando x aumenta de 0,5 para 1,0. A temperatura de Curie-Weiss (q C) mostra um aumento monotônico com x. A partir das isotermas MxH a 2 K, o momento de saturação foi calculado, sendo independente de x e aproximadamente constante com um valor médio de 7,3 µB. Medidas de susceptibilidade em campos estáticos e dinâmicos revelaram a existência de comportamentos de vidros magnéticos em todas as amostras abaixo da temperat ra de freezing (Tf). Observamos, nas ligas com altas concentrações de Gd, a presença de comportamentos ferromagnéticos e cluster-glass em baixas temperaturas. Concluímos que a interação de troca entre os átomos de Gd dentro dos clusters de Gd não é do tipo RKKY, e sim do tipo supertroca. O efeito magnetocalórico (MCE) foi investigado através da variação de entropia magnética ( D SM) em função da temperatura, para a remoção de um campo de 50 kOe Curva de D SMxT para as amostras com x < 0,2 apresentaram um formato típico de superferromagneto, consistente com a existência de clusters Gd nos filmes. Nas outras amostras em que o EMC foi analisado, a presença de clusters é observada pelo comportamento dessas curvas a baixa temperatura; a altas temperaturas o comportamento de D SM com T indica fortemente a presença de mais fases magnéticas no filme. O diagrama de fase baseado em TC e Tf, e sua dependência com x é apresentado / Abstract: Vapor condensation techniques are very useful for preparation of alloys whose components have no mutual solubility under equilibrium conditions In this work, one of these techniques ¿ sputtering ¿ has been used to fabricate metastable GdXCr1-X alloys whose magnetic properties were investigated as a function of the Gd concentration, x. Grazing incidence angle X-ray diffraction (GAXRD) and Rutherford backscattering spectroscopy were employed to characterize the film structure and elemental composition, respectively. The GAXRD measurements revealed, for the Gd fraction, a hcp structure for x ³ 0,88; for 0,16 £ x £ 0,76 the Gd fraction was amorphous. The existence of a bcc structure for x < 0,16 was observed in the diffractograms for the Cr phase, which was amorphous for x ³ 0,16. To investigate the magnetic properties, a SQUID magnetometer and a PPMS were used. The former was employed for magnetic moment measurements as a function of applied static field and temperature. The PPMS was used for ac-susceptibility determinations as a function of the frequency of the ac driving field, temperature, and applied static field. The complex magnetic nature of the Gd-Cr films was revealed from the MxH isotherms which did not show saturation even at the lowest temperatures, and did not exhibit a linear behavior at higher temperatures. Processing of the magnetic data has shown that the films exhibit a ferromagnetic behavior for x ³ 0,5 and paramagnetic one for all other Gd concentrations. The Curie temperature (TC) increased monotonically from 170 to 290 K as x increased from 0,5 to 1,0. A monotonical increase in the Curie-Weiss temperature ( q C ) with x was also observed for all films. From the extrapolated MxH isotherm at 2 K (saturation magnetization), the saturation moments were calculated and found to be nearly constant at about 7.3 µB. Both static and dynamic susceptibility measurements revealed the existence of a magnetic glassy behavior in all alloys, occurring below a freezing temperature Tf . For the higher concentration alloys, the ferromagnetic and the cluster glass state were observed at low temperatures. It was thus concluded that the exchange interactions within Gd atoms in the clusters were not of the RKKY but of the superexchange type. The magnetocaloric effect (MCE) was investigated from the magnetic entropy change ( DSM) as a function of temperature, for the removal of a 50 kOe field. Samples with x < 0,2 exhibited DSMxT curves whose shapes are typical of a superferromagnet, consistently with the existence of Gd clusters in the films. For all the other alloys whose MCE was investigated, the presence of clusters is manifested from the behavior of these curves at low temperatures; at higher temperatures, the evolution of DSM with T strongly indicated the presence of more than one magnetic phase in the alloys A magnetic phase diagram based on the Tf and Tc transition temperatures and their dependence on x is presented in this thesis / Doutorado / Física da Matéria Condensada / Doutor em Ciências

La recherche actuelle dans le domaine des nanosciences, l’assemblage supramoléculaire d’atomes métalliques et de molécules sur des surfaces ouvre la voie à des composants fonctionnels, utiles dans une multitude d’applications comme l’Optoélectronique, le magnétisme et la catalyse. Il a été démontré que dans certains cas, l’état de Spin Haut et une forte anisotropie magnétique apparaissent suite à un transfert d’électron entre ligands, surface et atome métallique. Le but de cette thèse porte sur l’auto-assemblage des 1,2,4,5-Tetracyanobenzene (TCNB) et des coordinations nanostructurelles des Fe-TCNB sur une surface d’Au(111). La formation de ces structures est conduite par les interactions non-covalentes. La spectroscopie à effet tunnel (STS) révèle que la molécule de TCNB est physisorbée sur la surface d’Au(111). Une analyse détaillée des spectres dI/dV effectués sur une monocouche de TCNB sur une surface d’Au(111) montre que la molécule de TCNB a un transfert de charge négligeable sur ce substrat avec une énergie d’adsorption de 0,5 eV par molécule. Les mesures STS révèlent un gap HOMO-LUMO de 3 eV, comme le prédit la théorie. En contrôlant les paramètres de fabrication, des composants nanostructurels avec différentes compositions chimiques ou des arrangements moléculaires ont été synthétisés. Les propriétés électroniques ont été caractérisées par une analyse spectroscopique dI/dV locale sur les centres métalliques à différentes étapes de formation des complexes Fe-(TCNB)x (x=4, 2). La déposition à très basse température forme un état intermédiaire métastable. Les données STM montrent que l’angle que forment le trièdre Fe-N-C est de 120°. La spectroscopie tunnel révèle que le Fe et la molécule de TCNB gardent leur identité spectroscopique, le Fe garde ses états de surface de la même façon que s’il avait été déposé seul sur une surface d’Au(111). Ceci indique que les molécules de TCNB sont virtuellement dans le même état électronique qu’avant la déposition du Fe. La situation change lorsque ce dépôt est effectué à température ambiante. Une augmentation de température agit sur l’interaction des composants transformant ainsi la formation en un complexe monomère de Fe(TCNB)4 avec un angle Fe-N-C de 180°. La spectroscopie STS sur ce complexe suggère fortement que la liaison de coordination est formée entre le Fe et la molécule de TCNB. Les calculs DFT soutiennent ces conclusions. Plus loin, une structure a été réalisée par la synthèse d’un réseau Fe(TCNB)2. Ce réseau a une structure carrée avec une séparation régulière entre les atomes de Fe. Les informations électroniques de la structure sont données par la molécule de FePc (où Pc représente la molécule de Phthalocyanine) pour identifier les pics de résonnance du spectre du réseau de Fe(TCNB)2. Une similitude apparait dans les spectres dI/dV effectués sur l’atome de Fe et sur les ligands dans les deux systèmes, indiquant que le Fe ressent un environnement similaire quand il est entouré de TCNB ou quand il est à l’intérieur d’une Phthalocyanine. Une analyse plus détaillée basée sur la formation des liaisons métal-ligands a été discutée. / In the bottom up approach of today’s nanoscience, the supramolecular assembly of metal atoms and molecules on surfaces is leading to functional compounds, relevant to many applications in optoelectronics, magnetism, and catalysis. It has been found that in some cases high magnetic spin states and strong magnetic anisotropy appear as a result of electron transfer between ligands, surface and metal atom. The focus of this thesis lies on the self assembling of 1,2,4,5-Tetracyanobenzene (TCNB) and Fe-TCNB coordination nanostructures on the Au(111) surface. The structural formation is directed by the non covalent interactions. Scanning tunneling spectroscopy (STS) reveal that the TCNB molecules are physisorbed on Au(111) surface. By detail analysis of the dI/dV spectra above the TCNB monolayer on the Au(111) surface, we found that the TCNB molecules on Au(111) shows a negligible charge transfer with Au(111) substrate and a small adsorption energy of 0.5 eV per TCNB molecules. STS measurement provide a HOMO-LUMO gap of 3 eV in agreement with DFT calculations. By controlling the fabrication parameters, surface coordination nanostructures with different chemical composition or molecular packing have been synthesized. The electronic properties have been characterized by the local dI/dV analysis of the metal centers at different steps of a Fe-(TCNB)x (x=4, 2) complexes formation. At low temperature deposition, first form an ordered metastable intermediate. STM data yield the bond angle between the Fe-N-C is 120°. The scanning tunneling spectroscopy reveal that Fe atoms and the TCNB molecules keep their identity while the Fe atoms localize the surface-state electrons similar to what they do on the bare Au(111) surface. This result indicates that the TCNB molecules are virtually in the same electronic state as before the Fe adsorption. The situations are different when the deposition performance at room temperature. When the temperature is changed, to room temperature, the original entities transform into the Fe(TCNB)4 monomer complexes with 180° Fe-N-C bond angles. The STS above the Fe(TCNB)4 complex strongly suggest that the coordination bond had been formed between the Fe atom and the TCNB ligands. DFT calculations support the conclusions and drawn from experimental studies and assist the interpretations of experiment. Further structural complexation is achieved by the synthesis of Fe(TCNB)2 network. The network has a square structure with a regular separation of the magnetic Fe atoms in the network. The electronic information is gathered from the spectroscopic labeling of FePc to identify some of the resonances of the Fe(TCNB)2 network. There are similar features are found in the dI/dV spectra above the Fe atoms and ligand in both system, indicating that the Fe somehow feels a similar environment from the TCNB ligands in the network and in the FePc molecules. Further analysis of this feature have been disused by means of metal-ligand bond formation.

Les conditions thermiques et le traitement du métal liquide pour la coulée centrifuge des tuyaux de canalisation permettent d'obtenir une solidification sous forme de graphite sphéroïdal sur l'ensemble de l'épaisseur. Il est parfois observé en peau des zones solidifiant selon le mode blanc qui peuvent induire des différences de réponses métallurgiques problématiques. La caractérisation de tuyaux de différents diamètres montre qu'une compétition entre la croissance de l'eutectique métastable et la germination et croissance de l'eutectique stable existe dès le tout début de la solidification. Pour préciser les conditions thermiques de cette compétition un dispositif de chute de goute sur substrat a été utilisé pour lequel la solidification rapide et dirigée se déroule avec mesure de l?évolution de la température aux premiers moments de la solidification (t<200 ms). La caractérisation des microstructures à l'état brut de coulée et après traitement thermique a montré que ce dispositif permettait de reproduire les conditions thermiques de la peau des tuyaux et de figer la structure précurseur de celle obtenue par coulée centrifuge. Un modèle physique décrivant les premiers instants de la solidification sous très fort gradient thermique d'une fonte inoculée et traitée au Mg est présenté, prenant en compte la cinétique de germination et croissance des nodules de graphite en compétition avec la solidification de l'eutectique métastable. La comparaison entre les résultats du modèle et les caractérisations microstructurales permet de préciser les scénarios de formation des microstructures en découplant l'influence du gradient thermique et de la vitesse de solidification / The thermal conditions and the treatment of the liquid metal for centrifugal casting of pipes lead to the solidification of the melt in the form of spheroidal graphite (SG) iron throughout the thickness. However it is sometimes observed zones that are solidified within the white mode (eutectic austenite / cementite) mainly in the skin of the product. These areas lead to differences which could be problematic. Further characterization of the microstructure of pipes shows that competition between the nucleation and growth of stable and metastable eutectic growth exists from the beginning of solidification. To clarify the thermal conditions of this competition an experimental device has been used. Liquid metal droplet fall on a cold substrate. Rapid directionnal solidification occurs and the temperature evolution of the lower surface of the droplet is recorded during the very first moment of solidification (< 200 ms). Characterization of droplet microstructures obtained in as-cast state and after heat treatment showed that the device is able to froze the solidified microstructure in an earlier stage of formation than in the as cast pipe. A physical model describing the first instants of the solidification under very high thermal gradient of a cast iron which is inoculated and treated with Mg is presented, taking into account the kinetics of nucleation and growth of graphite nodules in competition with the solidification of the metastable eutectic. The comparison between the calcluated results and microstructural characterizations allows to specify microstructures devlopment scenarios by decoupling the influence of the thermal gradient and solidification rate

Marine clay deposits are characterized by very soft to soft consistencies (undrained strength 1-50 kPa), presence of saline pore solution and low-swelling clays. Besides, loss of metastable structure on disturbance, poor undrained strengths of soft clays is contributed by high water contents. Presence of saline pore solution and low-swelling clays (illite, chlorite, kaolinite) play an important role in developing metastable structure of soil sediments deposited in marine environment. The pore solution salinity regulates the “physico-chemical (A - R) stress” that in turn has significant bearing on development of the metastable structure. Metastable structure refers to edge-face, edge-edge associations in card-house arrangement of platy/elongate particles that develop during deposition. Loss of metastable structure of soft marine clays upon disturbance leads to excessive settlements and slope failures. Besides A - R forces, metastable structure of marine clays is contributed by cementation bonds, thixotropic hardening, ion leaching, formation or addition of dispersing agents and chemical weathering. Secondary compression also causes bonding of micro-structural units that increase stiffness and strength of the metastable structure. Review of literature brings out that majority of studies examining the role of physico-chemical factors on the engineering behavior of marine clays have focused on illite rich sediments. However, non-swelling clay, namely, kaolinite is also encountered in marine deposits (example, Pusan clay, Singapore clay, Sarapui soft clays). Kaolinites differ from illites in being 1:1 mineral (unit layer comprises of 1 silica sheet bonded to 1 gibbsite sheet) and having strong hydrogen bonding between unit layers. Consequently, kaolinite particles are thick (0.3 to 3 ìm thickness) with low surface area (10 to 20 m2/g). Also the hydrogen bonding between unit layers do not allow them to separate on hydration. Combination of very low isomorphous substitution (Al for Si 1 in 400), low cation exchange capacity (3 meq/100g), and low surface area, lead to negligible development of diffuse double layer repulsion forces between kaolinite particles. Strong positive edge (developed on broken bonds at particle edges from adsorption of hydrogen ions) negative face attraction between kaolinite particles, encourages flocculation of particles at range of water contents. It was therefore considered of interest to examine the engineering response of kaolinites to changes in pore solution salinity from leaching effects. The focus of the thesis is hence to gain better understanding of physico-chemical (pore solution salinity, A - R forces) and mechanical (secondary compression, loss of overburden) factors towards development of metastable structure of kaolinite clays deposited in synthetic seawater environments in the context of their compressibility and undrained strength characteristics. Laboratory experiments are performed with kaolinites that are slurry consolidated in conventional consolidometers in saline and synthetic seawater solutions. The metastable structure developed by consolidated specimens is relevant to alluvial marine sediments that contain kaolinite (example, Pusan clay, Singapore clay, Sarapui soft clays). The structure of the thesis is as follows: Chapter 1 gives an introduction to the thesis. Chapter 2 provides a detailed review of literature on the role of chemical factors (pore solution composition, A - R forces, osmotic suction) and mechanical processes (secondary compression and overconsolidation) in developing metastable structure of kaolinite specimens subjected to slurry consolidation and the consequent influence of metastable structure on compression, undrained strength and sensitivity characteristics of clay specimens. The Chapter also defines the scope and objectives of the study. Chapter 3 details the experimental program undertaken to bring out the role of chemical factors and mechanical processes in influencing the 1-dimensional compression and undrained strength characteristics of slurry consolidated kaolinites prepared in saline medium. Chapter 4 delineates the role of chloride salt solutions (sodium, magnesium and calcium) and synthetic seawater solution in contributing to the metastable structure developed by slurry consolidated kaolinites at various vertical effective stress (óv’) and the consequent influence of metastable structure on 1-dimensional compression, undrained strength and sensitivity characteristics of the clay. Chapter 5 examines influence of secondary compression on metastable structure developed by kaolinites that were slurry consolidated in 24.53 g/L sodium chloride and synthetic seawater solutions and the consequence of the developed metastable structure on undrained strength and sensitivity. The chapter also examines the consequences of secondary compression experienced by soft overconsolidated kaolinites on their undrained strength and sensitivity characteristics. Chapter 6 examines the relative influence of differential osmotic stress and electrochemical stress on the consolidation behaviour of kaolinite specimens that are slurry consolidated in sodium chloride solutions. The osmotic efficiencies (á) of kaolinite were obtained using the Fritz-Marine Membrane Model. Chapter 7 summarizes the major conclusions of the thesis.

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Paramagnetické niklem stabilizované tenké vrstvy plošně centrovaného kubického Fe, epitaxně narostené na monokrystalickém substrátu Cu(100) jsou známy svou schopností strukturní a magnetické fázové přeměny při ozáření iontovým svazkem, a to do prostorově centrované kubické struktury charakteristické feromagnetickými vlastnostmi. Monokrystalický Cu(100) substrát je možné také nahradit Si(100) s mezivrstvou Cu(100). Pomocí fokusovaného iontového svazku lze dále snadno lokálně modifikovat magnetické vlastnosti ozařované vrstvy. Tato metoda přímého zápisu magnetických struktur je alternativou k běžným litografickým technikám, nabízející nové jimi nedosažitelné možnosti. Připravené magnetické struktury následně využíváme k propagaci spinových vln. V práci je představen celý proces od růstu vrstev, přes přípravu mikrostruktur, až po studium jejich struktury a statických i dynamických magnetických vlastností. S využitím vektorového síťového analyzátoru studujeme ve vrstvách a v mikrostrukturách připravených fokusovaným iontovým svazkem feromagnetickou rezonanci a propagující se spinové vlny. Zdrojem spinových vln o definovaných vlnových vektorech jsou litograficky připravené koplanární vlnovody, sloužící také k induktivní detekci vln. Pomocí feromagnetické rezonance kvantitativně určujeme materiálové charakteristiky jako jsou saturační magnetizace a parametr útlumu a ze spekter propagujících módů následně určujeme charakteristiky spinových vln, které porovnáváme s dalšími feromagnetickými materiály.

Magnetické nanostruktury mají zajímavé vlastnosti, které umožňují jejich aplikace v základním výzkumu i průmyslu. Jednou z těchto vědeckých disciplín je i magnonika - výzkumný obor, který se zabývá fyzikou spinových vln, které lze použít v nediskrétních výpočtech s nízkými ztrátami energie. Výroba magnetických struktur fokusovaným iontovým svazkem (FIB) je alternativní metoda k běžně používaným litografickým metodám. Materiál použitý v této práci - metastabilní železo - je schopen při ozáření iontovým svazkem podstoupit fázovou transformaci z paramagnetické plošně centrované kubické krystalové struktury na feromagnetickou fázi s prostorově centrovanou kubickou krystalovou strukturou. Jednou z vlastností, která ovlivňuje šíření spinových vlny, je magnetická anizotropie. Tato práce představuje vliv depozičních podmínek v ultra vysokém vakuu během přípravy metastabilní železné vrstvy na magnetickou anizotropii struktur vytvořených pomocí FIB do tohoto filmu. Dále prezentujeme souvislosti mezi parametry FIB, krystalografickými vlastnostmi výsledných struktur a jejich magnetickou anizotropií.

Maßgeschneiderte Eigenschaften von Funktionsmaterialien sind ein fundamentaler Aspekt für die Technologien unserer Gesellschaft und deren Weiterentwicklung. In diesem Zusammenhang bilden die Modifizierung bestehender Synthesestrategien und die Entwicklung neuartiger Synthesewege die grundlegende Voraussetzung für Innovation. Der Zugang zu den benötigten Materialien wird in den bis dato angewandten Synthesemethoden häufig durch die thermodynamische Stabilität einer Verbindung begrenzt. Zielstellung der vorliegenden Arbeit ist es, eine Strategie zur postsynthetischen Umwandlung und Modifizierung bereits vorhandener komplex strukturierter Feststoffe anzuwenden, durch die es gelingt, Zugang zu weiteren Materialien zu erhalten. Als Feststoffprekursoren wurden hierfür verschiedene ternäre und quaternäre, bismutreiche Subhalogenide gewählt, die bei niedrigen Temperaturen bis 70 °C mit dem Reduktionsmittel n-Butyllithium (nBuLi) zur Reaktion gebracht wurden, um diese in topochemischen Reaktionen zu neuen intermetallischen Phasen umzuwandeln. Die Bismutsubiodide Bi12Ni4I3, Bi8Ni8SI2 und Bi28Ni25I5 enthalten intermetallische Stäbe, deren Querschnitte nur vier bis elf Atome umfassen, was effektiven Durchmessern von ca. 0,8 bis 1,2 nm entspricht. Zudem befinden sich Iodidionen in den Kristallstrukturen, die die metallischen Stäbe voneinander separieren. Die reduktiven Behandlungen dieser Feststoffprekursoren führten jeweils zur quantitativen Deinterkalation der Iodidionen und dadurch zur Zusammenlagerung der metallischen Stäbe zu kompakten Stabpackungen. In Pseudomorphosen wurden zum einen Kristalle erhalten, die eine Vielzahl parallel angeordneter Bi3Ni-Faserbündel enthielten, zum anderen bildeten sich die bisher unbekannten, kristallinen Phasen Bi8Ni8S und Bi28Ni25. Während bei den Umwandlungen die strukturellen Charakteristiken der intermetallischen Teilstrukturen der Bismutsubiodide auf die reduzierten Phasen übertragen werden, ändern sich die elektronischen Situationen mit der Variation der Elektronenzahl. Dies lässt sich besonders gut am Beispiel der Umwandlung des Bismutsubiodids Bi28Ni25I5 in die reduzierte Phase Bi28Ni25 verdeutlichen. Die elektronische Struktur ändert sich durch die Reduktion kaum, sodass die zusätzlichen Elektronen im intermetallischen Teil antibindende Zustände füllen. Das intermetallische Bindungssystem verhält sich dabei wie ein strukturell rigides Elektronenreservoir und toleriert die Änderung der Elektronenzahl bei der topochemischen Umwandlung zu Bi28Ni25. Mit der elektronisch ungünstigen Situation geht die Metastabilität der reduzierten intermetallischen Phase einher. Die reduktive Behandlung des Bismutsubiodids Bi13Pt3I7 führte nicht nur zur selektiven topochemischen Deinterkalation von Iodidionen sondern zusätzlich zum Ausbau von Bismutatomen, wodurch die in Bi13Pt3I7 vorhandenen Iodidobismutatschichten in Iodidschichten umgewandelt werden. Die intermetallischen Schichten der Ausgangsverbindung bleiben erhalten und nähern sich an, sodass das bis dato unbekannte Bismutsubiodid Bi12Pt3I5 resultiert. Das topotaktische Fortbestehen der intermetallischen Schichten zeigt sich dabei an intermediär gebildeten Kompositkristallen aus Mutter- und Tochterverbindung. Durch den Abbau der isolierenden Iodidobismutat¬schichten erfolgen die elektronische Kopplung der intermetallischen Schichten und der Übergang des zwei-dimensionalen Metalls Bi13Pt3I7 in das dreidimensionale Metall Bi12Pt3I5. Die topochemische Reaktion wird durch eine Reaktionstemperatur von 45 °C limitiert: Bei erhöhter Reaktionstemperatur bis 70 °C tritt eine Umstrukturierung unter weiterem Iod- und Bismutausbau auf, und die metastabile, binäre Phase Bi2Pt(hP9) wird aufgebaut. Die dichte Kristallstruktur des erstmals dargestellten Bismutsubchlorids Bi12Rh3Cl2 baut sich aus einem intermetallischen [Bi4Rh]-Netzwerk auf, in dessen Kanäle Chloridionen eingeschlossen sind. Im Zuge der Niedertemperaturreaktion mit nBuLi erfolgt ein unerwarteter quantitativer Austausch der Chloridionen gegen Bismutatome, der die Kristalle des Subchlorids in Kristalle der binären Verbindung Bi14Rh3 überführt. Die kristallchemische Analyse zeigte, dass den [RhBi8/2]-Antiprismen des [Bi4Rh]-Netzwerks die Funktion von Scharnieren zukommt, welche eine Aufweitung des intermetallischen Netzwerks ermöglichen. So entstehen breite Diffusionspfade, und es resultiert ein dreidimensionales Transportsystem für den enormen Massetransport durch den Kristall. Bei der Austauschreaktion werden die zuvor unabhängig voneinander leitenden intermetallischen Stränge kantenverknüpfter [RhBi8/2]-Würfel elektrisch kontaktiert. Die physikalischen Eigenschaften ändern sich dabei maßgeblich: Aus dem eingeschränkten Metall Bi12Rh3Cl2 entsteht der metastabile Supraleiter Bi14Rh3. Mit zunehmender Kenntnis über die Strategien zur postsynthetischen Umwandlung und Modifizierung komplexer Strukturen können diese grundsätzlich dazu beitragen, Materialien mit technologisch relevanten Eigenschaften darzustellen. Insbesondere Phasen, die nur bei hohen Temperaturen thermodynamische Stabilität erlangen oder sogar unter allen Bedingungen metastabil vorliegen, werden durch die geschickte Wahl der Synthesestrategie zugänglich. Möglicherweise werden mit dem wachsenden Wissen zu neuartigen Synthesestrategien die chemischen und physikalischen Eigenschaften eines Materials auf diesem Weg gezielt veränderbar. Insbesondere die herausragenden Stabilitäten der nanoskaligen, intermetallischen Stäbe werfen zudem die Frage auf, ob diese durch die Reaktion mit oberflächenaktiven Reagenzien vereinzelt werden können, um neuartige nanoskalige Leiter herzustellen.:1 Motivation und Forschungsstand 2 Experimentelle Daten und Charakterisierungsmethoden 3 Dehalogenierung von Bismutsubhalogeniden mit eindimensionaler intermetallischer Teilstruktur 4 Topochemie an Bismutsubhalogeniden mit zweidimensionaler intermetallischer Teilstruktur und deren Niedertemperaturzersetzung 5 Topochemische Austauschreaktion im dreidimensionalen intermetallischen Netzwerk von Bismutsubhalogeniden 6 Zusammenfassung und Ausblick Quellenverzeichnis Abkürzungsverzeichnis Abbildungsverzeichnis Tabellenverzeichnis Publikationen Anhang Versicherung Erklärung

Epitaxial growth is an important technique for the fabrication of film structures with good crystalline quality, e.g., monoatomic overlayers, multilayers, compound materials, and ordered alloys. Such epitaxially grown films are technologically important materials with, e.g., adjustable electronic, magnetic, and optical properties. In case of coherent or pseudomorphic epitaxy, the overlayer adapts the in-plane lattice parameters of the substrate, i.e., the overlayer is strained to match the lattice parameters parallel to the substrate surface (in-plane directions). Simultaneously, a relaxation of the film dimension perpendicular to the substrate-film interface occurs (out-of-plane direction). Thus, coherent epitaxy provides a method to put phases under strain, and it can stabilise a metastable state of the film material, if the substrate lattice matches this metastable structure. Bulk-like properties in thick overlayers, which adopt the body-centred tetragonal (BCT) crystal structure and which grow coherently on a suitable substrate with quadratic surface symmetry, are modelled by the epitaxial Bain path (EBP) in this thesis. The knowledge of the EBP allows to study properties of the overlayer as function of the substrate lattice parameter. In particular, strain effects on the film material, magnetic order in the overlayer, and the existence of possible metastable states are investigated by means of density functional theory (DFT) in the local spin density approximation (LSDA), and in the singular case of uranium, employing the generalised gradient approximation (GGA). Note that a symmetry property of the BCT structure states, that it is identical to the body-centred cubic (BCC) structure or the face-centred cubic (FCC) structure for definite ratios of the tetragonal lattice parameters. Our definition of the EBP has two, previously not considered consequences for EBPs in general: an EBP can be discontinuous, and the high symmetry cubic structures (FCC and BCC) need not be points on the EBP. Both cases occurred for several elements considered in this thesis. If, however, a cubic structure is a point on the EBP, then a symmetry property guarantees that the total energy along the EBP, E(a), is stationary at this cubic structure. We computed the EBPs of all transition metals (TMs), the post TMs Zn, Cd, and Hg, the alkaline earth metals Ca, Sr, and Ba, the lanthanides La and Lu, and the actinide U (35 elements were treated in total). For each element but Zr, Hg, and U, there are exactly two structures whose energies are minima on the EBP, and which exhibit neither in-plane nor out-of-plane stresses; for Zr, Hg, and U there are three minima each. All other states on the EBP exhibit in-plane stresses because they are a strained form of the stress-free structures. The possibility of metastability of these particular, stress-free structures, i.e., stabilisation of these structures without bonding to the substrate, was investigated by stability conditions based on linear elasticity theory (except for U). We predict that ten FCC structures and three BCT structures not known from the respective phase diagrams may be metastable. We studied the properties of ferromagnetic (FM) states on the EBP for the elements Fe, Co, and Ni, and moreover predict, that Mn, Ru, Os, and U order ferromagnetically for certain states of the EBP. The latter three elements are paramagnetic in their ground states. The onset of ferromagnetism in Os and U is not accompanied by a simultaneously fulfilled Stoner criterion. According to our results, antiferromagnetic order (with moment sequences up-down or up-up-down-down on successive (001) planes) is never more stable than FM order on any EBP for any element investigated. On the basis of our comprehensive results for all TMs, we analysed trends across each of the three TM series and similarities among the three series. We demonstrate, that the type of the EBP (a classification of extrema of E(a) by symmetry into types) follows a characteristic trend across each of the three TM series. We discuss exceptions (Mn, Fe, and Zr) to this trend. Another trend, identical for the three series, is found for the BCT­-FCC structural energy difference as function of the d-band filling (evaluated for BCT structures that define extrema of E(a)), which follows a similar trend as the well studied BCC­-FCC structural energy difference. Clear similarities among the three periods of elements are also reflected in the bulk moduli and in the elastic constants of the cubic or tetragonal structures, that define the global and local minima of E(a). The mentioned similarities suggest, that many properties which are associated with the EBPs of TMs, can be attributed to the occupation of the d-band, which is the most dominant feature of the electronic structure of TMs.

Ce travail de thèse décrit la première observation directe de particules associées à la déplétion quantique et de premières mesures dans l’espace des impulsions d’un superfluide sur réseau. Ces observations ont été réalisées à partir d'un gaz dégénéré d'Hélium métastable sur un tout nouvel dispositif expérimental, dont la construction a été terminée au cours de cette thèse. Permise par l’Hélium métastable, notre détection électronique sensible à l’atome unique donne accès à la distribution tridimensionnelle dans l’espace des impulsions k.Nous avons d’abord développé une approche hybride pour la réalisation de condensats de Bose-Einstein, qui utilise un piège magnétique comme réservoir du piège dipolaire. Cette méthode permet la production rapide de condensats de Bose-Einstein toutes les 6 secondes sur notre expérience. Nous avons alors pu observer, pour la première fois, les particules excitées hors du condensat à cause des interactions (déplétion quantique). En particulier, nous avons observé la loi de puissance en 1/k4 dans la distribution pour de larges impulsions k, comme attendue dans la théorie de Bogoliubov. Enfin nous avons étudié les distributions de superfluide sur réseau. Il s’agit d’une première mesure de la distribution en impulsion dans un réseau comme le démontre les simulations numériques (Monte-Carlo quantique). Les effets de températures sur les distributions mesurées sont extrêmement visibles, ce qui ouvre la voie à une thermométrie des superfluides sur réseau. / In this thesis, we report the first observation of the particles associated with the quantum depletion and the first measurements of the momentum distribution of correlated superfluid lattice bosons. We performed the experiment with a degenerate metastable Helium gas with a novel experimental setup. Making possible with metastable Helium, our electronic detection allows single-atom detection in momentum space k.Firsly, we have demonstrated a new approach to Bose-Einstein condensation of metastable Helium using a hybrid trap, consisting of a magnetic quadrupole and a crossed optical dipole trap. It results in production of a condensate every 6 seconds. Then we observed the excited particles out of the condensate wavefunction due to presence of the interactions (quantum depletion). We observe atom distributions decaying at large momenta k with the 1/k4 power-law predicted by Bogoliubov theory. Furthermore we studied the three-dimensional far field distribution of correlated superfluid lattice bosons. The momentum distributions of the trapped atoms calculated with an ab-initio Monte-Carlo Worm algorithm for the experimental parameters are in excellent agreement with the measured distributions. The finite temperature effect is not negligible, paving the way for a precise thermometry.