Made available in DSpace on 2014-10-09T12:46:10Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:57Z (GMT). No. of bitstreams: 1 07537.pdf: 6037545 bytes, checksum: e5c0c7ed539b9c85328768099422ceff (MD5) / Dissertacao (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:35:27Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:05:40Z (GMT). No. of bitstreams: 0 / No Brasil e no mundo a tecnologia nuclear vem ocupando posição de destaque com diversas aplicações na indústria, geração de energia, meio ambiente e na medicina, melhorando a qualidade de exames e tratamentos, consequentemente, a vida das pessoas. O urânio é o principal elemento utilizado em instalações nucleares, servindo como material base desde a geração de eletricidade à fabricação de radiofármacos. Nos anos 50, em meio à guerra fria, a então recém-criada Agência Internacional de Energia Atômica se propôs a supervisionar instalações nucleares e incentivar a fabricação de combustíveis nucleares com baixo teor de urânio, conhecidos como combustíveis do tipo Material Test Reactor (MTR), fabricados inicialmente na forma de U3O8 e mais tarde o U3Si2, ambos dispersos em alumínio. A utilização desta tecnologia requer uma constante melhoria de todos os processos que envolvem a fabricação do MTR sujeita a diversos protocolos internacionais, os quais procuram garantir a confiabilidade desse combustível do ponto de vista prático e ambiental. Dentro desse contexto, o controle de impurezas, do ponto de vista da economia de nêutrons, afeta diretamente a qualidade de qualquer combustível nuclear, fazendo-se necessário um controle rigoroso. A literatura reporta procedimentos que, além de gerar resíduos, são demorados e dispendiosos, pois necessitam de curva de calibração univariada e materiais de referência. Assim, o objetivo deste trabalho é estabelecer e validar uma metodologia de análise química quantitativa não destrutiva, de baixo custo e tempo de análise, tal como, minimizar a geração de resíduo para a determinação multielementar dos maiores constituintes (Utotal e Si) e as impurezas (B, Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, Cd e outros) presentes em U3O8 e U3Si2, atendendo as necessidades de reatores nucleares na qualificação de combustíveis nucleares do tipo MTR. Para tanto, foi aplicada a técnica de fluorescência de raios X que permite análises químicas rápidas e não destrutivas, além de não necessitar de tratamentos químicos prévios (dissolução, digestão e outros) na fase de preparação de amostras. Para as correções de efeitos espectrais e de matriz foram aplicados e avaliados os métodos de parâmetros fundamentais, de curva de calibração univariada e de calibração multivariada. Os resultados foram comparados por meios de testes estatísticos em conformidade com a norma ISO 17025 com os MRCs (123(1-7) e 124(1-7)) de U3O8 da New Brunswick Laboratory (NBL) e 16 amostras de U3Si2 cedidas pelo CCN do IPEN-CNEN-SP. A quimiometria demonstrou-se um método promissor para a determinação de maiores e menores constituintes em combustíveis nuclear a base de U3O8 e U3Si2, uma vez que a precisão e exatidão são estatisticamente iguais aos métodos de análises volumétrica, gravimétrica e ICP-OES. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:41:52Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:08:05Z (GMT). No. of bitstreams: 0 / O objetivo deste trabalho foi determinar a influência do ferro e do manganês em uma liga de alumínio com 9% de silício (% em peso). Para isto, foram elaboradas duas famílias de liga Al-9%Si: uma com os teores de 0,1%, 0,4%, 0,8% e 1,2% de Fe e uma segunda liga de Al-9%Si-0,8%Fe com teores de 0,1%, 0,4% e 0,7% de Mn. Para a realização deste estudo, foram produzidos corpos de prova de tração fundidos em coquilha, segundo a norma ASTM B108. Os corpos de prova obtidos foram tracionados para avaliação das propriedades mecânicas, em seguida, foram submetidos a uma análise microestrutural por microscopia óptica (MO) e eletrônica de varredura (MEV). As superfícies de fratura dos corpos de prova tracionados foram também observadas por MEV com a finalidade de comparar o efeito das adições de Fe e Mn. O efeito da adição crescente de Fe na liga Al-9%Si foi observado no ensaio de tração que mostrou queda tanto nos limites de resistência e de escoamento como no alongamento, decorrentes da formação da fase β-Al5FeSi que apresentou morfologia em plaquetas, interrompendo a continuidade da matriz de alumínio. Para teores abaixo de 0,4% de Fe, ocorreu um ligeiro aumento da resistência mecânica que pode ser atribuído à formação da fase α-Al8Fe2Si, que apresentou morfologia tipo escrita chinesa, que não interrompe a continuidade da matriz. Com adição de teores crescentes de Mn na liga Al-9%Si-0,8%Fe ocorreu uma elevação do limite de resistência e do alongamento, mas uma queda do limite de escoamento, quando comparados com a mesma liga sem adição de Mn. Conclui-se que esse comportamento pode ser atribuído a mudança de morfologia do intermetálico de plaquetas para escrita chinesa que intercala a matriz dúctil com a fase frágil, devido a adição do Mn. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Os silicetos de metais de transição têm sido investigados para possíveis aplicações em altas temperaturas. A expansão térmica é uma das principais propriedades a serem consideradas nas aplicações. Este trabalho teve como objetivos a determinação dos coeficientes de expansão térmica das fases αTa5Si3 e Cr5Si3 e a investigação da formação da fase (Hf, Ti)5Si3. As ligas de Ta-Si e Cr-Si foram produzidas por fusão a arco. As ligas de Ta-Si foram tratadas termicamente a 1900 °C por 3 h em argônio, enquanto que as ligas de Cr-Si foram tratadas a 1200 °C por 24 h em argônio. As ligas foram caracterizadas por difratometria de raios X e microscopia eletrônica de varredura. As medidas de difratometria de raios X de alta resolução com fonte de luz síncrotron foram realizadas nas amostras contendo as fases de interesse, αTa5Si3 e Cr5Si3 num intervalo de temperatura entre ambiente e 800 °C. A fase αTa5Si3, de estrutura tetragonal (T2), apresentou expansão térmica de αa = 5,9(3).10-6 K-1 e αc = 9,2(4).10-6 K-1 na liga Ta62,5Si37,5 e αa = 6,2(3).10-6 K-1 e αc = 9,5(4).10-6 K-1 na liga Ta62Si38, resultando em uma anisotropia de αc/αa de 1,5 para ambas as amostras. A fase Cr5Si3 de estrutura hexagonal (D88) apresentou expansão térmica de αa = 17,1(3).10-6 K-1 e αc = 11,1(4).10-6 K-1 na liga Cr62,5Si37,5 e αa = 17,2(3).10-6 K-1 e αc = 10,7(4).10-6 K-1 na liga Ta62Si38, com anisotropia αc/αa de 1,5 e 1,6, respectivamente. Na segunda parte deste trabalho, as ligas de composições Hf(62,5-x)TixSi37,5 (0 ≤ x ≤ 62,5) com diferentes proporções de Hf e Ti foram preparadas por fusão a arco e tratadas termicamente a 1200 °C por 24 h em atmosfera de argônio. A formação da fase (Hf,Ti)5Si3 foi observada em todas as amostras preparadas. As amostras de composições Hf38,9Ti23,6Si37,5 e Hf22,5Ti40Si37,5 a Ti62,5Si37,5, apresentaram-se monofásicas. A variação nos parâmetros de rede a e c da fase hexagonal (Hf,Ti)5Si3 contendo diferentes teores de Hf e Ti mostrou que a fase constitui uma solução sólida em toda a extensão entre Hf5Si3 e Ti5Si3, com substituição parcial dos átomos de Hf por Ti. / The transition metal silicides have been investigated aiming high temperature applications. The thermal expansion is one of main properties for applications. The aim of this work was the evaluation of the thermal expansion coefficients for αTa5Si3 and Cr5Si3 phases and the investigation of (Hf, Ti)5Si3 phase formation. The Ta-Si and Cr-Si alloys were prepared by arc-melting. The Ta-Si alloys were heat-treated at 1900 °C for 3 h in argon atmosphere. The Cr-Si alloys were treated at 1200 °C for 24 h in argon. The alloys were characterized by X-ray diffractometry and scanning electron microscopy. The αTa5Si3 and Cr5Si3 phases were analyzed in high temperatures up to 800 °C using high-resolution X-ray diffraction with synchrotron radiation source. The thermal expansion coefficients for the αTa5Si3 tetragonal phase (T2) was found to be 5.9(3).10-6 K-1 and αc = 9.2(4).10-6 K-1 in Ta62.5Si37.5 composition alloy and αa = 6.2(3).10-6 K-1 and αc = 9.5(4).10-6 K-1 in Ta62Si38 composition alloy. The anisotropy αc/αa was determined to be 1.5 for both samples. The thermal expansion coefficients for Cr5Si3 hexagonal phase was found to be αa = 17.1(3).10-6 K-1 and αc = 11.1(4).10-6 K-1 for Cr62.5Si37.5 composition alloy and αa = 17.2(3).10-6 K-1 and αc = 10.7(4).10-6 K-1 for Ta62Si38 composition alloy. The values of the anisotropy αc/αa were respectively, 1.5 and 1.6. In the second part of this work, the alloys of Hf(62.5-x)TixSi37.5 (0 ≤ x ≤ 62.5) compositions with different proportion of Hf and Ti were prepared by arc-melting and heat-treated at 1200 °C for 24 h in argon atmosphere. The formation of (Hf,Ti)5Si3 phase was observed for all prepared alloys. The alloys of Hf38.9Ti23.6Si37.5 and Hf22.5Ti40Si37.5 to Ti62.5Si37.5 compositions were found to be single-phase. The variation in the lattice parameters a and c for the hexagonal (Hf,Ti)5Si3 phase with different proportion of Hf and Ti shown the formation of solid solution in all range between Hf5Si3 and Ti5Si3 with partial substitution of Hf by Ti.

Seltenerdsilizide RSi2 und deren verwandte R2TSi3-Verbindungen kristallisieren in hexagonalen AlB2- sowie tetragonalen ThSi2-ähnlichen Kristallstrukturen, unter denen es eine große strukturelle Vielfalt gibt, insbesondere im Hinblick auf die Ordnung von T- und Si-Atomen. Basierend auf einer ausführlichen Literaturrecherche mit einem Umfang von mehr als 300 Artikeln und 500 Strukturberichten wurde die kristallographische Familie eingehend charakterisiert und deren Symmetriebeziehungen herausgearbeitet. Das so entstandene Bärnighaus-Diagramm umfasst im Vergleich zu bisherigen Veröffentlichungen sechs zusätzliche Strukturtypen, deren Raumgruppen in dieser Arbeit teilweise erstmalig bestimmt wurden. Weiterhin konnten Zusammenhänge zwischen den beinhalteten Elementen der Verbindungen und deren Eigenschaften erarbeitet werden. Beispielsweise bilden sich signifikant häufiger geordneten Strukturen nach einer thermischen Behandlung. Darüber hinaus konnte hier eine Korrelation zwischen der elektronischen Struktur eines Hückel-Aromaten und der Si/T-Ordnung herausgearbeitet werden. Ergänzt wird die Arbeit durch Dichtefunktionaltheorieberechnungen, die zum einen Aufschluss über Formierungsenergien und somit über die potentielle Stabilität von bisher nicht berichteten Verbindungen geben. Zum anderen wurden die Bader-Ladungen der Atome berechnet, wodurch beispielsweise mögliche Überstrukturmodelle im tetragonalen Gitter auf nur ein plausibles Modell reduziert werden konnten. Abgerundet wird die Arbeit durch eigene Ergebnisse aus resonanten Synchrotronexperimenten, beispielhaft an dem Vertreter mit der größten Überstruktur: Ho2PdSi3. Für diese Verbindung gab es noch weitere mögliche Strukturmodelle, die jedoch dank der präsentierten Ergebnisse ausgeschlossen werden können.:Kurzfassung/Abstract 1. Einleitung 2. Grundlagen 2.1. Die Elemente 2.1.1. Aufbau 2.1.2. Bindungen 2.1.3. Atomradien 2.2. Kristallographie 2.2.1. Gliederung von Kristallstrukturen 2.2.2. Symmetrieabstieg 2.2.3. Raumgitter und reziprokes Gitter 2.2.4. Elektronen im Kristall 2.3. Resonante Röntgenbeugung 2.3.1. Röntgenabsorptionsspektroskopie 2.3.2. Röntgendiffraktion 2.3.3. Analyse der Diffraction Anomalous Fine Structure 3. Strukturelle Variationen der RSi2- und R2TSi3-Verbindungen: Charakterisierung und Ursachen 3.1. Kristallographische Übersicht der RSi2- und R2TSi3-Verbindungen 3.1.1. Vom AlB2-Typ abgeleitete Strukturen 3.1.2. Vom ThSi2-Typ abgeleitete Strukturen 3.1.3. Strukturbeschreibung 3.2. Systematisierung von Materialeigenschaften anhand von R–T-Diagrammen 3.2.1. Verteilung der Strukturtypen gemäß der Elementkombinationen 3.2.2. Gitterparameter und Si–T-Abstände 3.2.3. Thermische Behandlung 3.2.4. Elementradien und Radienverhältnis 3.2.5. Dichte und Packungsdichte 3.2.6. Elektronische Struktur 3.3. Abhängigkeiten zwischen den Materialeigenschaften 3.3.1. Korrelationen des kürzesten Si–T-Abstands d 3.3.2. Korrelationen des Quotienten c/a 3.3.3. Korrelationen des Quotienten qrad (und der Elementradien) 3.3.4. Korrelationen der thermischen Behandlung 3.3.5. Korrelationen der elektronischen Struktur 3.4. Stabilitätsanalysen basierend auf DFT-Rechnungen 3.4.1. Die Reihe der Co-Verbindungen 3.4.2. Die Reihe der Rh-Verbindungen 3.4.3. Die Reihe der Pt-Verbindungen 3.4.4. Die Gitterparameter von La2PdSi3 3.4.5. Tetragonales oder hexagonales BaSi2? 3.4.6. Orthorombisches Sr2AgSi3 3.4.7. Potentielle, tetragonale Struktur mit geordneten Si/T-Atomen 4. Überstrukturanalyse an Ho2PdSi3mit Diffraction Anomalous Fine Structure Analyse 4.1. Die Probe 4.2. Die Modelle 4.3. Durchführung 4.3.1. Details zu den Simulationen 4.3.2. Details zu den Experimenten 4.4. Auswertung 4.4.1. Die Holmium-L-Kanten 4.4.2. Die Palladium-K-Kante 5. Zusammenfassung Anhang A. Strukturparameter der RSi2- und R2TSi3-Verbindungen B. Die Strukturtypen und Wyckoff-Lagen der RSi2- und R2TSi3-Verbindungen C. Geometrische Betrachtungen der Gitter D. Hilfswerte für die DFT-Rechnungen E. Parameter der FDMNES-Simulatio F. Herleitung des Extinktionskorrekturterms G. Mittlere Fehlerquadrate der Fits an die XAFS- und DAFS-Experimente Tabellenverzeichnis Abbildungsverzeichnis Literaturverzeichnis Danksagung Eidesstattliche Erklärung

The main focus of the present work was the Ge-rich part of the binary Ba – Ge system, in which by inspecting the behavior of the clathrate-I Ba8Ge43 under pressure, several new phases were found. The new phases in this system have the following compositions: BaGe3 (with two modifications), BaGe5, BaGe5.5 and BaGe6, therefore they are quite close in composition range: 75% - ~85% at. Ge. Concerning the conditions required for the synthesis of each phase, several combinations of temperature and pressure were employed in order to find a stability range. It was possible to establish such a formation range for all phases. In some cases two phases were found for a given conditions and in many other cases three or more phases were found to coexist. Thus, the stability range of pressure and temperature for single phase formation turned out to be very narrow. By inspecting of some structural features, for instance the interatomic distances, it is found that the average of the Ge – Ge distances change in line with the composition, i.e. the shorter contacts belong to BaGe6 while the longer distances are present in BaGe3 (both modification). An opposite trend is observed for the calculated density of each phase (neglecting the tI32 form of BaGe3): the lower density is found for BaGe3 and the denser compound is found to be BaGe6. Of course this is not coincidence, since due to the Ge content, BaGe6 has the largest molar mass. Similarly, by examining the density as a function of the interatomic distance. In such case, the denser compound is characterized by shorter Ge – Ge contacts, while the less dense phase holds the longest Ge – Ge contacts. This is in agreement with the building motifs within each crystal structure: columns in BaGe3 (open framework) passing through layers in BaGe5, ending in a three-dimensional network (closed framework) in BaGe6.

La synthèse de siliciures métalliques sous la forme de films ultra-minces demeure un enjeu majeur en technologie CMOS. Le contrôle du budget thermique, afin de limiter la diffusion des dopants, est essentiel. Des techniques de recuit ultra-rapide sont alors couramment utilisées. Dans ce contexte, la technique de nanocalorimétrie est employée afin d'étudier, in situ, la formation en phase solide des siliciures de Ni à des taux de chauffage aussi élevés que 10^5 K/s. Des films de Ni, compris entre 9.3 et 0.3 nm sont déposés sur des calorimètres avec un substrat de a-Si ou de Si(100). Des mesures de diffraction de rayons X, balayées en température à 3 K/s, permettent de comparer les séquences de phase obtenues à bas taux de chauffage sur des échantillons de contrôle et à ultra-haut taux de chauffage sur les calorimètres. En premier lieu, il est apparu que l'emploi de calorimètres de type c-NC, munis d'une couche de 340 nm de Si(100), présente un défi majeur : un signal endothermique anormal vient fausser la mesure à haute température. Des micro-défauts au sein de la membrane de SiNx créent des courts-circuits entre la bande chauffante de Pt du calorimètre et l'échantillon métallique. Ce phénomène diminue avec l'épaisseur de l'échantillon et n'a pas d'effet en dessous de 400 °C tant que les porteurs de charge intrinsèques au Si ne sont pas activés. Il est possible de corriger la mesure de taux de chaleur en fonction de la température avec une incertitude de 12 °C. En ce qui a trait à la formation des siliciures de Ni à ultra-haut taux de chauffage, l'étude montre que la séquence de phase est modifiée. Les phases riches en m étal, Ni2Si et théta, ne sont pas détectées sur Si(100) et la cinétique de formation favorise une amorphisation en phase solide en début de réaction. Les enthalpies de formation pour les couches de Ni inférieures à 10 nm sont globalement plus élevées que dans le cas volumique, jusqu' à 66 %. De plus, les mesures calorimétriques montrent clairement un signal endothermique à haute température, témoignant de la compétition que se livrent la réaction de phase et l'agglomération de la couche. Pour les échantillons recuits a 3 K/s sur Si(100), une épaisseur critique telle que décrite par Zhang et Luo, et proche de 4 nm de Ni, est supposée. Un modèle est proposé, basé sur la difficulté de diffusion des composants entre des grains de plus en plus petits, afin d'expliquer la stabilité accrue des couches de plus en plus fines. Cette stabilité est également observée par nanocalorimétrie à travers le signal endothermique. Ce dernier se décale vers les hautes températures quand l'épaisseur du film diminue. En outre, une 2e épaisseur critique, d'environ 1 nm de Ni, est remarquée. En dessous, une seule phase semble se former au-dessus de 400 °C, supposément du NiSi2. / The synthesis of metal silicides in the form of ultra-thin films remains a major issue in CMOS technology. Controlling the thermal budget to limit dopant diffusion is essential and ultra-rapid annealing techniques are commonly used. In this context, the nanocalorimetry technique is used in situ to study Ni silicides phase formation at heating rate as high as 10^5 K/s. Ni films from 9.3 nm to 0.3 nm are carried out on calorimeters with either a-Si or Si(100) substrate. Ex situ temperature-resolved x-ray diffraction, scanned at low heating rate (3 K/s), is used in order to compare the phase sequence with the ones obtained at ultra-high heating rates. First, the use of c-NC calorimeters equipped with a Si(100) substrate, 340 nm thick, results in a major challenge. An abnormal endothermic signal is measured at high temperature. Results show that microdefects in the SiNx membrane create short circuits between the Pt heating strip of the calorimeter and the metal sample. This phenomenon decreases with the thickness of the metal sample and has no effect below 400 °C. Below this temperature the Si charge carriers are not activated. Then, the heat flow signal was corrected as a function of the temperature with an uncertainty of 12 ° C. In regard to the formation of Ni silicides at ultra-high heating rates, the study shows that the phase sequence is changed. On Si(100) substrate, the metal rich phases such as Ni2Si and theta -phase are no longer detected. Also, a solid state amorphization is favored at the beginning of the reaction. The enthalpies of formation for layers thinner than 10 nm are generally higher, up to 66 %, than those listed in literature for thick layers. Moreover, the calorimetric measurements clearly show an endothermic signal at high temperature, revealing a competition between the reaction of phase formation and the layer agglomeration. For sample annealed at 3 K/s on Si(100), the critical thickness as described by Zhang and Luo, is observed around 4 nm of Ni. A model is proposed in order to explain the increased stability when the layer thicknesses decrease. It is based on the fact that the diffusion of atoms is harder when grain sizes decrease. It also explains why the endothermic signals in nanocalorimetry shift toward higher temperatures when the layer thickness decreases. In addition, a second critical thickness of about 1 nm is noted. Below, it seems that only one phase forms, presumably the NiSi2.

Silizide spielen ein wesentliche Rolle in den technologisch fortschrittlichsten CMOS Bauteilen. Sie finden Verwendung als Kontaktmaterial auf den Aktivgebieten und dem Silizium Gatter von Transistoren. Diese Arbeit beschäftigt sich mit den Systemen: Co-Si, Co-Ni-Si und Ni-Si. Sowohl in situ Hochtemperatur-SR-XRD Experimente als auch CBED wurden zur Phasenidentifikation herangezogen. AES erlaubte es, Elementverteilungen in Schichtstapeln zu bestimmen. Für Studien über Agglomerationserscheinungen wurde REM eingesetzt. TEM und analytisches TEM trugen nicht nur zu Einblicken in Schichtstrukturen und Kornformen bei, sondern lieferten auch Daten zu Elementverteilungen in Silizidschichten. Diese Dissertation gliedert sich in zwei Hauptteile. Der erste Teil beschäftigt sich mit den Phasenbildungsabfolgen und den Phasenbildungs- und Umwandlungstemperaturen in nanoskaligen dünnen Schichten. Als Trägermaterial wurden einkristalline und polykristalline Siliziumsubstrate verwendet. Der Einfluß verschiedener Dotierungen im Vergleich zu undotierten Substraten sowie die Beeinflussung der Silizidierung durch eine Deckschicht wurden untersucht. Im zweiten Teil waren Größeneffekte verschiedener Schichtdicken und Agglomerationserscheinungen Gegenstand von Untersuchungen. Unterschiede bei der Silizidierung in Zusammenhang mit unterschiedlichen Schichtdicken wurden bestimmt. Darüberhinaus wurde eine ternäre CoTiSi Phase gefunden und identifiziert. Außerdem konnte die stark eingeschränkte Mischbarkeit der Monosilizide CoSi und NiSi gezeigt werden. Der thermische Ausdehnungskoeffizient von NiSi im Temperaturbereich 400?700°C und sein nicht-lineares Verhalten wurden bestimmt. / Silicides are an essential part of state-of-the-art CMOS devices. They are used as contact material on the active regions as well as on the Si gate of a transistor. In this work, investigations were performed in the systems Co-Si, Co-Ni-Si, and Ni-Si. In situ high temperature SR-XRD and CBED techniques were used for phase identification. AES enabled the determination of elemental concentrations in layer stacks. SEM was applied to agglomeration studies. TEM imaging and analytical TEM provided insights into layer structures, grain morphology as well as information about the distribution of chemical elements within silicide layers. This thesis is divided into two main parts. The first part deals with the phase formation sequences and the phase formation and conversion temperatures in nanoscale thin films on either single crystal or polycrystalline Si substrates. The effect of different types of dopants vs. no doping and the impact of a capping layer on the phase formation and conversion temperatures were studied. In the second part, size effects and agglomeration of thin silicide films were investigated. The effect of different layer thicknesses on the silicidation process was studied. Additionally, the degree of agglomeration of silicide films was calculated. Furthermore, the ternary CoTiSi phase was found and identified as well as the severely limited miscibility of the monosilicides CoSi and NiSi could be shown. The CTE of NiSi between 400?700 ±C and its non-linear behavior was determined.

Die Dissertation beschreibt Untersuchungen der intermetallischen Verbindungen TbxY1-xNi2B2C bzw. TbxEr1-xNi2B2C, Tb2PdSi3 sowie Dy2PdSi3, die sich auszeichnen durch physikalische Erscheinungen, die durch die Wechselwirkung der magnetischen Momente der Seltenerd (SE)-Ionen mit den Leitungselektronen hervorgerufen werden. Sie umfasst Beiträge zur Konstitution der Legierungssysteme, methodische Untersuchungen zur Einkristallzüchtung, zur Charakterisierung der Homogenität und Perfektion der Kristalle und zu physikalischen Eigenschaften (Supraleitung, Magnetismus). Die für das Erstarrungs- und Schmelzverhalten der intermetallischen Phasen relevanten quasi-binären Schnitte der Tb-(Y, Er)-Ni-B-C bzw. Tb(Dy)-Pd-Si-Phasendiagramme, die bisher noch nicht bekannt waren, konnten bestimmt werden. Damit wurden die Prozessparameter der Einkristallzüchtung durch tiegelfreies Zonenschmelzen optimiert. Die unterschiedlichen Erstarrungstypen, peritektische Erstarrung (SENi2B2C) bzw. kongruentes Erstarren (SE2PdSi3), wurden durch unterschiedliche Ziehgeschwindigkeiten bei der Einkristallzüchtung berücksichtigt. An den massiven Einkristallen wurden Homogenitätsuntersuchungen hinsichtlich Elementkonzentration und physikalischer Eigenschaften (Tc, Tn, RRR) als Funktion der Längskoordinate durchgeführt, die geringe Eigenschaftsunterschiede der einkristallinen Proben nachweisen. Aus der Zusammensetzungsänderung über die Kristalllänge konnte in Verbindung mit in-situ Messungen der Zonentemperatur ein einfaches Prozessmodell des Zonenschmelzens der untersuchten Verbindungen entwickelt werden. Die Korrelation von magnetischen und supraleitenden Eigenschaften der Borokarbidmischreihen werden primär vom Verhältnis der Seltenen Erden bestimmt aber auch durch die Konzentration der weiteren Elemente. An Einkristallen konnte eine Anisotropie des oberen kritischen Feldes der Supraleitung von TbxY1-xNi2B2C gezeigt werden, die durch die magnetischen Tb-Ionen bestimmt wird. Die Untersuchungen der Tb2PdSi3- und Dy2PdSi3-Einkristalle ergaben eine Anisotropie der magnetoelektrischen Eigenschaften. / In this thesis investigations of the intermetallic compounds TbxY1-xNi2B2C, TbxEr1-xNi2B2C, Tb2PdSi3 and Dy2PdSi3 are presented. These compounds exhibit interesting physical phenomena caused by the interaction of the rare earth (RE) magnetic moments on the conduction electrons. Moreover, contributions on the constitution of the alloy systems, basic investigations of crystal growth process, homogeneity, microstructure and physical properties (superconductivity, magnetism) of the crystals are given. The quasi-binary sections of the Tb-(Y, Er)-Ni-B-C and Tb(Dy)-Pd-Si-phase diagrams which are relevant for the crystallisation of the different intermetallic phases have been determined for the first time. They were utilised for optimisation of the process parameters of single crystal growth by floating-zone melting. Because of the different solidification modes of RENi2B2C (peritectic solidification) and RE2PdSi3 (congruent solidification) different growth velocities have been employed in crystal growth. The composition and the physical properties (Tc, Tn, RRR) have been investigated as function of the crystal axis co-ordinate. As these properties show only a slight shift over the crystal length samples are representative for the whole crystal. From the slight composition shift over the crystal length a process model of the floating zone growth has been developed utilising the in-situ measurements of the zone-temperature. The correlation of magnetic and superconducting properties of the borocarbide solid solution compounds are mainly governed by the RE-fraction but they are also influenced by the concentration of the other elements. For TbxY1-xNi2B2C single crystals an anisotropic upper critical field of superconductivity has been detected which is induced by the magnetic Tb-ions. The investigations of Tb2PdSi3 and Dy2PdSi3 revealed an anisotropy of the magnetoresistive properties.

Silicon-based nanostructures are essential building blocks for nanoelectronic devices and nano-electromechanical systems (NEMS), and their mechanical and electrical properties play an important role in controlling the functionality and reliability of the nano-devices. The objective of this dissertation is twofold: The first is to investigate the mechanical properties of silicon nanolines (SiNLs) with feature size scaled into the tens of nanometer level. And the second is to study the electron transport in nickel silicide formed on the SiNLs. For the first study, a fabrication process was developed to form nanoscale Si lines using an anisotropic wet etching technique. The SiNLs possessed straight and nearly atomically flat sidewalls, almost perfectly rectangular cross sections and highly uniform linewidth at the nanometer scale. To characterize mechanical properties, an atomic force microscope (AFM) based nanoindentation system was employed to investigate three sets of silicon nanolines. The SiNLs had the linewidth ranging from 24 nm to 90 nm, and the aspect ratio (Height/linewidth) from 7 to 18. During indentation, a buckling instability was observed at a critical load, followed by a displacement burst without a load increase, then a fully recoverable deformation upon unloading. For experiments with larger indentation displacements, irrecoverable indentation displacements were observed due to fracture of Si nanolines, with the strain to failure estimated to be from 3.8% to 9.7%. These observations indicated that the buckling behavior of SiNLs depended on the combined effects of load, line geometry, and the friction at contact. This study demonstrated a valuable approach to fabrication of well-defined Si nanoline structures and the application of the nanoindentation method for investigation of their mechanical properties at the nanoscale. For the study of electron transport, a set of nickel monosilicde (NiSi) nanolines with feature size down to 15 nm was fabricated. The linewidth effect on nickel silicide formation has been studied using high-resolution transmission electron microscopy (HRTEM) for microstructural analysis. Four point probe electrical measurements showed that the residual resistivity of the NiSi lines at cryogenic temperature increased with decreasing line width, indicating effect of increased electron sidewall scattering with decreased line width. A mean free path for electron transport at room temperature of 5 nm was deduced, which suggests that nickel silicide can be used without degradation of device performance in nanoscale electronics.