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This paper focuses on a study of temperature effects on tensile properties of a polyamide 12 based polymer. Specimens for testing were generated using the additive manufacturing process of laser sintering. Tensile tests were conducted according to DIN EN ISO 527 at temperatures between 20 °C and 140 °C. A Zwick 250N5A was used for the tests. Fine strain up to 0.25 % was measured using a MTS biaxial extensometer. Crosshead displacement was recorded as well and used for generation of stress-strain curves. Within the paper, Young's modulus, Poisson ratio, tensile strength, tensile strain at tensile strength, stress and elongation at break and yielding are reported. The study showed that all analyzed mechanical properties depend significantly on temperature. Above 100 °C strain raised up to 100 %, however, it was limited by the traveling limit of the machine. The collected data were embedded in a table-driven elastic plastic material model for finite element simulation of tensile tests. Good agreements of simulations and experiments were obtained at all temperatures.

Interface effects, which play a crucial role in semiconductors, are also important in oxides. Over the last years several oxide heterostructures were investigated with interface properties, which are not found in the bulk properties of the constituting materials. An exciting example is the interface between the two oxides Lanthanumaluminate (LAO) and Strontiumtitanate (STO) which was investigated in this work. Both materials are band-insulators, however a conducting layer can form at the interface, a so called quasi-two-dimensional electron gas (q2-DEG). After a brief introduction to this heterostructure the sample-preparation and characterization is described, and subsequently different projects are reported in detail. The investigation of the electronic transport properties as a function of the LAO film thickness revealed a transition from insulating to conducting behavior if the films exceed a critical thickness of 3 unit cells (uc). By electric field effect the conductivity of the interface can be tuned to a large extent. In samples with 3 uc of LAO a metal-insulator-transition can be induced. To be able to investigate defined structures a novel patterning technique was developed in the course of this thesis, which is based on the variation of the thickness of the epitaxial LAO. At 200 mK the q2-DEG condenses into a superconducting ground state. Investigations on bicrystalline samples reveal that the conducting interface is strongly influenced by dislocations in the STO substrate. Grenzflächeneffekte, die z.B. in Halbleitern eine bedeutende Rolle spielen, sind auch in Oxiden von großer Bedeutung. In den letzten Jahren wurden einige oxidische Heterostrukturen gefunden in denen die Grenzflächen Eigenschaften zeigten, die in den Volumeneigenschaften der verwendeten Materialien nicht auftreten. Ein spannendes Beispiel hierfür ist die in dieser Arbeit untersuchte Grenzfläche zwischen den beiden Oxiden Lanthanaluminat (LAO) und Strontiumtitanat (STO). Obwohl beide Materialien Bandisolatoren sind kann sich an der Grenzfläche eine leitfähige Schicht ausbilden, ein sogenanntes quasi-zwei-dimensionales Elektronengas (q2-DEG). Nach einer kurzen Einführung zu dieser Heterostruktur wird die Probenpräparation und Charakterisierung beschrieben, und anschließend werden die durchgeführten Projekte detailliert erläutert. Bei der Untersuchung der elektronischen Transporteigenschaften als Funktion der LAO Filmdicke wurde ein abrupter Übergang von isolierendem zu leitfähigem Verhalten beobachtet bei Überschreiten einer kritischen Dicke von 3 Einheitszellen (EZ). Per elektrischem Feldeffekt kann die Leitfähigkeit der Grenzfläche über einen großen Bereich eingestellt werden. Bei Proben mit 3 EZ LAO ist es sogar möglich einen Metall-Isolator-Übergang zu induzieren. Um definierte Strukturen untersuchen zu können, wurde des Weiteren ein neuartiges Strukturierungsverfahren entwickelt, das auf einer Variation der Dicke des epitaktischen LAO beruht. Bei ca. 200 mK findet eine Kondensation des q2-DEGs in einen supraleitenden Grundzustand statt. Untersuchungen an bikristallinen Proben zeigen, dass die leitfähige Grenzfläche empfindlich auf Versetzungen im STO Substrat reagiert.

With infrared ellipsometry and transport measurements we investigated the electrons at the interface between LaAlO3 and SrTiO3. We obtained a sheet carrier density of Ns~5-9x 10E13 cm^-2, an effective mass of m*~3m_e, and a strongly frequency dependent mobility. The latter are similar as in bulk SrTi1-xNbxO3 and therefore suggestive of polaronic correlations of the confined carriers. We also determined the vertical density profile which has a strongly asymmetric shape with a rapid initial decay over the first 2 nm and a pronounced tail that extends to about 11 nm., Comment: 4 pages, 3 figures, 1 EPAPS file (3 figures)