Institut fuer Festkoerperforschung. Scientific report 2000/2001

SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Institut fuer Feskoerperforschung. Scientific report 1999/2000

SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

32. IFF-Ferienkurs: Neue Materialien fuer die Informationstechnik Vorlesungsmanuskripte

SIGLEAvailable from TIB Hannover: RR 9223(7) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Entwicklung integrierter supraleitender Flussquantenoszillatoren fuer ultra-empfindliche submm-Wellenempfaenger auf der Basis der Nb- und NbN-Technologie Abschlussbericht

SIGLEAvailable from TIB Hannover: F00B1415+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman

Elastische Eigenschaften von Polymernetzwerken

Polymers are long chain molecules with important biological and technical applications. By introducing additional chemical bonds they can be crosslinked into networks. Subject of this thesis is the statistical mechanical treatment of the elastic properties of polymers and polymer networks. In the first part the first computer simulations of strained polymer networks are used to clarify the physical foundations of rubber elasticity. We investigate idealized model networks with a diamond lattice connectivity. By modifying the interaction potentials it is possible to simulate ensembles with and without topology conservation. The key element of the argumentation is the simultaneous measurement of the macroscopic restoring forces due to deformations and of those microscopic quantities from which the elastic properties are deduced in theories of rubber elasticity. It is shown that the classical moduli calculated form the change in the end-to-end distance distributions for the network strands are significantly smaller than the true moduli. To test a topological theory of rubber elasticity we determine the linking state for all pairs of meshes in the system. Using a distance dependent free energy for linked meshes the linking contribution to the modulus can be estimated within an affine approximation. The result is found to be in excellent agreement with the measured topology contribution. The second part deals with the elastic properties of c* gels. The classical theories of rubber elasticity are combined with recent results on the elastic properties of swollen polymers in a good solvent. The resulting stress-strain curves are non-linear. The deviations from the classical predictions are particularly strong for two dimensional networks adsorbed on a surface. Motivation for the third part were some recent observations on multiple stranded macromolecules. Generally such molecules have a very high bending stiffness. We propose a ''railway track'' model for the effects of backbone coupling. The model can be solved in two dimensions and displays an interesting new type of behaviour for a mechanical model without long-range interactions: a stiffness that is larger on small than on large lengthscales. An estimate shows that coupling effect could contribute to the large bending stiffness of double helical molecules. In the appendix a new algorithm for molecular dynamics simulations with short-range interactions is documented. An optimized implementation on the Cray Y/MP proved to be significantly faster than older programs. (orig.)170 refs.Available from TIB Hannover: RA 831(3040) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Benetzung in ternaeren Fluessigkeitsmischungen

The wetting behaviour of ternary fluid mixtures is investigated in this work. The first part deals with the wetting properties of the BEG model, a model for fluids with short-range interactions. We find two types of wetting in the BEG model: Wetting close to critical points of the fluid mixture (Cahn wetting), and wetting further away from the critical points, which occurs, if one of the interfacial tensions exceeds the other two very much. The transitions to Cahn wetting are critical. We have calculated the effective interfacial potential in the vicinity of critical wetting transitions and the critical exponents of the transitions. The transitions to the other type of wetting are first order. In the second part the BEG model is extended by two interactions which add amphiphilic properties to one of the fluid components. We investigate the wetting behaviour of the microemulsion phase. One of the interactions models the amphiphiles' property to assemble at interfaces. It reduces interfacial tensions and therefore supports wetting. Especially we find in agreement with experimental results, that it produces wetting of the microemulsion-air interface by the water phase. The other interaction induces structure into the microemulsion phase and therefore counteracts wetting. In the third part the twist grain boundary between lamellarly structured grains of ternary amphiphilic mixtures is investigated in a Ginzburg-Landau model, the #PHI#"6 model. We find that the interfacial tension depends on the interaction between the lamellae, i.-e. the compressibility of the system. The surfaces which the amphiphiles assemble on are not minimal surfaces, but the solution is rather a compromise between bending and compression energy. (orig.)SIGLEAvailable from TIB Hannover: RA 831(3879) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Magnetism and quantum-size effects of thin FCC films

The magnetism and the electronic structure of ultrathin FCC(100) transition metal films of Fe, Co, and Ni, as well as quantum-size and magnetic effects in thin Cu overlayers on these films have been investigated by spin- and angle-resolved photoemission. The electronic structure of FCC Co(100) films displays exchange split states with a typical exchange splitting of 1.5-1.6 eV near #GAMMA#. Magnetic surface states are observed in FCC Ni(100) with an exchange splitting of about 0.2 eV. These states are in good agreement with ab initio slab calculations. In thin FCC Fe films on Cu(100) and Co(100) two distinct regions in the magnetism and electronic structure are observed as a function of Fe film thickness. The first phase corresponds to a ferromagnetic high-spin phase with large magnetic moments. The second phase displays a magnetically alive surface region with strongly exchange split electronic states and thus large magnetic moments. The film interior of this second phase consist of local moments, which are reduced in comparison to the magnetic moments of the surface and do not display a long range magnetic order above 100 K. The experimental results agree well with corresponding ab initio calculations. Discrete spin-polarized sp-like states, which can be described in the framework of quantum well (QW) states, are investigated in Cu(100) overlayers on FCC Fe, Co, and Ni films. Both sp-like and d-like QW states are observed. Depending on the substrate, both intensity and binding energy changes of the Cu QW states are observed, which are in excellent agreement with ab initio calculations. For Cu on Co(100) the QW states that are responsible for both the long and the short coupling period in the interlayer exchange coupling across Cu(100) spacers are found. Thus a firm relation between the spin-polarized QW states and the oscillatory interlayer coupling is established. (orig.)162 refs.Available from TIB Hannover: RA 831(3503) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

"5"7Fe-Kernresonanz zur Untersuchung von Verunreinigungen und Defekten in Yttriumeisengranat

"5"7Fe-NMR is applied to study impurities and defects in yttrium iron garnet (Y_3Fe_5O_1_2), both in films grown by liquid phase epitaxy and in sintered polycrystalline samples. The NMR spectra and the nuclear relaxation have been investigated. Impurities can enter the garnet structure from the basic oxides (Ca,Si), the flux (Pb) or the crucible (Pt). A cation defect in the garnet structure causes a characteristic satellite structure in the NMR spectrum besides the main line caused by the unpertubed iron nuclei. The satellite structure depends on the lattice site where the defect is located. The satellite intensity is proportional to the defect concentration. The assignment of a given satellite to a specific defect can be made within a series of samples where the defect concentration is changed. Threevalent impurity cations cause satellites with a linewidth equal to the corresponding main line, whereas charged impurities produce broader satellites. This shows a correlation of at least one other defect in the neighborhood of the charged one achieving a local charge compensation. One specific defect, the so called anti-site defect Y"3"+ on octahedral ironsites can be observed in all samples in the range from 0.1 to 1% of the total Y content. In epitaxial films, the number of anti-site defects grows with the lead content. The nuclear spin-lattice relaxation time T_1, at T = 4.2 K shows large differences for different samples. A short T_1 in the range of 10 ms, often connected withe the relation T_2 #approx# 2 T_1, is attributed to the existence of Fe"2"+. With the addition of divalent impurities the relaxation behavior changes resulting in T_1 >> T_2 with T_1 in the range of seconds, which can be explained by the suppression of Fe"2"+-formation by the incorporated impurities. The nuclear relaxation is correlated with the optical absorption at #lambda# = 1.3 #mu#m of the garnet films in the way that a short T_1 is associated with a high absorption also caused by Fe"2"+ and vice versa. (orig.)SIGLEAvailable from TIB Hannover: RA 831(2947) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Untersuchungen der Zink-Diffusion und Defekterzeugung in Galliumarsenid

The following topics were dealt with: diffusion in semiconducting materials; zinc diffusion experiments; characterization of diffusion-induced defect structures in GaAs (dislocations, Ga precipitation)Available from TIB Hannover: RA 831(3390) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Dielektrische Resonatoren mit Hochtemperatur-Supraleiter Abschirmung zur Oszillatorstabilisierung

In der vorliegenden Arbeit wurden kompakte dielektrische Resonatoren mit einer Abschirmung aus HTSL-Filmen untersucht. Die Resonatoren bestehen aus jeweils einem Zylinder aus einkristallinem Sphir oder LaALO_3, der zentralsymmetrisch zwischen zwei epitaktischen YBa_2Cu_3O_7_-_#delta#-Filmen angeordnet ist. Zur Optimierung der Resonatoren wurden die Hochfrequenzeigenschaften der supraleitenden Abschirmung und des Dielektrikums untersucht. (orig./MM)Compact dielectric resonators provided with a shielding made of HTSC thin films are examined. The resonators consist of a cylinder made of monocrystalline sapphire or LaAlO_3, placed at central symmetry between two epitactic YBa_2Cu_3O_7_-_#delta# films. For optimization of the resonators, the high-frequency properties of the superconducting shielding and the dielectricum are examined. (orig./MM)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman