STRUCTURE AND SUPERCONDUCTIVITY IN TRANSITION METAL MULTILAYERS (X-RAY DIFFRACTION, SUPERLATTICE)

In this thesis the fabrication, structure and low temperature properties of metallic multilayers have been studied. Metallic multilayers of NbX where X = La, Cu and Zr were fabricated using magnetron sputtering. These samples were in turn examined separately with respect to their layer and interface structure and their superconductivity. The structural studies were carried out predominantly using x-ray scattering. In addition to x-ray scattering EXAFS measurements were made on the NbZr multilayers. The superconducting transition temperatures (T(,c)) were measured as a function of modulation wavelength (LAMDA) for each of the three multilayered systems.; Multilayers of Nb and La were made in which (LAMDA) was varied between (DBLTURN)6(ANGSTROM) and 150(ANGSTROM). The Nb:La layer thickness ratio varied between .2 and 3 with most samples having a thickness ratio equal to one. The structure of the Nb and La was independent of modulation wavelength for large (LAMDA). Niobium exists in its usual bcc phase with the {lcub}110{rcub} direction along the growth direction and La in the (alpha)-dhcp phase with the {lcub}100{rcub} direction along the growth direction. For large (LAMDA)(DBLTURN)66(ANGSTROM) the layering between Nb and La is quite good as indicated by 7 measurable orders of the superlattice reflections around the central lattice node. With respect to superconductivity, for the symmetric multilayers (t(,Nb) = t(,La)) T(,c)(DBLTURN)6.7K until (LAMDA)(DBLTURN)25(ANGSTROM) where it drops sharply. In the asymmetric samples the T(,c) is generally depressed at all modulation wavelengths as the composition goes from Nb rich to La rich.; In all of the NbCu multilayers the layer thickness was symmetrical with 18(ANGSTROM) (LESSTHEQ) (LAMDA) (LESSTHEQ) 55(ANGSTROM) > 0. This system showed a high degree of texture with the Nb(110) and the Cu(111) along the growth direction, however there is no inplane order. The diffracting domains appear to be rod shape with their axis parallel to the growth direction. Both the Nb and Cu maintained their bulk lattice constants at all modulation wavelengths, but the grain size decreases with (LAMDA). The NbCu interfaces are incoherent. The superconducting transition temperature is slightly (LAMDA) dependent, with an overall change of .82 K over this range of (LAMDA). The weak dependence of T(,c) on (LAMDA) is believed to be a consequence of the (LAMDA) dependent grain size and the conduction between the grains.; NbZr multilayers have coherent interfaces when (LAMDA) (LESSTHEQ) 51(ANGSTROM). In these samples (LAMDA) ranged from 200 (ANGSTROM) down to 4 (ANGSTROM). The interfaces are driven coherent by a transformation in the Zr lattice where Zr goes from hcp to bcc. In the coherent regime the composition modulation amplitude decreases rapidly. A preferential diffusion occurs during deposition in which the Zr atoms diffuse (probably substitutional) into the Nb layers. The T(,c) increases as (LAMDA) decreases reaching the value of 9.7 K for the homogeneous solution. The T(,c) is explained well by assuming the formation of an interfacial layer of high T(,c) NbZr solid solution.