Resistivity of Niobium/copper Superlattices.
Abstract
Artificial superlattices of niobium and copper were grown epitaxially on sapphire substrates mounted on a rotating platform by means of DC magnetron sputtering. Superlattices with alternating layers of equal thickness ranging from 2 to 5000 (ANGSTROM) were produced. The temperature dependence of the resistivity of the Nb/Cu superlattices was measured parallel to the layers in the temperature range 10 to 300 K. For all temperature measured, the temperature coefficient of resistivity (TCR) was positive for layer thickness greater than 10 (ANGSTROM) and negative for layer thickness less than 10 (ANGSTROM). The positive TCR resistivity data were analyzed as a function of temperature for fixed layer thickness, then as a function of layer thickness for fixed temperature. In the latter case the superlattice resistivity was found to fit the theories of size effect scattering of Fuchs and grain boundary scattering of Mayadas-Shatzkes. The negative TCR resistivity data were found to correspond to large residual resistivity and were analyzed according to the theory of Jonson and Girvin which reproduced the Mooij correlation. The temperature dependence of the conductivity of the negative TCR data were fit to a square root temperature dependence, a prediction prompted by the electron interaction theory of Altshuler and Aronov and the localization and interaction theory of McMillan for three dimensional systems. One of the predictions of the latter theory is that there should exist a regime of large residual resistivity between the Ioffe-Regel and the metal-nonmetal transition where the system is still metallic yet possesses a negative TCR, and this was found to be the case for Nb/Cu.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1983
- Bibcode:
- 1983PhDT........63W
- Keywords:
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- Physics: Condensed Matter