Low-temperature transport properties of ultrathin CoSi2 epitaxial films

Abstract

Low-temperature transport measurements (down to 18 mK) are performed in CoSi2 ultrathin films (down to 1.4 nm) epitaxially grown on silicon substrates. The low-temperature residual resistivity exhibits little dependence on the CoSi2 film thickness down to 10 nm. However, a steep increase is found below 10 nm, which is not taken into account by the Fuchs–Sondheimer [Proc. Cambridge Philos. Soc. 34, 100 (1938)] boundary scattering theory. Correlatively, the superconducting critical temperature of these CoSi2 films is abruptly depressed in the same thickness range. These two effects are phenomenologically explained by the presence of a perturbed layer, i.e., a CoSi2 interfacial layer in which the electronic transport properties are dramatically diminished.

Universal scaling of the critical temperature for thin films near the superconducting-to-insulating transition

“…We also examined our own new experimental data on NbN thin films. In these data, relating dT c to R s provided fits with reduced scatter relative to fits suggested by previous models [7][8][9][10][30][31][32]. Finally, we supply two possible explanations of the observed universal behavior.…”

“…Figures 1(a) and 1(b) show the dependence of T c on thickness and on sheet resistance for our NbN films, allowing a comparison of the data with the existing models [7][8][9][10][30][31][32]. Although a general trend can be seen in both T c (d) and T c (R s ), Chemical treatment of the substrate prior to deposition is suspected of influencing the properties of the red solid points here and in Fig.…”

“…Therefore, it is not important if T c is expressed as a function of d or of R s , as presumably, one parameter can be replaced by the other straightforwardly. Theoretically, the relationship ρ(d) is usually discussed in terms of derivatives of Fuchs's theory [30], sometimes combined with Matthiessen's rule [31]. However, surprisingly, to date, the existing theories encounter difficulties in fitting the experimental data, which are often scattered when plotted on a ρ(d) graph [32].…”

Physics and Techniques for the Investigation of the Properties of Ultra Small Systems

“…Electrical conduction in thin CoSi 2 films grown on Si(111) wafers has been demonstrated [Hensel et al (1985), Badoz et al, (1987)] to exhibit a remarkable degree of specular scattering of the conduction electrons from the surfaces of the silicide film. The interface between the CoSi 2 layer and the silicon substrate is almost atomically smooth due to the close lattice match between the two materials [Gibson et al (1982)].…”

“…As a consequence, although the electron mean free path is on the order of -500A, the resistivity of the thin films does not show an increase until the thickness is decreased below -150A. In addition, the CoSi 2 films exhibit a superconducting transition temperature on the order of 1.2K [Badoz et al, (1987)], with the transition temperature being suppressed roughly as the resistivity increases. This suppression occurs for film resistivities of -30(1/0 rather than the critical resistance for the metal insulator transition 4000/0 [Anderson, (1958), Mott and Davis, (1979)].…”