Appl. Phys. A55, 231-234 (1992) Applied Solids Physics A "" Surfaces © Springer-Verlag 1992 Magnetoconductivity of Thin Epitaxial Silver R. Schad, S. Heun, T. Heidenblut, and M. Henzler Universit~it Hannover, Institut f/Jr Festk6rperphysik, Appelstrasse 2, W-3000Hannover 1, Fed. Rep. Germany (Fax: +49-511/762-4877) Received 13 March 1992/Accepted 12 June 1992 Films Abstract. The magnetoconductance (MC) of thin epitaxial Ag films on Si(lll) surfaces is studied as a function of film thickness (1-125 monolayers (ML)) at 20 K under ultra high vacuum (UHV) conditions. Three different regimes of magnetoconductance are observed depending on the degree of disorder in the films which is controlled by film thick- ness and annealing procedures. Thick films (d > 3 ML) with diffuse electron transport show in the case of large elastic scattering times 70 a classical, negative MC c( B 2 and in the case of small T0 a positive MC due to weak localization effects. The MC of thin films (d < 2 ML) which have a conductance smaller than e2/h, i.e. localized electron states, is negative again. PACS: 73.50.Jt, 73.20.Nz, 73.60.Aq The conductivity of thin films may be reduced by orders of magnitude with respect to bulk values of the same mate- rial for various reasons. Structural defects, impurities, sur- faces and interfaces have to be considered. The magnetocon- ductance (MC) provides information to distinguish between different transport and scattering mechanisms. The classical MC can be observed in samples with a small degree of dis- order, i.e. large elastic scattering times T0, following usually a quadratic dependence of conductance G on the magnetic field B [1] (WcTO << 1): G(B) = G(O)/[1 + (w(ro) 2] --~ G(0)[1 - (wcT0)a], with wc = eB/m. (1) Sometimes deviations from (1) are observed due to partic- ularities of the bandstructure [1]. In films with a small TO (high degree of disorder) the classical MC is suppressed and new effects can be observed in the MC at low temperatures. These weak localization (WL) effects are due to coherent backscattering of the electron waves [4-8]. Prerequisites to observe these effects are diffuse charge transport and low temperatures to avoid inelastic scattering of the electrons which destroy the phase coherence of the electron waves. Magnetic fields lead to a reduction of WL too, allowing to investigate this phenomenon by means of the MC [4-8]. Ap- plying the appropriate theory [6, 7], the MC reveals different characteristic scattering times (elastic scattering time To, in- elastic scattering time Ti, spin-orbit scattering time %o and magnetic scattering time %) that are involved in the electron transport. Increasing further the disorder diffusive transport is no more possible since the elctron states are localized [2, 10, 11]. The MC in this regime of strong localization is not completely understood yet. Different theoretical predic- tions and experiments reveal contradictory results [3, 9, 12], even the sign of the MC is not always the same. It is the purpose of this paper to study the MC of epitaxial Ag films with different degrees of disorder. The disorder depends on film thickness and annealing procedures [13]. The conductivity varies over 6 orders of magnitude in the thickness range of 1-125 ML. The MC should show, which scattering and transport mechanisms are important for the films of a given thickness. 1 Experimental All preparations and measurements were done in an ultra high vacuum (UHV) system (base pressure 5 x 10-11 mbar) as described elsewhere [14]. The substrates are squares of Si(11 l) wafers with contact areas in the comers and notches on each side (see Fig. 1). The conductance is measured and evaluated according to van der Pauw [15]. Special care has 15 mm Fig. 1. A top view of the sample. In the shaded areas the silicon is covered with 150nm Mo to ensure a good electrical contact. The notches are sawed to reduce the influence of contact size onto the van der Pauw evaluation