Magnetoresistance and conductivity exponents of quench-condensed ultra-thin films of Bi

We have studied the magnetoresistance (MR) and evolution of conductivity wi th thickness of quench-condensed Bismuth films on substrates of various die lectric constants. Our results indicate a negative intial MR proportional t o the square of the magnetic field. The conductance shows a power-law kind of dependence on thickness, with an exponent close to 1.33, characterisitic of a 2-D percolating system, only when the films are grown on a thin (simi lar to 10 Angstrom) Germanium underlayer but not otherwise. (C) 2000 Elsevi er Science B.V. All rights reserved.