Electrical resistivity of thin films of potassium

The electrical resistivity of thin potassium films at 100°K has been measured as a function of thickness in the thickness range 148 to 1600 angstroms. The experimental results are in excellent agreement with Fuchs\u27 theoretical predictions in the range 500 to 1600 angstroms and show that the scattering of the electrons at the film surfaces is completely diffuse. Comparison of experimental and theoretical curves gives a bulk resistivity parameter of 1.85 microohm cm, a mean free path of 1180 angstroms, and an electron to atom density ratio of 1.01. The films were deposited on a pyrex substrate from a beam of potassium vapor in a vacuum chamber which had a pressure less than 5 x 10-8 mm of Hg. The film thickness, in each case, was computed from a known beam intensity, exposure time, and film density. A surface ionization detector was used to calibrate the beam intensity (J1) as a function of effusion oven temperature (To). The linear plot of log (J1To1/2) versus To-1 gave a heat of sublimation for potassium at 450°K of 21.1 kcal/mole in good agreement with Brewer\u27s value of 21.4 kcal/mole within our experimental error