EXTENSION OF THE FIELD-EMISSION FLUCTUATION METHOD FOR THE DETERMINATION OF SURFACE DIFFUSION COEFFICIENTS.

The use of scanning tunneling microscopy and related techniques for the determination of surface diffusion coefficients of adsorbates is discussed. Three schemes, all extensions of the field-emission current fluctuation method are presented and analyzed. The first consists of determining single site correlation functions with a STM in its more or less normal operating mode. The second consists of retracting the tip approximately one tip radius so that a circular region of high field is created on the flat surface from which field emission and diffusion-induced current fluctuations can be obtained. The third considers creation of a long narrow region of high field by placing a very fine cylindrical wire parallel to and above the plane substrate. This last scheme allows determination of diffusion anisotropy. Detailed expressions for the current correlation functions for the three schemes and criteria for allowed vibrational amplitudes and drift are derived. It is concluded that all three schemes should be feasible but probably would differ in the range of diffusion coefficient values they would be able to handle.