Surface diffusion measurements by digitized autocorrelation of field emission current fluctuations

Abstract

The operating criteria of analog and digital methods for obtaining field emission fluctuation autocorrelation functions for the determination of surface diffusion coefficients are discussed and the strengths and limitations of both methods pointed out. Two digital systems, one using a spiraltron for pulse counting, the other a fast phosphor-photomultiplier combination for the same purpose, are described and test results presented. Some results obtained digitally for W self-diffusion on W(123) and for oxygen diffusion on W(110) are presented and shown to agree with previous results obtained by the analog method. To illustrate the potential of the digital method for obtaining very small D values results for the diffusion of H on Re(112̄0) at 80 K are also presented. For this case τ0=13 s, and D=1×10−14 cm2 s−1.