RECENT SURFACE STUDIES USING BIASSED SECONDARY-ELECTRON IMAGING

The growth and surface diffusion of Cs on Si(100) and Ag on Fe(110) ha ve been studied using biassed secondary electron imaging (b-SEI) and A uger electron spectroscopy (AES). The b-SEI technique was found capabl e of detecting Cs on the Si surface with a 0.5% ML sensitivity. Unusua l diffusion profiles containing linear sections were obtained for cove rages (theta) < 1/2 ML. The general form of these profiles were reprod uced using a 2-phase model, where Cs chains act as sources of mobile a datoms, in conjunction with a diffusion coefficient of the form D simi lar to theta (1- C theta). This form of D, obtained from Boltzmann-Mat ano analysis, is consistent with diffusion theory including strongly r epulsive Cs-Cs interactions. An adatom diffusion energy, E(d), = 0.47 +/- 0.05 eV was found to be consistent with measurements of the diffus ion coefficient made in the temperature range 333 less than or equal t o T less than or equal to 363K. The growth mode for Ag on Fe(110) was determined by AES and b-SEI to be Stranski-Krastanov, with islands gro wing on top of two intermediate layers. Diffusion experiments conducte d on finite Ag patches show that following annealing, adatoms dissocia te from the islands and second monolayer and contribute to the observe d expansion of the first monolayer. The diffusion results also indicat e that while islands are still present, there is a competition between adatoms entering and leaving the second monolayer.