Scanning Microscopy


The growth and surface diffusion of Cs on Si(100) and Ag on Fe(110) have been studied using biassed secondary electron imaging (b-SEI) and Auger electron spectroscopy (AES).

The b-SEI technique was found capable of detecting Cs on the Si surface with a 0.5% ML sensitivity. Unusual diffusion profiles containing linear sections were obtained for coverages (θ) < 1/2 ML. The general form of these profiles were reproduced using a 2-phase model, where Cs chains act as sources of mobile adatoms, in conjunction with a diffusion coefficient of the form D ~ θ (1- Cθ). This form of D, obtained from Boltzmann-Matano analysis, is consistent with diffusion theory including strongly repulsive Cs-Cs interactions. An adatom diffusion energy, Ed, = 0.47 ± 0.05 eV was found to be consistent with measurements of the diffusion coefficient made in the temperature range 333 ≤ T ≤ 363K.

The growth mode for Ag on Fe(110) was determined by AES and b-SEI to be Stranski-Krastanov, with islands growing on top of two intermediate layers. Diffusion experiments conducted on finite Ag patches show that following annealing, adatoms dissociate from the islands and second monolayer and contribute to the observed expansion of the first monolayer. The diffusion results also indicate that while islands are still present, there is a competition between adatoms entering and leaving the second monolayer.

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