LINEAR DIFFUSION PROFILES DUE TO LONG-RANGE ADSORBATE INTERACTIONS - CS SI(100) AT LOW-COVERAGE/

Diffusion of Cs on Si(100) was examined using biased secondary electro n imaging, capable of detecting Cs coverages theta greater than or equ al to 0.005 ML. Unusual diffusion profiles, linear at low theta, with edges expanding as t(1/2), were obtained for theta < 1/2 ML. These res ults are modeled with a diffusion coefficient of the form D similar to D-1 + D-2(A/kT)[theta(1 - theta)]. This form is consistent with diffu sion theory including strongly repulsive Cs-Cs interactions, deduced f rom the decrease of the adsorption energy, q(theta), with coverage (dq /d theta similar or equal to -2 eV/ML). Measurements of D in the range 60 less than or equal to T less than or equal to 90 degrees C are con sistent with an adatom diffusion energy, E(d) = 0.47 +/- 0.05 eV.