Linear diffusion profiles due to long range adsorbate interactions: Cs/Si(100) at low coverage

• Published in: Physical review letters 1994-09, Vol.73 (10), p.1396-1399
• Main Authors: Milne, RH, Azim, M, Persaud, R, Venables, JA
• Format: Article
• Language: English
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.73.1396

Diffusion of Cs on Si(100) was examined using biased secondary electron imaging, capable of detecting Cs coverages Theta > =0.005 monolayer. Cs was deposited at room temperature onto Si substrate through a mask to form a series of patches. A large increase in the secondary electron field because of the dramatic decrease in work function was observed. This led to the detection of patches. Unusual diffusion profiles, linear at low Theta , with edges expanding as t exp 1/2 , were obtained for Theta < 1/2ML. These results were modeled with a diffusion coefficient of the form DapproxD sub 1 +D sub 2 (A/kT)[ Theta (1- Theta )]. This form was found to be consistent with diffusion theory including strongly repulsive Cs-Cs interactions. This was deduced from the decrease of the adsorption energy, q( Theta ), with coverage (dq/d Theta approx-2 eV/ML). Measurements of D in the range of 60 < =T < =90 deg C were consistent with an adatom diffusion energy, E sub d =0.47plus /minus0.05 eV.