Surface diffusivities from concentration profiles
Surf. Sci., 295 (1-2):
183 - 196 (1993)DOI: DOI: 10.1016/0039-6028(93)90195-P
Abstract
In diffusion over surfaces, diffusivities are often noticeably dependent
upon the concentration of adsorbed material. This effect has made
it difficult to derive reliable diffusivities from experiments on
macroscopic crystals. A method is proposed for analyzing experiments
in which spreading of an adsorbate is observed as a function of position
and time. The diffusivity D(c) is represented by a trial function
, in which D(0), a1, and a2 are arbitrary fitting pa profiles c1(x,t)
for a given choice of fitting parameters, obtained by numerical integration
of the diffusion equation, are then compared with the measured profiles.
This procedure is repeated with different values of the fitting parameters
until the best fit to experiment is obtained. Tests on concentration
dependent diffusivities of different types reveal that this procedure
is reliable, even when there is some competition between diffusion
and desorption.