Coverage-dependent diffusion of ammonia on Re(001)

Micha Asscher

doi:10.1117/12.180856

21 July 1994 Coverage-dependent diffusion of ammonia on Re(001)

Micha Asscher

Proceedings Volume 2125, Laser Techniques for Surface Science; (1994) https://doi.org/10.1117/12.180856
Event: OE/LASE '94, 1994, Los Angeles, CA, United States

Abstract

Diffusion of ammonia on Re(001) was studied utilizing optical second harmonic diffraction from surface coverage grating. The diffusion process at initial coverages NH₃/Re>0.15 could be simulated only if coverage dependent diffusion constant has been considered. The resulting diffusivity D((theta) )equalsD₀ exp(-E_m((theta) )/RT), is defined by a barrier for diffusion E_m((theta) )equalsE₀-(omega) Z(theta) , with activation energy at zero coverage E₀equals3.4+/- 0.8 kcal/mol, D₀equals2.8(DOT)10^-3cm²sec^{- 1}. The repulsion energy between pair of nearest neighbor molecules of (omega) equals0.4+/- 0.06 kcal/mol is obtained if an average of three nearest neighbors is assumed at the edge of the grating. The coverage effect on the diffusivity is found to correlate quantitatively with dipole-dipole repulsion between nearest neighbors. This results in a constant corrugation ratio E_diff/E_des, over the entire coverage range.

Citation Download Citation

Micha Asscher "Coverage-dependent diffusion of ammonia on Re(001)", Proc. SPIE 2125, Laser Techniques for Surface Science, (21 July 1994); https://doi.org/10.1117/12.180856

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