Structural Evolution of a Cyclooctatetraene Adlayer on Cu(111) during Isothermal Desorption
2018
Lau, J. A. | Calvo-Almazán, I. | Townsend, P. S. M. | Ward, D. J. | Jardine, A. P. | Allison, W. | Ellis, J. | Hinch, B. J. | Avidor, N.
The use of helium diffraction patterns to study desorption processes is explored as a novel extension to traditional methods based on helium specular reflection. The sample, cyclooctatetraene, adsorbed on Cu(111) provides a rich but complex structure. The modulation of cyclooctatetraene by Cu(111) is manifested as a convolution in the diffraction pattern, displaying an averaged super cell symmetry of (73×73)R30°. The adlayer expands during isothermal desorption, and the change in lattice constant provides a direct measure of the coverage as a function of time. We find a desorption energy of 0.96 ± 0.01 at saturation of the first layer and an upper limit of 1.62 ± 0.07 for isolated molecules. These values and details of the assigned structure indicate chemisorbed molecules with a planar conformation.
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