Structural Evolution of a Cyclooctatetraene Adlayer on Cu(111) during Isothermal Desorption

Abstract

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 . 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.

Evolution of ordered nanoporous phases during h-BN growth: controlling the route from gas-phase precursor to 2D material by in situ monitoring

“…45,46 Helium diffraction allows in situ measurements even at growth temperature, and is known for its unique sensitivity to adsorbates, including hydrogen atoms. [47][48][49][50][51][52][53][54][55] Furthermore, unlike other established techniques, 56 HAS is completely inert and does not modify the process under investigation. 57 While the specular reflection gives an estimate of adsorbate coverage on the clean surface, the angular distribution provides insight in the time evolution of periodic structures being formed on the surface.…”