Kinetic energy of adsorbed ⁴He on active Carbon fibre (ACF)

The adsorption of helium on Grafoil has been investigated in the past using n-diffraction and specific heat measurements. Theoretically, the interaction potential between a He atom and a graphite surface has been represented by a 6-12 Lennard-Jones potential and the equilibrium distance of the He atoms above the graphite plane was deduced. The results of the above studies were used to estimate the zero-point kinetic energy (KE) of the adsorbed He atoms in directions parallel and perpendicular to the graphite plane at coverages of - one monolayer. In the present work, we measured the zero-point KE of adsorbed He atoms on ACF surface using the Neutron Compton scattering (NCS) technique. In the nano-scale regime, the structure of the ACF resembles that of graphite; it was therefore possible to use the accumulated information on the He-Grafoil system and to apply it to that of the He-ACF system. The difference being mainly in the fact that our ACF sample has - 100 times larger specific surface area than Grafoil. In addition, because of the pore structure of the ACF, each He atom interacts with about twice the number of C-atoms than in the Grafoil case.