In situ inelastic neutron scattering studies of the rotational and translational dynamics of molecular hydrogen adsorbed in single-wall carbon nanotubes (SWNTs)

Inelastic neutron scattering (INS) spectra were measured in situ from progressively increased amounts of para-hydrogen physisorbed in bundles of single-walled carbon nanotubes at temperatures in the vicinity of 20 K. INS from the bound H2 molecules consists of two distinct parts carrying complementary information. In the low energy and momentum transfer region, at about 14.5 meV we observe a sharp line corresponding to rotational transitions between the ground para-J = 0 state and the ground ortho-J = 1 state without change of the translational state of the molecular centre of mass (CoM). This we call the “bound” spectrum. At higher energy transfers, a series of broad peaks are observed, corresponding to rotational transitions between the para-J = 0 state and different ortho-states (J = 1, 3, 5, … ,) shifted out in energy transfer by an amount equal to the CoM recoil energy. This we call the “recoil” spectrum. Both parts of each spectrum are analysed using the Young and Koppel model. From the “bound” spectrum we estimate the mean height of the barrier to rotation and the mean square displacements of the molecules accommodated at different adsorption sites. The “recoil” spectrum allows us to derive the mean translational kinetic energy of the adsorbed hydrogen as a function of the surface concentration

The role of hydrogen during plasma beam deposition of amorphous thin films

The influence of wall-associated H/sub 2/ molecules and other hydrogen-containing monomers on the degree of ionization in the expanding thermal plasma used for the fast plasma beam deposition of amorphous hydrogenated carbon (a-C:H) and amorphous hydrogenated silicon (a-Si:H) was determined. Deposition models are discussed with emphasis on the specific role of the ion during deposition. The connection between the role of atomic hydrogen and the degree of ionization in the plasma beam deposition of a-C:H and a-Si:H is addresse