A Neutron-Diffraction Study of the Solid Layers at the Liquid Solid Boundary in 4He-Films Adsorbed on Graphite

摘要: A neutron scattering study of the structure $^{4}\mathrm{He}$ films adsorbed on graphite is reported. Diffraction from helium monolayers at a temperature 1.2 K shows formation an incommensurate, triangular-lattice solid high density. As coverage increased above two layers, diffraction pattern changes indicating solidification second layer. The observed two-layer patterns can be indexed with either pair layers different densities or close-packed bilayer; experimental information available not sufficient to make more precise identification. measurement height first layer basal plane was also made. This done by determining coverage-dependent shift in position (002) peak (assumed arise interference between film and substrate scattering) fitting it simple structural model. Values for monolayer lattice constants possible bilayer structures are given.