The behavior of H on the Pd(111) surface was investigated via the elastic scattering of a mono-energetic thermal He beam. Marked changes in the intensifies of the diffraction peaks were a function of the sample temperature (140 to 350K), and were attributed to changes in the H coverage. A consistent explanation was obtained by considering the H system to be a correlated quantum fluid in which particle delocalization occurred at medium and low coverages.

C.R.Hsu, B.E.Larson, M.El-Batanouny, C.R.Willis, K.M.Martini: Physical Review Letters, 1991, 66[24], 3164-7