Low-energy vibrational dynamics of ultrathin organic adlayers: alkanethiols adsorbed on copper

The low-energy vibrational dynamics of alkanethiol monolayers adsorbed on t wo copper single-crystal surfaces [Cu(110), Cu(100)] has been measured by m eans of high-resolution inelastic helium-atom scattering. For the physisorb ed phase of the two thiols studied [C2H5SH and C7H15SH], a characteristic m ode of subthermal energy at about 6 meV was obtained which is attributed to the external vibration of the entire molecule perpendicular to the surface . In contrast, no distinct low-energy vibrations could be observed for the chemisorbed thiolate species, which forms well-ordered monolayer structures . (C) 2000 Elsevier Science B.V. All rights reserved.