Mapping the Diffusion Potential of a Reconstructed Au(111) Surface at Nanometer Scale with 2D Molecular Gas

Abstract

The adsorption and diffusion behaviors of benzene molecules on an Au(111) surface are investigated by low-temperature scanning tunneling microscopy. A herringbone surface reconstruction of the Au(111) surface is imaged with atomic resolution, and significantly different behaviors are observed for benzene molecules adsorbed on step edges and terraces. The electric field induced modification in the molecular diffusion potential is revealed with a 2D molecular gas model, and a new method is developed to map the diffusion potential over the reconstructed Au(111) surface at the nanometer scale.

Orientation Switching of Single Molecules on Surface Excited by Tunneling Electrons and Ultrafast Laser Pulses

“…The occupation ratio between two orientation states is determined by the energy difference of the two states, where the symmetric double-well potential is perturbated by the STM tip. The effect of tip-induced local electrostatic potential has been reported previously in various single molecule systems such as acetylene on Cu(001), benzene on Au(111), and iron phthalocyanine (FePc) on Au(111) . The local potential is roughly proportional to the sample bias and it reduces the effective energy barrier between two orientations of the azobenzene molecules anchored at kink sites.…”

Inducing Transient Charge State of a Single Water Cluster on Cu(111) Surface

“…The effect of dipole interaction can be excluded as well since a polarized molecule always feels a lateral force pointing toward the center of the tip where the magnitude of electric field is highest, which is opposite to our observations. Pure electronic vibration excitation, which shall result in random diffusion, 28 cannot explain the directional motion of water cluster either. For a statically charged cluster, the direction of Coulomb force depends on the bias, and the clusters would diffuse toward the tip under negative sample bias, which is not supported by the observations.…”

“…For negative sample bias, the water clusters move away from the tip center too, but the diffusion distance D depends weakly on the voltage amplitude (see Supporting Information Figure S1). We attribute the observed directional motion of water cluster to the consequence of transient Coulomb repulsive interaction, although there are many other methods and mechanisms that may result in the motion of molecules on surface, including STM tip manipulation, 27 thermal diffusion, dipole interactions, 28 electronic excitation, 29 photoexcitation, 30 and static Coulomb force. We can easily exclude the possibility of tip manipulation and photoexcitation since the STM tip in our experiment is stationary and there is no light illumination.…”

Hovering and Twirling of Tethered Molecules by Confinement between Surfaces

“…In the case of molecular reorientation, STM allows direct imaging of motion. , The topographic appearance of a molecule depends on the landscape of the surface potential at the adsorption site. A chemisorbed or physisorbed molecule may be stationary, locked in place by barriers to lateral motion, or it may appear simultaneously in multiple thermally accessible discrete orientations or be delocalized in a continuum of orientations and ultimately, as a lattice gas with free 2D transport on the surface . To induce motion in an otherwise stationary state, the molecule must be energized above the restraining potential barrier, and the controlled activation of such motion represents the rudiments of molecular motors.…”

“…A chemisorbed or physisorbed molecule may be stationary, locked in place by barriers to lateral motion, or it may appear simultaneously in multiple thermally accessible discrete orientations or be delocalized in a continuum of orientations and ultimately, as a lattice gas with free 2D transport on the surface. 10 To induce motion in an otherwise stationary state, the molecule must be energized above the restraining potential barrier, and the controlled activation of such motion represents the rudiments of molecular motors. There is now extensive literature on such motors 11 and action spectroscopy to characterize mechanisms at work.…”