Molecular Motion on Semiconductor Surface via Tip-enhanced Multiple Excitation

TL;DR

This study demonstrates that CO molecules on a Si(001) surface undergo tip-induced motion driven by multiple vibrational excitations, with local heating effects facilitating the process, revealing new insights into surface molecule dynamics.

Contribution

It shows for the first time that multiple vibrational excitations cause molecular motion on semiconductor surfaces, similar to metal surfaces, due to tip-induced local heating and inelastic electron scattering.

Findings

Lateral motion of CO depends hyperlinearly on tunneling current.

Activation barrier for motion is 0.11 eV, consistent with calculations.

Local heating by inelastic tunneling facilitates molecular displacement.

Abstract

In a low-temperature study with a scanning tunneling microscope (STM), the irreducible lateral motion of a CO molecule adsorbed on a Si(001) surface showed a hyperlinear dependence on the tunneling current. This dependence implies that the adsorbate displacement is caused by multiple excitations of adsorbate vibration modes, a situation thus far observed only at metal surfaces. The local vibronic temperature at the atomic scale on the surface heated by ohmic inelastic scattering of tunneling electrons indicates that there is an activation barrier of 0.11 eV for the irreversible motion of CO, in agreement with the adiabatic potential obtained from first-principles calculation. The highly efficient local heating is caused by a mid-gap state at the surface induced by the electric field of the STM tip.