Using image resonances to probe molecular conduction at the n-heptane/Au(111) interface

Area of Science:

• Surface science
• Femtochemistry
• Condensed matter physics

Background:

• Image resonances are quantum states formed by an electron interacting with its image charge in a metal surface.
• Understanding electron dynamics at surfaces is crucial for catalysis and electronic devices.

Purpose of the Study:

• To investigate the influence of n-heptane layer thickness on the binding energies and lifetimes of n=1 image resonances on Au(111).
• To elucidate the mechanism behind the observed changes in image resonance lifetimes.

Main Methods:

• Femtosecond time-resolved two-photon photoemission (TR-2PPE) spectroscopy was employed.
• The one-dimensional dielectric continuum model (DCM) was used to approximate the surface potential.
• Wave-packet propagation and a tight-binding Green's function approach were utilized to solve the DCM potential.

Main Results:

• The lifetime of the image resonance increased dramatically from ~4 fs on clean Au(111) to 1.6 ps with three layers of n-heptane.
• This lifetime extension is attributed to the tunneling barrier created by the n-heptane film's sigma-sigma* band gap.
• Binding energies and lifetimes were determined as a function of n-heptane thickness.

Conclusions:

• The n-heptane film acts as a significant barrier, prolonging image resonance lifetimes.
• The study highlights the utility of TR-2PPE spectroscopy in probing electron dynamics and surface properties.
• The findings offer insights into electron scattering and transport phenomena at organic-inorganic interfaces.