Integer Charge Transfer Model-PTCDA on MgO(001)/Ag(001) Probing the Transition from Single to Double Integer Charge...

Area of Science:

• Surface Science
• Materials Chemistry
• Physical Chemistry

Background:

• The integer charge transfer (ICT) model explains charge transfer in adsorbate/substrate systems based on substrate work function.
• Existing models well describe single integer charging but not double integer charging, which remains experimentally elusive.

Purpose of the Study:

• To extend the ICT model to the double integer charging regime.
• To experimentally investigate the transition from single to double integer charging.

Main Methods:

• Utilized Perylenetetracarboxylic-dianhydride (PTCDA) as a molecular adsorbate with high electron affinity.
• Employed ultrathin MgO(001) films on Ag(001) as a substrate with a tunable work function.
• Combined scanning tunneling microscopy (STM), photoemission spectroscopy (PES), work function measurements, and density functional theory (DFT) calculations.

Main Results:

• Observed the transition from single negative charging to double negative charging of PTCDA molecules.
• Identified distinct work function regimes corresponding to vacuum level alignment and Fermi level pinning for both single and double charging.
• Demonstrated double negative charging of PTCDA molecules at very low substrate work functions.

Conclusions:

• The study successfully extends the ICT model to the double integer charging regime.
• The findings provide experimental evidence for double integer charging in organic semiconductor/metal oxide systems.
• The work elucidates the complex charge transfer dynamics at interfaces with tunable work functions.