Single-molecule electron transport near a charge-trapping orbital-level alignment

Area of Science:

• Molecular electronics
• Quantum transport

Background:

• Molecular junction transport is dictated by orbital energy alignment.
• Charging effects significantly alter this alignment, but their impact on transport is not fully understood.

Purpose of the Study:

• Investigate distinct transport behaviors in single-molecule junctions.
• Understand the role of orbital energy shifts and environmental factors in molecular transport.

Main Methods:

• Combined scanning tunneling microscopy (STM) and non-contact atomic force microscopy (AFM) at low temperatures (5.5 K).
• Studied individual copper phthalocyanine (CuPc) molecules on a NaCl/Cu(100) substrate.
• Employed a pentacene molecule-functionalized tip to manipulate transport behaviors.

Main Results:

• Identified three distinct transport phenotypes: elastic tunneling, dynamic charging, and stable charge trapping.
• Transport behavior is critically dependent on the singly occupied molecular orbital (SOMO) energy relative to the electrode Fermi level.
• A ~100 meV energy shift near the Fermi level drastically alters charge-trapping lifetimes, indicating extreme sensitivity.

Conclusions:

• Atomic-scale dielectric disorder amplifies electronic inhomogeneities, leading to discrete transport regimes.
• Molecular conductance is highly sensitive to orbital alignment and local environmental engineering.
• Charge trapping regime exhibits remarkable sensitivity to minute energy shifts.