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Steric Effects on Single-Molecule Conductance in Flat-Lying Phenanthrene.

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  • 1Department of Physics, Binghamton University, Vestal, NY, USA.

Chemistry (Weinheim an Der Bergstrasse, Germany)
|April 17, 2024
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Summary

The position of anchoring groups on phenanthrene (PHE) derivatives influences single-molecule conductance. When laid flat on a gold substrate, all PHE derivatives showed consistent conductance around 0.1 G0, regardless of anchoring group position.

Keywords:
electron tunnelingmolecular electronicsorientation-dependent transportscanning-tunneling microscope break-junctionsteric effects

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Area of Science:

  • Molecular electronics
  • Quantum transport phenomena

Background:

  • Previous studies indicated anchoring group position significantly impacts phenanthrene (PHE) derivative conductance.
  • A consistent 0.1 G0 feature was observed across various PHE derivatives in prior research.

Purpose of the Study:

  • To investigate the underlying reasons for the consistent 0.1 G0 conductance feature in PHE derivatives.
  • To explore the influence of substrate interaction and tip positioning on PHE derivative conductance.

Main Methods:

  • Simulated PHE derivatives on a gold substrate using a scanning tunneling microscope (STM) model.
  • Calculated molecular conductance via non-equilibrium Green's function (NEGF) combined with density functional theory (DFT).
  • Varied STM tip locations to identify optimal conductive and energetically favorable configurations.

Main Results:

  • Optimal tip positions for maximal conductance and favorable energetics did not align.
  • When PHE derivatives were positioned flat on the substrate, conductance variations observed in erect junctions disappeared.
  • All flat-lying PHE derivatives exhibited calculated conductance values clustering around 0.1 G0.

Conclusions:

  • The consistent 0.1 G0 conductance in flat-lying PHE derivatives suggests substrate interactions and tip placement are critical.
  • The observed conductance is less sensitive to anchoring group position when PHE derivatives lie flat compared to erect configurations.