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Mechanical Deformation Distinguishes Tunneling Pathways in Molecular Junctions
Zuoti Xie, Ioan Bâldea1, Greg Haugstad
1Theoretische Chemie , Universität Heidelberg , INF 229, D-69120 Heidelberg , Germany.
Journal of the American Chemical Society
|December 12, 2018
Summary
Mechanical stretching of molecular junctions reveals distinct electron tunneling pathways. Stretching alkanethiols (C nT) shows no change in conductance, while oligophenylene thiols (OPT n) show a significant decrease, distinguishing localized from delocalized orbitals.
Area of Science:
- Molecular electronics
- Condensed matter physics
- Surface science
Background:
- Understanding electron tunneling through molecules is crucial for molecular electronics.
- Distinguishing between localized and delocalized orbital pathways is key to controlling molecular conductance.
- Mechanical strain's effect on molecular junctions is not fully understood.
Purpose of the Study:
- To investigate the impact of mechanical stretching on electron tunneling pathways in molecular junctions.
- To differentiate between sigma- (σ) and pi- (π) bonded molecular backbones under strain.
- To establish a method for distinguishing localized versus delocalized orbital contributions to tunneling.
Main Methods:
- Fabrication of molecular junctions using self-assembled monolayers (SAMs) of alkanethiols (C nT) and oligophenylene thiols (OPT n).
- Mechanical stretching of SAMs to tune interelectrode separation at the angstrom level.
- Measurement of molecular conductance (Gmolecule) as a function of molecular length and strain.
- Theoretical modeling to explain the observed strain-dependent conductance changes.
Main Results:
- Stretched alkanethiol (C nT) molecular junctions exhibited the same length dependence of conductance as unstretched junctions.
- Stretched oligophenylene thiol (OPT n) molecular junctions showed a 10-fold greater decrease in conductance with increasing molecular length compared to unstretched junctions.
- The divergent results were attributed to the strain-dependent electronic coupling (Γ) and the spatial extent of the principal tunneling orbital.
Conclusions:
- Mechanical stretching provides a powerful tool to distinguish between tunneling through localized (σ-bonded) and delocalized (π-bonded) orbitals.
- The strain sensitivity of electronic coupling (Γ) differs significantly between σ- and π-bonded systems.
- Angstrom-level control of interelectrode separation offers a strategy to probe orbital delocalization and electronic coupling in molecular junctions.
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