Conformation, and Charge Tunneling through Molecules in SAMs

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Self-assembled monolayers (SAMs) are crucial for molecular electronics.
• Charge tunneling (CT) is a fundamental process in molecular junctions.
• Understanding factors influencing CT rates is key to designing advanced electronic devices.

Purpose of the Study:

• To investigate the influence of molecular conformation on charge tunneling rates in SAMs.
• To analyze how different alkyl chain lengths and types affect molecular ordering and CT.
• To determine if monolayer thickness alone dictates charge transport efficiency.

Main Methods:

• Fabrication of molecular junctions using gold (Au) and gallium oxide (Ga2O3) electrodes.
• Formation of SAMs with amide-containing alkanethiols (S(CH2)2CONR1R2).
• Variation of alkyl chain lengths (R1 and R2) to control molecular conformation and homogeneity.
• Measurement of charge tunneling rates and analysis of monolayer thickness using X-ray photoelectron spectroscopy (XPS).

Main Results:

• Molecular conformation significantly influences charge tunneling rates, beyond just monolayer thickness.
• Well-ordered, trans-extended conformations exhibit different tunneling rates compared to those with gauche conformations.
• A decrease in CT rates (up to 6.3x) was observed when R1=R2 compared to R1=H for similar total chain lengths.
• Weaker correlation between current density and thickness was found when R1 ≠ H ≠ R2, indicating conformational effects.

Conclusions:

• Molecular conformation is a critical determinant of charge tunneling rates in SAMs.
• Monolayer thickness is not the sole factor governing charge transport; molecular arrangement plays a vital role.
• These findings provide a deeper understanding of charge transport mechanisms in molecular electronic systems.