Odd-even effects in charge transport across self-assembled monolayers

Area of Science:

• Materials Science
• Surface Chemistry
• Molecular Electronics

Background:

• Self-assembled monolayers (SAMs) are crucial for molecular electronics.
• Understanding charge transport through SAMs is key to developing new electronic devices.
• The "odd-even effect" in charge transport has been observed but requires precise measurement techniques.

Purpose of the Study:

• To investigate the influence of methylene chain parity (odd vs. even) on charge transport across n-alkanethiol SAMs.
• To assess the utility of eutectic gallium-indium (EGaIn) electrodes for sensitive charge transport measurements.
• To determine if the odd-even effect is statistically significant and explore its origins.

Main Methods:

• Formation of SAMs of n-alkanethiols on ultraflat template-stripped silver (Ag(TS)) surfaces.
• Fabrication of metal/SAM//oxide/EGaIn junctions using eutectic gallium-indium (EGaIn) top electrodes.
• Measurement of current density (J) across the SAMs as a function of chain length and parity.
• Statistical analysis of collected charge transport data.

Main Results:

• EGaIn electrodes, forming a thin oxide layer, enable stable conical microcontacts and high junction yields.
• The odd-even effect in charge transport is statistically discernible, with even-numbered alkanethiols showing higher current density than odd-numbered ones.
• The difference in current density is statistically significant, but differences in tunneling decay constant (β) or pre-exponential factor (J(0)) are not.

Conclusions:

• The EGaIn/oxide electrode system is sensitive to subtle structural differences in SAMs, enabling the observation of the odd-even effect.
• The study confirms a statistically significant odd-even effect in charge transport through n-alkanethiol SAMs.
• While the effect is observed, the precise molecular origins remain a topic for further investigation.