Jumping, Rotating, and Flapping: The Atomic-Scale Motion of Thiophene on Cu(111)

Area of Science:

• Surface Science
• Physical Chemistry
• Organic Electronics

Background:

• Self-assembled monolayers of sulfur-containing heterocycles and thiophene oligomers are crucial for organic electronics.
• Understanding molecule dynamics on surfaces is key to optimizing device performance.

Purpose of the Study:

• To investigate the dynamics of isolated thiophene molecules on a Cu(111) surface.
• To characterize diffusion, rotation, and other dynamic processes at the molecular level.

Main Methods:

• Helium spin-echo (HeSE) spectroscopy was employed to probe molecular motion.
• Density functional theory (DFT) calculations were used to complement experimental findings.

Main Results:

• Observed jump diffusion between atop sites with a 59-62 meV energy barrier.
• Identified activated rotation around a sulfur-copper anchor bond.
• Provided evidence for a new, weakly activated 'flapping' motion of the thiophene ring.
• Measured a high friction coefficient of 5 ± 2 ps⁻¹ and observed repulsive inter-adsorbate interactions.

Conclusions:

• The thiophene/Cu(111) system exhibits complex aperiodic dynamics.
• Helium spin-echo spectroscopy is a versatile tool for studying surface dynamics.
• The findings provide a benchmark for theoretical calculations of adsorbate-substrate interactions.