Controlling polaron formation at hematite surfaces by molecular functionalization probed by XUV reflection-absorption...

Area of Science:

• Materials Science
• Photocatalysis
• Surface Science

Background:

• Small polaron formation in hematite limits photocatalytic charge transport efficiency.
• Understanding surface polaron formation dynamics is crucial but not fully elucidated.
• Theoretical predictions suggest different kinetics and thermodynamics for surface vs. bulk polaron formation.

Purpose of the Study:

• To experimentally differentiate and compare surface and bulk polaron formation kinetics and energetics in photoexcited hematite.
• To investigate the influence of surface molecular functionalization on polaron formation dynamics.
• To provide insights into controlling electron transport in hematite.

Main Methods:

• Near grazing angle extreme ultraviolet reflection-absorption (XUV-RA) spectroscopy was employed for its surface sensitivity and femtosecond time resolution.
• Systematic comparison of polaron formation kinetics and energetics between surface and bulk hematite.
• Application of a Marcus type model to discuss kinetics and energetics.

Main Results:

• Surface polaron formation rate (250 ± 40 fs) is approximately three times slower than bulk polaron formation (90 ± 5 fs).
• Surface polaron formation rate can be systematically tuned by surface molecular functionalization.
• Slower surface polaron formation is attributed to greater lattice reorganization; functionalization tunes reorganization and stabilization energies.

Conclusions:

• Experimental differentiation of surface and bulk polaron formation is achieved using XUV-RA spectroscopy.
• Surface molecular functionalization provides a method to tune polaron formation kinetics and energetics.
• This tunability offers opportunities for synthetic control of electron transport in hematite for photocatalytic applications.