Imaging Field-Driven Melting of a Molecular Solid at the Atomic Scale

Area of Science:

• Surface Science
• Materials Science
• Physical Chemistry

Background:

• Solid-liquid phase transitions are fundamental physical processes.
• Capturing the full dynamics of these transitions at atomic resolution remains a challenge.
• Existing microscopy techniques have limitations in imaging dynamic phase changes.

Purpose of the Study:

• To develop a novel technique for controlling and imaging solid-liquid phase transitions in molecular systems.
• To achieve atomically resolved visualization of melting and freezing dynamics.
• To study nonequilibrium melting dynamics and resulting 2D equilibrium states.

Main Methods:

• Utilized a graphene field-effect transistor (FET) decorated with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane molecules.
• Applied electric fields to induce reversible solid-liquid phase transitions.
• Employed atomically resolved scanning tunneling microscopy to image phase-transition behavior.
• Visualized nonequilibrium melting dynamics by rapid electrical heating of the graphene substrate.

Main Results:

• Successfully controlled and imaged reversible solid-liquid phase transitions at the molecular level on the FET surface.
• Observed and visualized nonequilibrium melting dynamics and the evolution toward new 2D equilibrium states.
• Developed an analytical model explaining mixed-state phases based on spectroscopic measurements of molecular energy levels.
• Monte Carlo simulations confirmed the observed nonequilibrium melting dynamics.

Conclusions:

• The developed technique enables unprecedented atomically resolved imaging of solid-liquid phase transition dynamics.
• Electric field control on decorated FETs provides a powerful platform for studying molecular phase behavior.
• The findings offer insights into nonequilibrium processes and the formation of 2D equilibrium states in molecular systems.