Ordering in a fluid inert gas confined by flat surfaces

Area of Science:

• Materials Science
• Condensed Matter Physics
• Physical Chemistry

Background:

• Interfacial layering of simple liquids is theoretically predicted but lacks direct observational evidence.
• Understanding liquid behavior in confined spaces is crucial for materials science and nanotechnology.

Purpose of the Study:

• To provide direct observational evidence of interfacial layering in a simple liquid (xenon) confined in nanometer-scale cavities.
• To investigate the influence of interfacial layering on the phase behavior and structure of confined xenon.

Main Methods:

• High-resolution transmission electron microscopy (HRTEM) was used to image fluid xenon in faceted cavities within aluminum.
• Molecular dynamics (MD) simulations were performed to model xenon behavior in confined geometries.

Main Results:

• HRTEM revealed three distinct layers of xenon at the fluid-solid interface within small aluminum cavities.
• MD simulations showed that interfacial layering induces a density variation, causing xenon to condense into the body-centered cubic (BCC) phase.
• The BCC phase of confined xenon differs from the face-centered cubic (FCC) phase observed in bulk solid xenon and in larger cavities.

Conclusions:

• Direct observational evidence confirms interfacial layering of simple liquids at the nanoscale.
• Interfacial layering significantly impacts the condensed phase structure of confined fluids, leading to novel crystalline structures (BCC xenon).
• This finding has implications for understanding rheology and crystal growth dynamics in confined systems.