Superheating of confined Pb thin films

Area of Science:

• Materials Science
• Thermodynamics
• Condensed Matter Physics

Background:

• Superheating is a phenomenon where a material is heated above its melting point without becoming liquid.
• Understanding superheating in confined systems is crucial for advanced materials and nanotechnology.
• Previous studies on superheating primarily focused on bulk materials or isolated nanoparticles.

Purpose of the Study:

• To experimentally observe and characterize superheating in two-dimensional metal thin films.
• To investigate the influence of epitaxial interfaces on the superheating phenomenon.
• To elucidate the underlying thermodynamic mechanisms responsible for superheating in confined thin films.

Main Methods:

• Fabrication of approximately 20 nm thick lead (Pb) thin films confined by aluminum (Al) layers using cold rolling.
• Formation of semicoherent epitaxial Pb/Al interfaces.
• In situ X-ray diffraction analysis to monitor phase transitions and temperature.
• Thermodynamic analysis to interpret the observed superheating behavior.

Main Results:

• Experimental evidence of superheating in confined Pb thin films, exceeding the bulk melting point by at least 6°C.
• Observation that the confined Pb films remained solid above their bulk melting temperature.
• Identification of epitaxial Al/Pb/Al confinement as a key factor influencing the superheating.

Conclusions:

• The study reports the first experimental observation of superheating in metal thin films.
• The observed superheating is attributed to the suppression of molten droplet growth by the epitaxial confinement, rather than the suppression of melt nucleation.
• Findings provide new insights into the phase transition behavior of materials in nanoscale confinement.