Stationary Atoms in Liquid Metals and Their Role in Solidification Mechanisms

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• The distinction between liquid and solid metals is traditionally based on atomic motion.
• Solidification involves a transition from disordered to ordered atomic structures via nucleation.
• The role of stationary atoms within liquid metal phases remains poorly understood.

Purpose of the Study:

• To investigate the influence of stationary atoms on the solidification pathways of metal nanoparticles.
• To explore the formation of supercooled liquid metals and amorphous solidification.
• To understand the mechanisms of nucleation and phase transitions at the nanoscale.

Main Methods:

• Utilized spherical and chromatic aberration-corrected high-resolution transmission electron microscopy (HRTEM) at low accelerating voltages.
• Developed a methodology for atomic-resolution imaging of metal nanoparticles across a wide temperature range (20–800 °C).
• Performed time-series imaging and contrast analysis of individual 3-6 nm platinum, palladium, and gold nanoparticles during cooling.

Main Results:

• Identified stationary atoms within liquid metal nanoparticles, pinned at vacancy defect sites on graphene substrates.
• Observed that the number and arrangement of stationary atoms dictate solidification pathways: few random atoms promote nucleation, while numerous or perimeter-aligned atoms inhibit crystallization.
• Demonstrated that stationary atoms can stabilize liquid nanodroplets down to 200–300 °C, leading to amorphous solidification instead of crystallization.

Conclusions:

• The presence and behavior of stationary atoms in liquid metals significantly alter phase transition dynamics.
• Stationary atoms can induce supercooling and promote amorphous solidification in metal nanoparticles.
• Findings have implications for heterogeneous catalysis and thermal processes involving metal nanoparticles on carbon supports.