New discovery on liquid metal alloys may lead to high-efficiency electronics

Surface pattern formation during solidification of a Ag-Ga alloy looked through an optical microscope. (Image courtesy of FLEET).

A new paper in the journal Nature Synthesis presents the idea of a previously unidentified type of solidification pattern appearing on the surface of solidifying liquid metals.

In the view of the team working at the ARC Centre of Excellence in Future Low-Energy Electronics Technologies behind this proposal, the recently-discovered pattern resembles a famous line from a Chinese classic: “The long divided, must unite; long united, must divide. Thus it has ever been.”

The line belongs to Romance of the Three Kingdoms and to observe such a divergent-convergent pattern in liquifying metals, the researchers dissolved a small amount of metals such as silver (Ag) in low-melting-point solvent metals such as gallium (Ga) and investigated how the metallic components interact and separate to form patterns when the metallic liquid mixtures (alloys) solidify.

They found that a single silver–gallium system can produce distinct patterns such as particles or bundle-like structures of an Ag2Ga compound.

New discovery on liquid metal alloys may lead to high-efficiency electronics
Top: Divergent surface patterning spreading out from a ‘seed,’ meeting convergent patterning. Bottom: oscillatory bifurcation patterns on surface of solidified Ag-Ga alloy. (Image courtesy of FLEET).

The individual Ag2Ga structures that build the patterns are small, with micrometer or nanometer thicknesses, tens or hundreds of times thinner than a human hair.

Most surprisingly, the team observed that the patterns divide and unite in a repeated manner.

Pattern formation is a fundamental phenomenon in nature and some pattern types are more common than others. Among all the diverse patterning behaviors, divergent pattern formation, or bifurcation, is frequently seen because this particular arrangement generally favors energy conversion or distribution.

Its counterpart, convergent pattern growth, or inverse bifurcation, is encountered less frequently as it is contrary to the energetically favorable bifurcation.

According to the scientists, the strange cyclic divergent and convergent growth, called oscillatory bifurcation, is rare and has not been observed in solidification structures prior to this new study.

Despite this, they observed oscillatory bifurcation patterns on the surface of several liquid alloys after solidification, which suggests that this counter-intuitive behavior is quite general for solidification patterns forming on the surface of liquid metals.

Analogous to the dramatized novel, the team found that it is also the instability of the liquid metal surface that underlies the emergence of the oscillatory bifurcation patterns.

“Surface pattern formation of liquid metal alloys is a new but exciting topic. The surface or interfacial nature of the process enables us to better understand and control fundamental phase transition and pattern formation,” Jianbo Tang, first author of the study, said in a media statement.

“We will continue our work on designing crystalline surface patterns and structures using liquid metals to enable cutting-edge applications such as plasmonic sensing, high-efficiency electronics and optics, and high-precision spectroscopy.”