Discerning order from chaos: characterising the surface structure of liquid gallium†

Liquid metal (LM) technologies are rapidly advancing in modern materials science, with low melting point metals playing a pivotal role in emerging applications. Recent studies reveal that doped liquid gallium systems form spectacular and diverse surface structures during cooling, [Tang et al., Nat. Nanotechnol., 2021, 16, 431–439] sparking renewed interest in the possible geometric structuring at the surface of pure liquid gallium. Distinct from the known increase in surface density, this lateral surface order has long been hinted at experimentally and theoretically but has remained enigmatic. Here, we quantitatively characterise the depth and nature of this surface ordering for the first time, using highly accurate and large scale molecular dynamics simulations coupled with machine learning analysis techniques. We also quantify the enhanced structural order introduced by the addition of a gallium oxide film as well as the disruption due to a dopant (bismuth).