Wang Xipeng, Li Bo, Xu Xinliang, Han Yilong
Beijing Computational Science Research Center, Beijing 100193, China.
Department of Physics, the Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.
Soft Matter. 2021 Jan 21;17(3):688-693. doi: 10.1039/d0sm01589j. Epub 2020 Nov 20.
Dimensionality often strongly affects material properties and phase transition behaviors, but its effects on crystal surfaces, such as roughening and premelting, have been poorly studied. Our simulation revealed that these surface behaviors are distinct in monolayer and multilayer Lennard-Jones (LJ) crystals. Solid surfaces fluctuate as capillary waves during the roughening process, but complete roughening is preempted by premelting. As the melting temperature is approached, the thickness of the premelted liquid layer approaches a constant (i.e., blocked premelting) for monolayer crystals, but diverges as a power law (i.e., complete premelting) for bilayer and trilayer crystals. The surface liquids of monolayer crystals contain crystalline patches and exhibits rough liquid-vapour and liquid-crystal interfaces, in contrast to the normal surface liquids of bilayer and trilayer crystals. Monolayer crystals melt heterogeneously from the surface without forming a hexatic phase and produce many vacancies.
维度通常会强烈影响材料特性和相变行为，但其对晶体表面（如粗糙化和预熔化）的影响却鲜有研究。我们的模拟结果表明，这些表面行为在单层和多层 Lennard-Jones（LJ）晶体中有所不同。在粗糙化过程中，固体表面会像毛细波一样波动，但预熔化会抢先阻止完全粗糙化。随着接近熔化温度，单层晶体的预熔化液层厚度趋近于一个常数（即受阻预熔化），而双层和三层晶体的预熔化液层厚度则以幂律形式发散（即完全预熔化）。与双层和三层晶体的正常表面液体不同，单层晶体的表面液体包含晶体斑块，并呈现出粗糙的液-气和液-晶界面。单层晶体从表面非均匀熔化，不形成六方相，并产生许多空位。
