论文标题
液体AUSI薄膜和纳米级液滴中2D表面晶体的稳定性和能量学
Stability and energetics of 2D surface crystals in liquid AuSi thin films and nanoscale droplets
论文作者
论文摘要
金属共价二元液体的表面上的分离通常是非古典的，在极端情况下，例如AUSI，表面在熔点上方结晶。在这项研究中，我们采用原子级计算框架来研究AUSI膜和液滴的表面结晶，这是组成，温度和大小的函数。对于范围内的温度，$ t_s^\ ast = 765-780 $ k以上熔点$（t_s^\ ast \ aST \ oft1.3 \，t_m）$，薄膜和滴表面经历了第一阶过渡，从2D au $ _2 $ _2 $ _2 $ _2 $ _2 $ _2 $ _2 $ _2 $ _2 $ si Crystalline相位到后来的层次，但层次分层。薄膜表面表现出有效的表面张力，随着温度而增加，随着SI浓度的降低。另一方面，对于尺寸范围$ 10-30 $ nm的液滴，散装拉普拉斯压力会改变表面隔离，因为它是相对于紧张的散装而发生的。以上$ t_s^\ ast $尺寸对表面张力的效果很小，而对于$ t <t_s^\ ast $，表面层被紧紧地且由2D晶体组成，由2D晶体组成，这些晶粒边界疤痕被扩展的晶粒边界疤痕隔开，从而导致其能量学的大波动。作为特定应用，对Si表面通量的SI（111）底物上AUSI液滴的全原子模拟表明，取决于表面张力的表面张力通过在固体蒸气界面上形成前体润湿膜来破坏接触线，并且在基于VLS基于VLS基于NanAnowire的nanAnowire增长的尺寸时具有后果。我们的研究阐明了这些独特的二元合金中稳定性和表面能量之间的相互作用，并提供了用于利用其表面结构的途径，以用于多种应用，例如催化纳米晶的生长，Dealloying和聚合物结晶。
Segregation at surfaces of metal-covalent binary liquids is often non-classical and in extreme cases such as AuSi, the surface crystallizes above the melting point. In this study, we employ atomic-scale computational frameworks to study the surface crystallization of AuSi films and droplets as a function of composition, temperature and size. For temperatures in the range $T_s^\ast=765-780$K above the melting point $(T_s^\ast\approx1.3\,T_m)$, both thin film and droplet surfaces undergo a first order transition, from a 2D Au$_2$Si crystalline phase to a laterally disordered yet stratified layer. The thin film surfaces exhibit an effective surface tension that increases with temperature and decreases with Si concentration. On the other hand, for droplets in the size range $10-30$ nm, the bulk Laplace pressure alters the surface segregation as it occurs with respect to a strained bulk. Above $T_s^\ast$ the size effect on the surface tension is small, while for $T<T_s^\ast$ the surface layer is strained and composed of 2D crystallites separated by extended grain boundary scars that lead to large fluctuations in its energetics. As a specific application, all-atom simulations of AuSi droplets on Si(111) substrate subject to Si surface flux show that the supersaturation dependent surface tension destabilizes the contact line via formation of a precursor wetting film on the solid-vapor interface, and has ramifications for size selection during VLS-based routes for nanowire growth. Our study sheds light on the interplay between stability and energetics of surfaces in these unique class of binary alloys and offers pathways for exploiting their surface structure for varied applications such as catalytic nanocrystal growth, dealloying, and polymer crystallization.
