非球面杂质存在下多晶胶体单分子膜的结构表征
Structural characterisation of polycrystalline colloidal monolayers in the presence of aspherical impurities
摘要：
晶体材料中的杂质由于晶格缺陷和晶界的形成而将无序引入原本有序的结构中。所得到的多晶体的性质可能与理想单晶的性质显著不同。在这里，我们研究了一个准二维系统的胶体球含有一小部分的非球面杂质，并将所得的多晶单层。我们发现，在附近的杂质，下面的六方晶格是变形的，由于优先选择5倍协调的颗粒邻近杂质。这导致杂质周围的局部六方有序减少。增加杂质的浓度导致这些缺陷的数量增加，从而减少系统范围内的六方有序和相应的熵增加，从Voronoi单元区域的分布测量。此外，通过考虑取向相关性和直接识别结晶域，我们观察到平均多晶晶粒尺寸在增加杂质浓度时减小。我们的数据表明，对于所考虑的浓度，由于杂质的存在而引起的局部结构修改与其浓度无关，而较长长度尺度上的结构（即多晶晶粒的尺寸）由杂质浓度决定。
英文摘要：
Impurities in crystalline materials introduce disorder into an otherwise ordered structure due to the formation of lattice defects and grain boundaries. The properties of the resulting polycrystal can differ remarkably from those of the ideal single crystal. Here we investigate a quasi-two-dimensional system of colloidal spheres containing a small fraction of aspherical impurities and characterise the resulting polycrystalline monolayer. We find that, in the vicinity of an impurity, the underlying hexagonal lattice is deformed due to a preference for 5-fold co-ordinated particles adjacent to impurities. This results in a reduction in local hexagonal ordering around an impurity. Increasing the concentration of impurities leads to an increase in the number of these defects and consequently a reduction in system-wide hexagonal ordering and a corresponding increase in entropy as measured from the distribution of Voronoi cell areas. Furthermore, through both considering orientational correlations and directly identifying crystalline domains we observe a decrease in the average polycrystalline grain size on increasing the concentration of impurities. Our data show that, for the concentrations considered, local structural modifications due to the presence of impurities are independent of their concentration, while structure on longer lengthscales (i.e. the size of polycrystalline grains) is determined by the impurity concentration.
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