Departament de Ciència de Materials i Química Física & Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, c/ Martí i Franquès 1, 08028 Barcelona, Spain.
Nanoscale. 2017 Jul 20;9(28):10067-10074. doi: 10.1039/c7nr02818k.
We report on an extensive survey of (ZnO) nanostructures ranging from bottom-up generated nanoclusters to top-down nanoparticles cuts from bulk polymorphs. The obtained results enable us to follow the energetic preferences of structure and polymorphism in (ZnO) systems with N varying between 10-1026. This size range encompasses small nanoclusters with 10s of atoms and nanoparticles with 100s of atoms, which we also compare with appropriate bulk limits. In all cases the nanostructures and bulk systems are optimized using accurate all-electron, relativistic density functional theory based calculations with numeric atom centered orbital basis sets. Specifically, sets of five families of (ZnO) species are considered: single-layered and multi-layered nanocages, and bulk cut nanoparticles from the sodalite (SOD), body centered tetragonal (BCT), and wurtzite (WZ) ZnO polymorphs. Using suitable fits to interpolate and extrapolate these data allows us to assess the size-dependent energetic stabilities of each family. With increasing size our results indicate a progressive change in energetic stability from single-layered to multi-layered cage-like nanoclusters. For nanoparticles of around 2.6 nm diameter we identify a transitional region where multi-layered cages, SOD, and BCT nanostructures are very similar in energetic stability. This transition size also marks the size regime at which bottom-up nanoclusters give way to top-down bulk-cut nanoparticles. Eventually, a final crossover is found where the most stable WZ-ZnO polymorph begins to energetically dominate at N ∼ 2200. This size corresponds to an approximate nanoparticle diameter of 4.7 nm, in line with experiments reporting the observation of wurtzite crystallinity in isolated ligand-free ZnO nanoparticles of 4-5 nm size or larger.
我们报告了（ZnO）纳米结构的广泛调查，范围从自下而上生成的纳米团簇到从体多晶型物自上而下切割的纳米颗粒。所获得的结果使我们能够跟踪（ZnO）系统中结构和多晶型的能量偏好，其中 N 变化范围为 10-1026。这个尺寸范围包括具有 10 到 100 个原子的小纳米团簇和具有 100 个原子的纳米颗粒，我们还将其与适当的体相极限进行了比较。在所有情况下，使用基于全电子、相对论密度泛函理论的精确计算以及数值原子中心轨道基组对纳米结构和体系统进行了优化。具体来说，考虑了五组（ZnO）物种：单层和多层纳米笼，以及来自方钠石（SOD）、体心四方（BCT）和纤锌矿（WZ）ZnO 多晶型物的块状切割纳米颗粒。使用合适的拟合来插值和外推这些数据，使我们能够评估每个家族的尺寸依赖性能量稳定性。随着尺寸的增加，我们的结果表明，从单层到多层笼状纳米团簇，能量稳定性逐渐变化。对于直径约为 2.6nm 的纳米颗粒，我们确定了一个过渡区域，其中多层笼、SOD 和 BCT 纳米结构在能量稳定性方面非常相似。这个过渡尺寸也标志着自下而上的纳米团簇让位于自上而下的块状切割纳米颗粒的尺寸范围。最终，在 N ∼ 2200 处，发现了一个最终的交叉点，其中最稳定的 WZ-ZnO 多晶型物开始在能量上占主导地位。这个尺寸对应于一个约为 4.7nm 的纳米颗粒直径，与实验报告的孤立配体自由 ZnO 纳米颗粒的尺寸为 4-5nm 或更大时观察到纤锌矿结晶度的结果一致。
