Dipartimento di Fisica e Astronomia, Università di Catania, via S, Sofia 64, I-95123, Catania, Italy.
Nanoscale Res Lett. 2008 Oct 9;3(11):454-60. doi: 10.1007/s11671-008-9180-y.
We report on the calculations of the cohesive energy, melting temperature and vacancy formation energy for Au nanocrystals with different size supported on and embedded in SiO2. The calculations are performed crossing our previous data on the surface free energy of the supported and embedded nanocrystals with the theoretical surface-area-difference model developed by W. H. Qi for the description of the size-dependent thermodynamics properties of low-dimensional solid-state systems. Such calculations are employed as a function of the nanocrystals size and surface energy. For nanocrystals supported on SiO2, as results of the calculations, we obtain, for a fixed nanocrystal size, an almost constant cohesive energy, melting temperature and vacancy formation energy as a function of their surface energy; instead, for those embedded in SiO2, they decreases when the nanocrystal surface free energy increases. Furthermore, the cohesive energy, melting temperature and vacancy formation energy increase when the nanocrystal size increases: for the nanocrystals on SiO2, they tend to the values of the bulk Au; for the nanocrystals in SiO2 in correspondence to sufficiently small values of their surface energy, they are greater than the bulk values. In the case of the melting temperature, this phenomenon corresponds to the experimentally well-known superheating process.
我们报告了不同尺寸的金纳米晶体在 SiO2 上负载和嵌入时的内聚能、熔化温度和空位形成能的计算。这些计算是通过将我们以前关于负载和嵌入纳米晶体的表面自由能的数据与 W.H. Qi 为描述低维固体质热力学性质而开发的理论表面积差模型交叉进行的。这些计算是作为纳米晶体尺寸和表面能的函数进行的。对于负载在 SiO2 上的纳米晶体，作为计算的结果，我们得到，对于固定的纳米晶体尺寸，内聚能、熔化温度和空位形成能几乎是常数，作为其表面能的函数；而对于嵌入在 SiO2 中的纳米晶体，当纳米晶体表面自由能增加时，它们会减小。此外，当纳米晶体尺寸增加时，内聚能、熔化温度和空位形成能会增加：对于负载在 SiO2 上的纳米晶体，它们趋向于体相 Au 的值；对于表面能足够小的嵌入在 SiO2 中的纳米晶体，它们大于体相的值。在熔化温度的情况下，这种现象对应于实验上已知的过热过程。
