Holec David, Dumitraschkewitz Phillip, Vollath Dieter, Fischer Franz Dieter
Department of Materials Science, Montanuniversität Leoben, Franz Josef Straße 18, A-8700 Leoben, Austria.
Chair of Nonferrous Metallurgy, Department of Metallurgy, Montanuniversität Leoben, Franz-Josef-Straße 18, A-8700 Leoben, Austria.
Nanomaterials (Basel). 2020 Mar 8;10(3):484. doi: 10.3390/nano10030484.
Motivated by often contradictory literature reports on the dependence of the surface energy of gold nanoparticles on the variety of its size and shape, we performed an atomistic study combining molecular mechanics and ab initio calculations. We show that, in the case of Au nanocubes, their surface energy converges to a value for ( 0 0 1 ) facets of bulk crystals. A fast convergence to a single valued surface energy is predicted also for nanospheres. However, the value of the surface energy is larger in this case than that of any low-index surface facet of bulk Au crystal. This fact can be explained by the complex structure of the surface with an extensive number of broken bonds due to edge and corner atoms. A similar trend was obtained also for the case of cuboctahedrons. Since the exact surface area of the nanoparticles is an ill-defined quantity, we have introduced the surface-induced excess energy and discuss this quantity as a function of (i) number of atoms forming the nano-object or (ii) characteristic size of the nano-object. In case (i), a universal power-law behaviour was obtained independent of the nanoparticle shape. Importantly, we show that the size-dependence of the surface is hugely reduced if the surface area correction is considered due to its expansion by the electronic cloud, a phenomenon specifically important for small nanoparticles.
鉴于关于金纳米颗粒表面能对其尺寸和形状变化的依赖性，文献报道常常相互矛盾，我们进行了一项结合分子力学和从头算计算的原子研究。我们表明，对于金纳米立方体，其表面能收敛于体晶体（0 0 1）晶面的值。对于纳米球，也预测其表面能会快速收敛到一个单一值。然而，在这种情况下，表面能的值比体金晶体任何低指数表面晶面的表面能值都要大。这一事实可以通过表面的复杂结构来解释，由于边缘和角原子存在大量断键。对于八面体的情况也得到了类似的趋势。由于纳米颗粒的确切表面积是一个不明确的量，我们引入了表面诱导过剩能量，并将此量作为（i）构成纳米物体的原子数或（ii）纳米物体的特征尺寸的函数进行讨论。在情况（i）中，得到了与纳米颗粒形状无关的通用幂律行为。重要的是，我们表明，如果考虑由于电子云膨胀导致的表面积校正，表面的尺寸依赖性会大大降低，这一现象对于小纳米颗粒尤为重要。
