Université Paris Cité, CNRS, Laboratoire Matériaux et Phénomènes Quantiques (MPQ), 75013 Paris, France.
Laboratoire d'Etude des Microstructures, ONERA-CNRS, UMR104, Université Paris-Saclay, BP 72, Châtillon Cedex, 92322, France.
Phys Rev Lett. 2023 Jun 9;130(23):236201. doi: 10.1103/PhysRevLett.130.236201.
We combine electron microscopy measurements of the surface compositions in Cu-Au nanoparticles and atomistic simulations to investigate the effect of gold segregation. While this mechanism has been extensively investigated within Cu-Au in the bulk state, it was never studied at the atomic level in nanoparticles. By using energy dispersive x-ray analysis across the (100) and (111) facets of nanoparticles, we provide evidence of gold segregation in Cu_{3}Au and CuAu_{3} nanoparticles in the 10 nm size range grown by epitaxy on a salt surface with high control of the nanoparticles morphology. To get atomic-scale insights into the segregation properties in Cu-Au nanoparticles on the whole composition range, we perform Monte Carlo calculations employing N-body interatomic potentials highlighting a complete segregation of Au in the (100) and (111) facets for gold nominal composition above 70% and 60%, respectively. Furthermore, we show that there is no size effect on the segregation behavior since we evidence the same oscillating concentration profile from the surface to the nanoparticle's core as in the bulk. These results shed new light on the interpretation of the enhanced reactivity, selectivity, and stability of Cu-Au nanoparticles in various catalytic reactions.
我们结合电子显微镜对 Cu-Au 纳米粒子表面成分的测量和原子模拟来研究金的偏析效应。虽然这种机制在大块 Cu-Au 中已经被广泛研究，但在纳米粒子中从未在原子水平上进行过研究。通过在纳米粒子的（100）和（111）晶面上进行能量色散 X 射线分析，我们提供了在盐表面外延生长的 10nm 尺寸范围内的 Cu3Au 和 CuAu3 纳米粒子中存在金偏析的证据，对纳米粒子形态具有高度的控制。为了深入了解整个成分范围内 Cu-Au 纳米粒子的偏析特性，我们采用 N 体原子间势进行蒙特卡罗计算，突出显示 Au 在（100）和（111）晶面上的完全偏析，对于名义金含量分别高于 70%和 60%。此外，我们表明偏析行为不受尺寸影响，因为我们从表面到纳米粒子核心都证明了与体相相同的振荡浓度分布。这些结果为解释各种催化反应中 Cu-Au 纳米粒子增强的反应性、选择性和稳定性提供了新的视角。
