Laboratoire Matériaux et Phénomènes Quantiques, CNRS-UMR 7162, Université Paris Diderot--Paris 7, Case Courrier 7021, 75205 Paris Cedex 13, France.
Ultramicroscopy. 2011 Jan;111(2):149-54. doi: 10.1016/j.ultramic.2010.10.017. Epub 2010 Nov 7.
This paper reports the coupling of HRTEM and moiré pattern observations, allowing the determination of the thickness ratio of two superimposed crystals. Pseudo-lattice fringes are observed using identical TEM experimental conditions as for observing moiré patterns. The pseudo-lattice spacing is first calculated in the dynamical theory framework in two beam conditions. This approach shows a linear behavior of the spacing as a function of the thickness ratio of the two crystals. The roles of sample crystallographic orientation and sample thickness on the thickness ratio determination are discussed from multi-beam simulations. Finally, the method is applied on a bimetallic CuAg core-shell nanoparticle of a known structure. It is demonstrated that for this particle, the thickness ratio of Cu and Ag can be determined with an error that results in a precision less than 0.75 nm on the Cu and Ag thicknesses. The advantages of the technique are the use of an in-plane sample configuration and a single HRTEM image.
本文报道了 HRTEM 和条纹图案观察的耦合，允许确定两个叠加晶体的厚度比。使用与观察条纹图案相同的 TEM 实验条件观察到拟晶格条纹。拟晶格间距首先在双光束条件下的动力学理论框架中进行计算。该方法表明间距作为两个晶体的厚度比的函数呈线性行为。从多光束模拟讨论了样品晶体取向和样品厚度对厚度比确定的影响。最后，该方法应用于具有已知结构的双金属 CuAg 核壳纳米粒子。结果表明，对于该粒子，可以确定 Cu 和 Ag 的厚度比，其误差导致 Cu 和 Ag 的厚度的精度小于 0.75nm。该技术的优点是使用平面内样品配置和单个 HRTEM 图像。
