论文标题
纳米圆衍射
Nanopowder Diffraction
论文作者
论文摘要
在现有文献中，仍然存在对小纳米晶体观察到的粉末衍射现象的误解（$ d <10 $ nm），我们在这里提出了对可以通过原子模拟来解决的有关问题的系统和简洁审查。现在，可以验证粉末衍射的大多数现象学工具，遵循其热力学和对衍射模式的影响，以构建逼真的原子模型。这些模型涉及完美晶格的小切口以及典型的纳米晶体，以及典型的应变和断层，通过实验来近似实际的纳米晶体。讨论的例子涉及金属纳米晶体。我们描述了峰值移位的起源，该峰值移动的剪切主要是由于陡峭的斜率因子（原子散射和Lorentz）繁殖了宽的曲线。更详细地讨论了Debye总和中嵌入的Lorentz因子。对于用逼真的力场和实际纳米晶体放松的模型，峰值移位还包括表面弛豫的贡献，从而可以开发实验{\ it {intu}}方法对表面状态敏感的方法。这些结果将简要审查。对于小的FCC纳米晶体，我们讨论了多个（111）交叉对峰值变化和高度的重要性和影响。解释和可视化了完美多列簇的应变和尺寸效应 - Decahedra和Icosahedra。该手稿提出了新的方法来解释真实，缺陷（孪生）FCC纳米颗粒的粉末衍射模式，并指出Rietveld方法不合适的方法。
As in the available literature there are still misconceptions about powder diffraction phenomena observed for small nanocrystals ($D<10$ nm), we propose here a systematic and concise review of the involved issues that can be approached by atomistic simulations. Most of phenomenological tools of powder diffraction can be now verified constructing realistic atomistic models, following their thermodynamics and impact on the diffraction pattern. The models concern small cuts of the perfect lattice as well as relaxed nanocrystals also with typical strain and faults, proven by experiments to approximate the real nanocrystals. The discussed examples concern metal nanocrystals. We describe the origin of peak shifts that for cuts of the perfect lattice are mostly due to multiplying of broad profiles by steep slope factors -- atomic scattering and Lorentz. The Lorentz factor embedded in the Debye summation is discussed in more detail. For models relaxed with realistic force fields and for the real nanocrystals the peak shift additionally includes contribution from surface relaxation which enables development of an experimental {\it{in situ }} method sensitive to the state of the surface. Such results are briefly reviewed. For small fcc nanocrystals we discuss the importance and effect of multiple (111) cross twinning on the peak shift and height. The strain and size effects for the perfect multitwinned clusters -- decahedra and icosahedra, are explained and visualised. The manuscript proposes new methods to interpret powder diffraction patterns of real, defected (twinned) fcc nanoparticles and points to unsuitability of the Rietveld method in this case.
