Atom-by-atom analysis of small nanoparticles using high-field methods

纳米粒子以其独特的性质成为当前材料科学研究的热点之一。在这个项目中，我们的目标是对小于10 nm的颗粒进行原子分辨率和单原子化学分析，并利用它来回答关于元素分布和结构的基本问题，在这个尺寸范围内，许多颗粒系统表现出最出色的性能。目前，对这些非常小的颗粒进行化学分析是具有挑战性的，特别是当需要单原子基础上的信息时。如果这些颗粒能够以受控的方式被场蒸发，那么原子探针层析可以用来对它们进行单原子分析。在环境条件下使用沉积从粒子制备场发射器的尝试已经成功地对10 nm粒子进行了制备，但在数据质量和吞吐量方面受到限制。利用超高真空沉积技术，20年前已经成功地对Au团簇进行了尺寸为1 nm的成像，但仅限于系统内部产生的纯Au团簇。在这个项目中，我们将结合高场方法，特别是场电子显微镜(FEM)和场离子显微镜(FIM)与原子探针层析成像来研究小于10 nm的纳米粒子，并揭示其化学组成。这将通过构建一种新型的分析装置来实现，其中有限元/FIM与超高真空(UHV)电喷雾注射装置相结合。这使得粒子可以超清洁地沉积到超高压清洁的金属针尖基板上，这是高质量单原子分析纳米颗粒所必需的。通过有限元/有限元模拟观察单个粒子到达尖端的过程，可以精确控制这一过程。这使得可以使用场离子显微镜对颗粒进行结构分析。我们还将从理论上通过模拟和实验来评估粒子在场蒸发过程中的投影规律和蒸发序列，为精确的三维原子探针分析奠定基础。然后，我们将把这种形式的粒子场发射器尖端转移到专用的原子探测器中，在那里我们将以单原子灵敏度和亚纳米3D分辨率分析化学元素在粒子中的分布。这项技术将用于分析用于催化的金属核壳纳米颗粒、用于太阳能转换的掺杂半导体纳米颗粒以及通过模拟活体生物矿化的结晶过程获得的非经典结晶过程的中间体。在项目的第二阶段，我们将专注于围绕纳米颗粒合成的一些基本问题：成核的早期阶段和内部界面的作用。原子探针测量将用于区分催化中使用的各种系统中的团聚和Ostwald成熟，并评估故意添加的元素和合成残留物的界面/表面分离程度。

Nanoparticles are among the most researched topics in current materials science due to their unique properties. In this project, we aim to make atomic resolution, single atom chemical analysis available for particles smaller than 10 nm and use it to answer fundamental questions regarding elemental distributions and structure in a size range where many particle systems exhibit their most outstanding performance.Chemical analysis of these very small particles is currently challenging, especially when information on a single atom basis is required. Atom probe tomography could be used to perform single atom analysis of these particles if they can be field evaporated in a controlled manner. Attempts preparing field emitters from particles using deposition in ambient conditions have been successful for particles > 10 nm but limited in data quality and throughput. Using UHV deposition, imaging of Au clusters down to a size of 1 nm was already successful 20 years ago, but limited to pure Au clusters produced inside the system.In this project, we will combine high field methods, in particular field-electron (FEM) and field-ion microscopy (FIM) with atom probe tomography to investigate nanoparticles smaller than 10 nm and reveal their chemical makeup. This will be done by constructing a novel analysis setup where FEM/FIM are combined with an ultra-high vacuum (UHV) electrospray injection device. This allows for the ultra-clean deposition of particles onto a UHV clean metal tip substrate, required for high quality single atom analysis of nanoparticles. The process will be precisely controlled by the observation of the arrival of single particles on the tip via FEM/FIM. This allows for structural analysis of the particle using the field ion microscope. We will also assess the projection laws and evaporation sequence during the field evaporation of the particles both theoretically through simulations and experimentally to lay the groundwork for precise 3D atom probe analysis. We will then transfer the so-fashioned particle field emitter tips into a dedicated atom probe, where we will analyse the distribution of the chemical elements within particles with single atom sensitivity and sub-nm 3D resolution. This technique will then be applied to the analysis of metallic core-shell nanoparticles for catalysis, doped semiconductor nanoparticles for solar energy conversion and intermediates of nonclassical crystallization processes obtained by a crystallization processes mimicking biomineralization in vivo.In the second phase of the project, we will focus on some of the fundamental questions surrounding nanoparticle synthesis: the early stages of nucleation and the role of internal interfaces. Atom probe measurements will be used to distinguish agglomeration from Ostwald ripening in a variety of systems used in catalysis and to assess the extent of interfacial/surface segregation of deliberately added elements as well as synthesis residues.