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

纳米粒子由于其独特的性质而成为当前材料科学中最受关注的课题之一。在这个项目中，我们的目标是使原子分辨率，单原子化学分析可用于小于10 nm的颗粒，并用它来回答有关元素分布和结构的基本问题，在尺寸范围内，许多颗粒系统表现出最突出的性能。这些非常小的颗粒的化学分析目前是具有挑战性的，特别是当需要单原子基础上的信息。原子探针层析成像可以用来执行这些粒子的单原子分析，如果他们可以在一个受控的方式场蒸发。在环境条件下使用沉积从颗粒制备场致发射体的尝试对于> 10 nm的颗粒是成功的，但在数据质量和产量方面受到限制。20年前，利用超高真空沉积技术对1 nm以下的Au团簇进行了成功的成像，但仅限于系统内部产生的纯Au团簇。在本项目中，我们将联合收割机高场方法，特别是场电子显微镜（FEM）和场离子显微镜（FEM）与原子探针层析成像相结合，研究小于10 nm的纳米颗粒，并揭示其化学组成。这将通过构建一个新的分析设置，其中FEM/ESTA结合超高真空（UHV）电喷雾注射装置。这允许颗粒在UHV清洁金属尖端基底上的超清洁沉积，这是纳米颗粒的高质量单原子分析所需的。该过程将通过FEM/FEM观察尖端上单个颗粒的到达来精确控制。这允许使用场离子显微镜对颗粒进行结构分析。我们还将通过模拟和实验从理论上评估粒子场蒸发过程中的投影规律和蒸发顺序，为精确的3D原子探针分析奠定基础。然后，我们将把这种粒子场发射器尖端转移到一个专用的原子探针中，在那里我们将以单原子灵敏度和亚纳米3D分辨率分析粒子内化学元素的分布。该技术将应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体内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。原子探针测量将被用来区分团聚从奥斯特瓦尔德熟化在催化中使用的各种系统，并评估故意添加的元素以及合成残留物的界面/表面偏析的程度。

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.