Nanoparticle manipulation with atomic force microscopy techniques - (NANOPARMA)

原子力显微镜(AFM)已被证明是研究纳米级接触摩擦力的有力工具。不幸的是，这项技术在应用于研究两个摩擦表面的化学和结构性质时暴露出一些缺陷。AFM中使用的尖端是预制的。因此，两个摩擦表面中的一个通常由硅化合物组成，接触的有效尺寸将主要由商业上可用的尖端半径决定。然而，当前迫切需要解决的问题是接触面积的依赖性以及材料对摩擦学性能的影响。摩擦的接触面积对弥合纳米尺度和微米尺度之间的摩擦是至关重要的，这最终将使我们能够理解和控制宏观摩擦。另一方面，正确的材料选择有望产生新的摩擦效应，例如超润滑性。解决这个问题的方法是使用原子力显微镜作为操纵工具，通过控制纳米颗粒在表面的推动。在这种情况下，表面和纳米颗粒的性质可以从广泛的材料组合中选择。然后，原子力显微镜的尖端被用来沿着预定的路径推动单个粒子，同时评估摩擦力。除了回答有关纳米摩擦学基本问题的长期问题外，这些研究还将能够解决实际应用中粒子的受控运动问题。在这个合作研究项目中，我们计划系统地研究这些效应，包括不同尺寸、形状和表面官能团的纳米粒子，以及不同环境中不同粗糙度、结构和化学组成的衬底，从液体到超高真空。实验研究与关于操纵过程本身以及粒子平移过程中界面原子过程的理论研究是一致的。

Atomic force microscopy (AFM) has proven to be a powerful tool to investigate frictional forces of nanoscale contacts. Unfortunately, this technique reveals some drawbacks when applied to study chemical and structural properties of two rubbing surfaces. The tips used in AFM are prefabricated. Consequently one of the two rubbing surfaces usually consists of a silicon compound and the effective size of the contact will be mainly determined by commercially available tip radii. However, urgent current questions concern the contact area dependence as well as the influence of the material on tribological properties. The contact area dependence of friction is crucial in bridging the gap between nanoscale and microscale friction, which eventually will allow us to understand and control macroscopic friction. The right choice of materials, on the other hand, is expected to lead to new friction effects, like, e.g., superlubricity.A solution of this problem is to use the AFM as a manipulation tool, through the controlled pushing of nanoparticles on the surface. In this case the properties of the surfaces and the nanoparticles can be chosen from a wide range of material combinations. The AFM tip is then used to push the individual particles along predefined pathways, while simultaneously evaluating the frictional forces. Apart from answering long-standing questions regarding fundamental issues in nanoscale tribology, these studies will be able to address issues of controlled motion of the particles for practical applications. In this cooperative research project we propose to investigate these effects systematically, addressing nanoparticles with different sizes, shapes and functional groups on their surfaces, as well as substrates with different roughness, structure and chemical composition in different environments, from liquids to ultrahigh vacuum. The experimental studies are harmonized with theoretical investigations concerning the manipulation process itself, as well as the interfacial atomic processes during particle translation.