Atomic Wear

轴承或齿轮等机械部件的磨损限制了机器的使用寿命，并导致运营和原材料成本增加以及工厂停工时间。避免各种应用中的磨损和磨蚀具有巨大的经济和生态利益。经典的表面磨损理论将磨损分为粘着磨损和磨粒磨损。前者描述了表面的部分分离，而后者的过程的特征在于较软的表面被较硬的相对表面的凹凸不平所犁削。对潜在的原子磨损过程的一般微观理解还不存在。分析这些过程的一个有用的方法是分析单个微凸体的磨损。特别是原子力显微镜已被证明是一个有价值的工具，因为它的几何形状非常类似于理想的单一粗糙contact.New磨损模型，近年来已被激发的摩擦力显微镜研究的实验结果。纳米级接触的原子磨损具有非常低的值，每毫米滑动距离仅一个原子。因此，最近的方法来描述的过程模型，它作为分离的单个原子从表面上，克服能量障碍的速率与速率方程建模。尽管速率理论的首次成功应用，它只是几种可能的描述之一，验证原子磨损速率模型的关键实验将是系统测量纳米级接触的磨损作为温度的函数。这种实验迄今尚未进行，这是本提案的主要重点。一个中心问题是：在多大的温度下，原子磨损由热激活主导？在非常低的温度下，人们会期望过渡到非热磨损，遵守机械化学原理，即通过力的相互作用形成/破坏化学键。测量将使用三种模型材料系统进行，重点关注原子磨损的不同方面。在微真空条件下，利用摩擦力显微镜研究了离子晶体、聚合物和金刚石表面的原子磨损机理。对于速率模型的直接验证，将磨损量化为样本温度的函数。样品冷却/加热阶段允许评估从30 K到700 K的大温度范围。我们的中心项目的目标是找到和了解预期的过渡，从热激活到非热原子磨损过程。

The wear of mechanical components like bearings or gears limits the life time of machines and results in increased costs of operation and raw materials as well as down times of factories. Avoiding wear and abrasion in various applications is of enormous economical as well as ecological interest. The classic theory of surface wear distinguishes between adhesive and abrasive wear. The former describes the detachment of parts of the surface, while the latter process is characterized by the plowing of the softer surface by the asperities of the harder counter surface. A general microscopic understanding of the underlying atomic wear processes does not exist. A useful approach for the analysis of those processes is to analyze the wear of individual asperities. In particular the atomic force microscope has proven to be a valuable tool, since its geometry closely resembles the ideal single asperity contact.New wear models have in recent years been motivated by experimental results from friction force microscopy studies. The atomic wear for nanoscale contacts has extremely low values of only one atom per millimeter sliding distance. As a consequence recent approaches to describe the process model it as the detachment of individual atoms from the surface, where the rate of overcoming the energy barrier is modelled with the rate equation. Despite the first successful applications of the rate theory, it is only one of several possible descriptions.The key experiment to verify the rate model for atomic wear would be the systematic measurement of the wear of nanoscale contacts as a function of temperature. Such an experimental has not been conducted so far, and is the main focus of this proposal. One central question is: Up to which temperatures is atomic wear dominated by thermal activation? At very low temperatures one would expect a transition to athermal wear, obeying the principles of mechano-chemistry, i.e. the formation/breaking of chemical bonds by force interactions. The measurements will be conducted with three model material systems, to focus on different aspects of atomic wear. Using a friction force microscope in ultrahigh vacuum conditions the atomic wear mechanisms will be studied on ionic crystals, polymers as well as diamond surfaces. For the direct verification of the rate model the wear will be quantified as a function of sample temperature. A sample cooling/heating stage allows assessing a large temperature range from 30 K to 700 K. Our central project goal is to find and understand the anticipated transition from thermal activated to athermal atomic wear processes.