Studies on vacuum arc evaporation behavior of modified graphite cathodes and influence on particle-induced defects in deposited (t)a-C films with and without dopant

在薄膜PVD工艺中，真空电弧工艺在沉积用于工具和部件的硬质耐磨涂层方面发挥着突出的作用。除了具有几乎完全电离的高能涂层等离子体外，其主要优点是具有强大的蒸发技术，可以在涂层的工业沉积过程中实现稳定和高效的过程控制。电弧法生产的超硬四面体非晶态碳（ta-C）涂层在这方面发挥了特殊作用。由于其几乎普遍良好的摩擦学性能，它们正在越来越多的应用中得到应用。电弧工艺虽然有上述优点，但也有其固有的缺点，即喷射出液滴或粒子，这与电弧的阴极点处汽化阴极材料的放电过程有着内在的联系。这种现象在ta-C涂层中特别明显，并导致沉积涂层中的缺陷和硬粗糙度峰，这使得涂层在许多应用中无法使用，或者需要在涂层后平滑方面付出很大的努力。在最近的工作中，这方面的一个基本新方面得到了证明：在石墨阴极中添加低元素（5% at%）的研究中，产生了掺杂的ta-C薄膜，其颗粒诱导的缺陷密度在一定程度上是相当可观的，最高可降低10倍。这种情况令人惊讶，因为蒸发的阴极仍然由95%的石墨组成。颗粒还原有很大的元素依赖差异。由此可见，B和Mo引起的粒子诱导缺陷密度非常强，而Si引起的粒子诱导缺陷密度几乎没有变化。掺杂剂在ta-C（:X）薄膜中的粒子还原现象是一个以前未被探索过的，科学上有趣的现象，应该被彻底研究和理解。本研究项目的总体目标是了解影响石墨和复合石墨阴极电弧蒸发过程中颗粒形成的关键因素，以及它们与生长(t)a-C:X薄膜的结合。阴极、等离子体和薄膜生长的过程和现象将在上下文中进行分析和考虑，以便了解对掺杂ta-C层中粒子减少的决定性影响，并从中得出合适的模型。

Among the thin film PVD processes, the vacuum arc process plays a prominent role in the deposition of hard and wear-protective coatings for tool and component applications. The main advantage, in addition to the presence of an almost completely ionized, high-energy coating plasma, is a robust evaporation technology that allows stable and efficient process control during industrial deposition of the coatings. Superhard, tetrahedral amorphous carbon (ta-C) coatings produced by arc processes play a special role in this context. Thanks to their almost universally favorable tribological properties, they are being used in an increasing number of applications. For all the mentioned advantages of arc processes, they also have an inherent disadvantage, namely droplet or particle emission, which is intrinsically linked to the discharge process at the cathode spot of the arc from the vaporized cathode material. This phenomenon is particularly pronounced in ta-C coatings and leads to defects and hard roughness peaks in the deposited coatings, which make the coatings unusable for many applications or require a great effort in post-smoothing the coatings. A fundamentally new aspect in this context has been demonstrated in recent work: In investigations with low element additions (5 at%) to graphite cathodes, doped ta-C films were produced which exhibited a particle-induced defect density that was in part considerable, up to a factor of 10 lower. This circumstance is surprising in that the evaporated cathodes still consisted of 95% graphite. There were large element-dependent differences in particle reduction. Thus, B and Mo caused a very strong, while Si caused almost no change in the particle-induced defect density. The phenomenon of particle reduction in ta-C(:X) films by dopants is a previously unexplored, scientifically interesting phenomenon that should be thoroughly investigated and understood. The overall objective of this research project is to develop an understanding of the key factors influencing the formation of particles during arc evaporation of graphite and composite graphite cathodes and their incorporation into the growing (t)a-C:X films. The processes and phenomena at the cathode, in the plasma and in the film growth will be analyzed and considered in context in order to understand the decisive influences on the particle reduction in doped ta-C layers and to derive suitable models from them.