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，真空电弧工艺在工具和部件用硬涂层和耐磨涂层的沉积中起着重要的作用。除了几乎完全电离的高能涂层等离子体的存在外，主要优势是强大的蒸发技术，允许在工业沉积涂层期间进行稳定和高效的过程控制。在这一背景下，由电弧工艺制备的超硬四面体非晶碳(ta-C)涂层扮演着特殊的角色。由于它们几乎普遍具有良好的摩擦学性能，它们正被越来越多的应用所使用。尽管有上述所有电弧工艺的优点，但它们也有一个固有的缺点，即液滴或颗粒排放，这与电弧阴极点从蒸发的阴极材料放电的过程内在地联系在一起。这种现象在TA-C涂层中尤其明显，并导致沉积涂层中的缺陷和硬粗糙度峰，这使得涂层不能用于许多应用或需要付出巨大的努力来对涂层进行后光滑处理。在这一背景下，最近的工作展示了一个全新的方面：在对石墨阴极进行低元素添加(5at%)的研究中，制备出了掺杂的ta-C薄膜，其颗粒诱导的缺陷密度部分相当大，最高可低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。在颗粒还原上存在较大的元素依赖性差异。因此，B和Mo引起的颗粒诱导缺陷密度很强，而Si引起的颗粒诱导缺陷密度几乎没有变化。掺杂使Ta-C(：X)薄膜中的颗粒减少的现象是一个以前未被探索过的、具有科学意义的现象，应该被彻底地研究和理解。本研究项目的总体目标是了解影响石墨和复合石墨阴极在电弧蒸发过程中颗粒形成的关键因素以及它们在生长的(T)a-C：X薄膜中的结合。对阴极、等离子体和薄膜生长中的过程和现象进行分析和考虑，以了解对掺杂的Ta-C层中颗粒还原的决定性影响，并从中推导出合适的模型。

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.