Project "DVD III"
The research group of Prof. Haydn Wadley, University of Virginia (USA), has developed and continuously optimized a special technology for the vacuum coating preferably of parts, fibers, foams and powders during the past years. Compared to conventional PVD methods, this technology is characterized by improved material utilization and the ability to deposit vapor even on surfaces without direct „line-of-sight“ contact to the vapor source. The core elements of this technology, known as „Directed Vapor Deposition“ (DVD), are the contamination-free evaporation of the layer-forming material by means of electron beams of high power density combined with focusing and directed transport of the vapor particles in carrier gas streams. The admixture of reactive gas as well as the co evaporation of different materials are also possible, whereby the carrier gas ensures uniform mixing of the constituents and thus promotes the (reactive) deposition of compounds with homogeneous composition.
Fraunhofer FEP has contributed to the implementation of this process idea with special electron beam and plasma sources for the low-vacuum range. A certain disadvantage of the DVD process is that the increased working pressure leads to scattering and energy loss of the vapor particles, which adversely affects film growth. By means of plasma activation, however, these problems can be overcome and coatings can be deposited in the desired morphology. This can be controlled by the plasma parameters, whereas the directivity of the vapor stream must not be disturbed and universal applicability to a wide range of materials is required. Therefore, a „multi-jet hollow cathode“ plasma source was developed for „DVD III“. Activation of the vapor is achieved by four symmetrically acting hollow cathode arc discharges sequentially fed by a single MF pulse power supply.