A method for uniformly coating powdery substrates by magnetron sputtering

DC magnetron sputtering was used to coat fine-grained powders, i.e. hollow glass microspheres (particle diameter approx. 2–70 μm). To accomplish the exposure of the whole surface of each powder particle the powder was put into a rotating vessel which makes the particles tumble so that they are coated uniformly. However, there are problems of sticking and cluster formation of the powder during the sputtering process, which prevent the complete coating of the particles. To resolve this issue a concussion mechanism had been used which now was completely redesigned for better upscalability. This newly designed mechanism is based on gravity and will be described in this work as well as its ability to deposit metal and oxide films on powder particles. For the better understanding of the trickling behaviour of the used particles (glass microspheres), experiments addressing this behaviour with regard to different particle size distributions have been carried out in vacuum with the concussion mechanism and without it. Furthermore the influence of the sputter beam is taken into account. It will be shown that it is possible to coat powders, which strongly tend to agglutinate in vacuum and even more under sputter conditions, by using the new concussion mechanism.