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L. Stöttinger, A. Eder, G. Schmid, C. Eisenmenger-Sittner:
"Deposition of metallic coatings on transparent, non conductive granulates: a comparative study of the performance of two different coating mechanisms";
Poster: 20th International Vacuum Congress (IVC-20), Busan/Korea; 21.08.2016 - 26.08.2016.

The modification of the surface properties of granular or complexly shaped materials plays an increasingly important role in materials science and design, energy harvesting and storage and nano-bio applications. For instance the electrical conductivity of ceramic or dielectric materials can be drastically increased by the deposition of metallic coatings.
If Physical Vapor Deposition (PVD) methods are used to deposit the coatings, thorough intermixing and the prevention of agglomerations is paramount for the production of homogenous coatings with high thickness uniformity. A system capable of this task for small quantities of granulate is described in [1].
In this work the deposition system given in [1] was upscaled to handle quantities of about one litre of granulate. Two different mechanisms of granulate agitation, one based on the concussion mechanism given in [1] and one based on mechanical agitation by springs is presented. The latter mechanism principally bears the possibility to heat, cool or to apply a defined bias voltage to the granulate container by a central feedthrough.
Copper coatings of approximately 20 - 50 nm thickness were deposited on S38 hollow glass microspheres manufactured by 3M [2]. The mean diameter of the spheres is 20 µm with individual sizes ranging from 10 - 80 µm. Since both, coating and granulate, are transparent to visible light, the film thickness could be assessed by optical transmission measurements on the spheres. The thickness uniformity on single spheres as well as on large batches of spheres was comparable for both deposition mechanisms. Also the long time performance of the mechanism based on mechanical agitation by springs proved to be comparable to the concussion mechanism described in [1]. Therefore it can be concluded that both coating set-ups are capable of depositing uniform films on granulates with mean diameters ranging from 10 - 100 µm in quantities of up to one litre.
This work was supported by the Austrian Science Fund (FWF), Grant Number TRP-281

[1] G.H.S. Schmid, C. Eisenmenger-Sittner, Surface & Coatings Technology 236 (2013) 353-360
[2] http://multimedia.3m.com/mws/media/694361O/3m-glass-bubbles-s38.pdf, accessed 2016-03-28