Sputtering of tungsten nano-pyramids

The lifetime of plasma facing components in nuclear fusion reactors is strongly dependent on their erosion properties [1]. Materials with lowest possible sputtering yields are therefore highly desirable. While tungsten itself is a good choice as a first wall material due to its performance [2], the question arises if erosion rates can be further reduced by specific nanostructuring of the material's surface. It is known that surface roughness can lower the sputtering yields. This reduction was already demonstrated for structures with Gaussian distributed height values [3, 4] and also for highly oriented structures in the form of nano-columns [5, 6]. In this work, we focus on investigating the sputtering properties of tungsten nano-pyramids, which were obtained by depositing a 500 nm tungsten coating on top of chemically etched silicon substrates. The pyramidal surfaces were exposed to 2 keV Ar+ ion bombardment and the eroded particles were collected employing a quartz crystal microbalance as a catcher. In addition, simulation programs based on the binary collision approximation were used to model the ion-solid collisions [7]. First results regarding the emission profiles show that comparably large amounts of particles are emitted backwards, towards the direction of the incoming ion beam. While this effect might partially result from the specific pyramidal topography, other possible hypotheses including crystallinity effects are also conceivable. Nevertheless, the global sputtering yield of nano-pyramids was found to be reduced by approximately 50% compared to a flat reference sample.