Influence of surface roughness on the sputter yield of Mo under keV D ion irradiation

In this work the influence of surface roughness on the sputter yield of Mo under keV D ion bombardment was investigated for different impact angles. For this purpose, thin films of Mo (similar to 120 nm) were deposited by pulsed laser deposition onto graphite substrates with varying surface roughness (Ra ranging from 5 nm to 2-3 mu m). The as-deposited samples were irradiated at room temperature by 3 keV D-3(+) ions originating from an electron-cyclotron-resonance ion gun. Samples were exposed to D ions at angles between 0 degrees and 70 degrees and fluences in range of 10(23) D/m(2). The areal densities of the Mo marker layers were determined with Rutherford backscattering spectroscopy. For all the surfaces we observed a strong angular dependence of the sputter yield. For smooth and intermediate surface roughnesses, up to Ra similar to 280 nm, we obtained an increase of the sputter yield with the angle up to a factor of five compared to 0 degrees. In contrast, at the highest surface roughness in the 2-3 mu m range the sputtering yield decreases with increasing impact angle. The obtained data were compared to SDTrimSP-3D simulations. We obtained good agreement between the simulated and experimental sputter yield for surfaces for which we could provide high resolution atomic force microscopy (AFM) surface representations. As high-resolution surface mapping was not possible for surface roughness of 2-3 mu m, we found large deviation between the calculation and the measured data. The combination of measured and simulated data represent important input for predicting the erosion rates of surfaces at inner walls of thermonuclear fusion devices, which are expected to change surface roughness over time by sustained plasma exposure. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study found that the surface roughness has a significant influence on the sputter yield of Mo under keV D ion bombardment, with a strong angular dependence observed in the sputter yield. Smooth and moderately rough surfaces showed an increase in sputter yield at certain angles, while the highest roughness surfaces exhibited a decrease in sputter yield with increasing angle. The combination of measured and simulated data provides important insights for predicting erosion rates on surfaces in thermonuclear fusion devices.