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 (~ 120 nm) were deposited by pulsed laser deposition onto graphite substrates with varying surface roughness (Ra ranging from 5 nm to 2–3 µm). The as-deposited samples were irradiated at room temperature by 3 keV D3+ ions originating from an electron-cyclotron-resonance ion gun. Samples were exposed to D ions at angles between 0° and 70° and fluences in range of 1023 D/m2. 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 ~ 280 nm, we obtained an increase of the sputter yield with the angle up to a factor of five compared to 0°. In contrast, at the highest surface roughness in the 2–3 µm 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 μm, 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.