Erosion Behaviour of Metal‐Doped Carbon Layers in Deuterium Low Pressure Plasmas and the Determination by Optical Emission Spectroscopy

Abstract

The erosion behaviour of doped carbon materials was investigated in deuterium low pressure discharges. Therefore, amorphous carbon films on silicon substrates (film thickness ∼1 µm) with varying dopant species (V, Ti and W), dopant concentration (between 1 at% and 8.5 at%) and dopant distribution were exposed to the plasma. The dopant distribution is either atomically disperse or, by heating up to 1100 K, carbide grains in nm size are formed. All important plasma parameters are obtained by a combination of several diagnostic techniques like optical emission spectroscopy, energy resolved mass spectroscopy and Langmuir probe measurements. The morphology of the plasma treated surfaces was investigated afterwards by scanning electron microscopy and atomic force microscopy, the layer composition by ion beam analysis. Every investigated sample shows a strong decrease of the erosion yield with increasing fluence. The achieved erosion yields are clearly below the yield of undoped amorphous carbon and depend strongly on the dopant concentration. The lowest yields were achieved with the samples with atomically disperse dopant distribution due to metal enrichment at the surface.

Compilation of erosion yields of metal-doped carbon materials by deuterium impact from ion beam and low temperature plasma

“…Unaffected by this, the relative yields are reliable as long as for the D γ and He signal constancy is shown, which was always proven [23]. Evaluating only the data above 1x10 24 The ion beam data reveal the same tendency of continuous decreasing (Fig.…”

“…Unfortunately, the plasma needs some time to stabilize, depending on thermal stabilization and material properties, like absorption, and the status of the vessel wall [23,25,26]. This leads to a large uncertainty of the yields for the presented measurement for the first fluences of 1x10 24 ions/m 2 after insertion of the specimen into the vacuum chamber.…”

“…Because the absolute yield is scaled by the weight loss and the integrated carbon flux over the whole exposure containing the stabilization zone [23], measurements with lower total fluences exhibit a higher uncertainty in the yield scaling.…”

“…The total C flux was scaled 6 to the weight loss. Details to the photon flux calibration and further experimental details can be found in [23,24]. The measurements on pure graphites indicate constant, i.e., steady state erosion yield for plasma exposure (Fig.…”

“…In a small vacuum chamber (15 cm diameter, 10 cm height) specimens of maximal size of The overall erosion yield (eroded C atoms per incident ion) was gained from weight loss measurements scaled to the accumulated ion fluence and its fluence dependence from optical emission spectroscopy (OES) [23,24]. The time evolution of the photon flux of the C 2 swan and the CD Gerö band were measured to obtain the fluence dependent flux of eroded carbon, while the Balmer line D γ and a He line indicated the stability of the plasma.…”