Low-energy xenon ion sputtering of ceramics investigated for stationary plasma thrusters

Abstract

The low-energy sputtering of boron nitride, magnesium oxide, boron nitride and aluminum nitride ͑BNAlN͒, and boron nitride and silicon oxide (BNSiO 2 ) by xenon ions of bombarding energies 350, 500 eV, and 1 keV was studied experimentally. In order to measure the ion current without being significantly disturbed by slow ions, only planar probes were used during short duration sputtering experiments ͑of the order of 10 h͒. Moreover, slow ion current contribution was estimated by numerical simulations and subtracted from each ion current measurement. It was found that the ion-beam incidence effect on sputtering yields was not as important as for theoretical results or experimental results on quasinonrough solid surfaces, for which it is possible to observe a more pronounced angular dependence of the sputtering yield. This phenomenon is due to surface irregularities of ceramic materials and because of surface roughness the macroscopic sputtering yield should actually result from the convolution of the microscopic sputtering yield by the angular distribution of surface facet incidences. The irregular surface structure of ceramics like BNSiO 2 or BNAlN seems to be sputtered differently due to a differential erosion from grain to grain and from grain to surrounding matrix. This uneven erosion may be explained by the wide angular distribution of facet incidences of surface microprofiles and the various binding energies in the selvage of material. Finally, the dependence of sputtering yield at normal incidence on ion energy, in the range 0.35-1 keV, is almost a linear one.

Total and Differential Sputter Yields of Boron Nitride Measured by Quartz Crystal Microbalance and Weight Loss (Preprint)

“…The weight measurements were taken after the weight of the samples reached steady-state (it was checked that the weight increase is approximately the same for different samples). Similar effect was reported by Garnier 29 . …”

“…Where possible, we compare the measured yields with those from the limited published measurements. Figure 7a shows our HBC and HBR 350 eV measurements along with weight loss measurements by a Garnier et al 29 Figure 7b shows comparison with measurements by Garnier 29 at 500 eV and also shows reasonable agreement. Note that the lowest sputtering energies reported in these comparison studies were 300 eV by Britton 30 and 350 eV by the Garnier 29 , and apart from our own work we are not aware of other measurements below 300 eV.…”

Predicting Hall Thruster Operational Lifetime

“…Figures 8 and 9 show the data of boron nitride sputter yields as a function of incident angle and energy. 13 Corresponding curve fits are also shown. Figure 8 displays the angular dependence of the normalized sputter yield.…”

Use of emission spectroscopy for real-time assessment of relative wall erosion rate of BHT-200 hall thruster for various regimes of operation

“…Thus, assuming the emission intensity is linearly proportional to the Boron density, the observation indicates that the erosion rate increases One explanation for the dramatic increase in the Boron erosion rate for increased discharge voltage is that the ions impacting the thruster ceramic walls have much higher energies for high-voltage cases. Experiments of Boron Nitride bombarded by Xe + show that sputtering yield increases as the ion energy impinging on the surface increases [5,22,23,24].In addition, it is expected that the plasma temperature increases as the discharge voltage is increased.Such an increase in plasma temperature would increase the electron induced excitation collision rate, thus the emission intensity. In addition, increased plasma temperature would result in an increase in the wall temperature.…”