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Fig. 2


Time taken for plasma deposition (sputtering) to grow (remove) a monolayer, τmono (Eq. (25)), asa function of atmospheric gas pressure, pgas . We note that pgas acts as a proxy for atmospheric height and in general does not reflect the true local pressure. τmono is shown for an electron temperature Te = 1 eV and degrees of ionisation fe = 10−7 (dash), 10−4 (dot) and 1 (dot-dash). The light blue bands shows the effect of varying the electron temperature from Te = Tgas (upper boundary) to Te = 10 eV (lowerboundary), for each degree of ionisation. In this paper fe is treated as a parameter and is varied, from the values calculated in DRIFT-PHOENIX, to incorporate expected values from various non-thermal ionisation processes beyond thermal ionisation. As a consequence, as the number density of the electrons, ions and neutral particles change, the local gas pressure will change and deviate from its original DRIFT-PHOENIX calculated value. Therefore, the atmospheric pressure in the plots presented here act as a proxy for atmospheric height and in general doesn’t reflect the true local pressure. For comparison, also plotted is the time taken to grow or remove a monolayer of material through neutral gas-phase surface chemistry using DRIFT-PHOENIX: , where the total net growth of the dust grain is |χnet |, for the example atmospheres (Fig. 1) given by Teff = 2400 K, log g = 5.0 (cyan); Teff = 2400 K, log g = 3.0 (magenta); Teff = 1500 K, log g = 5.0 (green); and Teff = 1500 K, log g = 3.0 (red). At high atmospheric pressures the numerical jitter in corresponds to transitions between growth rates (χnet > 0) and evaporation rates (χnet < 0).

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