Temperature of Particulates in Low‐Pressure rf‐Plasmas in Ar, Ar/H₂ and Ar/N₂ Mixtures

Abstract

The temperature of micro-particles, confined in the sheath of a capacitively coupled low-pressure rf-discharge in front of an Adaptive Electrode, has been measured for different plasma conditions and in different gas mixtures by using temperature-dependent optical features of the particles. In the range from 10 to 50 Pa, the temperature increase with rising discharge power is found to be more pronounced at low pressures than at higher pressures. Addition of molecular gases to the argon-plasma may either result in a temperature decrease (as in the case of nitrogen) or in additional heating of the particles (when hydrogen is added). The measured particle temperature is discussed with respect to appearing plasma-particle interactions which contribute to the particle's energy balance.

On the heating of nano- and microparticles in process plasmas

“…Commonly, particles and surfaces in plasmas tend to be negatively charged [23][24][25][26][27][28][29][30][31][32][33][34][35] due to the much larger mobility of plasma electrons compared to that of positive ions. As the temperature of electrons in non-thermal plasmas is significantly higher than that of heavy species, the collection of electrons is even more pronounced in cold plasmas.…”

“…The electronic and energetic conditions at the surface of small particles in low pressure plasmas are affected by their size and geometry [36][37][38][39]. Quickly a balance is archieved [23,33,34], resulting in the establishment of an equilibrium temperature T µ .…”

“…Several studies addressed the grain temperature, both theoretically [39][40][41][42] and experimentally [33,34,[43][44][45][46][47]. For example, Daugherty and Graves measured the temperature-dependent decay time of the fluorescence of manganese activated magnesium fluorogermanate particles in a pulsed argon discharge during the plasma-off phase [43].…”

“…The experimental setup (PULVA-INP) as well as the procedure for the measurement of the particle temperature by temperature-dependent fluorescence have been extensively described elsewhere [33,34]. The plasma parameters n e and V e ,, measured by a Langmuir probe, show pronounced differences under admixture of molecular gas as depicted in figs.…”

“…The accommodation coefficient of the microparticles is estimated to be α μ ≈ 0.86 [34,47]. The emissivity is estimated to be ε = 0,5 [58].…”