Understanding the depletion of electrons in dusty plasmas at atmospheric pressure
Understanding the depletion of electrons in dusty plasmas at atmospheric pressure
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DOI：
10.1088/1361-6595/ab9cc3
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发表时间：
2020-07-01
影响因子：
3.8
通讯作者：
Sankaran, R. Mohan
中科院分区：
文献类型：
--
作者：
Abuyazid, Nabiel H.;Chen, Xiaoshuang;Sankaran, R. Mohan
利用常压等离子体系统在气相中进行NPs的成核和生长是合成新型尺寸控制材料的重要途径。在这里，我们研究了NPs对典型类型的连续流动、无衬底的大气压等离子体的影响，以了解它们对电子密度变化的潜在贡献。建立了串联等离子体系统，包括一个等离子体反应器，从氩气和己烷的混合物中产生碳质NPs，另一个相同的等离子体反应器，在那里注入生长的粒子并进行非侵入式电学和光学测量。通过电导率测量和等离子体流体模型得到的电子密度在np的存在下下降。然而，对照实验表明，电子耗竭的主要来源不是粒子本身，而是残余蒸气或以分子种或纳米团簇形式存在的反应副产物。常数蒙特卡罗模拟结果表明，在实验测量条件下，NPs没有足够高的浓度来降低电子密度；然而，如果分子或簇是可电离的，它们保持足够的浓度以耗尽电子密度。我们的研究表明，在大气压下，由于它们通常具有更大的电子密度值，产生粒子的等离子体与低压下的等离子体不同，纳米颗粒的形成不会产生相同的影响，而分子尺度的物种可能是一个更重要的考虑因素。
The nucleation and growth of NPs in the gas phase using atmospheric-pressure plasma systems is an important approach to synthesizing novel dimensionally-controlled materials. Here, we investigated the effect of the NPs on a typical type of continuous-flow, substrate-free plasma at atmospheric pressure to understand their potential contribution to electron density changes. A tandem plasma system was set up consisting of one plasma reactor that produced carbonaceous NPs from mixtures of argon and hexane, and another identical plasma reactor where the as-grown particles were injected and non-intrusive electrical and optical measurements were performed. The electron densities obtained from conductivity measurements and a plasma fluid model were found to decrease in the presence of NPs. However, control experiments revealed that the main source of the electron depletion was residual vapor or reaction byproducts in the form of molecular species or nanoclusters and not the particles themselves. These results were validated by constant number Monte Carlo simulations which showed that at the experimentally-measured conditions, the NPs were not of sufficiently high enough concentration to reduce the electron density; however, if molecules or clusters are ionizable, they remain in sufficient concentration to deplete electron densities. Our study shows that at atmospheric pressure, because of their typically larger electron density values, particle-producing plasmas are distinct from those at low pressure, and nanoparticle formation does not have the same impact while molecular-scale species may be a more important consideration.