In this work, the interactions between low-pressure plasmas and nanoparticles are studied with numerical models aimed at understanding the phenomena that affect the nanoparticles charge, charge distribution, heating, and crystallization dinamycs. At the same time other phenomena that affect the plasma properties resulting from the presence of nanoparticles are also studied: they include the power-coupling to the plasmas, the ion energy distribution and the electron energy distribution.
An analytical model predicting the nano-particle charge and temperature distributions in a low pressure plasma is developed. The model includes the effect of collisions between ions and neutrals in proximity
of the particles. In agreement with experimental evidence for pressures of a few Torr a charge distribution that is less negative than the prediction from the collisionless orbital motion limited theory is obtained. Under similar plasma conditions an enhanced ion current to the particle is found. Ion-electron recombination at the particle surface, together with other particle heating and cooling mechanisms typical of silane-argon plasmas, is included in a particle heating model which predicts the nano-particle temperature. The effect of plasma parameters on the nano-particle temperature distribution is discussed and the predictive power of the model is demonstrated against experimental evidence of temperature induced crystallization of silicon nano-particles.
The power coupled to the plasma is measured together with the impedance nature of the plasma, in the case of a pristine and dusty plasma. Nanoparticles are shown to strongly affect the electrical properties of the plasma, resulting in a much more resistive discharge.
A study of the ion energy distribution of ions impinging the sruface of nanoparticles is carried out and shows that ion-neutral collisions in proximity of the surface of the nanoparticle not only affects the particle charge but also the average energy of ions bombarding the particle surface. Finally the presence of nanaparticle in the plasma and their ability to selectively interact with electrons in a specific energy range is studied to the extent of investigating the effects of the presence of particles on the electron energy distribution of electrons.
University of Minnesota Ph.D. dissertation. Major: Mechanical Engineering. Advisor:Prof. Uwe R. Kortshagen. 1 computer file (PDF); xiii, 142 pages.
Charge and energy interactions between nanoparticles and low pressure plasmas..
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