UC Merced

Microplasmas have been receiving significant attention due to their miniaturized sizes, low power requirement, and overall desirable characteristics and exciting potential applications. To be able to take advantage of these characteristics, a solid understanding of the electron dynamics, heating mechanisms and the influence of different variables such as pressure, gap size, frequency, field emission and input power on microplasmas is required. This work mainly attempts to help readers obtain a better understanding of the fundamentals of argon microplasmas operating under various conditions including direct current and microwave regimes. The electron dynamics and heating mechanisms, as well as the influence of parameters mentioned above, are explored using a one-dimensional kinetic method called Particle-in-Cell with Monte Carlo collisions (PIC-MCC). The plasma density, potential, electric field, and electron temperature obtained from PIC-MCC are considered as the benchmark for comparing with the results obtained from continuum simulations using an in-house fluid model. The comparison demonstrates large discrepancies between the results under certain conditions implying the importance of calibrating the input transport properties used in continuum models. The quantitative understanding of the limitations of continuum simulations and techniques to improve their predictive capability are crucial to maximize the role of computations in understanding the operation of future microplasma devices. In addition, the role of the excitation frequency, pressure, and total power absorbed by the microplasma are studied for a range of microwave frequencies (1GHz-320GHz). The results indicate that the microplasma dynamics, for example, the number density profile and its peak location are governed by a rich interplay of several physical mechanisms which is a combination of pressure, frequency and the relative magnitudes of plasma frequency, electron momentum transfer collision frequency, and the angular excitation frequency. The final objective of the current work is to determine the role of field emission on operating modes of microwave microplasmas. The PIC-MCC simulations predict operation in two modes; an α-mode characterized by a positive differential resistance with negligible influence of boundary processes and a γ-mode with significant field-induced electron emission.