Analysis of Ion-Enhanced Field Emission and Field Emission-Driven Microdischarges

Microscale gaseous discharges under extremely small scale (< 10 μm) are quite different from their macro scale counterparts in many aspects. As recent research reveals, this difference is caused by ion-enhanced field emission, which refers to field emission that is activated by the uniquely high electric fields at the microscale and enhanced by ions generated from the discharge. By investigating several interesting examples of how microscale discharges behaves differently from large scale discharges, this dissertation reveals how field emission and microscale discharge interact with each other in detail.

The microscale breakdown phenomenon is studied by using PIC/MCC simulations. The study reveals the roles of ions and field emission (and their mutual relationship) and the extent to which ions enhance field emission and how this leads to breakdown. These simulations reveal that the net positive space charge that accumulates in the electrode gap enhances the electric field, subsequently enhancing field emission from the cathode. It is revealed that this coupling between field emission and the discharge is necessary in order for breakdown to occur. Quantum simulations are also carried out to investigate how ions generated from the discharge enhance the field emission in detail. The modified Paschen's curve is introduced to correctly predict microscale breakdown.

The PIC/MCC simulations also provide important information about the electron energy distribution of microscale discharges. A non-continuous distribution with discrete peaks corresponding to specific inelastic collisions is observed. The relative magnitude of these peaks and shape of the energy distribution can be directly controlled by the parameter pressure times distance (pd) and the applied potential across the gap. These parameters dictate the number of inelastic collisions experienced by electrons and as both increase, the distribution smoothes into a Maxwellian-like distribution.

The microscale glow discharge is selected as a post-breakdown example of how field emission interacts with microdischarge. A current-driven PIC/MCC mode is introduced to simulate microscale glow discharges, and the effect of field emission on the discharge is discussed.