Nanoscale Effects on Gas Breakdown and Electron Emission
Abstract
Accurately predicting gas breakdown voltage is becoming increasingly important as the trendtoward electronics miniaturization incre"ases. Microelectromechanical systems (MEMS), such asmicroactuators, pressure sensors, and high-frequency circuits, require microsca"le gaps and highoperating voltages. Accurate breakdown voltage predictions for these systems will preventdischarges that could dam"age or destroy the device. Conversely, microplasmas usemicrodischarges for various applications, such as electric micropropulsion a""nd environmentalmitigation. From a directed energy perspective, present research trends focus on developing microandnano-vacuum el""ectronics for providing increased power densities and frequency for directedenergy applications, including radar platforms for ship""board and aircraft systems. In particular,the Air Force and Navy have ongoing efforts exploring the field emission characteristics"" of arraysof carbon nanotubes, particularly exploring the implications of distance between emitters andvariation of work function"" on electric field characteristics.Although field emission systems provide high current at low voltage, system miniaturizationintr"oduces potential issues due to space charge and electric field that may result in space-chargelimited flow and even gas breakdown. Recent research into microscale devices at atmosphericpressure has demonstrated that field emission dominates breakdown rather tha"n conventionalTownsend discharge, which drives breakdown for larger devices at lower pressure. Analyticexpressions that provide un""iversal curves that are consistent for both noble and non-noble gaseshave demonstrated the relationship between voltage, pressure,"" and gap distance for this breakdownbehavior at microscale; however, nanoscale behavior, such as surface roughness or defects,prov"ides a major challenge to comparing theoretical and numerical results to experimental data formicroscale and smaller gaps due its effect on critical parameters related to field emission.This proposal aims to elucidate the impact of nanoscale effects on gas break"down formicroscale and smaller gaps through a combination of experiment, numerical analysis, andtheoretical analysis. The proposal"" will first assess the impact of surface irregularities, which alterthe work function and field enhancement factors that drive fiel"d emission. This will entailperforming molecular dynamics simulations to determine the implications of surface roughness onboth el"ectron emission and space charge effects to provide data to put into continuum models ofgas breakdown. Additionally, experiments an""d analytic models will determine the impact ofsurface roughness and various flaws on surface on the work function, which measures t"he energynecessary to remove an electron from the cathode and plays a crucial role in the determining thefield emission current. F"inally, assessment and application of analytic models relating fieldemission and space-charge limited flow, both at vacuum and gene""ral pressure, will elucidate thepotential impact of space charge on field enhancement. This is one of the major hurdles inconsiste"ntly relating experimental results for gas breakdown at microscale to numerical andanalytic models.The proposed effort will then apply the information learned about nanoscale effects toexperimental and theoretical analyses of gas breakdown for microscale gaps and smaller.Experimental measurements will be performed for gaps from microscale to approximately 100 nmfrom vacuum to atmospheric pressure to provide a full parametric study of the mechanismsresponsible for breakdown across a wide range of parameters. Analytic and numerical modelsdeveloped by the Principal Investigator~s group will then be modified to incorporate the effects ofsurface roughness and space charge on field enhancement and work function and compared to the parametric experiments. Further studies will explore the coupling of the existing models to theone-dime
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 01, 2017
- Source ID
- N000141712702
Entities
People
- Allen L Garner
Organizations
- Office of Naval Research
- United States Navy
- University of Virginia