Microplasma Source Of High Energy Electrons

Microplasmas have emerged over the last ten years as an important direction for plasma development, providing moderate (>1 torr) and atmospheric pressure discharges at modest power input that are being widely investigated for applications ranging from catalysis, reforming processes, remediation, to surface treatment and manufacturing. Many of these applications use discharges with hollow cathodes. Microdischarges based on hollow anode geometry have gained interest due to nonlocal electron energy distribution offering possibilities of controlling the electron energy distribution function. We have designed and tested a microplasma electron source based on hollow anode geometry and operating in a dc regime. The hollow anode plasma electron source was tested with N
2
, CO
2
, and CH
4
/CO
2
as operating gases and characterized using optical emission spectroscopy and electrical probe diagnostics. The results show that the hollow anode source has higher electron energy and lower density compared to a hollow cathode arrangement operating under similar experimental conditions. The microplasma electron source is stable at voltages of 400 – 800 V, and current <1 mA in a pressure range of 2 – 10 torr, suitable for use in an Environmental Scanning Electron Microscope. Tests of the plasma source in an ESEM demonstrate the possibility of surface modifications and diagnostics (such as measuring surface composition or cluster growth on the surface) without the need for sample removal or transfer.