Bulletin of the American Physical Society
64th Annual Gaseous Electronics Conference
Volume 56, Number 15
Monday–Friday, November 14–18, 2011; Salt Lake City, Utah
Session SF2: Microdischarges II |
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Chair: Steve Adams, AFRL Room: 255E |
Friday, November 18, 2011 8:00AM - 8:30AM |
SF2.00001: Microdisharges: novel designs and novel materials Invited Speaker: Following an initial surge in microdischarge applications, research in this area has followed two main approaches, with one approach focused on expanding the range of applications for both new and existing devices and the other approach concentrating on understanding the basic physics underlying device operation in these small-volume, high-pressure discharge devices. Despite the application of increasingly sophisticated diagnostic methods, there are still many areas where understanding is, at best, limited. The research reported here centres on understanding the importance of the materials used to fabricate microplasma devices, focusing on the operational behaviour of microhollow cathode discharges. We operate a range of devices that include discharges constructed from simple metal-insulator-metal sandwich structures, Si-SiO2-metal devices fabricated on silicon wafers and, most interestingly, diamond-diamond-metal devices fabricated using a combination of diamond CVD deposition and microlithography. We report on the effect of materials on device ignition, breakdown voltage, and IV characteristics, and we make tentative conclusions about device lifetimes. We will also report on new work involving novel geometries for microhollow cathode discharges, including multi- electrode devices. [Preview Abstract] |
Friday, November 18, 2011 8:30AM - 9:00AM |
SF2.00002: Spatially-resolved diagnostics of 1-GHz microdischarges Invited Speaker: This talk addresses the internal structure of atmospheric pressure microdischarges powered in the $f \sim $ 1 GHz frequency regime. Microwave power is focused into a sub-millimeter discharge gap using a resonating microstrip transmission line. The advantages of microwave excitation over low frequency operation include low power and discharge voltage ($<$1W, $<$ 100 V), no ion sputtering ($f$ $>$ $f_{pi})$, and stable steady-state cold plasma generation. Metastable argon density and the gas temperature were estimated by the optical absorption transition in Ar (1s$_{5}$-2p$_{8})$ at 801.4 nm using a laser diode focused to $\sim $30 microns. The gas temperature was estimated from the Ar line broadening due to collisions. Able inversion of the line-integrated density shows that the 200-micron wide central core of the microplasma is depleted of metastable atoms. Spatially-resolved continuum optical emission from electron recombination, however, shows that the microdischarge has a dense electron core. Gas temperatures are difficult to accurately extract from optical diagnostics due to the extreme depletion of commonly-used spectroscopic species from the microdischarge's central core (e.g., N$_{2}$, OH\c{ } Ar$^{m})$. In the case of the argon metastable line broadening, the higher density of Ar$^{m}$ in the peripheral regions masks the line width within the core. Numerical modeling interpolates the microplasma's core temperature based on measurements around the periphery. The model shows that the core temperature exceeds 1600 K, even though spatially-averaged nitrogen rotational spectra suggest that the gas temperature is typically only 400 K. Diagnostics are important to the successful development of microplasma applications. The presentation concludes with an example of low-temperature microplasma deposition using acetylene at 1 atm, and a discussion of scaling single microplasmas to long linear arrays that are appropriate for roll-to-roll plasma processing at atmospheric pressure. [Preview Abstract] |
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