Generation of a capacitively coupled microplasma and its application to the inner-wall modification of a poly(ethylene terephthalate) capillary

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Abstract
A parallel-plate capacitively coupled microplasma excited by a conventional operating frequency of 13.56 MHz has been generated both in a quartz tube with an inner radius of 1 or 2 mm and in a capillary, whose cross section is 65–500 μm×500–5000 μm, on a 20 mm×20 mm quartz chip. To attain a plasma ignition at a low rf power without reflection, a π-type matching circuit was miniaturized and suitably designed to satisfy the resonance condition with the excitation frequency, so that an atmospheric He discharge was obtained at an incident power of 1–3 W. The atomic excitation temperature in the atmospheric discharge was evaluated to be about 1900 K in terms of the atomic emission spectrum. Low-power (2–3 W) glow discharge of pure Ar was also attained at the pressure p given by (pd)min=0.5–0.8 Torr cm, where d is a discharge gap. The microplasma was applied to the inner-wall modification of a poly(ethylene terephthalate) (PET) capillary to demonstrate the electro-osmosis flow (EOF) control on a microcapillary electrophoresis (CE) chip. We found that the mobility of the EOF (μEOF) of the PET capillary treated by the downstream O2 plasma was 5.1×10−4 cm2/V s, which is about three times larger than that of the untreated PET capillary.

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