Normal glow discharges in micrometer scales are being widely studied for a variety of ultra ne processing technologies. DC glow discharge characteristics were investigated at an atmospheric pressure in the range of 0.1-1.65 MPa. The operational discharge characteristics such as voltage-current (V -I) measurement, discharge size, gas temperature, vibrational, and rotational temperatures were obtained for helium (He) and nitrogen (N 2 ) gases. Optical emission spectroscopy studies were carried out to measure rotational and vibrational temperatures using the nitrogen second positive system. Discharge above atmospheric pressure was characterized for the current range of 0.1-1.2 mA and an electrode gap of 5-250 µm. This paper presents evidence for a discharge size as small as 7 µm in N 2 and 16.7 µm in He, while operating at a low current of 0.5 mA and at high pressures of 1.65 and 0.34 MPa, respectively. To the best of our knowledge, this is the rst time an experimentally obtained normalized current density corrected with effective pressure has been estimated to be close to an analytical value (400 µA cm −2 Torr −2 ) for N 2 using a stainless-steel cathode at above atmospheric pressure. The observation of the breakdown of two different gases (N 2 and He), the V -I characteristics, and high current densities indicate that microplasma exhibits a stable glow discharge when a low capacitance external circuit is used. Rotational and vibrational temperatures are obtained in the ranges of 1186-2894 K and 4208-3608 K, respectively, for the pressure range of 0.10-1.65 MPa in N 2 gas for a constant discharge current of 0.5 mA and an electrode gap of 150 µm. It is also notable that the transition from non-equilibrium to equilibrium discharge in both rotational and vibrational temperatures was observed in N 2 at 0.86 MPa, without the transition to thermal plasma (arc discharge).

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