Observation of microplasma light emission
in narrow discharge gaps
Marius Blajan, and Kazuo Shimizu
Innovation and Joint Research Center, Shizuoka University,
3-5-1 Jyouhoku, Hamamatsu, 432-8561, JAPAN; E-mail：blajanmarius@yahoo.com

Introduction
Microplasma
canbefoundinmany
applications. In the last years, the technology
was used in applications such as NOx removal,surface
treatment
andsterilization
orinactivation of bacteria.

A high intensity electric field (107-108 V/m)assures the formation of microplasma and acorresponding discharge current.

Negative
electrode Negative glow
(high voltage)

The fundamental phenomena of microplasma
discharge are not fully understood. The
development and optimization of microplasma
technologies depend on the clarification ofmicroplasma physics. Our microplasma is adielectric barrier discharge at atmosphericpressure.

The streamer diameter was proportionallywith the discharge gap and thinner thanpreviously reported.

Diameter
Ø~10 µmDiameterØ~10µm60 µm
Grounded Positive Faraday dark
spaceelectrode column

Experimental Setup(1)Microplasma Electrodes

Fig. 5 Phenomena of microdischarges.

High voltage

Grounded

electrodeelectrode(negative)

The electrodes consist in perforated metallic
plates covered with a dielectric layer.

100 µmEmission Spectroscopy
Emission spectrum was measured
camera shutter opened for 1 µs.

with18000

Intensity (a.u.)

Ø~3 µm(a)

16000
14000

Ar I

Ar I

12000
10000

Ar I

8000
6000

Ar I

Ar I

High voltage

4000
2000

Fig. 1 Microplasma electrodes

Emission spectrum was measured by aspectrometer, an ICCD camera and aphotomultiplier
tube.
Photosof
microdischarges
weretaken
usingamicroscope and a digital camera.
Gas flow rate: Ar, N2/Ar and O2/Ar at 10L/min.

410

415420425430435440

Wavelength (nm)

18000
Ar
0.5% N2 in Ar(b) N SPS
2N SPS

16000

214000electrode

30 µm

12000

N2 SPS

10000
8000

N2 SPS

6000
4000

N2 SPS

OH

Fig. 8 Photo of a streamer from microplasma
discharge.

2000
0280 300 320 340 360 380 400 420 440 460 480 500
Wavelength (nm)16000

Intensity (a.u.)

14000

(c)

12000

0.5% O2 in Ar
1% O2 in Ar
ArOH

10000

1.2

Negative pulse

0.8
0.6
0.4(a)
Right electrode active
Left electrode active

0.2

8000

06000

02000

1.2

Wavelength (nm)Fig. 6 Emission spectrum of microplasma in: (a) Ar;(b) N2/Ar; (c) O2/Ar at -1.2 kV.

Measuredarea

Gas flow(a)LeftelectrodeactiveMeasured area

Gas flow

Gas flow

Rightelectrodeactive(b)Fig. 3 Measured area of emission spectra: (a)outside the electrode; (b) in discharge gap.
(3) Electrical Characteristics

N2 molecules excited argon neutrals andreaction in argon plasma with N2 addition:
Ar*+ N2(X1Σg+)v=0 → N2(C3πu)v’=0 + Ar
Spontaneous radiation of formed excitedstate of nitrogen:N2(C3πu)v’=0 → N2(B3πg)v’’=0 + hνSpatial distribution outside of electrodes
shows a distribution of about 1 mm for theOH peak at 309 nm and 500 µm for the Ar Ipeak at 696.54 nm respectively.

Very small discharge gaps and relatively low
discharge voltages (about 1 kV)

Relative intensity (a.u.)

1.2OH peak 309 nm

1Ar I peak 696.54 nm
0.80.6
0.40.2Grounded electrode

00200

400

600

800

1000

Distance (um)Fig. 4 Waveforms of the discharge voltage,corresponding discharge current and gate signal forICCD camera.

Fig. 7 Spatial distribution of OH radical and Ar I
at the outside of grounded electrode forelectrode arrangement shown in Fig. 3 (a).

203040 50 60 70 80
Discharge gap (µm)

90 100

Negative pulse

1Intensity (arb. units)

300 302 304 306 308 310 312 314 316 318 320

10Negative pulse

0LeftelectrodeactiveNegative pulse

14000Fig. 2 Experimental setup.

electrode(negative)

Intensity (arb. units)(2) Experimental setup

0

Intensity (a.u.)Electrode size was 20 mm versus 40 mm foremission spectroscopy analysis. Discharge gap
was set from 30 μm to 100 μm in this study.
A Marx Generator with MOSFET switches aspulse power supply:•Output Voltage: -2 kV negative•Rise time: 100 ns•Pulse width: 1 µs

Grounded

0.80.60.4(b)Right electrode active

0.2

Left electrode active
0010203040506070Discharge gap (µm)

8090100Fig. 9 Spatial distribution of N2 SPS peak at 337.1
nm in the discharge gap as shown in Fig. 3 (b) for:(a) 5% N2 in Ar; (b) pure N2 discharge.
Spatial distribution inside the discharge gap
shows a higher intensity towards thegrounded electrode (anode). A more diffuse
discharge for the 5% N2 in Ar and higher
fluctuations for N2 discharge.

Conclusions•Emission spectrum of microplasma shown
intensity peaks of N2 SPS, OH and ArI.
•Spatial distribution of ArI peak at 696.54
nm and OH peak at 309 nm outside thegrounded electrode was measured up to 500µm for ArI peak and 1 mm for OH peak
respectively.
•Streamer diameter was proportionally withthe discharge gap.
•Spatial distribution of N2 SPS peak at 337.1
nm in the discharge gap shown a higher
intensity near the grounded electrode(anode).