Light emission of microdisharges in microplasma
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,surfacetreatment
andsterilization
orinactivation of bacteria.

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

Negativeelectrode 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.

Diameter
Ø~10 µm60 µm(1)Microplasma Electrodes

Ø~10µmHigh voltage

Grounded

electrodeelectrode(negative)

Grounded Positive Faraday dark
spaceelectrode column

Experimental Setup

Diameter

100 µmFig. 5 Phenomena of microdischarges.

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

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

Ø~3 µm

with

18000

(a)

Intensity (a.u.)

16000
14000

Ar I

Ar I

12000
10000

High voltage
Ar I

8000
6000

Ar Ielectrode

Ar I

4000
2000

Fig. 1 Microplasma electrodes

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

410

415

420

425

430

435

440

30 µm

Wavelength (nm)

18000
16000
14000

Ar
0.5% N2 in Ar(b) N SPS
2N SPS
212000Fig. 8 Photo of a streamer from microplasma
discharge.

N2 SPS

10000
8000
6000
4000

1.1

N2 SPSN2 SPSOH

2000
0280 300 320 340 360 380 400 420 440 460 480 500
Wavelength (nm)Intensity (arb. units)(2) Experimental setup

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

Negative pulse

LeftelectrodeactiveMeasuredarea

Gas flow(a)LeftelectrodeactiveMeasured area

Gas flow

Gas flowRightelectrodeactive(b)0.90.80.7

Spatial distribution outside of electrodes
shows a distribution of about 1 mm for theOH peak at 309 nm and 500 µm for the Ar I
peak at 696.54 nm respectively.
1.2(3) Electrical Characteristics
Very small discharge gaps and relatively low
discharge voltages (about 1 kV)

Relative intensity (a.u.)

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

OH peak 309 nm

1Ar I peak 696.54 nm

0.5102030405060708090100

Discharge gap (µm)
1.2
1.1
10.9
0.8
0.7
0.6
0.50.40.30.20.1
0Negative pulse

Negative pulse

Right electrode active
Left electrode active(b)0102030405060708090100Discharge gap (µm)

Fig. 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.

0.8Conclusions

0.6•Emission spectrum of microplasma shown
intensity peaks of N2 SPS, OH and ArI.

0.4
0.2

Grounded electrode00200

4006008001000

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

Fig. 4 Waveforms of the discharge voltage,corresponding discharge current and gate signal for
ICCD camera.

Right electrode active
Left electrode active(a)0.6Intensity (arb. units)

Emission spectrum in Ar and Ar/N2 shows:•N2 second positive band system peaks at315.9, 337.1, 357.7, 380.4, 400 and 405 nm.
•OH peaks at 306.4, 307.8 and 308.9 nm.
•Ar I peaks were measured at 415.8, 419.1,419.8, 420.1, 426.6, 427.2, 425.9, 433.3,696.5, 706.7, 727.3, 738.3; 703.2, 750.4 and772.4 nm.
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 + hν

Negative pulse

10Fig. 2 Experimental setup.

electrode(negative)

0Intensity (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

The streamer diameter was proportionallywith the discharge gap and thinner thanpreviously reported. It has a wider area
towards negative electrode and a smaller
towards the grounded or positive one.

•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).