25E01
Transport of dust particles in multi-frequency capacitively coupled radiofrequency discharges
多重周波数容量結合型ＲＦ放電を用いたダストの輸送制御
G. Uchida, S. Iwashita, J. Schungel, M. Shiratani, and U. Czarnetzki
内田儀一郎, 岩下伸也，J. Schungel，白谷正治，U. Czarnetzki
Graduate School of Information Science and Electrical Engineering, Kyushu University
744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Institute for Plasma and Atomic Physics, Ruhr University Bochum, Germany
九州大学大学院システム情報科学研究院 〒819-0395 福岡市西区元岡744
ルール大学ボーフム 〒44780 ドイツボーフム市
The levitation position of micrometer-sized dust particles is controlled by the phase angle  of 13.56 and27.12MHz waveforms applied to a power electrode in geometrically symmetric capacitively coupled radio
frequency discharges via a Electrically Asymmetry Effect. Here, dc self bias voltage is a linear function of
the phase angle even in a geometrically symmetric CCRF plasmas, and controlled by the phase angle

We succeeded in transportation of dust particles toward a upper ground electrode by abruptly
changing phase angle  from 90 to 0 degrees.

1. Introduction
In plasmas, dust particles are negatively charged
up to form so-called ``plasma crystals'' under thestrong Coulomb interaction among the dust
particles [1-4]. There have been many experimentson the dust particles and various interesting featuresof dust-particle plasma have been clarified [5].
Moreover, dust-particle composite films have agreat potential for many application such as
catalysts, sensors, solar cell, Large scale Integration.
It is an essential issue to understand and control thecollective motion of dust particles levitating inplasmas in order to fabricate dust particle composite
films [6]. Particularly, the control of an electrostatic
field is quite important, because the charged
particles are sensitive to the electric field in plasma,and new dust-particle structures such as vortices
and void are generated and controlled by anappropriate potential structure. In this study, we
propose a novel method for the transport of dust
particles to substrates using the Electrical
Asymmetry effect (EAE) in dual-frequency
capacitively rf discharges [7,8].
2. Experiment
Experiments were carried out using a CCRF
discharge reactor, as shown in Fig. 1. The powered
and grounded electrodes of 100 mm diameter wereplaced at a distance of 20 mm in the reactor. Plasma
was generated by applying the phase locked 100
peak-to-peak voltage (Vpp) of 13.56 MHz and 27.12
MHz generated using two synchronized function
generators.

Figure 1. Experimental setup.

Here, the voltage waveform  is given by (t )  0 cos( 2ft   )  cos( 4ft),(1)

where 0 and  are the amplitude of each harmonic
and the variable phase angle between the harmonics,
respectively, and f is a fundamental frequency of
13.56 MHz. The pressure was sustained at 1-10 Pa
in an argon atmosphere. A filter blocked the otherharmonic behind each matching box, and the twovoltage waveforms were added and applied to thepowered electrode behind the filters. The plasmas
were shielded from the outer grounded chamber
walls by a glass cylinder, which realize
geometrically symmetric CCRF discharges. The
temperature of the reactor wall was kept at room
temperature to eliminate the influence ofthermophoretic force exerted on dust particles. SiO2
dust particles of 1.5 m in size were injected intothe reactor using a particle dispenser above theupper grounded electrode. For suppressing
agglomeration of dust particles a wire cloth meshhaving holes of 38 mm in size was equipped withthe particle dispenser. An aluminum ring having ahole of 60 mm in diameter was set on the lower
powered electrode to trap dust particles in the center
above the ring. Dust particles injected wereobserved using a two dimensional Laser Light
Scattering method [6, 9]. A laser sheet of 660 mW
at 532 nm was passed parallel to the surface of thetwo electrodes. The height and width of the laser
sheet was 20 mm and 1 mm, respectively. The
intensity of light scattered by particles was detected
at right angles with an ICCD camera or a CCD
camera equipped with an interference filter.
Figure 2 shows dc self-bias as a function of the phaseangle . We can clearly observe that the dc self bias
is controlled by changing the phase angle. Figure
3 shows dust-particle levitation positions as afunction of the phase angledust particle
position almost linearly decreases with increasing
the phase angleand quite sensitive to the dc selfbias.
4028.6Ar, SiO2 particle: 1.5 m
14.3

V13=V27= 70V

00.0-20-14.3-40-28.6-60

dc self bias (%)

dc self bias (V)20-42.9

2Pa-80-57.1-1000102030405060

7080

-71.4
90

phase angle (degree)

Fig.2. DC self bias as a function of phase angle (a)0deg@50V,

90deg@50V,

Dust particles

5(b)z (mm)

43214Pa, V13=V27=50V

0020

40

60

80

100

phase angle  (degree)

Fig.3. (a) Images of dust particles levitating in ion sheath.
(b) A levitation position of dust particles as a function ofphase angle Finally, we succeeded in the transportation of dust
particle toward upper a ground electrode byabruptly changing phase angle from 90 to 0
degrees as shown in Fig. 4. This method is quite
effective to control dust-particle motion in plasma.
References[1] H. Ikezi, Phys. Fluids 29, (1986)1764.
[2] J. H. Chu and Lin I, Phys. Rev. Lett. 72, (1994)4009.
[3] H. Thomas, G. E. Morfill, V. Demmel, J. Goree, B.
Feuerbacher, and D. Mohlmann, Phys. Rev. Lett. 73,(1994) 652.
[4] Y. Hayashi and K. Tachibana, Jpn. J. Appl. Phys., 33,(1994)L804.
[5] N. Sato, G. Uchida, R. Ozaki, S. Iizuka, and T.
Kamimura, in Frontiers in Dusty Plasmas, edited by
Y. Nakamura, T. Yokota, and P. K. Shukla(Elsevier Science, Amsterdam, 2000), p. 329.
[6] M. Shiratani, K. Koga, S. Iwashita and S. Nunomura,
Faraday Discuss. 137, 127[7] B. G. Heil, U. Czarnetzki, R. P. Brinkmann and T.
Mussenbrock, J. Phys. D: Appl. Phys. 41,(2008)165202 .
[8] J. Schulze, E. Schuengel and U. Czarnetzki, J. Phys.
D: Appl. Phys. 42, (2009)092005.
[9] K. Koga, S. Iwashita and M. Shiratani, J. Phys. D:Appl. Phys. 40, (2007)2267 .