S10-3

Novel Application of Microplasma
マイクロプラズマの新規応用
Kazuo Terashima, Jaeho Kim*, Katahira Ken, and Daisuke Ishihara
寺嶋和夫，金 載浩*，片平 研，石原大輔

Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8561, Japan
東京大学新領域創成科学研究科物質系専攻，〒277-8561 千葉市柏の葉5-1-5*
Department of Advanced Energy, Graduate School of Frontier Sciences, The University of Tokyo,
5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8561, Japan
東京大学新領域創成科学研究科先端エネルギー専攻，〒277-8561 千葉市柏の葉5-1-5

Recently, application of microplasma has been intensively performed in various fields. In this talk, as
the examples, we report our recent works on materials synthesis by microplasma processing under ahigh-pressure environment up to supercritical fluid (SCF) and in liquid, and microwave excited
atmospheric air maicroplasma based on microstrip technology.

1. Introduction
In these days, microplasma has been intensively
studied not only from the viewpoints of purescience but also application. Based on the uniquecharacteristics of microplasma, such as an
extraordinary
localityandhigh-density,
developments of various novel application
technologies are in progress. Those include, e.g.,novel materials processing, biomaterials treatment,chemical analysis, light sources of ultra-shortwavelengths, micro-machining and the functional
plasma devices. Figure 1 shows typical examples ofvarious micoplasma processing.
In this talk, as the examples, we report our recent
works on materials synthesis by microplasma
processing under a high-pressure environment up to
supercritical fluid (SCF) and in liquid, andmicrowave excited atmospheric air microplasma
based on microstrip technology.

2. Materials synthesis by microplasma in liquidand supercritical fluid
Generally speaking, for microplasma generation,
relatively high-pressure (high-density) environment
may be required. In other word, microplasma
allows us easy generation under a high-pressure
environment even up to SCF conditions and inliquid. In these exotic plasma media, new reactions
through plasma processing, leading to thefabrication of novel materials may be anticipated.
In fact, for example, we successfully fabricatedvarious carbon nanomaterials from CH4/He gas at
atmospheric pressure employing inductivelycoupled microplasma (ICMP) and dielectric barrierdischarge microplasma (DBDMP) in liquid solution.
Employing He/CH4-ICMP in water, we easily
fabricated graphite, carbon nano-onions, MW-CNT(multi-wall carbon nanotube) and distinctive
self-organized carbon nanostructures as shown inFig.2 [1].
On the other hand, SCF has attracted muchinterest in scientific and engineering fields due toits unique characteristics such as its transport
properties between gas and liquid [2]. There exists aFig. 1.

Fig.2 (a)SEM and (b) TEM of self-organized carbon
system prepared by microplasma processing in liquid.

(a)Application of micro-scale plasma processing.

(b)large density fluctuation resulting clusters ofvarious sizes near the critical point and these canresult in marked change in characteristics such as
thermal conductivity. The use of SCF offers several
advantages for processing, particularly in transportphenomena. During the past decade, theseadvantages have been successfully applied tomaterial processing. So, plasma processing, usuallyperformed in a gaseous environment, may yield ahigh efficiency by applying SCF conditions due to a
combination of advantages, such as the highactivity of plasmas and the superior transport
properties of SCF. In addition, SCF plasma isanticipated to contain radical and ion clusters inSCF, which may lead to novel phenomena andreactions. We succeeded in the synthesis ofnonequilibrium materials consisting of carbon
nanotubes and nanopolyhedra with arc-discharge
and DBD in SCF-CO2 without catalysis [3]. The
detail will be presented at the symposium.
3. Microwave (2.45GHz) excited atmospheric air
maicroplasma based on microstrip technology
A novel plasma system based on microstrip
technology was developed for the generation of
atmospheric pressure microplasmas [4]. A discharge
gap was placed between the striplines and theground plane on the transverse cross-section of thedirection of microwave propagation as shown Fig.3
and Fig.4. This plasma sources can provide thefollowing advantages. (1) Atmospheric pressure
eliminates the need for a vacuum pump. (2) No
electrode is needed, reducing the contamination ofplasma source by sputtering electrodes. (3)Microwave powers can be directed to the target areaprecisely, meaning no unnecessary radiation loss toexternal space and allowing the generation ofhigh-density plasmas. (4) Discharge can besustained stable over a wide range of gas pressures.
(5) Matching impedance was conducted with using
simple components. (6) The magnetron is usedcommercially in microwave (2.45GHz) ovens andthe semiconductor microwave power generator isused in wireless telecommunication system, making
the microwave source very economical. (7)Microstrip technology and small semiconductor
microwave source make it possible the low power
operation and the portable microplasma system.
This microstrip structure permits the strong
concentration of electric fields at the discharge gap,
which is confirmed by a computer simulation using

Fig. 3. A microstrip structure of the present system.

Fig.4

Picture of an actual system and excited plasma.

the 3-D simulation code based on the FDTD (FiniteDifference Time Domain) method, producing
atmospheric pressure plasmas even in air. The
microplasmas were sustained in the discharge gap(width:0.2mm, length: 6mm) at a microwave power of
1W. The experimentally measured rotational temperatureof nitrogen molecular was 800K, indicating theseplasmas to be non-thermal plasmas.

In future work, the proposed plasma system will
permit a potable plasma system and a large-scaleatmospheric pressure non-thermal plasma using thearray configuration as shown in Fig. 5. The detailwill be presented at the symposium.
.

Fig. 5. Schematics of large-scale atmospheric pressure
non-thermal plasma using the array configuration.

Acknowledgments
This work was supported financially in part by
Grants-in-Aid for Scientific Research (B) (GrantNo. 15360380) and Specific Research of Priority
Areas (Microplasma) (Grant No. 15075202) fromThe Ministry of Education, Culture, Sports, Scienceand Technology.
References[1] D.Ishihara,Y.Kasaki,T.Ito,Y.Shimizu,T.Sasaki,
N.Koshizaki,T.Sakurai, K.Terashima, submitting[2] C. A. Eckert, B. L. Knutson, P. G. Debenedetti,Nature, 383(1996) 313.
[3] T.Ito,K.Katahira,Y.Shimizu, T.Sasaki, N.Koshizaki,
K.Terashima, J.Mater.Chem., 14 (2004) 1513.
[4] J.Kim and K.Terashima, submitting