Observation of nanoparticle growth process using a high speed camera
Yasuhiko Morita1, Shinya Iwashita1,2, Daisuke Yamashita1, Giichiro Uchida1, Kunihiro Kamataki1,Hyunwoong Seo1, Naho Itagaki1,3, Kazunori Koga1, and Masaharu Shiratani1
1

Kyushu University, Fukuoka, JapanRuhr University Bochum, Germany
3
PRESTO JST, Tokyo, Japan

2

Abstract: Time evolution of spatial profile of nanoparticle amount in low pressure reactive
discharge plasmas have been measured to study effects of amplitude modulation of the plasmas on particle growth in the initial growth phase. Amplitude modulation of discharge voltage
leads to oscillate nanoparticle amount and their spatial profile. Growth of nanoparticles issuppressed by increasing the AM frequency.
Keywords: nanoparticle, plasma-nano interface, plasma fluctuation, amplitude modulated
discharge, laser light scattering
1. Introduction
Nanoparticle technology, which can be regarded as theextension of the conventional fine particle and powder
technology, is one of the core nanotechnologies. This
technology has a great potential in industrial and engineering areas such as catalysis [1-5], sensors [6], solarcell [7-9], hydrogen storage [10], Ultra-Large Scale Integration(ULSI)

biointerface [15].

[11-13],hard

coating[14],

andNanoparticle technology has many

issues including control of size, strurture, agglomeration,
morphology, surface, defect, dopant, and impurity of nanoparticles. One of the important and difficult issues ofnanoparticles is to tune variations of such features of nanoparticles. Although spatial and temporal fluctuation ofnanoparticle fabrication conditions leads to such variations, effects of fluctuations on such variations have notbeen clarified yet.

reactive plasmas, transports nanoblocks towards a substrate and arranges them on the substrate. We have developed several key control methods for a nano-factory inplasma: size and structure control of nanoparticles, control of their agglomeration, transport and sticking, andthen explain the combination of several types of control[24-35].
Recently, we have studied effects of plasma fluctuation
on growth of nanoparticles in reactive plasmas with amplitude modulation (AM) and clarified that plasma fluctuation leads to generation of high denisty of nanoparticles
with small size [32].
In this paper, we report time evolution of spatial profile of nanoparticle amount measured using an in-situ two
dimensional laser light scattering (2DLLS) method with ahigh speed camera and discuss effects of plasma fluctuation on nanoparticle growth in the initial growth phase.

Up to now, we have carried out systematic studies onparticle growth kinetics in a particle size range from
sub-nm to μ m in low-pressure, high-frequency discharges
employed for depositing Si thin films [16-23]. Based on
theresults,

wehaveproposed

theconceptof‘nano-factory in plasma’ which is a miniature version of amacroscopic conventional factory. A nano-factory inplasma produces nanoblocks and radicals (adhesives) in

2. Experimental Setup
Experiments

werecarriedoutusingacapacitively-coupled discharge reactor equipped with a
2DLLS system as shown in Fig. 1 [32]. A powered discelectrode of 60mm in diameter and 1mm in thickness was
set 20mm form an upper and lower grounded electrodesof 60mm in diameter. Ar diluted Si(CH3)2(OCH3)2

st21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia(DM-DMOS) was supplied to the reactor. The flow rateof Ar and DM-DOMS were 40 sccm and 0.2 sccm, respectively. The total gas pressure in reactor was 1.25

(a)Torr. To generate nanoparticles, we sustained a dis-(b)Fig. 1. Experimental setup.
charge by applying 120 peak-to-peak voltage Vpp of60MHz to the powered electrode for a discharge period
T = 8s. The corresponding discharge power was 30W.
Amplitude modulation of rf discharge voltage was carried out with a sinusoidal wave of a frequency fAM of 10and 20Hz. The AM level was 30%.
Time evolution of spatial profile of LLS intensityfrom nanoparticles was measured using the 2DLLS
method. For the 2DLLS method, a sheet beam of YAG(c)laser light of 2.0W at 532nm was passed parallel to thesurface of the upper grounded electrode through theaperture. The height and width of the sheet beam were
17mm and 3mm, respectively. Time evolution of spatial
profile of LLS intensity was measured with a highspeed camera (Photoron FASTCAM SA4) equippedwith an interference filter of a center wavelength of
532nm and the full width at half maximum of 2nm..
The spatial resolution is 950 × 287 mm2 and the frame
rate is 1000 s-1.

Fig. 2. Time evolution of spatial profile of nanoparticle
amount for fAM= 10 Hz druing (a) t = 3-3.25 s, (b) t =3. Results and Discussion
To obtain information on nanoparticle growth, we

5-5.25 s, and (c) t = 7-7.25 s.

st21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia

have measured time evolution of spatial profile of nanoparticle amount. Here, the nanoparticle amount is defined as LLS intensity which is proportional to the den-(a)sity of nanoparticles and the sixth power of their size,
because their size is much smaller than the wavelengthof the laser light, namely, in the Rayleigh scattering regime. Figure 2 shows time evolution of spatial profile ofnanoparticle amount at the center of electrode (r = 0 mm)
for fAM= 10 Hz. For t= 3 s, most nanoparticles are locatedat the plasma/sheath boundary near the powered electrode (z~2mm) where nanoparticles mainly generate andgrow. Large amount region of nanoparticles is oscillated
at 10 Hz. The large amount region extends when the(b)discharge power is high during each period of AM,
whereas it reduces when the discharge power is low. The
oscillation of the nanoparticle amount in the plasma bulk
center around z= 10 mm shows phase delay of 25° compared with those at the plasma/sheath boundaries near
the powered and grounded electrode as shown in Figs.
2(b) and 2(c). The phase delay corresponds to the extension speed of 70 cm/s. For the longer time scale, thelarge amount region extends gradually toward the upper
grounded electrode, and it reaches the plasma/sheathboundary near the upper grounded electrode around t= 7(c)s, which suggests that nanoparticles in the plasma growwith time.
Figure 3 shows time evolution of spatial profile ofnanoparticle amount at the center of electrode for fAM=
20 Hz. General behavior of nanoparticles for fAM=20 Hz
is similar to that for fAM= 10 Hz. Nanoparticle amountand nanoparticle located area for fAM= 20 Hz are muchsmaller than those for fAM= 10 Hz. These differences
between results in Figs. 2 and 3 indicate growth of na-Fig. 3. Time evolution of spatial profile of nanoparticle

noparticles is suppressed by increasing the AM frequen-amount for fAM= 20Hz druing (a) t = 3-3.25 s, (b) t =cy.

5-5.25 s, and (c) t = 7-7.25 s.

st21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia(2000).
4. Conclusions
We have measured time evolution of spatial profile ofnanoparticle amount in reactive plasmas to obtain information on effects of plasma fluctuation on the nanoparticle growth in the initial growth phase. Amplitude modulation of discharge voltage leads to oscillate nanoparticle
amount and their spatial profile. Growth of nanoparticles
is suppressed by increasing the AM frequency.
Further elaborate study is required to control of size,
strurture, agglomeration, morphology, surface, defect,dopant, and impurity of nanoparticles. Such control will
open a new era of nanoparticle technology.

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5. Acknowledgment
This work was partly supported by the Ministry ofEducation, Culture, Sports, Science and Technology(MEXT).

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