22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Study of the transport of nanoparticles in a cold plasma at atmospheric pressure
P. Brunet1,2, R. Rincon1, A. Hendaoui1, M. Chaker1 and F. Massines2
1
Institut National de la Recherche Scientifique, 1650 boulevard Lionel Boulet J3X1S2 Varennes, Canada
Laboratoire PROcédés Matériaux et Energie Solaire, UPR 8521, Tecnosud, 66100 Perpignan, France
2
Abstract: The transport of TiO 2 nanoparticles (NPs) in cold dielectric barrier discharge at
atmospheric pressure (APDBD) is studied by using a laser light scattering technique. TiO 2
nanoparticles are injected in the discharge by means of a nebulizer coupled to a spray
chamber which is used to prevent NPs agglomerations to reach the plasma. The influence
of both the carrier gas (N 2 ) flow and the type of nebulisation chamber used on the transport
of TiO 2 NPs is reported in this work. Furthermore, a correlation between diffusion
measurements and coverage of TiO 2 on the substrate can be found.
Keywords: DBD, atmospheric pressure, transport, nanoparticles, TiO 2 , deposition
1. Introduction :
The development of nanocomposite coatings is drawing
scientific attention since they offer an opportunity to
explore new behaviors and functionalities beyond that of
conventional materials [1]. Among other techniques,
low-temperature atmospheric pressure plasmas for the
synthesis of nanomaterials have been researched [2-4].
However, the creation of nanocomposite with plasma at
atmospheric pressure needs to face up to many
challenging steps such as minimizing nanoparticles
agglomeration and losses during the injection and
transport in the plasma or controlling the dispersion and
concentration of nanoparticle to produce a homogeneous
and high-quality deposition.
To have control of these parameters it is necessary to
perform a thorough study concerning the transport of the
nanoparticles inside the plasma. In this experimental
research, this demanding task has been carried out by
means of a non-intrusive technique which consists of
detecting nanoparticles by means of light scattering
measurements. This method is a usual technique to detect
nanoparticles used in low pressure plasma. Boufendi et
al. [5]. Furthermore, the influence of the N 2 flow and the
use of different nebulization chambers have been assessed
with regards to check quality of deposition in terms of
nanoparticles agglomeration and concentration of
nanoparticles in the coating produced. In addition, XPS
and SEM analysis have been performed on the deposited
layer to infer a relationship between the light scatter by
the nanoparticles and what is deposited on the substrate.
2. Experimental Setup:
2.1 Nanoparticles suspension
For this study nanoparticles of Aeroxide TiO 2 P25
(TiO 2 NPs) provide by Evonik society are used. TiO 2
NPs are suspended in isopropanol at 1%wt (which
corresponds to 1014 NPs/cm3). To keep the suspension
stable along the experiments, the solution was subjected
to an ultrasonic probe for 5 min. A syringe pump was
O-1-5
used to control the nanoparticle suspension flow
(50µl/min ) injected to the plasma by means of a
nebulizer and a spray chamber. In these experiments two
nebulisation chambers are used: cyclonic and Scott type
spray chambers to check which is the most suitable to
avoid agglomerations of NPs.
2.2 Reacto
Fig. 1 shows a schematic drawing of the plasma source.
The DBD discharge is generated between a grounded
bottom electrode (140 x 70 mm2) and two high voltage
top electrodes (20 x 70 mm2) which are covered by
alumina plates serving as dielectric barriers. The gap
between the bottom and top electrodes was set to 1 mm.
Although the deposition experiments can be performed in
dynamic mode with this system, the static mode was
chosen to study transport through the plasma.
positions
Fig. 1. Schematic representation of DBD discharge.
For all experiment, the ambient air was removed with a
primary vacuum pump, and then the reactor was filled
with ultra high purity nitrogen gas (UHP N 2 ) up to
atmospheric pressure in order to avoid contamination
during the deposition process. UHP N 2 flow controlled
by a Bronkorst flow meter was used as both the main gas
1
3. Results and discussion:
To infer the effect of the introduction of TiO 2 NPs on
both Rayleigh scattering effect and pure N 2 APDBD
kinetics optical emission spectroscopy technique was
used. In Fig. 2 it is possible to observe a comparison
between the radiation emitted by the plasma and the laser
at 405 nm before and after TiO 2 NPs injection. On one
hand, it can be clearly observed the emission of the 405
nm laser when TiO 2 NPs are in the plasma due to
Rayleigh scattering effect and on the other hand, the
decrease in the intensity of the N 2 Second Positive
System (C3∏ u →B3∏ g ) when nanoparticles are injected
which suggests that the regular N 2 DBD kinetics is
altered, this effect might be caused by the consumption of
the low energy electrons.
In order to study the transport of TiO 2 NPs through the
plasma, the scattering signal was thoroughly analysed in
the five-plasma positions represented in Fig. 1. Besides,
SEM and XPS analysis were conducted to correlate
diffusion measurements (transport within the plasma)
with the deposition topography and chemical
composition. Two different spray chambers were utilized
to perform the experiments: cyclonic and Scott type spray
chambers A set of experiments were carried out in N 2
plasma by varying the gas flow and keeping both the
concentration of the suspension (TiO 2 = 1% wg ) and the
velocity of injection (50 µl/min) constant.
2
Without nanoparticles
WIth nanoparticles
250000
200000
Intensity (ua)
and the carrier gas of TiO 2 suspended in isopropanol.
The total flow was 2 and 8 slm and injected into the
plasma through a 2 mm-slit placed between the upper
electrodes. The high sinusoidal voltage (7 kV) from a
waveform generator connected to an amplifier working at
a frequency of 2 kHz was applied to the upper electrodes.
Plasma conditions were monitored with a high voltage
probe (Tektronic P6015A 75 MHz) and a current probe
(Lilco LTD 13W5000 400Hz-100MHz) connected to a
digital oscilloscope (Tektronic wavejet).
To study the transport of TiO 2 NPs through the plasma,
five positions were considered as it is shown in Fig. 1.
A 405 nm laser (25 mV, CrystaLaser®) was utilized to
infer the diffusion of NPs in each plasma position. Laser
radiation was sent to the discharge while the detector was
placed at 90°. Both, the radiation emitted by the DBD
discharge and the light scattered by the NPs from the laser
were directed, by means of an optical set up, to the
entrance of a 500-mm focal length Andor Shamrock 500i
monochromator with 600 grooves/mm holographic
diffraction grating.
A CCD iStar camera (Andor
technology, 1024 x 256) was used as a radiation detector.
Surface topography and chemical composition of
deposited films were investigated by Scanning Electron
Microscopy
(SEM)
and
X-Ray
Photoelectron
Spectroscopy (XPS). The deposition of TiO 2 NPs was
performed on Silicon wafers.
Scattering signal
150000
100000
50000
0
360
380
400
420
440
Wavelength (nm)
Fig. 2.
Scattering
nanoparticles.
intensity
with
and
without
3.1: Scattering of TiO 2 with cyclonic chamber
In Fig. 3 different SEM images of deposition of TiO2
NPs in two extreme plasma positions (closest and farthest
positions related to NPs injection) for two different gas
flows (2 and 8 slm) with the cyclonic spray chamber are
shown. The SEM images on Fig. 3 show that the film is
very porous in the entrance of the plasma with
polydisperse particles.
a)
b)
Fig. 3. SEM image: a) For 2 slm: beginning and exit of
the plasma, and b) for 8 slm: beginning and exit of the
plasma for cyclonic chamber.
According to aforementioned figure, it seems as if the
gas flow does not play an important role in the deposition
of TiO 2 NPs in the position closest to the injection in
contrast to what is observed at the end of plasma where
isolated nanoparticles without covering he substrate can
be found.
Considering the lowest N 2 flow, NPs
agglomerations cannot reach the end of the plasma and
only the smallest ones are deposited whereas deposition
carried out with a higher flow shows that even at the end
of the plasma small and agglomerates NPs are deposited.
As it can be seen in Fig. 4 the evolution of the
scattering signal with regards to plasma position as well
as N 2 flow is in agreement with what is observed on the
SEM pictures. The decreasing of the signal from NPs
injection (higher concentration) to the exit (lower
concentration) for a N 2 flow of 1.3 slm is translated into a
O-1-5
8
150000
6
100000
4
50000
2
0
0
2
4
6
8
Position dans le plasma (mm)
10
Concentration TiO2 (%)
10
200000
Intensité (u.a)
12
Fig. 4. Concentration of Ti as a function of the scattering
intensity for two flow of N 2 for cyclonic chamber.
3.2. Scattering of TiO 2 with Scott type spray chamber
After the experiment with the cyclonic chamber, Scott
type spray chamber was used for comparison purposes.
The same procedure as it was previously described was
followed. Fig. 5 shows the SEM pictures of depositions
carried out with N 2 flow of 2 slm and 8 slm in two
extremes positions of the substrate (closest and farthest
positions related to NPs injection).
As it can be observed in Fig. 5, the size of particles is
smaller with a better coverage of the substrate even at the
end of the plasma as compared to the shape and coverage
of NPs introduced by using the cyclonic chamber.
Besides, with the Scott type spray chamber lesser
aggregates on the substrate can be found which suggests
that the Scott type chamber seems to be more efficient
than the cyclonic one in terms of avoiding agglomerations
in a NPs deposition.
O-1-5
b)
Fig. 5. SEM image: a) for 2 slm: beginning and exit of
the plasma, and b) for 8 slm: beginning and exit of the
plasma for Scott type chamber.
100000
90000
80000
70000
60000
50000
40000
30000
20000
10000
0
2l/min
8 l/min
2
4
6
8
Position dans le plasma (mm)
10
20
18
16
14
12
10
8
6
4
2
0
Concentration Ti (%)
N2 = 1,3l/min
N2 = 8l/min
250000
a)
Intensité (u.a)
fewest number of NPs which travel across the plasma thus
an important deposition of particles in positions closer to
NPs injection. In the case of a flow of 8 slm, the
scattering signal is quite constant hence more
nanoparticles pass through all the plasma.
The concentration and chemical composition of the
deposition was analyzed by XPS using a nonmonochromated 1253 eV, Mg Kα X-ray source. For all
the analysis the peak of C-C/C-H at 284.6 was taken as a
reference. With the help of casa XPS software all the
peak were fitted and the concentration of Ti in the surface
was obtained.
In Fig. 4 concentration of Ti is plotted as function of
deposition position and N 2 flow. As it can be observed,
Ti concentration in the deposited layer follows a similar
trend as scattering signal which highlights that the
transport of NPs is directly related to the composition of
the deposited layer. Thus this method seems to be a
simple way to deduce the concentration of Ti in the
substrate by the analysis of the scattered signal.
Fig. 6. Concentration of Ti as a function of the scattering
intensity for two flows of N 2 for Scott type chamber.
As for the concentration of Ti on the substrate,
scattering signal and Ti concentration follow a similar
trend as it was described in Fig. 4. However, in contrast
to the results found with the cyclonic chamber, there is
lower variation in the evolution along the plasma in terms
of concentration and scattering intensity. Furthermore,
the intensity of scattering signal is less important which
can be explained by the fact that a smaller size of
nanoparticles as it is observed in SEM pictures (Fig. 5).
4. Conclusion
In this research a study of TiO 2 NPs transport in a DBD
has been performed. TiO 2 NPs were injected into the
plasma as a solution in isopropanol by means of a
nebulizer and two different spray chambers (cyclonic and
Scott type) which are used to reduce agglomerations of
NPs reaching the plasma. NPs were followed through the
plasma by using the non-intrusive light scattering
technique with a low laser wavelength (405 nm). In
addition, SEM and XPS analysis were performed to
correlate the transport of TiO 2 NPs within the plasma
with the characteristic and concentration of NPs deposited
on the substrate.
It was found that the nebulization chamber played a key
role in terms of NPs distribution and agglomerations. The
Scott type spray chamber seemed to be the most
appropriate one producing fewer agglomerations. In
3
addition, a relationship between diffusion measurements
along the plasma and the concentration of Ti along the
deposition performed was found. This result join to the
fact that topography characteristics are related to the
diffusion intensity signal suggest that on one hand the
study of transport of NPs in the plasma is a key step to
produce high-quality nanocomposite coatings and on the
other hand the light scattering measurements can be used
as an indirect tool to extract NPs concentration on the
substrate.
5. Acknowledgements
The authors would like to acknowledge both the
“Agence Nationale de la Recherche” (project ANR-11IS09-0005) and the National Science and Engineering
Research Council (NSERC) from France and Canada for
their financial support.
6. References
[1] F. Hussain, M. Hojjati, M. Okamoto, R.E. Gorga,
Journal of Composite Materials, 1511, 40 (2006)
[2] J. Bardon, J. Bour, D. Del Frari, C. Arnoult, D. Ruch,
Plasma Processes and Polymers, S655, 6 (2009)
[3] F. Fanelli, A.M. Mastrangelo, F. Fracassi, Langmuir,
857, 30 (2014)
[4] X.L. Deng, C. Leys, D. Vujosevic, V. Vuksanovic, U.
Cvelbar, N. De Geyter, R. Morent, A. Nikiforov, Plasma
Processes and Polymers, 921, 11 (2014)
[5] L. Boufendi, J. Hermann, E. Stoffels, W. Stoffels, A.
Bouchoule, Annales de physique, C1-185, 19 (1994)
4
O-1-5