Plasma polymer clusters deposited by means of gas aggregation cluster source
P. Solař, O. Polonskyi, O. Kylián, A. Choukourov, A. Artemenko, D. Slavínská, H. Biederman
Department of Macromolecular Physics, Faculty of Mathematics and Physics, Charles University in Prague,
Czech Republic
Abstract: A cluster source based on an RF planar magnetron was used for plasma excitation of a working gas mixture of Ar and hexane in order to prepare plasma polymer
clusters. Increased pressure in the cluster source resulted in enhancement of gas phase
plasma polymerization processes and led to formation of polymeric particles in the
volume of the aggregation chamber. These particles (clusters) were further ejected
through an orifice of the cluster source into the main chamber with lower pressure and
were deposited onto a substrate.
We have done the characterization of the cluster source with respect to discharge power,
pressure and composition of the working gas mixture. The films deposited from the
cluster beams were characterized by SEM, AFM, XPS and FTIR.
Keywords: Plasma polymer clusters, Cluster source, RF discharge
11.5 sccm. The hexane fraction thereby varied from
2 % to 22 %. Pressure was measured by an MKS
Baratron gauge. The entire assembly of the cluster
source was mounted into a main chamber pumped by
rotary and diffusion pumps.
1. Introduction
Most of the works dealing with clusters or nanoparticles are concerned with metal or metal oxide
clusters [1, 2, 3]. Very few investigated the preparation of polymer clusters [4, 5]. These particles could
interact differently with matrix materials, possess
interesting properties or at very least cover one part of
the size spectrum, because they seem to be usually
bigger than the metal ones.
2. Experimental
Fig. 1: The schematic view of the cluster source. 1—Baratron
gauge, 2—conical nozzle, 3—orifice, 4—water cooling, 5—gas
inlet, 6—magnetron head, 7—target, 8—magnetron cooling,
9—plasma, and 10—clusters
Particles of plasma polymer were deposited on
glass and silicon substrates using a Haberland type
cluster source developed in our laboratory (Fig. 1) [6].
It is composed of a 2 in. water cooled planar magnetron placed into an aggregation chamber of 60 mm in
diameter ended with a conically shaped outlet with a
nozzle of 1.5 mm in diameter and 3 mm length. The
walls of the aggregation chamber were cooled by
water. The magnetron was operated using RF power
(13.56 MHz) in the range from 80 to 160 W. Mixture
of Ar and hexane at total pressure ranging from 60 to
210 Pa was used in this study. The hexane fraction
was controlled by varying the flow rate of hexane
with the total flow of the gas mixture set constant at
The deposition process was characterized by Quartz
Crystal Microbalance (QCM).
Structure of the resultant films was characterized by
SEM (Mira II, Tescan) and AFM (Dimension 3100,
Veeco Instruments, Inc.). Their chemical composition
was analyzed by XPS (Specs 100) and by FTIR
(Bruker Equinox).
1
show regions of maximal cluster production (160 Pa
pressure and 10 % of hexane fraction).
3. Results and Discussion
3.1. Deposition rate
The first task was to find the deposition conditions
that offer the highest deposition rate of clusters. The
deposition rate was measured in terms of the shift of
the QCM resonant frequency per time unit. The parameters tested were the total pressure, discharge
power and hexane content in the gas mixture. The
separate sets of the experiments were performed,
where one of these parameters was varied with the
others being fixed. Behavior of the deposition rate
with respect to the mentioned parameters is summarized in Tab. 1.
As can be seen from Tab. 1a, the deposition rate
increases linearly with increasing power of the discharge. At power of 150 W the fabrication of clusters
was not stable, probably because of the excessive
heating of the cluster source. Therefore, further experiments with varying pressure and hexane concentration were done at 120 W power to avoid the
problems with long term stability of the cluster formation process.
a)
Power
input
(W)
80
100
120
150
Deposition
rate
(Hz/min)
3
29
59
86
3.2. Cluster size
Power of discharge within the studied range does
not have significant influence on cluster size. This
was confirmed by SEM shown in Fig. 2. All the
clusters have diameters of approximately 110-150 nm
for the samples prepared at 100 and 150 W. It has to
be mentioned as well that both samples were deposited for the same period of time. The increased
coverage at 150 W power is consistent with the
higher deposition rate observed by the QCM measurements.
2 µm
b)
Total Deposition
pressure
rate
(Pa)
(Hz/min)
107
5
135
58
160
60
185
42
209
41
a)
c)
Hexane con- Deposition
centration
rate
(%)
(Hz/min)
1,7
10
3,5
43
7,0
63
11,3
58
16,5
27
21,7
12
2 µm
b)
Fig. 2: The SEM images (5x5 µm) of the plasma polymer clusters
deposited on silicon substrates at distance of 3 cm with various
power inputs a) 100W, b) 150W
Tab. 1: Deposition rate of plasma polymer clusters depending on
a) power input, b) total pressure, c) hexane ratio in working gas
mixture
Plasma polymers are usually light. Density of soft
hydrocarbon plasma polymers is reported to be about
1 g/cm3. It is reasonable to suggest that clusters of
hydrocarbon plasma polymers also have low density
and therefore their fluxes are readily deflected by the
The behavior of the total pressure and hexane fraction in the working gas is more complicated. Both
2
Grant Agency of Charles University in Prague under
the grant GAUK no. 437411.
aerodynamic flow of the carrying gas. This has two
important implications. First, this results in the
broadening of the deposition spot on the substrate as
compared to the beams of heavier clusters. For example, silver clusters exit the orifice with quite narrow spatial angle of 0.15 rad. The lighter plasma
polymer clusters are prone to influence of expanding
gas flow and divergence of their beam is several
times bigger. Second, aerodynamic mass filtration
occurs with the distance from the orifice as the
smaller clusters are more deflected than the bigger
ones.
References
[1] M. Drábik, A. Choukourov, A. Artemenko, O.
Polonskyi, P. Solař, O. Kylián, J. Matoušek, J.
Pešička, I. Matolínová, D. Slavínská and H. Biederman, Morphology of titanium nanocluster films
prepared by gas aggregation cluster source. Accepted
to Plasma Proc. Polym.
[2] M. Drabik, A. Choukourov, A. Artemenko, J.
Matousek, O. Polonskyi, P. Solar, J. Pesicka, J. Lorincik, D. Slavinska, H. Biederman, Surf. Coat.
Technol.(2011), doi:10.1016/j.surfcoat.2011.02.013
3.3. Chemical structure of clusters
The XPS measurements confirmed that the clusters
were composed of carbon with some oxidation (hydrogen cannot be detected by XPS). The typical
composition of the clusters was found to be 97% of
carbon and 3% of oxygen. Previous FTIR results
have shown CH3 and CH2 groups typical for plasma
polymer prepared from hexane precursor along with
some mild oxidation or dehydrogenation in some
cases of deposition conditions [4].
[3] O. Polonskyi, P. Solař, O. Kylián, M. Drábik, A.
Artemenko, J. Kousal, J. Hanuš, J. Pešička, I. Matolínová, E. Kolíbalová, D. Slavínská, H. Biederman,
Nanocomposite metal/plasma polymer films prepared by means of gas aggregation cluster source.
Submitted to Thin Solid Films.
[4] P. Solař, O. Polonskyi, A. Choukourov, A. Artemenko, J. Hanuš, H. Biederman, D. Slavínská, Surf.
Coat.
Technol.
(2011),
doi:10.1016/j.surfcoat.2011.01.059
4. Conclusions
It was proven that it was possible to prepare plasma
polymer clusters by means of the Haberland type
cluster source, using RF magnetron discharge in the
mixture of argon and hexane. Deposition rate of the
clusters was determined for various conditions depending on input power with linear relation and
having a maximum for both total pressure and hexane
ratio dependences. It was found that the size of the
clusters does not depend on deposition conditions,
only on the sample-orifice distance due to size separation as a result of deflection by residual carrying
gas.
[5] J. Wan, Z. Ma, M. Han, J. Hong, G. Wang, Solid
State Commun. 121 (2002) 251.
[6] O.Polonskyi, P. Solař, O. Kylián, M. Drábik, A.
Artemenko, J. Kousal, J. Hanuš, J. Pešička, I. Matolínová, E. Kolíbalová, D. Slavínská and H. Biederman, accepted to a special issue of Thin Solid
Films
Acknowledgment
This work was supported by the research plan
MSM0021620834 that is financed by the Ministry of
Education of the Czech Republic, by the grant agency
of the Academy of Sciences of the Czech Republic
under contract KAN101120701 and partly by the
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