22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Nanocomposite metal/plasma polymer films deposited by gas aggregation
sources of nanoparticles combined with magnetron sputtering of polymers
M. Petr, O. Kylián, J. Kratochvíl, T. Steinhartová, J. Hanuš, A. Kuzminova, A. Shukurov and H. Biederman
Charles University in Prague, Faculty of Mathematics and Physics, Prague, Czech Republic
Abstract: An alternative approach for production of nanocomposite materials is presented.
Combination of metal nanoparticles (Ag, Cu), produced by gas aggregation sources, with a
polymer matrix deposited by RF magnetron sputtering, enables to control independently
size and amount of metallic inclusions and the properties of matrix. Surface wettability,
roughness, optical properties and time stability of nanocomposites are reported.
Keywords: nanocomposites, nanoparticles, gas aggregation sources, magnetron sputtering
1. Introduction
Fabrication of thin films of metal/plasma polymer
nanocomposites is in the focus of scientific attention for
several decades, mainly due to a wide range of possible
applications. Commonly used vacuum based methods for
deposition of such materials are, for example,
simultaneous plasma polymerization and RF sputteretching, plasma polymerization of metal-organic
compounds or deposition from two independent
magnetrons. However, the main limitation of these
methods is an impossibility to control independently the
size and amount of metallic inclusions on one hand and
properties of surrounding polymeric matrix on the other
hand. In this study we present an alternative approach
that is based on the application of Haberland type of gas
aggregation source of metal nanoparticles [1] in
combination with RF magnetron sputtering of polymers.
The main aim of this study is to introduce this approach
as versatile tool for production of coatings with different
architectures. This is going to be demonstrated on
examples of nanocomposites produced using Ag and Cu
nanoparticles and matrix material deposited by RF
magnetron
sputtering
of
Nylon
6,6
and
poly(tetrafluoroethylene) (PTFE).
2. Experimental
Metallic (Ag and Cu) nanoparticles were produced by
gas aggregation sources described in more detail in
previous works [2, 3]. They are based on planar
magnetron placed into a water cooled gas aggregation
chamber ending in an orifice (1.5 mm in diameter) that
separated aggregation zone from the main deposition
chamber (see Fig. 1). Magnetrons were powered by DC
power supply operated in constant current mode. Argon
was used as a working gas.
The set-ups used for the deposition of RF magnetron
sputtered nylon or PTFE consisted of a vacuum chamber
(0.05 m3), which was equipped with water cooled planar
RF magnetron and pumped to base pressure lower than
0.01 Pa. The target material was standard Nylon 6,6 or
PTFE sheet (Goodfellow) of diameter 81 mm and
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Fig. 1. Gas aggregation source.
thickness 3 mm. The RF magnetron sputtering was
performed at pressure 3 Pa in an inert argon atmosphere.
The magnetrons were powered by a RF generator
operated at frequency 13.56 MHz through a match-box.
Applied RF power was 40 W in both cases. More detailed
information related to the deposition of sputtered PTFE
and Nylon films may be found in previous studies [4, 5].
The thickness of deposited coatings was monitored by
spectral ellipsometry (Woollam M-2000DI). Morphology
of samples was determined by means of SEM (Tescan
Mira II) and AFM (Quesant Q-scope 350). Optical
properties of prepared nanocomposites were studied by
UV-Vis spectrophotometer (Hitachi U-2900) in the
spectral range 325 - 900 nm. Finally, wettability of
samples was evaluated by means of a sessile water drop
method.
3. Results
The first and the simplest way for preparation of
nanocomposite materials is embedding of NPs between
two layers of plasma polymers. In this case the plasma
polymerized film acts as a barrier that shields NPs from
the surrounding environment. In order to demonstrate this
effect, samples with and without top layer of plasma
sputtered coatings were produced. The thickness of the
top layer ranged from 2 to 40 nm. The barrier effect was
subsequently measured for samples stored at ambient air
and immersed in deionized water by UV-Vis
1
spectrophotometry. As can be seen in Fig. 2, already
2 nm thick overcoat layer is sufficient to significantly
limit the ageing of Ag NPs, which is exhibited by
temporally stable shape and position of anomalous
absorption peak of silver . In the case of stability in water,
one order of magnitude thicker overlayer is desired, as it
is depicted in Fig. 3.
Fig. 3. UV-Vis spectra of a) Ag nanoparticles deposited
on sputtered PTFE and overcoated by b) 10 nm and c)
20 nm thick films of sputtered PTFE measured before and
after immersion in water. Ag deposition time 2 min,
pressure 30 Pa and magnetron current 0.1 A.
Fig. 2. Temporal evolutions of UV-Vis spectra of a) Ag
nanoparticles deposited on sputtered PTFE, and b)
overcoated by 2 nm film of sputtered PTFE. Ag
deposition time 2 min, pressure 30 Pa and magnetron
current 0.1 A.
The presence of Ag NPs layer in sandwich structure
naturally results in increased surface roughness of
fabricated coatings (see Fig. 4 for example) and with it
connected wettability, that in case of sputtered PTFE
decreases with increasing surface roughness of the
coatings. As can be seen in Fig. 5, this effect gradually
diminishes with increasing thickness of the overcoat
layer. This dependence may be explained by gradual
shielding of Ag NPs film and smoothening of the surface.
Moreover, in Fig. 5 also another important aspect of
produced coatings is apparent – the roughness and
wettability may be tuned by the size of employed NPs.
The surface roughness and wettability may be adjusted
not only by the size of NPs and thickness of the top layer,
but also by the amount of NPs that may be controlled by
the deposition time. As can be seen in Fig. 6, this enables
2
Fig. 4. AFM images of magnetron sputtered PTFE film
deposited on a) Si and b) Si pre-coated by Ag NPs film.
Ag deposition time 2 min, pressure 30 Pa and magnetron
current 0.1 A.
to produce coatings with water contact angles from 110o
up to almost 160°, i.e., coatings approaching
super-hydrophobicity.
The possibility to tailor surface roughness by amount of
NPs that form interlayer opens an additional possibility to
prepare surfaces with gradient character of wettability. In
order to demonstrate this option, the substrate was slowly
moved below the gas aggregation source. As can be seen
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Fig. 7. Demonstration of the possibility to produce
coatings with gradient surface wettability.
Fig. 5. SEM images of Ag NPs deposited with Ar
pressure in the aggregation chamber a) 28 Pa and b) 50 Pa
and c) static water contact angles on smooth sputtered
PTFE film and films sputtered over Ag NPs layer.
anomalous absorption are detectable that are characteristic
for Ag and Cu nanoparticles, respectively. The increasing
number of NPs layers results solely in gradually
increasing intensity of peaks of anomalous absorption. In
other words, this technique makes it possible to control
quantity of NPs in the coatings.
Fig. 6. Dependence of water contact angles on deposition
time of Ag NPs interlayer. The thickness of overcoat film
is 14 nm. Ag NPs were deposited at pressure 28 Pa and
magnetron current 0.1 A.
in Fig. 7, such approach indeed makes it possible to
control laterally surface density of NPs, which after
overcoating of such film results in a surface with
wettability gradient.
The second step of this study was the evaluation of
properties of sandwich nanocomposites composed from
more layers of metallic NPs separated by thin films of
plasma polymer, magnetron sputtered Nylon in this case.
As can be seen in Fig. 8, where examples of UV-Vis
spectra of composites Ag/sputtered Nylon and
Cu/sputtered Nylon are presented, in both cases peaks of
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Fig. 8. UV-Vis spectra of layered nanocomposites for
different number of NPs interlayers. a) Cu/sputtered
Nylon and b) Ag/sputtered Nylon nanocomposites.
Sequential deposition of NPs and plasma polymeric
matrix moreover enables to control amount of NPs in
individual layers as well as the distance between them
simply by adjusting the deposition times of both NPs and
plasma polymer. Last, but not least, different kinds of
3
NPs may be combined in one nanocomposite. In order to
demonstrate this approach, set of experiments was
performed, in which the layers of Ag and Cu NPs were
successively alternated. As it is demonstrated in Fig. 9,
this procedure led to appearance of both anomalous
absorption peaks. In other words, it is possible to tailor
optical properties of fabricated nanocomposites by proper
selection of NPs and their amount.
[4]
[5]
M. Drábik, et al. Plasma Process. Polymers, 7, 544
(2010)
O. Kylián, et al. J. Phys. D: Appl. Phys., 42,
142001 (2009)
Fig. 9. UV-Vis spectra of multilayered nanocomposites
with alternating interlayers of Cu and Ag NPs. N denotes
for the magnetron sputtered Nylon film.
4. Conclusions
In this study we present results reached by using
combination of gas aggregation sources of metallic NPs
with RF magnetron sputtering of polymers. It is shown
that multi-step deposition procedure with deposition of
metallic nanoparticles and plasma polymerized matrix
makes it possible to fabricate layered nanocomposite
coatings with controllable amount and size of metallic
nanoparticles (Ag, Cu in this study) and chemical
structure of matrix material (magnetron sputtered PTFE
or Nylon 6,6). It is also shown that this method enables
to combine more gas aggregation sources in one
deposition chamber, which opens possibility to produce
multilayered nanocomposite thin films with interlayers
containing different metallic nanoclusters. Finally, the
deposition process may be easily adapted also for
production of surfaces with gradient surface roughness.
Such deposited nanocomposite thin films open new
possibilities in production of functional materials, e.g.,
materials with tunable wettability, gradient coatings or
materials with tunable optical properties.
5. Acknowledgments
This research has been supported by the Charles
University in Prague, project GAUK No. 382313.
6. References
[1] H. Haberland, et al. J. Vac. Sci. Technol. A, 10,
3266 (1992)
[2] O. Polonskyi, et al. Thin Solid Films, 540, 65
(2013)
[3] O. Kylián, et al. Thin Solid Films, 550, 46 (2014)
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