FB100 Plasma Chemical
Processes
Mgr. Ondřej Jašek, Ph.D.
jasek@physics.muni.cz
Outline
• Plasma synthesis of Nanoparticles
• Basics of Dusty Plasmas
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Szabo D.V., Schlabach S., Inorganics, 2014, 2, 468-507.
Plasma synthesis of nanoparticles
Plasma synthesis of nanoparticles
• In plasma many input parameters such as pressure, flow rates, directly influence plasma
parameters such as temperature and concentration of various species and can not be tuned
independently
• Plasma synthesis of nanoparticles can be carried out in wide range of discharges driven from
DC to RF (13.56 or 27.12 MHz) to MW (2.45 GHz) sources.
• Low pressure setups are limited from point of view of amount of precursor so especially rf or
mw setups. Highest densities are achieved in laser plasmas. MW sources are industrially very
easily scalable and there is a lot such power sources in the industry.
Plasma synthesis of nanoparticles
• The plasma synthesis of nanoparticles differs from gas phase process due to the presence of
charged species and charged nanoparticles during the synthesis
• Pressure, temperature and electric field frequency are important parameters influencing
nucleation and growth of nanoparticles
• This is of course connected to thermal and non-thermal plasmas with their differences in electron
and neutral/heavy species temperature. For different discharges, especially pressures, we will get
different conditions for nanoparticle synthesis.
• Ability of nanoparticles to obtain charge and repel each other is connected with collision frequency
and frequency of electric field of power source.
• There is direct relationship between frequency of source field f and collision frequency z
E ~ (q/m) (z/(z2+f2))
maximum is reached when z=f
for z << f electrons are ionizing the nanoparticles,
nanoparticles have positive charge and are repeling
each other (mw discharges).
for z ≈ f we have mix of positively and negatively
charged nanoparticles which results in agglomeration.
for z >> f electrons are attached to nanoparticles
surface, nanoparticles carry negative charge and repel
each other (rf dicharges).
With increasing nanoparticle diameter increases
the charge it carries
D. Vollath, Plasma synthesis of nanopowders, J Nanopart Res (2008) 10:39–57, Szabo D.V., Schlabach S.,
Inorganics, 2014, 2, 468-507
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Plasma synthesis of nanoparticles
• RF sources and configurations – capacitive and inductively
coupled discharges with electrodes in or outside the reactor
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• Microwave plasma sources – thermal or close to thermal sources such as jets and torches
and non-thermal sources such as low pressure resonance cavities or surface wave discharges
(can be run also at atmospheric pressure)
• Central flow – coaxial or rotating gas feed of liquid or gas precursor, side feed mostly used for
powder precursor, influence of nozzle design
• Quench gas rapid cooling of nano powder limits the aggregation of nanoparticles, one can
also induce agglomeration by addition of neutralizing agent H2O > H+ + OH•
Influence temperature on crystallinity of nanoparticles
Plasma synthesis of nanoparticles
• Laser driven plasma have high density and high core temperature. The nanoparticle source can be in gas,
liquid or solid form. Laser energy dissociates and ionizes precursors and created atoms and molecules form
nucleation centers and grow into nanoparticles which eventually can agglomerate into bigger particles.
During the plume expansion, the temperature decreases and, as the vapor gets supersaturated, particles
are nucleated. Within the short time interval of supersaturation, the particles are formed. The lower the
gas pressure in the system, the faster expands the plume; the shorter is the time for particle formation.
This limits particle growth.
• However, with increasing supersaturation, the number of nuclei increases, a process that leads to small
particles, too.
• In industry most often used lasers are CO2 laser at 10,6 mm. To achieve efficient absorption in the gas
medium SF6 or C2H2 are added to gas mixture.
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Plasma synthesis of nanoparticles
• Synthesized nanoparticles can be also functionalized. It would be of
advantage to use the same plasma source for creating functional layer or
coating. If its not possible two coupled setups are used.
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Plasma synthesis of nanoparticles
Plasma synthesis of nanoparticles
• Influence of precursor densities/molecular weight on yield of nanoparticles for
example for SnCl4 and Sn(C4H9)4. One also needs to take into account also by
products of plasma reactions, if one can remove them by annealing or if they are
incorporated into the nanostructures.
• Influence of microwave frequency is given by collision frequency relation, but
because this frequency is almost always fixed in given device its not studied.
• Increased pressure leads to increase of particle diameter, one can also tube the
repulsion process of nanoparticles as mentioned above.
• Higher microwave power usually leads to bigger amount of smaller particles which
is probably related to increase of temperature and chemical reactivity which leads
to higher number of nanoparticle nuclei. Higher reaction rates also lead to cleaner
chemical composition and lower amount of un-reacted precursor.
• Residence time is plasma can influence properties of nanoparticles but it has to be
investigated in detail and experiment setup must be adjusted to such fine tuning.
Plasma synthesis of nanoparticles
Plasma synthesis of nanoparticles
Particle collection in plasma synthesis is carried out outside the reaction zone can
main methods are mechanical filtering and cyclones. Very effective is also electrostatic
deposition, possibly also done with addition of corona discharge. One can also use
drift of particle in temperature gradient so call thermophoresis.
Nanoparticle size monitoring during the synthesis:
Laser-light-scattering methods - Thomson scattering, Photo-emission and photoionization
methods, Modified Langmuir probe method etc. Y. Watanabe, Formation
and behaviour of nano/micro-particles in low pressure plasmas J. Phys. D: Appl. Phys.
39 (2006) R329–R361.
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Microwave plasma torch operating at 2,45 GHz,
(100 – 300 W) max. 2 kW power, dual gas flow
Center - Ar(500-1500 sccm)/
Outer – O2, H2, hydrocarbons, (250-1000 sccm)
Deposition in volume or on substrates
Plasma synthesis of nanoparticles – iron oxides
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Plasma synthesis of nanoparticles – iron oxides
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Plasma synthesis of nanoparticles – iron oxides
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Plasma synthesis of nanoparticles – iron oxides
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Low pressure surface-wave microwave discharge 2,45 GHz,
(100 – 800 W) max. 2 kW power, operating pressure 500 –
10000 Pa,
Gas flows - Ar(500-1500 sccm),
O2, H2, hydrocarbons, (250-1000 sccm), iron pentacarbonyl
Plasma synthesis of nanoparticles – iron oxides
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Ar discharge Ar + Fe(CO)5 discharge
Plasma synthesis of nanoparticles – iron oxides
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Fe(CO)5
Iron
cloud
Plasma synthesis of nanoparticles – iron oxides
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Sample LP16 Ar 280 sccm, 500 W, Ar+Fe(CO)5
Plasma synthesis of nanoparticles – iron oxides
Dusty plasmas
• Low-temperature plasmas containing charged nano or macroparticles.
• They are also called complex or colloidal plasmas. They exhibit collective behavior
with strongly coupled particles.
• Dusty plasmas is that the particles can arrange in ordered crystal-like structures,
so-called plasma crystals (1994).
• In the plasma, the particles acquire high negative charges of hundreds or
thousands of elementary charges due to the inflow of electrons and ions. Then,
the Coulomb interaction of neighboring particles by far exceeds their thermal
energy: the system is strongly coupled. The spatial and time scales of the particle
motion allow easy observation by video microscopy. Weak frictional damping
ensures that the dynamics and kinetics of individual particles become observable.
Thus, dusty plasmas enable the investigation of crystal structure, solid and liquid
plasmas, phase transitions, waves and many more phenomena on the kinetic
particle level.
• Dusty plasmas can be find in astrophysics, polymer plasma synthesis or
semiconductor industry, where dust removal is essential for functionality of
transistors or solar cells.
Dusty plasmas
http://www2011.mpe.mpg.de/pke/index_e.html
Dusty plasmas
• Dusty plasmas are at least three component plasmas (electrons, ions and dust). In this
sense, dusty plasmas are comparable to negative ion plasmas.
• The typical charge on the charge carriers (dust) are of the order of 10 000 elementary
charges which leads to strong coupling.
• The dust charge is variable and depends on the local plasma parameters. Thus, the charge
becomes a dynamic variable.
• The dust mass is by orders of magnitudes larger than that of electrons and ions. Thus the
dominant time scale is that of the dust plasma frequency wpd which is by orders of magnitude
smaller than that of electrons and ions leading to convenient time scales for the observation
of dynamic processes.
• The slow time scales allow that electrons and ions contribute to shielding which should
results in different shielding scales.
• The dust size is not negligibly small leading to surface phenomena and forces which are
unimportant in “usual” plasmas.
• Fundamentals of Dusty Plasmas Goree_LANL_PPSS07.pdf
• Dusty plasmas , V E Fortov, A G Khrapak, S A Khrapak, V I Molotkov, O F Petrov, Physics Uspekhi
47 (5) 447 ± 492 (2004).