MoS2 Nano-particle production

1
MoS2 Nano-particle production in a PACVD
environment
Eva Stoffels, Winfred Stoffels, Eindhoven
University of Technology, PO Box 513, 5600 MB
Eindhoven, The Netherlands stoffels_at_discharge.phys
.tue.nl Giacomo Ceccone, Francois Rossi, Rachid
Hasnaoui European Commission, Joint Research
Center, Ispra (VA), Italy. Hartmut Keune, G.
Wahl, Institut fuer Oberflaechentechnik und
Plasmatechnische Werkstoffentwicklung, Technische
Universitaet Braunschweig, Germany
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WHY ?

• The final aim is the deposition of a hard
  self-lubricating coating
• This is obtained by co-deposition of a hard TiN
  layer
• and lubricating MoS2 nano-particles
• During wear of the layer, MoS2 is released,
  providing in situ lubrication, without
  environmentally dangerous liquid lubricants
• Co-deposition will be obtained by CVD or PACVD.
• In this work focus on MoS2 nano-particle
  production

MoS2 particle
Particle lubricating the surface
Lubricating MoS2 film
TiN layer
substrate
3
HOW ?

• two chemistries
• A. H2S based 2MoCl5 4H2S H2 --gt 2MoS2
  10HCl
• H2S is in gas form--gt easy in use
• H2S is very poisonous --gt dangerous
• B. sulphur based 2MoCl5 4S 5H2 --gt2MoS2
  10HCl
• S needs to be evaporated
• S is not toxic and cheap
• two techniques
• 1. Condensation of particles in a thermal oven
  
• easy, but additional process step needed,
  
• only equilibrium chemistry --gt high pressure
• 2. Plasma assisted particle formation
• complex, but matching TiN PACVD conditions
• non-equilibrium chemistry available

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Setup
Pressure 0.05-5 Torr gas flows lt 200 sccm rf
power 0-500 W

• Deposition occurs in the main chamber, with
  optional (heated) substrate or rf-electode
• Thermal reactions occur in a thermal oven
• Evaporation chambers supply gaseous sulphur and
  MoCl5

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Particles trapped in plasma
-Nano-particles in a plasma acquire negative
charge -They are trapped near the plasma
glow-sheath edge -They fall on the substrate when
the plasma is off -In a ring shaped plasma they
are trapped vertically in the ring, but can
diffuse horizontally to the center and
deposit -Particles are observed by helium neon
laser light scattering
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Thermal oven Plasma

• Effective only at high pressures (gt10 Torr)
• Not compatible with PACVD TiN coating technology

• Fast and abundant particle
• formation
• Particle size below 100 nm
• Uniform size distribution
• Spherical shape

Sulphur H2S

• Low particle formation rate at sub-Torr pressures
• Chemistry compatible with TiN coating
• Various sizes
• Crystalline or amorphous

• Fast and abundant particle
• formation
• Spherical shape
• Crystalline and amorphous phase
• Sub-micrometer size and larger

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H2S Thermal oven

• Useful in CVD environment at pressures above 10
  Torr
• Potentially not compatible with the TiN
  chemistry
• 2TiCl4 N2 4H2 --gt 2TiN 8HCl
• Particle size can be controlled to sub-micrometer
  range
• particles are cauliflower like

Tvap 150 oC Tdep 400 oC H2 120 sccm H2S
200 sccm p 2 kPa (15 Torr)
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H2S Plasma

• Fast and abundant particle formation (size lt 100
  nm)
• co-deposition is possible

3 mm
Conditions(left) temperature evaporation oven
150 oC and main oven 160 oC, pressure 0.5 Torr,
rfpower 13 W, gas flow 10 sccm Ar through
evaporation chambers 5 sccm H2and 10 H2S through
main oven and 10 sccm H2 in main chamber reaction
time 10 minutes collected under plasma ring
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Sulphur Thermal oven

• Low particle formation rate, and large particles
• Crystalline and amorphous particles

Amorphous layer with nanoparticles large
crystals and nanoparticles
10 mm
Conditions temperature evaporation oven 150 oC
and main oven 450 oC, pressure 10 Torr gas
flow 20 sccm(left) and 50 sccm(right) Ar through
evaporation chambers 50 sccm(left) and 100
sccm(right) H2through main oven 100 sccm
Ar(left) and 100 sccm H2(right) in main
chamber reaction time 45 minutes(left) and 30
minutes(right)
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Sulphur Plasma

• Fast and abundant particle formation
• Crystalline and amorphous phase

1 mm
1 mm
Conditions temperature evaporation oven 150 oC
and main oven 160 oC, pressure 0.5 Torr,
rfpower 13 W, gas flow 5 sccm Ar through
evaporation chambers 5 sccm H2through main oven
and 10 sccm H2 in main chamber reaction time 10
times 2 minutes(left) and 20 times 30
seconds(right) (plasma off 15 seconds) collection
area under plasma ring(left) and in
center(right)
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Commercial MoS2

• MoS2 can be obtained commercially,
• For our purposes it is too large and contaminated
  by air exposure

3 mm
10 mm
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Conclusions

• MoS2 nano-particle production is possible under a
  
• variety of conditions using either H2S or
  sulphur
• in CVD and in PACVD
• Crystalline and amorphous material can be
  produced
• The size-range spans from nanometers up to tens
  of micrometers
• Plasma produced particles are formed faster,
• more abundant and at lower pressures
• Formation of titanium-sulphide and chlorine
  contamination are
• possible future problems for hybrid
  self-lubricating hard coatings,
• however the hardness of the hybrid layers is in
  the TiN range