MoS 2 Nano-particle production in a PACVD environment Eva Stoffels, Winfred Stoffels, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands 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

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 MoS 2 nano-particles During wear of the layer, MoS 2 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 MoS 2 nano-particle production substrate TiN layer MoS 2 particle Lubricating MoS 2 film Particle lubricating the surface

HOW ? two chemistries : A. H 2 S based: 2MoCl 5 + 4H 2 S + H 2 --> 2MoS HCl H 2 S is in gas form--> easy in use H 2 S is very poisonous --> dangerous B. sulphur based:2MoCl 5 + 4S + 5H 2 -->2MoS HCl 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 --> high pressure 2. Plasma assisted particle formation complex, but matching TiN PACVD conditions non-equilibrium chemistry available

Setup 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 MoCl 5 Pressure: Torr gas flows < 200 sccm rf power W

-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 Particles trapped in plasma

Thermal ovenPlasma Sulphur H 2 S Effective only at high pressures (>10 Torr) Not compatible with PACVD TiN coating technology Fast and abundant particle formation Particle size below 100 nm Uniform size distribution Spherical shape 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

H 2 S & Thermal oven Useful in CVD environment at pressures above 10 Torr Potentially not compatible with the TiN chemistry: 2TiCl 4 + N 2 + 4H 2 --> 2TiN + 8HCl Particle size can be controlled to sub-micrometer range particles are cauliflower like T vap = 150 o C T dep = 400 o C H 2 = 120 sccm H 2 S = 200 sccm p= 2 kPa (15 Torr)

H 2 S & Plasma Fast and abundant particle formation (size < 100 nm) co-deposition is possible 3  m Conditions(left): temperature evaporation oven 150 o C and main oven 160 o C, pressure 0.5 Torr, rfpower 13 W, gas flow 10 sccm Ar through evaporation chambers 5 sccm H 2 and 10 H 2 S through main oven and 10 sccm H 2 in main chamber reaction time: 10 minutes collected under plasma ring

3µm Sulphur & Thermal oven Low particle formation rate, and large particles Crystalline and amorphous particles 10  m Conditions: temperature evaporation oven 150 o C and main oven 450 o C, pressure 10 Torr gas flow20 sccm(left) and 50 sccm(right) Ar through evaporation chambers 50 sccm(left) and 100 sccm(right) H 2 through main oven 100 sccm Ar(left) and 100 sccm H 2 (right) in main chamber reaction time: 45 minutes(left) and 30 minutes(right) Amorphous layer with nanoparticleslarge crystals and nanoparticles

Sulphur & Plasma Fast and abundant particle formation Crystalline and amorphous phase 1  m Conditions: temperature evaporation oven 150 o C and main oven 160 o C, pressure 0.5 Torr, rfpower 13 W, gas flow 5 sccm Ar through evaporation chambers 5 sccm H 2 through main oven and 10 sccm H 2 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)

Commercial MoS 2 10  m 3  m MoS 2 can be obtained commercially, For our purposes it is too large and contaminated by air exposure

Conclusions MoS 2 nano-particle production is possible under a variety of conditions:using either H 2 S 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