Jozef Stefan Institute Plasma laboratory Ljubljana, Slovenia Chemical cleaning with neutral oxygen or nitrogen atoms Miran Mozetič Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics

Fast removal of HC deposits Benign to CFC No oksidation of metals Mednarodna podiplomska šola Jožefa Stefana Application of neutral atoms (O or N)

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Tokamak Remote O – atom source Connection tube

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics O atom source is inductively coupled RF plasma 1.2 kW 5kW We are building 15 kW source

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics O atom density at 500W These values are measured in a side tube. The density in the major discharge tube is 2x larger

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Connection tube is made from material with a low coefficient for heterogeneous surface recombination γ < The transmission of the tube depends on the recombination coefficient gas drift velocity length of the tube Drift velocity is close to sound velocity (300m/s)

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics FLUID simulations plasma Connection tube To pump

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Experiment fits the theory Oxygen atom density Tube length [m]

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Influence of effective pumping speed 8 m 3 /h 16m 3 /h

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Setup under construction plasma n = 4x10 22 m -3 n > 1x10 21 m -3 Experimental chamber 3m long tube Schott 8250 Roots 500m 3 /h Rotary 100m 3 /h

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Experimental chamber O atom inlet To pumps Heatable sample holder Oxidation probability depends on type of CH temperature

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics HC film prepared by magnetron sputtering in Ar + H2 (pretty hard coating) n O = m -3

Introduction to reactive plasma Plasma is created in many gaseous discharges, but … Mednarodna podiplomska šola Jožefa Stefana

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics … but only inductively coupled RF plasma is cold and extremely reactive

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Surface effects depend on plasma parameters Discharge parameters Surface effects Plasma parameters gas mixture pressure gas flow type of discharge voltage current magnetic field reactor composition structure morphology wettability compatibility

Plasma parameters may change without changing discharge parameters Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics

Another example: O density during activation of textile Example: H density in a pyrex reactor Mednarodna podiplomska šola Jožefa Stefana

It pays to measure the neutral atom density during plasma processing of materials Mednarodna podiplomska šola Jožefa Stefana Recommended tool: catalytic probe

Catalytic probes: operation principles There is a flux of O atoms on catalytic surface O atoms recombine on the surface O + O O eV Power dissipated on the surface P = ½ W d j O The catalyst is heating at dT/dt = P/mc p (often over 10K/s) Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Catalyst material Optical fibre Probe tip O O2O2 Surface recombination x 5.2 eV

A typical probe temperature in H rich atmosphere Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics

A catalytic probe Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Catalytic probes (FOCP version) Probe tip The right choice of catalytic material depends on particular requirements Our choice: copper with γ = 0.18

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics The temperature of the probe tip can be too high if plasma is fully dissociated Warning We have destroyed many probes

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics O atom density in a MW plasma

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics O atom density during titration with NO

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics If your plasma is too aggressive … … place the probe in a side - vessel

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Experimental chamber: Pyrex tube with diameter 11 cm

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Schematic of the discharge chamber O 2 inlet To pump Sample holder sampleCatalytic probe

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics Rotatable nickel plate 90 o 180 o probe

Jozef Stefan Institute, Department of Surface Engineering and Optoelectronics CONCLUSION: RF plasma at about 100 Pa is an excellent source of O atoms Values over 1x10 22 m -3 are obtained Catalytic probes are suitable for real time measuring of O atom density