Jari Koskinen 1 Thin Film Technology Lecture 2 Vacuum Surface Engineering Jari Koskinen 2014

Jari Koskinen 2 Vacuum surface engineering 1.Vacuum technology 2.Surface phenomena 3.Surface energetic ion interaction

Jari Koskinen 3 Vacuum surface engineering 1.Vacuum technology 2.Surface phenomena 3.Surface energetic ion interaction

Jari Koskinen 4 Vacuum system VACUUM GAUGE VACUUM CHAMBER FLANCE PUMP RESUDUAL GAS

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Jari Koskinen 6 Large surfaces, upscaling

Jari Koskinen 7 Residual gas pump desorption diffusion of dissolved molecules permeation leak Pumping of: Residual gas: Adsorption – Desorption Diffusion of dissolver or trapped gas Permeation trough materials Leaks

Jari Koskinen 8 Units of pressure UltraGood High HighInter- mediate Rough Total pressure of residual gasses

Jari Koskinen 9 Sources of residual gas High vacuum pumping speed leak Good High vacuum desorption from walls baking Ultra high vacuum impurities internal leaks material selection diffusion permeation

Jari Koskinen 10 UltraGood High HighInter- mediate Rough Total pressure of residual gasses Average mean free path (distance between collission) in nitrogen residual gas

Jari Koskinen 11 Average mean free path (distance between collission) in nitrogen residual gas UltraGood High HighInter- mediate Rough Total pressure of residual gasses

Jari Koskinen 12 Phases of residual gas UltraGood High HighInter- mediate Rough Total pressure of residual gasses d = diameter of chamber Viscotic < d/100 Intermediate Molecular >> d

Jari Koskinen 13 Phases of residual gas UltraGood High HighInter- mediate Rough Total pressure of residual gasses d = diameter of chamber Viscotic < d/100 Intermediate Molecular >> d

Jari Koskinen 14 Time to form one molecular layer on surface UltraGood High HighInter- mediate Rough Total pressure of residual gasses

Jari Koskinen 15 Vapour and liquid in vacuum pump balance: pumping = evaporation pressure constant until all liquid is pumped balance: condensation = evaporation

Jari Koskinen 16 Critical temperatures and pressures for some residual gasses above T c no liquid pump Helium Hydrogen Nitrogen Carbon monoxide Argon Oxygen Methane Carbon dioxide Chlorine Ether Ethanol Carbon tetraclor. Water Gas or vapor

Jari Koskinen 17 Vacuum pumps Positive displacement (mechanical pumps) Momentum transfer (molecular pumps) Entrapment

Jari Koskinen 18 Mechanical pumps Rotary vaneRootsDiafragma

Jari Koskinen 19 Mechanical pumps Scroll pumppump

Jari Koskinen 20 Momentum transfer Turbo molecularmolecularOil diffusion pump pump

Jari Koskinen 21 Entrapment cryo pumppump ion pump

Jari Koskinen 22 Pumps and vacuum ranges

Jari Koskinen 23 Vacuum gauges Mechanical – diaphragm Electronic Piezoresitive (strain gauge) Capacitive Magnetic Piezoelectric Optical Potentiometric Resonant Thermal conductivity – Pirani Ionzation gauge Hot cathode Cold cathode (Penning)

Jari Koskinen 24 Gauges ionization gauge hot filamentPirani

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Jari Koskinen 26 Residual gas analyser SRS RGA100 Residual Gas Analyzer

Jari Koskinen 27 Vacuum systems

Jari Koskinen 28 Vacuum systems

Jari Koskinen 29 Gas flow in vacuum systems Q = C(P 1 – P 2 ) P1P1 P2P2 C conductance l/s Q gas troughput [pressure*volume/s] in series: in parallel:

Jari Koskinen 30 Conductance of various geometries M. Ohring

Jari Koskinen 31 Vacuum systems

Jari Koskinen 32 Vacuum system design

Jari Koskinen 33 Vacuum surface engineering 1.Vacuum technology 2.Surface phenomena 3.Surface energetic ion interaction

Jari Koskinen 34 Surface energy γ surface tension = dW work needed to form surface dA In thermodynamic equilibrium:

Jari Koskinen 35 Contact angle Young equation S solid L liquid G gas Spreading parameter S Complete wetting when S ≈ 0 non-wetting when S ≈ -2 Υ LG

Jari Koskinen 36 Surface reconstruction 

Jari Koskinen 37 Surface structure and defects 

Jari Koskinen 38 Adsorption Physisorption Chemisorption

Jari Koskinen 39 Adsorption Physisorption Chemical bonding: polaroization (van der Waals) Bonding energy ≈ – 0.5 eV Bond length ≈ 3 – 10 Å For example: nobel gas or molecules on materials Possibly precursion state before chemisorption

Jari Koskinen 40 Adsorption Chemisorption Chemical bonding: charge exchange Bonding energy ≈ 0.5 – 5 eV Bond length ≈ 1 – 3 Å For example: H, O, N, CO on metals Dissociation of molecule Final absorption

Jari Koskinen 41 Desorption Adsorbed molecule receives energy E D in order to leave surface thermal radiation photons electrons ions electric field

Jari Koskinen 42 Balance of absorption - desorption collisions of molecules (gas) S sticking coefficient E D energy for desorption P pressure Coverage ≈ High P, low T more adsorption E D large, full coverage very little adsorption in UHV

Jari Koskinen 43 Surface diffusion

Jari Koskinen 44 Surface diffusion  Diffusion is thermally activated random movement of adsorbed atoms  D = D 0 e -E act /kT  E act large -> slow diffusion  T high – fast diffusion Surface diffusion of Cu on Cu(111) E act

Jari Koskinen 45 Work function  Work function ϕ  E F Fermi energy  D dipole potential

Jari Koskinen 46 Work function of some metals Adsorbed atoms alloying effect work function

Jari Koskinen 47 Solubility of gasses into metals

Jari Koskinen 48 Vacuum surface engineering 1.Vacuum technology 2.Surface phenomena 3.Surface energetic ion interaction

Jari Koskinen 49 Energetic ion surface interactions

Jari Koskinen 50 Secondary electrons

Jari Koskinen 51 Desorption, cleaning

Jari Koskinen 52 Sputtering

Jari Koskinen 53 Collision cascade, thermal spike K. Nordlund

Jari Koskinen 54 Thermal spike _au.gif HY Nordlund simulations anims.html gif/au500.avi 10 keV Au ion to Au surface

Jari Koskinen 55 doping, compounds