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SCPY 661 Effects and applications of low energy ion beam with polymeric- and biomaterials

Lecture plan. Physics of gas discharges Ionisation Positive ions sources Negative ion sources Charged particle optics. Ion sources. . Plasmas. Plasma is electrically neutral Charged particles excert a force on each other within shielding distance Plasma is electrically conducting Electric

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SCPY 661 Effects and applications of low energy ion beam with polymeric- and biomaterials

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    1. SCPY 661 Effects and applications of low energy ion beam with polymeric- and biomaterials Harry J. Whitlow Department of Physics PO Box 35 (YFL) FIN-40014 University of Jyvskyl Finland Harry_J.Whitlow@phys.jyu.fi

    2. Lecture plan Physics of gas discharges Ionisation Positive ions sources Negative ion sources Charged particle optics

    3. Ion sources

    4. Plasmas Plasma is electrically neutral Charged particles excert a force on each other within shielding distance Plasma is electrically conducting Electric field only penitrate as far as Debeye screening length lD Electron and ions have different tempertures (1 eV = 11 600 K) Plasma density ~1010-1016 e cm-3

    5. Gas discharge physics-I Ionisation by electron impact Aq+ + e- ?A(q+1)+ + 2e- Aq+ + e- ?A*(q+1)+ + e- A*q+ ? A(q+1)+ + e- Under action of the electric field the electrons are accelerated between collsionsso they gain enough energy to electron impact ionise another atom

    6. Gas discharge physics-II Across dx the change in the number of electrons crossing the plane If n0 e- emitted by cathode, integrating gives: If no losses for the whole tube: a is the Townsends first ionisation coefficient or gas multiplication factor

    7. Gas discharge physics-III If the mean free path of an electron in the E field direction is l then: a must depend on the number of atom it encounters per unit distance, which at constant temperature Then lumping together and replacing the unknown function f by F:

    8. Types of gas discharge High frequency AC Linear high frequency discharge Cathode little importance Significant fraction of charged particles cannot escape the discharge space Electrodes can be outside the plasma AC magnetic field Discharge tube inside solenoid AC current in solenoid induces circular currents Tokamak

    9. Processes in plasma

    10. Duoplasmatron ion source

    11. Penning Ion Sources The electrons spiral path increases the probability for ionisation PIG sources give higher currents and higher charge states than duoplasmatrons

    12. Penning ion source

    13. Rf ion source

    14. RF ion source

    16. Electron cyclotron resonance sources Plasma trapped in a magnetic bottle Longitudinal + hexapole field Microwave excitation Higher frequencies give higher charge states

    17. Electron Cyclotron Resonance (ECR) sources

    18. ECR sources Small ECR source for low energy ion irradiation in Jyvskyl

    19. 6.4 GHz ECR ion source Used for off-line materials irradiation Used as gas ion injector for cyclotron Source of highly charged heavy ions.

    20. High current gridded ion sources High currents 0.03-1 A Large area homogeneous irradiation Suitable for ion beam assisted deposition, sputtering etching etc

    21. R.F. plasma processing Substrate on cathode Plasma etching Substrate on anode Sputter deposition of cathode material

    22. RF plasma etch/deposition system

    23. Inductively coupled plasma source

    24. ECR ion source

    25. Charge exchange negative ion sources (Alphatros)

    26. Alphatros charge-exchange oven

    27. Ionisation potentials and electron affinities

    28. Sputtering of negative ions

    29. SNICS (Source of negative ions by Cs sputtering)

    30. Accelerator physics reductio ad absurdum. Harry J. Whitlow Department of Physics, University of Jyvskyl

    31. Beam transport and ion optics

    32. Lorentz force

    33. Acceleration in a homogeneous electric field Acceleration of a charged particle in an electric field is the basis of most practical accelerators

    34. Acceleration schemes

    35. Electrostatic deflectors

    36. Bending / analysis magnets

    37. Wein filters EB filter

    38. Quadrupole magnets Scalar potential of the field in cylindrical and Cartesian coordinates

    40. Quadrupole doublet A single quadrupole element makes beam converge in one direction and diverge in a perpendicular direction Quadrupole used in multiplets to achieve simulatanious focussing in x and y directions

    42. Ion implanters Low current: Used for doping semiconductors P+, B+, As+, In+, Sb+ High current O+ ions for production of SIMOX material N+,C+ for hardening metals by synthesis of metal nitrides, carbides etc. Metal ions for improvement of corrosion resistance

    43. State of the art semiconductor ion implantation system

    44. What is a tandem accelerator? Compact size is based on charge exchange

    45. The End

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