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1 PIII for Hydrogen Storage Child's Plasma Sheath Model and Theoretical Considerations Emmanuel Wirth, prof. L. Pranevičius, 2006-01-27 Project: “ORGANIZATION.

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Presentation on theme: "1 PIII for Hydrogen Storage Child's Plasma Sheath Model and Theoretical Considerations Emmanuel Wirth, prof. L. Pranevičius, 2006-01-27 Project: “ORGANIZATION."— Presentation transcript:

1 1 PIII for Hydrogen Storage Child's Plasma Sheath Model and Theoretical Considerations Emmanuel Wirth, prof. L. Pranevičius, Project: “ORGANIZATION OF HYDROGEN ENERGY TECHNOLOGIES TRAINING” Project code: BPD2004-ESF /0045

2 2 Outline of the presentation Current plasma hydriding /PIII Simple Model of the sheath : Child law Calculations Conclusions

3 3 DC/AC Plasma Treatment/ PIII Near anode there is a negative space charge Near cathode, the cathode sheath is a zone of intensive ionisation Not suitable for good extraction of H Substrate at the Anode Substrate at the Cathode If AC A and C are equivalent

4 4 Plasma Immersion Ion Implantation System Negative bias of the substrate  electrons near the substrate are rejected  positive charge space (sheath) near the substrate Plasma created by an auxiliary device Plasma Surface is the Source of ions Plasma CathodeAnode Substrate U < 0

5 5 Child Langmuir law C.D.Child, Phys. Rev. 32 (1911) 492. and I.Langmuir, Phys. Rev. (Ser.II) 2 (1913) 450. Maximum ion current Solution of the the Poisson's Equation ε 0 = F.m -1 m i = kg (for H) e = C Only when space charge ≠ 0 V 0 = Absolute value of sheath potential drop s = length of the sheath

6 6 Child law sheath After a transition time the sheath become a Child law sheath: Debye length: Screening distance over which external electrical field are excluded in the plasma

7 7 Values of ionic current densities J i strongly depends on electronic density (= ion density in plasma) If P , J i  ( constant ionization ratio) This is the very maximum that you can reach!

8 8 Values of the sheath length Sheath Size depend on n e The device should be bigger than the sheath assumption: kTe ≈ 2 eV

9 9 Effect of the electronic density on the sheath length Many parameters influences the e- density (P, type of gas, geometry of chamber,..) but if P , n e , s  Sheath can be in order of meters The less the e- density is the bigger the sheath is

10 10 2 cases for the sheath Collisionless regime If s < λ, ions pass the sheath like in vacuum (no energy loss) Collisional regime If s > λ, ions perform collisions Some energy is lost You cannot reach the maximum voltage You do not obtain the theoretical maximum ions flux U < s

11 11 Comparison Sheath Length/Mean Free Path (1) Mean free path for hydrogen plasma depending on the pressure S= cross section N= number of particles per unit volume Distance between 2 collisions Calculation for Hydrogen gas

12 12 Comparison Sheath Length/Mean Free Path (2) In some case you may have s > λ If P  mean free path  you have collision in sheath If P  you avoid collisions but ion flux 

13 13 Possible PIII systems + : Easy to use - : Pressure must be higher (λ), collisions problems PIII + : Higher plasma density, higher ion flux - : Contamination of the magnetron, λ The exact ion energy, flux cannot be known

14 14 Conclusion (1) PIII is better than DC/AC Plasma Treatment for Hydriding Independent control of parameters But The right choice of P and V must be done If P too high  Collisions:Loss of E (s/  If P too low  low ion flux If V too high  sheath > chamber If V too low  low ion energy

15 15 Conclusion (2) Main Parameter in PIII: Gas Pressure Voltage Pulse width (in case of pulsed plasma) Furthers informations? A.Anders, Surf. Coat. Technol.183 (2004)


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