Ion Energy Distribution and Carbon Clusters in Ion Sources: Experimental Analysis, Slides of Physics

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LAYOUT

 Introduction

 Experimental Techniques

 Experimental

 Results & Discussion

 Conclusion

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ION ENERGY DISTRIBUTION

 Plasma based ion sources have got inherent energy

spread. Energy distribution can result from number of causes;  A spatial variation in the potential of the point in the source where an ion was created.  the thermal energy that is characteristics of the temperature of the ions in an ion source.  Charge exchange which might occur in the region of extraction or initial acceleration.

 Ions created by sputtering originate from

equipotential surface and have an energy distribution characteristic of secondary electrons (peaked at ≈ 5 eV) and has low intensity high- energy tail extending into few hundreds of eV

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VACUUM SYSTEM

 Ion can only move under vacuum condition, so we need to develop a vacuum system.

 There are varieties of pumps, Some of these pumps available are rotary, diffusion and turbo molecular pump.

 The rotary vacuum pumps can attain pressures

as low as 10-3^ torr. roughing is done by this (until approximately 10 -2^ torr is achieved).

 The oil diffusion pumps is operated with oil with

low vapor pressure. Its purpose is to achieve higher vacuum.

 Turbo molecular Pumps can generate many

degrees of vacuum from intermediate up to ultra high vacuum levels

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DUOPLASMATRON ION SOURCE

 The ion source consist of three electrodes.  Hollow cathode (HC)  Intermediate Electrode (IE)  Anode (A)

 HC provides electrons to produce discharge.

 The glow discharge of the noble gas, is initiated by two well-defined electron energy regimes; high energy  10eV, electrons near the cathode surface and low energy ones  1eV, in the positive column  The sputtered atoms may include ions, neutrals, excited and Meta-stable atoms.  Due to the pressure gradient the species, which are not attracted by the cathode, move towards the anode via IE and extracted by an extractor lens.^5

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ENERGY ANALYZER

+V

• V

r 2

r 1

r

Ion Beam In

Ion Beam Out 7

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WORKING PRINCIPLE OF ENERGY

ANALYZER

Electrostatic force (provided by – V and +V) and centripetal force (provided by curved path) must balance, ( Fc=Fe ) for uniform circular motion. In our design r 1 = 58.0 mm r 2 = 68.0 mm Therefore E = 0.158 Eo

Eo = Energy of Incoming beam & E = Applied electrical energy In this way energy analyzer acts as energy filter.

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2

1 0 ln r

r E  E

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EXPERIMENTAL PROCEDURE

 Ion source is operated at a discharge voltage of Vdis=0.8 kV with discharge current of Idis= 100mA.

 Ar is used as support gas to initiate the discharge at 1.0 mbar.

 Ions are extracted through extractor by applying voltage Vext = 2 kV.

 Ion beam is accelerated from charged particle accelerator to different acceleration voltages.

 Positive and negative voltages are provided simultaneously to the plates of energy analyzer using high voltage supplies controlled by software developed in Labview.

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EXPERIMENTAL PROCEDURE

 The 90 energy analyzer bends the beam and is detected by faraday cup placed at exit of analyzer.

 Electrometer reads the current at faraday cup and feeds back the signal to the data acquisition software which plots output current Vs applied voltage on the plates.

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ENERGY SPECTRA AT COLLIMATION OF 5.6 

(^00 1 2 3 )

1

2

3

7.67 keV

5.14 keV

I(pA)FC

EA plates voltage (kV)

Energy spectrum of ion beam (12 keV)

(^00 1 2 3 )

2

4

6

15.8 keV

18.16 keV

I(pA)FC

EA plates voltage (kV)

Energy spectrum of ion beam (22 keV)

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ENERGY SPECTRUM AT 12 keV BEAM ENERGY Graphite Cathode collimation of full angle divergence (θ) of 2.8

1.0 1.2 1.4 1.

(2)

(1) 8.3 keV

8.78 keV IFC

(pA)

Energy of E-field applied (keV)

(7.91-8.54)(8.54-9.17)

25.6%

74.3%

Area Ratio (%)

Energy Range (keV)

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ENERGY SPECTRUM AT 22 keV BEAM ENERGY

2.4 2.6 2.8 3.0 3.

2.5 (^) (3)

(1) (2)

18.25 keV

15.9 keV 16.6 keV

IFC

(pA)

Energy of E-field applied (keV)

(15-16.33)(16.33-17.91)(18.2-18.33)

43.8%^ 48.9%

7.29%

Area Ratio (%)

Energy Range (keV)

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ENERGY SPECTRUM AT 27 keV BEAM ENERGY

(19.4-20.8)(20.8-23.3) (26.6-26.83)

12.4%

52.5%

35% Area Ratio (%)

Energy Range (keV)

2.8 3.2 3.6 4.0 4.

0

1

2

3

4

(3)

(1)^ (2)

26.64 keV

20.44 keV 21.32 keV

IFC

(pA)

Energy of E-field applied (keV)

Sr. No

Peak. No.

Peak energy in spectrum (keV)

Applied ion beam energy (keV)

FWHM (keV)

Difference in energy (%)

a

1 8. 12.

0. 2 8.78 0.27^ -28.

b

1 12. 17.

0. 2 12.60 0.56^ -27.

c

1 15. 22.

1. 2 16.60 1.38^ -26. 3 18.25 0.02 -16.

d

1 20. 27.

1. 2 21.32 1.79^ -23. 3 26.64 0.06 -1.

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ENERGY SPECTRUM AT 5 keV BEAM ENERGY Aluminium Cathode

0.2 0.4 0.6 0.8 1.

(2)

(1) 3.4 keV

3.8 keV

IFC

(pA)

Energy of E-field applied (keV)

(0.47-0.57)(0.58-0.63)

74.8%

Area Ratio (%)^ 25%

Energy Range (keV)