I.A.E.A. ViennaCRP Atomic and Molecular Data for Plasma Modelling

Coordination Meeting 17-20 November, 2008

INTERACTION OF SLOW IONS

WITH SURFACES:

ION SURVIVAL PROBABILITY

ON CARBON, TUNGSTEN AND BERYLLIUM SURFACES

(ROOM TEMPERATURE AND HEATED)

ZDENEK HERMAN and JAN ŽABKA

J. Heyrovský Institute of Physical Chemistry, v.v.i.

Academy of Sciences of the Czech Republic,

Prague

IAEA, Vienna, 17-20 Novermber, 2008

EXPERIMENT

ION SURVIVAL PROBABILITYpercentage of incident ions

surviving a surface collision as product ions

SA = 100 Σ Iprod / Iinc (%)

( Iinc = Itarg,m + Σ Iprod )

Experimental determination

1. Direct measurement of projectile ion current incident on the target (Itarg,m)

2. Determination of total current of product ions from ion current to the detector, collecting efficiency of the apparatus, and angular distributions

PERCENTAGE OF SURVIVING IONS, Sa(%)CARBON (HOPG), INC. ANGLE 300 (w.r. to the surface)

Einc= 16.3 eV Einc=31.3 eV Einc=46.3 eV

projectile Sa(%) Sa(%) Sa(%)

C3H2+•(1-propene) 1.7±0.1 2.5

C3H3+(c-propane) 3.6±0.3

C3H3+(1-propene) 7.8±0.5

C3H3+(propane) 6.3 5.5±0.3 3.9

C3H4+•(c-propane) 2.3±0.7 2.0 ±0.7

C3H4+•(1-propene) 1.8±0.1

C3H5+(c-propane) 2.5±0.2 2.0 ±0.7

C3H5+(1-propene) 2.3±0.9

C3D5+(D-propane) 9.9±1.4

C3H5+(propane) 11.2±0.7 4.6±0.2

C3H6+•(c-propane) 1.8±0.5 2.2±0.1

C3H6+•(1-propene) 0.7±0.3 3.8±0.9

C3D6+•(D-propane) 4.8±0.9

C3H6+•(propane) 6.6±0.9 7.2±1.2 6.8±2

C3D7+(D-propane) 20 ±3 16 ±3

C3H7+(propane) 11.9 ±4 17 ±6

C3D8+•(D-propane) 1.4 ±0.7

C3H8+•(propane) 0.7±0.3 2.7 ±0.5 4.2 ±2

PERCENTAGE OF SURVIVING IONS C3Hn+, Sa (%)

(room-temperature carbon (HOPG) surfaces)

incident angle: 300 with respect to the surface

SURFACE 15.4 eV 30.9 eV 45.4 eV

ROOM-TEMP

CD4+• W

BeHOPG

0.050.05

0.37±0.1

0.05

0.34±0.2

0.120.05

0.27±0.2

CD5+ W

BeHOPG

5.82.1

12.5±5

0.82.1

12±5

1.21.2

(18±7)

C2D4+• W

BeHOPG

0.170.4

1.0±0.5

0.170.7

1.0±0.4

0.19

0.9±0.2

C2H5+ W

HOPG2.7

1.1±0.031.6

1.0±0.10.85

0.3±0.03HEATED

CD4+• W

BeHOPG

0.03

0.5

0.020.080.23

0.02

CD5+ W

BeHOPG

1.1 0.5 0.50.15(23)

C2D4+• W

BeHOPG 0.35

0.10.4

0.4±0.05

C2H5+ W 0.56 0.32 0.24

ION SURVIVAL PROBABILITY, Sa (%)

CONCLUSION: survival probability on W or Be usually about 5-10x smaller than on HOPG

1.COLLISIONS OF CDn+ (n=3-5) WITH CARBON (HOPG),

ROOM TEMPERATURE, Φs = 300

VERY LOW ENERGY 3 – 11 eV

ION SURVIVAL PROBABILITY

Sa(%)

SA decreases below Einc. = 10 eV to zero

PROBABILITY OF ION SURVIVAL DEPENDENCE ON INCIDENT ANGLE

IONS FROM ETHANOL (SS SURFACE COVERED BY HYDROCARBONS)

C2H5OH+•

C2H5OH2+, C2H5O+

CONCLUSIONS

- survival probability depends strongly on incident angle: lower for steep collisions

- survival much higher for ions of low ionization energy (usually closed-shell ions), for ions of IE> ~10.5 eV about an order of magnitude lower

5 10 15

0

5

10

15

CO+

2

C2H+

4

C2H+

2

C3H+

6

CD+

3

CD+

4

C3H+

8

C3H+

4

C2H+

5

C2H+

3

C3H+

5

C3H+

3

C7H+

8

C3H+

7

CD+

5

C1 C2 C3 C7

Ar+, CO+

2

Sa

[ % ]

IE [eV]

C7H+

7

Ar+

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface at room temperature, E inc = 30 eV, inc. angle 300 w.r. to the surface)

correctly should be recombination energy (RE) of the projectile ion, but RE values little known, replaced by well-known ionization energies of the projectile ions (IE)

in most cases RE = IE, sometimes RE<IE (CH4+)

SURFACES HYDROCARBONS

C-chain IE (eV) n-alkanes olefins (C-C=C-….)

C4 10.53 9.1 C5 10.35 9.04 C6 10.13 8.97 C7 9.92 8.84 C8 9.86 8.91 C9 9.72 8.90 C10 9.65 8.90____________________________________

n-alkanes (pump oil) crack to form olefins

5 10 15

0

5

10

15

20

25

30

35

CD+

5

CD+

5

C2H+

4

C2H+

2CD+

3 CD+

4

C2H+

5

C2H+

3

CD+

5

Sa

[ % ]

IE [eV]

N2

+

HOPGheated 600o

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface HEATED, Einc = 30 eV, inc. angle 300 w.r. to the surface)

5 10 15

0.01

0.1

1

10

1,3,5-Triaz

NH+

3

3-F-BzN

Bz

y = (3.9±0.5) + (-0.39±0.04).x

C1 C2 C3 C7

Ar+, CO+

2

CO+

2

C2H+

4

C2H+

2

C3H+

6

CD+

3

CD+

4

C3H+

8C

3H+

4

C2H+

3

C2H+

5

C3H+

5

C3H+

3

C7H+

8C3H+

7

CD+

5

Sa

[ % ]

IE [eV]

C7H+

7

Ar+

Styr

5 10 15

0.01

0.1

1

10

y = (3.9±0.5) + (-0.39±0.04).x

C1 C2 C3 C7

Ar+, CO+

2

CO+

2

C2H+

4

C2H+

2

C3H+

6

CD+

3

CD+

4

C3H+

8C

3H+

4

C2H+

3

C2H+

5

C3H+

5

C3H+

3

C7H+

8C3H+

7

CD+

5

Sa

[ % ]

IE [eV]

C7H+

7

Ar+

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface, room temperature Einc = 30 eV, inc. angle 300 w.r. to the surface)

SEMILOG PLOT

*) data from A.Somogyi..(V.H.Wysocki),JACS 13(2002)1151

5 10 15

1E-3

0.01

0.1

1

10

HOPG Heatedy = (5.4±1.1) + (-0.5±0.1).x

y = (3.9±0.5) + (-0.39±0.04).x

C2H+

4

C2H+

2

CD+

3

CD+

4

C2H+

3

C2H+

5

CD+

5

Sa

[ % ]

IE [eV]

N2

+

HOPG Room Temp

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES (Carbon (HOPG) surface, Einc = 30 eV, inc. angle 300 w.r. to the surface)

SEMILOG PLOT

COMPARISON:

- ROOM-TEMPERATURE (hydrocarbon-covered)

- HEATED (“naked”) SURFACES

RT: slope -0.39 ± 0.04

HEATED: slope -0.5 ± 0.1

log SA = a - b (IE)

Analogy with the Arrhenius equation?

(dependence of rate constant of a chemical reaction on temperature T)

log k = a – b/T

k = A exp (- E / RT)

5 10 150.0

0.5

1.0

1.5

2.0

2.5

WolframRoom Temp

N+

2CD+

4

C3H+

8

C3H+

5

C3H+

3

C3H+

7

CD+

5

Sa

[ % ]

IE [eV]

Ar+

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES Einc = 30 eV, inc. angle 300 w.r. to the surface

TUNGSTEN

• ROOM-TEMPERATURE SURFACE

• HEATED ( 6000C) SURFACE

10 15

1E-3

0.01

0.1

1

10

Sa

[ % ]

N+

2

y = (2.5±0.4) + (-0.36±0.04).x

N+

2

CD+

4

C2H+

2

C2H+

4

C2H+

5

CD+

5

Ar+

CD+

4

C3H+

8

C3H+

5

CD+

5

C3H+

3

y = (2.9±0.2) + (-0.35±0.02).x

C3H+

7

IE [ eV ]

Wolfram at Room Temperature

Wolfram heated ~ 600oCE = 30.0 eV

inc. Angle = 30o

meas. ang. 49oEva => 19o

8.10.08

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES Einc = 30 eV, inc. angle 300 w.r. to the surface

TUNGSTENSEMILOG PLOT

• ROOM-TEMPERATURE SURFACE

• HEATED ( 6000C) SURFACE

CONCLUSION

Very similar slopes (-0.35 – 0.36) on both RT and HEATED W- surface

5 10 15

1E-3

0.01

0.1

1

10

C3H+

8

C3H+

7

C3H+

3

C3H+

5CD+

5

CD+

4

N+

2

Ar+

y = (2.9±0.2) + (-0.35±0.02).x

y = (3.9±0.5) + (-0.39±0.04).x

C1 C2 C3 C7

Ar+, CO+

2

CO+

2

C2H+

4

C2H+

2

C3H+

6

CD+

3

CD+

4

C3H+

8C

3H+

4

C2H+

3

C2H+

5

C3H+

5

C3H+

3

C7H+

8C

3H+

7

CD+

5

Sa

[ % ]

IE [eV]

C7H+

7

Ar+

HOPG Room T

Wolfram Room T

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES Einc = 30 eV, inc. angle 300 w.r. to the surface

SEMILOG PLOTSCOMPARISON OF ROOM-TEMPERATURE SURFACES

• CARBON (HOPG)

• TUNGSTEN (W)

• BERRYLIUM (Be)

CONCLUSION

Similar slopes (-0.35- 0.39), similar behavior of surfaces covered by a hydrocarbon layer

log SA = a - b (IE)

____________________________________surface a b____________________________________

C (HOPG) - H 5.4 ± 0.1 0.5 ± 0.1 C (HOPG)-RT 3.9 ± 0.5 0.39 ± 0.04

W – H 2.5 ± 0.4 0.36 ± 0.04W – RT 2.9 ± 0.2 0.35 ± 0.02

Be – RT (3.9 ± 0.5) (0.39?) Be – H ??

_____________________________________

ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES

SEMILOG PLOT

CONCLUSIONS

1. Survival probability of ions in collisions with surfaces, SA, changes over several orders of magnitude (from ~10% to 10-3% ) depending on the type of ion, type of surface and incident angle.

2. SA for even-electron ions (low ionization energies) appears to be much higher than for radical cations (open-shell ions, higher ionization energies)

3. A dependence of SA vs. IE of the projectile ion shows a drastic change (from ~10 % to less than 1%) at IE ~ 9 - 10 eV. For surfaces covered with hydrocarbons this correlates well with the IE of C4-C10 olefins with non-terminal C=C.

4. A dependence log SA vs. IE shows a good correlation over many orders of magnitude

log SA = a – b (IE)

with „a“ dependent on the type of the surface, and b = - 0.35 - 0.4 for room-temperature (hydrocarbon-covered surfaces)