I.A.E.A. Vienna
CRP 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 PROBABILITY
percentage 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=11.7 eV
projectile
Sa(%)
Einc= 16.3 eV
Sa(%)
Einc=31.3 eV
Einc=46.3 eV
Sa(%)
Sa(%)
0.22+0.04
0.34+0.2
12.0+5
0.26+0.16
0.27+0.26
18+7
0.1±0.03
0.06±0.01
0.08±0.02
2.4 ±
0.7±o.1
0.9±0.2
0.3±0.03
NON-HEATED
CD3+
CD4+
CD5+
C2H2+
C2D2+
C2H3+
C2H4+
C2D4+
C2H5+
HEATED
CD3+
CD4+
CD5+
0.12+0.03
0.37+0.06
12.5+5
0.1±0.03
6.4±0.4
2.3±0.6
0.3±0.03
1.1±0.03
0.09
0.5
4.1±0.7
1.2
1.0±0.4
1.0±0.1
0.1
0.23
23
C2H2+
0.1±0.04
0.1±0.04
0.36
+
C2D2
0.07±0.2
+
C2H3
3.6±0.2
5
+
C2H4
0.2±0.05
0.8±0.2
+
C2D4
0.4±0.05
-------------------------------------------------------------------------------------------------------------
PERCENTAGE OF SURVIVING IONS C3Hn+, Sa (%)
(room-temperature carbon (HOPG) surfaces)
Einc= 16.3 eV
projectile
Sa(%)
Einc=31.3 eV
Einc=46.3 eV
Sa(%)
Sa(%)
C3H2+•(1-propene)
1.7±0.1
2.5
C3H3+(c-propane)
C3H3+(1-propene)
C3H3+(propane)
3.6±0.3
7.8±0.5
5.5±0.3
3.9
6.3
C3H4+•(c-propane)
C3H4+•(1-propene)
2.3±0.7
1.8±0.1
2.0 ±0.7
C3H5+(c-propane)
C3H5+(1-propene)
C3D5+(D-propane)
C3H5+(propane)
2.0 ±0.7
11.2±0.7
2.5±0.2
2.3±0.9
9.9±1.4
4.6±0.2
2.2±0.1
3.8±0.9
6.6±0.9
1.8±0.5
0.7±0.3
4.8±0.9
7.2±1.2
C3H6+•(c-propane)
C3H6+•(1-propene)
C3D6+•(D-propane)
C3H6+•(propane)
C3D7+(D-propane)
C3H7+(propane)
C3D8+•(D-propane)
C3H8+•(propane)
20 ±3
11.9 ±4
0.7±0.3
1.4 ±0.7
2.7 ±0.5
incident angle: 300 with respect to the surface
6.8±2
16
17
±3
±6
4.2 ±2
ION SURVIVAL PROBABILITY, Sa (%)
ROOM-TEMP
CD4+•
CD5+
C2D4+•
C2H5+
HEATED
CD4+•
CD5+
C2D4+•
C2H5+
SURFACE
15.4 eV
30.9 eV
45.4 eV
W
Be
HOPG
W
Be
HOPG
W
Be
HOPG
W
HOPG
0.05
0.05
0.37±0.1
5.8
2.1
12.5±5
0.17
0.4
1.0±0.5
2.7
1.1±0.03
0.05
0.12
0.05
0.27±0.2
1.2
1.2
(18±7)
0.19
W
Be
HOPG
W
Be
HOPG
W
Be
HOPG
W
0.03
0.5
1.1
0.35
0.56
0.34±0.2
0.8
2.1
12±5
0.17
0.7
1.0±0.4
1.6
1.0±0.1
0.02
0.08
0.23
0.5
0.1
0.4
0.4±0.05
0.32
0.9±0.2
0.85
0.3±0.03
0.02
0.5
0.15
(23)
0.24
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
1,5
ION SURVIVAL
PROBABILITY
+
CD5 (x 0.1)
Sa(%)
1,0
SA [%]
C 2D 4
+
SA decreases below
Einc. = 10 eV to zero
0,5
CD4
+
CD3
+
0,0
0
10
20
30
Einc [eV]
40
50
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
ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES
(Carbon (HOPG) surface at room temperature, Einc = 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)
15
+
C7H7
+
CD5
in most cases RE = IE, sometimes RE<IE (CH4+)
+
C3H7
+
C7H8
C-chain
n-alkanes
IE (eV)
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
10
Sa [ % ]
SURFACES HYDROCARBONS
C1
C2
C3
C7
+
+
Ar , CO2
+
C3H3
5
+
C3H5
+
C2H3
+
C2H4
+
C3H4
+
C3H8
+
+
C2H5
0
5
C3H6
+
C2H2
+
CD3
10
IE [eV]
+
CD4
+
CO2
Ar
15
+
ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES
(Carbon (HOPG) surface HEATED, Einc = 30 eV, inc. angle 300 w.r. to the surface)
35
+
CD5
HOPG
heated 600o
30
+
CD5
25
+
Sa [ % ]
CD5
20
15
10
5
+
C2H3
+
C2H5
+
C2H4
+
CD3
0
5
+
C2H2 CD+
4
10
IE [eV]
+
N2
15
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
10
CD5
C7H7
10
+
C7H8
+
C3H7
+
+
+
+
CD5Styr
C7H7
+
C7H8 Bz
+
C3H7
+
+
+
C3H5
C3H3
+
C3H5
+
C2H3
C3H3
+
C2H3
3-F-BzN
+
+
1
Sa [ % ]
C2H5
C3H8
+
C3H6
C2H4
+
CD4
+
CD3
0.1
+
C3H6
C1
C2
C3
C7
+
+
Ar , CO2
+
Ar
+
NH3
+
+
CD3
+
C2H2
C1
C2
C3
C7
+
+
Ar , CO2
0.01
y = (3.9±0.5) + (-0.39±0.04).x
+
C2H4
CD4
0.1
+
C2H2
0.01
+
C2H5
y = (3.9±0.5) + (-0.39±0.04).x
+
+
10
IE [eV]
15
Ar
+
CO2
CO2
5
+
C3H8
1,3,5-Triaz
1
+
Sa [ % ]
+
C3H4
+
C3H4
5
10
15
IE [eV]
*) data from A.Somogyi..(V.H.Wysocki),JACS 13(2002)1151
ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES
(Carbon (HOPG) surface, Einc = 30 eV, inc. angle 300 w.r. to the surface)
SEMILOG PLOT
+
CD5
COMPARISON:
- ROOM-TEMPERATURE (hydrocarbon-covered)
10
+
C2H3
- HEATED (“naked”) SURFACES
HOPG Room Temp
RT:
slope -0.39 ± 0.04
HEATED: slope -0.5 ± 0.1
log SA = a - b (IE)
Sa [ % ]
y = (3.9±0.5) + (-0.39±0.04).x
1
+
C2H5
+
C2H4
+
CD4
+
CD3
0.1
+
C2H2
0.01
HOPG Heated
Analogy with the Arrhenius equation?
y = (5.4±1.1) + (-0.5±0.1).x
(dependence of rate constant of a chemical reaction on
temperature T)
log k = a – b/T
+
N2
1E-3
k = A exp (- E / RT)
5
10
IE [eV]
15
ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES
Einc = 30 eV, inc. angle 300 w.r. to the surface
TUNGSTEN
2.5
+
C3H7
• ROOM-TEMPERATURE SURFACE
1.5
Sa [ % ]
• HEATED ( 6000C) SURFACE
Wolfram
Room Temp
2.0
+
C3H3
1.0
+
CD5
+
C3H5
0.5
+
C3H8
+
CD4
+
N2 Ar
0.0
5
10
IE [eV]
15
+
ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES
Einc = 30 eV, inc. angle 300 w.r. to the surface
TUNGSTEN
SEMILOG PLOT
10
Wolfram at Room Temperature
o
Wolfram heated ~ 600 C
E = 30.0 eV
o
inc. Angle = 30
o
o
meas. ang. 49 Eva => 19
• ROOM-TEMPERATURE SURFACE
+
• HEATED ( 6000C) SURFACE
C3H7
+
1
C3H3
+
CD5
CONCLUSION
Very similar slopes (-0.35 – 0.36) on
both RT and HEATED W- surface
Sa [ % ]
+
C3H5
+
C2H5
y = (2.9±0.2) + (-0.35±0.02).x
+
CD5
+
C3H8
+
0.1
C2H4
+
CD4
y = (2.5±0.4) + (-0.36±0.04).x
0.01
+
CD4
+
C2H2
+
Ar
+
N2
1E-3
+
N2
10
IE [ eV ]
15
8.10.08
ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES
Einc = 30 eV, inc. angle 300 w.r. to the surface
SEMILOG PLOTS
COMPARISON OF ROOM-TEMPERATURE SURFACES
+
+
CD5
C7H7
+
10
C7H8
+
C3H7
HOPG Room T
+
C3H3
y = (3.9±0.5) + (-0.39±0.04).x
+
C3H5
CARBON (HOPG)
•
TUNGSTEN (W)
•
BERRYLIUM (Be)
+
C3H4
+
C3H7
+
C3H8
+
Sa [ % ]
•
+
C2H3
+
C2H5
1
+
CD5
C1
C2
C3
C7
+
+
Ar , CO2
0.1
C3H3
+
C3H6
+
C2H4
+
C3H5
+
CD4
+
CD3
+
C3H8
+
C2H2
CONCLUSION
+
Similar slopes (-0.35- 0.39), similar
behavior of surfaces covered by a
hydrocarbon layer
CD4
Wolfram Room T
0.01
y = (2.9±0.2) + (-0.35±0.02).x
+
Ar
+
CO2
+
Ar
+
N2
1E-3
5
10
IE [eV]
15
ION SURVIVAL PROBABILITY vs. IONIZATION ENERGY OF PROJECTILES
SEMILOG PLOT
log SA = a - b (IE)
____________________________________
surface
a
b
____________________________________
C (HOPG) - H
C (HOPG)-RT
5.4 ± 0.1
3.9 ± 0.5
0.5 ± 0.1
0.39 ± 0.04
W–H
W – RT
2.5 ± 0.4
2.9 ± 0.2
0.36 ± 0.04
0.35 ± 0.02
Be – RT
Be – H
(3.9 ± 0.5)
(0.39?)
??
_____________________________________
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 nonterminal 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 roomtemperature (hydrocarbon-covered surfaces)