I.A.E.A. Vienna
CRP Atomic and Molecular Data for Plasma Modelling
Coordination Meeting 18-20 June, 2007
INTERACTION OF SLOW IONS
WITH SURFACES:
COLLISIONS OF SMALL HYDROCARBON IONS WITH
CARBON, TUNGSTEN AND BERYLLIUM SURFACES
ZDENEK HERMAN, JAN ŽABKA, ANDRIY PYSANENKO
J. Heyrovský Institute of Physical Chemistry, v.v.i.
Academy of Sciences of the Czech Republic,
Prague
IAEA, Vienna, 18-22 June, 2007
AIM
Studies of polyatomic ions in scattering experiments:
Ion survival probability, energy transfer at surfaces, fragmentation and chemical
reactions at surfaces
SURFACES INVESTIGATED
- (carbon surfaces (15 – 45 eV))
HOPG (highly-oriented pyrolytic graphite), Tokamak tiles
a) room-temperature (covered with hydrocarbons)
b) heated to 6000 C 1(“clean”)
- carbon (HOPG) surfaces at 3 – 10 eV
room temperature, scattering kinematics
- tungsten surfaces (15 – 45 eV)
room-temperature and heated
- beryllium surfaces (15 – 45 eV
room-temperature and heated
PROJECTILE IONS
small hydrocarbon ions : CH3+, CH4+•, CH5+ (D, 13C); C2Hx+ (x=2-5), C3Hx+ (x=2-8),
cations and dications C7Hn+/2+ (n=6-8)
MEASUREMENTS
- mass spectra of ion products
- translational energy distributions of ion products
- angular distributions of ion products
EXPERIMENT
PROCESSES OBSERVED
•neutralization of ions
(survival pobability)
•surface-induced dissociations
(energy partitioning)
•chemical reactions at surfaces
(H-atom, CHn-transfer)
•scattering kinematics
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
CD5+ (HOPG)
MASS SPECTRA OF PRODUCTS
ΦS = 300
CD5+ : close-shell, non-reactive projectile ion
HOPG
+
CD5
2500
+
CD5
+
2000
CD5
(a)
+
Einc(CD5) = 10.5 eV
1500
Observation:
+
1000
CD3
-only decreasing product dissociation with
decreasing incident energy
500
CD5+→ CD3+ + D2
Intensity, [a.u.]
0
+
CD5
+
CD5
300
(b)
+
Einc(CD5) = 5.9 eV
200
+
CD3
100
0
(c)
+
300
CD5
+
CD5
200
+
Einc(CD5) = 3.6 eV
100
+
CD3
0
15
20
25
m/z
30
35
40
(ΔE ~ 2 eV)
CD5+ (HOPG)
ANGULAR DISTRIBUTIONS OF PRODUCTS
+
CD5
+
Einc (CD5)= 10.45 eV
Einc(CD5+) = 10.45 eV
Intensity [a.u.]
'
90
D[deg]
80
70
60
50
40
30
40
50
60
70
CD5+
30
80
'
D [deg]
+
CD3
+
Einc (CD5)= 10.45 eV
Intensity [a.u.]
90
'
D[deg]
80
70
60
50
40
30
30
40
50
'
60
D [deg]
70
80
CD3+
CD5+ (HOPG)
TRANSLATIONAL ENERGY DISTRIBUTIONS OF PRODUCTS
CD5
+) = 10.45 eV
E
(CD
inc
5
+
CD3+
35
60
40
100
0
0
100
10
50
0
0
80
o
o
49
45
150
200
150
40
100
'
100
50
45
60
100
o
o
150
P(Etr) [a.u.]
200
50
50
0
0
150
o
o
50
50
0
0
80
60
100
20
50
50
60
55
60
60
o
o
100
'
P( E'tr ) [a.u.]
20
50
20
P( E'tr ) [a.u.]
40
'
40
o
o
35
150
o
P(Etr) [a.u.]
o
P(Etr) [a.u.]
P( E'tr ) [a.u.]
80
40
40
20
20
0
0
0
1
2
3
4
E'tr [V]
5
6
7
8 0
1
2
3
4
5
E'tr [V]
6
7
8
0
0
0
1
2
'
3
Etr [V]
4
5
6 0
1
2
'
3
Etr [V]
4
5
6
CD5+ (HOPG)
KINEMATICS: VELOCITY SCATTERING DIAGRAM
Einc(CD5+) = 10.45 eV
CD5+ (HOPG)
KINEMATICS: EVALUATION
Einc(CD5+) = 10.45 eV
60
o
50
+
CD3
+
o
45
CD5
Same peak velocity of CD5+ and
CD3+: fragmentation AFTER
interaction with surface
2.
Effective surface mass for
collisions of CD5+:
meff = 62 m.u.
(2xC2H5-, 4xCH3-)
o
40
o
35
30
1.
o
o
0
1
2
3
4
3.80km/s
5
6
7
8
9
velocity [km/s]
CM
3.
Inelastic collisions:
inelasticity in C.M.
T = 62/84 Einc = 7.7 eV
T’ = 0.29 T
ΔT = T – T’ = 5.49 eV
+
vinc(CD5)=
9.58 km/s
CD3+ (HOPG)
ANGULAR DISTRIBUTIONS OF PRODUCTS
Einc(CD3+) = 8.3 eV
background
+
CD3
+
fast deflected
Einc (CD3)=inelastic
8.30 eV
scattering
Intensity [a.u.]
'
90
D[deg]
80
70
60
50
40
30
40
50
'
D [deg]
60
70
80
30
CD3+ (HOPG)
CD3-->HOPG-->CD3
TRANSLATIONAL ENERGY DISTRIBUTIONS
OF PRODUCTS
P(E'tr) [a.u.]
20
o
40
Einc(CD3+) = 8.3 eV
10
0
30
P(E'tr) [a.u.]
o
50
20
10
15
0
P(E'tr) [a.u.]
o
60
10
5
0
0
1
2
3
4
5
6
E'tr [a.u.]
7
8
9
10
CD3+ (HOPG)
KINEMATICS: EVALUATION
Einc(CD3+) = 8.3 eV
60
o
50
+
CD3
1.
No fragmentation of the
projectile CD3+.
2.
Effective surface mass for
collisions of CD3+:
o
40
meff = 29 m.u.
o
(C2H5-, 2xCH3-)
30
o
3.
0
1
2
3
4
5
6
7
8
9
Inelastic collisions:
inelasticity in C.M.
velocity [km/s]
T = 29/47 Einc = 5.12 eV
4.15km/s
T’ = 0.51 T
ΔT = T – T’ =2.62 eV
CM
+
vinc(CD3)=
9.43 km/s
+
120
+
100
80
CD4+ • (HOPG)
HOPG
CD4
+
CD3
CD2H
+
+
MASS SPECTRA OF PRODUCTS
(a)
CD4
Einc(CD4)= 10.5 eV
Φs = 300
open-shell, reactive projectile radical ion
FAST
Observation:
+
CD4
60
Intensity, [a.u.]
40
CD4H
20
- simple fragmentation of projectile ions
+
CD4+•→ CD3+ + D• (ΔE = 1.8 eV)
0
- chemical reaction with surface material
(b)
+
120
+
CD4
CD4
CD4+• + H-S → CD4H+ → CD3+ +HD
+
Einc(CD4)= 6.0 eV
100
80
→ CD2H+ + D2
FAST
- fast deflected CD4+ projectile ions of
incident energy
60
40
+
CD3
20
0
15
CD4H
20
m/z
+
25
30
SUMMARY
VERY LOW ENERGY (3-10 eV) SCATTERING ON ROOM-TEMPERATURE
CARBON SURFACE
1. Ion survival probability decreases below 10 eV towards zero
2. Non-reactive ions (CD5+, CD3+): only inelastic collisions, fragmentation indicates
dissociation AFTER interaction with the surface (CD5+)
3. Kinematic analysis: determination of effective mass of the surface involved in the
inelastic collision (different for different ions).
4. Reactive ions (CD4+•): both fragmentation and chemical reaction with surface
material (H-atom transfer from surface hydrocarbons: a very sensitive reaction
tracing hydrocarbon on the surface).
2. COLLISIONS WITH TUNGSTEN SURFACE
Sample Material:
99.9% w-sheet (0.05 mm) cleaned mechanically or chemically to remove surface impurities
Observation
Unheated fresh sample: about 5 % of projectile ions deflected with full incident energy
(evidently not hitting the surface at all)
Heated sample: heating decreases the amount of deflected ions to 0.05 % or less
Room-temperature sample after heating: the amount of deflected ions remains under 0.1%
XPS analysis of the sample
Unheated fresh sample: tungsten oxides and small amount of tungsten carbide + hydrocarbon
C-H groups on the surface
Sample after heating: decrease of tungsten oxides, sharp increase of tungsten carbides (2.5times: evidently degradation of surface hydrocarbons)
CONCLUSION
1. Fresh sample: Islands of insulating matter (presumably tungsten oxides) cause part of
projectile ions to be deflected by surface charge
2. Heating decreases the amount of surface oxides and strongly increases the amount of
non-insulating tungsten carbide (collisions mostly with WC on the surface)
3. Room-temperature sample after heating: hydrocarbon layer of mostly WC surface
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
MASS SPECTRA OF PRODUCT IONS
C2D3
200
+
500
+
Room temperature
C2D2H
150
+
C2D2
+
C2D4
100
+
C2D4 "Fast "
50
C3H2D
+
C2DH
0
30
CD5
Einc= 30.9 eV
Intensity [counts/2s]
Intensity [counts/2s]
C2D4
+
35
+
CD3
+
Einc= 30.9 eV
+
Room temperature
400
300
200
+
CD5
100
40
0
500
45
15
20
25
30
Intensity [counts/2s]
Intensity [counts/2s]
200
+
150
100
C2D3
o
Heated ~ 600 C
+
C2D2
50
+
C2D4 "Fast "
0
30
35
40
m/z
45
400
o
Heated ~ 600 C
300
+
CD3
200
CD5
100
0
15
20
+
25 m/z
30
TRANSLATIONAL ENERGY DISTRIBUTIONS OF PRODUCTS
--------- heated to 6000C
--------- room temperature
CD5
100
+
CD4
100
P(E'tr)
[a.u.]
P(E'tr)
[a.u.]
15.4 eV
80
60
60
40
40
40
20
20
20
0
0
0
30.9 eV
30.9 eV
80
60
60
40
40
40
20
20
20
0
0
0
45.4 eV
45.4 eV
80
60
60
40
40
40
20
20
20
0
0
5
10
15
20
Etr' [eV]
25
30
35
40
45.4 eV
80
60
0
30.9 eV
80
60
80
15.4 eV
80
60
80
C2D4
100
P(E'tr)
[a.u.]
15.4 eV
80
+
+
0
0
5
10
15
20
Etr' [eV]
25
30
35
40
0
5
10
15
20
Etr' [eV]
25
30
35
40
SUMMARY
COLLISIONS OF SMALL HYDROCARBON IONS:
TUNGSTEN VS. CARBON SURFACES
1. W-surface: fraction of projectile ions deflected by surface charges (up to 5 % on fresh
room-temp surface), decreases with or after heating of the surface. Probable reason:
islands of W-oxides on the surfaces
2. Survival probability: on W-surfaces up to 10-times smaller than on C-surfaces (HOPG)
3. W-surface at room–temperature covered with hydrocarbons: analogous to C- surfaces
- fragmentation and chemical reactions of radical projectile ions
- CH4+: H-atom transfer, formation of C2- and C3- hydrocarbons;
- C2D4+: H-atom transfer, formation of C3- hydrocarbons
W-surface heated: only fragmentation of projectile ions: analogous to C-surfaces
4. Inelasticity of surface collisions (from product ion translational energy distributions):
- similar on W-surfaces to that on C-surfaces
room-temperature: collisions with hydrocarbons on the surfaces
heated: collision with WC on the surface(?)
- heated surfaces usually less inelastic (similarly as on C-surfaces)
- for C1-projectile ions: less inelastic with increasing incident energy, i.e.
fraction of energy in translation slightly increases
3. COLLISIONS WITH BERYLLIUM SURFACES
Sample Material:
Be-foil, 0.5 mm, >99% Be (Goodfellow), cleaned mechanically to remove surface impurities
Observation
Unheated fresh sample: several % of projectile ions deflected with full incident energy (evidently not
hitting the surface at all)
Heated sample: heating decreases the amount of deflected ions to 0.05 % or less
Room-temperature sample after heating: the amount of deflected ions remains under 0.1%
XPS analysis of the sample
Unheated fresh sample: on the surface Be-oxides, Be-carbides, 42 % Be as metal; 78% hydrocarbon
C-H groups on the surface, small amount of carbon (~10%) also in C=O and COOH groups
Sample after heating: Be as metal decreases to 9 %, sharp increase of Be-carbides (to 18% - 32%)
carbidic phase covered with hydrocarbons on room-temperature surface; surface also contains
Be-oxides (67% of Be in oxides)
CONCLUSION
1. Fresh sample: Islands of insulating matter cause part of projectile ions to be deflected by surface
charge
2. Heating decreases the amount of insulating material on the surface and strongly increases the
amount of Be-carbide.
3. Room-temperature sample after heating: hydrocarbon layer on at least part of the surface (BeC).
CD5+ - Be
ANGULAR DISTRIBUTION OF PRODUCTS
ΦS = 300, room-temperature surface after heating
+
CD3
+
Einc (CD5)= 45.4 eV
Intensity [a.u.]
'
90
D[deg]
80
70
CD3+
Einc = 45.4 eV
60
50
40
30
40
50
60
70
30
80
'
D [deg]
+
CD3
+
Einc (CD5)= 30.9 eV
Intensity [a.u.]
90
'
D[deg]
80
70
60
50
40
30
30
40
50
'
60
D [deg]
70
80
CD3+
Einc = 30.9 eV
CD5+ - Be
TRANSLATIONAL ENERGY DISTRIBUTION OF PRODUCTS
ΦS = 300, room-temperature surface after heating
Room Temperature
Ei=30,9 eV
Ei=45.0
Einc = 30.9 eV
Room Temperature
Einc = 45.4 eV
600
100
+
CD3
50
+
400
o
'D=50
CD3
o
'D=56
200
0
0
0
2
4
6
8
10
12
14
16
18
0
20
5
10
15
20
25
10
15
20
25
600
+
800
CD3
600
400
o
'D=57
400
200
21%
0
o
'D=56
200
56%
38%
+
CD3
0
0
2
4
6
8
10
12
14
100
16
18
20
50
55%
150
o
'D=57
38%
5
200
+
CD5
0
+
CD3
100
53%
o
'D=52
50
22%
40%
23%
0
0
0
2
4
6
8
10
12
14
16
18
20
0
5
10
E'tr [eV]
Energy losses (21%, 38%,56%) recalculated to CD5+
15
20
25
E'tr [eV]
C2D4+• - Be
ANGULAR DISTRIBUTION OF PRODUCTS
0+
Einc = 15.8 eV, ΦS = 30
C D , room-temperature surface after heating
2
3
+
Einc (C2D4)= 15.8 eV
Intensity [a.u.]
'
90
D[deg]
C2D3+
C2D4+→ C2D3+ + D
→ C2D4H+ → C2D3+ + HD
80
70
60
50
40
30
40
50
60
70
30
80
1. Simple dissociation
2. chemical reaction + dissociation
'
D [deg]
C2D2H
+
+
Einc (C2D4)= 15.8 eV
Intensity [a.u.]
90
'
D[deg]
80
70
60
50
40
30
30
40
50
'
60
D [deg]
70
80
C2D2H+
C2D4+ → C2D4H+ → C2D2H+ + D2
chemical reaction + dissociation
C2D4+• - Be
TRANSLATIONAL ENERGY DISTRIBUTION OF PRODUCTS
ΦS = 300, room-temperature surface after heating
Ei=15.8 V
Room Temperature
30
+
C2D3
20
o
'D=36
C2D3+
C2D4+→ C2D3+ + D
10
0
0
2
4
6
8
12
10
→ C2D4H+ → C2D3+ + HD
1. Simple dissociation
80
+
C2D3
60
2. chemical reaction + dissociation
o
'D=55
40
20
0
0
2
4
6
8
12
10
100
80
Observation:
+
60
C2D3
40
'D=68
o
23%
20
37%
57%
0
0
2
4
6
8
10
Einc = 15.8 eV
12
E'tr [eV]
Three different energy losses to 23%, 37%,
and 57% of Einc, probability angle-dependent;
presumably scattering from different surface
material
C2D4+• - Be
TRANSLATIONAL ENERGY DISTRIBUTION OF PRODUCTS
0, room-temperature surface after heating
ΦSV = 30room
E =15.8
Temperature
i
80
70
60
C2D2H
50
'D=62
+
C2D2H+
o
C2D4+ → C2D4H+ → C2D2H+ + D2
40
(chemical reaction + dissociation)
30
20
Einc = 15.8 eV
10
0
0
2
4
6
8
10
12
60
50
C2D2H
40
'D=75
+
o
30
39%
20
10
25%
0
0
2
4
6
8
10
12
E'tr [eV]
Observation:
Surface chemical reaction:
Two different energy losses to
25% and 39% of Einc, probability
angle-dependent; presumably
scattering from different surface
material.
Evidently, high-energy (59% Einc)
and low-angle scattering is nonreactive (only fragmentation)
C2D4+• - Be
ANGULAR DISTRIBUTION OF PRODUCTS
Einc = 15.8 eV, ΦS = 300, heated surface to 6000C
HEATING UTR ~ 39 V E (C D+)=15.8 eV
inc
2 4
+
C2 D3
C2D3+
'
N[deg]
Intensity [a.u.]
90
80
70
60
50
40
30
20
30
40
50
'
D [deg]
60
70
80
C2D4+• - Be
TRANSLATIONAL ENERGY DISTRIBUTION OF PRODUCTS
E =15.8 V surface
HEATING
V oC
Einc = 15.8 eV, ΦS = 300, heated
to40600
i
40
+
C2D3
20
o
'D=60
0
0
1
2
3
4
5
6
7
8
9
10
150
+
100
C2D3
50
'D=55
o
0
0
1
2
3
4
5
6
7
8
9
10
120
100
+
C2D3
80
60
o
'D=55
42%
40
28%
20
0
0
1
2
3
4
5
6
7
8
9
10
E'tr [eV]
C2D4+• - Be
KINEMATICS: EVALUATION
Einc = 15.8 eV, ΦS = 300, room-temperature and heated
75
o
o
68
o
66
o
o
62 61
55
+
C2D3
o
+
heated, C2D3
C2D2H
+
36
o
o
30
0
1
2
3
4
3.8km/s
A: meff = 59 m.u. (2BeO)
B: meff = 47 m.u. (3 CH3, C3H7)
C: meff = 30 m.u. (2CH3, C2H5),
A
5
6
4.8km/s
6.15km/s
B
7
8
9
velocity [km/s]
C
+
No chemical reaction in low-angle scattering
vinc(C2D4)=
9.77 km/s
SUMMARY
SCATTERING ON BERYLLIUM SURFACES
1. Survival probability comparable to that on W-surfaces (lower than on carbon)
2. On fresh room-temperature surfaces several % of incident ions deflected
without collision, heating and after heating this fraction decreases to ~0.1 %
or less.
3. Reactive ions (CD4+, C2D4+): on room-temperature surfaces both simple
dissociation and chemical reaction (+ dissociation). Main reaction : H-atom
transfer from reaction with surface hydrocarbons (similarly as on C or W).
4. Scattering on Be-surfaces more complex than on C or W: structures both in
angular distributions and translational energy distributions. Presumably
connected with various materials on the surface (oxides, carbides, only
partially covered with hydrocarbons on room-temperature surfaces).
POSITIONS OF PEAKS
IN TRANSLATIONAL ENERGY DISTRIBUTION OF PRODUCTS
(MEAN INELASTICITY OF SURFACE COLLISIONS)
100
100
CD
4
4
50
HOPG - room temperature
HOPG - heated
50
SS - hydrocarbons
+
(C2H5OH )
0
HOPG - room temperature
+
(C2H5OH )
0
C2H+
CD+
tr
E' /Einc [%]
W - room temperature
W - heated
C2D+
+
5
5
50
0
50
0
10
20
30
40
Einc [eV]
50
60
0
0
10
20
30
40
Einc [eV]
50
60
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