collaborators prague: j. Žabka, j. roithová, j. jašík, z. dolejšek, j. kubišta
DESCRIPTION
ENERGY TRANSFER, DISSOCIATION AND CHEMICAL REACTIONS IN COLLISIONS OF SLOW POLYATOMIC IONS WITH SURFACES ZDENEK HERMAN V. Čermák Laboratory J. Heyrovsk ý Institute of Physical Chemistry Academy of Sciences, Prague. Collaborators Prague: J. Žabka, J. Roithová, J. Jašík, Z. Dolejšek, J. Kubišta - PowerPoint PPT PresentationTRANSCRIPT
ENERGY TRANSFER, DISSOCIATION AND CHEMICAL REACTIONS IN COLLISIONS
OF SLOW POLYATOMIC IONS WITH SURFACES
ZDENEK HERMANV. Čermák Laboratory
J. Heyrovský Institute of Physical Chemistry Academy of Sciences, Prague
CollaboratorsPrague: J. Žabka, J. Roithová, J. Jašík, Z. Dolejšek, J. Kubišta
Innsbruck: T.D. Märk,, L. Feketeová
(A. Qayyum, T. Tepnual, C. Mair, P.Scheier, S. Matt-Leubner)
FundingEURATOM,, I.A.E.A., Grant Agency of the Czech Republic, GA Academy of Sciences, CZ-A cooperation programs
AIMStudies of polyatomic ions in scattering experiments:
(i) Energy transfer at surfaces (ion activation in MS)
(ii) Surface-induced dissociation- chemical reactions at surfaces
(iii) Survival probability in surface collisions
SURFACES INVESTIGATED- self-assembled monolayers (SAM surfaces)
CF-SAM: -S-(CF2)10-CF3
CH-SAM: -S-(CH2)11-CH3
COOH-SAM: -S-(CH2)11-COOH
- stainless steel (covered by hydrocarbons)
- carbon surfaces HOPG (highly-oriented pyrolytic graphite)
a) covered by hydrocarbonsb) at 1000K (“clean”)
Tokamak bricks
PROJECTILE IONS
ethanol polyatomic ions : C2H5OH+•, C2H5O+, C2H5OH2+; toluene ions
small hydrocarbon ions : CH3+, CH4
+•, CH5+ (D, 13C); C2Hx
+ (x=2-5), C3Hn
+ (n=3-8)
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)
•quasi-elastic scattering of projectiles
ENERGY PARTITIONING IN POLYATOMIC ION-SURFACE COLLISIONS
BASIC EQUATION
ETOT = Etr + (Eint) = E’int + E’tr + E’surf
EVALUATION
P(E’int) from the extent of fragmentation (mass spectra) + break-down pattern
P(E’tr) from direct measurements
P(E’surf) from the difference
DEPENDENCE ON - incident ion energy
- incident angle
- type of surface
- surface temperature
20 25 30 35 40 45 50
0
20
40
60
80
100
m/z
c)COOH-SAM
20 25 30 35 40 45 50
0
20
40
60
80
100
b)CH-SAM
20 25 30 35 40 45 50
0
20
40
60
80
100
a)CF-SAM
32.0 eV
21.1 eV
11.1 eV
0 2 4 6 8 10
C2H5
+
C2H4
+
C2H5OH+
C2H5O+
CH2OH+
CH3
+
C2H3
+
COH+
E int
( eV )
ENERGY PARTITIONING EXAMPLE OF EVALUATION FOR CF-SAM, Etr= 21.1 eV
mass spectra P(E’int) P(E’tr) P(v’)
CONCLUSIONS - strongly inelastic collisions - practically the same velocity distributions for product ions: dissociation after the interaction with the surface in a unimolecular way
32.0 eV
21.1 eV
11.1 eV
0 2 4 6 8 10
C2H5
+
C2H
4
+
C2H
5OH
+
C2H
5O
+
CH2OH
+
CH3
+
C2H
3
+
COH+
E int
( eV )
0 2 4 6 8
(d)CH/SS
E´int (eV)
N=60o, (22.3 V)
(c)COOH-SAM
N=60o, (22.3V)
(b)CH-SAM
N=80o, (22.4 V)
N=60
o, (21.8 V)
P(E
' int) (a)
CF-SAM
N=80
o, (22.0 V)
N=60
o, (21.1 V)
N=40
o, (21.0 V)
P(E’int):
INTERNAL ENERGY OF SURFACE-EXCITED IONS P(E’int) P( E’ int) incident energy dependence (CF-SAM) various surfaces
0 1 2 3 4 5
Eint(CH4
+)
P(E'int
)
E'int
[eV]
CH2
+
CH3
+CH4
+
51.6 eV H NH exp. exp. calc.
CD4
+ 5.0 10.3 10.3
CD3
+ 54.3 50.9 67.8
CD2
+ 40.8 38.8 21.9
H NH exp. exp. calc.
CD4
+ 28.5 34.8 31.3
CD3
+ 49.5 48.7 55.7
CD2
+ 22.0 16.5 13.0
31.6 eV
NON-HEATED(room temperature)HEATED
~600oC
16.6eV H NH exp. calc. exp. calc.
CD4
+ 61.0 61.0 45.7 45.6
CD3
+ 29.9 34.7 48.3 48.5
CD2
+ 9.1 4.3 5.9 5.9
P(E’int): INTERNAL ENERGY DISTRIBUTIONS OF SURFACE-EXCITED IONS
Projectile ion: CH4+
Heated and non-heated HOPG surface
Mean internal energy ~ 5-6% Einc
0 5 10 15 20 25
0
20
40
60
80
100
P(E')
P(E')
N= 80o
E' [eV]
P(E')
0.520.18
0.30
0 5 10 15 20 250
20
40
60
80
100
E'int
E'tr
E'int
E'trE'
surf
E'surf
E'int E'
trE'
surf
N= 60
o
0.46
0.37
0.17
0 5 10 15 20 250
20
40
60
80
100
N= 40
o
0.66
0.16
0.18
ENERGY PARTITIONING
INCIDENT ANGLE DEPENDENCE INCIDENT ENERGY DEPENDENCE
CF-SAM, Einc = 22 eV SS-hydrocarbons, N=600
ENERGY PARTITIONING
DIFFERENT SURFACES
CONCLUSIONS
- P(E’int) does not depend on incident angle
- relative fractions of P(E’int), P(E’tr), P(E’surf) practically independent of collision energy
- P(E’int) practically the same for all studied surfaces (Epeak~6% Etr), only for CF-SAM about 3-times higher (~18%)
0 5 10 15 20 250
20
40
60
80
100SS/CHP(E')
E'int
E'tr
E'surf
0.620.32
0.06
0 5 10 15 20 250
20
40
60
80
100
P(E')
P(E')
CH-SAMP(E')
0.30
0.06
0.64
0 5 10 15 20 250
20
40
60
80
100
E'int
E'tr
E'int E'tr
E'surf
E'surf
E'intE'tr
E'surf
COOH-SAM
0.68
0.27
0.05
0 5 10 15 20 250
20
40
60
80
100
CF-SAM
0.46
0.370.17
0 5 10 15 20 250
20
40
60
80
100SS/CHP(E')
E'int
E'tr
E'surf
0.620.32
0.06
0 5 10 15 20 250
20
40
60
80
100
P(E')
P(E')
CH-SAMP(E')
0.30
0.06
0.64
0 5 10 15 20 250
20
40
60
80
100
E'int
E'tr
E'int E'tr
E'surf
E'surf
E'intE'tr
E'surf
COOH-SAM
0.68
0.27
0.05
0 5 10 15 20 250
20
40
60
80
100
CF-SAM
0.46
0.370.17
PERCENTAGE OF SURVIVING IONS, Sa(%)
PERCENTAGE OF SURVIVING IONS, Sa(%)
TABLE 2: Survival probability, Sa (%) of ions in collision of C7H82+/+,
C7H72+/+ and C7H6
2+/+ with HOPG surface at room temperature*
Einc= 10.3 eV Einc= 25.3 eV
projectile Seff 10-6 Sa (%) Seff 10-6 Sa (%)
C7H82+ 3.6 1.4 6.4 2.5 11 4 20 7
C7H72+ 14 4 25 9 13 2 23 4
C7H62+ 4.0 1.6 7.2 2.5 18 4 32 7
C7H8+ 6.3 1.0 11 2
C7H7+ 7.7 2.0 14 4
* Incident angle N = 60 .
PERCENTAGE OF SURVIVING IONS, Sa(%)
0
5
5x
0
5
10
CD5
+CD
5
+
CD4
+ CD4
+
CD3
+CD
3
+
0
50
8x
0
25
50
5x
15 20 25 30 35 40 450
50
100
150 60x
15 20 25 30 35 40 450
50
100
10x
0
5
10
0
5
10
0
1
2
5
10
m/z
0.5
1.0
(b) 51.2 eV(a) 31.2 eV
15 20 25 30 35 40 450
100
200
I (a.u.)
CD5
+
CD5
+
(c)
x20
m/z
0
5
10
CD4
+
CD4
+
(b)
0
5
CD3
+
(a)CD
3
+
C2Xn+
C2Xn+
C2Xn+
C3
C3
C3
MASS SPECTRA
CDX+, HOPG, Einc = 51.6eV, N=60o
HEATED NON HEATED
• C2X3+ (X=H,D) formation :
interaction of the projectile with terminal CH3 - group
• CD4H+ formation :interaction of CD4
+. with terminalH-atom, direct H-atom transfer
• C3+ - group formation : C3H3
+ mainly reaction, C3H5+ (C3H7
+) mainly sputtering
SUGGESTED MECHANISMS
(CD4H+) : (diss) : (C2H3+) = 10 : 3: 1
15 16 17 18 19 20
(b)CD3
+CD5
+
CD3
+CD5
+
v' [km/s]
E'tr [eV]
20 25 30 35 40 45
(a)
P(v')
P(Etr')
CD5
+
CD3
+
16.6 eV
CD5
+
CD3
+
(d)16.6 eV
(b)31.6 eV
(a)
(e)31.6 eV
0 5 10 15 20 25 30 35
(c)51.6 eV
0 5 10 15 20
P[v']
(f)
P[E'tr]
51.6 eV
E'tr [eV] v' [km/s]
PRODUCT ION TRANSLATION ENERGY DISTRIBUTION
51.6eV
CD5+, HOPG, N=60o
HEATED NON HEATED
CONCLUSIONS:
1.Practically the same velocity of product ion species - dissociation after surface interaction
2. Inelastic collisions:
E’tr of product ions: heated ~ 75% Einc
non-heated ~ 40-50% Einc
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 440
20
40
60
80
100
C2H
3
+, E
inc = 46.3 eV
I [a
rb.
un
its]
m/z [ thomson ]
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 440
20
40
60
80
100
C2H
2
+, E
inc = 46.3 eV
I [a
rb.
un
its]
m/z [ thomson ]
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 440
10
20
30
40
50
C2H
3
+, Einc
= 46.3 eV
I [a
rb.
un
its]
m/z [ thomson ]
HEATED NON HEATED
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 440
10
20
30
40
50
C2H
2
+, E
inc = 46.3 eV
I [a
rb.
un
its]
m/z [ thomson ]
MASS SPECTRA
25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 450
1
2
3
4
5
6
7
8
9
C2D
3
+
C2D
2
+
C2D
4
+
I [a
rb. u
nits
]
m/z [ thomson ]
HEATED NON-HEATED chemical reaction sputtering background
Ek = 46.3 eV
37 38 39 40 41 42 43 440.00
0.05
0.10
0.15
0.20
0.25
0.30 39:40:41:42=0.03:0.35:0.4:0.14
39 0.03 0.03
40 0.34 0.38
41 0.51 0.43
42 0.12 0.15
C3Xn+
MASS SPECTRA C2D4+: FORMATION OF C3 - GROUP
0 5 10 15 20 25 30 35
46.3eV
E'tr [eV]
31.3eV
20oC
600oC
C2H
3
+ + HOPG -> C2H
3
+
16.6eV
P[E
' tr]
0 5 10 15 20 25 30 35
Calculated from product C2H
3
+
46.3eV
E'tr [eV]
21.3eV
20oC
600oC
C2H
5
+ + HOPG -> C2H
5
+
11.6eV
P[E
' tr]
PRODUCT ION TRANSLATION ENERGY DISTRIBUTIONS
C2H3+, C2H5
+, HOPG, N=60o
CH4+(R)
CH4+ (NR)
INITIAL INTERNAL ENERGY
OF PROJECTILES:
EFFECT ON DISSOCIATION
Projectile ion preparation
(R): relaxed ions (Colutron source)
(NR): non-relaxed ions (Nier source)
CH4+
Estimated internal energy (from differences in crossings and thresholds of CERMS curves)
(Eint)max < 1.8-2.1 eV
Estimated (Eint)max of CH4+ (from break-down pattern and photoelectron spectra:
<1.8 eV
CONCLUSION
Initial Eint fully available for dissociation
C2H4+(C2H4) (NR)
C2H4+(R)
C2H4+(C2H6) (NR)
INITIAL INTERNAL ENERGY
OF PROJECTILES:
EFFECT ON DISSOCIATION
Projectile ion preparation
(R): relaxed ions (Colutron source)
(NR): non-relaxed ions (Nier source)
C2H4+
Estimated internal energy (from differences in crossings and thresholds of CRMS curves)
<Eint> ~ 1.5 eV
CONCLUSIONS
1. Energy transfer in collisions of polyatomic ions with surfaces:
- unimolecular decomposition after surface interaction
- internal excitation of projectiles: independent of incident angle,
mean value mostly about 6% of incident E (CF-SAM: about 18%)
- translational energy of products: decreases with incident angle
- relative fractions (P(E’int), P(E’tr), P(E’surf)) do not change with incident energy
2. Initial internal energy of projectile ions:
fully available in dissociative processes
3. Survival probability on C/hydrocabons:
- about 0.1 % for cations of RE>10.5 eV,
- about 1-10 % for cations of RE<10.5 eV (closed-shell ions)
4. Chemical reactions of radical hydrocarbon ions on C/hydrocarbons:
- H-atom transfer,
- C2 from C1 or C3 from C2: interaction of the projectile with the terminal CH3- group
MOTIVATION FROM FUSION RESEARCH
1.Collisions of hyperthermal particles with solid surfaces (limiters, divertors) leads to erosion of material by physical and chemical processes
2. Products of these collsions (ionic, neutral) again interact with plasma and solid surfaces
3. Importance of molecular species
EARLIER DEMAND
Interaction of atomic and molecular species with exposed surfaces of fusion vessels (carbon, tungsten): from plasma temperature energy range 10 - 50 eV
NEW DEMAND
Lower plasma temperatures important, too:
surface interactions of hyperthermal particles of energies 1 - 10 eV