Particle – Induced Desorption
of Biphenyl Alkanethiol
and Benzohydroxamic Acids
from Metallic Surface
SABINA WYCZAWSKA
Laboratory for Solid State Physics and Magnetism,
Katholieke Universiteit Leuven,
11 November 2006
1
Outline
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Introduction
Experimental setup
Biphenyl alkanethiol (BPn)
Polymorphism in BPn/Au
Odd/even effect in BPn/Au
Benzohydroxamic acids (BHA)
Solvents and substituents dependent
of BHA
• Flight time distribution of BHA
2
Introduction
Self-Assembled Monolayer: (SAM)
Highly ordered and oriented assemblies that are formed
spontaneously by the adsorption of a surfactant with a
specific affinity of the headgroup to a substrate.
Tail
Spacer
Head
Substrate
Typical mM
concentrations
in solvent (ethanol)
Tail
: surface properties
Spacer : intermolecular interactions
ordening and orientation molecules
Head : bound to substrate atom
Introduction
Interaction of energetic projectiles with self-assembled
monolayers:
 Characterization:
damage induced during standard characterization
techniques such as SIMS and AES
 Controlled modification:
SAMs are promising to be used as ultrathin resist in
lithographic patterning
Aim: to investigate the fundamental influence of
the detailed geometric and electronic structure
of SAMs and other organic molecules on
projectile-induced desorption
3
4
Experimental procedure
Ar+ ions
Organic layer
substrate
4
Experimental procedure
detector
+
Ar+ ions
Δt
+
Mass selection
+ +
+ +
laser pulse
K.E. selection
substrate
Experimental procedure
5
Ionization of neutral molecules
+
M
 Detection of neutral molecules
 Photo-ionization but also photofragmentation
l
0
l
M
Experimental procedure
5
Ionization of neutral molecules
+
M
259 nm
259 nm
 Detection of neutral molecules
 Photo-ionization but also photofragmentation
Resonance-enhanced multiphoton ionization
M* Introduction of a suitable chromophore
M*  resonance enhanced
 increase of the ionization efficiency
 reduction of laser intensity
0
 reduction of the photofragmentation
M
Aromatic rings act as chromophores [1]
1. Vandeweert et al., Nucl. Instrum. and Meth. in Phys. Res. B 164-165 (2000)
Nd:YAG
Dye
Laser
Ionizing
Lasersystems
Nd:YAG
OPO
Ion Gun
Frequency
Doubling
Spectra Physics
Frequency
Doubling &
Tripling
Experimental setup
6
l = 259nm
Fphoton = 1017ph/cm2
(m/Dm)lin = 200
(m/Dm)ref = 800
Ultra High
Vacuum
Chamber
Time-of-Flight
Mass Spectrometer
Sample
P = 10-10 Torr
15 keV Ar+
Fion = 1011ions/cm²
Electron Gun
7
Biphenyl alkanethiol
We investigated biphenyl-based SAMs:
BPn, n=1, 2, 3, 4, 5, 6
CH3
2 hybridizations:
sp
R
C
S
(CH2)n
Phenyl
chromophore
BP2
S
4,4’-biphenyl-substituted
alkanethiol
=180°
Au
sp3
R
S
Au
C
=104°
Experimental observables
8
1. Flight-time distributions:
 probing ion signal in function of flight time
( = difference between ion and laser pulse)
Ion signal (arb.u.)
 kinetic energy of desorbing particles
T
Ar+ irradiation BP2/Au
m/z = 168
40
60
B
0
20
2 ejection mechanisms: [2]
1. Ballistic ejection:
direct momentum
transfer (~ 1 eV)
2. Thermal-like ejection:
bond cleavage by
reactive species
(~ 0.02 eV)
80 100 120 140 160
Flight time (µs)
2. Riederer et al., J. Am. Chem. Soc. 119 (1997)
9
Experimental observables
2. Desorption fragmentation pattern:
Ion Signal (arb.u.)
 probing which particles are desorbed
168 Ar+ irradiation
181
228
165 194
BP2/Au:
195
167
CH3
CH2
181
40
80 120 160 200 240 280 320 360 400
Mass (a.m.u.)
 parent molecule desorbed
 desulphurized fragment desorbed
 m/z = 181 photofragment
 m/z = 168 desorbed
 m/z = 165 photofragment
CH2
Au
S
227
Au
Polymorphism in BPn/Au
10
Detailed geometric and electronic structure depends
on growth parameters [3]
a BP4/Au:
(b)
b BP4/Au:
(c)
BP3/Au:
(a)
[21
1]
 grown at 295 K
 27.01 Ų/molecule
 C-S-Au bond angle
 > 130°
Only one phase –
 post-annealed
no changes when
at 423 K
prepared at
 32.4 Ų/molecule
elevated
 C-S-Au bond angle
temperature
 < 130°3. Cyganik et al., J. Am. Chem. Soc. 126 (2004)
Polymorphism in BPn/Au
n = even
β- & -BPn
α-BPn



Au
• prepared at 295 K
• C-S-Au angle
 > 130°


Au
• prepared at 423 K
• C-S-Au angle
 < 130°

11
Polymorphism in BPn/Au
12
Ion signal (arb.u.)
Ion-induced desorption:
181
a BP4/Au
BP4
168 BP4-S
Probing desorption mass
spectra during 15-keV
Ar+ irradiation of a and
b/ even BPn/Au
181
BP4-S b BP4/Au
difference in desorption
behavior of BP4 and
BP4-S
168
BP4
0
40
80 120 160 200 240 280 320 360 400
Mass (a.m.u.)
13
Polymorphism in BPn/Au
Normalized ion signal (arb.u.)
Ion-induced desorption:
BPn
0.3
a phase
b/ phase
0.2
0.2
0.1
0.1
0.0
2
3
4
n
5
6
BPn-S
0.3
0.0
2
3
4
5
6
n
Desorption probability of the
parent molecule is larger for a
than for b/ even BPn/Au
Desorption probability of the
BPn-S molecule is larger for
b/ than for a even BPn/Au
 bond scission efficiency of
 bond scission efficiency of
the S-Au bond is larger for a
than for b/ even BPn/Au
the C-S bond is larger for b/
than for a even BPn/Au
13
Polymorphism in BPn/Au
Normalized ion signal (arb.u.)
Ion-induced desorption:
BPn
0.3
a phase
b/ phase
0.2
0.2
0.1
0.1
0.0
2
3
4
n
5
6
BPn-S
0.3
0.0
2
3
4
5
6
n
RT BP5/Au and HT BP5/Au:
no change in desorption probability
 changes in bond scission efficiency between
a and b/ even BPn/Au are related to
structural change and not to annealing
Polymorphism in BPn/Au
Discussion:
optimization
bond geometry
 ~ 104 

Au



Au
 > 130 
optimization
2 dimensional
packing
intermolecular
interactions
suppressed
due to energy
addition

a even BPn/Au:

14
Au
b even BPn/Au:


 < 130 
Au

Polymorphism in BPn/Au
Discussion:
a even BPn/Au:



Au
 > 130 
S-Au weakest bond
b/ even BPn/Au:



Au
 < 130 
C-S weakest bond
15
Odd/even effect in BPn/Au
16
Detailed geometric and electronic structure depends
on growth parameters and alkane chain: [3,4]
a BP4/Au:
BP3/Au:
(b)
(a)
[21
1]
 grown at 295 K
 27.01 Ų/molecule
 C-S-Au bond angle
 > 130°
3. Cyganik et al., J. Am. Chem. Soc. 126 (2004)
 grown at 295 K
 21.6 Ų/molecule
 C-S-Au bond angle
 ~ 109°
4. Azzam et al., Langmuir, 19 (2003)
Odd/even effect in BPn/Au
n = odd
n = even
α-BPn




Au
prepared at 295 K
• C-S-Au angle
 ~ 109°
•


Au
prepared at 295 K
• C-S-Au angle
 > 130°
•
17
18
Odd/even effect in BPn/Au
Ion signal (arb.u.)
Ion-induced desorption:
181 BP3-S
168
BP3/Au
BP3
168
BP4/Au
181
BP4-S
BP4
0
40
80
120
160
200
240
280
320
360
400
Probing desorption
mass spectra during
15-keV
Ar+ irradiation of odd
and even BPn/Au
difference in desorption
behavior of BPn and
BPn-S
19
Odd/even effect in BPn/Au
Normalized ion signal (arb.u.)
Ion-induced desorption:
0.20
0.5
BPn
BPn-S
0.16
0.4
0.12
0.3
0.08
0.2
0.04
0.1
0.00
1
2
3
n
4
5
6
Desorption probability of the
parent molecule is larger for
even than for odd BPn/Au
 bond scission efficiency of
the S-Au bond is larger for
even than for odd BPn/Au
0.0
1
2
3
n
4
5
6
Desorption probability of
BPn-S molecule is larger for
odd than for even BPn/Au
 bond scission efficiency
of the C-S bond is larger for
odd than for even BPn/Au
20
Odd/even effect in BPn/Au
Discussion:
Odd BPn/Au:



Even BPn/Au



Au
 ~ 109
 > 130
both interactions result
in same structure
conflict between
interactions
C-S weakest bond
Au
S-Au weakest bond
21
Conclusions BPn
competition between molecule-substrate bond
and intermolecular interactions
difference in geometric and electronic structure
changes in bond scission efficiency induced
by projectile irradiation
difference in desorption probability
of different molecular fragments
22
BHA
• benzohydroxamic acids
• Formula - C7H7NO2
23
BHA
Hydroxamic acids and derivatives are
important molecules in:
• biology: antibacterial and antifungal
agents, enzyme inhibitors;
• medicine: anticancer agents, anemia
treatments, antibiotics;
• industry: pharmaceutical, corrosion
inhibitors.
24
BHA
Z- amide
(water, methanol)
E –amide
(acetone, methanol)
5. B.Garcia, et. al, Inorganic Chemistry 2005 (44) 2908
25
BHA
-H
-C
BHA
-O
p-CL-BHA
-N
- Cl
p-metoxy-BHA
p-nitro-BHA
26
Our interest
• new kind of organic layer;
• BHA as non toxic corrosion inhibitor
(passivation);
• solvents and substituents
dependent;
27
Electro polishing process
• electric current
passes through
submerged
workpiece
Copper
Copper
85% H3PO4
VUB - Brussels
28
Spincoating
• fluid resin
deposited in
centre of
substrate
• spun at high
speed ± 3000
rpm.
VUB - Brussels
29
Mass spectra
-0.026
39
-0.028
average of all measurements
for p-methoxy BHA/water
37
signal [arb. u.]
-0.030
heavy masses
Cu benzene
-0.032
-0.034
56
-0.036
-0.038
-0.040
27
52
50
14
30
28
24
63
108
78
65
133
40
103
91
-0.042
20
40
60
80
100
mass [amu]
118124
120
140
30
O
BHA
N
OH
H
-0.006
37
-0.008
56
52
50
27
30
-0.009
53
78
65
14
-0.010
56
-0.018
BHA/water
full average
signal [arb. u.]
39
-0.007
signal [arb. u.]
63
63
-0.019
40
-0.020
-0.021
91
94
BHA/methanol
Full average
38
28
29 37
27
24
65
78
51
92
130
-0.022
-0.011
20
40
60
80
100
mass [amu]
120
140
20
40
60
80
100
120
140
mass [amu]
 organic molecules fragments in both cases: 78, 91;
 a bit less amount of organic material on MeOH
dissolved samples
31
O
p-Cl-BHA
N
H
Cl
p-Cl-BHA/water
full average
56
38
-0.004
52
56
63
p-Cl-BHA/methanol
full average
52
-0.009
signal [arb. u.]
signal [arb. u.]
-0.008
OH
63
-0.010
38
40
-0.011
31 36
28
34
-0.012
51
65
13
-0.006
27
36
25
26 40 50
59
65 79
71
93
104
78
68
-0.005
115
-0.007
92
81
79
98
-0.013
-0.008
20
40
60
80
100
mass [amu]
120
140
20
40
60
80
100
120
140
mass [amu]
 organic molecules fragments: 78, 92;
 less organic signal from MeOH dissolved samples;
32
O
p-methoxy-BHA
C
H3C
-0.026
39
-0.028
signal [arb. u.]
signal [arb. u.]
-0.030
-0.032
-0.034
56
-0.036
-0.038
-0.040
27
52
50
14
30
28
24
63
108
78
40
40
103
91
60
-0.018
40
30
15
218
42
37
241
65
78
83 92
97 105 120
133
-0.042
20
52 63
29
27
-0.019
65
p-methoxy_BHA/methanol
full average
56
-0.017
80
100
mass [amu]
120
140
133
130
263
-0.020
118124
N
H
O
-0.016
average of all measurements
for p-methoxy BHA/water
37
OH
20
40
60
80
100
120
mass [amu]
 organic molecules fragments from H2O dissolved
samples: 65, 78, 91, 104, 108, 118, 133 amu;
 a few signal from p-methoxy-BHA/MeOH samples;
 the best covered copper surface by molecules
dissolved from water solution;
140
33
O
p-nitro-BHA
N
H
NO 2
-0.015
-0.036
p-nitro_BHA/water
full average
56
27
-0.017
52
63
25
38
-0.018 13
29
41
65
27
56
-0.037
signal [arb. u.]
signal [arb.u.]
-0.016
52
26
-0.038
p-nitro-BHA/methanol
full average
63
39
-0.039
-0.040
65
14
3741
50
80
51
78
-0.041
94
91
-0.019
20
40
60
80
100
mass [amu]
110
108
70
123
120
91
116
-0.042
140
OH
20
40
60
80
100
128134
120
140
mass [amu]
 organic molecules fragments from MeOH: 78, 92, 108;
 a little amount of material from water dissolved
surface;
 most probably more than one possible orientation on
the surface;
34
Cu isotopes:
63 amu – 69%
65 amu – 31%
Copper
0.35
0.06
Cu/H2O
Cu/MeOH
0.30
ion signal [arb. u.]
0.05
Cu63
Cu65
0.04
Cu63
Cu65
0.25
0.20
0.03
0.15
0.02
0.10
0.01
0.05
0.00
0.00
0
2
4
6
flight time [µs]
8
10
0
2
4
6
8
flight time [µs]
- copper distribution doesn’t depend on solvent;
- max. of FT – 2 µs;
10
35
p-Cl-BHA/Cu
0.012
0.018
p-Cl-BHA/H2O
0.010
p-Cl-BHA/MeOH
0.016
ion signal [arb. u.]
ion signal [arb. u.]
0.014
0.008
0.006
63
65
0.004
63
65
0.012
0.010
0.008
0.006
0.004
0.002
0.002
0
5
10
15
flight time [µs]
20
25
30
0
5
10
15
20
25
30
flight time [µs]
- H2O dissolved - distribution of copper is broader and
shifted to lower kinetic energies;
-MeOH dissolved – the same as for pure copper;
36
Maximum of FT distribution
10
Cu 63
8
time of delay [µs]
 samples dissolved
in methanol show
small changes in
distribution;
 copper from water
dissolved samples is
sputtered with lower
kinetic energy;
 p-nitro-BHA
behaves different
than the others
samples;
water
methanol
6
4
2
Cu
BHA
Cl-BHA methoxy-BHAnitro-BHA
sample
37
Conclusions BHA
1. Water dissolved:
Cu surface well covered by organic molecules for
BHA and p-methoxy-BHA
2. Methanol dissolved:
small density of molecules or only fragments of
molecules on the surface
3. Samples with p-nitro-BHA in MeOH show a distinct
velocity distribution
4. Organic layer formation is solvent dependent:
water is the best solvent for sample preparation
(except for p-nitro-BHA)
Thank you