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Harald Etschmaier. Langmuir-Blodgett films and chemically reactive Self Assembled Monolayers in Organic Thin film Transistors. IF – Seminar, Graz, 9.1.2008. Outline. Part I: Langmuir Blodgett films The Method Characterization Modified OTFTs Part II: Chemically Reactive SAMs Theory Setup - PowerPoint PPT Presentation
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University of Technology Graz - Institute of Solid State Physics
1
Harald Etschmaier LB-films and SAMs in [email protected]
Langmuir-Blodgett films and chemically reactive Self Assembled Monolayers in
Organic Thin film Transistors
Harald Etschmaier
IF – Seminar, Graz, 9.1.2008
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Outline
Part I: Langmuir Blodgett films– The Method
– Characterization
– Modified OTFTs
Part II: Chemically Reactive SAMs– Theory
– Setup
– Measurements and results
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Motivation
LB-films form a very regular structure on the substrate and allow a easy control of the surface wettability.
We hope that these properties can yield a better grain formation when growing pentacene on top and hence result in a better mobility in the transistor.
Organic Electronics, Hagen Klauk, Wiley-VCH Verlag (2006)
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Idea of the LB-film
• Principle copied from nature
• Cell membrane is stabilized by surrounding water
www.molecularexpressions.com
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
The technical approach
Binks, B.P. Adv. Colloid Interface Sci., 34 (1991) 343
• Apply non-soluble molecules on water surface
• transfer one by one monolayer to substrate by dipping and removing
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
The Langmuir Blodgett Trough
• Force Sensor is measuring the surface pressure (=surface tension of pure water – surface tension of water with floating molecules)
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
The moleculePentacosa-10,12-diynoic acid
so-called diacetylene
Polymerization upon exposure to UV stabilizes layer
Single Monolayer transistors have been build from these films
Monolayer Transistor Using a Highly Ordered Conjugated Polymer as the Channel, Scott et al., Nano letter Vol.6, 2006
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Layer formation
• Diacetylene is dissolved in chloroform and dropped on the surface
• The barrier compresses the molecules to a solid stateliquid
gaseous
solid
Multiple layers
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Layer transfer
Adam, G.; Läuger, P.; Stark, G.; Physikalische Chemie und Biophysik
• wettability of sample changes for each dipping
• in theory any number of monolayers possible
University of Technology Graz - Institute of Solid State Physics
10
Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Sample preparation
SiOx substrates with different pretreatments:
1. Oxygen plasma etched hydrophilic
2. HDMS layer hydrophobic
3. Perflourinated SAM super hydrophobic
Optional polymerization on water surface or directly on substrate
Cd-Ions in the head group of the diacetylene to stabilize the layer and improve XRR-contrast
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Recorded area transfer
outin
in
out
Decrease of surface area gives a good feedback for layer deposition
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
XRR - Different layer thickness
0 3 6
3 LB layers 9 LB layers
Inte
nsity
[a.u
.]
2[deg.] 5.2 5.6
3 LB layers 9 LB layers
Inte
nsi
ty [a
.u.]
2[deg.]
1.6 2.0
3 LB layers 9 LB layers
Inte
nsi
ty [a
.u.]
2[deg.]
Some kind of wetting layer is always the same
The Bragg Peak develops with increasing number of LB layers
DI Heinz-Georg Flesch
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
XRR – illuminated and not illuminated
0 1 2 3 4 5 6 7
3 LB layers 3 LB layers (no cross-linking) 9 LB layers
Inte
nsi
ty [a
.u.]
2[deg.]
-Smaller and broader Bragg Peak for not polymerized sample (worse multilayer stacking)
-Minimum shifts upon polymerization, but stays the same independent from number of LB layers
DI Heinz-Georg Flesch
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
XRR
D-spacing of layers approximately 4.8 nm (one repeated unit consists of two LB layers)
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
AFM
Center of sample (LB-film)
Edge of sample (SIOx substrate)
AFM can proof that something was deposited
DI Heinz-Georg Flesch
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
AFM
0.0 2.0x10-7 4.0x10-7 6.0x10-7 8.0x10-7 1.0x10-61.0x10-9
1.5x10-9
2.0x10-9
2.5x10-9
3.0x10-9
3.5x10-9
4.0x10-9
he
igh
t
distance
cross section 1
~1,25nm
~2nm
AFM data gives no clear result for the layer thickness
DI Heinz-Georg Flesch
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Pentacene DepositionNo LB-film 1 monolayer diacetylene
Dr. A
nja Haase
•Higher nucleation density, three dimensional grains
•Better homogeneity in depth and a lower density of defects
•Disordered solid made of dendritic grains
•High concentration of defects , mainly located at grain boundaries
Kalb et al. / Synthetic Metals 146 (2004) 279-282
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Light Microscope
Pentacene on LB-film
Pentacene on SiOx
SiOx
Pentacene on SiOx
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
FETs
No improvement achieved so far – Further experiments in process!
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Part II
Time resolved measurements of chemically reactive SAMs
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Setup
Application of CSTS SAM on SiOx substrate
Spin coating of P3HT Evaporation of Au
contacts Electrical characterization
e- assisted Pt coating
Au contact
P3HT
CSTS
SiOX
Si
165nm SiOX
CSTS
P3HT
VS VD
VG
AuAu
S
S
R1
R1
P3HT
Pacher et al., submitted
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Doping and Dedoping mechanism
SiOx
SiO O
O
S
OH
OO
SiOx
SiO O
O
S
O-
OO
SS
R
R
n
SS
R
R
nH
SS
R
R
n
SiOx
SiO O
O
S
O-NH4+
OO
Doping Dedoping
NH3
SiOx
SiO O
O
S
Cl
OO
SiOx
SiO O
O
S
Cl
OO
SS
R
R
n
SS
R
R
n
SS
R
R
n
SiOx
SiO O
O
S
NH2
OO
Doping
2 NH3NH4
+Cl-
T-SA
T-SC
Pacher et al., submitted
Shifts the threshold voltage by up to 60V to negative values
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Creating the gas mixture
Argon
AmmoniaFlow meters
Valves
Measuring cell
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
The measuring cell
Potassic-bromide windows
Three-way valves
Spring contacts
Source Drain Gate
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Results – threshold voltage
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Results – threshold voltage
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Results - mobility
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Conclusions from preliminary experiments
Ammonia increases hysteresis: Molecules diffuse into bulk and cause additional trap states
Ammonia decreases mobility: Additional scattering centres
The threshold voltage drops irreversibly upon exposure to Ammonia by. Quantity is dependent on time and concentration. further experiments
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Additional observations
After reaction with ammonia FETs are very sensitive to light: Turn-on-voltage shifts by up to 70V upon illumination.
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Additional observations
Measurements influence device characteristics
University of Technology Graz - Institute of Solid State Physics
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Harald Etschmaier Seminar - Graz, 9.1.2008 LB-films and SAMs in [email protected]
Co-Workers
FETs– Peter Pacher, Andrej Golubkov, Egbert Zojer
SAMs– Alexandra Lex, Gregor Trimmel, Christian Slugovc
AFM, XRR– Heinz Georg Flesch, Roland Resel, Anja Haase
LB-films– Martin Weis, Julius Cirak