Download 2009S-SAMsonFGNPs

Molecular Self-assembled
Monolayers on Au{111}
surface
By: Sung Chou
Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas
Outline
► Introduction
► Motivation
► What
are Alkanethiols?
► What are Self-Assembled Monolayers (SAM)?
► Formation of Hybrid SAM
► Preparation of PTCDI/Melamine SAM Networks
► Initial results
► UV visible test
► Current results
► Conclusion
► Plans/Future
Self assembled monolayer of alkanethiols. Source:
http://www.nd.edu/~djacobs/sam.jpg
Introduction
► Self
assembled monolayers (SAM) can act as a robust platform for
developing nanostructures
► Combine PTCDI/Melamine and alkanethiols to create a hybrid SAM system
 PTCDI/Melamine provides nano-scale precision
 Alkanethiols provide versatile functionalization
PTCDI/Melamine
SAM network on
Au {111} surface
Alkanethiol added to
form hybrid SAM
system
Rafael Madueno et. al. Nature 454, 618 (2008)
PTCDI: perylene3,4,9,10-tetracarboxylic
di-imide
Melamine: 1,3,5triazine-2,4,6triamine
Motivation
► SAMs
provide a functional and versatile
platform for nanostructures of an
extended length scale
 Nano and Microelectromechanical systems
(NEMS and MEMS)
 Modeling attachments to cell membranes
► Surface
modifications
 Hydrophobic coatings, e.g. for automobile
windshields
 Controlling electron transfer on electrodes
in electrochemistry
 Protecting metals from harsh substances
► Could
function as a chemical sensor
SAMs could potentially provide
an easy to develop platform for
MEMS, such as this ratcheting
mechanism ~50μm across
What are Alkanethiols?
► Alkanes
 Simple single-bonded hydrocarbons
 Examples: propane, octane, decane
► Thiol
 Functional group composed of a sulfur and a
hydrogen
C10H22, Decane
► Alkanethiols
 Alkanes with a thiol head group
 Example: 1-decanethiol, CH3(CH2)8CH2SH
1-decanethiol, SH as thiol head group
General thiol
functional group
What are Self-Assembled
Monolayers (SAM)?
► Spontaneously
produced, single-molecule thick, layers which coat a
substrate surface
 Alkanethiols bind onto gold surface
 Thiol functional group loses hydrogen
 Molecule converts to alkanethiolate (R―S-)
Formation of Hybrid SAM
► PTCDI
(blue rectangle) and melamine (red triangle) fit together to form
hexagonal network structure
► Alkanethiols (black circle) bond to gold surface, framed by
PTCDI/melamine network
Preparation of PTCDI/Melamine
SAM Networks
Preparation of PTCDI/Melamine SAM
Networks
► Step
1:
 The PTCDI and Melamine are both mixed with DMF (Dimethylformamide) in
separate test tubes
 Both solutions shaken over night by the shaker machine
 Centrifuge both solutions about 30 minutes
 Extract the clear liquid, leaving behind undissolved solids
 Repeat the process until little or no solid substance can be seen in either
solution
Undissolved PTCDI or Melamine
Uniformly
dissolved solution
Preparation of PTCDI/Melamine SAM
Networks
► Step
2:
 Mix both solutions in the ratio of 1:4 PTCDI:Melamine
 The Au/mica substrate is immersed in the PFA vial containing the
PTCDI/Melamine solution
 Heat the substrate and solution at 100°C inside an oven for 5 minutes
 Rinse the substrate with DMF and blow dry with nitrogen
Gold substrate
PTCDI/Melamine
Solution
Network formation
Initial results
Scanning Tunneling Microscopy (STM)
► Atomically
sharp tip
► DC bias between tip & surface
► Bring tip close to surface
► Current very sensitive to gap distance
► Negative
feedback (z)
 Current too high = tip raised
 Current too low = tip lowered
 Feedback always active
► Tip
rastered across surface (x, y)
 Grayscale image displayed
 Dark = lower
 Light = higher
STM Micrograph
► Some
hexagonal structure
can be seen
► Alkanethiols not added yet
► Dark region indicates deep
areas
STM image of the PTCDI/Melamine SAM in
the Nature article
40 nm x 40 nm
STM image of our prepared PTCDI/Melamine
SAM
Fourier Transform Image
► Image
mean in center
► Points away from center
represent higher frequencies
► Distance between each cell is
~0.5 nm
► Distance is supposed to be
~3.5nm according to the
article
 Suspect Melamine was not
fully dissolved in DMF
 Impurity in solutions
► Size
is too small to allow
addition of alkanethiols
► 2nd and 3rd attempts yielded
the same result
Fourier transform of the STM image
The Ultra violet visible test
UV Visible Test
► UV-Vis
test performed to check concentration of dissolved solids
► UV light shined on sample
Sample
Light source
Separate detector
Diffraction grating
Detector
mirrors
UV Visible Test
► Chromophores
wavelengths
in an organic substance absorb characteristic
 Chromophore is a part of a molecule responsible for its color
► Resulting
absorption spectrum used to determine properties of a sample
 Type and amount of substance
 Structure
UV Visible Test
► Each
sample should have approximately 2x the concentration as the
previous, or 2x the emitted intensity
► Test results show that PTCDI is dissolving the way we expect
K. Balakrishnan et. al. J. Am.
Chem. Soc. 128, 7390 (2006)
Successive samples scaled by factors of 2
Current results
STM Micrograph
► 4th
attempt of PTCDI/Melamine
network
40 nm x 40 nm
STM image of the prepared PTCDI/Melamine SAM
Fourier Transform Image
measured distance is 0.488nm
FFT image[pm]
► The
Distance[Gm-1]
Conclusion
► We
were able to produce saturated solutions
of PTCDI-Melamine along with their optical
characterization
► The experiment was performed 4 times
► Our results are fairly consistent despite our
effort to obtain the original result
► Some vital information might have been left
out in the paper
► Efforts to contact the research group failed
?
Trial
Spacing (nm)
1
0.500
2
0.503
3
0.497
4
0.488
Plans/Future
► UV-Vis
characterization of saturated solutions of PTCDI and Melamine
in order to examine the absorption properties
► Optimization of the SAM preparation conditions:
 ratio of mixing
 growth temperature
 time, etc.
► Insertion

of alkanethiol and other less-studied thiols and functional
molecules (e.g. octylthiocyanates, Azides) in the PTCDI/Melamine
network
► Putting PTCDI/Melamine SAM network on Flat Gold Nano Particles
(FGNPs) and study optical properties (absorption/fluorescence).

Acknowledgements
► Dr.
Lloyd A Bumm, Dr. Abhijit Biswas, Daminda Dahanayaka, Chris
Schroeder, Matt Whiteway
THANK YOU