molecular self-assembled monolayers on au{111} surface by: sung chou advisors: dr. lloyd a. bumm,...
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Molecular Self-assembled Molecular Self-assembled Monolayers on Au{111} Monolayers on Au{111}
surfacesurface
By: Sung ChouBy: Sung Chou
Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit BiswasAdvisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas
OutlineOutline► IntroductionIntroduction► MotivationMotivation► What are Alkanethiols?What are Alkanethiols?► What are Self-Assembled Monolayers (SAM)?What are Self-Assembled Monolayers (SAM)?► Formation of Hybrid SAMFormation of Hybrid SAM► Preparation of PTCDI/Melamine SAM NetworksPreparation of PTCDI/Melamine SAM Networks► Initial resultsInitial results► UV visible testUV visible test► Current resultsCurrent results► ConclusionConclusion► Plans/FuturePlans/Future
Self assembled monolayer of alkanethiols. Source: http://www.nd.edu/~djacobs/sam.jpg
IntroductionIntroduction► Self assembled monolayers (SAM) can act as a robust platform for Self assembled monolayers (SAM) can act as a robust platform for
developing nanostructuresdeveloping nanostructures► Combine PTCDI/Melamine and alkanethiols to create a hybrid SAM Combine PTCDI/Melamine and alkanethiols to create a hybrid SAM
systemsystem PTCDI/Melamine provides nano-scale precisionPTCDI/Melamine provides nano-scale precision Alkanethiols provide versatile functionalizationAlkanethiols provide versatile functionalization
PTCDI: perylene-3,4,9,10-tetracarboxylic di-imide
Melamine: 1,3,5-triazine-2,4,6-triamine
PTCDI/Melamine SAM network on Au {111} surface
Alkanethiol added to form hybrid SAM system
Rafael Madueno et. al. Nature 454, 618 (2008)
MotivationMotivation► SAMs provide a functional and SAMs provide a functional and
versatile platform for nanostructures versatile platform for nanostructures of an extended length scaleof an extended length scale Nano and Microelectromechanical Nano and Microelectromechanical
systems (NEMS and MEMS)systems (NEMS and MEMS) Modeling attachments to cell Modeling attachments to cell
membranesmembranes► Surface modificationsSurface modifications
Hydrophobic coatings, Hydrophobic coatings, e.g. e.g. for for automobile windshieldsautomobile windshields
Controlling electron transfer on Controlling electron transfer on electrodes in electrochemistryelectrodes in electrochemistry
Protecting metals from harsh Protecting metals from harsh substancessubstances
► Could function as a chemical sensorCould function as a chemical sensor
SAMs could potentially SAMs could potentially provide an easy to develop provide an easy to develop platform for MEMS, such as platform for MEMS, such as this ratcheting mechanism this ratcheting mechanism ~50~50μμm acrossm across
What are Alkanethiols?What are Alkanethiols?► AlkanesAlkanes
Simple single-bonded hydrocarbonsSimple single-bonded hydrocarbons Examples: propane, octane, decaneExamples: propane, octane, decane
► ThiolThiol Functional group composed of a sulfur and a Functional group composed of a sulfur and a
hydrogenhydrogen► AlkanethiolsAlkanethiols
Alkanes with a thiol head groupAlkanes with a thiol head group Example: 1-decanethiol, CHExample: 1-decanethiol, CH33(CH(CH22))88CHCH22SHSH
C10H22, Decane
1-decanethiol, SH as thiol head group
General thiol functional group
What are Self-Assembled What are Self-Assembled Monolayers (SAM)?Monolayers (SAM)?
► Spontaneously produced, single-molecule thick, layers which Spontaneously produced, single-molecule thick, layers which coat a substrate surfacecoat a substrate surface Alkanethiols bind onto gold surfaceAlkanethiols bind onto gold surface Thiol functional group loses hydrogenThiol functional group loses hydrogen Molecule converts to alkanethiolate (R―S-)Molecule converts to alkanethiolate (R―S-)
Formation of Hybrid SAMFormation of Hybrid SAM► PTCDI (blue rectangle) and melamine (red triangle) fit together PTCDI (blue rectangle) and melamine (red triangle) fit together
to form hexagonal network structureto form hexagonal network structure► Alkanethiols (black circle) bond to gold surface, framed by Alkanethiols (black circle) bond to gold surface, framed by
PTCDI/melamine networkPTCDI/melamine network
Preparation of PTCDI/Melamine Preparation of PTCDI/Melamine SAM NetworksSAM Networks
Preparation of PTCDI/Melamine Preparation of PTCDI/Melamine SAM NetworksSAM Networks
► Step 1:Step 1: The PTCDI and Melamine are both mixed with DMF The PTCDI and Melamine are both mixed with DMF
(Dimethylformamide) in separate test tubes(Dimethylformamide) in separate test tubes Both solutions shaken over night by the shaker machineBoth solutions shaken over night by the shaker machine Centrifuge both solutions about 30 minutes Centrifuge both solutions about 30 minutes Extract the clear liquid, leaving behind undissolved solidsExtract the clear liquid, leaving behind undissolved solids Repeat the process until little or no solid substance can be seen in Repeat the process until little or no solid substance can be seen in
either solutioneither solution
Undissolved PTCDI or MelamineUndissolved PTCDI or Melamine Uniformly Uniformly dissolved dissolved solutionsolution
Preparation of PTCDI/Melamine Preparation of PTCDI/Melamine SAM NetworksSAM Networks
► Step 2:Step 2: Mix both solutions in the ratio of 1:4 PTCDI:MelamineMix both solutions in the ratio of 1:4 PTCDI:Melamine The Au/mica substrate is immersed in the PFA vial containing the The Au/mica substrate is immersed in the PFA vial containing the
PTCDI/Melamine solutionPTCDI/Melamine solution Heat the substrate and solution at 100Heat the substrate and solution at 100°C inside an oven for 5 °C inside an oven for 5
minutesminutes Rinse the substrate with DMF and blow dry with nitrogenRinse the substrate with DMF and blow dry with nitrogen
Gold Gold substratesubstrate
PTCDI/PTCDI/Melamine Melamine SolutionSolution
Network formationNetwork formation
Initial resultsInitial results
Scanning Tunneling Microscopy (STM)Scanning Tunneling Microscopy (STM)► Atomically sharp tipAtomically sharp tip► DC bias between tip & surfaceDC bias between tip & surface► Bring tip close to surfaceBring tip close to surface► Current very sensitive to gap distanceCurrent very sensitive to gap distance
► Negative feedback (z)Negative feedback (z) Current too high = tip raisedCurrent too high = tip raised Current too low = tip loweredCurrent too low = tip lowered Feedback always active Feedback always active
► Tip rastered across surface (x, y)Tip rastered across surface (x, y) Grayscale image displayedGrayscale image displayed Dark = lowerDark = lower Light = higherLight = higher
STM MicrographSTM Micrograph► Some hexagonal Some hexagonal
structure can be seenstructure can be seen► Alkanethiols not added Alkanethiols not added
yetyet► Dark region indicates Dark region indicates
deep areasdeep areas
40 nm x 40 nm
STM image of our prepared PTCDI/Melamine SAM
STM image of the PTCDI/Melamine SAM in the Nature article
Fourier Transform ImageFourier Transform Image► Image mean in centerImage mean in center► Points away from center Points away from center
represent higher represent higher frequenciesfrequencies
► Distance between each Distance between each cell is ~0.5 nmcell is ~0.5 nm
► Distance is supposed to Distance is supposed to be ~3.5nm be ~3.5nm according to according to the articlethe article Suspect Melamine was not Suspect Melamine was not
fully dissolved in DMFfully dissolved in DMF Impurity in solutionsImpurity in solutions
► Size is too small to allow Size is too small to allow addition of alkanethiolsaddition of alkanethiols
► 22ndnd and 3 and 3rdrd attempts attempts yielded the same resultyielded the same result
Fourier transform of the STM image Fourier transform of the STM image
The Ultra violet visible testThe Ultra violet visible test
UV Visible TestUV Visible Test► UV-Vis test performed to check concentration of dissolved solidsUV-Vis test performed to check concentration of dissolved solids► UV light shined on sampleUV light shined on sample
Separate detector
Light source
Sample
Diffraction grating
Detector
mirrors
UV Visible TestUV Visible Test► Chromophores in an organic substance absorb characteristic Chromophores in an organic substance absorb characteristic
wavelengthswavelengths Chromophore is a part of a molecule responsible for its colorChromophore is a part of a molecule responsible for its color
► Resulting absorption spectrum used to determine properties of Resulting absorption spectrum used to determine properties of a samplea sample Type and amount of substanceType and amount of substance StructureStructure
UV Visible TestUV Visible Test► Each sample should have approximately 2x the concentration as Each sample should have approximately 2x the concentration as
the previous, or 2x the emitted intensitythe previous, or 2x the emitted intensity► Test results show that PTCDI is dissolving the way we expectTest results show that PTCDI is dissolving the way we expect
Successive samples scaled by factors Successive samples scaled by factors of 2of 2K. Balakrishnan et. al. J.
Am. Chem. Soc. 128, 7390 (2006)
Current resultsCurrent results
STM MicrographSTM Micrograph► 44thth attempt of attempt of
PTCDI/Melamine networkPTCDI/Melamine network
STM image of the prepared PTCDI/Melamine SAM
40 nm x 40 nm
Fourier Transform ImageFourier Transform Image► The measured distance is 0.488nmThe measured distance is 0.488nm
FFT im
age[p
m]
Distance[Gm-1]
ConclusionConclusion► We were able to produce saturated We were able to produce saturated
solutions of PTCDI-Melamine along with solutions of PTCDI-Melamine along with their optical characterizationtheir optical characterization
► The experiment was performed 4 timesThe experiment was performed 4 times► Our results are fairly consistent despite Our results are fairly consistent despite
our effort to obtain the original resultour effort to obtain the original result► Some vital information might have been Some vital information might have been
left out in the paperleft out in the paper► Efforts to contact the research group Efforts to contact the research group
failedfailed
Trial Spacing (nm)
1 0.500
2 0.503
3 0.497
4 0.488
?
Plans/FuturePlans/Future► UV-Vis characterization of saturated solutions of PTCDI and UV-Vis characterization of saturated solutions of PTCDI and
Melamine in order to examine the absorption propertiesMelamine in order to examine the absorption properties► Optimization of the SAM preparation conditions: Optimization of the SAM preparation conditions:
ratio of mixingratio of mixing growth temperaturegrowth temperature time, etc.time, etc.
► Insertion of alkanethiol and other less-studied thiols and Insertion of alkanethiol and other less-studied thiols and functional molecules (functional molecules (e.g.e.g. octylthiocyanates, Azides) in the octylthiocyanates, Azides) in the PTCDI/Melamine networkPTCDI/Melamine network
► Putting PTCDI/Melamine SAM network on Flat Gold Nano Putting PTCDI/Melamine SAM network on Flat Gold Nano Particles (FGNPs) and study optical properties Particles (FGNPs) and study optical properties (absorption/fluorescence). (absorption/fluorescence).
AcknowledgementsAcknowledgements► Dr. Lloyd A Bumm, Dr. Abhijit Biswas, Daminda Dahanayaka, Dr. Lloyd A Bumm, Dr. Abhijit Biswas, Daminda Dahanayaka,
Chris Schroeder, Matt WhitewayChris Schroeder, Matt Whiteway
THANK YOU