molecular self-assembled monolayers on au{111} surface by: sung chou advisors: dr. lloyd a. bumm,...

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Molecular Self- Molecular Self- assembled Monolayers assembled Monolayers on Au{111} surface on Au{111} surface By: Sung Chou By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas Biswas

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Page 1: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 2: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: 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

Page 3: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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)

Page 4: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 5: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 6: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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-)

Page 7: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 8: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

Preparation of PTCDI/Melamine Preparation of PTCDI/Melamine SAM NetworksSAM Networks

Page 9: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 10: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 11: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

Initial resultsInitial results

Page 12: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 13: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 14: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 15: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

The Ultra violet visible testThe Ultra violet visible test

Page 16: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 17: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 18: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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)

Page 19: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

Current resultsCurrent results

Page 20: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

Page 21: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

Fourier Transform ImageFourier Transform Image► The measured distance is 0.488nmThe measured distance is 0.488nm

FFT im

age[p

m]

Distance[Gm-1]

Page 22: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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

?

Page 23: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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).

Page 24: Molecular Self-assembled Monolayers on Au{111} surface By: Sung Chou Advisors: Dr. Lloyd A. Bumm, Dr. Abhijit Biswas

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