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Self Assembly
July 9, 2008 Summer 2008 Nanotechnology Institute
Making Nanostructures: Nanomanufacturing
"Top down" versus "bottom up" methods
•Lithography•Deposition•Etching•Machining
•Chemical•Self-Assembly
What drives self assembly?
As you view some of the following images you should consider the question:
Tobacco Mosaic Virus
wisc.edu
nih.gov
Gecko feet
Diatoms
priweb.org
sinancanan.net
Abalone
The Cell and Its Hierarchy
ebi.ac.uk
Whitesides et al. Science 295, 2418 (2002);
Self assembly at all scales?
What drives self assembly?
• Static assembly (thermodynamic free energy minimum) -- once formed it is stable• Dynamic assembly (kinetically formed, not necessarily thermodynamic minimum) -- not necessarily stable
• Forces of chemical bonding (4)• covalent, ionic, van derWaals, hydrogen
• Other forces (magnetic, electrostatic, fluidic, ...)• Polar/Nonpolar (hydrophobicity)• Shape (configurational)• Templates (guided self assembly)• Kinetic conditions (e.g., diffusion limited)
Excerpt from Letter of Benjamin Franklin to William Brownrigg (Nov. 7, 1773)
...At length being at Clapham, where there is, on the Common, a large Pond ... I fetched out a Cruet of Oil, and dropt a little of it on the Water. I saw it spread itself with surprising Swiftness upon the Surface ... the Oil tho' not more than a Tea Spoonful ... which spread amazingly, and extended itself gradually till it reached the Lee Side, making all that Quarter of the Pond, perhaps half an Acre, as smooth as a Looking Glass....
A nanofilm!
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LangmuirFilm pressure
e.g., steric acid
monolayer filmwater
hydrophilic end
hydrophobic end
of an amphiphilicmolecule
Langmuir-Blodgett FilmMust control movablebarrier to keep constantpressure
multiple dips -multiple layers
solid
liquid
SAM: Self Assembled Monolayer
Review article: J.C. Love, et al., Chem. Rev. 2005, 105, 1103(G. Whitesides group, Chem Dept, Harvard)
HS(CH2)nX alkanethiol on gold (Au)
where X is the end group of the chain –CH3, –OH, or –COOH
Longer alkanethiol molecules have greater thermodynamic stability
SAM: Self Assembled Monolayer
• Chemisorbed molecules• Stabilized by intermolecular van der Waals interaction
solid
moleculesfrom solution
SAMs on Nanoparticles
J.C. Love, et al., Chem. Rev. 2005, 105, 1103
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gold NP
There are now many configurations and uses of SAMs
imperfect packing
SAMs via Microcontact Printing
J.C. Love, et al., Chem. Rev. 2005, 105, 1103
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A type ofstamping!
(silicon rubber)
SELF ASSEMBLY with DIBLOCK COPOLYMERS
Block “A” Block “B”
10% A 30% A 50% A 70% A 90% A
~10 nm
Ordered Phases
PMMA PS
Scale set by molecular size
CORE CONCEPT FOR NANOFABRICATION Deposition
Template
EtchingMask
NanoporousMembrane
Remove polymerblock within cylinders(expose and develop)
Versatile, self-assembling, nanoscale lithographic system
(physical orelectrochemical)
nanoporous template
Nanomagnets in a Self-Assembled Polymer Mask
1x1012 magnets/in2
Data Storage......and More
Metal Nanorings
Ferromagnetic cobalt rings as small as 15 nm OD
Larger Nanorings
RingsHoles
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Mohan Srinivasarao, et al. Science 292, 79 (2001).
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Kinetic Self-Assembly - by Breath Figures
Polystyrene Film
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More Fabrication by Breath Figures
UMass: Alexander Böker, Yao Lin, Kristen Chiapperini, Reina Horowitz, Mike Thompson, Vincent Carreon, Ting Xu, Clarissa Abetz, Habib Skaff, A. D. Dinsmore, Todd Emrick and Thomas P. Russell, Nature Materials 3, 302 - 306 (2004)
a, Breath-figure pattern obtained with pure polystyrene. b, Optical and c, confocal fluorescence microscope images of different areas of a sample obtained from solvent-casting a polystyrene film from chloroform with CdSe nanoparticles. Scale bars: 16 mum. The inset in c shows a fluorescence intensity scan along the line indicated.
Conjugate molecular pairing
biotin-avidin pair (site-specific binding)
"key &lock"
Microfluidic Assembly
Application: RFID tags(radio frequency identification)
Alien Technology
An alternative to "pick and place" -- for tiny parts.
Microfluidic Assembly
Application: RFID tags(radio frequency identification)
Alien Technology
An alternative to "pick and place" -- for tiny parts.
Really Large Scale Self-Assembly
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Giant's Causeway, Northern Ireland
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