Self Assembly July 22, 2009 Summer 2009 Nanotechnology Institute.
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Transcript of Self Assembly July 22, 2009 Summer 2009 Nanotechnology Institute.
Self Assembly
July 22, 2009 Summer 2009 Nanotechnology Institute
Making Nanostructures: Nanomanufacturing
"Top down" versus "bottom up" methods
•Lithography•Deposition•Etching•Machining
•Chemical•Self-Assembly
What drives and governs self assembly?
As you view 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?
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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
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Nanoparticle Monolayer Formed at a Liquid-Air Interface
Nanoparticle Monolayer Formation
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Nature Materials MOVIE
toluene
Requirements:• rapid evaporation• excess dodecane present• attractive interation to liq-air interface and between particles
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)
Array Period = 24 nm Pore Diameter = 14 nm
MW = 42,000PS/PMMA
TEMPLATE CHARACTERIZATION
100 cpp
SEMSAXS
Improving Order: Guided Assembly in a Trench: Graphioepitaxy
UMass-Seagate
assemble here
side view
top
view
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
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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.
Anodized Aluminum Oxide Templates
Aluminum
Nanoporousaluminum
oxide (AAO)~ 40 V
counter electrode
Anodization Acid Bath
I
e.g., • Keller, et al., J. Electrochem. Soc. 100, 411 (1953) • Masuda & Fukuda, Science 268, 1466 (1995)
(oxalic, sulfuric, orphosphoric acid)
Masuda, et al.
Proposed AAO Growth Mechanism
Figure adapted fromJessensky, Müller, & Gösele, Appl. Phys. Lett. 72, 1173 (1998)
Al2O3
E
Al
Al3+ O2-
• Density mismatch between Al and Al2O3
• Some Al3+ goes to solution
• Mechanical stress yields pore growth in uniform hexagonal array
Pore diameters of ~ 10-400 nm possibleby choice of anodizationconditions
Improving AAO Order at Surface
SiC stamp
Aluminum
anodize
e.g., Masuda et al., Appl. Phys. Lett 71, 2770 (1997);Choi, et al., J. Vac. Sci. Tech. B 21, 763 (2003)
Ni in Anodized Aluminum Oxide Template
SEM MFM
Nielsch, et al. Appl. Phys. Lett. 79, 1360 (2001).
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Large Scale Self-Assembly (Geological)
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Giant's Causeway(Northern Ireland)
Volcanic basalt cooled rapidly to form these (mostly) hexagonally shaped columns
Microfluidic Assembly
Application: RFID
Alien Technology
Nanoscale Phase SeparationIBM "air gap" technology
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Introducing nanoscale air pockets into the insulating material separating wires on a computer chip -- lowers the capacitance
flow direction
Parts, having unique shape, are delivered via fluid flow to mating pockets on an assembly substrate.
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Molecular Recognition("lock and key" bonding)
biotin-avidin pair (site-specific binding)thymine (T) adenine (A)
guanine (G) cytosine (C)
hydrogen bonding
Using Synthetic DNA for Designer Structures
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Ned Seeman, NYU
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Designer DNA molecules can be synthesized chemically, and allowed to assemble into a specific configuration of lowest energy.
Programmed DNA Folding to Make "DNA Origami"P.W.K. Rothemund, Nature 440, 297 (2006)
Additional examples to amplify concepts
• balls in a box• magnets• crystallization
Forces (non-directional or directional), shape, thermal agitationNanoscale self assembly• coffee stain• nanoparticle assembly by droplet• others