Self Assembly

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Self Assembly

• Nanotechnology Institute
• Summer 2009

Mark Tuominen University of Massachusetts
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(No Transcript)
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Overview

• Self assembly defined
• Self assembly as a process
• Self assembly in nature
• Self assembly in nanotechnology
• Modeling self assembly
• Harnessing self assembly

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Self Assembly Defined

• Static assembly (thermodynamic free energy
  minimum) -- once formed it is stable
• Dynamic assembly (kinetically formed, not
  necessarily thermodynamic minimum) -- not
  necessarily stable

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Making Nanostructures Nanomanufacturing

• "Top down" versus "bottom up" methods

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Tobacco Mosaic Virus
wisc.edu
nih.gov
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Gecko feet
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Diatoms
sinancanan.net
priweb.org
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Abalone
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The Cell and Its Hierarchy
ebi.ac.uk
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Self assembly at all scales?
Whitesides et al. Science 295, 2418 (2002)
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What drives and governs self assembly?

• 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)

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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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Langmuir Film - of an amphiphilic molecule
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Langmuir-Blodgett Film
solid
Must control movable barrier to keep
constant pressure
liquid
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SAM Self Assembled Monolayer
alkanethiol on gold (Au)
HS(CH2)nX
where X is the end group of the chain
CH3, OH, or COOH
Longer alkanethiol molecules have greater
thermodynamic stability
Review article J.C. Love, et al., Chem. Rev.
2005, 105, 1103 (G. Whitesides group, Chem Dept,
Harvard)
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SAM Self Assembled Monolayer
Molecules from solution
solid

• Chemisorbed molecules
• Stabilized by intermolecular van der Waals
  interaction

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Nanoparticle Monolayer Formation
toluene
Nature Materials MOVIE

• Requirements
• rapid evaporation
• excess dodecane present
• attractive interaction to liquid-air interface
  and between particles

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SELF ASSEMBLY with DIBLOCK COPOLYMERS
Block B
Block A
PS
PMMA
Scale set by molecular size
Ordered Phases
10 A
30 A
50 A
70 A
90 A
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CORE CONCEPT FOR NANOFABRICATION
(physical or electrochemical)
Remove polymer block within cylinders (expose and
develop)
Versatile, self-assembling, nanoscale
lithographic system
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TEMPLATE CHARACTERIZATION
PS/PMMA - MW 42,000
SEM
SAXS
Array Period 24 nm Pore Diameter 14 nm
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Improving Order Guided Assembly in a Trench
Graphioepitaxy
side view
assemble here
top view
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Nanomagnets in a Self-Assembled Polymer Mask
nanoporous template
1x1012 magnets/in2
Data Storage... ...and More
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Metal Nanorings
Ferromagnetic cobalt rings as small as 15 nm OD
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More Fabrication by Breath Figures
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.
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)
Mohan Srinivasarao, et al. Science 292, 79 (2001).
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Anodized Aluminum Oxide Templates
counter electrode
Nanoporous aluminum oxide (AAO)
40 V
Aluminum
I
(oxalic, sulfuric, or phosphoric acid)
Anodization Acid Bath
Masuda, et al.
e.g., Keller, et al., J. Electrochem. Soc. 100,
411 (1953) Masuda Fukuda, Science
268, 1466 (1995)
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Proposed AAO Growth Mechanism

• 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 possible by choice
of anodization conditions
Figure adapted from Jessensky, Müller, Gösele,
Appl. Phys. Lett. 72, 1173 (1998)
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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)
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Ni in Anodized Aluminum Oxide Template
SEM
MFM
Nielsch, et al. Appl. Phys. Lett. 79, 1360 (2001).
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Microfluidic Assembly
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)
hydrogen bonding
thymine (T) adenine (A) guanine (G)
cytosine (C)
biotin-avidin pair (site-specific binding)
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Using Synthetic DNA for Designer Structures
Designer DNA molecules can be synthesized
chemically, and allowed to assemble into a
specific configuration of lowest energy.
Ned Seeman, NYU - http//seemanlab4.chem.nyu.edu/
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Programmed DNA Folding to Make "DNA Origami"
P.W.K. Rothemund, Nature 440, 297 (2006)
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Additional examples to amplify concepts

• Balls in a box
• Magnets
• Crystallization
• Coffee stain
• Nanoparticle assembly by droplet
• Forces (non-directional or directional), shape,
  thermal agitation
• Nanoscale self assembly

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Summary

• Types of self assembly
• Principles of self assembly
• Mathematics of self assembly
• Self Assembly in nature
• Self assembly in nanotechnology

Self assembly is a key function in the process
of life if not the organization of the entire
universe
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Permissions

• Permission to use this presentation granted by
  Mark Tuominen - Professor of Physics Co-Director
  of the Center for Hierarchical Manufacturing and
  MassNanoTech
• 411 Hasbrouck Laboratory, Amherst MA 01003
  tuominen_at_physics.umass.edu
• Phone [phone] Fax [phone]
• NSF Nanoscale Science and Engineering Conference
  Website
• http//umassk12.net/nano/materials/web2011/
• Please do not redistribute without permission!