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