Assembly

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self assembly 2011 - UMassK12

Self

Assembly

Nano Education Institute 2011


Making Nanostructures:

Nanomanufacturing

"Top down" versus "bottom up" methods

•Lithography

•Deposition

•Etching

•Machining

•Chemical

•Self-Assembly


First a case you already know: The nanofilm

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....

Franklin made

this

observation,

but did not

determine the

thickness.


Agnes Pockels

• The first person to make worthwhile, reproducible

measurements on monolayers was Agnes Pockels who lived in

Braunschweig, Germany. Agnes Pockels was the original

housewife superstar. She performed her first experiments on

monolayers in her kitchen in her home, starting in about

1882. She used a tin tray as the water container and a small

disk suspended from a balance with a slide weight to measure

the surface tension of the water.

• By contaminating the water surfaces with different materials,

Pockels created monolayers and observed their properties when

confining the water surfaces to various areas using waxed tin

strips. Pockels observed that the surface tension of a water

surface varies with its size and depends on the type of

contamination.

• She sent an account of her work to Lord Rayleigh, who

recommended its publication in the journal Nature. Lord

Rayleigh had a similar interest in the science of interfaces and

was inspired by Pockels to make his own experiments, from

which he concluded that these layers were just a single

molecule thick.


Langmuir-Blodgett

Film

of an amphiphilic

molecule

hydrophobic end

hydrophilic end

e.g., steric acid

monolayer film

pressure

water


Langmuir-Blodgett Film Transferred to a

solid

Solid Surface

Must control movable

barrier to keep constant

pressure

liquid

multiple dips -

multiple layers


As you view the following

images you should consider

the question:

What drives and governs

self assembly?


Tobacco Mosaic Virus

wisc.edu

nih.gov


Gecko feet


Diatoms

sinancanan.net

priweb.org


Abalone


ebi.ac.uk

The Cell and Its Hierarchy


Self assembly

at all scales?

Whitesides et al. Science 295,

2418 (2002);


What drives self assembly?

• Static assembly (thermodynamic free energy

minimum; requires agitation) -- 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)


SAM: Self Assembled Monolayer

molecules

from solution

solid

• Chemisorbed molecules

• Stabilized by intermolecular van der Waals interaction


SAM: Self Assembled Monolayer

alkanethiol

on gold (Au)

HS(CH 2

) n

X

where X is the end group of the chain

–CH 3

, –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)


gold NP

SAMs on

Nanoparticles

There are now many

configurations and uses

of SAMs

imperfect

packing

J.C. Love, et al., Chem. Rev. 2005, 105, 1103


Nanoparticle Monolayer Formed at a Liquid-Air Interface


Nanoparticle Monolayer Formation

toluene

Nature Materials MOVIE

Requirements:

• rapid evaporation

• excess dodecane present

• attractive interation to liqair

interface and between

particles


SELF ASSEMBLY with DIBLOCK COPOLYMERS

Block “A”

PMMA

Block “B”

PS

~10 nm

Scale set by molecular size

Ordered Phases

10% A 30% A 50% A 70% A 90% A


CORE CONCEPT

FOR NANOFABRICATION

Deposition

Template

(physical or

electrochemical)

Etching

Mask

Remove polymer

block within cylinders

(expose and develop)

Nanoporous

Membrane

Versatile, self-assembling, nanoscale lithographic system


TEMPLATE CHARACTERIZATION

SAXS

PS/PMMA

MW = 42,000

SEM

100 cpp

Array Period = 24 nm

Pore Diameter = 14 nm


Improving Order: Guided Assembly in a Trench:

Graphioepitaxy

side view

assemble here

top

view

UMass-Seagate


Nanomagnets in a Self-Assembled Polymer Mask

nanoporous template

1x10 12 magnets/in 2

Data Storage...

...and More


Ferromagnetic cobalt rings

as small as 15 nm OD

Metal Nanorings


Kinetic Self-Assembly - by Breath Figures

Polystyrene Film

Mohan Srinivasarao, et al. Science 292, 79 (2001).


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)


Anodized Aluminum Oxide Templates

~ 40 V

counter electrode

Nanoporous

aluminum

oxide (AAO)

Aluminum

I

Anodization Acid Bath

(oxalic, sulfuric, or

phosphoric acid)

e.g., • Keller, et al., J. Electrochem. Soc. 100, 411 (1953)

• Masuda & Fukuda, Science 268, 1466 (1995)

Masuda, et al.


Proposed AAO Growth Mechanism

Al 3+ O 2-

E

Al 2 O 3

• Density mismatch between

Al and Al 2

O 3

• Some Al 3+ goes to solution

• Mechanical stress yields

pore growth in uniform

hexagonal array

Al

Pore diameters of

~ 10-400 nm possible

by choice of anodization

conditions

Figure adapted from

Jessensky, Müller, & Gösele, Appl. Phys. Lett. 72, 1173 (1998)


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).


Molecular Recognition

("lock and key" bonding)

hydrogen bonding

thymine (T)

guanine (G)

adenine (A)

cytosine (C)

biotin-avidin pair (site-specific binding)


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


Programmed DNA Folding to Make "DNA Origami"

P.W.K. Rothemund, Nature 440, 297 (2006)


Microfluidic Assembly

Application: RFID

Alien Technology

flow direction

Parts, having unique shape, are

delivered via fluid flow to mating

pockets on an assembly substrate.

Nanoscale Phase Separation

IBM "air gap" technology

Introducing nanoscale air pockets into the insulating

material separating wires on a computer chip -- lowers

the capacitance


Large Scale Self-Assembly (Geological)

Giant's Causeway

(Northern Ireland)

Volcanic basalt cooled rapidly to form these (mostly)

hexagonally shaped columns


Explore concepts of self assembly in the classroom

• Balls in a box (best packing)

• Straws or toothpicks in a container (lattice and defects)

• How shape influences packing density and the symmetry

of assembled structures

• Objects floating on water (Cheerios and other shapes)

• Two-dimensional array of magnets; floating magnets -

attractive and repulsive cases

• Crystallization - explore how conditions influence size

and perfection of crystals

Underlying principles: forces (non-directional or

directional), shape, thermal agitation

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