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Top-Down Nanomanufacturing
David T. Shaw State University of New York at Buffalo Contents
Introduction Learning bottom-up synthesis from nature
Self assembly Hierarchical assembly Building blocks Introduction
How Do You Naomanufacture?
Sculpt from bulk Lithography Etching Ion beam milling Ball milling
Assemble Nanoscale building blocks (BBs) nanocrystal Synthesis
Vapour Deposition Sol-gel Pyrolysis Self assembly Top-down
Fabrication for Moores Law of Miniaturization Integration of
Top-down and Bottom-up nanomanufacturing
Integrated multifunctional nano-assembly onto bio-MEM devices and
lead to scalable and cost effective nanomanufacturing X. Zhang et
al, Journal of Nanoparticle Research 6: 125130, 2004. Future
Integrated Nano-Systems
Bottom-up (sensors, memories, etc.) will be integrated with
top-down nanocomponents C. Sun, X. Zhang UC Berkeley Future
Development of Information Technology Dip Pen Nanolithography
Strategies for Nanostructure Fabrication
Two complimentary strategies can be used in the fabrication
ofnanostructures: top-down and bottom-up approaches. J. Mater.
Chem. 2004, 14, Strategies for Making Things
M. Boncheva and G. M. Whitesides, MRS Bull (30) Oct 2005 Strategies
for Making Things
The general scheme of making things, at size scales ranging from
nanometers to kilometers, includes fabri-cation by hands and
robots, photolithography, STMwriting. Things, however, can also be
made in a different way: that is, by self-assembly. Self-assembly
was originally defined in molecular systems as a process in which
molecules or parts ofmolecules spontaneously form ordered
aggregates,usually by non-covalent interactions. Self-assembled
Things Of Different Scales
M. Boncheva and G. M. Whitesides, MRS Bull (30) Oct 2005 (a) A
hollow TiO2 colloidal crystal; (b) An asymmetric, 3D silicon micro-
mirror formed from a planar precursor by surface tension-powered
selffolding; (c) Alarge-area array of silicon segments
self-assembled on a flexible, nonplanar support; (d )An elastomeric
globe self-assembled from a flat, 2D projection of the Earth; (e) A
simple 3D electrical circuit surrounding a spherical cavity; (f) A
self-assembled simple-cubic lattice of brass beads. The inset shows
a detail of thestructure. Learning Bottom-up Synthesis From Nature
Examples Of Self Assembled Bionanomaterials
Natural biomaterials contain layered, tough biocomposites that have
yet to be duplicated in the lab. Sarikaya et al, Nature Materials
(03) Calcium Carbonate Platelets Organic Films Zaremba, Chem Mater
(96) Examples Of Self Assembled Bionanomaterials
4 nm Vukusic et al, Nature, 01 Natures Examples Of Self Assembled
Nanostructures Natures Examples Of Self Assembled Nanostructures
Natures Examples Of Self Assembled Nanostructures Self-Assembled
Biological Machines
55 years ago the first semiconductor translistor was the size of a
match head, which alredy was much smaller that the vacume tube.
Today we can pack millions of transistors in that same space, with
180nm individual size. What will the future bring? A full logic
gate smaller that a nanometer and opperating at the speed of light,
using a nanotech wonder, the quantum dot. Bottom Up
Nanomanufacturing Self Assembly Bottom Up Nanomanufacturing Self
Assembly
Spontaneous organization of building blocks with dimensions ranging
from nanometers to microns. Two prominent components: Building
blocks -- size, shape, surface structure Interactive forces between
building blocks Bottom Up Nanomanufacturing Self Assembly
A challenge for perfecting structures made by self-assembly
chemistryis to find ways of synthesizing BBs not only with the
right composition but also having the same size and shape. Ideally,
BBs should be monodisperse. Most BBs, however, have some degree of
polydispersity. Any deviation from monodispersity in size and shape
would lead todefects in the assembled system. Equally demanding is
to control surface structure of BBs, includingcharge and
functionality. Surface properties will control the inter actions
between BBs. Benefits of Self Assembly Building Blocks (BBs) and
Self Assembly
Many factors must be considered when we approachthe bottom-up
nanomanufacturing by self assembly including BBs, forces on BBs,
andfunctional nanotechnological applications. Forces on BBs
Strategies for Nanostructure Fabrication
Bottom-up approach for nanostructures using nano- particles as
building blocks Example: Opals: The fascinating interference
colorsstems from Bragg diffraction of light by the regular lattice
of silica particles nm in diameter. Attractive Features of
Self-Assembly
Self-assembly proceeds spontaneously The self-assembled structure
is close to thermodynamic equilibrium Self-assembly tends to have
less defects,with self-healing capability Why Should We Deal With
Self Assembly?
Like atoms or molecules, nanocrystals can be treated as artificial
atoms and used as the building blocks of condensed matter.
Assembling nanocrystals into solids opens up the possibilities of
fabricating new solid-state materials and devices with novel or
enhanced physical and chemical properties, as interactions between
proximal nano crystals give rise to new collective phenomena.
Stabilization Of Colloids
Fundamental problem: The thermodynamically stable state of metals,
semiconductors, and polymers is bulk material, not colloidal
particles.Stable colloidal dispersions require an interfacial
stabilizer, which is achemical that reduces the interfacial free
energy between the particle and the solvent and makes short range
forces between the particlesrepulsive. R. P. Andres Science (1996)
Gold Colloidal Nanoparticles
In the case of our gold nanoparticles, the stabilizer is citrate
ion, whose negative charge is opposite to that of positive gold
ions on the particle surface.The excessnegative charge due to
adsorption of citrateon the surface of the particles makes
theparticles repel one another.Our polystyrene latex also is charge
stabilized. Dissociation of a fraction of the sodium ions of the
sodium 4-styrenesulfonate units of the poly-mer leaves the
particles with a negative charge. The stabilizer often is a
surfactant, which is a chemical compound such as sodium dodecyl
sulfate (SDS) whose structure hasone end that is chemically
attracted to theparticle and the other end chemically attract-ed to
the solvent.However, there are no sur- factants in our gold
nanoparticle and polystyrene latex preparations. R. P. Andres,
Science (1996) Self-Assembled Monolayers (SAMs)
Ordered molecular aggregates that form a monolayer of material on a
surface. Formation of SAMs: Alkyl thiols RSH react with Au(0)
surface, forming RS-Au(I) adducts: If R is a long chain, van der
Waals interactions between the RS units leadto the formation of a
highly orderedmonolayer on the surface. The thermodynamic stability
of SAMsincreases with the length of the alkyl chain. Substrate and
Ligand Pairs for Forming SAMs Alkanethiolate SAMs on Gold Surfaces
SAMs Based on Polymer BBs
A film formed by the triblock molecules, revealing regularly sized
and shaped aggregates that self assemble into monolayer
nanostructures. Stupp et al, Science( 97) Solution-based Molecular
Manipulation for BBs Synthesis
Mesoporous molecular nanostructures are used as templates for
nanocrystal synthesis. Phase sequence of surfactant-water binary
system Self-Assembly of Surfactant (Soap) Molecules Self-Organized
Nanostructures
Regularly sized and shaped nanostructures can be tiled into
superlattices of varying geometries and symmetries. Stupp et al,
Science(97) Hierarchical Assembly What is Hierarchical
Assembly?
A characteristic feature of self-assembly is hierarchy. Primary
building blocks associate into more complex secondary structures
that are integrated into the next size level in the hierarchy. This
organizational scheme continues until the highest level in the
hierarchy is reached. Driving Forces on Various Scales
Molecular Scale: H-bonding, hydrophoic interaction, electrostatic
forces, lock-key type interactions, and van der Waals forces Nano-
and Mesoscale: capillary forces, external fields (gravitational,
centrifugal, magnetic, electric, optical, ), surface tension,
electrostatic forces, shear forces, and molecule-based interactions
Driving Forces: Attractive vs. Repulsive Template-Assisted
Assembly
Aqueous dispersion of colloidal polystyrene or silica particles are
assembled on a solid surface patterned with relief structures.
These patterned structures areused as templates for assembling of a
variety of nano-particles Yin et al., J. Am. Chem. Soc. 2001, 123,
8718 Surfactant-Assisted Assembly
Assembly of CeO2 nanoparticles (5 nm) into hierarchically
structured nanoporous materials using block copolymers. The force
between particles (Van der Waals force) is weak, surfactants are
used to provide the necessary bonding to formself-assembled
nanoporous materials. Corma et al., Nat. Mater. 2004,3, 394
Charge-Driven Assembly
Assembly of negatively charged gold and silica nanoparticles into
hollowmicrospheres directed by positivelycharged poly (L-lysine)
Murthy et al., J. Am. Chem. Soc. 2004,126, 5292 Self-Assembly of
Nanoparticles to Superlattices
Nanocrystals are able toassemble into close-packed ordered
superlattices underthe following conditions: narrow size
distribution (< 5%) surfactant that is strong enough to separate
the individual nanocrystals slow drying rate so that the
nanocrystals can move to suitable positions Schematic illustration
of self-assembled, passivated nanocrystal superlattices of
spherical (a) and faceted (b) particles Wang, Adv.
Mater.1998,10,13-30 Self-Assembled Nanocrystal Superlattices
Solid, periodic arrays composed of nanocrystals and surfactants
have been synthesized into one-, two and three-D superlattices.
Very narrow size distribution of weakly interacting nanocrystals:
The narrower the particle size distribution, the easier it is to
obtain long-range superlattice ordering. Delicate interplay between
interparticle attractions strong enoughto drive superlattice
crystallization, yet weak enough to allow annealing. The
macroscopic properties of the nanocrystal super-lattices are
determined not only by the properties of each individual particle,
but also the interaction/coup-ling between the nanocrystals
interconnected and isolated by a monolayer of thin organic
molecules. Wang, Adv. Mater.1998,10,13-30 Lock-and-key
Assembly
Schematic representation showing possible approaches to the
directed self-assembly of metallic (1. and 2.), and bimetallic (3.)
macroscopic materials using antibody/anti-gen cross-linking of
inorganic nanoparticles. Shenton et al, Adv Mater(1999)11,
Synthesis of One-Dimensional Nanostructures
Six strategies for achieving one-D growth of wires, rods, belts and
tubes Self-assembly of 0D nano-structures Dictation by the
anisotropic crystallographic structure of a solid Confinement by a
liquid droplet Direction through the use of a template Kinetic
control provided bycapping reagent Size reduction of a 1D
microstructure Y. N. Xia et al, AdvMater15,353(03) Self Assembly of
Nanoparticles into 1D Nanostructures
A, B) Structures that were assembled from 150 nm poly styrene
beads, and 0 nm Au colloids, respectively, by templating against
120nm-wide channelAn L-shaped chain of spheres assembled against
the template.D) Template-based self-assembled spiral chain of
polystyrene beads Growth of TiO Self-Assembled Nanocrystals
(a)-(d): Progression of chain development: a) single primary
crystallite;(b) four primary crystallites forming a single crystal
via oriented attachment; (c) five primary crystallites forming a
single crystal via oriented attachment;(d) single crystals of
anatase with magnified attachment interfaces. L. Penn et al,
Geochim. Cosmochim. Acta, 63,1549 (99) Spontaneous Organization of
Single CdTeNanoparticles into Luminescent Nanowires
Tang et al., Science,297, 237 (02) Self-Assembled In2O3 Nanowire
Networks
The nanostructures were synthesized by a vapor transport and
condensation method SEM and TEM images of the In2O3 nanowire and
nanocrystal chains. Big crystals are part of the network. a) SEM
image showing the nanocrystal chains. b) SEM image showing the
network junctions. c) SEM image showing the nanowire and
nanocrystal chains. d) TEM bright field image of part of a
nanocrystal chain. Building Blocks (BBs) Building blocks of
nanostructured materials
Synthesis of nanoscale materials can be dividedinto wet and dry
methods. By dry methods the material is made in solid form from
vapor phase precursors and used directly in the form it was made.
By wet methods materials are made by chemical reactions in solution
or on a solid support, and separation of the desired material from
unwanted solid or liquid materials is necessary The Building Blocks
(BBs)
Metal nanoparticles and nanowires Nanotubes Semiconductor
nanospheres, rods, wires, etc. Carbon nanotubes Organic BBs - DNA,
proteins, etc. Cells, viruses, etc. Nanoparticle Synthesis
Colloidal metal and colloidal semiconductor particles are made
fromsolutions of precursor chemical compounds by chemical reactions
that produce the insoluble metal or semiconductor particles. For
gold nanoparticles the reaction is reduction of gold ions by
citrate ions in aqueous solution. Au3++ citrate--->Au0+oxidized
citrate Synthesis of Nanoparticles in Laboratory Semiconductor
nanoparticles
Semiconductor particles such as cadmium selenide (CdSe) can be
synthesized in either aqueous or organic solutions.One example of
an aqueous method is As prepared, the CdSe particles are stabilized
by citrate ion, but thecitrate can be replaced a polymer such as
poly(cysteine acrylamide)that has both thiol groups that bind to
the Cd surface of the particle and multiple negative charges.The
necessary chemical properties of the stabilizer are that it has
functional groups to bind to the metalatoms on the particle surface
and another structural component that is well-solvated.
Semiconductor Nanoparticles: High Temperature Synthesis
Injection of precursor compounds into a surfactant solution at oC
rapidly nucleates nanocrystals.Growth at a rate slower than the
rate of nucleation narrows the particle size distribution.Standard
deviations of diameters of 5% or less have been achieved. The
advantage of high temperature is that the semiconductor in the
particle is still be fluid, allowing atomic rearrangements to reach
the stable crystal lattice. Biosynthesis of Monodisperse Rod-like
Polymers as BBs
Bacterial biosyntheses, in which artificial genes encoding of
polymers are expressed in bacterial vectors, offer the opportunity
to produce BBs with well defined dimensions. Applications of these
monodispersed rod-like polymeric crystals include two-dimensional
diffraction gratings, membranes with controlled thickness and
permeability. Yu et al, Nature (97) Nanocrystal Bacterial Cells as
BBs
Crystalline bacterial cell surface layers (S-layers) can be
isolated and harvested from a variety organisms. Sleytr et al ( 01)
Bacterial S Layers as Porous Membrane Supports
Isolated S-layer subunits from a variety of organisms are capable
of recrystallizing into membrans for the support of bilayers.
Sleytr et al (01)