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 Moore’s 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: 125–130, 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 of nanostructures: top-down and bottom-up approaches. J. Mater. Chem. 2004, 14, 459-468

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, STM writing. 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 of molecules 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) A large-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 the structure.

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

Nature’s Examples Of Self Assembled Nanostructures

Nature’s Examples Of Self Assembled Nanostructures

Nature’s 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 chemistry is 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 to defects in the assembled system. Equally demanding is to control surface structure of BBs, including charge 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 approach the bottom-up nanomanufacturing by self assembly – including BBs, forces on BBs, and functional 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 colors stems from Bragg diffraction of light by the regular lattice of silica particles 100-500 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 a chemical that reduces the interfacial free energy between the particle and the solvent and makes short range forces between the particles repulsive. 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 excess negative charge due to adsorption of citrate on the surface of the particles makes the particles 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 has one end that is chemically attracted to the particle 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 lead to the formation of a highly ordered monolayer on the surface. The thermodynamic stability of SAMs increases 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 are used 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 form self-assembled nanoporous materials. Corma et al., Nat. Mater. 2004,3, 394

Charge-Driven Assembly Assembly of negatively charged gold and silica nanoparticles into hollow microspheres directed by positively charged poly (L-lysine) Murthy et al., J. Am. Chem. Soc. 2004,126, 5292

Self-Assembly of Nanoparticles to Superlattices Nanocrystals are able to assemble into close-packed ordered superlattices under the 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 enough to 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)11,449-452

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 by capping reagent Size reduction of a 1D microstructure Y. N. Xia et al, Adv Mater15,353(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 channel An L-shaped chain of Au@SiO2 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 CdTe Nanoparticles 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 divided into 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 from solutions 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 the citrate 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 metal atoms 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 250-300oC 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)