Introduction to Chemistry of Nanomaterials

UEET103/UEET235Lecture I

Prof. Petr VanýsekDepartment of Chemistry and Biochemistry

4 September 2012

Why Study Chemistry?

• Chemistry is the study of the properties of materials and the changes that materials undergo.

• Chemistry is central to our understanding of other sciences.

• It is substantial part of nanoscience and nanotechnology

The Study of Chemistry

The Molecular Perspective of Chemistry• Matter is the physical material of the universe.• Matter is made up of relatively few elements.• On the microscopic level, matter consists of

atoms and molecules.• Atoms combine to form molecules.• As we see, molecules may consist of the same

type of atoms or different types of atoms.

Molecular Perspective of Chemistry(Space filling models)

How to understand structures

Space fillingWire frameBall and stick

Classification of Matter

Three States of Matter• Matter can be a gas, a liquid, or a solid.• These are the three states of matter.• Gases take the shape and volume of their

container.• Gases can be compressed to form liquids.• Liquids take the shape of their container, but

they do have their own volume.• Solids are rigid and have a definite shape and

volume.

Classification of Matter

Properties of MatterProperties of Matter

Physical vs. Chemical Properties• Physical properties can be measure without changing the

basic identity of the substance (e.g., color, density, odor, melting point)

• Chemical properties describe how substances react or change to form different substances (e.g., hydrogen burns in oxygen, iron (steel) corrodes (oxidizes) in air)

• Intensive physical properties do not depend on how much of the substance is present.– Examples: density, temperature, and melting point.

• Extensive physical properties depend on the amount of substance present.– Examples: mass, volume, pressure.

States of Matter

Solid Keeps shape Keeps volume

Salt, gold, copper

Liquid Takes shape of container

Keeps volume

Water, alcohol, oil

Gas Takes shape of container

Takes volume of container

Air, argon, helium, methane

Plasma – like a gas of charged particles.

Takes shape of container

Takes volume of container

Stars, nebula, lightning, plasma reactors

Matter• Solution: A uniform mixture of two substances

such that molecules are separate from each other and move around randomly. Usually these are liquids. Solutions are usually transparent.

• Colloids: A mixture of much larger particles ranging from 20 nm to 100 μm. Milk and paint are examples of colloids.

• Grains: Some materials are made up of many small crystals called grains. A grain is an individual crystal of such a solid. Different grains may have the crystal lattice oriented in different directions.

Elements, Atoms and Molecules• Atoms: All matter is made up of tiny particles called atoms.

• Molecules: Sometimes two or more atoms are found bound together to form molecules.

• The atoms can be categorized into about 115 different types based on the charge of the nucleus.

• Elements are made up of only one type of atom.

• The element carbon takes the form of graphite, diamond and buckminsterfullerene as well as others.

• It is only possible to change one type of atom into another through nuclear processes such as take place in a nuclear power plant, the sun, atomic bombs or particle accelerators.

• The elements do not change in ordinary chemical reactions.

Units of measurement

Basic unit “one meter”prefixes used to describe smaller units:

millimeter (10-3 m)micrometer (10-6 m)nanometer (10-9 m) (from Greek

“nanos”, a dwarf)picometer (10-12 m)“size” of an atom (10-10 m)

Squared and cubed distance

Area = distance squared

Volume = distance cubed

the liter is a basic volume unit in chemistry, is is one decimeter cubed, of 10x10x10=1000 cm cubed. It is somewhat larger than one quart

Why dimensions matter?Nanomaterials – particles of nanometer size

Nano-scale materials often have very different properties from bulk materials

e.g. color and reactivity

•30nm particle has 5% of atoms on the surface

•10nm particle has 20% of atoms on the surface

•3nm iron particle has 50% of atoms on the surface

What is nanotechnology?

Ability to understand, create, and use structures, devices and systems that have fundamentally new properties and functions because of their nanoscale structure

Ability to image, measure, model, and manipulate matter on the nanoscale to exploit those properties and functions

Ability to integrate those properties and functions into systems spanning from nano- to macro-scopic scales

Research and technology development aimed to understand and control matter at dimensions of approximately 1 - 100 nanometer – the nanoscale

Moore’s Law - one motivation for nanotechnology

Size-Dependent Properties

Even on macro scale properties of material can depend on the size of the object treated.

For example,(1) Dissolving powder vs. dissolving large chunks

(2) Starting fire with a timber log vs. using kindling

Size-Dependent Properties

Powder has larger surface area than a chunk of the same material exposed to the liquid, which does the dissolution

Splints made from a log have much larger surface area than the log from which they came – hence large surface exposure to air (oxygen) needed for combustion.

Size-Dependent PropertiesAt the nanometer scale, properties become dramatically size-dependent.For example,(1) Thermal properties – melting temperature(2) Mechanical properties – adhesion, capillary forces(3) Optical properties – absorption and scattering of light(4) Electrical properties – tunneling current(5) Magnetic properties – superparamagnetic effectNew properties enable new applications

An electronic device with a nanotube

1. What could be the purpose of this device?2. What methodology has to be mastered?3. What (if anything) is wrong with this picture?

"Lately the prefix trend has been shrinking. During the 1980s, 'mini-' gave way to 'micro-,' which has yielded to 'nano-.' In the new millennium, companies such as Nanometrics, Nanogen and NanoPierce Technologies have all embraced the prefix, despite complaints their products were hardly nano-scale (a billionth of a meter or smaller). Even Eddie Bauer sells stain-resistant nano-pants. (They're available in 'extra-large' for the retailer's not-so-nano customers.)“

(Alex Boese, "Electrocybertronics." Smithsonian, March 2008)

e.g., 3 nm CdSe nanocrystal melts at 700 K compared to bulk CdSe at 1678 K

Melting Temperature

Nanocrystal size decreases…

surface energy increases…

…melting point decreases

The melting point of gold particles decreases dramatically as the particle size gets below 5 nm

Source: Nanoscale Materials in Chemistry, Wiley, 2001

Electrical Properties: Tunneling currentAt the nanometer scale, electrical insulators begin to block current flow.

The current increases exponentially as the thickness of the insulator is decreased.

Certain phenomena occur only when characteristic dimensions reach the nanometer scale

e.g., quantum tunneling effects:When you put a voltage across an insulator, then the current is given by U=IR. When the insulator becomes small (less than 100 nm) the current is much higher by orders of magnitude than predicted due to tunneling

Historical Use of Nanoparticles: Stained Glass

The Lycugus Cup. This cup is made of dichroic glass that has colloidal gold and silver nano-scale particles in the glass. When held up to the light, the ordinarily green cup (from the silver particles) shows up as red due to the gold nanoparticles in the glass. More information, and the original images are available from The British Museum. 

What is nanotechnology?

Ability to understand, create, and use structures, devices and systems that have fundamentally new properties and functions because of their nanoscale structure

Ability to image, measure, model, and manipulate matter on the nanoscale to exploit those properties and functions

Ability to integrate those properties and functions into systems spanning from nano- to macro-scopic scales

Research and technology development aimed to understand and control matter at dimensions of approximately 1 - 100 nanometer – the nanoscale

Why is nanotechnology unique?Surface effects are very important: surface to volume ratio is extremely large

Think of water flowing through your garden hose -

the fluid right near the wall acts very differently than the rest of the fluid. This has a negligible effect on the water coming out of the hose end.

When the garden hose shrinks to nanoscale dimensions -

all of the fluid is “near the wall”, and the laws that predict how much fluid comes out as a function of pressure no longer apply.

Why is nanotechnology unique?For materials with more than one atom, not only can the arrangement of atoms at the surface be different, but the composition can be different.

Say we have the compound AB-

Overall, we have equal amounts of A and B, but it is possible that at the surface we have more A than B.

In conventional materials, this surface enhancement of A does not affect the bulk properties, since the amount of material at the surface is miniscule.

In nanomaterials, this surface enhancement not only affects the “surface” properties, but it also affects the “bulk” properties since there is much more B in the bulk, since the amount of material at the surface is significant.

Unique properties of the material when the size goes down

•Quantum size effects result in unique mechanical, electronic, photonic, and magnetic properties of nanoscale materials

•Chemical reactivity of nanoscale materials greatly different from more macroscopic form, e.g., gold

•Vastly increased surface area per unit mass, e.g., upwards of 1000 m2 per gram

•New chemical forms of common chemical elements, e.g., fullerenes, nanotubes of carbon, titanium oxide, zinc oxide, other layered compounds

Atoms and molecules are generally less than a nm and we study them in chemistry. Condensed matter physics deals with solids with infinite array of bound atoms. Nanoscience deals with thein-between meso-world

• Quantum chemistry does not apply (although fundamental laws hold) and the systems are not large enough for classical laws of physics

• Size-dependent properties

• Surface to volume ratio- A 3 nm iron particle has 50% atoms on the surface- A 10 nm particle 20% on the surface- A 30 nm particle only 5% on the surface

Source: Nanoscale Materials in Chemistry, Ed. K.J. Klabunde, Wiley, 2001

SURFACE vs. VOLUME

Many existing technologies already depend on nanoscale materialsand processes- photography, catalysts are “old” examples- developed empirically decades ago

• In existing technologies using nanomaterials/processes, role of nanoscale phenomena not understood until recently; serendipitous discoveries

- with understanding comes opportunities for improvement

• Ability to design more complex systems in the future is ahead- designer material that is hard and strong but low weight- self-healing materials

• Nanocrystalline materials• Nanoparticles• Nanocapsules• Nanoporous materials• Nanofibers• Nanowires• Fullerenes• Nanotubes• Nanosprings• Nanobelts• Dendrimers

• Molecular electronics• Quantum dots• NEMS, Nanofluidics• Nanophotonics, Nano-optics• Nanomagnetics• Nanofabrication• Nanolithography• Nanomanufacturing• Nanomedicine• Nano-bio

Various Nanomaterials and Nanotechnologies

NANOSCALE PROPERTIES• Size-dependent properties

color, specific heat, melting point, conductivity…..

• I-U of a single nanoparticle (Electrochemistry)

• Adsorption- principles- some examples

• Nanomaterial reinforcement in composites- multifunctionality- self-healing

• Cluster- A collection of units (atoms or reactive molecules) of up to

about 50 units• Colloids

- A stable liquid phase containing particles in the 1-1000 nm range. A colloid particle is one such 1-1000 nm particle.

• Nanoparticle- A solid particle in the 1-100 nm range that could be

noncrystalline, an aggregate of crystallites or a single crystallite

• Nanocrystal- A solid particle that is a single crystal in the nanometer range

SOME CONCEPTS AND DEFINITONS

• For semiconductors such as ZnO, CdS, and Si, the bandgap changes with size of the particle

- Bandgap is the energy needed to promote an electron from the valence band to the conduction band

- When the bandgaps lie in the visible spectrum, a change in bandgap with size means a change in color

• For magnetic materials such as Fe, Co, Ni, Fe3O4, etc., magnetic properties are size dependent

- The ‘coercive force’ (or magnetic memory) needed to reverse an internal magnetic field within the particle is size dependent

- The strength of a particle’s internal magnetic field can be size dependent

• In a classical sense, color is caused by the partial absorption of light by electrons in matter, resulting in the visibility of the complementary part of the light

• On most smooth metal surfaces, light is totally reflected by the high density of electrons, hence no color, just a mirror-like appearance.

• Small particles absorb, leading to some color. This is a size dependent property.Example: Gold, which readily forms nanoparticles but is not

easily oxidized, exhibits different colors depending on particle size.

- Gold colloids have been used to color glasses since early days of glass making. Ruby-glass contains finely dispersed gold-colloids.

- Silver and copper also give attractive colors

COLOR

Surface Adsorption

• Adsorption is like absorption except the adsorbed material is held near the surface rather than inside

• In bulk solids, all molecules are surrounded by and bound to neighboring atoms and the forces are in balance. Surface atoms are bound only on one side, leaving unbalanced atomic and molecular forces on the surface. These forces attract gases and molecules Van der Waals force, physical adsorption or physisorption

• At high temperatures, unbalanced surface forces may be satisfied by electron sharing or valence bonding with gas atoms chemical adsorption or

chemisorption- Basis for heterogeneous catalysis (key to production of fertilizers,

pharmaceuticals, synthetic fibers, solvents, surfactants, gasoline, other fuels, automobile catalytic converters…)

- High specific surface area (area per unit mass)

• Physisorption of gases by solids increases with decreasing T and with increasing P• Weak interaction forces; low heats of adsorption

< 80 kJ/mol; physisorption does not affect the structure or texture of the absorbent

• Desorption takes place as conditions are reversed• Mostly, testing is done at LN2 temperature

(77.5 K at 1 atm.). Plot of gas adsorbed as volume Va at 0° C and 1 atm (STP) vs. P/Po (Po is vapor pressure) is called adsorption isotherm.

Nanomaterial reinforcement in composites

• Processing them into various matrices follow earlier compositedevelopments such as

- Polymer compounding- Producing filled polymers- Assembly of laminate composites- Polymerizing rigid rod polymers

• Purpose- Replace existing materials where properties can be superior- Applications where traditionally composites were not a

candidate

• Nanotechnology provides new opportunities for radical changesin composite functionality

• Major benefit is to reach percolation threshold at low volumes(< 1%) when mixing nanoparticles in a host matrix

• Functionalities can be added when we control the orientation of the nanoscale reinforcement.

1. What novel quantum properties will be enabled by nanostructures (at room temperature)?

2. How different from bulk behavior?

3. What are the surface reconstructions and rearrangements of atoms in nanocrystals?

4. Can carbon nanotubes of specified length and helicity be synthesized as pure species? Heterojunctions in 1-D?

5. What new insights can we gain about polymer, biological…systems from the capability to examine single-molecule properties?

6. How can one use parallel self-assembly techniques to control relative arrangements of nanoscale components according to predesigned sequence?

7. Are there processes leading to economic preparation of nanostructures with control of size, shape, etc., for applications?

Some fundamental science issues

Forms of materialDIAMOND - GRAPHITE

Forms of materialCARBON - GRAPHITE

Fullerenes

Fullerenes

The Nobel Prize in Physics 2010

Awarded jointly to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene" University of Manchester, UK

The Nobel Prize in Physics 2010Graphene

Graphene is an atomic-scale honeycomb lattice made of carbon atoms. [Photo: Alexander Alus www.nobelprize.org]

Carbon nanotube – extremely strong

Theoretical tensile strength 300 GpaHighest reported 63 Gpa

Kevlar 2.7 GPa steel piano wire 2.4 GPaspider silk 1 GPadiamond - up to 60 GPa

Single walled nanotube

How is the strength measured?

Theoretical calculation

Experiment

Atomic force microscopy

Min-Feng Yu, Oleg Lourie, Mark J. Dyer, Katerina Moloni,Thomas F. Kelly, Rodney S. RuoffScience Vol 287, 28 Jan. 2000)

Inserting nanotubes into a circuit

Single electron transistor

NanofabricationTop-down: Chisel away material to make nanoscale objects

Bottom-up: Assemble nanoscale objects out of even smaller units (e.g., atoms and molecules)

Ultimate Goal: Dial in the properties that you want by designing and building at the scale of nature (i.e., the nanoscale)

Top-Down: Photolitography

Chisel away material to make nanoscale objects

Bottom-Up: Molecular Self-Assembly

Assemble nanoscale objects out of even smaller units (e.g., atoms and molecules)

Carbon Nanotube Synthesis

Acceptance of nanotechnology