Block 1 - Nanotechnology Fundamentals

Nanotechnology Size Range

0-100 nm

0D Nanostructure

All 3 dimensions nanoscale

ex. nanoparticle

1D Nanostructure

Two dimensions nanoscale, one extruded dimension

ex. nanowires, nanotubes

2D Nanostructure

One dimension nanoscale

ex. thin film

Nanowire vs. Nanorod

Nanowires generally have a higher aspect ratio than nanorods

What happens to surface area to volume ratio as particle size decreases?

SA:V increases

Why does higher SA:V increase reactivity?

A greater fraction of atoms are exposed at the higher energy surface

Why can ~5nm gold be catalytic while bulk gold is relatively inert?

Small AuNPs have much greater SA:V ratio, resulting in more accessible, high energy surface atoms

Quantum Confinement

Nanoscale confinement changes electron behavior and the material’s electronic/optical properties

Effect of decreasing semiconductor NP size on band gap

Size decreases, quantum confinement increases, band gap increases

Effect on decreasing nanoparticle size on emmited light?

higher energy, shorter wavelength emission

Quantum dot size and color

Smaller = bluer

Larger = redder

Why can crystal structure change at the nanoscale?

The balance between surface energy and bulk energy changes as particle size decreases

Superparamagnetism

NPs become magnetized in an external magnetic field, but do not retain magnetization after the field is removed

Superparamagnetic NP with external magnetic field ON

Magnetic moment aligns with applied field

Superparamagnetic NP after external field is removed

Magnetic moment can freely reorient, no retained magnetization

Single-domain magnetic NP

A sufficiently small magnetic NP that behaves as one magnetic domain

Bottom-up Fabrication

Builds nanostructures from atoms, molecules, or smaller building blocks

Ex. PVD, CVD, Sol-Gel, wet chemical synthesis, self-assembly

Top-down Fabrication

Starts with larger/bulk material and patters or reduces it down to nanoscale dimension

Ex. Nanolithography, nanofabrication

Three major reasons nanoscale materials differ from bulk materials?

• High SA:V ratio

• Quantum effects

• Altered surface/bulk energetics