Fabrication of Nanostructures

Two Fundamental Approaches

Top Down Removing material from a larger structure of make

smaller ones. Etching This is the one we will be talking about.

Bottom Up Adding material to already small structures to

create larger ones. Molecular Chemistry

Top down Techniques for Making Nanostructures

E-Beam Lithography.

Scanning Tunneling Microscopy.

Self Assembly.

E-beam Lithography

Minimum features 4nm.

Typical features 20-50nm. As a result of back scattering of electrons.

Uses and high energy electron beam to break or add bonds to the photoresist.

E-beam Lithography Photo resists

The high energy electron beam breaks the bonds of

positive photoresist.

The electron beam creates bonds in negative

photoresist.

The most common e-beam photoresist is

polymethylmethacrylate (PMMA).

E-beam Examples

Single Electron Transistor

Currents consist of individual electrons

Fabrication with STM

Minimum features: atomic manipulation

Maximum features: couple nanometers.

Operation of STM

Electrons in the STM tip are able to tunnel through

the small gap between the tip and the sample.

The tip is scanned across the sample.

The STM controller maintains a constant current and

adjust the vertical position to do so.

The vertical position is measured, and is a direct

representation of the surface of the material.

STM Example

Fabrication of Quantum-Dots using STM

Self Assembly

A very thin layer of material is deposited onto a

substrate of other material.

Stresses occur as a result of the mismatch of crystal

lattices between two different materials.

The thin material tends to clump up forming quantum

dots.

Example of Self Assembled Quantum-Dots