fabrication of nanostructures
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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
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