Growth of Nanostructures

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Lecture 8

• Growth of Nanostructures
• Nano/Micro Fabrication

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Molecular Beam Epitaxy
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RHEED
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Quantum Dots Grown Using MBE
Electronic Structure of InAs Pyramidal Quantum
Dots http//www.sst.nrel.gov/research/InAs.html
Three-dimensional AFM image of CdSe QDs deposited
on ZnCdMgSe barriers. The inset shows a histogram
of the QD height Courtesy Prof. TamargoS
group- CCNY .
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MOCVD
H2AsH3
RF Coils
Gas
Al(CH3)3 Ga(CH3)3 H2
Exhaust
Mixing Chamber
Substrate
Ga(CH3)3 AsH3 gt 3CH4GaAs
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Other Epitaxial Techniques

• Liquid Phase Epitaxy
• - Dipping or Tipping
• Chemical Beam Epitaxy
• - Combination of MBE and MOCVD

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Laser Assisted Vapor Deposition
He
H2
SiH4, SF6, H2
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Laser Assisted Catalytic growth
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Chemical Vapor Deposition
Solid Products (thin films and powders)
Precursor
Reactor
Gas Phase products
Energy
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Precursor Considerations
Volatility vapor pressure - simple molecules with
high vapor pressure are rare determined by
molecular weight and molecularity (degree
polymerized) - result of structure and bonding
control - temperature, valving Stability,
Reactivity, and Safety bond strength, bond
dissociation energy - affects process temperature
and film composition (purity) thermal stability
in storage and delivery into the reactor
reactivity of the precursor and byproducts
towards other substances (including biological
objects like us) Single-Source
Precursor providing more than one element into
the film simpler delivery system uniform
elemental distribution at atomic level possible
limited composition range Common
Precursors hydrides MHx -         SiH4, GeH4,
AlH3(NMe3)2, NH3, PH3 ...   halides MXy -
TiCl4, TaCl5, MoF6, WF6, ...   metal-organics
- metal alkyls AlMe3, AliBu3, Ti(CH2tBu)4 ....
metal alkoxides Ti(OiPr)4, Cu(OtBu)4 ....
metal dialkylamides Ti(NMe2)4, Cr(NEt2)4 ....
metal diketonates Cu(acac)2, Pt(hfac)2 ....
metal carbonyls Fe(CO)5, Ni(CO)4 .... others
complexes with alkene, allyl, cyclopentadienyl,
..... ligands many precursors have mixed ligands
http//chiuserv.ac.nctu.edu.tw/htchiu/cvd/essenti
al.html
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Energy sources and Reactor types
Thermal Energy resistive heating - tube furnace
quartz tungsten halogen lamp (very good heat
source) - radiant heating radio-frequency -
inductive heating laser as thermal energy source
Photo Energy UV-visible light laser as photo
energy source
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PECVD
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Atomic Layer Deposition
Show ALD intro presentation
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Carbon nanotube growth
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Carbon Nanotubes
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Nanochemistry

• Preparation of a wide aray of nanoparticles
  metal, semiconductor, polymer etc.
• Multilayer core-shell
• Nanopatterning
• Self organization into periodic and aperiodic
• Insitu fabrication of nanosclae probs and sensors

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Nanochemistry
Amphiphilic molecules for electronic thin
films Amphiphilic derivatives of polythiophene
and other molecules are chemically coded for
self-assembly on water surfaces.
Organic nanostructures Nanowires of amphiphilic
polythiophene.
Gold nanoclusters for self-assembling molecular
electronics Nanophase litography Organization of
gold nanowires by controlling the nanoscale phase
behavior of phospholipids.
http//www.nano.ku.dk/research/nanochemistry/
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Colloidal Synthesis
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Colloidal Quantum Dots
Evident Technologies Troy NY
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Reverse Micelle Synthesis
C. Kitchens, Auburn University
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• Nano and Micro Fabrication Techniques

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Microfabrication Photolithography

• Surface Preparation
• Coating (Spin Casting)
• Pre-Bake (Soft Bake)
• Alignment
• Exposure
• Development
• Post-Bake (Hard Bake)
• Processing Using the Photoresist as a Mask
• Stripping
• Post Processing Cleaning (Ashing)

• Positive and Negative photoresists
• Masks
• Some issues edge bead

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Tools for Photolithography
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Two photon polymerization
JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 21, NO. 3,
MARCH 2003
18 October 2004 / Vol. 12, No. 21 / OPTICS
EXPRESS 5221
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Interference Lithography
Appl. Phys. Lett., Vol. 82, No. 8, 24 February
2003
H. Smiths group at MIT
J. Appl. Phys., Vol. 82, No. 1, 1 July 1997
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Nanosphere Lithography
J. Phys. Chem. B, Vol. 105, No. 24, 2001
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Other Techniques

• Plasmon based
• Phase mask
• Dip Pen
• Nano imprinting
• Soft Lithography
• Photonic alignment

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