• Remember:
1-D Nanorods
– Tomorrow (4/30): Lab #2 report is due
– Monday (5/4): Paper w/ group members name,
email, project topic is due
– Wed (5/6): Alissa + Mine, Quiz 2 covering material
from 4/27 – 5/4
1
http://www.technologyreview.com/news/409496/flexible-nanowire-solar-cells/
Techniques for 1-D Nanostructure Formation
• Spontaneous Growth
Bottom-up
• Template-based Synthesis
• Electrospinning
http://mrsec.umd.edu/Research/Seeds.html#Template
• Lithography
Top-down
2
Spontaneous Growth:
• Anisotropic Growth
– Growth rate of planes
– Growth imperfections
– Accumulation of impurities
http://www.its.caltech.edu/~atomic/snow
crystals/designer2/designer2.htm
http://www.softmachines.org/wordpress/?p=202
3
Oriented attachment
• Solution method, controlled with ligands and
growth conditions
CrystEngComm, 2014,16,
1419-1429
4
Talapin Group, U Chicago https://talapinlab.uchicago.edu/page/nanocrystal-synthesis
Oriented Attachment
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Hydrothermal Synthesis
• Like heat up method for nanocrystlas
• Can be free standing or on substrate
PbTiO3
Chem. Soc. Rev., 2014,43, 2187-2199
6
Evaporation (Dissolution) –
Condensation Growth
Evaporation-Condensation
• Helical Nanostructures & Nanorings (Wang, 2003)
Wang, Z. L. MRS Bull.
2007,
8
VLS or SLS Growth
•
•
VLS: Vapor-Liquid-Solid
SLS: Solution-Liquid-Solid
•
Impurity or catalyst introduced
•
Different from Evaporation-Condensation
1. No screw dislocations in growth direction
2. Impurities always required
3. Liquid-like globule always found in tip of nanowires
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VLS Growth Method
1. Growth species evaporated
2. Growth species diffused and dissolved into droplet
3. Droplet (with growth species) deposits on growth
surface
4. Growth species diffused and precipitated onto
growth surface
10
N & N, Fig. 4.11
VLS Growth: Control of Nanowire Size
• Dependent on size of liquid catalyst droplets
– Small droplets:
• thin layer of catalyst on substrate
• anneal at high temperature
Gudiksen, M.S., et al., J. Phys. Chem. B105, 4062 (2001).
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Classic: Si Nanowire/Gold Catalyst
• Filler Group, Georgia Tech
http://fillergroup.gatech.edu/research/
12
Si Nanowire Growth
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Techniques for 1-D Nanostructure Formation
• Spontaneous Growth
Bottom-up
• Template-based Synthesis
• Electrospinning
http://mrsec.umd.edu/Research/Seeds.html#Template
14
Template-Based Synthesis
•
•
Used for polymers, metals, semiconductors, oxides
Membranes as templates
Methods of filling
1. Electroplating
2. Colloid, melt, or vapor
Aluminum oxide template
Sensors 2005, 5, 245-249
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Template-based Synthesis
Requirements for Membranes
1. Chemically and thermally inert during synthesis
2. Depositing materials must “wet” internal pores
3. Growth:
• Nanorods/Nanowires:
•
•
Must start from one end of pore end at opposite
Nanotubules:
•
Must start from pore wall and move in
4. Easy release of nanostructures after synthesis
16
Template-Based Synthesis
• Ran Research Group, Penn State
http://research.chem.psu.edu/axsgroup/Ran/research/templatesynthesis.html
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Electrochemical Deposition
Method:
1. Charged growth species moves through solution in one
direction when electric field applied
2. Charged growth species reduced at deposition surface
(also an electrode)
http://tutors4you.com/electrochemicalcell.jpg
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Electrochemical Deposition
N & N, Fig. 4.21
• Products:
– Metals: Ag, Ni, Co, Cu, Au nanowires: <10 nm- 200 nm dia
– Semiconductors: CdSe, CdTe
– Polymers: polyporrole
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Template Filling
•
•
Liquid precursor poured into template pores
Requirements:
1. “Wetability” of pore walls
2. Template materials must be inert
3. Control of shrinkage during solidification
Can use centrifugation
•
Vapor precursor can be used
Diffuse gas through porous material, then heat
20
Positive Templates
Polypyrrole on DNA
• Green rod is DNA or CNT
Nanoscale, 2014, 6, 4027-4037
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Step/Groove Templates
GaN Nanowires
Weizmann Institute
http://wis-wander.weizmann.ac.il/nanowires-getinto-the-groove#.VD3YEvldWSo
• Guide horizontal growth of nanostructures
• Used w/ Evaporation-Condensation or VLS
22
Techniques for 1-D Nanostructure Formation
• Spontaneous Growth
Bottom-up
• Template-based Synthesis
• Electrospinning
http://mrsec.umd.edu/Research/Seeds.html#Template
23
Electrospinning
• Electrical forces at surface overcome surface tension 
Electrically charge jet is ejected
• Fiber can be directed or accelerated by electrical forces
• Product: 30+ types of polymer, 40 -500 nm diameter
– Can be collected in sheets or other forms
– Morphology depends on:
• Solution concentration
• Applied electric field strength
• Feeding rate of precursor solution
N & N, Fig. 4.33
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Electrospinning
http://www.centropede.com/UKSB2006/ePoster/images/background/ElectrospinFigure.jpg
http://nano.mtu.edu/documents/Electrospinning.swf
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Electrospinning
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• http://www.jove.com/video/2494/electrospinnin
g-fundamentals-optimizing-solution-apparatus
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Lab #3 – Surface Modification
• Form a SAM on a copper substrate
• Observe change in surface properties w/
different tail groups
– Like dissolves like
– Hydrophilic : charged, H-bonding, large dipole
– Hydrophobic : neutral, no H-bonding, small dipole
• What will the difference be between water drop
on hydrophilic vs hydrophobic surface?
28
Lab #3 – Surface Modification
• Thiols (-SH) bind to metal surface like copper
• Copper is easily oxidized to cuprous oxide
(Cu2O)
• Use Ferric chloride to etch the oxide layer
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