1-D Nanorods• Remember:

– 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/

• Spontaneous Growth

• Template-based Synthesis

• Electrospinning

• Lithography

Techniques for 1-D Nanostructure Formation

Bottom-up

Top-down

http://mrsec.umd.edu/Research/Seeds.html#Template

2

Spontaneous Growth:

• Anisotropic Growth– Growth rate of planes– Growth imperfections– Accumulation of impurities

http://www.softmachines.org/wordpress/?p=202

http://www.its.caltech.edu/~atomic/snowcrystals/designer2/designer2.htm 3

Oriented attachment• Solution method, controlled with ligands

and growth conditions

4

CrystEngComm, 2014,16, 1419-1429

Talapin Group, U Chicago https://talapinlab.uchicago.edu/page/nanocrystal-synthesis

Oriented Attachment

5

Hydrothermal Synthesis• Like heat up method for nanocrystlas• Can be free standing or on substrate

6Chem. Soc. Rev., 2014,43, 2187-2199

PbTiO3

Evaporation (Dissolution) – Condensation Growth

Evaporation-Condensation• Helical Nanostructures & Nanorings (Wang,

2003)

8

Wang, Z. L. MRS Bull. 2007,

VLS or SLS Growth• VLS: Vapor-Liquid-Solid• SLS: Solution-Liquid-Solid

• Impurity or catalyst introduced

• Different from Evaporation-Condensation1. No screw dislocations in growth direction

2. Impurities always required

3. Liquid-like globule always found in tip of nanowires

9

VLS Growth Method

1. Growth species evaporated2. Growth species diffused and dissolved into

droplet3. Droplet (with growth species) deposits on

growth surface4. Growth species diffused and precipitated

onto growth surface

N & N, Fig. 4.11

10

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).

11

Classic: Si Nanowire/Gold Catalyst

• Filler Group, Georgia Techhttp://fillergroup.gatech.edu/research/

12

Si Nanowire Growth

13

• Spontaneous Growth

• Template-based Synthesis

• Electrospinning

Techniques for 1-D Nanostructure Formation

Bottom-up

http://mrsec.umd.edu/Research/Seeds.html#Template

14

Template-Based Synthesis• Used for polymers, metals, semiconductors,

oxides• Membranes as templates

Methods of filling1. Electroplating2. Colloid, melt, or vapor

15Aluminum oxide templateSensors 2005, 5, 245-249

Template-based Synthesis

Requirements for Membranes

1. Chemically and thermally inert during synthesis

2. Depositing materials must “wet” internal pores3. 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 Statehttp://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 applied2. Charged growth species reduced at deposition

surface (also an electrode)

http://tutors4you.com/electrochemicalcell.jpg 18

Electrochemical Deposition

• Products:– Metals: Ag, Ni, Co, Cu, Au nanowires: <10 nm- 200

nm dia– Semiconductors: CdSe, CdTe– Polymers: polyporrole

N & N, Fig. 4.21

19

Template Filling• Liquid precursor poured into template

pores• Requirements:

1. “Wetability” of pore walls2. Template materials must be inert3. Control of shrinkage during solidification

Can use centrifugation

• Vapor precursor can be used Diffuse gas through porous material, then heat

20

Positive Templates

• Green rod is DNA or CNTNanoscale, 2014, 6, 4027-4037

21

Polypyrrole on DNA

Step/Groove Templates

• Guide horizontal growth of nanostructures• Used w/ Evaporation-Condensation or VLS22

GaN NanowiresWeizmann Institutehttp://wis-wander.weizmann.ac.il/nanowires-get-into-the-groove#.VD3YEvldWSo

• Spontaneous Growth

• Template-based Synthesis

• Electrospinning

Techniques for 1-D Nanostructure Formation

Bottom-up

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

24

Electrospinning

http://nano.mtu.edu/documents/Electrospinning.swf

http://www.centropede.com/UKSB2006/ePoster/images/background/ElectrospinFigure.jpg

25

Electrospinning

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• http://www.jove.com/video/2494/electrospinning-fundamentals-optimizing-solution-apparatus

27

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 29