1. Nanostructure Formation: 1-D

2. 1-D Nanostructures Whiskers and fibers Nanorods Nanowires
Carbon Nanotubes
1-D nanostructure term: Aspect ratio = length ÷ diameter
6 : 1
12 : 1
4 : 1
36 : 1

3. Fun fact…
All these nano words are made up as scientists make new structures and there’s not much consistency yet…
What word would you invent?? 

4. Let’s give this set of notes some context…
What are some uses of 1-D nanostructures?

5. Carbon NT fibers
Transistors use CNT instead of Silicon
Solar cells use tall thin strands of silicon to trap light

6. Techniques for 1-D Nanostructure Formation
Spontaneous Growth
Template-based Synthesis
Electrospinning
Lithography
Bottom-up
Top-down

7. Anisotropic Growth (aniso = uneven)
Spontaneous Growth: Evaporation (dissolution)-Condensation (AKA ROCK CANDY ANALOGY AGAIN)
Anisotropic Growth (aniso = uneven)
Side effects:
Growth imperfections
Accumulation of impurities

8. Evaporation-Condensation Growth Example
“Nanobelts”

9. Evaporation-Condensation Growth Example
Helical Nanostructures & “Nanorings”

10. VLS or SLS Growth VLS: Vapor-Liquid-Solid SLS: Solution-Liquid-Solid
1st Step with both: Impurity or
catalyst introduced
Growth species evaporated
Growth species diffused and dissolved into droplet
Droplet (with growth species) deposits on growth surface
Growth species diffused and precipitated onto growth surface

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

12. Techniques for 1-D Nanostructure Formation
Spontaneous Growth
Template-based Synthesis
Electrospinning
Bottom-up

13. Template-Based Synthesis
Used for polymers, metals, semiconductors, oxides
Membranes as templates
Methods:
Electroplating & Electrophoretic Deposition
Colloid Dispersion, Melt, or Solution Filling
(may also involve chemical reactions)

14. Electrochemical Deposition
Only for electrically conductive materials
Metals, alloys, semiconductors, some polymers
Electroplating is electrochemical deposition

15. Electrochemical Deposition
Method:
Charged growth species moves through solution in one direction when electric field applied
Charged growth species reduced at deposition surface (also an electrode)

16. If you put a template at the cathode, a metal will fill the pore, creating a nanowire!
Product examples:
Metals: Ag, Ni, Co, Cu, Au nanowires: <10 nm- 200 nm dia
Semiconductors: CdSe, CdTe
Polymers: polyporrole

17. CVD / Centrifugation (it’s sort of like the Gravitron ride at a carnival!)
Chemical Vapor Deposition (CVD)
Diffuse gas through porous material; heat
Centrifugation
Combine sol and porous material
Spin at 1500 rpm for 60 minutes
Heat to 650 ˚C for 60 minutes
Forcecentrifugation > Forcerepulsion between particles

18. Techniques for 1-D Nanostructure Formation
Spontaneous Growth
Template-based Synthesis
Electrospinning
Bottom-up

19. Electrospinning
Electrical forces at surface overcome surface tension  (aka electricity destroys the surface tension that was holding the drop of liquid together before)
Fiber can be directed or accelerated by electrical forces
Product: 30+ types of polymer, nm diameter
Can be collected in sheets or other forms
Morphology depends on:
Solution concentration
Applied electric field strength
Feeding rate of precursor solution

20. Electrospinning