Nanostructure Formation: 1-D

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 Bottom-up • Spontaneous Growth • Template-based Synthesis • Electrospinning • Lithography Top-down

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

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 Bottom-up • Spontaneous Growth • Template-based Synthesis • Electrospinning

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) http://www.flashscience.com/chemistry/copper_plating.htm

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 http://www.youtube.com/watch?v=4F2gfuKwn6k http://www.youtube.com/watch?v=ewmdPNfyBzI

18. Techniques for 1-D Nanostructure Formation Bottom-up • Spontaneous Growth • Template-based Synthesis • Electrospinning http://mrsec.umd.edu/Research/Seeds.html#Template

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, 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

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