1. 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/

2. 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

3. Spontaneous Growth: Anisotropic Growth –Growth rate of planes –Growth imperfectionsGrowth imperfections –Accumulation of impurities http://www.softmachines.org/wordpress/?p=202 http://www.its.caltech.edu/~atomic/snow crystals/designer2/designer2.htm 3

4. 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

5. Oriented Attachment 5

6. Hydrothermal Synthesis Like heat up method for nanocrystlas Can be free standing or on substrate 6 Chem. Soc. Rev., 2014,43, 2187-2199 PbTiO 3

7. Evaporation (Dissolution) – Condensation Growth

8. Evaporation-Condensation Helical Nanostructures & Nanorings (Wang, 2003) 8 Wang, Z. L. MRS Bull. 2007,

9. 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 9

10. 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 N & N, Fig. 4.11 10

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). 11

12. Classic: Si Nanowire/Gold Catalyst Filler Group, Georgia Tech http://fillergroup.gatech.edu/research/ 12

13. Si Nanowire Growth 13

14. Spontaneous Growth Template-based Synthesis Electrospinning Techniques for 1-D Nanostructure Formation Bottom-up http://mrsec.umd.edu/Research/Seeds.html#Template 14

15. Template-Based Synthesis Used for polymers, metals, semiconductors, oxides Membranes as templates Methods of filling 1.Electroplating 2.Colloid, melt, or vapor 15 Aluminum oxide template Sensors 2005, 5, 245-249

16. 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

17. Template-Based Synthesis Ran Research Group, Penn State http://research.chem.psu.edu/axsgroup/Ran/research/templatesynthesis.html 17

18. 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 18

19. 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

20. 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

21. Positive Templates Green rod is DNA or CNT NanoscaleNanoscale, 2014, 6, 4027-4037 21 Polypyrrole on DNA

22. Step/Groove Templates Guide horizontal growth of nanostructures Used w/ Evaporation-Condensation or VLS 22 GaN Nanowires Weizmann Institute http://wis-wander.weizmann.ac.il/nanowires-get- into-the-groove#.VD3YEvldWSo

23. Spontaneous Growth Template-based Synthesis Electrospinning Techniques for 1-D Nanostructure Formation Bottom-up http://mrsec.umd.edu/Research/Seeds.html#Template 23

24. 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

25. Electrospinning http://nano.mtu.edu/documents/Electrospinning.swf http://www.centropede.com/UKSB2006/ePoster/images/background/ElectrospinFigure.jpg 25

26. Electrospinning 26

27. http://www.jove.com/video/2494/electrospinnin g-fundamentals-optimizing-solution-apparatus 27

28. 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

29. Lab #3 – Surface Modification Thiols (-SH) bind to metal surface like copper Copper is easily oxidized to cuprous oxide (Cu 2 O) Use Ferric chloride to etch the oxide layer 29