1. UCI C h e m i s t r y P e n n e r G r o u p Nanowire "Thinning" by Kinetically Controlled Electrochemical Stripping: A New Route to Ultra Small Metal Nanowires 2005 IM-SURE Symposium Mike Thompson, R.M. Penner. Department of Chemistry. UC Irvine

2. UCI C h e m i s t r y P e n n e r G r o u p 1.Electrochemical Step Edge Decoration (ESED) as a method for making metal nanowires. 2.My mission: Make smaller Sb and Au nanowires 3. Smaller nanowires: Results and discussion outline

3. UCI C h e m i s t r y P e n n e r G r o u p 1.Electrochemical Step Edge Decoration (ESED) as a method for making metal nanowires. 2.My mission: Make smaller Sb and Au nanowires 3. Smaller nanowires: Results and discussion outline

4. UCI C h e m i s t r y P e n n e r G r o u p Electrochemical Step Edge Decoration:

5. UCI C h e m i s t r y P e n n e r G r o u p

6. UCI C h e m i s t r y P e n n e r G r o u p Our electrochemical setup…

7. UCI C h e m i s t r y P e n n e r G r o u p Potential (mV vs. SCE) Current (  A) E ox E nuc E grow Three steps : oxidation, nucleation, and growth Sb 3+ + 3 e - Sb 0 Sb 0 Sb 3+ + 3 e -

8. UCI C h e m i s t r y P e n n e r G r o u p 4 s16 s 256 s128 s 64 s32 s ESED allows for size selective growth (MoO 2 wires pictured):

9. UCI C h e m i s t r y P e n n e r G r o u p 1.Electrochemical Step Edge Decoration (ESED) as a method for making metal nanowires. 2.My mission: Make smaller Sb and Au nanowires 3. Smaller nanowires: Results and discussion outline

10. UCI C h e m i s t r y P e n n e r G r o u p Potential (mV vs. SCE) Current density (  A cm -2 ) E grow, 75 s E ox, 5s E nucl, 40 ms A case study using antimony nanowires… 5 mM SbCl3, 0.1 M Tartaric Acid, 0.1 M Nitric Acid

11. UCI C h e m i s t r y P e n n e r G r o u p 122 nm

12. UCI C h e m i s t r y P e n n e r G r o u p

13. UCI C h e m i s t r y P e n n e r G r o u p THESE WIRES ARE TOO BIG! Antimony nanowires with diameters larger than 40 nm have no interesting properties, and thus are useless. How can we reduce the minimum size of these wires (from 120 nm to 40 nm)? The answer is simple: Use electrochemistry to slowly etch them away.

14. UCI C h e m i s t r y P e n n e r G r o u p Using kinetically-controlled anodic etching to make the wires smaller... Potential (mV vs. SCE) Current (  A) Sb 3+ + 3 e - Sb 0 Sb 0 Sb3 + + 3 e -

15. UCI C h e m i s t r y P e n n e r G r o u p Penner, JPC-B 106 (2002) 3339. Walter et al. ChemPhysChem 4 (2003) 131. nanowire smoothing is predicted by the growth law... R= nanowire radius i dep =constant deposition current V m =molar volume n=moles of e - F= the Faraday L= nanowire length

16. UCI C h e m i s t r y P e n n e r G r o u p kinetically controlled stripping causes a constant anodic current density, thus... Thompson, Menke, Penner. in preparation

17. UCI C h e m i s t r y P e n n e r G r o u p 1.Electrochemical Step Edge Decoration (ESED) as a method for making metal nanowires. 2.My mission: Make smaller Sb and Au nanowires 3. Smaller nanowires: Results and discussion outline

18. UCI C h e m i s t r y P e n n e r G r o u p Choosing the right stripping potential… Potential (mV vs. SCE) Current (  A) Sb 3+ + 3 e - Sb 0 Sb 0 Sb3 + + 3 e -

19. UCI C h e m i s t r y P e n n e r G r o u p -0.060 V -0.025 V Stripping is extremely sensitive to the applied potential…

20. UCI C h e m i s t r y P e n n e r G r o u p No stripping 122 nm

21. UCI C h e m i s t r y P e n n e r G r o u p 73 nm 250 s stripping

22. UCI C h e m i s t r y P e n n e r G r o u p 33 nm 500 s stripping

23. UCI C h e m i s t r y P e n n e r G r o u p 33 nm

24. UCI C h e m i s t r y P e n n e r G r o u p

25. UCI C h e m i s t r y P e n n e r G r o u p Gold nanowires are interesting and difficult to make small…try stripping! Oxidation: 5s @ 0.8V Nucleation: 100ms @ -1.0 V Growth: 30 s @ 0.45 V

26. UCI C h e m i s t r y P e n n e r G r o u p 158 nm 145 nm

27. UCI C h e m i s t r y P e n n e r G r o u p No stripping 145 nm 158 nm

28. UCI C h e m i s t r y P e n n e r G r o u p 600 s 1200 s 109 nm 66 nm

29. UCI C h e m i s t r y P e n n e r G r o u p

30. UCI C h e m i s t r y P e n n e r G r o u p THANK YOU! Thanks also to: Prof. Reg Penner Erik Menke Ben Murray Said Shokair and UROP staff Konstantin Arutyunov Funding provided by: NSF UROP EU Commission ULTRA 1-D project for the HOPG