1 / 56

Size Matters

Size Matters. Why small is different. Simon Brown MacDiarmid Institute and Department of Physics University of Canterbury, Christchurch, New Zealand NZIP Conference, Christchurch, July 2009. Silicon. Silicon. Diamond Structure Lowest energy configuration. The surface of Silicon (111).

adele
Download Presentation

Size Matters

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Size Matters Why small is different Simon Brown MacDiarmid Institute and Department of Physics University of Canterbury, Christchurch, New Zealand NZIP Conference, Christchurch, July 2009

  2. Silicon

  3. Silicon • Diamond Structure • Lowest energy configuration

  4. The surface of Silicon (111) • Model • But what happens to the dangling bonds?

  5. The best way of imaging surfaces • Scanning Tunneling Microscope (STM) • UHV STM / AFM installed at UC, Jan 2009

  6. The surface of Silicon (111) • Model • But what happens to the dangling bonds?

  7. The surface of Silicon (111) • Image from Scanning Tunnelling Microscope (STM) • “Reconstruction” minimises energy

  8. The surface of Silicon (001) • Image from Scanning Tunnelling Microscope (STM)

  9. The surface of Silicon (001) • Image from Scanning Tunnelling Microscope (STM)

  10. Gold

  11. Gold – a close packed structure • Face-centred cubic

  12. Surface of Gold Paweł Kowalczyk (UC)

  13. Surface of Gold Paweł Kowalczyk (UC)

  14. Surface of Gold (111) • “Herringbone” reconstruction

  15. Nanoparticles • Mostly surface! • Here: 42 / 55 atoms are on surface

  16. Size matters • In small metal particles (e.g. Au) • Five-fold symmetry is forbidden in large crystals • not space-filling Icosahedron Cuboctahedron Truncated decahedron Large (>4 nm) Small (<2nm) Medium (~3nm)

  17. Structure of small gold clusters • 2D versus 3D structures Johansson et al, Phys. Rev. A 77, 053202 (2008)

  18. Gold • Gold nanoparticles look red!

  19. Catalysis by Gold Nanoparticles • Oxidation of CO: CO + O → CO2 Goodman et al, Top. Catal. 14, 71 (2001).

  20. Catalysis by Gold Nanoparticles • Atomic arrangement on Au surface is critical • CO + O → CO2 Goodman et al, Top. Catal. 14, 71 (2001).

  21. Melting point changes • Dramatic decrease at small sizes Sn S. L. Lai et al., PRL 77, 99 (1996)

  22. Surface melting Shaun Hendy, IRL

  23. Its not all about the surface • Quantum Effects

  24. Its not all about the surface • New materials, new properties • Carbon nanotubes are • Strongest material known • Highest conductivity known

  25. Some “new” phenomena for metal nanoparticles • Coalescence • Bouncing • Sometimes nanoparticles act more like liquids than solids

  26. How to make nanoparticles (“clusters”) Cluster source: highly flexible • e.g. Si for transistors, Cu for interconnects, Pd for hydrogen sensors • Proof of concept with Sb, Bi – interesting electronic properties • Change cluster size through temperature, gas type and pressure • Change cluster velocity through gas flow rate

  27. Simple Nanodevices Made from Nanoparticles Schmelzer et al, Phys. Rev. Lett. 88, 226802 (2002)

  28. Large metal particles do not coalesce • (Obviously!)

  29. But liquid drops do… Spreading of droplets of silicone oil on a highly wet-able substrate Ristenpart et al, PRL 97, 064501 (2006)

  30. Metal nanoparticles coalesce “Frozen” by immediate exposure to air Allowed to evolve in vacuum for 3 days 30nm Bi clusters Convers, Natali et al (to be published)

  31. Coalescence Increase in conductance Convers, Natali et al (to be published)

  32. Rayleigh Instability Decrease in conductance Lord Rayleigh, On the instabilities of jets, Proc. Lond. Math. Soc. 10, 4 (1878)

  33. Large balls bounce

  34. Liquid droplets also bounce…. Jayaratne and Mason, Proc. Roy. Soc. London. Ser. A, 280, 545 (1964)

  35. …. but they also wet surfaces

  36. Clusters partially wet surfaces • Bismuth on SiOx

  37. Molecular Dynamics Simulations – Nanoparticle Bouncing Awasthi et al, PRL 97, 186103 (2006)

  38. Nanoparticle Bouncing Awasthi et al, PRL 97, 186103 (2006); PRB 76, 115437 (2007)

  39. Nanoparticle Bouncing Elastic Sticking Awasthi et al, PRL 97, 186103 (2006); PRB 76, 115437 (2007)

  40. Nanoparticle Bouncing Elastic Bouncing Awasthi et al, PRL 97, 186103 (2006); PRB 76, 115437 (2007)

  41. Nanoparticle Bouncing Plastic Sticking Awasthi et al, PRL 97, 186103 (2006); PRB 76, 115437 (2007)

  42. Nanoparticle Bouncing Plastic Bouncing Awasthi et al, PRL 97, 186103 (2006); PRB 76, 115437 (2007)

  43. Templated devices • Bouncing of clusters off flat surfaces governs cluster assembly 30nm Sb clusters Partridge et al, Nanotechnology 15, 1382 (2004)

  44. No Lift-off lithography 30nm Bi clusters Reichel et al, Appl. Phys. Lett, 89, 213105 (2006).

  45. Metal Oxide Sensors: SnO2 • Metal Oxides are usually semiconductors • Metal oxides can be used for many types of gas sensors Lassesson et al, Nanotechnology19, 015502 (2008).

  46. SnO2 Sensors: H2 T=80ºC • 6nm Sn clusters • oxidised: 200ºC, 18hrs • doped with 1nm Pd Lassesson et al, Nanotechnology19, 015502 (2008).

  47. H H H H H H H H A Response Mechanism • Metal Oxides are commonly n-type semiconductors • Electrons carry the current

  48. H H H H H H H H Response Mechanism • A reducing gas reacts with surface

  49. Response Mechanism • Surface defects (donors) are created + + + + + + + + + + + + + + + + + +

  50. Response Mechanism • Surface defects (donors) are created • Additional electrons are released into the wire • The current increases + + + + + + + + + + + + + + + + + +

More Related