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Controlled Coupling and Occupation of Silicon Atomic Quantum Dots

At room temperature. Controlled Coupling and Occupation of Silicon Atomic Quantum Dots. M. Baseer Haider, Jason L Pitters, Gino A. DiLabio, Lucian Livadaru, Josh Y Mutus, Robert A. Wolkow. NINT Scientists Gino DiLabio Jason Pitters NINT Scientist dedicated to commercialization ventures

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Controlled Coupling and Occupation of Silicon Atomic Quantum Dots

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  1. At room temperature Controlled Coupling and Occupation of Silicon Atomic Quantum Dots M. Baseer Haider, Jason L Pitters, Gino A. DiLabio, Lucian Livadaru, Josh Y Mutus, Robert A. Wolkow

  2. NINT Scientists • Gino DiLabio • Jason Pitters • NINT Scientist dedicated to commercialization ventures • Stas Dogel • NINT Instrument design Engineer • Mark Salomons • Technician • Martin Cloutier • Postdocs • Baseer Haider • Lucian Livadaru • Radovan Urban • Peter Ryan • Paul Piva • Students • Manuel Smeu, Co-supervised with Hong Guo/McGill • Janik Zikovsky • Shoma Sinha • Cristian Vesa • Marco Taucer

  3. Single, small ensembles, and large arrays of Dangling Bonds are wonderful – let’s discuss small groups of Si DBs today

  4. 2.25 Å 3.84 Å 7.68 Å Si (100)-H, 2x1

  5. STM DB (Dangling Bond) Creation

  6. 10 nm Just a demo But interesting in itself Can for example decorate each point with a molecule Or with a metal atom

  7. Neutral DBs Negative DBs Low doped n-type Silicon CB High doped n-type Silicon EF CB VB EF VB 35x35 nm, 2V, 0.1nA 35x35 nm, 2.2 V, 0.1nA One electron per DB Two electrons per DB e- tip tip 1 e- = neutral 2 e- = 1 neg charge

  8. e Field regulation of single-molecule conductivity by a charged surface atom Paul G. Piva, Gino A. DiLabio, Jason L. Pitters, Janik Zikovsky, Moh’d Rezeq, Stanislav Dogel, Werner A. Hofer & Robert A. Wolkow Nature 435, 658-61 (2005) Lopinski, Wayner, and Wolkow, Nature406, 48 (2000)

  9. Pitters, J. L.; Piva, P. G.; Tong, X.; Wolkow, R. A., Nano Lett.;3, 1431-1435 (2003). Pitters, J. L. & Wolkow, R. A., J. Am. Chem. Soc. 127, 48–-49 (2005). Dangling bond capping => Charge elimination and therefore Field elimination Also single molecule sensing

  10. All that was an aside • Showing Dangling Bond (DB) as a point charge • Returning now to interactions among DBs

  11. 1e- 1e- NEW DB3 DB1 DB1 1e- 1e- Not 2e- DB2 DB2 DB distance is 8.2Å 10x10nm, 2V, 0.2nA

  12. Unfavourable CBM Vel/2 E0 E0 t U/2 R12 R12 4d VBM (a) (b)   Coulombic repulsion limits filling of DB’s Coupled DB’s are “self-biased”

  13. Rare tunneling Very High Tunnel Rate

  14. II 15.6 Å III I 11.5 Å 23.2 Å Distance dependent coupling 2e- 1e- Bandwidth of amplifier is ~5kHz.

  15. Charging state probabilities for a 4DB cell 6x6 nm, 2V, 0.08 nA Room temp Low temp

  16. 6x6 nm, 2V, 0.08 nA

  17. Quantum-Dot Cellular Automata High Density Low power consumption Patterned Q-dot clusters using e-beam lithography prepared samples Typically ~10 nm clusters spaced by tens of nm Operated at mK temperatures and local electrostatic tuning in order to achieve the appropriate filling. wire majority gate fanout inverter Lent, C. S.,Tougaw, P. D., Porod, W. & Bernstein, G. H. Nanotechnology4, 49-57, (1993).

  18. Unfavourable Vpert CBM Vel/2 E0 E0 t U/2  R12 R12 4d  VBM (c) (a) (b) Tilting the potential This creates a situation where the forward and reverse tunnel rates are not equivalent

  19. ~ 3 nm Watch: Symmetry breaking will occur when a 3rd DB added Watch: This DB will brighten when a nearby DB added An H-terminated Silicon surface A 3rd DB acts as an electrostatic perturbation – it shifts charge in pre-existing coupled pair This is single electron state control The Si DBs are atomic quantum dots The grouping is an artificial molecule A 2nd dangling bond is about to be created One H atom removed with STM tip the pre-existing and the new DB are lighter in appearance – evidence of rejection of charge The resulting silicon “dangling bond” is negatively charged with one electron The empty state allows electron tunneling between the two atoms! Resulting in local energy level shifts, manifest as a dark feature in STM

  20. These entities aresmall .

  21. play fun movie QCA/computer

  22. though enmeshed in silicon lattice, single Si atoms can stand out to act as quantum dots (remarkably like a dopant) • Ultimate small dot –> wide level spacing -> Room Temperature • Qdots are identical • multiple dots can be tunnel coupled • electron filling is geometry controlled - “self-biased” • can electrostatically control electronic configuration • immune to stray charge (beyond ~3 nm) • QCA cells have been electrostatically set in one binary state – not yet dynamically • 2 coupled dots are candidate charged qubit • PRL 102, 46805 (2009)

  23. the end

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