Controlled Coupling and Occupation of Silicon Atomic Quantum Dots

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Controlled Coupling and Occupation of Silicon
Atomic Quantum Dots
At room temperature

• M. Baseer Haider, Jason L Pitters, Gino A.
  DiLabio, Lucian Livadaru, Josh Y Mutus, Robert A.
  Wolkow

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• 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

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Single, small ensembles, and large arrays of
Dangling Bonds are wonderful lets discuss
small groups of Si DBs today
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Si (100)-H, 2x1
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STM DB (Dangling Bond) Creation
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10 nm
Just a demo But interesting in itself Can for
example decorate each point with a molecule Or
with a metal atom
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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
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Field regulation of single-molecule conductivity
by a charged surface atom Paul G. Piva, Gino A.
DiLabio, Jason L. Pitters, Janik Zikovsky, Mohd
Rezeq, Stanislav Dogel, Werner A. Hofer Robert
A. Wolkow Nature 435, 658-61 (2005)
Lopinski, Wayner, and Wolkow, Nature 406, 48
(2000)
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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 gt Charge elimination and
therefore Field elimination Also single molecule
sensing
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• All that was an aside
• Showing Dangling Bond (DB) as a point charge
• Returning now to interactions among DBs

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DB distance is 8.2Å
10x10nm, 2V, 0.2nA
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Coulombic repulsion limits filling of DBs
Coupled DBs are self-biased
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Rare tunneling
Very High Tunnel Rate
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Distance dependent coupling
2e-
1e-
Bandwidth of amplifier is 5kHz.
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Charging state probabilities for a 4DB cell
6x6 nm, 2V, 0.08 nA
Room temp
Low temp
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6x6 nm, 2V, 0.08 nA
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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. Nanotechnology 4, 49-57, (1993).
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Tilting the potential
This creates a situation where the forward and
reverse tunnel rates are not equivalent
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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
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These entities are small
.
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play fun movie QCA/computer
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• though enmeshed in silicon lattice, single Si
  atoms can stand out to act as quantum dots
  (remarkably like a dopant)
• Ultimate small dot gt wide level spacing -gt 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)

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the end