controlled coupling and occupation of silicon atomic quantum dots m. baseer haider, jason l pitters,...
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Controlled Coupling and Occupation of Silicon Atomic
Quantum Dots
M. Baseer Haider, Jason L Pitters, Gino A. M. Baseer Haider, Jason L Pitters, Gino A. DiLabio, Lucian Livadaru, Josh Y Mutus, Robert A. DiLabio, Lucian Livadaru, Josh Y Mutus, Robert A.
WolkowWolkow
At room temperatureAt room temperature
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
Single, small ensembles, and large arrays of Dangling Bonds are wonderful – let’s discuss small
groups of Si DBs today
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STM DB (Dangling Bond) CreationSTM DB (Dangling Bond) Creation
10 nm
Just a demoBut interesting in itselfCan for example decorate each point with a moleculeOr with a metal atom
Low doped n-type Silicon
Neutral DBs
High doped n-type Silicon
Negative DBs
35x35 nm, 2V, 0.1nA 35x35 nm, 2.2 V, 0.1nA
CB
VB
EF
CB
VB
EF
One electron per DB Two electrons per DB
e- tip
tip1 e-= neutral 2 e-
= 1 negcharge
-20 0 20 40 60 80 1000
1
2
3
4
Hei
gh
t (Å
)
Distance (Å)
-1.6 V -1.8 V -2.4 V
e
Field regulation of single-molecule conductivity by a charged surface atomPaul G. Piva, Gino A. DiLabio, Jason L. Pitters, Janik Zikovsky, Moh’d Rezeq, Stanislav Dogel, Werner A. Hofer & Robert A. WolkowNature 435, 658-61 (2005)
Lopinski, Wayner, and Wolkow, Nature 406, 48 (2000)
-20 0 20 40 60 80 100
0
1
2
3
4
Distance (Å)H
eigh
t (Å
)
Si
SiSi
Si
SiSi
Si Si
SiSi
Si
SiSi
Si
H
H H
H
H
N
O
Si
SiSi
Si
SiSi
Si Si
SiSi
Si
SiSi
Si
H
H H
H
H
O
N
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
• All that was an asideAll that was an aside
• Showing Dangling Bond (DB) as a point Showing Dangling Bond (DB) as a point chargecharge
• Returning now to interactions among DBsReturning now to interactions among DBs
CBM
VBM
Vel/2
R12 R12 4d
E0
(a) (b)
Unfavourable
E0 t U/2
Coulombic repulsion limits filling of DB’s Coupled DB’s are “self-biased”
III
II
I23.2 Å
15.6 Å
11.5 Å
0 5 10 15 20 25 30 0.0 0.2 0.4 0.6 0.8 1.0 1.2
Pro
babi
lity
DB separation
[Å]
III II I
Distance dependent couplingDistance dependent coupling
2e-
1e-
Bandwidth of amplifier is ~5kHz.
Quantum-Dot Cellular Quantum-Dot Cellular AutomataAutomata
High DensityLow power consumption
Patterned Q-dot clusters usinge-beam lithography prepared samplesTypically ~10 nm clusters spaced by tens of nm
Operated at mK temperatures and local electrostatictuning in order to achieve the appropriate filling.
wire
inverter
fanoutmajority gate
Lent, C. S.,Tougaw, P. D., Porod, W. & Bernstein, G. H. Nanotechnology 4, 49-57, (1993).
Tilting the potentialTilting the potential
CBM
VBM
Vel/2
R12 R12 4d
E0
E0 t U/2
(a) (b) (c)
Unfavourable Vpert
This creates a situation where the forward and reverse tunnel rates are not equivalent
An H-terminated Silicon surface
~ 3 nm
One H atom removed with STM
tip
The resulting silicon “dangling
bond” is negatively charged with one
electron
Resulting in local energy level shifts, manifest as a dark
feature in STM
A 2nd dangling bond is about to be
created
the pre-existing and the new DB are
lighter in appearance – evidence of
rejection of chargeThe empty state allows electron
tunneling between the two atoms!
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
Watch: Symmetry breaking will occur when a 3rd DB added
Watch: This DB will brighten when a nearby DB added
• though enmeshed in silicon lattice, single Si atoms though enmeshed in silicon lattice, single Si atoms can stand out to act as quantum dots (remarkably can stand out to act as quantum dots (remarkably like a dopant)like a dopant)
• Ultimate small dot –> wide level spacing -> Room Ultimate small dot –> wide level spacing -> Room TemperatureTemperature
• Qdots are identicalQdots are identical
• multiple dots can be tunnel coupledmultiple dots can be tunnel coupled
• electron filling is geometry controlled - electron filling is geometry controlled - “self-“self-biased”biased”
• can electrostatically control electronic configurationcan electrostatically control electronic configuration
• immune to stray charge (beyond ~3 nm)immune to stray charge (beyond ~3 nm)
• QCA cells have been electrostatically set in one QCA cells have been electrostatically set in one binary state – not yet dynamicallybinary state – not yet dynamically
• 2 coupled dots are candidate charged qubit2 coupled dots are candidate charged qubit
• PRL 102, 46805 (2009)PRL 102, 46805 (2009)