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

Si (100)-H, 2x1Si (100)-H, 2x1

3.84 Å

7.68 Å

2.25 Å

HH

HH

HH

HH

HHH

HHH

HH

HH

HH

HH

HHH

HHH

HH

HH

HH

HH

HHH

HHH

HH

HH

HH

HHHH

HHH

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

DB1

DB2

DB1

DB2

NEWDB3

10x10nm, 2V, 0.2nA DB distance is 8.2Å

1e-

1e-

1e-

1e-

Not 2e-

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”

Very High Tunnel Rate

Rare tunneling

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.

6x6 nm, 2V, 0.08 nA

Charging state probabilities for a 4DB cell

Room temp

Low temp

6x6 nm, 2V, 0.08 nA

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

.

These entities are small

play fun movie play fun movie QCA/computerQCA/computer

• 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)

the end