Click to edit Master subtitle styleCSIRO IT

Progress towards the measurement of a small spin system using a nanoSQUID

January 2006

S.K.H. Lam, W. Yang, K. Lo, D.L. Tilbrook

Industrial Physics

Frontiers in Quantum NanoscienceSir Mark Oliphant and PITP Conference

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Contents

1. Nanosquid Properties

Device realization and fabrication

Noise properties of the device

2. Placement of small object on the device

Electron beam induced deposition

Self assembly monolayer

Dispersion and manipulation of nanoparticle

3. Summary and Outlook

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Potential Applications

Low field NMR and NQR

Molecular fingerprint

Forensic science

Nanometrology

Quantum Computing

Qubit based on energy state of high magnetic anisotropy magnetic cluster 1-3

Qubit based on spin state of single phosphor atom or quantum dot 4, 5

1. Leuenberger et al., Quantum Computing in molecular magnets, Nature, 410, 789 (2001).

2. Tejada et al., Magnetic qubits as hardware for quantum computers, Nanotechnology, 12, 181 (2001).

3. Meier F. et al., Quantum Computing with Spin Cluster Qubits, PRL, 90, 047901 (2003).

4. Kane B.E. A silicon-based nuclear spin quantum computer, Nature, 393 133 (1998).

5. Hanson et al. Zeeman Energy and Spin Relaxation in a One-Electron Quantum Dot, PRL, 91, 196802-1, (2003).

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Realisation of a Niobium Nanosquid

200 nm

junctions

SQUID loop

• 20 nm thick Nb-film, Tc ~ 9K

• Junctions based on Nb nanobrigdes ~ 100 nm wide

• fabricated by electron beam lithography and reactive ion etching

• SQUID-loop: 200 nm x 200 nm

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Low field (T) NMR

Bp

Bm

NMR measurement setup

Glass fibre dewar and coil set

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Characteristics of the NanoSQUID

I

-0.05 0.00 0.05 0.10 0.15 0.20 0.25-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

SQ

UID

ou

tpu

t a

rbitr

ary

un

it

time (s)

bias current

input field

185Vbias.opj

SQUID operation in the small signal regime (~0.1 o)

V

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0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.0

0.5

1.0

1.5

2.0

SQ

UID

ou

tpu

t vo

ltag

e (

Vrm

s/rH

z)

Input voltage through the coil (Vrms/rHz)Fig. 2

Characteristics of the NanoSQUID

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Noise Properties - Static Field Measurements

0.1 1 10 100 1000 10000

1E-6

1E-5

1E-4

SQ

UID

flu

x n

ois

e (

o/r

Hz)

frequecny (Hz)

Bp = 0

Bp = 1 mT

Bp

Fig. 3

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Electron Beam Induced Deposition

Fig. 4a : an electron beam induced contamination patch in the SQUID hole

Fig. 4b

~ 20 nm

~ 200 nm

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Magnetic Properties of Ferritin

Ferritin is an iron storage protein

Iron oxyhydroxide core 70 Å diameter surrounded by protein shell of ~120 Å

Antiferromagnetic below 12K.

Small net magnetic moment per particle: net spin ~ 200 spins

Zero field cooled magnetic measurement of ferritin in a SQUID

Magnetometer

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Self Assembled Monolayer

S

O

H

O

S

OO

N OO

S

O

NH

O

NH2

FF

EDC/NHS

MPA SAMs

Ferritin particle

• A schematic diagram to show the attachment of a ferritin particle on the Au surface through the activated carboxyl group of the MPA (3-mercaptopropionic acid) SAM molecules.

• The carboxyl groups were activated by placing the gold electrodes with 75 mM 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and 50 mM N-hydroxysuccinimide (NHS) in 50 mM phosphate buffer, pH 6.8 for 30 min.

Fig. 5

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Electrochemical Studies of Ferritin on Gold

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

-8.0x10-6

-6.0x10-6

-4.0x10-6

-2.0x10-6

0.0

2.0x10-6

4.0x10-6

6.0x10-6

8.0x10-6

C

urr

en

t (A

)

Voltage (V) vs. Ag/AgCl

•The peak at 0.25 V and the dip at – 0.38 V indicate that the oxidization of Fe2+ to Fe3+ and the reduction of Fe3+ to Fe2+ respectively.

Fig. 6

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Particle Manipulation with an AFM

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