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

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Progress towards the measurement of a small spin
system using a nanoSQUID
S.K.H. Lam, W. Yang, K. Lo, D.L. Tilbrook
Frontiers in Quantum Nanoscience Sir Mark
Oliphant and PITP Conference
January 2006
Industrial Physics
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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 Dispersio
n 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
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 (mT) NMR
NMR measurement setup Glass fibre dewar and coil
set
Bp Bm
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Characteristics of the NanoSQUID
B
I
SQUID operation in the small signal regime (0.1
Fo)
V
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Characteristics of the NanoSQUID
Fig. 2
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Noise Properties - Static Field Measurements
Bp
Fig. 3
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Electron Beam Induced Deposition
f 20 nm
f 200 nm
Fig. 4b
Fig. 4a an electron beam induced contamination
patch in the SQUID hole
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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

• 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-dimeth
  ylaminopropyl) 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

• 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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