Click to edit Master subtitle style CSIRO 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 Nanoscience Sir Mark Oliphant and PITP Conference

2 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

3 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, (2003). 4. Kane B.E. A silicon-based nuclear spin quantum computer, Nature, (1998). 5. Hanson et al. Zeeman Energy and Spin Relaxation in a One-Electron Quantum Dot, PRL, 91, , (2003).

4 Realisation of a Niobium Nanosquid 200 nm junctions SQUID loop 20 nm thick Nb-film, T c ~ 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

5 Low field (  T) NMR BpBmBpBm NMR measurement setup Glass fibre dewar and coil set

6 Characteristics of the NanoSQUID I  SQUID operation in the small signal regime (~0.1  o ) V

7 Fig. 2 Characteristics of the NanoSQUID

8 Noise Properties - Static Field Measurements Bp Fig. 3

9 Electron Beam Induced Deposition Fig. 4a : an electron beam induced contamination patch in the SQUID hole Fig. 4b  ~ 20 nm  ~ 200 nm

10 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

11 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-dimethylaminopropyl) carbodiimide (EDC) and 50 mM N- hydroxysuccinimide (NHS) in 50 mM phosphate buffer, pH 6.8 for 30 min. Fig. 5

12 Electrochemical Studies of Ferritin on Gold The peak at 0.25 V and the dip at – 0.38 V indicate that the oxidization of Fe 2+ to Fe 3+ and the reduction of Fe 3+ to Fe 2+ respectively. Fig. 6

13 Particle Manipulation with an AFM

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