Towards nano-mri in mesoscopic transport systems P. Peddibhotla, M. Montinaro, D. Weber, F. Xue, and M. Poggio Swiss Nanoscience Institute Department of Physics University of Basel Switzerland 3 rd Nano-MRI Research Conference July 2010, Domaine du Tremblay
New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices 16.07.2010 2
New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator 16.07.2010 3
arxiv:0910.0005 16.07.2010 4
New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator mechanically detected magnetic resonance of nuclear spin ensembles within mesoscopic structures (e.g. QDs, nanotubes) 16.07.2010 5
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Nuclear spins in QDs In a QD, a single electron spin interacts with 10 4-10 5 nuclear spins Hyperfine interactions cause decoherence of the electron spin MRFM may provide a way to directly observe this small ensemble of nuclei J. M. Taylor et al., Nat. Phys. 1, 177(2005). 16.07.2010 7
MRFM of nuclei in QDs QD 16.07.2010 8
New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator mechanically detected magnetic resonance of nuclear spin ensembles within mesoscopic structures (e.g. QDs, nanotubes) sensitive detection of cantilever motion 16.07.2010 9
Mechanical Force Transducers F x F kx We have a nano-mechanical transducers of force into displacement. We require a sensor for mechanical displacement. 16.07.2010 10
Sensors for Mechanical Displacement Tunneling Optical Deflection Optical Interferometry Microwave Interferometry Magnetomotive Piezoelectric Capacitive 16.07.2010 11
STM Detection 16.07.2010 12
Capacitive detection 10 15 m/ Hz 16.07.2010 13
Capacitive detection 1 10 12 m/ Hz 16.07.2010 14
Spectral Density (Ang 2 / Hz) Spectral Density (Å 2 / Hz) Spectral Density (A 2 / Hz) Spectral Density (Amp 2 / Hz) Measurement of Cantilever Thermal Noise DC V sd drive: 2.0 mv 101 0 0.1 10-1 10-21 10-12 m / (Hz) 1/2 1E-21 0.01 10-2 1E-3 10-3 1E-4 10-4 1E-5 10-5 4500 4.50 4750 4.75 5000 5.00 5250 5.25 Frequency (khz) Frequency (Hz) 10-22 1E-22 10-23 1E-23 10-24 1E-24 10-25 1E-25 16.07.2010 15
New Lab: Goals & Motivation A system capable of coupling nano-mechanical cantilevers to mesoscopic transport devices measurement of single electron states and spin states using a mechanical oscillator mechanically detected magnetic resonance of nuclear spin ensembles within mesoscopic structures (e.g. QDs, nanotubes) sensitive detection of cantilever motion 16.07.2010 16
Basic Setup Diagram cantilever laser Device (e.g. QPC, SET, microwire) 16.07.2010 17
Displacement Spectral Density (m 2 /Hz) 1E-18 10 1E-19 10 T = 400 mk Q = 18,000 k = 45 mn/m 1E-20 10 1E-21 10 1E-22 10 2750 2800 2850 2900 2950 Frequency (Hz) January 2009 March 2010 16.07.2010 18
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UHV BeCo springs chip carrier Soft Cu braids T = 300 mk 3D positioning of sample Cantilever holder & interferometer Interferometer with 10-12 m/hz socket 1/2 4 coaxial touch cables sensorsfor RF signals 20 wire-bondable contacts to sample sample/device holder 3D positioners & scanners Rf coax lines 16.07.2010 20
Basic Setup Diagram cantilever laser Device (e.g. QPC, SET, microwire) 16.07.2010 21
RF coax connections piezo actuator lens cantilever chip device (e.g. microwire, QPC, SET) wire-bonding pads 22
QPC Samples markers 200 nm 16.07.2010 23
Coupling to a Carbon Nanotube cantilever Ti-Au leads CNT 16.07.2010 24
Carbon Nanotube Samples 1 mm 16.07.2010 25
Carbon Nanotube Samples 16.07.2010 26
cantilever chip cantilever nanotube devices bonds & pads Si sample reflection of cantilever chip 27.04.2010 27
Interferometer laser beam Ultrasensitive cantilever Resonant slice (B = 2.70 T) 1 H Nuclear spin i rf Magnetic tip Microwire generating 115 MHz magnetic field
Cantilevers & sample preparation A tiny CaF2 sample was glued to the end of an ultrasolf Si cantilever with the aid of a needle held by a micro-manipulator Cantilever nanotube 5 mm tip 5 mm CaF 2 needle Cantilever CaF 2 Cantilever 16.07.2010 29
Microwires & magnetic tips for MRFM FeCo tip Au microwire Effort at making a high gradient tip 16.07.2010 30
New microwire MRFM geometry The cantilever s axis of rotation is parrallel to the applied magnietic field B 0. B 0 points in the plane of the device surface (for mesoscopic transport measurements) This configuration avoids magnetic dissipation known to be present even in nonmagnetic cantilevers. B0 16.07.2010 31
Spectral Density (m 2 /Hz) Force (an 2 ) First MRFM Signal Microwire 5000 4000 19 F CaF 2 Crystal Particle B = 2.8 T T = 600 mk 3000 1 H 2000 1000 100 110 120 130 Frequency (MHz) CaF 2 Cantilever 1E-19 1E-20 1E-21 cantilever thermal noise spin noise 1E-22 2525 2550 2575 2600 Frequency (Hz) 16.07.2010 32
Force (an 2 ) Gradient & RF field Magnitude Nutation Experiment T = 600 mk 1000 900 800 700 B 1 field 4.5 mt 190 khz T = 600 mk B rf 4.5 mt RF field (190 khz) B tip 10 6 T/m lateral field gradient B tip B rf 600 500 i rf 400 0.0 5.0µ 10.0µ 15.0µ 20.0µ Pulse width (s) 16.07.2010 33
Topical Review Force-detected nuclear magnetic resonance: Recent advances and future challenges M. Poggio and C. L. Degen, Nanotechnology, in press; arxiv:1006.3736 (2010). 16.07.2010 34
Group members PhD Students Post-doc Masters Student Phani Peddibhotla Michele Montinaro Dr. Fei Xue Benedikt Herzog Dennis Weber 16.07.2010 35