NIRT: Nanoscale Magnetic Microscopy with Multi-Photon Absorption Polymers and Y-Junction Nanotubes

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This proposal was received in response to Nanoscale Science and Engineering initiative, NSF 01-157, category NIRT. It focuses on innovative approaches to nanoscale subsurface spin imaging, including three MRFM (magnetic resonance force microscopy) schemes and one novel non-mechanical spin sensing scheme using giant magnetoresistance (GMR) detection. A research team composed of a condensed matter physicist, a physical chemist, a materials scientist and a theoretical physicist will design and develop nanoscale probes for MRFM as well as MFM (magnetic force microcopy). Carbon nanotube and multi-photon absorption (MPA) fabricated polymer cantilevers, in linear and various forked geometries, will be employed for piezoresistive, optical waveguide and RF impedance detection of specimen spins, with anticipated sensitivities to the single spin level. Novel attogram-sized ferromagnetic nanorods will be synthesized and attached to the cantilevers for use as gradient generators/spin probes. In addition to individual magnetic spin sensors, arrays of MRFM sensors will be made, with each sensor having an integrated three-dimensional radio frequency microcoil fabricated via MPA, facilitating spatial and temporal spin correlation measurements toward nanoscale functional MRI. There is much to be gained by advancing spin-detection technology toward the single-spin level, with potential applications in information technology, medicine and scientific exploration. MRFM, which is developing into a most highly sensitive measurement technique, stands to play a major role in this goal. Molecular-scale devices, such as carbon and other types of nanotubes, will play an increasingly important role as well. To reach this goal, several impediments must be obviated, such as thermal noise, the spectral function of which defines a set of parameters to be optimized in the quest for single spin detection, 3-D molecular imaging, dynamic visualization and beyond. Another impediment is the traditional optical detection using visible light, the wavelength of which is larger than the required physical dimensions of the resonating magnetic sensor. The approaches of this program are designed to overcome these obstacles. In addition to the four senior personnel, this interdisciplinary research program will involve numerous graduate students, undergraduates, and select high school students during summer months, covering a broad range of topics such as nanoscale magnetometry, micro and nanofabrication, carbon nanotube synthesis, multi-photon absorption, nanomagnet synthesis, and theoretical aspects of magnetism, nanotubes and semiconductors.