Micromechanical sensing of magnetic force was used to detect nuclear magnetic resonance with exceptional sensitivity and spatial resolution. With a 900 angstrom thick silicon nitride cantilever capable of detecting subfemtonewton forces, a single shot sensitivity of 1.6 x 10(13) protons was achieved for an ammonium nitrate sample mounted on the cantilever. A nearby millimeter-size iron particle produced a 600 tesla per meter magnetic field gradient, resulting in a spatial resolution of 2.6 micrometers in one dimension. These results suggest that magnetic force sensing is a viable approach for enhancing the sensitivity and spatial resolution of nuclear magnetic resonance microimaging.
A magnetic resonance force microscope was used to demonstrate three-dimensional nuclear magnetic resonance imaging with micrometer-scale spatial resolution. The sample was mounted on a silicon nitride cantilever that served as a micromechanical force sensor. A nearby magnetic tip generated a field gradient of 22 G/μm. A three-dimensional magnetic resonance force map of the 1H spins in the sample was produced by lateral scanning of the magnetic tip relative to the sample and by varying the rf frequency of the spin excitation. The real-space spin density of the sample was reconstructed from the force map by means of a deconvolution technique. The spatial resolution achieved in the experiment was ∼3 μm in the axial direction.
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