Low-Field Nuclear Magnetic Resonance Force Microscopy of Micro-Fluids

We report the design and first results of a Nuclear Magnetic Resonance Force Microscopy (NMRFM) probe for studying ¹H resonance in room-temperature micro-liquids at a low field of 0.3 T, as well as plans for restricted-diffusion and single-shot-T₁ studies. We use contained aqueous samples protected from high vacuum of order 10^-5 torr, at which our cantilever quality factors are ~1000, providing a force sensitivity of order 10^-12 N. Our micromagnet-on-oscillator sensor has detected the ¹H resonance in a resonant volume of 10^-6 µl. Magnetic field scans exhibit a broad, asymmetric peak as the resonant volume sweeps through, and then out of, the sample; the NMR nature of the detection was verified by the shifting of the peak with frequency over 16.5-17.5 MHz. We also report a procedure for measurement of T₁ with a single cyclic adiabatic inversion pulse by monitoring the decay of the spin magnetization during our 100-300-ms-long pulse. Spin diffusion measurements are also planned, by first exciting the spins in a few-µm resonant slice, then detecting the diffusing spin magnetization over a long (~50-µm) region of sample.