Three-dimensional imaging with a nuclear magnetic resonance force microscope

Abstract

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.

Magnetic resonance force microscopy with a ferromagnetic tip mounted on the force detector

“…The ultra-high force sensitivity of the resonator (demonstrated in the atomic force microscope) enables much higher sensitivity to spin magnetization in MRFM and thus much higher spatial resolution than is achievable in conventional MRI. MRFM has been successfully demonstrated in electron spin resonance (ESR) [3][4][5][6][7], ferromagnetic resonance (FMR) [8], and nuclear magnetic resonance (NMR) [9,10]. For instance, spatial resolution of ∼ 1 µm has been achieved in NMR [9,10], already an order of magnitude better than conventional MRI.…”

“…MRFM has been successfully demonstrated in electron spin resonance (ESR) [3][4][5][6][7], ferromagnetic resonance (FMR) [8], and nuclear magnetic resonance (NMR) [9,10]. For instance, spatial resolution of ∼ 1 µm has been achieved in NMR [9,10], already an order of magnitude better than conventional MRI. Further increase of the sensitivity and resolution can be achieved by performing MRFM at cryogenic temperatures, by increasing the field gradient and by improving the performance of the micro-mechanical resonators [11].…”

Combined Al-protection and HF-vapor release process for ultrathin single crystal silicon cantilevers

“…The use of magnetic resonance in combination with scanning tip microscopy was first suggested in 1991 in a theoretical contribution by Sidles, who proposed the mechanical detection of the precession of single spins on a surface [1]. MRFM has been successfully demonstrated for electron spin resonance [2], ferromagnetic resonance [3] and nuclear magnetic resonance [4]. Recently, Rugar et al [5] has presented the detection of an individual electron spin with an improvement in sensitivity of 10 7 times over the original MRFM setup.…”

Advances in mechanical detection of magnetic resonance

“…47 Even the first demonstration of "magnet on tip" MRFM, though a remarkable development, employed a large enough magnetic tip that the gradient was not much larger than in early experiments. 48 By gluing magnets as small as 5 m to commercial silicon nitride cantilevers and operating the cantilevers within a few tens of nanometers of a surface, Bruland et al 49 were able to detect electron spin resonance using magnetic field gradients as large as 2.5ϫ 10 5 T / m. The sensitive slice in these experiments was only a nanometer thick, on the order of molecular dimensions.…”

“…75 Many of these experiments required long imaging times, achieved with careful closed-loop control of scanning; 76,77 acquisition times as long as ten days have been demonstrated in a 3D ESR imaging experiment. 76 Three dimensional imaging was extended, early on, to include nuclear magnetic resonance, by scanning the field and sample, 47 again using a deconvolution of the force map to construct an image. A one dimensional image in GaAs was demonstrated with 170 nm resolution 78 in an experiment in which the GaAs was optically pumped with circularly polarized light to increase nuclear spin polarization.…”