Force-detected nuclear magnetic resonance: recent advances and future challenges

Abstract

We review recent efforts to detect small numbers of nuclear spins using magnetic resonanceforce microscopy. Magnetic resonance force microscopy (MRFM) is a scanning probetechnique that relies on the mechanical measurement of the weak magnetic force between amicroscopic magnet and the magnetic moments in a sample. Spurred by the recent progressin fabricating ultrasensitive force detectors, MRFM has rapidly improved its capability overthe last decade. Today it boasts a spin sensitivity that surpasses conventional, inductivenuclear magnetic resonance detectors by about eight orders of magnitude. In thisreview we touch on the origins of this technique and focus on its recent applicationto nanoscale nuclear spin ensembles, in particular on the imaging of nanoscaleobjects with a three-dimensional (3D) spatial resolution better than 10 nm. Weconsider the experimental advances driving this work and highlight the underlyingphysical principles and limitations of the method. Finally, we discuss the challengesthat must be met in order to advance the technique towards single nuclear spinsensitivity—and perhaps—to 3D microscopy of molecules with atomic resolution.