SiNW and apparatus. a, Scanning electron micrograph of a SiNW substrate showing several SiNWs representative of the type used in this study. Scale bar is 5 μm. b, The tip of the SiNW used in this study with the polystyrene coating. The dashed lines indicate the outer diameter of the SiNW. Scale bar is 100 nm. c, Schematic of the experimental setup. Prior to the experiment, a single SiNW on the substrate is selected and coated with polystyrene. The SiNW tip is brought near the constriction in the rf wire. Focused, polarized laser light is used to detect the displacement of the specific SiNW with the polystyrene. d, Experimental apparatus
Magnetic resonance force microscopy (MRFM) was proposed as a means of magnetic resonance imaging with the eventual goal of achieving the sensitivity to image individual molecules with atomic spatial resolution1.
We report the use of a silicon nanowire mechanical oscillator as a low-temperature nuclear magnetic resonance force sensor to detect the statistical polarization of 1H spins in polystyrene. Under operating conditions, the nanowire experienced negligible surface-induced dissipation and exhibited a nearly thermally-limited force noise of 1.9 aN2/Hz in the measurement quadrature. In order to couple the 1H spins to the nanowire oscillator, we have developed a new magnetic resonance force detection protocol which utilizes a nanoscale current-carrying wire to produce large time-dependent magnetic field gradients as well as the rf magnetic field.
We have demonstrated a new route to ultrasensitive MRFM detection using SiNW oscillators and the MAGGIC spin detection protocol. The use of bottom-up NEMS oscillators as force detectors opens the door for greatly improved force sensitivity. Furthermore, the ability to generate large time-dependent field gradients may enable efficient methods for nanoscale magnetic resonance imaging. Together, these new tools promise to advance MRFM closer toward the goal of molecular imaging.