Si nanowire probe with Nd-Fe-B magnet for attonewton-scale force detection

In this study, we have developed a 210 nm-wide and 32 μm-long silicon nanowire probe with a silicon mirror using a silicon-on-insulator wafer in order to improve sensitivity of force detection for magnetic resonance force microscopy (MRFM). Additionally, a Nd-Fe-B magnet has been integrated at the end of the nanowire. The fabricated nanowire probe shows a resonance frequency of 11.256 kHz and a factor of 12 800 after annealing at 800 °C for 2 h in forming gas. The probe exhibits attonewton sensitivity, and the measurement of force mapping based on electron spin resonance is demonstrated for 3D imaging of radicals. The detected force and magnetic field gradient are approximately 82 aN and ∼70.1 G μm^-1 at room temperature. The radical density is calculated as 4.6 × 10¹⁸ spins cm^-3.