Fabrication and evaluation of single-crystal silicon cantilevers with ultra-low spring constants

We successfully fabricated single-crystal silicon cantilevers with spring constants as low as 10(-5) N m(-1) for use in magnetic resonance force microscopy applications. The fabricated ultra-thin silicon cantilevers had thicknesses ranging from 200 to 400 nm, lengths ranging from 340 to 450 mu m and a width of 5 mu m. We characterized their force sensitivity in the vacuum range from ambient pressure to 10(-3) Pa and the temperature range from 15 to 300 K. A minimum value is observed for the internal friction, Q(-1), at 160 K, which corresponds to an activation peak due to phonon scattering by atomic-scale defects. The best force sensitivity was achieved at 20 K, where it was increased by a factor of 10 as compared to that observed at room temperature.