Fabricating overhanging magnets for use in magnetic resonance force microscopy using a XeF2 isotropic etch.

Pushing magnetic resonance force microscopy towards single proton sensitivity demands meeting the nanofabrication challenge of producing an attonewton-sensitivity cantilever with a magnetic tip whose diameter is 50 nm or less. At the same time, the cantilever should also experience low force noise (and force gradient noise) near the surface of technologically interesting samples. Ideally then, the magnetic tip would overhang the leading edge of the cantilever -- to increase the signal created by the magnet while simultaneously minimizing the noise created by the rest of the cantilever interacting with the surface. We will show that the isotropic etchant XeF$_{2}$ can be used to underetch a single crystal silicon cantilever to create an overhanging magnet. This etch is a controllable etch process with high selectivity to metals that can be used not only to produce magnetic resonance force microscopy cantilevers, but other overhanging metallic structures as well.