Batch bulk-micromachined high-precision metal-on-insulator microspires and their application to scanning tunneling microscopy

A batch fabrication technology of high-precision metal-on-insulator microspires has been developed. In the fabrication process, only a self-convergent bulk micromachining by hydrofluoric acid isotropic etching is employed to sharpen fused silica. In the isotropic wet-etch process, convex corners, once they appear on the etched spires, are kept even in over-etching. This convex-corner preservation effect allows us to define the nanometer-scale profiles at the apex of the spires with micrometer-scale mask patterns. By sputtering platinum on the fabricated silica spires, we have succeeded in building exceptionally tall (0.15 mm) and nanopointed (50 nm curvature radius) metal-on-insulator spires having our designed apex structure. Clear scanning tunneling microscopy (STM) images of highly oriented pyrolytic graphite surface have been obtained by applying the microspire to an STM probe, thus verifying their applicability to an STM tip.