Microfabrication of colloidal scanning probes with controllable tip radii of curvature

Abstract

We report the first batch-fabrication method to create colloidal scanning probes based on standard micromachining processes. Microfabrication of colloidal probe arrays having smooth surface profiles with radius of curvature ranging from nanometers to tens of microns is successfully demonstrated. A new mold filling technology is developed where bulk-etched cavities with sharp endpoints are transformed into cavities with curved endings via spin coating of a liquid filling material (photoresist). The curved profile is then replicated into a stable metallic mold by evaporating a layer of aluminum, after which mold-transfer scanning probe (SP) fabrication is conducted to create colloidal probes. Multiple control knobs were developed and characterized for accurate control of the tip radius of curvature. By adjusting the solid content of the filling material, the number of spin-coat cycles, and the cavity geometry, different mold profiles and thereby tip radii of curvature were achieved. The new controllable technology allows rapid microfabrication of singular or arrayed colloidal scanning probes with different tip radii of curvature which will be useful for many biological and nanotechnology applications.