Photoluminescence emission from a nanofabricated scanning probe tip made of epitaxial germanium

We discuss a new type of nanoscale photon source constituted by a micro-pyramid made of epitaxial semiconductor material (Ge) attached to a silicon cantilever optimized for Atomic Force Microscopy and shaped by means of low-current Focused Ion Beam (FIB) milling. The optical characterization of these tips demonstrates sizeable photoluminescence emission at the direct energy gap of Ge (1550 nm). We have checked by independent measurements on the nano-patterned epitaxial material prior to the tip shaping process that the photoluminescence yield is not significantly affected by FIB milling, indicating that the optical properties of the material in this wavelength range are preserved. We envisage an application of this tool as a scanning probe in apertureless scanning near-field optical microscopy.