Insulating tip for scanning near-field microwave microscopes: Application to van der Waals semiconductor imaging

Scanning nonlinear dielectric microscopy, a scanning near-field microwave microscopy (SNMM) technique, has been effectively used for characterizing semiconductor materials and devices by detecting variations in capacitance between a conductive tip and sample. However, for semiconductors without surface insulating layers, either native oxides or intentionally fabricated ones, conventional conductive tips are unsuitable because direct tip–sample contact induces charge injection, hampering the imaging of intrinsic semiconductor properties, particularly dominant carrier concentration distributions. To address this limitation, we propose an insulating tip, prepared by depositing a thin insulating layer on a conductive tip. We demonstrate that this insulating tip enables the imaging of intrinsic semiconductor properties while preventing charge injection. Our approach can be extended to other SNMM techniques, thereby broadening their applications in semiconductor material and device characterization.