A variable cryogenic temperature near-field scanning optical microscope

We describe a novel variable (cryogenic) temperature near-field scanning optical microscope (VT-NSOM) designed specifically for submicron imaging of materials and devices over a temperature range of 12–300 K. In high vacuum, we cool only the sample stage of the compact NSOM, thereby maintaining a large scan area (35 μm×35 μm) at low temperatures and enabling rapid (∼30 min) temperature changes. With incorporation into an external conventional optical microscope, the VT-NSOM is capable of imaging a single submicron feature over the entire temperature range. We demonstrate the performance of the instrument by examining the photoresponse of threading dislocation defects in relaxed GeSi films.