PIEZORESISTIVE CANTILEVERS AS OPTICAL SENSORS FOR SCANNING NEAR-FIELDMICROSCOPY

To combine the high lateral resolution of AFM with near-field optical measurements, we propose the use of microfabricated piezoresistive can tilevers as miniaturized photosensitive elements. The silicon-based se nsors consist of a p-doped piezoresistive path, which also includes th e tip. The resistance of this path can be changed either by pressure o n the lever or by light. For combined optical and topographical measur ements, an evanescent field is created. Because the AFM tip is the onl y part of the cantilever that is exposed to the evanescent field, the tip can be used as a near-field optical probe. It is possible to extra ct the exponential decay of the evanescent field from combined force/o ptical measurements. To decouple optical and topographical information , the intensity of the evanescent field is modulated and the optical s ignal is measured with the lock-in technique.