A MULTIPURPOSE SCANNING NEAR-FIELD OPTICAL MICROSCOPE - REFLECTIVITY AND PHOTOCURRENT ON SEMICONDUCTOR AND BIOLOGICAL SAMPLES

A multipurpose scanning near field optical microscope (SNOM) operating at ambient pressure is described with the aim of characterizing: the inner parts of biological molecules and any semiconductor or metal mic rostructure. Therefore, in addition to the requirements of reliability and mechanical stability we have carefully considered analyzing a sam ple with all available geometries for input/output of photons, in orde r to get as much information as possible. The SNOM unit consists of tw o separable cylindrical supports; the lower one contains the sample ho lder mounted on top of a piezoelectric scanner which is contained in a motor controlled x-y-z stage.; A piezo-modulated stretched optical fi ber with a few tens of nanometer pinhole and a shear-force apparatus m ounted inside the top cylinder allow for topography measurements. The reflectivity of the sample can be measured by applying different metho ds: the sample can be illuminated on top by an external source, as wel l as by the optical fiber used for the detection of the reflectivity s ignal. An aperture in the lower cylinder allows for illumination of th e sample on the back: in this case the fiber collects the evanescent w ave induced at the top of the sample. Another aperture in the lower cy linder allows measurement of the reflected light which includes a cont ribution due to the interaction with the fiber. Also photocurrent expe riments can be easily performed by illuminating the sample with the fi ber and detecting the transmitted signal using a current-voltage conve rter mounted inside the top cylinder. A video-camera that can reach 17 0 enlargements is mounted on the top cylinder for positioning the fibe r on particular regions of the sample. Reflectivity and photocurrent m easurements have been performed on uncoated neurons, CsI compound, Au/ GaAs, and PtSi/Si systems,reaching a resolution well below the diffrac tion limit. (C) 1998 American Institute of Physics. [S0034-6748(98)004 09-2].