Extending the Possibilities of Near-Field Scanning Optical Microscopy for Simultaneous Topographical and Chemical Force Imaging

Abstract

The Near-field Scanning Optical Microscope (NSOM) is an innovative new form of surface microscopy, which can be used to obtain local spectroscopic information about surfaces, enabling the characterization of nanometer-sized regions. The most important component of this instrument is the scanning probe tip. In this paper, we discuss the production of a novel fiber optic probe that can be used in local spectroscopy with an NSOM, but also for simultaneous imaging of topography and chemical forces. The probe consists of a bent, tapered silicon dioxide optical fiber. We have determined the rates of selective wet chemical etching of germanium dioxide doped pure silica optical fibers and used this information to optimize the probe etching process. A systematic approach for the development and testing of such probes is presented. The performance of the optical probes was characterized using surfaces prepared by the technique of microcontact printing. Phase and friction images of these surfaces were obtained using both standard atomic force microscopy tips and the optical fiber probe. The new optical probe was capable of distinguishing between different chemical regions on the patterned surface.