Apertureless near-field scanning Raman microscopy using reflection scattering geometry

Abstract

The combination of near-field scanning optical microscopy and Raman spectroscopy provides chemical/structural specific information with nanometer spatial resolution, which are critically important for a wide range of applications, including the study of Si devices, nanodevices, quantum dots, single molecules of biological samples. In this paper, we describe our near-field Raman study using apertureless probes. Our system has two important features, critical to practical applications. (1) The near-field Raman enhancement was achieved by Ag coating of the metal probes, without any preparation of the sample, and (2) while all other apertureless near-field Raman systems were constructed in transmission mode, our system works in the reflection mode, making near-field Raman study a reality for any samples. We have obtained the first 1D Raman mapping of a real Si device with 1 s exposure time. This is a very significant development in near-field scanning Raman microscopy as it is the first demonstration that this technique can be used for imaging purpose because of the short integration time. In addition, the metal tips used in our set-up can be utilized to make simultaneous AFM and electrical mappings such as resistance and capacitance that are critical parameters for device applications.