Application of a Modulating Technique to Detect Near-Field Signals Using a Conventional IR Spectrometer with a Ceramic Light Source

Abstract

The goal of the present study is to obtain broadband near-field infrared (IR) spectra by combining Fourier-transform infrared spectroscopy (FTIR) with scattering near-field optical microscopy (s-SNOM). A stage was added to the IR spectrometer with a ceramic light source in order to modulate the probe-sample distance, and the second harmonic component was extracted by a lock-in amplifier. The detected IR signal intensity decreased exponentially with the distance between the probe tip and an Au mirror, with a localization scale of approximately 100 nm. An area with Au islands formed by electron beam lithography was scanned with the modulation system with mapping steps of X = 80 nm and Y = 133 nm. The obtained IR intensity image matches the topographic image, indicating sub-micron spatial resolution. These results indicate that the addition of the modulation system to the broadband near-field IR spectrometer was successful in obtaining localized near-field signals and sub-micron spatial resolution, even using a ceramic IR light source. [DOI: 10.1380/ejssnt.2011.40]