Undergraduate Honors Theses

Thesis Defended

Spring 2013

Document Type

Thesis

Department

Physics

First Advisor

Prof. Markus Raschke

Abstract

Scattering scanning near-field optical microscopy (s-SNOM) is a powerful technique for measuring spectroscopic properties of materials with spatial resolution previously unobtainable due to the diffraction limit. s-SNOM combines scanning probe microscopy (SPM) with spectroscopy to provide sub-diffraction limited spatial resolution information about optical and related properties of matter. Discriminating the weak elastic s-SNOM signal from various undesirable background signals is critical to the success of s-SNOM as a measurement technique. Traditionally this discrimination is achieved through lock-in detection, in which the s-SNOM signal is restricted to, and measured at harmonics of an atomic force microscope tip oscillation frequency Ω. However, this detection technique neglects information at all undetected harmonics. To overcome this loss of information, for my honors thesis, I developed a new s-SNOM detection scheme based upon the real-time acquisition of the s-SNOM signal to ensure no information is lost. With this new detection scheme I have been able to simulate gated detection elastic s-SNOM –a measurement which has not yet been realized experimentally– and determine that it provides no more than background-ridden information readily obtainable with lock-in detection. I have also been able to generate, for the first time, an experimental reconstruction of the distance dependence of the tip-sample interaction for elastic s-SNOM measurements and compare it to theoretical models.

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