Direct and quantitative absorptive spectroscopy of nanowires

Abstract

Photonic nanostructures exhibit unique optical properties that are attractive in many different applications. However, measuring the optical properties of individual nanostructures, in particular the absorptive properties, remains a significant challenge. Conventional methods typically provide either an indirect or qualitative measure of absorption. The objective of this thesis is to therefore demonstrate a method capable of directly and quantitatively measuring the absorptive properties of individual nanostructures. This method is based on atomic force microscope (AFM) cantilever thermometry where a bimorph cantilever is used as a heat flux sensor. These sensors operate on the principle of a thermomechanical bending response and by virtue of their dimensionality, are capable of picowatt sensitivity. To validate the use of this technique, a single silicon nanowire is measured. By attaching a silicon nanowire to a cantilever and illuminating the sample with monochromatic light, the absolute absorptance spectrum of the nanowire was measured and shown to match well with theory. This spectroscopic technique can conceivably be used to measure even smaller samples, samples which cannot be characterized using conventional methods.