FIP Seminar: Near-field microscopy for nanoscale materials characterization

Conventional far-field optical spectroscopic techniques can provide valuable information about structural, electronic, and temporal properties of materials. However, they are also subject to the diffraction limit of light, leading to difficulties resolving important interfacial information. Near-field microscopy techniques, in contrast, can break the diffraction limit through the use of a nanometer probe to provide high spatial resolution and access to novel material excitations, but interpretation can be challenging due to the convolutional effects of the near-field interaction. I will discuss the use of near-field optical microscopy as a non-destructive method for in operando chemical, structural, and electronic imaging in nanomaterials, focusing on the study of axially-doped silicon nanowires (SiNWs). We can detect local changes in the electrically-active doping concentration from the free-carrier absorption in both n-type and p-type doped SiNWs. The ~10 nm spatial resolution, 1/1000th the wavelength, allows us to directly measure dopant transition abruptness and charge carrier properties in the vicinity of interfaces in single and multi-junction SiNWs. I will discuss experimental and computational considerations in near-field microscopy across a wide spectral range, focusing on applications that demonstrate the importance of understanding the influence of the nanoscale probe and controlling near-field interactions. Our studies allow us to uniquely characterize how local properties affect functionality for optoelectronic and photovoltaic devices.

Joanna Atkin obtained her B.S. from Victoria University of Wellington, in New Zealand. She completed her PhD at Columbia University in New York, and went on to work as a postdoctoral researcher at the University of Washington and the University of Colorado, Boulder, where she worked on the development of near-field spectroscopy techniques. She joined the University of North Carolina at Chapel Hill in 2015. Her research focuses on advancing near-field spectroscopy for photonic, energy and biological applications. She has received an NSF CAREER award for her work characterizing semiconducting nanostructures.