Spring Chemistry 501 Seminar
UT Host: Dr. Tessa Calhoun
Speaker: Dr. Joanna Atkin
Assistant Professor Department of Chemistry
Univeristy of North Carolina at Chapel Hill
Title: “Near-Field Optical Spectroscopy for the Study of Semiconducting Nanostructures”
Abstract: Semiconducting nanostructures have been proposed as material platforms for a wide variety of photonic, electronic, and photovoltaic elements. In order to realize these applications, careful design and characterization of electronic properties such as dopant concentration, activation, and distribution are needed. I will discuss the use of near-field optical microscopy as a non-destructive method for chemical, structural, and electronic imaging in nanomaterials. Near-field optical techniques break the diffraction limit to access nanometer scale information through the lightning-rod properties of an illuminated scanning probe microscopy tip. Many nanoscale optical spectroscopies can be realized using this approach, but signal interpretation is often challenging due to convolutional effects between the tip and sample. I will discuss experimental and theoretical considerations in quantitative near-field optical microscopy in general, and then focus on a specific application, 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 high spatial resolution (< 20 nm) allows us to directly measure dopant transition abruptness and charge carrier properties in the vicinity of interfaces in single and multi-junction SiNWs, both in the infrared and the microwave spectral regimes. However, the tip is perturbative in terms of both the electromagnetic wave (frequency-resolved) and electrostatic (charge carrier redistribution) interactions, and this affects the measured results, in particular in nanostructures. Our results demonstrate the utility of near-field spectroscopy in understanding local properties of nanomaterials, but emphasize the little-understood role of the tip in scanning probe microscopies in general.
Bio: 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. She joined the University of North Carolina at Chapel Hill in 2015.
Dial-In Information
Zoom: https://tennessee.zoom.us/j/99904763018
Password: 061993
Thursday, March 25, 2021 at 4:30pm to 5:30pm
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- Chemistry
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Linda Sherman
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