PhD Dissertation Defense by Chih-Feng Wang on Near-Field and Far-Field Microscopic and Spectroscopic Characterizations of Coupled Plasmonic, Excitonic and Polymeric Materials

Departmental News

Chih-Feng Wang

Posted: August 11, 2019

Date: Monday, August 19th, 2019  

Time: 1:00 PM

Location:  CHTM, Room 101

Map to CHTM:

ADA Accommodations are available.


Mr. Chih-Feng Wang, Ph.D. Candidate

Committee members:

Dr. Terefe G. Habteyes, Committee Chair, Chemistry
Dr. Kevin J. Malloy, P&A (Emeritus)
Dr. Alejandro Manjavacas, P&A
Dr. Hou-Tong Chen, LANL
Dr. Oleg Mitrofanov, UCL


The properties of localized surface plasmon (LSP) have been broadly applied for chemical sensing, surface enhanced Raman spectroscopy, biomedical imaging, and photothermal treatment. By exploiting the well-established plasmonic effects, the spectroscopic analysis of intriguing quantum phenomena, i.e. excitonic interband and intersubband (ISB) transition in the semiconductor heterostructures, was boosted in both far- and near-field optical measurements. For the far-field characterization, the colloidal plasmonic nanoparticles, e.g. Au nanorods (AuNRs), were used to increase the quantum efficiency of InGaAs/GaAs single quantum well such that the LSP enhancement mechanism of absorption (excitation) and spontaneous emission (Purcell effect) were distinguished by analyzing the temperature dependent photoluminescence (PL) LSP enhancement factors at different GaAs capping layer thickness. The results suggest that colloidal plasmonic nanoparticles can be used as nanoprobes for investigating carrier transport phenomena in arbitrary semiconductor heterostructures. Furthermore, plasmonic, excitonic and polymeric materials are investigated using scattering-type scanning near-field optical microscopy (s-SNOM) that achieve a few nanometers spatial resolution. Using poly (4-vinylpyridine) (P4VP) polymer as a model system in vibrational infrared imaging, the vertical sensitivity of s-SNOM is analyzed quantitatively. This has been demonstrated on sloped ultra-thin P4VP film resulting in 5 nm vertical sensitivity restricted by near-field phase reversal contrasts and signal-to-noise-ratio of Au substrate. By developing a model that does not include that probe dimension, the dielectric constant of the polymer is extracted from the near-field images obtained using mid-infrared excitation wavelengths. Finally, the coupling effect of intersubband transitions with infrared plasmonic antennae is investigated using broadband infrared source Fourier transform infrared (FTIR), known as nano-FTIR. This approach has allowed us to investigate the coupling effect by spectroscopically probing individual plasmonic nanoantenna placed on AlInAs/InGaAs quantum wells. This work is the first observation on the strong light-matter interaction in the single nanoantenna regime and mapping dispersion characteristics of the nanoantenna and ISB polariton states in QWs by probing a set of nanoantennae of different sizes.