Research

Electrochromic Materials and Devices

Electrochromic transitional metal oxides with intervalence electrons and excellent electrochemical kinetics show dramatic color changes at various valence states upon redox reactions, which enable them as an emerging category of energy storage supercapacitors with visualized energy status. Yet, the ion insertion/de-insertion induced charge transfer nanomechanics, i.e., repetitive electrode size change and generated stress/strain during electrochemical cycling, termed the “nanomechanical breathing” effect, has remained unexplored. Electro-chemo mechanics is the focus here due to its intimate correlation to the elastic and plastic deformation at the interface and device durability. 

Advanced Characteristics via AFM

Atomic Force Microscopy (AFM) is a powerful tool in materials science, physics, and engineering for characterizing surfaces at the nanoscale. This project investigates the surface characteristics of tomographic, mechanical, and electrical properties: 1) The AFM measures force-displacement curves by recording the force between the tip and the sample as a function of the distance the tip moves to reveal the mechanical properties at the nanoscale; 2) In Kelvin Probe Force Microscopy (KPFM), a conducting tip with a known work function is given an AC bias that scans the sample surface. This process localizes the contact potential difference between the tip and the sample surface, which is then used to generate a surface potential map; 3) In-situ/Operando AFM is an informative technique used to observe and measure the properties of materials in real-time under operational conditions. This method enables the study of dynamic changes and interactions on material surfaces while they are actively undergoing processes such as chemical reactions, electrical operations, or mechanical stress.

Microelectronics and Sensors

This translational research focuses on developing extended gate field-effect transistor (EGFET) miniaturized sensor systems for real-time continuous monitoring of ionic concentrations. The design offers high sensitivity and specificity in detecting fluoride ions released by perfluorosulfonic acid membrane-based fuel cells. We characterize both N-type and P-type metal-oxide field effect transistors (MOSFET) in the transfer characteristics (Id vs. Vgs) and output (Id vs. Vds) characteristics, across a wide range of concentrations, from parts per million to parts per billion, without buffer saline or redox markers. The small, user-friendly, and cost-effective sensor systems hold great potential to be integrated into fuel cell electrical vehicles as state-of-health indicators for degradation prediction and predictive maintenance. The transistor-based current and voltage amplifiers also show broad applications in environmental and biosensing.