(6gq) Structural and Electronic Transformations in Dynamic Semiconductor Nanomaterials

Recent advances in colloidal synthesis techniques to control size, shape and mesostructure of semiconductors have created high performance optoelectronic materials with unique properties. Semiconductor nanomaterials have been developed for applications such as optoelectronic switches, tunable photo-voltaic and light-emitting devices, high-rate electrodes for electrochemical storage and ‘smart window’ coatings. At sub-micron scales the optical and electronic properties of semiconductors are fundamentally altered by atomistic and quantum confinement effects, yielding new functionalities beyond the limits of bulk materials. Ultimately, the design of semiconductor nanomaterials for responsive applications requires precise understanding of how charges, potentials and ions behave across nanoscale interfaces.

Nanostructured semiconductors are particularly compelling for use in electrochromic ‘smart window’ coatings, which selectively filter solar radiation to offset seasonal heating, cooling and lighting loads. During my pre-doctoral work with Prof. Delia Milliron at the University of Texas I studied the electrochromic effect in metal oxide nanocrystal films. I found that by carefully controlling the electrochemical potential across a TiO₂-electrolyte interface, reversible colorations can be independently controlled in both the infrared and visible. The infrared coloration is enabled by the confinement of free electrons at the nanocrystal surface, which interact strongly with light through localized surface plasmon resonance. The small size of TiO₂ nanocrystals also allows small cations, such as Li⁺, to rapidly insert into the crystal structure at particular electrochemical potentials, inducing a visible darkening. Thus, a single nanostructured material can control infrared and visible optical coloration for next-generation ‘smart window’ coatings. Moreover, these independent measurements of distinct optical modulations paint a vivid picture of local nanoscale transformations. I have since exploited the infrared plasmonic response to make fundamental discoveries of charge transport in degenerate metal oxide nanocrystals, and probed the visible coloration of lithiated TiO₂ particles to study the kinetics of ion diffusion in situ during electrochemical charging.

My general research interest is to explore how interfacial nanostructure affects electronic and structural transformations of solution processed semiconductors. My goal is to develop precise in situ optical and electrochemical spectroscopy experiments to study the unique structure-property relationships of dynamic nanomaterials. My work is supported by the synthetic control afforded by colloidal processing techniques and atomistic models of charge and ion transport. I plan on organizing my research around three main thrusts:

1. How does nanoparticle structure impact electrochemical charging?
2. How can electronic transformations in nanostructures be controlled for responsive optical filters?
3. How do interfaces mediate crystal growth and phase transformations to form unique nanomaterials?

The nanostructure of colloidal building blocks plays a pivotal role in my current investigations of the growth of solution-processed hybrid perovskite films for photodetectors and photovoltaics. As a postdoctoral researcher in Prof. Michael Chabinyc’s group at the University of California, Santa Barbara, I am studying a layered phase of hybrid organic-inorganic perovskites that can be formed by mixing alkylammonium spacer molecules with perovskite precursors. This anisotropic nanomaterial shows tunable optical and electronic properties depending on the dimensions of confined 2-D layers. The nanoscale arrangement of spacer molecules within these layered perovskites is revealed by distinct optical characteristics that can be probed in situ during growth, and I am currently designing experiments to pinpoint the origins of defects and inhomogeneity during film growth that impact device performance.

Teaching Interests:

My driving goal as a teacher is to cultivate an engaged and responsive learning environment. During my graduate studies I worked with my doctoral advisor to design two chemical engineering courses from the ground up: an undergraduate core class in materials science for engineers, and a graduate-level course in materials physics. To encourage participation and active feedback from our students, we incorporated multiple avenues for student response, including peer-directed projects, informal quizzes and mid-semester surveys. Some of these tools I developed during a graduate course I took in engineering assessment and curriculum design. I follow these same goals as a mentor, and strive for open communication and regular feedback routines to ensure a productive relationship. I have found that my research routinely launches me back to my core chemical engineering curriculum, and I enjoy using my research as a teaching device. I have also been a consistent advocate for STEM education in public schools through my leadership role on a non-profit outreach organization I co-founded as an undergraduate in New York City. As a faculty member I will seek new opportunities to engage the local community in STEM-oriented exposure and mentorship activities.