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Annealing without Heat: Materials Processing using Photons

Annealing without Heat: Materials Processing using Photons

Wednesday, May 20, 2020 at 4:00 pm
Prof. Julia Hsu, University of Texas, Dallas

Annealing using hot plates or ovens is a common method to stimulate chemical reactions or phase transformation in materials, to remove remnant reactants or solvents, or to improve a material’s crystallinity or electrical properties. However, it posts insurmountable challenges when making metal oxide films on flexible substrates such as paper or plastics, because the high temperature needed to convert or activate metal oxides can damage the low-temperature substrate materials and the drastically different coefficient of thermal expansion (CTE) of the film and the substrate would lead to mechanical failures in the brittle oxide films. In this talk, I will discuss how we use to light to initiate metal oxide conversion from sol gel precursor films, using it to form patterns without needing photoresist. Additionally, for high-speed roll-to-roll processing envisioned for large-scale manufacturing, typical annealing time of 10 minutes will translate to a unrealistic oven of 100 m long (at 10 m/min). We recently demonstrate replacing thermal annealing with photonic curing. In photonic curing, short pulses (25 µs to 100 ms) of broadband (200 – 1500 nm) light from a xenon flash lamp are delivered to the sample. The energy is preferentially absorbed by the film, leading to selective heating of the film while the substrate remains cool, hence avoiding damaging the substrate or causes thermal stress in the film from CTE mismatch. I will discuss the application of this approach to make organic-inorganic halide perovskite solar cells and ZrO2 dielectrics.

Biography: Julia W. P. Hsu is Professor of Materials Science and Engineering and Texas Instruments Distinguished Chair in Nanoelectronics at the University of Texas at Dallas. She has a B.S.E. from Princeton University and a Ph.D. in Physics from Stanford University and is a Fellow of the American Physical Society, the Materials Research Society and the American Association for Advancement of Science. Her research is wide ranging and includes transition metal dichalcogenide and metal oxide nanomaterials, and inorganics and organic-based solar cells.