Thermal Dynamics Effects using Pulse-Shaping Laser Sintering of Printed Silver Inks.

In recent years, additive manufacturing has been evolving towards flexible substrates for the fabrication of printable electronic devices and circuits. Generally polymer-based, these emerging substrates suffer from their heat sensitivity and low glass-transition temperatures. As such they require new highly-localized sintering processes to treat the electronic inks without damaging the polymer-based substrate. Laser-based sintering techniques have shown great promises to achieve high-quality sintering locally, while controlling the heat penetration to preserve the polymer substrates integrity. In this report, we explore new optimization pathways for dynamic laser-based sintering of conductive silver inks. Multiple passes of a pulsed laser are first performed while varying pulse train frequencies and pulse energies as an attempt to optimize the properties of the silver inks. Then, time-domain pulse shaping is performed to alter the properties of the conductive inks. Together, these pathways allow for the careful control of the time-domain laser energy distribution in order to achieve the best electronic performances while preserving the substrate's integrity. Sheet resistance values as low as 0.024Ω/□ are achieved, which is comparable to conventional 1-hour oven annealing, with the processing time dramatically reduced to the milisecond range. These results are supported by finite element modeling of the laser-induced thermal dynamics.

Molecular self-organization in cylindrical nanocavities.

We studied molecular organization in cylindrical nanocavities using liquid crystals. NMR analysis shows high surface-induced ordering way above the bulk critical temperature. The surface-order evolution reveals replacement of the isotropic phase by a paranematic phase and surface-induced disordering in the nematic phase. Due to strong surface potential and nanoconfinement, complete wetting and continuous evolution of the surface-order parameter are observed through the nematic-paranematic transition. As we show, the counter-intuitive absence of complete phase transition at the interface while an abrupt phase transition was measured in the averaged order parameter is in good agreement with established theories.