Printing Nanoscale Things: Metals, Oxides, and Quantum Dots: Special Nano/Bio Seminar

Seminar | August 29 | 4-5 p.m. | 177 Stanley Hall

 Prof. Yeon Sik Jung, KAIST, Materials Science & Engineering

 Berkeley Nanosciences and Nanoengineering Institute

This talk will introduce deep-nanoscale fabrication technologies based on synergic combinations of self-assembly, photolithography, and transfer-printing applicable to a variety of material systems including polymers, oxides, metals, quantum nanostructures for high-performance sensors, photovoltaics, and displays.

In particular, this talk will report on our recent innovation: highly precise patterning of colloidal QDs in omni-resolution scale (single-QD resolution up to entire film) using programmed self-assembly. Our immersion transfer-printing (iTP) enables a printing of a full-color QD array with unprecedented resolution of > 350 PPD. The electroluminescent QD light-emitting diodes (EL-QLEDs) fabricated using our technique exhibit excellent current efficiency and EQE, outperforming previously reported transfer-printed devices by an order of magnitude.

At the second part of this talk, I will introduce a highly effective strategy to enhance the photoluminescence (PL) of QD composite films through an assembly of QDs and poly(styrene-b-4-vinylpyridine)) (PS-b-P4VP) block copolymer (BCP). A BCP matrix casted under controlled humidity provides multi-scale phase-separation features based on (1) sub-μm-scale spinodal decomposition between polymer-rich and water-rich phases and (2) sub-10-nm-scale microphase separation between polymer blocks. The BCP-QD composite containing bi-continuous random pores achieves significant enhancement of both light absorption and extraction efficiencies via effective random light scattering. Moreover, the microphase-separated morphology substantially reduces the Förster resonance energy transfer efficiency from 53% (pure QD film) to 22% (BCP-QD composite), collectively achieving an unprecedented 21-fold enhanced PL over a broad spectral range.

At the third part, this talk will demonstrate woodpile-structured Ir, consisting of 3D-printed, highly-ordered Ir nanowire building blocks, as an exemplary catalyst structure to markedly improve oxygen evolution reaction (OER) mass activity via combined enhancements of electrochemically active surface area (ECSA) and ECSA-specific activity compared to conventional nanoparticle-based catalysts. This well-controlled geometry afforded a 36-fold enhancement in the mass activity of the OER catalyst when used in a single-cell PEMWE, compared to the case of using Ir nanoparticles. Systematic control of the 3D geometry reveals that facile transport of evolved O2 gas bubbles is an important contributor for the improved ECSA-specific activity and mass activity.

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Yeon Sik Jung did his PhD at MIT and postdoc here at LBNL (Go Bears!) in 2009. This year he was selected for membership in Y-KAST.

 leesw@berkeley.edu