Yingjie’s paper on photoinitated transformation of nanocrystal superlattice polymorphs online

Congratulations to Yingjie, Jen-Yu, Daniel and Yuanze on publishing the paper on “Photoinitiated transformation of nanocrystal superlattice polymorphs assembled at a fluid interface

The directed assembly of nanoscale building blocks into complex superstructures is of widespread scientific and technological interest. Scientists and engineers have been intrigued by the prospects of tailoring self-assembly processes to create materials whose properties and function can be tuned through the interaction between constituent particles. In particular, recent reports of superlattice structure transformations leading to epitaxially connected nanocrystal superlattices with long-range atomic coherence have generated significant interest as a platform for novel, quasi 2D ‘designer materials’. To date, experimental methods to initiate this structure transformation have relied on rather coarse chemical or thermal triggers. Progress to bring the prospect of these nanocrystal solids to technological fruition is limited by the lack of processing methods that enable spatial programming of the transformation and the extent of the transformation.

In this article, we combine, for the first time, advances in nanocrystal self-assembly at fluid interfaces with photolithographic patterning. We demonstrate nanocrystal superlattice structure transformation (from 6-fold to 4-fold symmetric) can be spatially programmed by digital light processing and the addition of a photoacid generator to the fluid subphase. We describe our approach as the ‘optically-driven reorganization of colloidal assemblies’ (ORCA). Beyond the ability to spatially program the extent and 2D pattern of the transformation, our detailed structural and chemical analysis also provides new insights into the relationship between nanocrystal ligand coverage and superlattice structure. We quantified how increasing photodosage decreases nanocrystal ligand coverage, which in turn impacts the effective sphericity of the ligand shell and drives the hexagonal-to-square superlattice structure transformation.

The work described in this manuscript provides new understanding of and control over the thermodynamic stability and kinetic lability of ligand-passivated nanocryst

als. Building on these fundamental scientific insights, the method presents new opportunities to create nanocrystal superlattice structures with programmable structures; we anticipate that this ability will spur many new advances in the field of nanocrystal superlattices and their enabled technologies.

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