It
has been a longstanding challenge to rationally synthesize thin
films of organic two-dimensional (2D) crystals with large single-crystalline
domains. Here, we present a general strategy for the creation of 2D
crystals of covalent organic frameworks (COFs) on the water surface,
assisted by a charged polymer. The morphology of the preorganized
monomers underneath the charged polymer on the water surface and their
diffusion were crucial for the formation of the organic 2D crystals.
Thin films of 2D COFs with an average single-crystalline domain size
of around 3.57 ± 2.57 μm2 have been achieved,
and their lattice structure, molecular structure, and grain boundaries
were identified with a resolution down to 3 Å. The swing of chain
segments and lattice distortion were revealed as key factors in compensating
for the misorientation between adjacent grains and facilitating error
corrections at the grain boundaries, giving rise to larger single-crystalline
domains. The generality of the synthesis method was further proved
with three additional 2D COFs. The oriented single-crystalline domains
and clear grain boundaries render the films as model materials to
study the dependence of the vertical conductivity of organic 2D crystals
on domain sizes and chemical structures, and significant grain boundary
effects were illustrated. This study presents a breakthrough in the
controlled synthesis of organic 2D crystals with structural control
at the molecular level. We envisage that this work will inspire further
investigation into the microstructure–intrinsic property correlation
of 2D COFs and boost their application in electronics.
There is demand for scaling up 3D printing throughput, especially for the multi-photon 3D printing process that provides sub-micrometer structuring capabilities required in diverse fields. In this work, high-speed projection multi-photon printing is combined with spatiotemporal focusing for fabrication of 3D structures in a rapid, layer-by-layer, and continuous manner. Spatiotemporal focusing confines printing to thin layers, thereby achieving print thicknesses on the micron and sub-micron scale. Through projection of dynamically varying patterns with no pause between patterns, a continuous fabrication process is established. A numerical model for computing spatiotemporal focusing and imaging is also presented which is verified by optical imaging and printing results. Complex 3D structures with smooth features are fabricated, with millimeter scale printing realized at a rate above 10−3 mm3 s−1. This method is further scalable, indicating its potential to make fabrications of 3D structures with micro/nanoscale features in a practical time scale a reality.
Nanolithographic printing by direct laser writing (DLW) photopolymerization has attracted increased attention in recent years, as the speed of this printing has increased, while the feature sizes that have been realized have decreased well into the nanoscale regime. Specifically, isopropyl thioxanthone (ITX) has been utilized as one of the common photoinitiators in DLW polymerization processes because of its high-efficiency photoinitiating abilities and its ability to have its initiation properties inhibited through the application of a second wavelength of light. However, improved photoinitiating materials that are built from this successful archetype are required, by both academic and industrial circles, if advanced highthroughput nanomanufacturing techniques are to be implemented. Here, nextgeneration thioxanthone-based photoinitiators with tailored optical and charge transfer properties were computationally designed and subsequently synthesized. Particularly, branches with specifically modulated electron donor and electron acceptor qualities, relative to the ITX core, were coupled to the initial thioxanthone substrate. After having their molecular and optical properties characterized in full, it was evident that these initiators possessed a clear advancement in terms of photopolymerization initiation relative to ITX. As such, a champion photoinitiator chemistry was brought forward to demonstrate enhanced two-photon polymerization DLW such that superresolution properties were exhibited. In this way, we introduce a clear means by which to systematically design future photoinitiators for enhanced two-photon polymerization DLW nanoprinting processes.
We document the design, synthesis, and characterization of the first low glass transition temperature, n-type (i.e., preferentially-reduced) radical polymer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.