Jen-Yu’s paper (with Tangi Aubert, Wiesner group) on 3D printing in Nature Communications

Congratulations to Jen-Yu and the rest of the ream for publishing their work on Porous cage-derived nanomaterial inks for direct and internal three-dimensional printing  in Nature Communications.


The convergence of 3D printing techniques and nanomaterials is generating a compelling opportunity space to create advanced materials with multiscale structural control and hierarchical functionalities. While most nanoparticles consist of a dense material, less attention has been paid to 3D printing of nanoparticles with intrinsic porosity. Here, we combine ultrasmall (about 10 nm) silica nanocages with digital light processing technique for the direct 3D printing of hierarchically porous parts with arbitrary shapes, as well as tunable internal structures and high surface area. Thanks to the versatile and orthogonal cage surface modifications, we show how this approach can be applied for the implementation and positioning of functionalities throughout 3D printed objects. Furthermore, taking advantage of the internal porosity of the printed parts, an internal printing approach is proposed for the localized deposition of a guest material within a host matrix, enabling complex 3D material designs.

Paper on Quantum Dot Dimerization now in ACS Nano

Congratulations to Isaiah Chen (in Paulette Clancy’s group at JHU) and the rest of the team at Cornell (Jessica, Daniel, and Michelle) for publishing the paper in ACS Nano ‘the role of dimer formation in the nucleation of superlattice transformations and its impact on disorder’ 

This paper focuses on elucidating the mechanism of the self-assembly of colloidal nanocrystals to form epitaxially connected superstructures, which researchers know needs to be practically perfect to allow coherent charge transport. The community is currently unable to create superlattices with the desired fidelity because we lack an understanding of how nanocrystals assemble and attach to form a bridged superlattice.

This paper sheds light on this mechanism using a molecular-scale computational approach to simulate the assembly process, informed by molecular-scale information from cutting-edge imaging techniques to help both in setting up the initial pre-assembled starting point and validating the computational predictions. Our two key results in this paper are to (i) uncover the significant influence of dimerization during assembly; and (ii) establish precisely and quantifiably exactly how tolerant the (essentially irreversible) attachment of nanoparticles to form a fully connected superlattice will be to positional and rotational disorder in the pre-assembled system. This new definition will assist researchers to find ways to stay within these tolerances as they pursue the goal of perfectly connected superlattices.

 

Pulsing electrochemical CO2 reduction paper published in ACS Catalysis

Congratulations to Kevin, Rileigh and the rest of the team for publishing their work in ACS Catalysis (10.1021/acscatal.0c02630)

Electrochemical CO2 reduction (CO2R) on copper has garnered strong interest as a promising pathway to convert CO2 emissions into higher value chemicals including fuels and hydrocarbon feedstocks. We previously reported  (Kimura et al. ChemSusChem (2018)) that the application of a pulsed potential during CO2R improved selectivity toward converting CO2 to higher order products, suppressed undesirable H2 production, and maintained electrode stability. The working hypothesis which emerged from the initial study was that the pulsing-dependent product selectivity was related to dynamic changes in species adsorbed to the electrode surface.

In this study we set out to establish deeper fundamental insights into the mechanism by applying  in-situ techniques. We used in-situ X-ray adsorption spectroscopy to identify and monitor the bulk Cu valence state remained reduced during the pulsing, but found surface hydroxides (OHads) were adsorbing during the anodic pulsed potential. We combined these spectroscopic insights with the recent findings by Iijima et al. (ACS Catalysis (2019)), in which in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy was used to demonstrate the effect of surface hydroxides promoting CO adsorption and preventing Cu deactivation. We concluded the pulsed mechanism favors CO2 reduction and increases stability due to two effects: 1) proton desorption/displacement by OHads during the anodic potential, which suppresses H2 production and 2) the accumulation of OHads, promoting COads and preventing Cu deactivation.

 

 

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.

4D-STEM paper published in Nano Letters

Congratulations to Jessica and the rest of the team on publishing the 4D-STEM paper in Nano Letters.

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’. Although experimental protocols for the formation of high quality superlattices in which constituent nanocrystals are registered to within a single atomic bond length have been established, significant gaps persist in our fundamental understanding of several aspects of the underlying mechanism by which these structures form.

In this article, we apply advanced electron diffraction to investigate the superlattice transformation of lead chalcogenide (PbX, X=S, Se) nanocrystals leading up to 2D oriented attachment. We present unprecedented detail into the exact position and 3D crystallographic alignment of each polyhedral NC in the assembly derived from nanobeam electron diffraction pattern maps acquired with an electron microscope pixel array detector (EMPAD). This analysis reveals that the nanocrystals are strongly coupled along the <11n>AL direction and undergo translation with nearly constant in-plane atomic lattice orientation throughout the transformation. The rich experimental results presented here provide new mechanistic insights into the self-assembly and oriented attachment.

 

 

In situ GISAXS study published

Our recent work on the self-assembly of nanoparticles on a glycol surface was accepted for publication in Langmuir. Exciting in situ X-ray scattering experiments done with the amazing Detlef Smilgies at CHESS. It is also Tyler’s first paper, congrats!
https://pubs.acs.org/doi/10.1021/acs.langmuir.0c00524