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1. Galvanic replacement of intermetallic nanocrystals as a route toward complex heterostructures

   https://doi.org/10.1039/D0NR08255D  

   Chen, Alexander N. ; Endres, Emma J. ; Ashberry, Hannah M. ; Bueno, Sandra L. ; Chen, Yifan ; Skrabalak, Sara E. ( February 2021 , Nanoscale)

   null (Ed.)

   Galvanic replacement reactions are a reliable method for transforming monometallic nanotemplates into bimetallic products with complex nanoscale architectures. When replacing bimetallic nanotemplates, even more complex multimetallic products can be made, with final nanocrystal shapes and architectures depending on multiple processes, including Ostwald ripening and the Kirkendall effect. Galvanic replacement, therefore, is a promising tool in increasing the architectural complexity of multimetallic templates, especially if we can identify and control the relevant processes in a given system and apply them more broadly. Here, we study the transformation of intermetallic PdCu nanoparticles in the presence of HAuCl 4 and H 2 PtCl 6 , both of which are capable of oxidizing both Pd and Cu. Replacement products consistently lost Cu more quickly than Pd, preserved the crystal structure of the original intermetallic template, and grew a new phase on the sacrificial template. In this way, atomic and nanometer-scale architectures are integrated within individual nanocrystals. Product morphologies included faceting of the original spherical particles as well as formation of core@shell and Janus-style particles. These variations are rationalized in terms of differing diffusion behaviors. Overall, galvanic replacement of multimetallic templates is shown to be a route toward increasingly exotic particle architectures with control exerted on both Angstrom and nanometer-scale features, while inviting further consideration of template and oxidant choices. 

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2. Stability of Polyethylene Glycol-Coated Copper Nanoparticles and Their Optical Properties

   https://doi.org/10.3390/coatings12060776  

   Okyere, Deborah ; Manso, Ryan H. ; Tong, Xiao ; Chen, Jingyi ( June 2022 , Coatings)

   Oxidation is a corrosion reaction where the corroded metal forms an oxide. Prevention of oxidation at the nanoscale is critically important to retain the physicochemical properties of metal nanoparticles. In this work, we studied the stability of polyethylene glycol (PEG) coated copper nanoparticles (PEGylated CuNPs) against oxidation. The freshly-prepared PEGylated CuNPs mainly consist of metallic Cu which are quite stable in air although their surfaces are typically covered with a few monolayers of cuprous oxide. However, they are quickly oxidized in water due to the presence of protons that facilitate oxidation of the cuprous oxide to cupric oxide. PEG with carboxylic acid terminus could slightly delay the oxidation process compared to that with thiol terminus. It was found that a solvent with reducing power such as ethanol could greatly enhance the stability of PEGylated CuNPs by preventing further oxidation of the cuprous oxide to cupric oxide and thus retain the optical properties of CuNPs. The reducing environment also assists the galvanic replacement of these PEGylated CuNPs to form hollow nanoshells; however, they consist of ultra-small particle assemblies due to the co-reduction of gold precursor during the replacement reaction. As a result, these nanoshells do not exhibit strong optical properties in the near-infrared region. This study highlights the importance of solvent effects on PEGylated nonprecious metal nanoparticles against oxidation corrosion and its applications in preserving physicochemical properties of metallic nanostructures. 

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3. Reaction stoichiometry directs the architecture of trimetallic nanostructures produced via galvanic replacement

   https://doi.org/10.1039/D2NR06632G  

   Kar, Nabojit ; McCoy, Maximilian ; Zhan, Xun ; Wolfe, Joshua ; Wang, Zhiyu ; Skrabalak, Sara E. ( January 2023 , Nanoscale)

   Galvanic replacement (GR) of monometallic nanoparticles (NPs) provides a versatile route to interesting bimetallic nanostructures, with examples such as nanoboxes, nanocages, nanoshells, nanorings, and heterodimers reported. The replacement of bimetallic templates by a more noble metal can generate trimetallic nanostructures with different architectures, where the specific structure has been shown to depend on the relative reduction potentials of the participating metals and lattice mismatch between the depositing and template metal phases. Now, the role of reaction stoichiometry is shown to direct the overall architecture of multimetallic nanostructures produced by GR with bimetallic templates. Specifically, the number of initial metal islands deposited on a NP template depends on the reaction stoichiometry. This outcome was established by studying the GR process between intermetallic PdCu (i-PdCu) NPs and either AuCl 2 − (Au 1+ ) or AuCl 4 − (Au 3+ ), producing i-PdCu–Au heterostructures. Significantly, multiple Au domains form in the case of GR with AuCl 2 − while only single Au domains form in the case of AuCl 4 − . These different NP architectures and their connection to reaction stoichiometry are consistent with Stranski–Krastanov (SK) growth, providing general guidelines on how the conditions of GR processes can be used to achieve multimetallic nanostructures with different defined architectures. 

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4. Molecular-replacement phasing using predicted protein structures from AWSEM-Suite

   https://doi.org/10.1107/S2052252520013494  

   Jin, Shikai ; Miller, Mitchell D. ; Chen, Mingchen ; Schafer, Nicholas P. ; Lin, Xingcheng ; Chen, Xun ; Phillips, George N. ; Wolynes, Peter G. ( November 2020 , IUCrJ)

   null (Ed.)

   The phase problem in X-ray crystallography arises from the fact that only the intensities, and not the phases, of the diffracting electromagnetic waves are measured directly. Molecular replacement can often estimate the relative phases of reflections starting with those derived from a template structure, which is usually a previously solved structure of a similar protein. The key factor in the success of molecular replacement is finding a good template structure. When no good solved template exists, predicted structures based partially on templates can sometimes be used to generate models for molecular replacement, thereby extending the lower bound of structural and sequence similarity required for successful structure determination. Here, the effectiveness is examined of structures predicted by a state-of-the-art prediction algorithm, the Associative memory, Water-mediated, Structure and Energy Model Suite ( AWSEM-Suite ), which has been shown to perform well in predicting protein structures in CASP13 when there is no significant sequence similarity to a solved protein or only very low sequence similarity to known templates. The performance of AWSEM-Suite structures in molecular replacement is discussed and the results show that AWSEM-Suite performs well in providing useful phase information, often performing better than I-TASSER-MR and the previous algorithm AWSEM-Template . 

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5. Copper Oxidation Improves Dodecanethiol Blocking Ability in Area‐Selective Atomic Layer Deposition

   https://doi.org/10.1002/admi.202200587  

   Liu, Tzu‐Ling ; Bent, Stacey F. ( May 2022 , Advanced Materials Interfaces)

   In recent years, area‐selective atomic layer deposition (AS‐ALD) has attracted increasing interest for its applications in back‐end interconnect processes, and selective deposition of Al₂O₃is of particular interest because Al₂O₃can serve as an etch hard mask. However, Al₂O₃is one of the most difficult ALD systems to block. In this work, a strategy is presented to enhance the blocking ability of dodecanethiol (DDT) self‐assembled monolayers (SAMs) against Al₂O₃ALD. It is shown that by conducting DDT deposition on a slightly oxidized Cu surface, which is mainly composed of Cu₂O, rather than on a freshly acid‐etched Cu surface, which mainly consists of metallic Cu, the quality of the DDT SAM can be improved. It is further shown that the DDT SAMs formed on Cu₂O‐covered Cu substrates are about 3–4 times more effective in blocking Al₂O₃than that on acid‐etched Cu surfaces when ALD is performed under subsaturation condition. However, as the Cu oxidation process continues, CuO is formed and the blocking ability of DDT degrades. Finally, selective Al₂O₃deposition on DDT‐treated Cu/low‐kpatterns using the combined strategy of Cu oxidation and subsaturation conditions achieves selectivity of 0.99 after 4 nm of Al₂O₃ALD.

    

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