Direct Observation of Early Stages of Growth of Multilayered DNA-Templated Au-Pd-Au Core-Shell Nanoparticles in Liquid Phase

We report here on direct observation of early stages of formation of multilayered bimetallic Au-Pd core-shell nanocubes and Au-Pd-Au core-shell nanostars in liquid phase using low-dose in situ scanning transmission electron microscopy (S/TEM) with the continuous flow fluid cell. The reduction of Pd and formation of Au-Pd core-shell is achieved through the flow of the reducing agent. Initial rapid growth of Pd on Au along <111> direction is followed by a slower rearrangement of Pd shell. We propose the mechanism for the DNA-directed shape transformation of Au-Pd core-shell nanocubes to adopt a nanostar-like morphology in the presence of T30 DNA and discuss the observed nanoparticle motion in the confined volume of the fluid cell. The growth of Au shell over Au-Pd nanocube is initiated at the vertices of the nanocubes, leading to the preferential growth of the {111} facets and resulting in formation of nanostar-like particles. While the core-shell nanostructures formed in a fluid cell in situ under the low-dose imaging conditions closely resemble those obtained in solution syntheses, the reaction kinetics in the fluid cell is affected by the radiolysis of liquid reagents induced by the electron beam, altering the rate-determining reaction steps. We discuss details of the growth processes and propose the reaction mechanism in liquid phase in situ

CuS2‐Passivated Au-Core, Au3Cu-Shell nanoparticles analyzed by Atomistic-Resolution Cs-Corrected STEM

Au-core, Au3Cu-alloyed shell nanoparticles passivated with CuS2 were fabricated by the polyol method, and characterized by Cs-corrected scanning transmission electron microscopy. The analysis of the high-resolution micrographs reveals that these nanoparticles have decahedral structure with shell periodicity, and that each of the particles is composed by Au core and Au3Cu alloyed shell surrounded by CuS2 surface layer. X-ray diffraction measurements and results from numerical simulations confirm these findings. From the atomic resolution micrographs, we identified edge dislocations at the twin boundaries of the particles, as well as evidence of the diffusion of Cu atoms into the Au region, and the reordering of the lattice on the surface, close to the vertices of the particle. These defects will impact the atomic and electronic structures, thereby changing the physical and chemical properties of the nanoparticles. On the other hand, we show for the first time the formation of an ordered superlattice of Au3Cu and a self-capping layer made using one of the alloy metals. This has significant consequences on the physical mechanism that form multicomponent nanoparticles

Trimetallic nanostructures: the case of AgPd–Pt multiply twinned nanoparticles

We report the synthesis, structural characterization, and atomistic simulations of AgPd–Pt trimetallic (TM) nanoparticles. Two types of structure were synthesized using a relatively facile chemical method: multiply twinned core–shell, and hollow particles. The nanoparticles were small in size, with an average diameter of 11 nm and a narrow distribution, and their characterization by aberration corrected scanning transmission electron microscopy allowed us to probe the structure of the particles at an atomistic level. In some nanoparticles, the formation of a hollow structure was also observed, that facilitates the alloying of Ag and Pt in the shell region and the segregation of Ag atoms on the surface, affecting the catalytic activity and stability. We also investigated the growth mechanism of the nanoparticles using grand canonical Monte Carlo simulations, and we have found that Pt regions grow at overpotentials on the AgPd nanoalloys, forming 3D islands at the early stages of the deposition process. We found very good agreement between the simulated structures and those observed experimentally

Direct Observation of Early Stages of Growth of Multilayered DNA-Templated Au-Pd-Au Core-Shell Nanoparticles in Liquid Phase

We report here on direct observation of early stages of formation of multilayered bimetallic Au-Pd core-shell nanocubes and Au-Pd-Au core-shell nanostars in liquid phase using low-dose in situ scanning transmission electron microscopy (S/TEM) with the continuous flow fluid cell. The reduction of Pd and formation of Au-Pd core-shell is achieved through the flow of the reducing agent. Initial rapid growth of Pd on Au along direction is followed by a slower rearrangement of Pd shell. We propose the mechanism for the DNA-directed shape transformation of Au-Pd core-shell nanocubes to adopt a nanostar-like morphology in the presence of T30 DNA and discuss the observed nanoparticle motion in the confined volume of the fluid cell. The growth of Au shell over Au-Pd nanocube is initiated at the vertices of the nanocubes, leading to the preferential growth of the {111} facets and resulting in formation of nanostar-like particles. While the core-shell nanostructures formed in a fluid cell in situ under the low-dose imaging conditions closely resemble those obtained in solution syntheses, the reaction kinetics in the fluid cell is affected by the radiolysis of liquid reagents induced by the electron beam, altering the rate-determining reaction steps. We discuss details of the growth processes and propose the reaction mechanism in liquid phase in situ.</p

Direct Observation of Early Stages of Growth of Multilayered DNA-templated Au-Pd-Au Core-Shell Nanoparticles in Liquid Phase - File set

<div>The files in this dataset contain raw scanning transmission electron microscopy (STEM) images and the video files recorded from the screen of the STEM during the dynamic data acquisition, along with the Supplementary Materials Information. <br></div><div>Gatan files have a DM3 file extension and TIA files have EMI/SER file extensions. To view and process bright field TEM images, the Reader can use a Gatan free offline software called Gatan Microscopy Suite® software (GMS, Gatan Microscopy Suite® (GMS) software version 3.x - http://www.gatan.com/installation-instructions). .</div><div>To view the HAADF-STEM images, the program Emispec ES Vision (FEI, https://www.fei.com/software/) or TIA_Reader.jar plugin from ImageJ (Image J, (https://imagej.net/Welcome ?), plug-in (https://imagej.nih.gov/ij/plugins/tia-reader.html). </div><div><br></div><div>The STEM data uploaded herein are used to generate figures, linear plots, and tables associated with the data analysis in the manuscript.</div><div><br></div><div>Number of files in corresponding Figures:</div><div>Figure 1: 5 files;</div><div>Figure 2: 6 files;</div><div>Figure 3: 6 files;</div><div>Figure 4: 19 files;</div><div>Figure 5: 4 files;</div><div>Figure 6: 2 files;</div><div>Figure 7: 13 files.</div><div><br></div><div>Supplementary Materials provide additional information on nanoparticls synthesis, electron dose rate and dose calculations, Pd shell growth calculations, and cited references. </div><div>The associated files include SF 1, SF 2, Supplementary Table 1, and Supplementary Table 2. </div><div><br></div><div>Number of files in Supplementary Materials:</div><div>Supplementary Figure 1: 6 files;</div><div>Supplementary Figure 2: 12 files;</div><div>Supplementary Figure 3: 13 files;</div><div>Supplementary Table 1: 1 file;</div><div>Supplementary Table 1: 1 file.</div><div><br></div

Strain-release mechanisms in bimetallic core-shell nanoparticles as revealed by Cs-corrected STEM

Lattice mismatch in a bimetallic core–shell nanoparticle will cause strain in the epitaxial shell layer, and if it reaches the critical layer thickness misfit dislocations will appear in order to release the increasing strain. These defects are relevant since they will directly impact the atomic and electronic structures thereby changing the physical and chemical properties of the nanoparticles. Here we report the direct observation and evolution through aberration-corrected scanning transmission electron microscopy of dislocations in AuPd core– shell nanoparticles. Our results show that first Shockley partial dislocations (SPD) combined with stacking faults (SF) appear at the last Pd layer; then, as the shell grows the SPDs and SFs appear at the interface and combine with misfit dislocations, which finally diffuse to the free surfaces due to the alloying of Au into the Pd shell. The critical layer thickness was found to be at least 50% greater than in thin films, confirming that shell growth on nanoparticles can sustain more strain due to the tridimensional nature of the nanoparticles

Cs-corrected STEM characterisatioin of Au@Pd Core@Shell nanocubes

Bimetallic (BM) nanoparticles exhibit different properties depending upon the variation of composition and structure. In this work, we report the detailed analysis of core-shell Au-Pd nanocubes obtained by seed mediated growth process, investigated by means of aberration-corrected scanning transmission electron microscopy (STEM), conventional transmission electron microscopy (TEM), tomography 3D reconstruction and strain mapping. Strain mapping and 3D reconstruction showed for the first time that the nanocube is distorted inwards at all faces. The nano-tripod analysis showed the presence of an incomplete FCC layer only in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures. The characterization revealed that nanocubes are formed by concave high index facets of the {410} family with all six faces distorted. The distortion of all faces of nanocube is demonstrated using tomography 3D reconstruction. Detailed analysis of nano-beam electron diffraction (NBD) and high resolution STEM images showed that Pd atoms grow epitaxially on the Au core in both structures. The stability of the nanostructure is provided by the strain. The nano-tripod analysis showed the presence of an incomplete FCC layer in the surface that acts as an HCP layer. The study showed that there is no loss of crystallinity by the presence of two metals in both the structures