Biobased Polymers Enabling the Synthesis of Ultralong Silver Nanowires and Other Nanostructures.

Conventional polyol synthesis of silver nanowires has exclusively relied on polyvinylpyrrolidone (PVP), a nonbiodegradable polymer with no viable alternatives. The underlying reaction mechanism remains unclear. Herein, we discovered a new sustainable solution by employing biobased cellulose derivatives, including hydroxyethyl cellulose (HEC), as effective substitutes for PVP.

Development of a ReaxFF Reactive Force Field for Pt/Cl Systems with Application to Platinum Metal Etching with Chlorine and Hydrogen Chloride Gases.

In this study, we present the development of a ReaxFF Pt/Cl/H reactive force field designed to elucidate the etching process by Cl for Pt surfaces. The ReaxFF force field parameters were optimized based on a quantum mechanical training set, which included adsorption energies of Cl and dissociation of HCl on Pt(100) and Pt(111) surfaces, energy/volume relations of PtCl crystals, and Cl diffusion on Pt(100) and Pt(111) surfaces. The predictive capability of the force field was further established through molecular dynamics simulations, which investigated the interactions of Cl and HCl molecules with the (100) and (111) surfaces of c-Pt crystalline solid slabs.

Structural classification of Ag and Cu nanocrystals with machine learning.

We use machine learning (ML) to classify the structures of mono-metallic Cu and Ag nanoparticles. Our datasets comprise a broad range of structures - both crystalline and amorphous - derived from parallel-tempering molecular dynamics simulations of nanoparticles in the 100-200 atom size range. We construct nanoparticle features using common neighbor analysis (CNA) signatures, and we utilize principal component analysis to reduce the dimensionality of the CNA feature set.

Elucidating the Role of Reduction Kinetics in the Phase-Controlled Growth on Preformed Nanocrystal Seeds: A Case Study of Ru.

This study demonstrates the crucial role of reduction kinetics in phase-controlled synthesis of noble-metal nanocrystals using Ru nanocrystals as a case study. We found that the reduction kinetics played a more important role than the templating effect from the preformed seed in dictating the crystal structure of the deposited overlayers despite their intertwined effects on successful epitaxial growth. By employing two different polyols, a series of Ru nanocrystals with tunable sizes of 3-7 nm and distinct patterns of crystal phase were synthesized by incorporating different types of Ru seeds.

Uneven Strain Distribution Induces Consecutive Dislocation Slipping, Plane Gliding, and Subsequent Detwinning of Penta-Twinned Nanoparticles.

Twin structures possess distinct physical and chemical properties by virtue of their specific twin configuration. However, twinning and detwinning processes are not fully understood on the atomic scale. Integrating high resolution transmission electron microscopy and molecular dynamic simulations, we find tensile strain in the asymmetrical 5-fold twins of Au nanoparticles leads to twin boundary migration through dislocation sliding (slipping of an atomic layer) along twin boundaries and dislocation reactions at the 5-fold axis under an electron beam.

Minimum Free-Energy Shapes of Ag Nanocrystals: Vacuum vs Solution.

We use two variants of replica-exchange molecular dynamics (MD) simulations, parallel tempering MD and partial replica exchange MD, to probe the minimum free-energy shapes of Ag nanocrystals containing 100-200 atoms in a vacuum, ethylene glycol (EG) solvent, and EG solvent with a PVP polymer containing 100 repeat units. Our simulations reveal a shape intermediate between a Dh and an Ih, a Dh-Ih, that has distinct structural signatures and magic sizes. We find several prominent features associated with entropy: pure FCC nanocrystals are less common than FCC crystals containing stacking faults, and crystals with the minimum potential energy are not always preferred over the range of relevant temperatures.

Diffusion growth mechanism of penta-twinned Ag nanocrystals from decahedral seeds.

Crystals with penta-twinned structures can be produced from diverse fcc metals, but the mechanisms that control the final product shapes are still not well understood. By using the theory of absorbing Markov chains to account for the growth of penta-twinned decahedral seeds via atom deposition and surface diffusion, we predicted the formation of various types of products: decahedra, nanorods, and nanowires. We showed that the type of product depends on the morphology of the seed and that small differences between various seed morphologies can lead to significantly different products.

Theory of Anisotropic Metal Nanostructures.

A significant challenge in the development of functional materials is understanding the growth and transformations of anisotropic colloidal metal nanocrystals. Theory and simulations can aid in the development and understanding of anisotropic nanocrystal syntheses. The focus of this review is on how results from first-principles calculations and classical techniques, such as Monte Carlo and molecular dynamics simulations, have been integrated into multiscale theoretical predictions useful in understanding shape-selective nanocrystal syntheses.

Chloride enables the growth of Ag nanocubes and nanowires by making PVP binding facet-selective.

Solution-phase synthesis of metal nanocrystals with multiple additives is a common strategy for control over nanocrystal shape, and thus control over their properties. However, few rules are available to predict the effect of multiple capping agents on metal nanocrystal shapes, making it hard to rationally design synthetic conditions. This work uses a combination of seed-mediated growth, single-crystal electrochemistry, and DFT calculations to determine the roles of PVP and Cl in the anisotropic growth of single-crystal and penta-twinned silver nanocrystals.

Nanoparticle Assembly and Oriented Attachment: Correlating Controlling Factors to the Resulting Structures.

Nanoparticle assembly and attachment are common pathways of crystal growth by which particles organize into larger scale materials with hierarchical structure and long-range order. In particular, oriented attachment (OA), which is a special type of particle assembly, has attracted great attention in recent years because of the wide range of material structures that result from this process, such as one-dimensional (1D) nanowires, two-dimensional (2D) sheets, three-dimensional (3D) branched structures, twinned crystals, defects, etc. Utilizing in situ transmission electron microscopy techniques, researchers observed orientation-specific forces that act over short distances (∼1 nm) from the particle surfaces and drive the OA process.

Green chemistry and first-principles theory enhance catalysis: synthesis and 6-fold catalytic activity increase of sub-5 nm Pd and Pt@Pd nanocubes.

Synthesizing metal nanoparticles with fine control of size, shape and surface properties is of high interest for applications such as catalysis, nanoplasmonics, and fuel cells. In this contribution, we demonstrate that the citrate-coated surfaces of palladium (Pd) and platinum (Pt)@Pd nanocubes with a lateral length <5 nm and low polydispersity in shape achieve superior catalytic properties. The synthesis achieves great control of the nanoparticle's physico-chemical properties by using only biogenic reagents and bromide ions in water while being fast, easy to perform and scalable.

OptiBoost: A method for choosing a safe and efficient boost for the bond-boost method in accelerated molecular dynamics simulations with hyperdynamics.

Accelerated molecular-dynamics (MD) simulations based on hyperdynamics (HD) can significantly improve the efficiency of MD simulations of condensed-phase systems that evolve via rare events. However, such simulations are not generally easy to apply since appropriate boosts are usually unknown. In this work, we developed a method called OptiBoost to adjust the value of the boost in HD simulations based on the bond-boost method.

The influence of iodide on the solution-phase growth of Cu microplates: a multi-scale theoretical analysis from first principles.

We use first-principles density functional theory (DFT) to quantify the role of iodide in the solution-phase growth of Cu microplates. Our calculations show that a Cu adatom binds more strongly to hcp hollow sites than fcc hollow sites on iodine-covered Cu(111) - the basal facet of two-dimensional (2D) Cu plates. This feature promotes the formation of stacking faults during seed and plate which, in turn, promotes 2D growth.

Solution-Phase Growth of Cu Nanowires with Aspect Ratios Greater Than 1000: Multiscale Theory.

Penta-twinned metal nanowires are finding widespread application in existing and emerging technologies. However, little is known about their growth mechanisms. We probe the origins of chloride- and alkylamine-mediated, solution-phase growth of penta-twinned Cu nanowires from first-principles using multiscale theory.

Adsorption of alkylamines on Cu surfaces: identifying ideal capping molecules using first-principles calculations.

We used dispersion-corrected density-functional theory to perform an search over a series of primary alkylamines, including linear, branched, and cyclic molecules, to identify capping molecules for shape-selective Cu nanocrystal synthesis. We identify several attributes associated with successful capping agents. Generally, molecules with good geometric matching to the Cu surfaces possessed the strongest molecule-surface chemical bonds.

Adsorption of ethylenediamine on Cu surfaces: attributes of a successful capping molecule using first-principles calculations.

The shape-controlled synthesis of Cu nanocrystals can benefit a wide range of applications, though challenges exist in achieving high and selective yields to a particular shape. Capping agents play a pivotal role in controlling shape, but their exact role remains ambiguous. In this study, the adsorption of ethylenediamine (EDA) on Cu(100) and Cu(111) was investigated with quantum density functional theory (DFT) to reveal the complex roles of EDA in promoting penta-twinned Cu nanowire growth.

Understanding the Solution-Phase Growth of Cu and Ag Nanowires and Nanocubes from First Principles.

In this feature article, we provide an account of the Langmuir Lecture delivered by Kristen Fichthorn at the Fall 2020 Virtual Meeting of the American Chemical Society. We discuss how multiscale theory and simulations based on first-principles DFT were useful in uncovering the intertwined influences of kinetics and thermodynamics on the shapes of Ag and Cu cubes and nanowires grown in solution. We discuss how Ag nanocubes can form through PVP-modified deposition kinetics and how the addition of chloride to the synthesis can promote thermodynamic cubic shapes for both Ag and Cu.

Synthesis of Citrate-Coated Penta-twinned Palladium Nanorods and Ultrathin Nanowires with a Tunable Aspect Ratio.

Green and scalable methodologies for the preparation of metal nanoparticles with fine control of shape and size are of high interest in many areas including catalysis, nanomedicine, and nanodiagnostics. In this contribution, we describe a new synthetic method for the production of palladium (Pd) penta-twinned nanowires and nanorods utilizing sodium citrate, formic acid, ascorbic acid, and potassium bromide (KBr) in water, without the use of surfactants or polymers. The synthesis is green, fast, and without the need of complex setups.

Development and initial applications of an e-ReaxFF description of Ag nanoclusters.

Metal nanocrystals are of considerable scientific interest because of their uses in electronics, catalysis, and spectroscopy, but the mechanisms by which nanocrystals nucleate and grow to achieve selective shapes are poorly understood. Ab initio calculations and experiments have consistently shown that the lowest energy isomers for small silver nanoparticles exhibit two-dimensional (2D) configurations and that a transition into three-dimensional (3D) configurations occurs with the addition of only a few atoms. We parameterized an e-ReaxFF potential for Ag nanoclusters (N ≤ 20 atoms) that accurately reproduces the 2D-3D transition observed between the Ag and Ag clusters.

Influence of Gravity on the Sliding Angle of Water Drops on Nanopillared Superhydrophobic Surfaces.

Molecular dynamics (MD) simulations were used to study the effects of gravity, solid surface energy, and the fraction of water-solid interface area on the water droplet sliding angles on nanopillared surfaces. To effectively simulate the influence of gravity on drop sliding, we developed a protocol in which we scale the value of gravitational acceleration used in our simulations according to the Bond number (). In this way, we approximate the behavior of drops larger than we can effectively simulate using MD.