While alloy, core-shell and Janus binary nanoclusters are found in more and more technological applications, their formation mechanisms are still poorly understood, especially during synthesis methods involving physical approaches. In this work, we employ a very simple model of such complex systems using Lennard-Jones interactions and inert gas quenching. After demonstrating the ability of the model to well reproduce the formation of alloy, core-shell or Janus nanoparticles, we studied their temporal evolution from the gas via droplets to nanocrystalline particles. In particular, we showed that the growth mechanisms exhibit qualitative differences between these three chemical orderings. Then, we determined how the quenching rate can be used to finely tune structural characteristics of the final nanoparticles, including size, shape and crystallinity.
Bimetallic nanoparticles (BNPs) exhibit diverse morphologies such as core-shell, Janus, onion-like, quasi-Janus, and homogeneous structures. Although extensive effort has been directed towards understanding the equilibrium configurations of BNPs, kinetic mechanisms involved in their development have not been explored systematically. Since these systems often contain a miscibility gap, experimental studies have alluded to spinodal decomposition (SD) as a likely mechanism for the formation of such structures. We present a novel phase-field model for confined (embedded)systems to study SD-induced…
The nucleation and growth of pure titanium nanoparticles in a low-pressure sputter plasma has been believed to be essentially impossible. The addition of impurities, such as oxygen or water, facilitates this and allows the growth of nanoparticles. However, it seems that this route requires so high oxygen densities that metallic nanoparticles in the hexagonal aTi-phase cannot be synthesized. Here we present a model which explains results for the nucleation and growth of titanium nanoparticles in the absent of reactive impurities. In these experiments, a high partial pressure of helium gas was a…
A constant supply of oxygen has been assumed to be necessary for the growth of titanium nanoparticles by sputtering. This oxygen supply can arise from a high background pressure in the vacuum system or from a purposely supplied gas. The supply of oxygen makes it difficult to grow metallic nanoparticles of titanium and can cause process problems by reacting with the target. We here report that growth of titanium nanoparticles in the metallic hexagonal titanium (αTi) phase is possible using a pulsed hollow cathode sputter plasma and adding a high partial pressure of helium to the process instead…
Nanoparticle formation by femtosecond laser ablation is investigated for different experimental conditions. Dynamics of the laser plume expansion is visualized based on numerical simulations and the possibility of primary nanoparticle formation is analyzed. Calculations are performed for metals under different background conditions. The effects of the background environment are considered, including initial expansion stage of the ejected atoms and clusters, nucleation, collisions, and longer scale nanoparticle evolution. Nanoparticle size distribution is shown to evolve from a decreasing funct…
Ice formation is one of the most common and important processes on earth and almost always occurs at the surface of a material. A basic understanding of how the physicochemical properties of a material's surface affect its ability to form ice has remained elusive. Here, we use molecular dynamics simulations to directly probe heterogeneous ice nucleation at a hexagonal surface of a nanoparticle of varying hydrophilicity. Surprisingly, we find that structurally identical surfaces can both inhibit and promote ice formation and analogous to a chemical catalyst, it is found that an optimal interact…
The ability to design synthesis processes that are out of equilibrium has opened the possibility of creating nanomaterials with remarkable physico-chemical properties, choosing from a much richer palette of possible atomic architectures compared to equilibrium processes in extended systems. In this work, we employ atomistic simulations to demonstrate how to control polymorph selection via cooling rate during nanoparticle freezing in the case of Ni$_3$Al, a material with a rich structural landscape. State-of-the-art free-energy calculations allow to rationalize the complex nucleation process, d…
Nanometer copper ferrite, as a kind of nanometer particle with catalytic activity, and its photothermal and magnetothermal effects as ferrite, can be widely used in different fields. It is a general way to obtain the nano effect of the target by controlling the particle size. In this paper, the crystallization process of hydrothermal/solvothermal synthesis was analyzed, and the nucleation model was established to simulate the effects of solvent, reaction temperature and cooling time on the particle size of copper ferrite nanoparticles. Through Monte Carlo method and energy function, the ratio …
An overarching computational framework unifying several optical theories to describe the temporal evolution of gold nanoparticles (GNPs) during a seeded growth process is presented. To achieve this, we used the inexpensive and widely available optical extinction spectroscopy, to obtain quantitative kinetic data. In situ spectra collected over a wide set of experimental conditions were regressed using the physical model, calculating light extinction by ensembles of GNPs during the growth process. This model provides temporal information on the size, shape, and concentration of the particles and…
Growth evolution of InN nanostructures via a chemical vapor deposition technique is reported using In_2O_3 as precursor material and NH_3 as reactive gas in the temperature range of 550-700 ^oC. Morphology of the nanostructures solely depends on the growth temperature, evolving from quantum dot sized nanoparticles to nanorods. It is found that 630 ^oC is the threshold temperature for nanorod growth. At 630 ^oC, nucleation starts with multifaceted particle having {10-12} surface planes. Subsequently, hexagonal polyhedral NRs are grown along the [0001] direction with non-polar surfaces of m-plan…
Future decades will experience tons of silicon waste from various sources, with no reliable recycling route. The transformation of bulk silicon into SiO2 nanoparticles is environmentally significant because it provides a way to recycle residual silicon waste. To address the needs of silicon recycling, we develop a top-down approach that achieves 100% conversion of bulk silicon to silica nanoparticles with outcome sizes of 8-50 nm. In addition to upcycling the potential of silica, our method also possesses several advantages, such as simplicity, scalability and controllable particle size distri…
Mechanisms of Nanoscroll Formation and Particle Encapsulation in Janus MXenes
Institute of Sustainable and Autonomous Maritime Systems, University of Duisburg-Essen（杜伊斯堡-埃森大学可持续与自主海事系统研究所）；Department of Physics and Energy Engineering, Amirkabir University of Technology（阿米尔卡比尔理工大学物理与能源工程系）；Autonomous and Energy-efficient Maritime Technologies, Technische Universität Berlin（柏林工业大学自主与节能海事技术部门）；Institute of Fundamental Technological Research, Polish Academy of Sciences（波兰科学院基础技术研究所以）
In this work, optimized size distribution and optical properties in colloidal synthesis of gold nanoparticles (GNPs) were obtained using a proposed ultrasonic Tuerkevich-Frens method. The effect of three ultrasound (20 kHz) irradiation powers has been analyzed as size and shape control parameter. The GNPs colloidal solutions were obtained from chloroauric acid (HAuCl$_{4}$) and trisodium citrate ($\rm C_{6}H_{5}Na_{3}O_{7}\cdot 2H_{2}O$) under continuous irradiation for 1 hour without any heat or stirring. The surface plasmon resonance (SPR) was monitored in the UV-Vis spectra every 10 minutes…
Molecular dynamics simulation is employed to understand the thermodynamic behavior of cuboctahedron (cub) and icosahedron (ico) nanoparticles with 2-20 number of full shells. The original embedded atom method (EAM) was compared to the more recent highly optimized version as inter-atomic potential. The thermal stability of clusters were probed using potential energy and specific heat capacity as well as structure analysis by radial distribution function, G(r), and common neighbor analysis (CNA), simultaneously, to make a comprehensive picture of the solid state and melting transitions. The resu…
Thermal Control of Size Distribution and Optical Properties in Gallium Nanoparticles
Instituto de Sistemas Optoelectrónicos y Microtecnología, Universidad Politécnica de Madrid（马德里理工大学光电系统与微技术研究所）；Departamento de Ingeniería Eléctrica, Electrónica Automática y Física Aplicada, Universidad Politécnica de Madrid（马德里理工大学电气、电子自动与应用物理系）；Departamento de Ciencia de los Materiales e IM y QI, Universidad de Cádiz（加的斯大学材料科学及IM和QI系）
Linear complexions are defect phases that form in the presence of dislocations and thus are promising for the direct control of plasticity. In this study, atomistic simulations are used to model the effect of linear complexions on dislocation-based mechanisms for plasticity, demonstrating unique behaviors that differ from classical dislocation glide mechanisms. Linear complexions impart higher resistance to the initiation and continuation of dislocation motion when compared to solid solution strengthening in all of the face-centered cubic alloys investigated here, with the exact strengthening …
Stress field modification near linear complexions increases the effective obstacle size and strengthening effect
Hopkins Extreme Materials Institute, Johns Hopkins University（霍普金斯极端材料研究所，约翰斯·霍普金斯大学）；Materials Department, University of California, Santa Barbara（加州大学圣塔芭芭拉分校材料系）；Department of Materials Science and Engineering, Johns Hopkins University（约翰斯·霍普金斯大学材料科学与工程系）
