Molecular Dynamics Simulations of Silver-induced Crystallization in Silicon Nanocluster

Metal-induced crystallization (MIC) has been investigated extensively as an alternative crystallization process in the silicon based photovoltaic industry. In this work, we simulate a nanoscale version of this process by using molecular dynamics simulation involving liquid Si nanoclusters inoculated with Ag atoms in Ar thermal bath. The simulations reveal that the energy released during coalescence of the silver silicide region is the main factor to remelt the surface of the Si nanocluster. In an earlier report, Ag nanoparticles is observed to induced crystallization in 12-15 nm- diameter silicon cluster, which upon further cooling results in nano-polycrystalline silicon core and segregated Ag sub-shells. The work focuses on the crucial conditions that influence the MIC process, such as (i) number of Ag atoms per unit volume, (ii) initial temperature of Si cluster, (iii) crystallization temperature and (iv) cooling rate of the Si cluster. The results presented in this study provide insight into the effect of the first three parameters. Also, the results suggest that the coalescence of eutectic phase is the essential step which induces the crystallization

Atom-level growth mechanism of nanoparticles by magnetron sputtering inert gas condensation

"There's Plenty of Room at the Bottom.", the lecture by Prof. Richard Feynman on December, 29th, 1959 at Caltech, USA, describes the field, which is "not quite the same as the others in that it will not tell us much of fundamental physics but it is more like solid-state physics in the sense that it might tell us much of great interest about the strange phenomena that occur in complex situations." This simple inspiring idea has often been referred to as the first "seed" of one of the most promising interdisciplinary branches of science, nanoscience. Nanoparticles (NPs), one of the primary building blocks for nanostructures and its application, have been incidentally synthesized and used by ancient Romans when manufacturing beautiful cups. Modern technology requires the synthesis of NPs to be precise for specific application. The composition, structure, morphology and size are four parameters which dominate the properties of NPs. How to develop a method which can control these parameters accurately and precisely is an essential question for the researchers of nanoscience. Among the wide range of existing synthesis methods, magnetron sputtering inert gas condensation has been commonly used during recent years. The method allows simultaneous control of composition, magnetron power, inert gas pressure, NP drift velocity, and aggregation zone length. To achieve a reliable control of the fabricated NPs, it is essential to understand how the nano-scale growth is influenced by these experimental conditions. In this thesis, the growth mechanisms of Si, NiCr and Fe nanoparticles are studied using multi-scale simulation methods. We investigate the effects of the macro-scaled experimental parameters on the structural properties of nanoparticles. The work presented here is a step towards the understanding of the growth process of NPs in inert gas condensation chambers and the precise control of NP properties

Generalized Algorithm for Recognition of Complex Point Defects in Large-Scale \beta-Ga2O3\rm {Ga_2O_3}

The electrical and optical properties of semiconductor materials are profoundly influenced by the atomic configurations and concentrations of intrinsic defects. This influence is particularly significant in the case of $\beta$-$\rm {Ga_2O_3}$, a vital ultrawide bandgap semiconductor characterized by highly complex intrinsic defect configurations. Despite its importance, there is a notable absence of an accurate method to recognize these defects in large-scale atomistic computational modeling. In this work, we present an effective algorithm designed explicitly for identifying various intrinsic point defects in the $\beta$-$\rm {Ga_2O_3}$ lattice. By integrating particle swarm optimization and hierarchical clustering methods, our algorithm attains a recognition accuracy exceeding 95% for discrete point defect configurations. Furthermore, we have developed an efficient technique for randomly generating diverse intrinsic defects in large-scale $\beta$-$\rm {Ga_2O_3}$ systems. This approach facilitates the construction of an extensive atomic database, crucially instrumental in validating the recognition algorithm through a substantial number of statistical analyses. Finally, the recognition algorithm is applied to a molecular dynamics simulation, accurately describing the evolution of the point defects during high-temperature annealing. Our work provides a useful tool for investigating the complex dynamical evolution of intrinsic point defects in $\beta$-$\rm {Ga_2O_3}$, and moreover, holds promise for understanding similar material systems, such as $\rm {Al_2O_3}$, $\rm {In_2O_3}$, and $\rm {Sb_2O_3}$.Comment: 11 pages, 7 figure

RESURF Ga2_{2}O3_{3}-on-SiC Field Effect Transistors for Enhanced Breakdown Voltage

Heterosubstrates have been extensively studied as a method to improve the heat dissipation of Ga$_{2}$O$_{3}$ devices. In this simulation work, we propose a novel role for $p$-type available heterosubstrates, as a component of a reduced surface field (RESURF) structure in Ga$_{2}$O$_{3}$ lateral field-effect transistors (FETs). The RESURF structure can eliminate the electric field crowding and contribute to higher breakdown voltage. Using SiC as an example, the designing strategy for doping concentration and dimensions of the $p$-type region is systematically studied using TCAD modeling. To mimic realistic devices, the impacts of interface charge and binding interlayer at the Ga$_{2}$O$_{3}$/SiC interface are also explored. Additionally, the feasibility of the RESURF structure for high-frequency switching operation is supported by the short time constant ($\sim$0.5 ns) of charging/discharging the $p$-SiC depletion region. This study demonstrates the great potential of utilizing the electrical properties of heat-dissipating heterosubstrates to achieve a uniform electric field distribution in Ga$_{2}$O$_{3}$ FETs.Comment: 6 pages, 7 figures, under revie

Orientation-Dependent Atomic-Scale Mechanism of β\beta-Ga2O3\mathrm{Ga}_{2}\mathrm{O}_{3} Thin Film Epitaxial Growth

$\beta$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ has gained intensive interests of research and application as an ultrawide bandgap semiconductor. Epitaxial growth technique of the $\beta$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ thin film possesses a fundamental and vital role in the $\mathrm{Ga}_{2}\mathrm{O}_{3}$-based device fabrication. In this work, epitaxial growth mechanisms of $\beta$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ with four low Miller-index facets, namely (100), (010), (001), and ($\overline{2}$01), are systematically explored using large-scale machine-learning molecular dynamics simulations at the atomic scale. The simulations reveal that the migration of the face-centered cubic stacking O sublattice plays a predominant role in rationalizing the different growth mechanisms between (100)/(010)/(001) and ($\overline{2}$01) orientations. The resultant complex combinations of the stacking faults and twin boundaries are carefully identified, and shows a good agreement with the experimental observation and ab initio calculation. Our results provide useful insights into the gas-phase epitaxial growth of the $\beta$-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ thin films and suggest possible ways to tailor its properties for specific applications.Comment: 6 pages, 5 figures, under peer revie

Spatial distribution of particles sputtered from single crystals by gas cluster ions

Volume: 406 Host publication title: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and AtomsThe results of molecular dynamics simulations of the bombardment of the Cu (100) and Mo (100) single-crystals by 10 keV Ar cluster ions of different sizes are presented in this paper. Spatial distributions of sputtered material were calculated. The anisotropy of the angular distributions of sputtered atoms was revealed. It was found that the character of the anisotropy is different for Cu and Mo targets. The reasons leading to this anisotropy are discussed according to the dependences of the angular distributions on the cluster size and on the target material.Peer reviewe

Piezoelectric Wind Energy Harvesting from Self-Excited Vibration of Square Cylinder

Self-excited vibration of a square cylinder has been considered as an effective way in harvesting piezoelectric wind energy. In present work, both of the vortex-induced vibration and unstable galloping phenomenon process are investigated in a reduced velocity (Ur=U/ωn·D) range of 4≤Ur≤20 with load resistance ranging in 100 Ω≤R≤1 MΩ. The vortex-induced vibration covers presynchronization, synchronization, and postsynchronization branches. An aeroelectromechanical model is given to describe the coupling of the dynamic equation of the fluid-structure interaction and the equation of Gauss law. The effects of load resistance are investigated in both the open-circuit and close-circuit system by a linear analysis, which covers the parameters of the transverse displacement, aerodynamic force, output voltage, and harvested power utilized to measure the efficiency of the system. The highest level of the transverse displacement and the maximum value of harvested power of synchronization branch during the vortex-induced vibration and galloping are obtained. The results show that the large-amplitude galloping at high wind speeds can generate energy. Additionally, energy can be harvested by utilization of the lock-in phenomenon of vortex-induced vibration under low wind speed

Large-scale atomistic study of plasticity in amorphous gallium oxide with a machine-learning potential

Compared to the widely investigated crystalline polymorphs of gallium oxide (Ga2O3), knowledge about its amorphous state is still limited. With the help of a machine-learning interatomic potential, we conducted large-scale atomistic simulations to investigate the glass transition and mechanical behavior of amorphous Ga2O3 (a-Ga2O3). During the quenching simulations, amorphization of gallium oxide melt is observed at ultrahigh cooling rates, including a distinct glass transition. The final densities at room temperature have up to 4% variance compared to experiments. The glass transition temperature is evaluated to range from 1234 K to 1348 K at different cooling rates. Structural analysis of the amorphous structure shows evident similarities in structural properties between a-Ga2O3 and amorphous alumina (a-Al2O3), such as radial distribution function, coordination distribution, and bond angle distribution. An amorphous gallium oxide structure that contains approximately one million atoms is prepared for the tension simulation. A highly plastic behavior is observed at room temperature in the tension simulations, comparable to amorphous alumina. With quantitative characterization methods, we show that a-Ga2O3 can possibly has a higher nucleation rate of localized plastic strain events compared to a-Al2O3, which can increase the material's resistance to shear banding formation during deformation.Comment: 15 pages, 7 figures, under revie

Formation and emission mechanisms of Ag nanoclusters in the Ar matrix assembly cluster source

In this paper, we study the mechanisms of growth of Ag nanoclusters in a solid Ar matrix and the emission of these nanoclusters from the matrix by a combination of experimental and theoretical methods. The molecular dynamics simulations show that the cluster growth mechanism can be described as "thermal spike-enhanced clustering" in multiple sequential ion impact events. We further show that experimentally observed large sputtered metal clusters cannot be formed by direct sputtering of Ag mixed in the Ar. Instead, we describe the mechanism of emission of the metal nanocluster that, at first, is formed in the cryogenic matrix due to multiple ion impacts, and then is emitted as a result of the simultaneous effects of interface boiling and spring force. We also develop an analytical model describing this size-dependent cluster emission. The model bridges the atomistic simulations and experimental time and length scales, and allows increasing the controllability of fast generation of nanoclusters in experiments with a high production rate.Peer reviewe

Study on Fluid-Induced Vibration Power Harvesting of Square Columns under Different Attack Angles

A model of the flow-vibration-electrical circuit multiphysical coupling system for solving square column vortex-induced vibration piezoelectric energy harvesting (VIVPEH) is proposed in this paper. The quasi steady state theory is adopted to describe the fluid solid coupling process of vortex-induced vibration based on the finite volume method coupled Gauss equation. The vibrational response and the quasi steady state form of the output voltage are solved by means of the matrix coefficient method and interactive computing. The results show that attack angles play an important role in the performance of square column VIVPEH, of which α=45° is a relatively ideal attack angle of square column VIVPEH