Largest Standard Cluster Analysis Research Articles

Influence of cooling rate on microstructure and defect evolution in GaAs during solidification

The fabrication of high-quality GaAs crystals is essential to approach optimal performance in optoelectronic and microelectronic devices. In this study, a molecular dynamics simulation study was conducted for the solidification of liquid GaAs at three cooling rates (1010 K s−1, 1011 K s−1, and 1012 K s−1) at 300 K. The structural evolution in terms of crystal structure and defect formation in GaAs was thoroughly investigated using pair distribution function, average atomic energy, the largest standard cluster analysis, and visualization techniques. The results showed that the cooling rate of 1010 K s−1 led to the development of the best crystal quality with ease of eutectic twin grain boundary coherent twin boundary formation. Increasing the cooling rates to 1011 K s−1 and 1012 K s−1 resulted in the amorphous structure. Both high and low cooling rates profoundly affected the formation of As8 structure, but a maximum amount of 2.2% of As8 crystal structure was formed at a cooling rate of 1011 K s−1. The reduction in cooling rate to 1010 K s−1 induced the formation of numerous Schottky and Frenkel types of partial dislocations in the GaAs system. Results of this study can serve as potential guidelines to the theory of crystal growth and may be implemented in the fabrication of high-quality GaAs crystals for optimal device performance.

Formation and fracture of Mg88Al6Zn6 MGs analyzed by topologically close-packed cluster correlation

The microstructure of metallic glasses (MGs) significantly impacts glass transition and mechanical properties, but the current research on this topic is still not comprehensive enough. Therefore, the rapid solidification and tensile processes of Mg88Al6Zn6 MGs have been investigated in this paper by molecular dynamics simulations and their microstructure has been analyzed by the Largest Standard Cluster Analysis (LaSCA). The results show the transformation of other clusters to topological close-packed (TCP) and defective TCP (D-TCP) clusters during the rapid solidification process. The transformation rate slows down significantly near the glass transition temperature (Tg) 530 K, and the two finally reach 39.19%. These clusters can be divided into five groups (c1–c5) based on their correlation indexes, and their dynamic behavior and hereditary are discussed. Clusters with strong correlations tend to form larger-sized medium-range ordered nanoclusters, which serve as the “structural skeleton” of MGs. During the tensile process, TCP and D-TCP clusters with a lower average atomic potential energy (−0.57 eV) exhibit a higher packing density and structural stability, consequently enhancing the strength of MGs (3.29 GPa). Furthermore, the larger-sized nanoclusters formed by strongly correlated clusters also contribute to the strength of local regions, thereby improving the overall tensile performance of MGs. These findings offer valuable insights into the microstructural mechanisms involved in the formation and fracture of MGs.

The mechanical properties of TCP phase of rapidly cooled molybdenum

The rapidly-cooling of pure molybdenum (Mo) at 1010 Ks−1 and the uniaxial tensile of the solid at a strain rate of 2 × 10 s−1 were studied by molecular dynamics simulation; then the structure evolution was investigated in terms of pair distribution function and the largest standard cluster analysis. It is found that Mo melt was cooled into a complex crystal with multiple characteristic lengths. Further analysis revealed that it is a mixture topological close packing (TCP) crystal composed of the dominated A15 phase (Mo-A15) and the less Z phase, with H phase as twin grain boundary. The Phonon spectrum, potential energy, and cohesion energy revealed that Mo-A15 is stable slightly inferior to Mo-bcc. Compared to the prevailing bcc Mo, Mo-A15 holds much higher Young’s modulus, ultimate tensile strength, and Yield strength, being a representative material for barrier layer with high hardness.

Effect of graphene on solid–liquid coexistence in Cu nanodroplets

The microstructure determines the macro properties, so the chemical and physical properties of nanoparticles can be tuned by changing their structures. A molecular dynamics simulation for the rapid solidification of Cu nanodroplets on the graphene sheet is conducted to investigate the effect of substrate on nanoparticles. The phase transition, structure evolution, and crystallinity are quantified by the potential energy, the largest standard cluster analysis, and Bond-orientation order parameters. It is found that the solidification is inhomogeneous and stepwise crystallization. Interestingly, originating from the graphene wettability, different solid–liquid coexistence states are obtained that may have the potential to modify the chemical and physical reactions on nanoparticles. The temperature of this solid–liquid coexistence state depends strongly on the structural evolution of crystallization and thus can be regulated by the wetting properties of the graphene substrate. These results significantly extend the fundamental understanding of heterogeneous nucleation in nanodroplets, providing important insights for designing and fabricating composite materials with multifunctional properties.

Effect of graphene substrate on melting of Cu nanoparticles

A nanoparticles-graphene-based composites (NGC) can be produced by placing a metallic nanoparticle on the graphene or its derivative carrier. Molecular dynamics simulations were employed to investigate the structural evolution of Cu NGC during rapid heating, in terms of the largest standard cluster analysis (LaSCA). It is found that the Cu nanoparticles melt through three stages of surface melting, split-melting and rapid melting, instead of shell by shell from surface to center. The grapheme substrate improves the structure stability by lowering potential energy and increasing the melting point of Cu nanoparticles; it not only leads to non-isotropic melting but also introduce a liquid-liquid transition after all fcc atoms decomposed. These findings provide important insights for the melting of NGCs and will guide their preparation, utilization, modification, and other technologies.

LaSCA: A Visualization Analysis Tool for Microstructure of Complex Systems

Over the past few decades, plenty of visualization software for the structural analysis of disordered/complex systems has been developed, but the uniqueness and correctness of structural quantification for such systems are still challenging. This paper introduces a visualization analysis tool based on the largest standard cluster analysis (LaSCA), which satisfies the three essential requirements for general structural analysis: physical correctness, objective identification, and injective representation. The specific functionalities of LaSCA include the directed graph model of complex systems, novel structural parameters, topologically close-packed structures, arbitrary partial pair distribution functions, the identification of long-range ordered structures, the adaptive selection of graphical elements, the tracking display of atom ID, user-defined view angles, various options for atom selection, and so on. The program is efficiently based on OpenGL hardware acceleration, employing special algorithms to treat bonds as cylinders or lines and treat atoms as spheres, icosahedrons, tetrahedrons, or points. LaSCA can process more than 1.2 million atoms within 50 s on a PC with 1 GB memory and four cores (Intel Core i7-9700). It is robust and low-cost for surveying short-, medium-, and long-range ordered structures and tracking their evolutions.

Molecular dynamics simulations of GaAs crystal growth under different strains

The high-quality growth of GaAs crystals is extremely essential for the fabrication of high-performance high-frequency microwave electronic devices and light-emitting devices. In this work, the molecular dynamics (MD) simulation is used to simulate the induced crystallization of GaAs crystal along the [110] orientation. The effects of strain on the growth process and defect formation are analyzed by the largest standard cluster analysis, the pair distribution function, and visualization analysis. The results indicate that the crystallization process of GaAs crystal changes significantly under different strain conditions. At the initial stage, the crystal growth rate of the system decreases after a certain tensile strain and a large compressive strain have been applied, and the greater the strain, the lower the crystallization rate is. In addition, as the crystal grows, the system forms a zigzag interface bounded by the {111} facet, and the angle between the growth plane and the {111} facet affects the morphology of the solid-liquid interface and further affects the formation of twins. The larger the applied tensile strain and the smaller the angle, the more twin defects will form and the more irregular they will be. At the same time, a large proportion of the dislocations in the system is associated with twins. The application of strain can either inhibit or promote the nucleation of dislocations, and under an appropriate amount of strain size, crystals without dislocations can even grow. The study of the microstructural evolution of GaAs on an atomic scale provides a reference for crystal growth theory.

The concealed solid-solid structural phase transition of Fe70Ni10Cr20 under high pressure

The structural evolution of melts during solidification under high pressure is important for understanding their properties. In this paper, the phase transition of Fe70Ni10Cr20 during rapid cooling under high pressures ranging from 50 to 100 GPa was investigated by molecular dynamics simulation. The structural evolution was quantified in terms of the average potential energy, the pair distribution function, and the Largest Standard Cluster Analysis (LaSCA). A potential energy curve can only reveal a liquid-solid transition (LST), but LaSCA unveils that LST always results in a meta-stable bcc state that then converts to fcc/hcp crystals through a concealed solid-solid structural transition (SST). The crystallization of Fe70Ni10Cr20 melts can be a multi-intermediate-state transition (MisT) or a single-intermediate-state transition (SisT). The selection of SisT and MisT is discussed based on structure and energy. In addition, identified by our software a double hexagonal close-packed phase can be observed in a probability ∼25% of all simulated samples. These findings will enrich the solidification theory.

Evolution characteristics of topologically close-packed structures during rapid solidification of TiAl alloy

<p indent="0mm">Rapid solidification is one of the material processing methods. In this study, the rapid solidification process of TiAl alloys at a cooling rate of 2 ×<sc> 10¹¹ K/s</sc> was simulated using molecular dynamics. The properties of the system were analyzed using the potential energy, pair distribution function, largest standard cluster analysis (LaSCA), and visualization methods. Notably, after the melt processes of supercooled liquid and solid, the system with a high Al content undergoes amorphization, and that with a low Al content undergoes crystallization. In the amorphous system, topologically close-packed (TCP) LaSCA can well characterize the microstructure of TiAl alloy. Notably, different subsets of TCP structures show different evolutionary trends during amorphization. Different evolutionary characteristics provide proof that explains the vitrification characteristics of TiAl alloy. This finding can be the basis for the analysis of the correlation between glass-forming capability and amorphous structures.

Microstructure evolution of Si nanoparticles during the melting process: Insights from molecular dynamics simulation

Si nanomanufacturing has attracted considerable attention in the manufacturing of advanced thermoelectric materials and microelectronics owing to its compatibility with the semiconductor industry. The microstructure determines physical and chemical characteristics of a material; however, it is difficult to observe the microstructural evolution using traditional experimental methods. In this study, the melting process of Si nanoparticles is studied in depth by classical molecular dynamics (MD) simulation. Using the entropy of the largest standard cluster and the pair distribution function, the microstructural evolution characteristics can be determined. The transformation of Si-like structures was examined by largest standard cluster analysis (LaSCA). The results show that the melting process begins at the surface and rapidly penetrates into the nanoparticles at a high heating rate, indicating a liquid nucleation and growth (LNG) mode. At a higher heating rate, the temperature range of the solid and liquid coexistence will be larger. This study provides an understanding of the melting behavior of Si nanoparticles at the atomic scale and a useful reference for the preparation and processing of nanodevices.

Crystallization insights revealed by simulation solidification study of Fe63Ni33Co4 alloy melt at subcritical cooling rate

The rapid solidification of Fe63Ni33Co4 alloy at the subcritical cooling rate (1×1013 K/s) has been investigated by molecular dynamics (MD) simulation. The macroscopic phase transitions were analyzed in terms of the variation of potential energy and the related microscopic structure evolutions were depicted by the largest standard cluster analysis (LaSCA). It was found that such Fe63Ni33Co4 melt experiences liquid-liquid transition, liquid-solid transition, and solid-solid transition, which are respectively linked with the evolutions of amorphous local structures with 3-, 4- and 5-fold symmetries, BCC structures and FCC/HCP clusters. These findings shed new light on the complicated solidification mechanism of alloys from local cluster structural evolution features.

Numerical recognition of C15 unit in rapid solidification Ni&lt;sub&gt;70&lt;/sub&gt;Ag&lt;sub&gt;30 &lt;/sub&gt;nanoparticles

Simulation has become an important tool in materials science, it is a prerequisite to study the correlation between the structure and properties of materials, in that the structural characteristics of the system from the atomic coordinates output can be obtained by simulations. For simple (FCC, HCP, and BCC) crystals containing only 2-6 atoms, in the numerical analysis method, what needs to be determined is only the local characteristics of each atom. However, it is extremely computationally intensive to determine the cells containing tens or hundreds of atoms. The combination of numerical analysis and visualization is one of the methods to solve this kind of problem. In this work, Ni&lt;sub&gt;70&lt;/sub&gt;Ag&lt;sub&gt;30&lt;/sub&gt; nanoparticles are simulated by molecular dynamics. It is found that the nanoparticles contain FCC crystals and a large number of complex topologically close-packed (TCP) structures. Using the analysis software based on the largest standard cluster analysis (LaSCA), the C15 phase of TCP atoms in nanoparticles is determined by topology configuration analysis and crystallography knowledge. The analytical ideas provide the algorithm logic fordeveloping the numerical recognition software for complex crystal structures in the future.

The role of TCP structures in glass formation of Ni50Ag50 alloys

A molecular dynamics simulation of rapid cooling at a cooling rate of 1011 K/s for Ni50Ag50 alloys was conducted. The rapid cooling process was analyzed by using the system energy, the pair distribution function, and the largest standard cluster analysis. It is found that with a crystallization-like energy curve the solidification of Ni50Ag50 alloy experiences a liquid-liquid and a liquid-solid transition (LLT and LST), finally result in an amorphous solid. In LLT stage the topologically close-packed (TCP) short-range order structures of both crystal (S666) and glass (S555) increase; whereas only glass medium-range order structures are formed. TCP-based long-range order (LRO) structures of glass do not increase until the beginning of the LST. Even in solid (T < Tg) the LRO parameter based on ICO structures fluctuates violently, while that based on TCP structures is quite stable. Therefore, TCP not only is the basic structural characteristics of disordered system but also reasonably represents the metastability of metallic glasses. These findings not only clarify the importance of LLT for the glass forming ability of alloys, but also fully demonstrate the effectiveness and necessity of TCP structures for describing the structure of amorphous systems.

Influence of cluster correlation on nanoclusters in Fe-Ni amorphous alloys

To investigate the relationship between cluster correlation index and nanoclusters during rapid solidification, a molecular dynamics (MD) simulation study has been performed for FexNi(100−x)(40 ≤ x ≤ 80) amorphous alloys. Six kinds of common amorphous clusters with great similarity are explored by the newly developed Largest Standard Cluster Analysis (LSCA). The spatial distribution of clusters is analyzed by the correlation index, which is divided into strongly correlated clusters and weakly correlated clusters, and the effects of two different correlation clusters on the formation of nanoclusters are quantitatively researched. The results reveal that the Z14 correlation index of own connection is the strongest and increases with the increase of Fe content, while the correlation index between A13 and D-A13 is the weakest and it is not obvious with the increase of Fe content. In addition, Fe-rich alloys are more likely to congregate to form large-sized nanoclusters with high packing density due to the strong correlation index.

The topologically close-packed Fe70Cu15Ni15 nanoparticles- A simulation study

The classical molecular dynamics simulation is performed to investigate the frozen structure obtained by rapid cooling Fe70Cu15Ni15 nanodroplets, in terms of the system energy, the pair distribution function (PDF), and the largest standard cluster analysis (LaSCA). Interestingly, all frozen nanodroplets have a core-shell structure with copper atoms on the surface, whether they are amorphous or crystalline nanoparticles. Besides the familiar body-centered cubic (BCC) structure, a topologically close-packed (TCP) nanoparticle is observed for the first time. For a type of nanodroplets, the larger the size, the higher the onset temperature of crystallization, and the lower the potential energy of the nanoparticles at 300 K. For BCC nanoparticles crystallinity increases with size, but this is not the case for TCP nanoparticles. These findings indicate a simple and efficient way to produce core-shell nanoparticles.

Study on Si-like and topologically close-packed structures during rapid solidification of Au-Si alloys

A molecular dynamics (MD) simulation has been conducted to investigate the Si-like and topologically close-packed (TCP) structures in AuxSi(100−x) alloys during rapid solidification at the cooling rate of 1 × 1011 K/s. A new method named largest standard cluster analysis (LSCA) is performed to analyze and characterize the microstructural evolution during solidification. Results indicate that it is difficult to crystallize for each kind of Au-Si alloy, but eventually freeze into amorphous solids. The Si-like structures with low coordination number are significantly formed in the Si-rich alloys with Au content CAu≤30%, while TCP structures with higher packing density prefer to form in the Au-rich alloys with CAu≥80%. Moreover, the Si-like Medium-range order (MRO) structures are more likely to link with each other by 1100 bond-type, while the more denser TCP MROs are inclined to combine by 1551 bond-type. This provides new analysis ideas and methods for studying the amorphous structure between transition metal and semiconductor.

Crystallization behavior of Fe70Ni10Cr20 during rapid solidification under different cooling rates

Understanding the microstructure during the solidification of alloy is of great significance. In this paper, a molecular dynamics simulation for the rapid cooling of Fe70Ni10Cr20 was conducted at 6 cooling rates within 0.1∼10 K/ps, and the structure was analyzed in terms of the average potential energy, the pair distribution function, the largest standard cluster analysis, and the visualization. It was found that like pure metals, Fe70Ni10Cr20 is extremely difficult to vitrify, but easy cooled into the face-centered cubic (fcc) crystal. A well-mixed alloy liquid can be cooled into solids without significant separation of the three elements. Although energetically unfavorable, a small number of body-centered cubic structures formed at the beginning of phase transition and then decreases rapidly at lower cooling rates. As the screw dislocation in the fcc crystal, the hexagonal close-packed atoms can transfer to fcc ones by slight slides of the close-packed planes; and whether such slides can take place depends on the distribution of fcc crystal regions.

Molecular dynamics simulation of rapid solidification of Cu&lt;sub&gt;64&lt;/sub&gt;Zr&lt;sub&gt;36&lt;/sub&gt; nanodrops of different sizes

It is difficult to obtain bulk amorphous alloys experimentally due to the limitation of cooling technology and the ability to form amorphous alloy. However, the rapid cooling of nano-droplets is relatively easy, so the simulation research of nano-droplets is easier to verify experimentally. In this work, the molecular dynamics simulation for the rapid cooling of Cu&lt;sub&gt;64&lt;/sub&gt;Zr&lt;sub&gt;36&lt;/sub&gt; nano-droplets of different sizes is conducted at a cooling rate of 1.0 × 10&lt;sup&gt;12&lt;/sup&gt; K/s, and the evolution of microstructure is analyzed in terms of the average potential energy, the pair distribution function, the three-dimensional visualization, and the largest standard cluster analysis. The analysis of the energy curves and the characteristic length for short-range-ordered microstructure show that the solidification process for all nano-droplets undergoes liquid-liquid transition and liquid-solid transition, and finally forms amorphous nanoparticles. Comparing with the icosahedron, the evolution of the topologically close-packed (TCP) structures can reflect the basic characteristics of phase transitions effectively. Based on the evolution of TCP clusters, the entire solidification process of nano-droplets can be divided into four stages: embryo, aggregation, growth and coarsening. The TCP structure embodies the basic structural characteristics of amorphous nano-droplets and particles, which is of great significance in perfecting the solidification theory.

Pressure effect on structure and properties of rapidly cooled Mg70Zn30 alloy

A set of classic molecular dynamics simulations at a cooling rate of 0.1 K/ps have been performed to investigate the effect of pressure ranging from 0 to 4 GPa on the solidification of liquid Mg70Zn30 alloy, by means of the average atomic energy, the largest standard cluster analysis and 3D visualization. It is found that pressure plays an important role in both the glass transition and the structure of the final solid. Tg-P (Tg is the end temperature of the glass transition) is a monotonically increasing curve with the increase rate decreases significantly at P > 0.1 GPa. However, the structure parameters based on short-range order and icosahedrons are not monotonically dependent on pressure. Interestingly, the pressure dependence of the structure parameters based on topologically close-packed (TCP) structures is highly consistent with Tg-P. Therefore, TCP is an essential characteristic and plays an important role in glass transition. In addition, the pressure enhances the contribution of Mg atoms to the formation of Zn-rich TCP structures. These findings shed new light on understanding the pressure-structure relationship of metallic glasses.

Solid−solid phase transition of tungsten induced by high pressure: A molecular dynamics simulation

Abstract The phase transition of tungsten (W) under high pressures was investigated with molecular dynamics simulation. The structure was characterized in terms of the pair distribution function and the largest standard cluster analysis (LSCA). It is found that under 40−100 GPa at a cooling rate of 0.1 K/ps a pure W melt first crystallizes into the body-centred cubic (BCC) crystal, and then transfers into the hexagonal close-packed (HCP) crystal through a series of BCC−HCP coexisting states. The dynamic factors may induce intermediate stages during the liquid−solid transition and the criss-cross grain boundaries cause lots of indistinguishable intermediate states, making the first-order BCC−HCP transition appear to be continuous. Furthermore, LSCA is shown to be a parameter-free method that can effectively analyze both ordered and disordered structures. Therefore, LSCA can detect more details about the evolution of the structure in such structure transition processes with rich intermediate structures.