Reactive Force Field-based Molecular Dynamics Research Articles

Insights into FinFET Structure Collapse: A Reactive Force Field-Based Molecular Dynamics Investigation

As miniaturization progresses, pattern collapse during the drying step of wet cleaning processes has become a critical issue in the semiconductor industry. In this study, we used reactive molecular dynamics simulations to analyze pattern collapse, with a focus on bondings and reactions. To simulate pattern deformation during the drying process of wet cleaning, we created a FinFET model as a HAR structure. The surface of this model was terminated with hydrogen atoms. The widths between the patterns were changed in order to create a Laplace pressure difference when water molecules were placed on the surface. The model was simulated by placing water molecules up to half the height of the pattern. As a result, the pattern was deformed. Furthermore, by removing water molecules and changing the Laplace pressure balance, it was found that the pattern contacted each other at the tip. The pattern remained in contact when water molecules were removed from the model. In the contact area, the covalent bonds, such as Si-Si and Si-O-Si, were not formed, but instead, hydrogen-to-hydrogen van der Waals bonds were formed between patterns. We calculated the total van der Waals forces between hydrogen atoms at the contact surfaces using the Hamaker equation and calculated the elastic force of the patterns using the beam deflection formula. Our calculations showed that the total van der Waals forces between hydrogen atoms at the contact surfaces were larger than the elastic force of the patterns, indicating that van der Waals forces could be a factor in maintaining the contact of the patterns.

Reactive force field-based molecular dynamics simulation of the interaction between plasma reactive oxygen species and the receptor-binding domain of the spike protein in the capsid protein of SARS-CoV-2

Under the pressures of the current global pandemic, researchers have been working hard to find a reliable way to suppress infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent the spread of COVID-19. Studies have shown that the recognition and binding of human angiotensin-converting enzyme 2 by the receptor-binding domain (RBD) of the spike protein on the surface of SARS-CoV-2 is a crucial step in viral invasion of human receptor cells, and blocking this process could inhibit the virus from invading normal human cells. Plasma treatment can disrupt the structure of the RBD and effectively block the binding process. However, the mechanism by which plasma blocks recognition and binding is not clear. In this study, the reaction between reactive oxygen species (ROS) in plasma and a molecular model of the RBD was simulated using a reactive molecular dynamics method. The results showed that the destruction of the RBD by ROS was triggered by hydrogen abstraction reactions: O and OH abstracted H atoms from the RBD, while the H atoms of H2O2 and HO2 were abstracted by the RBD. This hydrogen abstraction resulted in the breakage of C–H, N–H, O–H and C=O bonds and the formation of C=C and C=N bonds. The addition reaction of OH increased the number of O–H bonds and caused the formation of C–O, N–O and O–H bonds. The dissociation of N–H bonds led to the destruction of the original peptide bond structure and amino acid residues, changed the type of amino acid residues and caused the conversion of N–C and N=C and C=O and C–O. The simulation partially elucidated the microscopic mechanism of the interaction between ROS in plasma and the capsid protein of SARS-CoV-2, providing theoretical support for the control of SARS-CoV-2 infection by plasma, a contribution to overcoming the global pandemic.

Reactive Force Field-Based Molecular Dynamics Simulations on the Thermal Stability of Trimesic Acid on Graphene: Implications for the Design of Supramolecular Networks

Reactive Force Field-Based Molecular Dynamics Simulations on the Thermal Stability of Trimesic Acid on Graphene: Implications for the Design of Supramolecular Networks

Effects of interlayer confinement and hydration on capacitive charge storage in birnessite.

Nanostructured birnessite exhibits high specific capacitance and nearly ideal capacitive behaviour in aqueous electrolytes, rendering it an important electrode material for low-cost, high-power energy storage devices. The mechanism of electrochemical capacitance in birnessite has been described as both Faradaic (involving redox) and non-Faradaic (involving only electrostatic interactions). To clarify the capacitive mechanism, we characterized birnessite's response to applied potential using ex situ X-ray diffraction, electrochemical quartz crystal microbalance, in situ Raman spectroscopy and operando atomic force microscope dilatometry to provide a holistic understanding of its structural, gravimetric and mechanical responses. These observations are supported by atomic-scale simulations using density functional theory for the cation-intercalated structure of birnessite, ReaxFF reactive force field-based molecular dynamics and ReaxFF-based grand canonical Monte Carlo simulations on the dynamics at the birnessite-water-electrolyte interface. We show that capacitive charge storage in birnessite is governed by interlayer cation intercalation. We conclude that the intercalation appears capacitive due to the presence of nanoconfined interlayer structural water, which mediates the interaction between the intercalated cation and the birnessite host and leads to minimal structural changes.

Illuminating Invisible Grain Boundaries in Coalesced Single-Orientation WS2 Monolayer Films.

Engineering atomic-scale defects is crucial for realizing wafer-scale, single-crystalline transition metal dichalcogenide monolayers for electronic devices. However, connecting atomic-scale defects to larger morphologies poses a significant challenge. Using electron microscopy and ReaxFF reactive force field-based molecular dynamics simulations, we provide insights into WS2 crystal growth mechanisms, providing a direct link between synthetic conditions and microstructure. Dark-field TEM imaging of coalesced monolayer WS2 films illuminates defect arrays that atomic-resolution STEM imaging identifies as translational grain boundaries. Electron diffraction and high-resolution imaging reveal that the films have nearly a single orientation with imperfectly stitched domains that tilt out-of-plane when released from the substrate. Imaging and ReaxFF simulations uncover two types of translational mismatch, and we discuss their origin related to relatively fast growth rates. Statistical analysis of >1300 facets demonstrates that microstructural features are constructed from nanometer-scale building blocks, describing the system across sub-Ångstrom to multimicrometer length scales.

Reaction Mechanisms and Interfacial Behaviors of Sodium Silicate Glass in an Aqueous Environment from Reactive Force Field-Based Molecular Dynamics Simulations

Corrosion of silicate glasses in aqueous environment is common and it impacts many physical and chemical properties of these materials that have wide ranges of industrial and technological applicat...

Impact of the phenyl thioether contents on the high frequency dielectric loss characteristics of the modified polyimide films

With the combination of the phenyl thioether group into the molecular chain of polyimide, the high frequency dielectric loss of the modified polyimide film can be effectively reduced, which will avail this insulating material of application in high frequency electrical equipment. In the proposed study, polyimide films containing different proportions of phenyl thioether were prepared via alternating thermal imidization method and the impact of phenyl thioether contents on the high frequency dielectric loss characteristics investigated. Frequency-domain dielectric spectrum analysis indicated that the dielectric loss of the modified films decreased in the first instance and then roared again with increased phenyl thioether content, among which cases the lowest dielectric loss factor (tanδ = 0.000929 at 1 kHz) occurred in the film with phenyl thioether content of 40%. Both X-ray diffraction (XRD) and Ultraviolet-visible spectroscopy (UV–Vis) measurements, with reactive force field-based molecular dynamics simulation, were utilized to further elucidate the influencing mechanism of phenyl thioether content on dielectric loss characteristics. When the content of phenyl thioether was <40%, the charge transfer effect decreased with the increased phenyl thioether content, gradually reducing the degree of micro-crystallinity in the modified polyimide, and thereby increasing the dispersion of dipole moment that directly led to the reduced dielectric loss. When the phenyl thioether content is higher than 40%, the charge transfer effect reversed, which results in the PI film with increased crystalline region caused by the tighten molecular stacking and has the increased dielectric loss. Synthesis of the low-dielectric-loss polyimide films can be then optimized for high frequency applications.

Atomistic Simulations of Al(100) and Al(111) Surface Oxidation: Chemical and Topological Aspects of the Oxide Structure

The chemical and topological aspects of short- and medium-range atomic ordering on oxidized Al(100) and Al(111) surfaces have been studied by employing reactive force field-based molecular dynamics (ReaxFF-MD) simulations as a function of O2 gas density at 300 K. We found two oxide film growth regimes, compatible with experimental and recent modeling data. Trend of changes in oxide film thickness with increasing oxygen gas density agrees with available literature data, while slightly thicker oxide film forms on the Al(100) substrate. Chemical descriptors of short- and medium-range correlation manifest difference in atom environment between two ultrathin oxide films as [3,4]Al and [2,3]O-coordinated species dominate. In turn, a highly liquid-like structure of ultrathin oxide film develops on the Al(100) surface compared to an amorphous nature of the Al(111) oxide film with slightly lower thickness. Three-dimensional analysis of oxide structures reveals a medium-range atomic order formed by the arrangement ...

ReaxFF Molecular Dynamics Study on the Influence of Temperature on Adsorption, Desorption, and Decomposition at the Acetic Acid/Water/ZnO(101̅0) Interface Enabling Cold Sintering.

The reaction dynamics of a liquid-solid interface with the example of an acetic acid/water solution interacting with a ZnO(101̅0) surface was investigated using ReaxFF reactive force field-based molecular dynamics. The interactions were studied over a broad temperature range to assess the kinetics and reaction pathways. Two different acetic acid dissociation mechanisms are observed in the simulations: (1) deprotonation to surface cation, which produces a terminal hydroxyl and (2) deprotonation to a bridging hydroxyl, which results in water production. An increase in temperature promotes the dissociation of acetic acids and its adsorption to surface at first, but as the temperature increase continues, the surface coverage by acetates decreases due to evaporation from the surface or decomposition. The acetate decomposition starts with a nucleophilic attack of oxygen to methyl carbon and results in the production of carbon dioxide, which is consistent with experimental findings in the literature. The coverage of the surface by water molecules decreases as the system is heated up, which is also observed in other molecular dynamics studies. At elevated temperatures, acetate molecules are more stable than water molecules or bridging hydroxyls on the surface. These simulations validate the ReaxFF method for the water/organic mixture and metal oxide surface interactions and provide insights into structure and reactivity of aqueous solvents on metal oxide surfaces at elevated temperatures. Adsorption trends that are observed in this study are consistent with phenomenological Langmuir models. The reaction of acetic acid decomposition to smaller molecules such as CO2 and CH2O agrees with experimental observations. Understanding the details of these dynamic surface reactions are critical to understand important new cold sintering processes that utilize transient liquid and solid reactions, and the latter could be used to predict solvent selection for cold sintering.

Reactive Molecular Dynamics Simulations of Self-Assembly of Polytwistane and Its Application for Nanofibers

We investigated the self-assembly and mechanical properties of polytwistane (PT), particularly a seven-strand PT rope, using reactive force field-based molecular dynamics simulations at different temperatures. We show that upon self-assembly due to strong van der Waals interaction among PT units, PTs form a twisted structure (ropelike) with a twisting angle of ∼0.16 rad/nm at 300 K, which makes them mechanically stronger. The PT rope has high Young’s modulus (∼0.45 TPa) at 300 K. Interestingly, Young’s modulus increases with temperature for the seven-strand PT rope, whereas it decreases with temperature for a single-strand PT. This is because in the case of the seven-strand PT, the twisting angle also contributes to the elastic property of the PT rope and twisting depends on the temperature. We estimate a maximum load transfer of ∼1.1 and ∼3.3 nN to the central unit at 100 and 300 K, respectively. Hence, the amount of load transfer critically depends on the twisting in the rope. The fracture behavior of t...

Nanoporous silica gel structures and evolution from reactive force field-based molecular dynamics simulations

Nanoporous silica-rich gel formed on silicate glass surfaces during dissolution in aqueous environment is critical in elucidating the corrosion mechanisms and the long-term residual dissolution behaviors. Silica gel models were created using two types of methods with reactive force field-based molecular dynamics simulations. The results show that the remnant silica gels created from the ISG bulk structure have a more isolated and closed pore morphology and slightly higher glass network connectivity. This contrasts with the gel structures created by hydrogarnet defect formation that exhibit more connected pore morphologies. The remnant gel structures show lower water diffusivity which was explained by the nano-confinement effect of water molecules due to frequent interactions of water molecules with adjacent silica walls and the more isolated pore morphology in the remnant gel structures. These results reveal the complexity in terms of micro and atomic structures of these silica gels, and both structure features have impact on water transport in the gel layer hence the passivating effect that controls the long-term dissolution behavior of these glasses.

Molecular Dynamics Simulations of Perfluoropolyether Lubricant Degradation in the Presence of Oxygen, Water, and Oxide Nanoparticles using a ReaxFF Reactive Force Field

The degradation of a perfluoropolyether lubricant, i.e., D4OH, was studied in the presence of a number of different components in a computer hard disk drive using ReaxFF reactive force field-based molecular dynamics simulations. The chemical reaction between nine D4OH strands with oxygen, water, oxide nanoparticles including SiO2, goethite (FeO(OH)), and Fe2O3 was simulated by using reactive molecular dynamics simulation at T = 1500 K. All oxide nanoparticles were used in three different configurations: (1) untreated – cut from the crystalline structure without further treatment; (2) pretreated with dry air; and (3) pretreated with wet air to simulate a realistic environment. It was observed that water molecules strongly affect the degradation rate of the D4OH lubricant while oxygen molecules do not play a significant role. Moreover, the results indicated that the presence of these nanoparticles in any form accelerates the lubricant degradation. Untreated silica and Goethite nanoparticles have stronger ef...

Effect of temperature on the growth ofa-axis ZnO films: a reactive force field-based molecular dynamics study

Abstract