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Van der Waals Integration of Bismuth Quantum Dots–Decorated Tellurium Nanotubes (Te@Bi) Heterojunctions and Plasma‐Enhanced Optoelectronic Applications
摘要： Crystallization is relevant to many disciplines, and the control of crystallization of molecules is of importance to a great range of technological applications. It has been well established that a variety of surfaces can serve as possible nucleation sites for heterogeneous crystallization. However, it is still unknown what features of such system may be crucial and whether just a single molecule might serve as a nucleation site for crystallization. Therefore, to probe this question, we have investigated the nucleation of a prototypical multicomponent crystal, clathrate hydrates. As multicomponent crystalline compounds, clathrate hydrates have drawn considerable attention because of their scientific and industrial importance. Clathrate hydrates can occur in several possible structures, where the size of guest molecules and their ability to fit into water cages is a crucial factor. Despite the fact that in most applications, for example in oil?gas pipelines, clathrate hydrates form from gas mixtures that feature a variety of sizes of guest molecules, the possible roles of these species in hydrate formation has remained essentially unexplored. Herein, we investigate the impact of the presence of 2,2-dimethylbutane (DMB) on the nucleation of methane hydrate. Our simulation results provide clear evidence that DMB can serve as a nucleation site and can promote the formation of methane hydrates. The low mobility of the DMB molecule, and the longer residence time and hydrate-like structure of water molecules in its hydration shell appear as important contributors to its behavior. These results demonstrate that the presence of a somewhat larger hydrocarbon in low concentration can significantly impact hydrate nucleation and hence have immediate impact in, for example, flow assurance in oil?gas pipelines. More generally, the results presented herein indicate that single molecules in an otherwise homogeneous solution can promote crystal nucleation by stabilizing early stage structural fluctuations in the liquid.
关键词： crystallization,clathrate hydrates,molecular dynamics simulations,methane hydrate,2,2-dimethylbutane,nucleation
更新于2025-09-11 14:15:04
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Self-assembled monolayer for polymer-semiconductor interface with improved interfacial thermal management
摘要： Reliability and lifespan of highly miniaturized and integrated devices will be effectively improved if excessive accumulated heat can be quickly transported to heat sinks. In this study, both molecular dynamics (MD) simulations and experiments were performed to demonstrate that self-assembled monolayers (SAMs) have high potential in interfacial thermal management and can enhance thermal transport across polystyrene (PS) / silicon (Si) interface, modelling the common polymer/semiconductor interfaces in actual devices. The influence of packing density and alkyl-chain length of SAMs are investigated. Firstly, MD simulations show that the interfacial thermal transport efficiency of SAM is higher with high packing density. The interfacial thermal conductance (ITC) between PS and Si can be improved up to 127 ± 9 MW m-2 K-1, close to the ITC across metal and semiconductor interface. At moderate packing density, the SAMs with less than 8 carbon atoms in alkyl-chain show superior improvements over those with more carbons due to the assembled structure variation. Secondly, time-domain thermoreflectance technique was employed to characterize the ITCs of a bunch of Al/PS/SAM/Si samples. C6-SAM enhances the ITC by 5 folds, from 11 ± 1 MW m-2 K-1 to 56 ± 17 MW m-2 K-1. The interfacial thermal management efficiency will weaken when alkyl-chain exceeds 8 carbon atoms, which agrees with the ITC trend from MD simulations at moderate packing density. The relationship between SAM morphology and interfacial thermal management efficiency is also discussed in detail. This study demonstrates the feasibility of molecular level design for interfacial thermal management from both theoretical calculation and experiment, and may provide a new idea for improving the heat dissipation efficiency of micro devices.
关键词： polymer/semiconductor interface,time-domain thermoreflectance,molecular dynamics simulation,self-assembled monolayer,interfacial thermal management
更新于2025-09-11 14:15:04
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Influence of π spacer of donor-acceptor-π-acceptor sensitizers on photovoltaic properties in dye-sensitized solar cells
摘要： On the basis of organic dyes (E)-3-(6-(7-(bis(4-methoxyphenyl)amino)benzo[c] [1,2,5]thiadiazol-4-yl)-4,4-dimethyl-4H-cyclopenta[2,1-b:3,4-b']dithiophen-2-yl)-2-cyanoacrylic acid (1) and (E)-3-(6-(7-(bis(4-methoxyphenyl)amino)benzo[c] [1,2,5]thiadiazol-4-yl)-4-methyl-4H-dithieno[3,2-b:2′,3′-d]pyrrol-2-yl)-2-cyanoacrylic acid (2), two new D-A-π-A dyes, (E)-3-(7-(7-(bis(4-methoxyphenyl)amino)benzo[c] [1,2,5]thiadiazol-4-yl)benzo [2,1-b:3,4-b']dithiophen-2-yl)-2-cyanoacrylic acid (3) and (E)-3-(9-(7-(bis(4-methoxyphenyl)amino)benzo[c] [1,2,5]thiadiazol-4-yl)-2,3-dihydrodithieno[3′,2':3,4; 2″,3'':5,6]benzo[1,2-b] [1,4]dioxin-6-yl)-2-cyanoacrylic acid (4) are designed with diphenylamine as donor, 2-cyanoacrylic acid as acceptor along with different π group. Besides the frontier orbital energy levels and absorption spectra, the interfacial properties of dye-TiO2 adsorbed system is considered. After adsorption, the energy level of both dye and TiO2 surface shifts, which would affect the overall performance. More important, the short-circuit current density (JSC), open-circuit voltage (VOC), and photon-to-electron conversion efficiency (PCE) are calculated, which is helpful to determine the effect of π group on the donor-acceptor-π-acceptor dyes. The negative influence of aggregation for the dye-TiO2 adsorbed system is also considered to evaluate the overall photovoltaic performance. The molecular simulations are carried out to explore the dynamic properties of aggregation.
关键词： Dye sensitized solar cells,Molecular dynamics simulations,Photon-to-electron conversion efficiency,Electronic coupling,Aggregation
更新于2025-09-11 14:15:04
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Mechanism Analysis of PCC Harmonic Resonance Based on Nonlinear Self-Oscillation Concept in a High-Power Grid-Tied Photovoltaic Plant
摘要： Polycrystalline materials can be divided into four types of microstructural components, including grain cell (GC), grain boundary (GB), triple junction (TJ) and vertex points (VP). Nanoindentation at different microstructural components on the polycrystalline materials surface can lead to different plastic deformation behaviors of the polycrystalline materials. Due to experimental limitations, the indentation-induced internal stress and defect evolution process are difficult to investigate directly, especially for the polycrystalline materials with grain size less than 100 nm. The molecular dynamics (MD) simulations were performed to unravel the initial indentation position effect on the elasticity/plastic deformation mechanism of polycrystalline copper. The results reveal that the initial indentation position governs the indentation force variation and defect distribution range due to the different dimensionalities of the microstructural components. The defect propagation as well as the internal stress transmission in the GC regions tend to transfer to the low-dimensional microstructural components of the interfaces. In addition, the atomic internal stress and potential energy accumulation/release of the microstructural component atoms during the nanoindentation process are also investigated, revealing that the atomic internal stress and potential energy in the VPs vary earliest, followed by the TJs, GBs and GCs.
关键词： microstructural component,initial indentation position,molecular dynamics,polycrystalline material,Nanoindentation
更新于2025-09-11 14:15:04
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Nonlinear vibrations of circular single-layer black phosphorus resonators
摘要： A strong nonlinear relationship between the displacement and the load in single-layer black phosphorus sheets (SLBPs) was observed under the large deflection by nanoindentation experiments. However, is rarely considered in the Nano-Electro-Mechanical-System (NEMS) resonators based on the SLBPs. In this letter, nonlinear static and dynamics behaviors of circular SLBPs (CSLBPs) are investigated using molecular dynamics (MD) simulations and a nonlinear orthotropic plate model (NOPM), respectively, where the geometrical nonlinearity is systematically considered in the NOPM. Our results show that the response-frequency curves of forced vibrations in CSLBPs meet clear hardening-type nonlinearity. The damping ratios of CSLBPs are proportional to the square of the vibration amplitude. In particular, the NOPM together with the law of energy equipartition is further utilized to study the nonlinear thermal vibrations of the CSLBPs. Checking against present MD calculations shows that the solution of the present NOPM has high accuracy. The present study should be of great help for designing NEMS resonators based on two-dimensional (2D) orthotropic materials.
关键词： nonlinear orthotropic plate model,black phosphorus,nonlinear vibrations,molecular dynamics,resonators
更新于2025-09-11 14:15:04
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Delocalized Nonlinear Vibrational Modes in Graphene: Second Harmonic Generation and Negative Pressure
摘要： With the help of molecular dynamics simulations, delocalized nonlinear vibrational modes (DNVM) in graphene are analyzed. Such modes are dictated by the lattice symmetry, they are exact solutions to the atomic equations of motion, regardless the employed interatomic potential and for any mode amplitude (though for large amplitudes they are typically unstable). In this study, only one- and two-component DNVM are analyzed, they are reducible to the dynamical systems with one and two degrees of freedom, respectively. There exist 4 one-component and 12 two-component DNVM with in-plane atomic displacements. Any two-component mode includes one of the one-component modes. If the amplitudes of the modes constituting a two-component mode are properly chosen, periodic in time vibrations are observed for the two degrees of freedom at frequencies ω and 2ω, that is, second harmonic generation takes place. For particular DNVM, the higher harmonic can have frequency nearly two times larger than the maximal frequency of the phonon spectrum of graphene. Excitation of some of DNVM results in the appearance of negative in-plane pressure in graphene. This counterintuitive result is explained by the rotational motion of carbon hexagons. Our results contribute to the understanding of nonlinear dynamics of the graphene lattice.
关键词： molecular dynamics,nonlinear dynamics,second harmonic generation,delocalized nonlinear vibrational mode,graphene,negative pressure
更新于2025-09-10 09:29:36
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[Advances in Experimental Medicine and Biology] Glycobiophysics Volume 1104 || Synchrotron-Radiation Vacuum-Ultraviolet Circular-Dichroism Spectroscopy for Characterizing the Structure of Saccharides
摘要： Circular-dichroism (CD) spectroscopy is a powerful tool for analyzing the structures of chiral molecules and biomolecules. The development of CD instruments using synchrotron radiation has greatly expanded the utility of this method by extending the spectra to the vacuum-ultraviolet (VUV) region below 190 nm and thereby yielding information that is unobtainable by conventional CD instruments. This technique is especially advantageous for monitoring the structure of saccharides that contain hydroxy and acetal groups with high-energy transitions in the VUV region. Combining VUVCD spectra with theoretical calculations provides new insight into the contributions of anomeric hydroxy groups and rotational isomers of hydroxymethyl groups to the dynamics, intramolecular hydrogen bonds, and hydration of saccharides in aqueous solution.
关键词： Glycoprotein,Hydration,Circular dichroism,Synchrotron radiation,Time-dependent density functional theory,Molecular dynamics simulation,Saccharide,Intramolecular hydrogen bond,Solution structure,Structural dynamics,Vacuum ultraviolet,Glycosaminoglycan
更新于2025-09-10 09:29:36
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Let Digons be Bygones: The Fate of Excitons in Curved π-Systems
摘要： We explore the diverse origins of unpolarized absorption and emission of molecular polygons, consisting of π-conjugated oligomer chains held in a bent geometry by strain controlled at the vertex units. For this purpose, we make use of atomistic nonadiabatic excited-state molecular dynamics simulations of a bichromophore molecular polygon (digon) with bent chromophore chains. Both structural and photoexcited dynamics were found to affect polarization features. Bending strain induces exciton localization on individual chromophore units of the conjugated chains. The latter display different transition dipole moment orientations, a feature not present in the linear oligomer counterparts. In addition, bending makes exciton localization very sensitive to molecular distortions induced by thermal fluctuations. The excited-state dynamics reveals an ultrafast intramolecular energy redistribution that spreads the exciton equally among spatially separated chromophore fragments within the molecular system. As a result, digons become virtually unpolarized absorbers and emitters, in agreement with recent experimental studies on the single-molecule level.
关键词： transition dipole moment,unpolarized absorption and emission,π-conjugated oligomer chains,molecular polygons,nonadiabatic excited-state molecular dynamics,exciton localization
更新于2025-09-10 09:29:36
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The model of the fullerene C60 and its ions C60+, C60??pseudopotentials for molecular dynamics purposes
摘要： The model pseudopotentials of C?60, C60 and C+60 have been constructed on the base of the total electrostatic potentials obtained as a result of ab initio-based calculations. The radial distance dependence of the pseudopotential is obtained by averaging with respect to the spherical angles of the total electrostatic potential. The role of the electronic correlations is investigated by comparison results of using of the di?erent exchange-correlation functional within the density functional theory. All pseudopotentials are ?tted by the ?ne approximation functions and can be applied for molecular dynamics tasks.
关键词： molecular dynamics,electronic correlations,pseudopotentials,fullerene C60,ab initio calculations
更新于2025-09-10 09:29:36
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Terahertz Time Domain Spectroscopy of Transformer Insulation Paper after Thermal Aging Intervals
摘要： An accelerated thermal aging process was used to simulate the condition of paper insulation in transformer oil-paper systems. Optical parameters of the insulation paper after various aging intervals were analyzed with terahertz time-domain spectroscopy (THz-TDS) over the range 0.1~ 1.8 THz. The result shows that the paper had seven absorption peaks at 0.19, 0.49, 0.82, 1.19, 1.43, 1.53, and 1.74 THz, and density functional theory of B3LYP/6-311G+ (d, p) was used to simulate the molecular dynamics of the repeating component (cellobiose) of the cellulose paper. Theoretical spectra were consistent with experiment, which had absorption peaks at 0.18, 0.82, 1.47, and 1.53 THz in the same frequency range. At the same time, the paper samples after various aging intervals had different refractive indexes, and least squares ?tting revealed a linear relationship between the degree of polymerization and the refractive index of the paper. Hence, this paper demonstrates that THz-TDS could be used to analyze the aging condition of transformer insulation paper and provides the theoretical and experimental basis for detection.
关键词： transformer insulation paper,novel diagnostic technique,molecular dynamics simulation,DFT,terahertz-time-domain spectroscopy
更新于2025-09-10 09:29:36