- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Revisiting the structures and energies of silicon ?110? symmetric tilt grain boundaries
摘要： Atomistic simulations of 18 silicon ?110? symmetric tilt grain boundaries are performed using Stillinger Weber, Tersoff, and the optimized Modified Embedded Atom Method potentials. We define a novel structural unit classification through dislocation core analysis to characterize the relaxed GB structures. GBs with the misorientation angle h ranging from 13.44° to 70.53° are solely composed of Lomer dislocation cores. For GBs with h less than but close to 70.53°, GB 'step' appears and the equilibrated states with lowest GB energies can be attained only when such GB 'step' is located in the middle of each single periodic GB structure. For the misorientation angles in the range of 93.37° ￡ h ￡ 148.41°, GB structures become complicated since they contain multiple types of dislocation cores. This work not only facilitates the structural characterization of silicon ?110? STGBs, but also may provide new insights into mirco-structure design in multicrystalline silicon.
关键词： silicon,structural units,energies,grain boundaries,atomistic simulations,dislocation cores
更新于2025-09-23 15:22:29
-
Plasmon-enhanced inelastic scattering by 2D and 3D superlattices made of silver nanocrystals
摘要： The lattice dynamics of natural crystals, artificial superlattices, or self‐organized nanocrystals intimately mix confinement, coupling, periodicity, and dissipative effects. The low wavenumber vibrational response of the new class of nanomaterials called “supercrystals” does contain relevant information concerning finite size effects on atomic movements inside each nanocrystal, mechanical coupling between adjacent nanocrystals, coherent behavior of the total assembly due to its superperiodicity, and finally finite‐time effects due to damping. All these aspects concerning the dynamical behavior of silver supercrystals has been analyzed using plasmon resonance Raman scattering. Owing to the highly uniform size and chemical environment of the nanocrystals, the confinement and homogeneous damping of their fundamental vibrations are carefully analyzed. The signature of their internal atomic arrangements, as a reminiscence of bulk phonons, is also explored. It is shown that for low particles diameter (?5 nm), deviations from the continuum elastic approximation occur and that the vibrational response is more sensitive to atomic arrangements and surface effects inside the nanocrystals than to spatial coherence effects between them.
关键词： atomistic simulations,supercrystals,damping,low wavenumber,metallic nanocrystals
更新于2025-09-23 15:21:01
-
The effect of pulse duration on nanoparticle generation in pulsed laser ablation in liquids: Insights from large-scale atomistic simulations
摘要： The generation of colloidal solutions of chemically clean nanoparticles through pulsed laser ablation in liquids (PLAL) has evolved into a thriving research field that impacts industrial applications. The complexity and multiscale nature of PLAL make it difficult to untangle the various processes involved in the generation of nanoparticles and establish the dependence of nanoparticle yield and size distribution on the irradiation parameters. Large-scale atomistic simulations have yielded important insights into the fundamental mechanisms of ultrashort (femtoseconds to tens of picoseconds) PLAL and provided a plausible explanation of the origin of the experimentally observed bimodal nanoparticle size distributions. In this paper, we extend the atomistic simulations to short (hundreds of picoseconds to nanoseconds) laser pulses and focus our attention on the effect of the pulse duration on the mechanisms responsible for the generation of nanoparticles at the initial dynamic stage of laser ablation. Three distinct nanoparticle generation mechanisms operating at different stages of the ablation process and in different parts of the emerging cavitation bubble are identified in the simulations. These mechanisms are (1) the formation of a thin transient metal layer at the interface between the ablation plume and water environment followed by its decomposition into large molten nanoparticles, (2) nucleation, growth, and rapid cooling/solidification of small nanoparticles at the very front of the emerging cavitation bubble, above the transient interfacial metal layer, and (3) spinodal decomposition of a part of the ablation plume located below the transient interfacial layer, leading to the formation of a large population of nanoparticles growing in a high-temperature environment through inter-particle collisions and coalescence. The coexistence of the three distinct mechanisms of the nanoparticle formation at the initial stage of the ablation process can be related to the broad nanoparticle size distributions commonly observed in nanosecond PLAL experiments. The strong dependence of the nanoparticle cooling and solidification rates on the location within the low-density metal-water mixing region has important implications for the long-term evolution of the nanoparticle size distribution, as well as for the ability to quench the nanoparticle growth or dope them by adding surface-active agents or doping elements to the liquid environment.
关键词： phase explosion,pulsed laser ablation in liquids,molecular dynamics simulations,hydrodynamic instability,atomistic simulations,nanoparticles,nucleation and growth
更新于2025-09-19 17:13:59
-
Pentacene Crystal Growth on Silica and Layer-Dependent Step-Edge Barrier From Atomistic Simulations
摘要： Understanding and controlling the growth of organic crystals deposited from the vapor phase is important for fundamental materials science and necessary for its application in pharmaceutical and organic electronics industries. Here this process is studied for the paradigmatic case of pentacene on silica by means of a specifically tailored computational approach inspired by the experimental vapor deposition process. This scheme is able to reproduce the early stages of the thin film formation, characterized by a quasi layer-by-layer growth, thus showcasing its potential as a tool complementary to experimental techniques for investigating organic crystals. Crystalline islands of standing molecules are formed at a critical coverage, as a result of a collective reorientation of disordered aggregates of flat-lying molecules. The growth then proceeds by sequential attachment of molecules at the cluster and then terrace edges. Free energy calculations allowed us to characterize the step edge barrier for descending the terraces, a fundamental parameter for growth models for which only indirect experimental measurements are available. The barrier is found to be layer dependent (approximately 1 kcal/mol for the first monolayer on silica, 2 kcal/mol for the second monolayer) and to extend over a distance comparable with the molecular length.
关键词： pentacene,atomistic simulations,silica,step-edge barrier,crystal growth
更新于2025-09-11 14:15:04
-
Hydrophilicity and Water Contact Angle on Methylammonium Lead Iodide
摘要： Surface properties are often assessed with measurements of the contact angle of a water drop. The process is however flawed for the very important class of hybrid perovskite materials, extensively employed in solar cells and optoelectronics research, because they are water soluble and their surface degrades during contact angle measurements. While hybrid perovskites are considered to be highly hydrophilic, a contact angle with water of 83° can be measured, as if they were almost hydrophobic. By combining experiments and simulations, the actual value is explained as the result of the interaction of water with degraded superficial layers that form over sub-millisecond time scale at the water/perovskite interface. The models are validated against contact angle measurements for water on a variety of substrates, and are referenced to with the Young–Dupré relation between liquid–solid adhesion and contact angle. Present work reconciles the hydrophilic nature of methylammonium lead iodide with the apparent hydrophobic behavior in contact angle measurements, proposing a methodology for the study of contact angle on evolving substrates.
关键词： hybrid perovskites,atomistic simulations,degradation,molecular dynamics,PbI2
更新于2025-09-09 09:28:46