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Glass (Selected Properties and Crystallization) || 9. Crystallization of Undercooled Liquids: Results of Molecular Dynamics Simulations
摘要： The present contribution is devoted to molecular dynamics (MD) simulations modeling of the kinetics of spontaneous crystal nucleation in under-cooled one-component Lennard-Jones liquids and detailed comparison with the basic assumptions and results of classical nucleation theory (CNT). In the MD-computations the following spectrum of properties of the respective nucleating systems under consideration is determined: nucleation rate, J, diffusion coefficient of the crystal clusters in cluster size space, D, non-equilibrium Zeldovich factor, Z, size of the critical crystal nucleus, n?, pressure inside the critical crystal nucleus, p?. Based on these data, the interfacial energy density of the critical crystal nucleus is determined. Simultaneously, the interfacial energy density is computed by molecular dynamics methods for the planar interface liquid-crystal. It is found that for typical sizes of the critical nuclei in the range of 0.7–1.0 nm the value of the effective specific interfacial energy differs from that of the planar interface by less than 15 %. A comparison of the molecular dynamics results with the classical nucleation theory shows that for the considered case of crystallization of one-component liquids MD simulation results are in good agreement with the classical nucleation theory not only with respect to the final result, the nucleation frequency, but also with respect to the parameters D, Z, n?. Consequently, the results of molecular dynamics simulations of crystallization in one-component liquids demonstrate the validity of the basic assumptions and the final results of CNT for this particular case of phase formation.
关键词： molecular dynamics simulations,nucleation rate,critical crystal nucleus,Lennard-Jones liquids,classical nucleation theory,interfacial energy density,crystallization,undercooled liquids
更新于2025-09-16 10:30:52
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Plasmonic Bubble Nucleation in Binary Liquids
摘要： Metal nanoparticles under laser irradiation can produce enormous heat due to surface plasmon resonance. When submerged in a liquid this can lead to the nucleation of plasmonic bubbles. In the very early stage, the nucleation of a giant vapor bubble was observed with an ultrahigh-speed camera. In this study, the formation of this giant bubble on gold nanoparticles (GNPs) in six binary liquid combinations has been investigated. We find that the time delay between the beginning of the laser heating and the bubble nucleation is determined by the absolute amount of dissolved gas in the liquid. Moreover, the bubble volume mainly depends on the vaporization energy of the liquid, consisting of the latent heat of vaporization and the energy needed to reach the boiling temperature. Our results contribute to controlling the initial giant bubble nucleation and have strong bearings on applications of such bubbles.
关键词： binary liquids,Plasmonic bubbles,dissolved gas,vaporization energy,nucleation,gold nanoparticles
更新于2025-09-16 10:30:52
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Non-classical nucleation pathways revealed by scanning tunneling microscopy of epitaxy of covalent materials
摘要： Identifying atomic/molecular mechanism is crucial for understanding crystallization and epitaxial growth and to enable controlled synthesis of high-quality devices and desired crystalline structures. Using scanning tunneling microscopy, we studied early stages of Si epitaxy on a Si(111) surface mediated by a Pb monolayer. A type of highly mobile magic clusters was observed only when they were trapped at boundary or defect sites. Magic clusters also formed cluster aggregates temporarily. Adding more Si transformed the aggregates into immobile metastable or stable structures. Here we propose a scenario involving concerted chemical reactions of multiple, co-localized magic clusters with the activation energies decreasing with increasing number of clusters. This scenario may be modified to understand nucleation and growth of many covalent materials as well as crystallization in numerous synthetic and natural systems.
关键词： magic clusters,Nucleation and growth,chemical reactions,covalent materials,non-classical nucleation
更新于2025-09-12 10:27:22
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Enhanced Nucleation of Atomic Layer Deposited Contacts Improves Operational Stability of Perovskite Solar Cells in Air
摘要： Metal-halide perovskites show promise as highly efficient solar cells, light-emitting diodes, and other optoelectronic devices. Ensuring long-term stability is now a major priority. In this study, an ultrathin (2 nm) layer of polyethylenimine ethoxylated (PEIE) is used to functionalize the surface of C60 for the subsequent deposition of atomic layer deposition (ALD) SnO2, a commonly used electron contact bilayer for p–i–n devices. The enhanced nucleation results in a more continuous initial ALD SnO2 layer that exhibits superior barrier properties, protecting Cs0.25FA0.75Pb(Br0.20I0.80)3 films upon direct exposure to high temperatures (200 °C) and water. This surface modification with PEIE translates to more stable solar cells under aggressive testing conditions in air at 60 °C under illumination. This type of “built-in” barrier layer mitigates degradation pathways not addressed by external encapsulation, such as internal halide or metal diffusion, while maintaining high device efficiency up to 18.5%. This nucleation strategy is also extended to ALD VOx films, demonstrating its potential to be broadly applied to other metal oxide contacts and device architectures.
关键词： perovskite solar cells,barrier layer,nucleation,stability testing,atomic layer deposition
更新于2025-09-12 10:27:22
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Non-Photochemical Pulsed-Laser-Induced Nucleation in a Continuous-Wave-Laser-Induced Phase-Separated Solution Droplet of Aqueous Glycine Formed by Optical Gradient Forces
摘要： A centimeter-sized, laser-induced phase-separated (LIPS) solution droplet, which was formed by tightly focusing a continuous-wave near-infrared laser beam at the glass/solution interface of a millimeter-thick layer of glycine in D2O with a supersaturation ratio, S, of 1.36 was irradiated with a single unfocused nanosecond near-infrared laser pulse in order to study the effect of non-photochemical laser-induced nucleation (NPLIN) on the droplet, as well as to help characterize the behavior of the LIPS droplet. Additionally, a control NPLIN experiment was conducted on an S = 1.50 supersaturated solution of glycine/D2O in the same cell to better understand the differences between NPLIN in a LIPS droplet and an ordinary supersaturated solution. These experiments revealed that NPLIN could nucleate crystals within a LIPS droplet, although the growth of these crystals was inhibited during the first 5 min of the droplet’s relaxation. For the first 40 min of its relaxation, the LIPS droplet was observed to be more labile to spontaneous nucleation than the control S = 1.50 solution, although the growth of spontaneously nucleated crystals was also inhibited during the first 5 min of the droplet’s relaxation. This suggests that although the macroscopic phase boundary between the LIPS droplet and the surrounding solution disappeared after approximately 5 min, the full microscopic relaxation of the LIPS droplet took at least 40 min. The resulting crystals were analyzed using powder X-ray diffraction, and 100% of crystals formed within the LIPS droplet induced by NPLIN with linearly polarized light and by spontaneous nucleation were α-glycine, while crystals formed outside of the LIPS droplet were mixtures of α- and γ-glycine. The results suggest that the LIPS droplet and the surrounding solution are not equilibrium phases of aqueous glycine, but phases in which optical gradient forces have induced a partitioning of large and small solute clusters.
关键词： Polymorphism,Optical gradient forces,Laser-induced phase separation,Non-photochemical laser-induced nucleation,Glycine
更新于2025-09-12 10:27:22
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Lead Oxalate-Induced Nucleation Retardation for High-Performance Indoor and Outdoor Perovskite Photovoltaics
摘要： Perovskite solar cells have attracted worldwide attention as one of the key research areas in the field of thin film photovoltaics. Although, they exhibit easy solution-processability, it is important to effectively control the crystallization of the light absorbing layer which affects the performance and stability of devices. Here, we present lead oxalate (PbC2O4) as a non-halide lead constituent of the perovskite precursor solution, which contributes to anion replacement during thin film annealing. This strategy limits the perovskite nucleation rate and retards crystallization. As a result, we achieved excellent perovskite film with larger grains and less defects. The open circuit voltage of the optimal device under one sun illumination rose to 1.12 V with a power conversion efficiency (PCE) of 20.20%. In addition, the indoor PCE at 1000 lux can reach 34.86%. This non-halide lead compound dopant provides a guide on the crystallization of perovskite materials and paves a way for the fabrication of non-halide perovskite solar cells.
关键词： PbC2O4,Perovskite solar cells,Nucleation retardation,Non-halide lead dopant
更新于2025-09-12 10:27:22
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CsPbBr3 quantum dots assisted crystallization of solution-processed perovskite films with preferential orientation for high performance perovskite solar cells
摘要： The performance of hybrid perovskite solar cells (PSCs) is significantly influenced by the crystallization and morphology of perovskite films. Herein, a novel method of CsPbBr3 quantum dots (QDs) assisted nucleation is applied to prepare high quality solution-processed methylammonium lead iodide (MAPbI3) films by employing CsPbBr3 QDs as an additive into diethyl ether anti-solvent. The appropriate amount of CsPbBr3 QDs can act as effective heterogeneous nucleation centers, leading to the formation of smooth and pinhole-free perovskite films with increased grain size. Furthermore, the growth direction of MAPbI3 grains is regulated by CsPbBr3 QDs, exhibiting preferential orientation of (110) plane. Therefore, the MAPbI3 films with CsPbBr3 QDs modification show reduced defects and increased carrier lifetime. As a result, the champion PSC with a maximum power conversion efficiency (PCE) up to 20.17% is achieved and 85% of its initial PCE is maintained after aging 1000 hours at room temperature under a relative humidity of 50%. This work demonstrates a feasible way to prepare high quality perovskite films for optoelectronic applications.
关键词： preferred orientation,heterogeneous nucleation centers,perovskite solar cells,CsPbBr3 QDs
更新于2025-09-12 10:27:22
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PbS Quantum Dots as Additives in Methylammonium Halide Perovskite Solar Cells: the Effect of Quantum Dot Capping
摘要： Colloidal PbS quantum dots (QDs) have been successfully employed as additives in Halide Perovskite Solar Cells (PSCs) acting as nucleation centers in the perovskite crystallization process. For this strategy, the surface functionalization of the QD, controlled via the use of different capping ligands, is likely of key importance. In this work, we examine the influence of the PbS QD capping on the photovoltaic performance of methylammonium lead iodide PSCs. We test PSCs fabricated with PbS QD additives with different capping ligands including methylammonium lead iodide (MAPI), cesium lead iodide (CsPI) and 4-aminobenzoic acid (ABA). Both the presence of PbS QDs and the specific capping used have a significant effect on the properties of the deposited perovskite layer, which affects, in turn, the photovoltaic performance. For all capping ligands used, the inclusion of PbS QDs leads to the formation of perovskite films with larger grain size, improving, in addition, the crystalline preferential orientation and the crystallinity. Yet, differences between capping agents were observed. The use of QDs with ABA capping had higher impact on the morphological properties while the employment of CsPI ligand was more effective on the optical properties of the perovskite films. Taking advantage of the improved properties, PSCs based on the perovskite films with embedded PbS QDs exhibit an enhanced photovoltaic performance, observing the highest increase with ABA capping. Moreover, bulk recombination via trap states is reduced when the ABA ligand is used as capping of the PbS QD additives in the perovskite film. We demonstrate how surface chemistry engineering of PbS QD additives in solution-processed perovskite films opens a new approach towards the design of high quality materials, paving the way to improved optoelectronic properties and more efficient photovoltaic devices.
关键词： nucleation centers,PbS quantum dots,perovskite solar cells,photovoltaic performance,capping ligands
更新于2025-09-11 14:15:04
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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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Ultrafast Modulation of Thermoplasmonic Nano-Bubbles in Water.
摘要： Thermo-optically generated bubbles in water provide a powerful means for active matter control in microfluidic environments. These bubbles are often formed via continuous-wave illumination of an absorbing medium resulting in bubble nucleation via vaporization of water and subsequent bubble growth from the inward diffusion of gas molecules. However, to date such bubbles tend to be several microns in diameter, resulting in slow dissipation. This limits the dynamic rate, spatial precision and throughput of operation in any application. Here we show that isolated plasmonic structures can be utilized as highly localized heating elements to generate thermoplasmonic nanobubbles that can be modulated at frequencies up to several kilohertz in water, orders of magnitude faster than previously demonstrated for microbubbles. The nanobubbles are envisioned as advantageous localized active manipulation elements for high throughput microfluidic applications.
关键词： thermoplasmonic bubbles,nanobubbles,thermoplasmonic phase change,bubble nucleation,thermoplasmonics
更新于2025-09-11 14:15:04