Preferential Nucleation Research Articles

Tracking cubic ice at molecular resolution.

Ice is present everywhere on Earth and has an essential role in several areas, such as cloud physics, climate change and cryopreservation. The role of ice is determined by its formation behaviour and associated structure. However, these are not fully understood1. In particular, there is a long-standing debate about whether water can freeze to form cubic ice-a currently undescribed phase in the phase space of ordinary hexagonal ice2-6. The mainstream view inferred from a collection of laboratory data attributes this divergence to the inability to discern cubic ice from stacking-disordered ice-a mixture of cubic and hexagonal sequences7-11. Using cryogenic transmission electron microscopy combined with low-dose imaging, we show herethe preferential nucleation of cubic ice at low-temperature interfaces, resulting in two types of separate crystallization of cubic ice and hexagonal ice from water vapour deposition at 102 K. Moreover, we identifya series of cubic-ice defects, including two types of stacking disorder, revealing the structure evolution dynamics supported by molecular dynamics simulations. The realization of direct, real-space imaging of ice formation and its dynamic behaviour at the molecular level provides an opportunity for ice research at the molecular level using transmission electron microscopy, which may be extended to other hydrogen-bonding crystals.

Nucleation-controlled growth of Cu thin films electrodeposited directly on ALD Ru diffusion barrier in additive-free electrolyte for Cu interconnect

Direct Cu electrodeposition on a 3-nm-thick atomic-layer-deposited (ALD) Ru diffusion barrier layer was investigated for Cu interconnect in Si-based microelectronic devices. A Cu-ammonia-citrate (Cu-NH3-Cit) electrolyte was employed with no additives. The nucleation behavior of Cu on Ru was dependent on the cathodic potential applied to ALD Ru/SiO2/Si wafer specimen whether it is instantaneous or progressive. Preferable instantaneous nucleation with a high area density of Cu nuclei on Ru contributed to the formation of uniform Cu thin films. Lastly, direct Cu electrodeposition onto Ru at a constant cathodic potential of −1.0 V filled 30-nm-wide and 120-nm-deep trenches with void-free Cu.

Electrostatic Epitaxy of Orientational Perovskites for Microlasers.

Orientational growth of single-crystalline structures is pivotal in the semiconductor industry, which is achievable by epitaxy for producing thin films, heterostructures, quantum wells, and superlattices. Beyond silicon and III-V semiconductors, solution-processible semiconductors, such as metal-halide perovskites, are emerging for scalable and cost-effective manufacture of optoelectronic devices, whereas the polycrystalline nature of fabricated structures restricts their application toward integrated devices. Here, electrostatic epitaxy, a process sustained by strong electrostatic interactions between self-assembled surfactants (octanoate anions) and Pb2+ , is developed to realize orientational growth of single-crystalline CsPbBr3 microwires. Strong electrostatic interactions localized at the air-liquid interface not only support preferential nucleation for single crystallinity, but also select the crystal facet with the highest Pb2+ areal density for pure crystallographic orientation. Due to the epitaxy at the air-liquid interface, direct growth of oriented single-crystalline microwires onto different substrates without the processes of lift-off and transfer is realized. Photonic lasing emission, waveguide coupling, and on-chip propagation of coherent light are demonstrated based on these single-crystalline microwires. These findings open an avenue for on-chip integration of single-crystalline materials.

Enhanced precipitation kinetics in non-stretched Al-Cu-Li-Mg-Ag-(Sc)-(Zr) alloys

This work investigates the impact of Sc and Zr on the precipitation kinetics in an Al-Cu-Li alloy in the absence of pre-stretching. Modern Al-Cu-Li alloys usually require pre-stretching to accelerate the formation kinetics of the T1 precipitates. A combination of in-situ Small-Angle X-ray Scattering (SAXS) and hardness are used to monitor the precipitation kinetics in an Al-Cu-Li alloy with and without Sc and Zr. The presence of Al3(Sc, Zr) dispersoids is found to significantly accelerate the precipitation kinetics. Surprisingly, transmission electron microscopy (TEM) reveals the absence of T1 precipitates in the peak aged condition and instead reveals that θ′ precipitates dominate the microstructure. Atom probe tomography (APT) and density functional theory (DFT) calculations reveals that the Al3Zr-shell of the dispersoids is a preferred heterogeneous nucleation sites of θ′ precipitates. Additions of Sc and Zr can hence be a suitable solution to promote precipitation in Al-Cu-Li alloys where the pre-stretching is not applicable.

Short crack propagation near coherent twin boundaries in nickel-based superalloy

Short crack propagation near a coherent twin boundary in polycrystal nickel alloy is investigated with 3D crystal plasticity extended finite element modelling (CP-XFEM), utilising reconstructed experimentally characterised microstructures and crack path observations. Short 3D cracks at coherent twin boundaries are shown to grow on parallel (111) slip planes at very high rate so as to be an intrinsic part of the nucleation process. This is found to occur predominantly because of the stress states established by twin/parent constraint driven by the local elastic anisotropy. If elastic isotropy is modelled, crack growth is found to be non-planar and inclined to the twin boundary. The twin/parent twist angle is also found to influence local stress state, such that the actual 60° twist angle gives rise to the highest local stresses, preferential crack nucleation and rapid growth parallel to the twin boundary, and the deviations from 60° change the crack morphology and rate of growth.

A novel precipitation mechanism of Laves phase in Fe-30Cr-2Mo super ferritic stainless steel: In-situ phase transformation

Laves phase is generally prejudicial to the performance of ferritic stainless steels, so understanding the underlying formation mechanism should be technologically useful. Here we demonstrate a new precipitation behavior of Laves phase in Fe-30Cr-2Mo super ferritic stainless steel by using transmission electron microscopy. It is revealed that the MC carbides firstly precipitate adhere to the M2SC carbosulphides with an orientation relationship (OR) of (0001)M2SC//(111¯)MC and [112¯0]M2SC//[011]MC. Subsequently, the interfaces between MC carbides and ferrite matrix provide preferential nucleation sites for Laves phases, which hold OR with MC as follows: (111¯)MC//(0003)Laves and [011]MC//[112¯0]Laves. Notably, the transformation from MC to Laves phases is an in-situ process based on the dissolution of MC carbide, which supplies the niobium element for nucleation and growth of Laves phase. This work enriches the recognition of the precipitation mechanism of Laves phase, and should therefore facilitate the design of high-performance ferritic stainless steels.

C-S-H Seeds Accelerate Early Age Hydration of Carbonate-Activated Slag and the Underlying Mechanism

The slow hardening process of carbonate-activated slag limits its application as a construction material. This paper aims to provide an acceleration method for the early age hydration of carbonate-activated slag by applying calcium silicate hydrate (C-S-H) seeds and unveil the underlying mechanism. The results show that the incorporation of C-S-H seeds significantly accelerates the early age reaction of carbonate-activated slag and shortens the setting time. With 4% of calcium silicate hydrate (C-S-H) seeds, the 1d-compressive strength of carbonate activates slag can achieve 25.4 MPa. The C-S-H seeds acts as the preferred nucleation sites for the strength-giving phase C-A-S-H gel and the carbonate-containing phases (e.g., calcite, gaylussite, hydrotalcite, etc.), and accelerates hydration. The dormant period of samples with C-S-H seeds becomes negligible, confirming that the seeding effect that controls the saturation limits of the pore solution is the major reason for the accelerated hydration.

Water vapor condensation on substrates with nanoscale hydrophilic spots: A molecular dynamics study

Because of preferable nucleation and departure characteristics, hybrid wetting substrates have been widely used to enhance condensation. Nanoscale hydrophilic spots are expected to reduce the adhesive force between the droplet and substrate, thereby promoting droplet departure; however, whether such hydrophilic spots can enhance nucleation and cluster growth remains poorly understood. Using molecular dynamics simulations, this work studies vapor condensation on a hydrophobic background substrate decorated with nanoscale hydrophilic spots. The results show that on the substrate with larger isolated hydrophilic spots, a higher probability of vapor molecules colliding with hydrophilic spots leads to faster nucleation. In the growth stage, the time-evolved size and surface area of the cluster follow N ∼ t3/2 and A ∼ t, respectively. With a fixed size of hydrophilic spots, increasing the hydrophilic spot density is found to enhance nucleation probability and increase the number of formed clusters; however, the competition between nucleation sites also suppresses the growth of individual clusters. Besides, an interesting phenomenon is observed that there is a critical size of hydrophilic spots below which vapor condensation cannot take place on the spots. This phenomenon can be explained by the fact that the hydrophobic atoms surrounding a hydrophilic spot weaken the affinity of the hydrophilic atoms that are located at the boundary of the hydrophilic spot, and thus reduce the interaction between the hydrophilic spot and vapor molecules. This edge effect will become extremely prominent if increasing the nucleation site number with a fixed hydrophilic atoms ratio. As a result, an appropriate nucleation site number should be designed to obtain the best condensation performance.

Crystallographic controlled exsolution and metal partitioning in magmatic sulfide deposits

Magmatic sulfide liquids are effective at concentrating a range of metals. Within magmatic sulfide systems pentlandite, an exsolution product of monosulfide solid solution (MSS), is the primary host of Ni, Co and significant concentrations of Pd. Over the last decade, LA-ICP-MS mapping has revealed non-uniform metal distributions and complexity to the metal patterns such as zonation and the linear alignment of elements. Whereas the compatibility and partitioning behavior of chalcophile elements during sulfide fractionation are well constrained, there is little knowledge on the crystallographic control exerted on metal distributions.In this study, LA-ICP-MS mapping of globular sulfides from the Crystal Lake Intrusion, Ontario (Canada), is complimented by EBSD analysis, revealing a strong crystallographic control on both the concentration of metals and pentlandite exsolutions. Elements considered incompatible in the high temperature monosulfide solid solution (MSS) phase (e.g., Cr, V, As, Pb, Ag, Bi and Pd) are preserved as a microfabric, showing preferential concentration in association with the (0001) basal plane of pyrrhotite and adjacent pentlandite. Where the [0001] axis is viewed perpendicular to the cut surface, the microfabric is considered to be an intersection lineation between the basal (0001) plane and the surface of the cut section.Pentlandite textures described in magmatic sulfide deposits include granular, fan and laths/blades. Our observations indicate that marginal pentlandite exsolutions, are in optical continuity with granular exsolutions, providing insights into the growth of pentlandite at MSS grain boundaries. We conclude that all pentlandite forms are crystallographically controlled by the hexagonal mineral system of MSS/pyrrhotite, with the [0001] c-axis of pyrrhotite corresponding to the 〈111〉 axis of pentlandite. This axis also acts as a twinning rotation axis for the two identified pentlandite orientations. Fan and lath textured exsolutions are considered geometrically equivalent structures, being reconstructed as flat disc–shapes developed parallel to the basal (0001) plane of pyrrhotite, which acts as a preferred nucleation site. A network of low-angle grain boundaries are recognized as hexagonal or rectangular structures within pyrrhotite, with the morphology shown to be dependent on the orientation of the crystals. As these features are again geometric equivalents, they can be reconstructed as intragrain hexagonal prisms. We speculate due to their localized development, that they could represent a plastic response of the pyrrhotite to accommodate the increase in volume suggested to be associated with late pentlandite exsolutions and thus are the result of static lattice recovery.The microstructural and trace element observations presented here provide new context to some of the common textural features of magmatic sulfide deposits, while importantly highlighting the strong crystallographic control on both metal distributions and sulfide textures. This study also importantly recognizes the dominance of hexagonal pyrrhotite within the ores of the Crystal Lake Intrusion and likely other magmatic sulfide deposits. This has implications for mineral processing as its non-magnetic properties can result in dilution of Ni-Cu-PGE ores and thus requires special attention for the flotation strategy.

Electrode-level strategies enabling kinetics-controlled metallic Li confinement by the heterogeneity of interfacial activity and porosity

Three-dimensional (3D) host architectures have emerged as promising strategies for resolving the critical issues of Li metal anodes, namely, severe volume changes and growth of Li dendrites during battery cycling. However, preferential Li plating on top of the host architecture often causes early cell failure. Herein, we demonstrate that the controlled heterogeneity of interfacial activity and the porous structure at the electrode level enables confined Li metal storage in host architectures consisting of metal-organic framework (MOF)-derived carbon. 3D electrochemical simulations show that carbon activity (lithiophilicity) and interparticle porosity play critical roles in controlling the competing kinetics of charge transfer and Li+ transport, thereby regulating the Li-plating behavior. The enhanced lithiophilicity at the electrode bottom, combined with the increased interparticle porosity at the top, is predicted to promote the preferential nucleation of Li and subsequent upward growth from the bottom. Based on the proposed design principles, high-capacity and long-cycling host architectures based on MOF-derived carbon are constructed via two-step electrophoretic deposition (EPD): densely populated Ag-incorporated carbon at the bottom in combination with sparsely populated Ag-free carbon at the top. The heterogeneous host architecture fabricated by EPD spatially confines a large amount of Li metal (6 mAh cm–2) without significant volume changes and exhibits a long cycle lifetime of over 900 cycles. This study provides an effective strategy for designing advanced Li metal anodes by controlling the competing reaction kinetics in 3D host architectures.

Memory Re-Condensation

This paper reveals a phenomenon of memory in dropwise condensation in open air. After a first condensation process and complete evaporation of the condensed droplets, further condensations proceed with droplets nucleating at the very places where former droplets evaporated. The origin of this phenomenon is due to the incorporation of airborne salts during the first droplet condensation and its further concentration during droplet evaporation. Salts act as preferential nucleation sites and humidity sinks. The potential impact of this phenomenon on controlled breath figure patterns and plant metabolism is discussed.

Linear arrays of InGaAs quantum dots on nanostructured GaAs-on-Si substrates

Linear arrays of high-quality quantum dots (QD) integrated in Si are an ideal platform in exploring the manipulation and transmission of quantum information. Understanding QD self-organization mechanisms on substrates compatible with Si technology is therefore of great practical importance. Here we demonstrate the epitaxial growth of linear arrays of InAs and InGaAs QDs from As2 and In molecular beams on bare and GaAs-coated Si(001) substrates, patterned by high-resolution laser interference nanolithography. Atomic force microscopy, in combination with high-resolution scanning and transmission electron microscopies, show that these arrays exhibit an improvement in growth selectivity, lateral order and size uniformity of the QDs when a pseudomorphic 1 nm-thick GaAs buffer layer is grown prior to InAs deposition. In addition, preferential nucleation of InxGa1-xAs QDs along the 〈110〉 -oriented edges of the nanostructured GaAs-on-Si(001) substrate results from In adatom migration from (111) to (001) nanofacets and the erosion of the wetting and buffer layers caused by the Ga-In intermixing at the step edge during the Stranski-Krastanov transition. These are key elements in the formation of linear arrays of coherent QDs, which differ in morphology and structure from those obtained on both GaAs(001) and Si(001) planar surfaces.

Investigation of the relationship between the microstructural evolution mechanism and mechanical properties in hot rolled Fe-0.2C–6Mn–3Al steel

The objective of the present research is to investigate the influence of the microstructural evolution mechanism on mechanical properties during deformation. For this purpose, hot rolled Fe-0.22C-6.12Mn-3.08Al steel is subjected to intercritical annealing at 740 °C for 10 min. The annealed specimen contains a mixture of lath-like α-ferrite and reverted γ, whose volume fraction is approximately 38.7%. During deformation, once the critical stress caused by the severe dislocation pile-ups is reached, the strain/stress-induced phase transformation occurs. First, grain boundaries of γ/α serve as the preferential nucleation sites for fresh α′-martensite. Subsequently, fresh α′-martensite nucleates inside reverted γ. In the meantime, the interfacial α′-martensite grows continuously into the reverted γ interior. During deformation (prestrain at 0.0%, 5.1% and 7.8%), the misorientation (MO) in α-ferrite+α′-martensite continuously rises from 0.63° to 0.67°; nevertheless, the MO in reverted γ increases from 0.65° to 0.73° and then rapidly decreases to 0.69°. Hence, the phase transformation of reverted γ is accompanied by obvious stress softening; thus, effective work hardening occurs in the subsequent deformation region due to α-ferrite and fresh α′-martensite. This phenomenon greatly enhances the strength and delays necking, e.g., the annealed specimen possesses outstanding mechanical properties (992 MPa, 47.6% and 47.2 GPa × %). Once necking occurs, the residual reverted γ is rapidly consumed in the necking region. Hence, the hardness in the necking region (5.31 ± 0.20 GPa) is much higher than that in the uniform deformation region (4.53 ± 0.17 GPa) due to the abundant hard fresh α′-martensite.

Strain-induced ordered Ge(Si) hut wires on patterned Si (001) substrates.

Ge/Si nanowires are predicted to be a promising platform for spin and even topological qubits. While for large-scale integration of these devices, nanowires with fully controlled positions and arrangements are a prerequisite. Here, we have reported ordered Ge hut wires by multilayer heteroepitaxy on patterned Si (001) substrates. Self-assembled GeSi hut wire arrays are orderly grown inside patterned trenches with post growth surface flatness. Such embedded GeSi wires induce tensile strain on the Si surface, which results in preferential nucleation of Ge nanostructures. Ordered Ge nano-dashes, disconnected wires and continuous wires are obtained correspondingly by tuning the growth conditions. These site-controlled Ge nanowires on a flattened surface lead to the ease of fabrication and large-scale integration of nanowire quantum devices.

Periodic Arrays of Metal Nanoclusters on Ultrathin Fe-Oxide Films Modulated by Metal-Oxide Interactions.

Rational design of highly stable and active metal catalysts requires a deep understanding of metal-support interactions at the atomic scale. Here, ultrathin films of FeO and FeO2-x grown on Pt(111) are used as templates for the construction of well-defined metal nanoclusters. Periodic arrays of Cu clusters in the form of monomers and trimers are preferentially located at FCC domains of FeO/Pt(111) surface, while the selective location of Cu clusters at FeO2 domains is observed on FeO2-x /Pt(111) surface. The preferential nucleation and formation of well-ordered Cu clusters are driven by different interactions of Cu with the Fe oxide domains in the sequence of FeO2-FCC > FeO-FCC > FeO-HCP > FeO-TOP, which is further validated by density functional theory calculations. It has been revealed that the p-band center as a reactivity descriptor of surface O atoms determines the interaction between metal adatoms and Fe oxides. The modulated metal-oxide interaction provides guidance for the rational design of supported single-atom and nanocluster catalysts.

Origin of the nucleation preference of coherent and semicoherent nanoprecipitates in Al–Cu alloys based on atomistically informed classical nucleation theory

The age-hardening response during the heat-treatment process of Al–Cu alloys is significantly and nonlinearly influenced by the type and size of metastable precipitates formed. In Al–Cu alloys, a semicoherent θ′ phase, usually observed after the formation of coherent Guinier–Preston (GP) zones during aging, is the key strengthening precipitate. Thus, identifying the energetics of preferential nucleation of these precipitates is essential for clarifying the optimal conditions for the formation of precipitates that effectively contribute to hardening. In this study, using classical nucleation theory (CNT) along with a recently developed machine-learning-based interatomic potential with near first-principles accuracy, we characterized the nucleation preference of coherent GP zones and semicoherent θ′ nanoprecipitates in Al–Cu alloys at various temperatures and solute concentrations. Our atomistically informed CNT model revealed the overall temperature and solute-concentration dependencies of the nucleation barriers of the nanoprecipitates, which determine the crossover temperatures at which the ease of formation of each precipitate alternates at the solute concentration of interest. The predicted results were in good agreement with the previous experimental observations. The findings of this study contribute to furthering the understanding of the driving forces for nucleation of precipitates in Al–Cu alloys at an atomic level and provide theoretical guidance for identifying the optimal age-hardening response.

Directional Ion Transport Enabled by Self‐Luminous Framework for High‐Performance Quasi‐Solid‐State Lithium Metal Batteries

Composite gel polymer electrolyte (CGPE), derived from ceramic fillers has emerged as one of the most promising candidates to improve the safety and cycling stability of lithium metal batteries. However, the poor interface compatibility between the ceramic phase and polymer phase in CGPE severely deteriorates lithium-ion pathways and cell performances. In this work, a fluorescent ceramic nanowire network that can palliate the energy barrier of photoinitiators and contribute to preferential nucleation and growth of polymer monomers is developed, thus inducing polymer segment orderly arrangement and tightly combination. A proof-of-concept study lies on fabrications of poly(ethylene oxide) closely coating on the ceramic nanowires, thus dividing the matrix into mesh units that contribute to directional lithium-ion fluxand dendrite-free deposition on the metallic anode. The CGPE, based on the state-of-the-art self-luminous framework, facilitates high-performance quasi-solid-state Li||LiFePO4 cell, registering a high capacity of 143.3 mAh g-1 after 120 cycles at a mass loading of 12mg cm-2 . X-ray computed tomography provides an insight into the relationship between directional lithium-ion diffusion and lithium deposition behavior over the electrochemical processes. The results open a door to improve the electrochemical performances of composite electrolytes in various applications.

Enhanced thermo-mechanical processing through stress-induced martensitic transformation and its effect on grain refinement in metastable β titanium alloys

Stress-induced transformations in retained metastable phase are known deformation mechanisms that provide additional plasticity in several alloy systems. In the present study on metastable β Ti-10V-2Fe-3Al (Ti-1023) and Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloys, stress-induced martensitic transformation (SIMT) has been effectively demonstrated to result in achieving a noticeable cold reduction of ∼43% and ∼45%, respectively. A significant fraction of stress-induced α″ martensites provide preferential nucleation sites for new strain-free grains formation upon recrystallization annealing. The thermomechanical treatment resulted in grain refinement by ∼93% and ∼80%, respectively, for Ti-1023 and Ti-5553 alloys. Electron Probe Micro Analyzer (EPMA) confirms the role of alloying element (such as Fe, Mo, V, Cr and Al) diffusivities resulting in altering the stability of the β phase as a function of recrystallization annealing time. Further, the effect of grain size on the SIMT ability based on microhardness variations has been deduced.

Microstructure and texture evolution in (VCoNi)99.9C0.1 medium entropy alloy during deformed and annealing treatments

The microstructure and texture evolution of (VCoNi)99.9C0.1 medium entropy alloy under homogenized, rolled and annealed conditions are systematically investigated. The equiaxed coarse grains of homogenized samples are elongated along rolling deformation direction, and then transformed to equiaxed fine grains after annealing. The distribution of coarse particles develops along grain boundary for as-homogenized and as-rolled samples; while disappears after annealing. Random texture of homogenized sample is changed to Bs-type texture after rolling, which is ascribed to local chemical ordering induced by planar slip and shear band. Bs-type texture is retained in as-annealed sample due to the absence of preferential orientation nucleation and sluggish diffusion.

Effect of solution treatment on static recrystallization of a post-deformed GH4586 superalloy

Solution treatment was carried on a post-deformed GH4586 superalloy in the solution temperature range of 1020°C to 1100°C and solution time of 2 h and 4 h. The results showed that the static recrystallization (SRX) occurred due to the residual distortion energy caused by high temperature deformation. With increasing solution temperature from 1020°C to 1100°C, the average grain size of γ matrix firstly decreased and then increased. With increasing solution time from 2 h to 4 h, the average grain size of γ matrix gradually increased from 24.2±3.2 μm to 30.9±3.8 μm. Grain boundaries and twinning boundaries are the main nucleated site for SRX. And when solution treated at 1020°C for 2 h, carbides can also become the preferential nucleation position. In addition, by analysing the relative deviation (v/vm ) distributions of Σ3 boundaries, it could be found that the higher solution temperature would lead to the increasing fraction of coherent Σ3 boundaries and the decreasing fraction of incoherent ones. Besides, the annealing twins nucleated and grew gradually during the migration of recrystallized grain boundaries, and their length fraction increased from 10.0% to 54.9% with increasing solution temperature.