Nucleation Density Research Articles

(Invited) The Impact of Interface Layer on Li Plating and Stripping Morphology

Li metal is the preferred anode material for high energy Li batteries. However, a stable plating and stripping of Li metal at the anode−solid electrolyte interface (SEI) remains a significant challenge, particularly at practically feasible current densities. The formation of the SEI layer can significantly change the Li-nucleation density and growth morphology. With multiscale modeling, these factors can be investigated in more detail. Upon, lithiation, while a classical nucleation and growth model can describe the nucleation density of Li clusters and the charging rates in ultrahigh vacuum, a trace amount of reactive gas (oxygen for example) can change Li growth morphology. Reactive molecular dynamics simulations revealed that the fine balance between Li growth rate and the reaction rate of the thin lithium-oxide shell on the surface of the metallic Li can lead to Li nanowire formation. During delithiation, the accumulation of Li vacancies can lead to void generation and interface delamination. A DFT-informed kinetic Monte Carlo (KMC) model was developed to investigate the impact of the SEI layer, stack pressure, and alloying effects. The contact area is then incorporated into a 1D Newman battery model to simulate the impact of the contact area on the battery performance.

Inclusion/Exclusion Behaviors of Small Molecules during Crystallization of Polymers in Miscible PLLA/TAIC Blend.

In this work, PLLA/TAIC has been taken as a model system to investigate the inclusion and exclusion of small molecules during the crystallization of polymers in their miscible blend. Our results indicate that it is the growth rate and diameter of PLLA spherulites that dominate the localization of TAIC. On the one hand, crystallization temperature plays an important role. Crystallization at higher temperature corresponds to higher growth rates and a greater diameter of PLLA spherulites. The former improves the ability of PLLA crystals to trap TAIC while the latter leads to a lower volume fraction of space among neighboring PLLA spherulites. The combination of the two contributes to the enhanced inclusion behaviors. On the other hand, when compared to melt crystallization, cold crystallization results in much smaller spherulites (from higher nucleation density) and sufficient space among spherulites, which accounts for the enrichment of TAIC in interspherulitic regions and for its enhanced exclusion. In the adopted polymer–small molecule blend, TAIC can enrich in interspherulitic regions even in its miscible blend with PLLA, which can be attributed to its stronger diffusion ability.

Large and Uniform Single Crystals of MoS2 Monolayers for ppb-Level NO2 Sensing

Recently, unprecedented interest has been immersed toward the synthesis of two-dimensional (2D) transition metal dichalcogenides via the chemical vapor deposition (CVD) system. Synthesis of a uniform and large-sized monolayer MoS2 atomic thin film via CVD is still a major bottleneck owing to strong dependence on diverse associated growth parameters. In this work, we have proposed the most viable recipe which is suitable for controlling the nucleation density of Mo and producing a 90 μm-long MoS2 monolayer crystal and (695 × 394.8) μm2 large MoS2 monolayered film on SiO2/Si and c-plane sapphire, respectively. Moreover, MoS2 monolayer sensing performance has been thoroughly investigated for NO2 exposure at room temperature with a varying response of 4–57.5 for the 100–100 ppm level. Furthermore, the MoS2 monolayer sensor exhibits an ultrasensitive NO2 detection with limit of detection and limit of qualification values of 1.4 and 4.6 ppb, respectively. In addition, the first-principles-based density functional theory has been employed to analyze the adsorption of NO2 on the surfaces of the 2D MoS2 monolayer. It is observed that the electronic band gap of the MoS2 monolayer after NO2 adsorption is reduced by 0.7 eV due to molecular orbital hybridization.

Role of Ultrasonic Treatment on Microstructure, Multiscale Mechanical, and Tribological Behavior of 2D Tungsten Disulfide Reinforced Aluminum Composites

This article is the first report on the role of ultrasonic treatment (UST) on microstructural evolution, multiscale mechanical behavior, and tribological response in 2D tungsten disulfide (WS2) reinforced aluminum (Al6061) matrix composites. Delaunay triangulation calculations show that UST for 45 s enables a fourfold enhancement in the dispersion parameter of WS2 reinforcements in the Al6061 matrix from 0.08 to 0.32. Improved WS2 dispersion contributes to higher nucleation density with 52.7% grain refinement efficiency, achieving a fine‐grained Al6061–WS2 composite. The role of UST‐induced 2D reinforcement dispersion on the elastic deformation is established at progressively increasing length scales from individual grains to the bulk composite. It is accomplished by integrating the nanodynamic modulus mapping technique with a finite element modeling framework built on experimentally acquired microstructures and localized elastic moduli. It delineates a directly proportional relationship between UST‐induced dispersion and elastic modulus enhancement at all length scales from 10 to 700 μm. Excellent dispersion of the 2D layered WS2 homogenizes the tribological response of the composite material with a tenfold reduction in the volume of material lost during wear.

Chemical Vapor-Deposited Graphene on Ultraflat Copper Foils for van der Waals Hetero-Assembly.

The purity and morphology of the copper surface is important for the synthesis of high-quality, large-grained graphene by chemical vapor deposition. We find that atomically smooth copper foils—fabricated by physical vapor deposition and subsequent electroplating of copper on silicon wafer templates—exhibit strongly reduced surface roughness after the annealing of the copper catalyst, and correspondingly lower nucleation and defect density of the graphene film, when compared to commercial cold-rolled copper foils. The “ultrafoils”—ultraflat foils—facilitate easier dry pickup and encapsulation of graphene by hexagonal boron nitride, which we believe is due to the lower roughness of the catalyst surface promoting a conformal interface and subsequent stronger van der Waals adhesion between graphene and hexagonal boron nitride.

Effective Optical Properties of Laterally Coalescing Monolayer MoS2.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) exhibit compelling dimension-dependent exciton-dominated optical behavior influenced by thickness and lateral quantum confinement effects. Thickness quantum confinement effects have been observed; however, experimental optical property assessment of nanoscale lateral dimension monolayer TMDCs is lacking. Here, we employ ex situ spectroscopic ellipsometry to evaluate laterally coalescing monolayer metalorganic chemical vapor deposited MoS2. A multisample analysis is used to constrain Bruggeman and Maxwell-Garnett effective medium approximations and the effective dielectric functions are derived for laterally coalesced and uncoalesced MoS2 films (∼10-94% surface coverage for ∼10-140 nm lateral grain sizes). This analysis demonstrates the ability to probe MoS2 optical exciton behavior at growth-relevant grain sizes in relation to chemical vapor nucleation density, ripening, and lateral growth conditions. Our analysis is pertinent toward expected in situ epitaxial 2D TMDC film growth metrology to enable the facile development of monolayer films with targeted process-dependent optical properties.

Refined nickel nucleation and plated metal adhesion induced by pulsed light-induced plating on picosecond laser-ablated silicon solar cells

This study reports the impact of pulsed Ni light-induced plating (LIP), compared to the commonly used galvanostatic Ni LIP, on the initial Ni nucleation and subsequently plated busbar adhesion of Cu-plated laser-ablated p-type passivated emitter and rear Si solar cells. Initial Ni nucleate sizes decreased from 27.8 ± 9.1 to 25.4 ± 7.9 nm when the pulse-on current density during pulsed Ni LIP was increased from 50 to 178 mA cm−2, and were smaller than the 30.4 ± 9.7 nm nucleates observed with galvanostatic plating at 25 mA cm−2 after the same charge had been delivered to the surface. The density of Ni nucleation was also increased for pulsed LIP. This increased density of smaller Ni nucleates was attributed to the higher pulse-on currents inducing a larger surface potential which favoured nucleation over Volmer Weber 3D island growth of Ni. It also led to a greater density of adhesive anchor points along busbars which contributed to more adhesive plated contacts with busbar pull forces as high as 3 N mm−1 being measured when the pulse-on current density was 100 mA cm−2. However, it is shown that higher pulse-on current densities can result in unintended parasitic reactions, such as H2 evolution, and reduced busbar adhesion.

Mechanisms of Exclusive Scale Formation in the High Temperature Oxidation of Alloys

The high temperature oxidation of alloys is most often considered within the continuum framework developed by C. Wagner. We argue that in order to make progress in understanding exclusive scale formation, one needs to examine the atomic-scale kinetic processes that today are amenable to a variety of experimental, computational and theoretical approaches. In our discussion, we suggest that there is an analogy between the kinetic processes required for exclusive scale formation and thin film layer-by-layer growth. In both cases, the magnitude of the Ehrlich-Schwoebel barrier sets an effective length scale for growth, that if too large, results in three-dimensional rather than lateral island or oxide growth. In this event, exclusive scale formation can only occur if there is a sufficiently large density of oxide nucleation events at the surface of the alloy. We suggest that a suitably identified, dilute alloy component, could serve as a “surfactant” that segregates to the surface and is capable of enhancing the nucleation density.

Lithiophilic pore-gradient structured and oxygen-enriched carbon fiber as dense lithium nucleation enabler for stable lithium metal batteries

Lithium (Li) metal is the ultimate anode material for next generation batteries, thanks to its ultrahigh theoretical specific capacity and lowest reduction potential. However, an unstable solid electrolyte interphase caused by uneven Li deposition and infinite volume expansion of Li obstruct the commercialization of Li metal anodes. Herein, we introduce a unique strategy to tune lithiophobic carbon fiber (CF) to lithiophilic pore-gradient structured and oxygen-enriched carbon fiber (PGOCF) as dense Li nucleation enabler. The simultaneous regulation of surface chemistry and structure of CF is simply achieved by using CoAl layered double hydroxide as an etchant-protectant agent in thermal treatment, in which the porosifying role of Co and the protecting role of Al elements synergistically affect the morphology of PGOCF. The O enriched PGOCF (the atomic O ratio of 10.55%) can exhibit strong Li absorption, lowering Li nucleation barrier, and the pore-gradient structure of PGOCF can effectively lower Li nuclei-substrate contact angle, leading to dense and uniform Li electrodeposition. As a result, PGOCF exhibits an impressive electrochemical performance. When paired with a LiFePO4 cathode, Li@PGOCF delivers a specific capacity of 138.3 mA h g−1 at 2C with an exceptional capacity retention of 98.3% for 500 cycles.

Effect of B Segregation at Prior Austenite Grain Boundaries on Microstructures and Toughness in the Heat‐Affected Zone of Mg‐Deoxidized Shipbuilding Steel Plates

The effect of B segregation at prior austenite grain boundary (PAGB) on the microstructure and toughness in the heat‐affected zone (HAZ) after high heat input welding at kJ cm−1 for Mg‐deoxidized shipbuilding steel plates is clarified. With 0.0022 wt.% B addition, B segregation occurs at PAGBs in two forms: solute B and fine Fe23(BC)6 precipitates. B segregation with a concentration of about 4 at.% decreases boundary energy by 0.13 J m−2, which reduces the nucleation density of boundary ferrites by increasing the critical activation energy of ferrite nucleation. Thus, coarse grain boundary ferrites (GBFs) and ferrite side plates (FSPs) are suppressed with film‐like allotriomorphic ferrites formed at PAGBs, and ferrite transformation temperature reduces from 712–543 to 679–541 °C. In B‐free steels, (Fe, Mn)3C particles form at PAGBs with the Mn‐depleted zone (MDZ) at around (Fe, Mn)3C, promoting GBFs and FSPs. However, (Fe, Mn)3C precipitates and MDZ are not observed at PAGBs with B addition, because B segregation delays Mn diffusion to PAGBs. Thus, GBFs and FSPs reduce, and intragranular acicular ferrites (IAFs) increase with B addition, making the dislocation density and high‐angle grain boundary density increase, which improve HAZ toughness at −40 °C from 40 to 141 J.

The Effect of Interlayer Microstructure on the Thermal Boundary Resistance of GaN-on-Diamond Substrate

Diamond has the highest thermal conductivity of any natural material. It can be used to integrate with GaN to dissipate heat from AlGaN/GaN high electron mobility transistor (HEMT) channels. Much past work has investigated the thermal properties of GaN-on-diamond devices, especially the thermal boundary resistance between the diamond and GaN (TBReff,Dia/GaN). However, the effect of SiNx interlayer structure on the thermal resistance of GaN-on-diamond devices is less investigated. In this work, we explore the role of different interfaces in contributing to the thermal boundary resistance of the GaN-on-diamond layers, specifically using 100 nm layer of SiNx, 80 nm layer of SiNx, 100 nm layer of SiNx with a 20 nm × 20 nm periodic structure. Through combination with time-domain thermoreflectance measurement and microstructural analysis, we were able to determine that a patterning SiNx interlayer provided the lower thermal boundary resistance (32.2 ± 1.8 m2KGW−1) because of the diamond growth seeding and the diamond nucleation surface. In addition, the patterning of the SiNx interlayer can effectively improve the interface bonding force and diamond nucleation density and reduce the thermal boundary resistance of the GaN-on-diamond. This enables significant improvement in heat dissipation capability of GaN-on-diamond with respect to GaN wafers.

Advanced Atomic Layer Deposition: Ultrathin and Continuous Metal Thin Film Growth and Work Function Control Using the Discrete Feeding Method.

The ultrathin and continuous ruthenium (Ru) film was deposited through an improved atomic layer deposition (ALD) process with a discrete feeding method (DFM), called DF-ALD, employing a cut-in purge step during the precursor feeding. The excess precursor molecules can be physically adsorbed onto the chemisorbed precursors on the substrate during precursor feeding, which screens the reactive sites on the surface. Using DF-ALD, surface coverage of precursors was enhanced because the cut-in purge removes the physisorbed precursors securing the reactive sites beneath them; thus, nucleation density was greatly increased. Therefore, the grain size decreased, which changed the microstructure and increased oxygen impurity concentration. However, a more metallic Ru thin film was formed due to thermodynamic stability and improved physical density. Consequently, DF-ALD enables the deposition of the ultrathin (3 nm) and continuous Ru film with a low resistivity of ∼60 μΩ cm and a high effective work function of ∼4.8 eV.

Nucleation growth mechanism of diamond on 4H-SiC substrate by microwave plasma chemical vapor deposition

Diamond was deposited on mirror-like polished, grinded, and grooved 4H-SiC substrates by microwave plasma chemical vapor deposition. The nucleation process and grain morphology varied with different growth time and concentrations of methane in hydrogen were observed by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. It was shown that the nucleation density increased by three orders of magnitude on the grinded substrate, compared with mirror-like polished substrate. The concentration of methane is critical factor that affected the nucleation density, grain size and developing facet. Furthermore, the transformation from nucleation to continuous film was revealed on side wall of the grooved substrate. And the nucleation growth mechanism of diamond on the 4H-SiC substrate was discussed, and a four-stage nucleation growth mechanism has been proposed with the formation of carbon clusters by converting from sp1 to sp2 and sp3 carbon, shaping into preferred crystal planes and forming a well-defined cubo-octahedral diamond grains before producing a compact and coalesced diamond film.

Electrophoretic Deposited Quartz Powder-Assisted Growth of Multicrystalline Silicon

Ingot multicrystalline silicon (Mc-Si) needs to be improved in quality and reduced in cost compared with Czochralski monocrystalline silicon. A uniform and dense quartz nucleation layer was obtained by the electrophoretic deposition of quartz powder on the surface of the silicon wafer. The deposited silicon wafer was annealed at 600 °C for 1 h, and one side of the silicon wafer with the quartz layer was glued to the crucible. During the growth of Mc-Si crystal, the dense quartz powder can play a nucleation role. The results show that the average lifetime of the minority carriers a of quartz-assisted silicon ingot is 7.4 μs. The overall dislocation density of an electrophoretic deposition quartz-assisted silica ingot is low, and the defect density in the middle of the silica ingot is 1.5%, which is significantly lower than that of spray quartz (3.1%) and silicon particle (4.2%). Moreover, electrophoretic deposited quartz-assisted mc-Si can obtain oriented grains, which offers a potential to apply alkaline texturing on mc-Si wafers.

Concentration-driven polymorphic mesocrystal and morphosynthetic transformation toward omni-adsorbent with the widest range of pores

• Synthetic strategy for Zn–NDC polymorphic mesocrystals (ZPM) is developed. • Initial concentration of precursor governs assembly behavior of primary building units. • Morphosynthetic transformation of ZPM produces exceptionally pore-diversified mesocarbon. • Hierarchical pore architecture of mesocarbons provides “omni-scale” adsorptive capability. Mesocrystal constituted by individual nanocrystals is of particular interest owing to its combinative and exceptional features. In this study, we present a synthesis strategy for polymorphic metal–organic mesocrystal governed by different building principles through bio-inspired particle-mediated growth. The control of initial nucleation density enables the primary structure to be differentiated into various morphologies composed of identical crystalline building units. The varying primary structures produce distinctive mesocrystals with unique hierarchical architecture through particle-mediated growth. Furthermore, the hierarchical architectures of the mesocrystals, which originated from their polymorphism, are inherited into respective mesocarbon through a simple thermal conversion process. The atomic-distributed Zn species throughout the mesostructure further contribute to the development of micro- and mesopores by self-vanishing reduction. As a result, the mesocarbon has diversified pore architecture with an unexpectedly wide range of pores. The exceptional pore architecture of the mesocrystal exhibits universal adsorption capability for “omni-scale” adsorbate molecules from angstrom and nano to micro scale.

Growth and characterization of uniformly distributed triangular single-crystalline hexagonal boron nitride grains on liquid copper surface

Single-layer hexagonal boron nitride (h-BN) is a two-dimensional (2D) material with a wide band gap and extraordinary mechanical, thermal and optical properties. It has promising applications in optoelectronics, electronics and photovoltaics. Low-pressure (150 Pa) chemical vapor deposition (LPCVD) was used to prepare uniformly distributed single-crystalline triangular h-BN grains and continuous film on liquid copper surface. A series of microscopic and spectroscopic methods were performed to characterize the morphology, crystalline structure and quality, component and thickness. It was found that h-BN grains turned into circles at higher background pressure (1000 Pa), which was due to the change in the growth mechanism from equilibrium controlled to deposition controlled. Small islands formed on primary h-BN grains because of higher concentration of precursor product. Compared to the higher background pressure, the synthetic h-BN films at low background pressure exhibited larger domain size, lower nucleation density, and no adlayer growth. Due to randomly distributed polar h-BN grains, the grain boundaries formed along the h-BN domains after merging. Typical patterns formed via the coalescence of triangular h-BN grains indicating the merging mode of growth, including edge-to-edge and edge-to-point modes. This work provides a pathway for the preparation of uniformly distributed single-crystalline h-BN grains and an in-depth understanding of the growth and merging process on liquid Cu surface.

Enhanced Condensation on Soft Materials through Bulk Lubricant Infusion (Adv. Funct. Mater. 17/2022)

Bulk Lubricant Infusion In article number 2109633, Dimos Poulikakos and co-workers show that bulk lubricant infusion in soft materials can significantly increase condensate droplet shedding through a large reduction in viscoelastic dissipation, while simultaneously promoting high droplet nucleation density. This behavior markedly enhances water condensation and promotes the suitability of such materials for passive water harvesting.

Impact of nitrogen doping on homoepitaxial diamond (111) growth

The impacts of nitrogen (N) doping on the lateral growth mode during two-dimensional (2D) nucleation, on the growth rate, and the incorporation of nitrogen (concentration [N]) of (111)-oriented diamond films were investigated by modulating the [N2]/[CH4] gas admixture ratio. The 2D nucleation density first increased with increasing [N2]/[CH4] ratio between 0.02 and 20%. Further increase of the [N2]/[CH4] ratio to up 200% caused a decrease of the nucleation density. The growth rates showed the similar N-doping dependence as the nucleation density variation. This is attributed to an initial increase of CN radicals in the regime 0.02 to 20%, followed by a reduction of CHx radicals in the regime 20 to 200%. The nitrogen incorporation concentration increases with increasing the [N2]/[CH4] ratio. The highest nitrogen concentration with 2 × 1020 atoms/cm3 is detected with [N2]/[CH4] = 200% and a relatively low nucleation density is achieved. These results are beneficial for the optimized formation of nitrogen-vacancy centers used in a quantum metrology and for device application such as inversion-channel diamond MOSFETs.

Rotational epitaxy of h-BN on Cu (110)

The growth of wafer-scale, single-crystalline hexagonal boron nitride (h-BN) monolayers on catalytic metallic substrates, requires a sparse nucleation density. At high temperatures (>1000 ∘C), preparation of vicinal Cu (110) with H2 annealing is reported to provide preferential nucleation of single antiphase domains of h-BN with facets parallel to Cu steps. We have used in situ low-energy electron microscopy (LEEM) to image nucleation and growth of h-BN islands on a Cu (110) single crystal at lower temperatures (650–750)∘C. With H2 annealing, diffraction (LEED) and dark field imaging (LEEM) confirmed the formation of three sets of h-BN antiphase domains. Two sets are epitaxially aligned with four Cu 〈11〉 in-plane directions, the lowest lattice mismatch available. While alignment is excellent in one direction, the other trigonal directions are 10.4∘ rotationally mismatched. A third pair of antiphase domains nucleates aligned with 〈10〉 in-plane directions. These domains are midway, rotated 5.2∘ with respect to either type of {111} domain, and have the lowest interfacial energy. Localized defects were found to correlate with every island nucleation event.

Effects of Substrates on Nucleation, Growth and Electrical Property of Vertical Few-Layer Graphene.

A key common problem for vertical few-layer graphene (VFLG) applications in electronic devices is the solution to grow on substrates. In this study, four kinds of substrates (silicon, stainless-steel, quartz and carbon-cloth) were examined to understand the mechanism of the nucleation and growth of VFLG by using the inductively-coupled plasma-enhanced chemical vapor deposition (ICPCVD) method. The theoretical and experimental results show that the initial nucleation of VFLG was influenced by the properties of the substrates. Surface energy and catalysis of substrates had a significant effect on controlling nucleation density and nucleation rate of VFLG at the initial growth stage. The quality of the VFLG sheet rarely had a relationship with this kind of substrate and was prone to being influenced by growth conditions. The characterization of conductivity and field emissions for a single VFLG were examined in order to understand the influence of substrates on the electrical property. The results showed that there was little difference in the conductivity of the VFLG sheet grown on the four substrates, while the interfacial contact resistance of VFLG on the four substrates showed a tremendous difference due to the different properties of said substrates. Therefore, the field emission characterization of the VFLG sheet grown on stainless-steel substrate was the best, with the maximum emission current of 35 µA at a 160 V/μm electrostatic field. This finding highlights the controllable interface of between VFLG and substrates as an important issue for electrical application.