Lateral Growth Mode Research Articles

Marangoni‐Driven Self‐Assembly MXene As Functional Membrane Enables Dendrite‐Free and Flexible Zinc–Iodine Pouch Cells

AbstractZn metal is a promising anode material in aqueous batteries, but the direct use of Zn foil encounters severe issues of dendrite formation and side reactions, causing short cycle life. Conventional thick and rigid insulating protection layers may impede Zn ion diffusion and detach during mechanical deformation of the battery. Herein, a dendrite‐free zinc anode is demonstrated by grafting a thin (≈10 nm) Ti3C2Tx MXene functional membrane which is formed via Marangoni‐driven self‐assembly. The thin MXene membrane initiates uniform nucleation and promotes deposition of (002)‐oriented Zn in a lateral growth mode. Meanwhile, the membrane functions as a soft, stress‐adaptive, and protective layer to the underneath active zinc. This functional membrane renders Zn anode with improved cycling stability without notable dendrite formation or side‐reaction products. Flexible Zn─I2 pouch cells fabricated from the MXene‐covered Zn foil (20 µm thick) anode and a modified ZnI2 cathode demonstrate stable capacity up to 1500 cycles and unchanged voltage upon various mechanical deformations. This work affords new insights into designing functional soft membranes for constructing flexible Zn‐based energy devices.

Surface morphology, microstructure and emissivity of rhenium electrodeposited from molten salts

Rhenium (Re) has a high melting point and unique high temperature mechanical properties, making it an optional material that acts as a high emissivity coating on the outer wall of iridium/rhenium combustion chambers, improving their radiant heat dissipation. In this study, the effects of the electrodeposition (ED) process parameters in molten salts on the surface morphology, microstructure, and emissivity of Re coatings were investigated. The emissivity of the coating was related to the oxygen content, preferred orientation and, particularly, its morphology. The emissivity of the Re coatings increases with decreasing average radius or increasing surface density of the coating characteristic microstructures. With increasing cathodic overpotential, corresponding to high CsCl content or high current density or low molten salt temperature, the Re coating tended to change from lateral growth mode to outward growth mode, with preferred growth plane of the coating changing from (200) to (110), and meanwhile the surface morphology of the Re coating changing from stout branch-like to spiked starfish-like, leading to an increase in emissivity. The optimal deposition process parameters for the high emissivity black Re coatings were as follows: temperature ranging from 720 °C to 780 °C, cathode current density of 50 mA/cm2 to 90 mA/cm2, and the CsCl content higher than 60 wt%. The obtained black Re coatings had an emissivity higher than 0.7, with a preferred growth crystal plane of (110), and a typical spiky starfish shaped micromorphology.

Growth of single-crystal black phosphorus and its alloy films through sustained feedstock release

Black phosphorus (BP), a fascinating semiconductor with high mobility and a tunable direct bandgap, has emerged as a candidate beyond traditional silicon-based devices for next-generation electronics and optoelectronics. The ability to grow large-scale, high-quality BP films is a prerequisite for scalable integrated applications but has thus far remained a challenge due to unmanageable nucleation events. Here we develop a sustained feedstock release strategy to achieve subcentimetre-size single-crystal BP films by facilitating the lateral growth mode under a low nucleation rate. The as-grown single-crystal BP films exhibit high crystal quality, which brings excellent field-effect electrical properties and observation of pronounced Shubnikov-de Haas oscillations, with high mobilities up to ~6,500 cm2 V-1 s-1 at low temperatures. We further extend this approach to the growth of single-crystal BP alloy films, which broaden the infrared emission regime of BP from 3.7 μm to 6.9 μm at room temperature. This work will greatly facilitate the development of high-performance electronics and optoelectronics based on BP family materials.

Effect of cerium-rich mischmetal content on the growth morphology and microstructure evolution of undercooled Al-70 wt%Si alloys

The Al-70 wt%Si alloys with various cerium-rich rare earth contents undercooled by electromagnetic levitation were investigated, and the nucleation and growth, growth mode, and morphology evolution of primary Si were observed and recorded using a high-speed camera and scanning electron microscope. When the undercooling is lower than ΔT1, primary Si is coarse long plates with specific edges and faces, showing a characteristic of the lateral growth mode. When undercooling approaches ΔT2, the recalescence interface becomes dendritic and massive, and dendritic primary Si covers the surface of the alloys. The growth mode of primary Si shows a mixed growth mode of lateral and non-lateral. When undercooling exceeds ΔT2, the recalescence interface takes on a parallel shape and the morphology of primary Si transforms to homogeneous and fine spherical shapes with smooth surfaces, indicating a characteristic of the non-lateral growth mode. With an increasing RE content, critical undercooling, ΔT1 and ΔT2, gradually decreases, with the lowest values of 78 and 180 K for an RE content of 1.5%.

Controlled vapor phase growth of germanium selenide and germanium microflakes

Graphene and transition metal dichalcogenides have been intensively investigated in recent years. Germanium selenide (GeSe) has emerged lately as a new low-symmetry two-dimensional material due to its extraordinary in-plane anisotropic electrical, optical, and optoelectronic properties. However, the controlled synthesis of large-scale GeSe flakes is still a significant challenge because of its strong interlayer coupling and low lattice symmetry. In this work, we have achieved the synthesis of rectangular GeSe microflakes (MFs) with lateral sizes up to 0.33 mm on the glass substrate via a vapor phase deposition technique. The lateral size, thickness, and growth mode of GeSe MFs can be effectively tuned based on space-confined and substrate engineering strategies. Germanium (Ge) MFs with triangular and hexagonal morphologies were simultaneously fabricated in the high-temperature zone. Our experimental results demonstrated that the growth temperature plays an important role in the selective growth of GeSe and Ge MFs. A corresponding growth mechanism has been discussed in detail based on systematic characterizations. Our work provides a new route for the controlled growth of large-size GeSe and Ge MFs, which promotes a promising future in the fields of novel optoelectronic devices.

Graphene-driving strain engineering to enable strain-free epitaxy of AlN film for deep ultraviolet light-emitting diode

The energy-efficient deep ultraviolet (DUV) optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitaxy. In this work, we have prepared the strain-free AlN film with low dislocation density (DD) by graphene (Gr)-driving strain-pre-store engineering and a unique mechanism of strain-relaxation in quasi-van der Waals (QvdW) epitaxy is presented. The DD in AlN epilayer with Gr exhibits an anomalous sawtooth-like evolution during the whole epitaxy process. Gr can help to enable the annihilation of the dislocations originated from the interface between AlN and Gr/sapphire by impelling a lateral two-dimensional growth mode. Remarkably, it can induce AlN epilayer to pre-store sufficient tensile strain during the early growth stage and thus compensate the compressive strain caused by hetero-mismatch. Therefore, the low-strain state of the DUV light-emitting diode (DUV-LED) epitaxial structure is realized on the strain-free AlN template with Gr. Furthermore, the DUV-LED with Gr demonstrate 2.1 times enhancement of light output power and a better stability of luminous wavelength compared to that on bare sapphire. An in-depth understanding of this work reveals diverse beneficial impacts of Gr on nitride growth and provides a novel strategy of relaxing the vital requirements of hetero-mismatch in conventional heteroepitaxy.

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.

MOVPE growth of Si-doped GaN cap layers embedding GaN nanowires with multiple-quantum shells

In this study, the growth mechanisms of n-type gallium nitride (GaN) cap layers for embedding nanowire-based multi-quantum-shell (NW-MQS) with a tunnel junction were investigated using the metal–organic vapor-phase epitaxy method. Herein, instead of a p-type GaN layer, n-type GaN cap layers were applied as a contact layer to the anode electrode via a tunnel junction. NW-MQSs were prepared in a rectangular grid arrangement aligning with the m- and a-axis of GaN. The growth mode of the cap layers was controlled in three stages using different growth pressures and temperatures. The first cap layer was a faceted growth mode primarily comprising the r-plane, the second was a lateral growth mode that expanded the area of the c-plane, and the third was an acceleration of lateral growth. Finally, cap layers with a flat surface were realized. Void formation in the cap layers occurred only between the NW-MQSs along the m-axis of GaN. This observation can be attributed to the difference in the coalescence of the cap layers in the a- and m-axis directions. We believe that the NW-MQS structure with the cap layer that was optimized in this study can be used as a highly efficient optical device.

Growth Mechanisms and Morphology Engineering of Atomic Layer-Deposited WS2.

Transition-metal dichalcogenides (TMDs) have attracted intense research interest for a broad range of device applications. Atomic layer deposition (ALD), a CMOS compatible technique, can enable the preparation of high-quality TMD films on 8 to 12 in. wafers for large-scale circuit integration. However, the ALD growth mechanisms are still not fully understood. In this work, we systematically investigated the growth mechanisms for WS2 and found them to be strongly affected by nucleation density and film thickness. Transmission electron microscope imaging reveals the coexistence and competition of lateral and vertical growth mechanisms at different growth stages, and the critical thicknesses for each mechanism are obtained. The in-plane lateral growth mode dominates when the film thickness remains less than 5.6 nm (8 layers), while the vertical growth mode dominates when the thickness is greater than 20 nm. From the resulting understanding of these growth mechanisms, the conditions for film deposition were optimized and a maximum grain size of 108 nm was achieved. WS2-based field-effect transistors were fabricated with electron mobility and on/off current ratio up to 3.21 cm2 V-1 s-1 and 105, respectively. Particularly, this work proves the capability of synthesis of TMD films in a wafer scale with excellent controllability of thickness and morphology, enabling many potential applications other than transistors, such as nanowire- or nanosheet-based supercapacitors, batteries, sensors, and catalysis.

The role of the cytoskeletal proteins MreB and FtsZ in multicellular cyanobacteria.

Multiseriate and true-branching cyanobacteria are at the peak of prokaryotic morphological complexity. However, little is known about the mechanisms governing multiplanar cell division and morphogenesis. Here, we study the function of the prokaryotic cytoskeletal proteins, MreB and FtsZ in Fischerella muscicola PCC 7414 and Chlorogloeopsis fritschii PCC 6912. Vancomycin and HADA labeling revealed a mixed apical, septal, and lateral trichome growth mode in F.muscicola, whereas C.fritschii exhibits septal growth. In all morphotypes from both species, MreB forms either linear filaments or filamentous strings and can interact with FtsZ. Furthermore, multiplanar cell division in F.muscicola likely depends on FtsZ dosage. Our results lay the groundwork for future studies on cytoskeletal proteins in morphologically complex cyanobacteria.

Quasi-2D Growth of Aluminum Nitride Film on Graphene for Boosting Deep Ultraviolet Light-Emitting Diodes.

Efficient and low‐cost production of high‐quality aluminum nitride (AlN) films during heteroepitaxy is the key for the development of deep ultraviolet light‐emitting diodes (DUV‐LEDs). Here, the quasi‐2D growth of high‐quality AlN film with low strain and low dislocation density on graphene (Gr) is presented and a high‐performance 272 nm DUV‐LED is demonstrated. Guided by first‐principles calculations, it is found that AlN grown on Gr prefers lateral growth both energetically and kinetically, thereby resulting in a Gr‐driven quasi‐2D growth mode. The strong lateral growth mode enables most of dislocations to annihilate each other at the AlN/Gr interface, and therefore the AlN epilayer can quickly coalesce and flatten the nanopatterned sapphire substrate. Based on the high quality and low strain of AlN film grown on Gr, the as‐fabricated 272 nm DUV‐LED shows a 22% enhancement of output power than that with low‐temperature AlN buffer, following a negligible wavelength shift under high current. This facile strategy opens a pathway to drastically improve the performance of DUV‐LEDs.

Microstructural modification of Ni electrodeposit in an acidic NiCl2 solution

Electrowinning is an important process to extract Ni from aqueous solutions. In this work, the characteristics of electro-deposited Ni were modified by employing magnetic agitation and flowing bubbles in an acidic chloride solution. The nucleation and growth of Ni grains were analyzed in the electro-crystallization. Phase compositions and morphologies of the modified deposits were characterized. As well, the positive effects of magnetic agitation and flowing bubbles on the electrowinning process were discussed. Mass transportation of Ni 2+ ions was efficiently accelerated by magnetic agitation and upwards flowing bubbles. The preferential growth of Ni deposit was also facilitated along the (111) orientation. The nucleation and growth of Ni crystals proceeded in the instantaneous nucleation mode and the lateral growth mode, respectively. The introduction of magnetic agitation and upwards flowing bubbles can promote the detachment of hydrogen gas and be available for the enhancement of current efficiency. • Microstructure of Ni deposit was modified by magnetic agitation and flowing bubbles. • Mass transfer of Ni 2+ ions during electrowinning was accelerated. • Nucleation mode of Ni was transformed from instantaneous to progressive. • Preferential growth of (111) plane orientationally was promoted. • Compact deposit consisting of bar grains was formed in the lateral growth mode.

Characteristic enhancement of InGaN-based light emitting diodes grown on pattern sapphire substrates

Blue light-emitting diodes (LEDs) with an InGaN multi-quantum well (MQW) structure were fabricated on cone-shaped patterned sapphire substrate (PSS) using a single growth process of metal organic chemical vapor deposition (MOCVD). The PSS was proved to be an efficient method to decrease the threading dislocation (TD) density in GaN epifilm with the lateral growth mode on PSS. The LED designed on PSS increased the electroluminescene (EL) intensity. The internal quantum efficiency is increased by reducing the dislocation density, and light extraction efficiency is also enhanced owing to PSS.

Characteristic Enhancement of InGaN-Based Light Emitting Diodes Grown on Pattern Sapphire Substrates

Blue light-emitting diodes (LEDs) with an InGaN multi-quantum well (MQW) structure were fabricated on cone-shaped patterned sapphire substrate (PSS) using a single growth process of metal organic chemical vapor deposition (MOCVD). The PSS was proved to be an efficient method to decrease the threading dislocation (TD) density in GaN epifilm with the lateral growth mode on PSS. The LED designed on PSS increased the electroluminescene (EL) intensity. The internal quantum efficiency is increased by reducing the dislocation density, and light extraction efficiency is also enhanced owing to PSS.

Carbide-leading texture of eutectic microstructure in As-cast high chromium cast balls

An unusual texture was observed in eutectic microstructure of high chromium cast balls. Amount of eutectic carbides, different from the eutectic austenite, were almost parallel to the cast ball surface. There were low-angle boundaries in the austenite grains or the carbide grains. It is seen that carbides have an axial nucleation mode and a lateral growth mode. Neither oriented nucleation nor oriented growth can account for the austenitic behavior individually. Really, austenite grows dependently of contiguous carbides, whose orientation is affected by both the spatial limit of contiguous carbides and the solidification temperature gradient. Finally, eutectic carbides effect the orientation of eutectic microstructure during solidification including the austenite deflection orientation.

Turbostratic multilayer graphene synthesis on CVD graphene template toward improving electrical performance

Multilayer graphene was synthesized by overlayer growth of graphene on a monolayer graphene template using a chemical vapor deposition method under a high process temperature of 1300 °C. Structural analysis using Raman spectra revealed that the synthesized multilayer graphene forms highly crystalline graphene layers with a turbostratic stacking structure. Atomic force microscope images indicated that the step edges of the grown graphene layer proceed via lateral growth mode. The electrical transport properties of the synthesized multilayer graphene showed higher conductivity and carrier mobility than those of the monolayer graphene template. The improvement of the electrical transport properties is caused by the turbostratic stacking structure that has the electronic band dispersion similar to that of monolayer graphene. This result means that the synthesis of graphene layers grown on the graphene template is effective to improve the carrier transport properties in multilayer graphene sheets.

Investigation of GaN with Low Threading Dislocation Density Grown on Graphene/Sputtered AlN Composite Substrate

High‐quality GaN film is grown on graphene with the underneath sputtered AlN modified layer using metal organic chemical vapor deposition. Due to the modulation effect of sputtered AlN on the surface potential and the chemical reactivity of graphene, the nucleation probability of GaN is significantly improved. The GaN epitaxial layer shows excellent crystal quality and surface morphology, and has very low threading dislocation density of 1.78 × 108 cm−2. Furthermore, the mechanism of threading dislocation suppression is revealed according to the transmission electron microscope results. The improved nucleation probability and enhanced lateral growth mode lead to the formation of short‐range stacking faults in c‐plane GaN, which block the propagation of threading dislocations along the growth direction. Moreover, the formation and evolution mechanism of the short‐range stacking faults are discussed. The results in this work not only offer a promising approach to propel the widespread application of GaN on graphene, but also provide a new idea for the regulation and suppression of defects in the growth of nitride semiconductors.

Sericin protein as a conformal protective layer to enable air-endurable Li metal anodes and high-rate Li-S batteries

As the most promising anode material for next-generation Li batteries, Li metal never loses the academic attention due to its inherent superiority in high theoretical capacity and low redox potential. However, Li dendrites formed during cycling stubbornly hinder the pace of commercializing high-energy-density Li metal batteries. Here sericin endowed with abundant lithiophilic and anionphilic functional groups on its polypeptide chain is proposed as a conformal protective coating on both Cu and Li metal anodes. The resulting increase of Li-ion transference number (as high as 0.876) and mitigation of tip effect are favorable for the homogeneous Li deposition in island-like or lateral growth mode at electrode/electrolyte interface. Long cycle life (335 cycles) and high Coulombic efficiency (98%) are obtained in sericin decorated Li/Cu cells. Even under extremely high current density of 10 mA cm−2 based on a large capacity of 5 mAh cm−2, the sericin decorated Li anode also enables a superior cycle stability (160 cycles) in the symmetric cells. The conformal sericin coating effectively inhibits the corrosion of air to Li metal. Sericin modified Li-S batteries exhibit greatly enhanced rate performance (452.8 mAh g−1 at 5 C) and cycling performance (667.8 mAh g−1 after 520 cycles at 1 C).

V-Defect and Dislocation Analysis in InGaN Multiple Quantum Wells on Patterned Sapphire Substrate

InGaN/GaN multiquantum well (MQW) structures have been grown on cone-shaped patterned sapphire substrates (CPSS) by metalorganic chemical vapor deposition (MOCVD). From the transmission electron microscopy (TEM) results, we found that most of the threading dislocations (TDs) in the trench region of the CPSS were bent by lateral growth mode. Also the staircase-like TDs were observed near the slant region of the cone pattern, they converged at the slope of the cone patterned region by staircase-upward propagation, which seems to effectively prevent TDs from vertical propagation in the trench region. The associated dislocation runs up into the overgrown GaN layer and MQW, and some (a+c) dislocations were shown to decompose inside the multi-quantum well, giving rise to a misfit segment in the c-plane and a V-shape defect. From cross-sectional TEM, we found that all V defects are not always connected with TDs at their bottom, some V defects are generated from the stacking mismatch boundaries induced by stacking faults which are formed within the MQW due to the strain relaxation.

Dislocation Evolution and Microstructural Properties on GaN Grown on Cone Patterned Sapphire Substrate

GaN epifilms are grown on the cone patterned sapphire substrates (CPSS) and the conventional sapphire substrates (CSS) by metal-organic chemical vapor deposition (MOCVD) using a two-step growth. We investigated dislocation structures and density in the GaN epifilms grown on CPSS and CSS using high resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM). HRXRD measurement shows that GaN epifilms grown on CPSS have lower dislocation density than the CSS, especially the edge dislocation density. This consequence is confirmed by metallographs of etched GaN. From the TEM results, we found that most of the threading dislocations (TDs) in the trench region of the CPSS were bent by lateral growth mode. The bending of dislocations and presence of voids dramatically prevent the generation of threading dislocations on the surface due to the induced lateral overgrowth mode. The high Raman peak intensity of the GaN epifilms grown on CPSS with a low full width at half maximum (FWHM) indicates that there is an improvement in the quality of the GaN compared to GaN epifilms grown on CSS.