Template For Growth Research Articles

Epitaxial Single-Crystal Growth of Transition Metal Dichalcogenide Monolayers via the Atomic Sawtooth Au Surface.

Growth of 2D van der Waals layered single-crystal (SC) films is highly desired not only to manifest the intrinsic physical and chemical properties of materials, but also to enable the development of unprecedented devices for industrial applications. While wafer-scale SC hexagonal boron nitride film has been successfully grown, an ideal growth platform for diatomic transition metal dichalcogenide (TMdC) films has not been established to date. Here, the SC growth of TMdC monolayers on a centimeter scale via the atomic sawtooth gold surface as a universal growth template is reported. The atomic tooth-gullet surface is constructed by the one-step solidification of liquid gold, evidenced by transmission electron microscopy. The anisotropic adsorption energy of the TMdC cluster, confirmed by density-functional calculations, prevails at the periodic atomic-step edge to yield unidirectional epitaxial growth of triangular TMdC grains, eventually forming the SC film, regardless of the Miller indices. Growth using the atomic sawtooth gold surface as a universal growth template is demonstrated for several TMdC monolayer films, including WS2 , WSe2 , MoS2 , the MoSe2 /WSe2 heterostructure, and W1- x Mox S2 alloys. This strategy provides a general avenue for the SC growth of diatomic van der Waals heterostructures on a wafer scale, to further facilitate the applications of TMdCs in post-silicon technology.

Macroscopic properties of single-crystalline and polycrystalline graphene on soft substrate for transparent electrode applications

Large-area graphene synthesized by a chemical vapor deposition (CVD) method is promising for a flexible, stretchable transparent electrode but suffers from structural defects such as grain boundaries, which causes to degrade its physical properties. Recently, preparation methods of large-scale growth templates for single-crystalline graphene (SCG) were reported, but the macroscopic properties of SCG have not been adequately examined yet. Here, an SCG-based flexible, stretchable graphene transparent electrode is successfully demonstrated, which shows superior optoelectrical, electromechanical, and barrier properties compared to polycrystalline graphene (PCG)-based transparent electrodes. The result exhibits the grain boundary effect of graphene on soft substrates on a macroscopic scale and a great promise toward realizing a tremendous performance improvement of graphene-based flexible transparent electrodes on a large scale.

Temperature Effect on the Topotatic Synthesis of Spinel MnCoO Nanoparticles for Efficient Oxygen Reduction Electrocatalyst

In this study, we demonstrated the temperature effect of our previously developed topotatic catalysis for the formation of Mn0.005Co2.995O4 (MnCoO) spinel nanoparticles. Topotatic catalysis induces spinel MnCoO nanoparticles through the redox reaction of the metal cation (Co2+ and Mn2+) on the Co(OH)2 nanosheet surface, acting as a growth template. This study particularly elucidates the temperature effect on spinel MnCoO nanoparticles' size, morphology, and crystallinity based on their electrocatalytic performance in an oxygen reduction reaction (ORR). We found that lower temperature produces an amorphous phase, whereas higher temperature induces a large aggregate. We obtained the monodispersed MnCoO nanocubes at approximately 90°C, exhibiting the best ORR performance with an electron‐transfer number of 3.86.

Bioactive Materials for Soft Tissue Repair.

Over the past decades, age-related pathologies have increased abreast the aging population worldwide. The increased age of the population indicates that new tools, such as biomaterials/scaffolds for damaged tissues, which display high efficiency, effectively and in a limited period of time, for the regeneration of the body's tissue are needed. Indeed, scaffolds can be used as templates for three-dimensional tissue growth in order to promote the tissue healing stimulating the body's own regenerative mechanisms. In tissue engineering, several types of biomaterials are employed, such as bioceramics including calcium phosphates, bioactive glasses, and glass–ceramics. These scaffolds seem to have a high potential as biomaterials in regenerative medicine. In addition, in conjunction with other materials, such as polymers, ceramic scaffolds may be used to manufacture composite scaffolds characterized by high biocompatibility, mechanical efficiency and load-bearing capabilities that render these biomaterials suitable for regenerative medicine applications. Usually, bioceramics have been used to repair hard tissues, such as bone and dental defects. More recently, in the field of soft tissue engineering, this form of scaffold has also shown promising applications. Indeed, soft tissues are continuously exposed to damages, such as burns or mechanical traumas, tumors and degenerative pathology, and, thereby, thousands of people need remedial interventions such as biomaterials-based therapies. It is known that scaffolds can affect the ability to bind, proliferate and differentiate cells similar to those of autologous tissues. Therefore, it is important to investigate the interaction between bioceramics and somatic/stem cells derived from soft tissues in order to promote tissue healing. Biomimetic scaffolds are frequently employed as drug-delivery system using several therapeutic molecules to increase their biological performance, leading to ultimate products with innovative functionalities. This review provides an overview of essential requirements for soft tissue engineering biomaterials. Data on recent progresses of porous bioceramics and composites for tissue repair are also presented.

Bandgap-Coupled Template Autocatalysis toward the Growth of High-Purity sp2 Nanocarbons.

Extraordinary properties and great application potentials of carbon nanotubes (CNT) and graphene fundamentally rely on their large‐scale perfect sp2 structure. Particularly for high‐end applications, ultralow defect density and ultrahigh selectivity are prerequisites, for which metal‐catalyzed chemical vapor deposition (CVD) is the most promising approach. Due to their structure and peculiarity, CNTs and graphene can themselves provide growth templates and nonlocal dual conductance, serving as template autocatalysts with tunable bandgap during the CVD. However, current growth kinetics models all focus on the external factors and edges. Here, the growth kinetics of sp2 nanocarbons is elaborated from the perspective of template autocatalysis and holistic electronic structure. After reviewing current growth kinetics, various representative works involving CVD growth of different sp2 nanocarbons are analyzed, to reveal their bandgap‐coupled kinetics and resulting selective synthesis. Recent progress is then reviewed, which has demonstrated the interlocking between the atomic assembly rate and bandgap of CNTs, with an explicit volcano dependence whose peak would be determined by the environment. In addition, the topological protection for perfect sp2 structure and the defect‐induced perturbation for the interlocking are discussed. Finally, the prospects for the kinetic selective growth of perfect nanocarbons are proposed.

Synthesis of a zigzag carbon nanobelt.

The structure-selective precise synthesis of carbon nanotubes (CNTs) has been long sought in materials science. The aromatic molecules corresponding to segment structures of CNTs, that is, carbon nanobelts (CNBs), are of interest as templates for CNT growth. Among the three types of CNB (armchair, chiral and zigzag CNBs), zigzag CNBs have been considered the most difficult type to synthesize. Here we report the synthesis, isolation and structural characterization of a zigzag CNB. The synthesis involves an iterative Diels-Alder reaction sequence followed by reductive aromatization of oxygen-bridged moieties. As predicted by theoretical calculations, this CNB was isolated as a stable compound. The structure of the zigzag CNB was fully characterized by X-ray crystallography and its wide energy gap with blue fluorescence properties was revealed by photophysical measurements. With synthetic strategies towards all three types of CNB in hand, the road to the precise synthesis of CNTs can now proceed to the next stage.

GaN Nanowire Growth Promoted by In-Ga-Au Alloy Catalyst with Emphasis on Agglomeration Temperature and In Composition.

The crystallographic orientation control of GaN nanowires (NWs) has been widely investigated by varying the V–III ratio. Here, we report the tuning of crystallographic orientation of GaN NWs by varying the composition of indium (In) in gallium–gold (Ga–Au) alloy catalyst using metal–organic chemical vapor deposition (MOCVD). The c-plane GaN thin film and sapphire substrate are used as growth templates. We found that the substrates of same orientation have a negligible influence on the orientation of the GaN NWs. The catalyst composition and the dimensions of alloy droplets determine the morphology of the NWs. The density of the NWs was controlled by tuning the droplet size of the alloy catalysts. With the constant V/III ratio, the crystallographic orientation of the GaN NWs was tuned from m- to c-axis by increasing the In composition inside alloy catalyst.

Epitaxy of an Organic Semiconductor Templated by Molecular Monolayer Crystals

Molecular template growth is an efficient approach to enhance the crystallinity of organic semiconductor materials deposited by physical vapor deposition methods. Lattice matching, large grain size, and large monolayer coverage are critical figures of merits to evaluate effective templates. Here, solution-processed molecular monolayer crystals (MMCs) with 100% monolayer coverage and large single-crystalline domain size present the optimum form of molecular templates, which are successfully utilized for the growth of organic semiconductor thin films. Commensurate epitaxy growth over a large area was observed, and the reason for widely observed lamella structures in thin films was disclosed. In addition, the MMCs are proven effective in templating the growth of various high-performance organic semiconductor materials into orientated thin films. The MMC template provides an efficient approach to enhance the crystallinity and regulate the molecular orientation of organic semiconductor thin films.

Strain-relaxed tetragonal MAPbI3 results in efficient mesoporous solar cells

In mesoporous organo-halide perovskite solar cells, the coexistence of tetragonal phase and cubic phase in the perovskite layer is found to result in strained crystal structure at the mesoporous TiO 2 (mp-TiO 2 )/perovskite heterointerface. This results in structural defects pinholes, grain boundaries, and interfacial porosity which is detrimental towards photovoltaic performance and device stability. The strain at the interface originates from the lattice mismatch between the mp-TiO 2 nanoparticles (NPs) and perovskite. Here, a transformative approach is demonstrated to realize relaxed and high purity tetragonal phase MAPbI 3 (RP) near the mp-TiO 2 interface region. This approach involves inserting a ~2 nm lattice matched buffer layer of cubic CsPbBr 3 between mp-TiO 2 NPs and MAPbI 3 , which serves as a template for epitaxial growth for top MAPbI 3 . The solar cell with relaxed MAPbI 3 shows a power conversion efficiency (PCE) of 22.12% with significantly enhanced environmental, light, and thermal stability. • Strain engineering is invoked to achieve strain-relaxed and tetragonal MAPbI 3 at the mp-TiO 2 /MAPbI 3 heterointerface. • The modified relaxed MAPbI 3 -based device exhibits a PCE of 22.12%. • The modified devices show enhanced environmental, thermal, and light stabilities.

Nitride‐Oxide‐Metal Heterostructure with Self‐Assembled Core–Shell Nanopillar Arrays: Effect of Ordering on Magneto‐Optical Properties

Magneto-optical (MO) coupling incorporates photon-induced change of magnetic polarization that can be adopted in ultrafast switching, optical isolators, mode convertors, and optical data storage components for advanced optical integrated circuits. However, integrating plasmonic, magnetic, and dielectric properties in one single material system poses challenges since one natural material can hardly possess all these functionalities. Here, co-deposition of a three-phase heterostructure composed of a durable conductive nitride matrix with embedded core-shell vertically aligned nanopillars, is demonstrated. The unique coupling between ferromagnetic NiO core and atomically sharp plasmonic Au shell enables strong MO activity out-of-plane at room temperature. Further, a template growth process is applied, which significantly enhances the ordering of the nanopillar array. The ordered nanostructure offers two schemes of spin polarization which result in stronger antisymmetry of Kerr rotation. The presented complex hybrid metamaterial platform with strong magnetic and optical anisotropies is promising for tunable and modulated all-optical-based nanodevices.

Synthesis of textured Li0.33La0.55TiO3 solid electrolytes by molten salt method

Li0.33La0.55TiO3 (LLTO) with perovskite structure has very high grain conductivity. In this article, textured LLTO is synthesized by molten salt method. The X-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM) reveal that the reaction temperature and molten salts have effect on the template growth of LLTO. When the temperature does not reach the synthetic temperature of LLTO, some intermediate phases appear. As the temperature increases, the morphology of LLTO samples gradually changes from a rod-like structure to a sheet-like one. It is demonstrated that textured LLTO prepared by molten salt method shows highly (200) preferred orientation with a Lotgering factor of 0.66. The relative density of LLTO pellets reaches 94.9% together with a relatively high ionic conductivity of 2.70 × 10−5 S/cm. The growth mechanism of textured LLTO is discussed in terms of temperature- and molten salt-dependent diffusion of Ti elements; furthermore, the stable environment formed by LiCl–KCl molten salt can promote its preferential growth.

Copper sulfide as the cation exchange template for synthesis of bimetallic catalysts for CO2 electroreduction.

Among metals used for CO2 electroreduction in water, Cu appears to be unique in its ability to produce C2+ products like ethylene. Bimetallic combinations of Cu with other metals have been investigated with the goal of steering selectivity via creating a tandem pathway through the CO intermediate or by changing the surface electronic structure. Here, we demonstrate a facile cation exchange method to synthesize Ag/Cu electrocatalysts for CO2 reduction using Cu sulfides as a growth template. Beginning with Cu2−xS nanosheets (C-nano-0, 100 nm lateral dimension, 14 nm thick), varying the Ag+ concentration in the exchange solution produces a gradual change in crystal structure from Cu7S4 to Ag2S, as the Ag/Cu mass ratio varies from 0.3 to 25 (CA-nano-x, x indicating increasing Ag fraction). After cation exchange, the nanosheet morphology remains but with increased shape distortion as the Ag fraction is increased. Interestingly, the control (C-nano-0) and cation exchanged nanosheets have very high faradaic efficiency for producing formate at low overpotential (−0.2 V vs. RHE). The primary effect of Ag incorporation is increased production of C2+ products at −1.0 V vs. RHE compared with C-nano-0, which primarily produces formate. Cation exchange can also be used to modify the surface of Cu foils. A two-step electro-oxidation/sulfurization process was used to form Cu sulfides on Cu foil (C-foil-x) to a depth of a few 10 s of microns. With lower Ag+ concentrations, cation exchange produces uniformly dispersed Ag; however, at higher concentrations, Ag particles nucleate on the surface. During CO2 electroreduction testing, the product distribution for Ag/Cu sulfides on Cu foil (CA-foil-x-y) changes in time with an initial increase in ethylene and methane production followed by a decrease as more H2 is produced. The catalysts undergo a morphology evolution towards a nest-like structure which could be responsible for the change in selectivity. For cation-exchanged nanosheets (CA-nano-x), pre-reduction at negative potentials increases the CO2 reduction selectivity compared to tests of as-synthesized material, although this led to the aggregation of nanosheets into filaments. Both types of bimetallic catalysts are capable of selective reduction of CO2 to multi-carbon products, although the optimal configurations appear to be metastable.

Recent progress in metal-organic framework/graphene-derived materials for energy storage and conversion: design, preparation, and application.

Graphene or chemically modified graphene, because of its high specific surface area and abundant functional groups, provides an ideal template for the controllable growth of metal–organic framework (MOF) particles. The nanocomposite assembled from graphene and MOFs can effectively overcome the limitations of low stability and poor conductivity of MOFs, greatly widening their application in the field of electrochemistry. Furthermore, it can also be utilized as a versatile precursor due to the tunable structure and composition for various derivatives with sophisticated structures, showing their unique advantages and great potential in many applications, especially energy storage and conversion. Therefore, the related studies have been becoming a hot research topic and have achieved great progress. This review summarizes comprehensively the latest methods of synthesizing MOFs/graphene and their derivatives, and their application in energy storage and conversion with a detailed analysis of the structure–property relationship. Additionally, the current challenges and opportunities in this field will be discussed with an outlook also provided.

Surface Nanostructure Control with Poly(ethylene glycol) (PEG) Spacer by Templateless Electropolymerization

Controlling the shape of surface nanostructures is fundamental for various potential applications for examples, in water harvesting systems, liquid transportation or oil/water separation membranes. In this paper, the creation of porous surface structures is made by a process called templateless electropolymerization, in which water (H2O) is oxidized/reduced to form gas (O2/H2) bubbles onto the surfaces and acting as soft template for the polymer growth. Keeping the monomer (thieno[3,4-b]thiophene) and the substituent (pyrene) constant, we demonstrate how a flexible PEG spacer can affect the structure shape. When the PEG spacer increases, the structures change from nanotubes (1D growth) to nanoribbons (2D) and after to hollow nanospheres (3D), which also affects the wetting properties.

Delicate control of crystallographic Cu2O derived Ni–Co amorphous double hydroxide nanocages for high-performance hybrid supercapacitors: an experimental and computational investigation

The reasonable design of the composition and hollow structure of electrode materials is beneficial for promoting the electrochemical properties and stability of electrode materials for high-performance supercapacitors, and it is of great significance to understand the inherent effect of these features on their performance. In this paper, the amorphous Ni-Co double hydroxide nanocages with hollow structures (Ni-Co ADHs) including quasi-sphere, cube and flower are delicately tailored via a Cu2O template-assisted approach. By combining experimental characterization and density functional theory (DFT) calculations, we systematically study the morphological growth of Cu2O templates under different conditions and the electrochemical performance of Ni-Co ADHs. Due to the coordination and synergistic effect between different components, the unique hollow structure and the nature of amorphous materials, Ni-Co ADHs deliver a high specific capacitance of 1707 F g-1 at 1 A g-1. The DFT calculations demonstrate that Ni-Co ADH nanocages exhibit an optimal redox reaction energy barrier and immensely promote the performance. In addition, a hybrid supercapacitor assembled with Ni-Co ADHs as a cathode and active carbon (AC) as an anode shows a high energy density of 33.8 W h kg-1 at a power density of 850 W kg-1 and exhibits an excellent cycling performance with a retention rate of 98% after 50 000 cycles. The successful synthesis of Ni-Co ADH nanocages, combined with rational computational simulations, indicates the excellent electrochemical performance and the potential utilization of amorphous hollow nanomaterials as electrodes for supercapacitors.

Synthesized and characterization of open-ended Ta3N5 nanotube arrays for the preparation of growth template

In this article, a two-step anodization method was applied to tantalum foils to grow compact open-ended tantalum oxide nanotube arrays, which were subsequently subject to high temperature nitridation. The nitride nanotube arrays were characterized with SEM, XRD, and electrochemical tests including I-V and Mott-Schottky analysis. The phases in the nitrided nanotube arrays may consist of Ta3N5, TaN, TaN0.5, N-Ta2O, or the amorphous oxide. The duration of the second anodization step was found to play a key role on the microstructure and the carrier density of the nitride nanotube arrays. It is found that the duration of the second anodization has to be more than 20 min to obtain a specimen with a top layer of Ta3N5, which can work as a photo electrode or a template for the growth of photo catalyst nanomaterials.

Fabrication of van der Waals heterostructures through direct growth of rhenium disulfide on van der Waals surfaces

The growth of van der Waals (vdW) heterostructures has been desired to achieve two-dimensional (2D) layered heterostructures with various types of junctions for new functional device applications. ReS2 is one of the most promising semiconducting 2D materials for providing new electronic and optoelectronic properties when integrated into a vdW heterostructure. However, owing to its low-symmetry distorted 1T crystalline structure, there are few reports on continuous high-quality vdW heterostructures unlike those on 2D materials with a symmetric 2H crystalline structure. Herein, we report on the first demonstrated ReS2/HfS2 and ReS2/h-BN vdW heterostructures through the direct growth of ReS2 films on exfoliated HfS2 and h-BN with symmetric 1T (HfS2) and 2H (h-BN) crystalline structures. Few-layered continuous ReS2 films were grown on vdW surfaces of exfoliated 2D material flakes with highly crystalline structures, and the growth behavior is explained through a surface-dependent direct growth process with vdW epitaxy. This work verifies that symmetry-free direct growth of 2D vdW heterostructures can be achieved using a 2D material as the growth template with a high growth rate, which provides a path for developing various types of multi-functional vdW heterostructures.

Controlling facets and defects of InP nanostructures in confined epitaxial lateral overgrowth

The selective area growth technique, confined epitaxial lateral overgrowth (CELO), enables the growth of lateral III-V heterojunctions integrated on mismatched substrates. In CELO, effective control of facet shapes, as well as defect-free growths are essential to fabricating high-quality nanostructures with custom geometries. Here, the effects of growth temperature, V/III ratio, template alignments, and substrate orientations on the observed facets and defect densities in CELO grown InP and related materials on InP substrates are investigated. The nanostructure facets and defects are determined using a combination of plan-view and cross-sectional transmission electron microscopy. For homoepitaxial CELO growth on InP (100) substrates, growth temperatures below $575{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, and high V/III ratios of 450 aid in increasing the surface areas of the {111}B facets, while reducing defect densities. Further, by changing template alignments, the effective areas of overgrowth can be tuned, and defects can be lowered, with templates aligned along $[0\overline{1}0]$ yielding the largest defect-free areas. By aligning templates in the $[\overline{1}10]$ orientation on a (110) InP substrate, near defect-free overgrowth with perfectly flat perpendicular single ($1\overline{1}$ 0) facets can be achieved. This is an essential feature to enable the growth of lateral III-V heterojunctions, as is demonstrated by growing InP/InGaAs CELO heterojunctions with {110} facets.

Electrografting and electropolymerization of nanoarrays of PANI filaments through silica mesochannels

Vertically aligned mesoporous silica films electrogenerated on indium-tin oxide (ITO) electrodes are used as hard templates for the electrochemical growth of polyaniline (PANI) nanofilaments. To ensure proper adhesion of PANI to the underlying ITO surface, aniline moieties are first covalently attached to the bottom of mesochannels via electrografting of aminophenyl diazonium cations, serving in a second step as precursors for PANI growth by electropolymerization of aniline through the silica mesochannels. This was achieved by cyclic voltammetry or potentiostatically at an applied potential of +0.85 V (vs. Ag/AgCl), the latter offering a better control of the nanofilaments length by tuning the electropolymerization time. PANI wires remain attached to ITO after etching of the silica membrane, confirming the importance of initial electrografting. Although PANI nanofilaments in the silica membrane remain electroactive, enhanced peak currents were observed after silica removal as PANI nanofilaments offer a larger effective surface area to the electrolyte solution.

Large-Area Graphene Transfer through Synthesis of an Interfacial Release Layer between Epitaxial Cu(Ni)(111) and Al2O3(0001) Template

As the pioneer two-dimensional material with outstanding properties, graphene is still lacking a CMOS compatible handling process, both for growth and transfer. This restriction slows down the application of large-scale-high-quality monolayer graphene (MLG). The synthesis of wafer-scale single-crystal MLG has matured utilizing a single-crystal Cu(111) deposit epitaxially on c-plane sapphire as a growth template[1,2]. However, the non-straightforward intercalation base transfer process [3] becomes a bottleneck. Hence, an interfacial release layer between Cu and sapphire could provide an alternative route for the graphene transfer process.Here, we report on the synthesis of large-area multilayer graphene at the interface of epitaxial Cu(Ni)(111)/ Al2O3(0001) using atmospheric pressure chemical vapor deposition (CVD). The interfacial carbon layer (ICL) was synthesized by introducing CH4 and H2 gases in the CVD chamber at 1050°C, and characterized by micro-Raman spectroscopy, XRD, and AFM. Carbon layers with thickness up to 80nm were observed at the interface between 500nm thick Cu and Al2O3.The effects of the partial pressure of gases - PH2 and PCH4 – and template substrate on the growth dynamics were investigated systematically by optical microscopy and image analysis. The growth rate and deposition area of ICL are positively correlated with PCH4. In the Cu85Ni15(111) system, ICL coverage is significantly lower compared to Cu(111). This is attributed to the faster growth rate of a top surface MLG, which blocks the access of carbon into the interface of Cu(Ni)/Al2O3. A higher PH2 slows down the MLG growth, leading to a denser ICL deposition in both substrates.The growth mechanism of this ICL is also proposed as the result of two competing effects: 1. The high PCH4 environment drives the decomposed carbon species to the interface from the top surface by diffusion through the bulk of the catalytic metal. 2. The blockage of carbon access to the bulk of metal once the top layer MLG is closed.After process optimization, the ICL could be synthesized simultaneously with top layer high-quality CVD MLG. In the future, this process could provide opportunities to enable CMOS compatible large-scale-high-quality MLG transfer. K. Verguts et al., ECS J. Solid State Sci. Technol., 5, Q3060–Q3066 (2016).M. Huang et al., ACS Nano, 12, 6117–6127 (2018).K. Verguts et al., ACS Appl. Mater. Interfaces, 9, 37484–37492 (2017).