High-index Planes Research Articles

Synthesis of Chiral Ag, Pd, and Pt Helicoids inside Chiral Silica Mold.

Chiral inorganic nanomaterials hold significant promise for various applications, including enantioselective catalysis, polarization-controlling optical devices, metamaterials, and enantioselective molecular sensors. In our previous work, we presented a method for synthesizing chiral Au 432 helicoid III (Au helicoids) from peptides and amino acids, where helical gaps are intricately arranged with 432 symmetry within single cubic nanoparticles. In this study, we have achieved the fabrication of chiral silica molds through Au etching subsequent to the silica coating of Au helicoids. We demonstrate that these molds serve as geometrically confined reactors capable of producing chiral Ag, Pd, and Pt 432 helicoid III (Ag, Pd, and Pt helicoids). The morphology of the synthesized Ag, Pd, and Pt helicoids closely resembles that of the Au helicoids, exhibiting a superior g-factor compared to other reported chiral structures of each material. Notably, the Ag and Pd helicoids are found to be single-crystalline, with high-index planes exposed within the gaps. We believe that this silica mold-based approach can be generalized to synthesize chiral nanomaterials of various metal and even oxide materials.

Investigating chiral morphogenesis of gold using generative cellular automata.

Homochirality is an important feature in biological systems and occurs even in inorganic nanoparticles. However, the mechanism of chirality formation and the key steps during growth are not fully understood. Here we identify two distinguishable pathways from achiral to chiral morphologies in gold nanoparticles by training an artificial neural network of cellular automata according to experimental results. We find that the chirality is initially determined by the nature of the asymmetric growth along the boundaries of enantiomeric high-index planes. The deep learning-based interpretation of chiral morphogenesis provides a theoretical understanding but also allows us to predict an unprecedented crossover pathway and the resulting morphology.

High-efficient carbon dioxide-to-formate conversion on Bi5O7NO3 by tuning the exposure of crystal plane during reconstruction in electrolysis

The electrochemical conversion of carbon dioxide into formic acid offers an effective approach for utilizing carbon dioxide resources. Bismuth (Bi)-based catalysts have garnered significant attention in this field. However, designing high-performance Bi-based catalysts is challenging due to difficulties in accurately adjusting the reconstruction of such catalysts during electrolysis. In this study, we reported that nitrate ions positively influence the reconstruction of Bi5O7NO3 (BON), thereby outperforming Bi2O3 during ECO2RR. BON attained a Faraday efficiency of formate (FEHCOOH) and partial current density of 95.3 % and 25.1 mA/cm2 at −0.9 V vs RHE, respectively, surpassing the performance of Bi2O3 (90.2 % and 15.4 mA/cm2). The layered structure of BON mitigates Bi agglomeration during electrolysis, thus providing a large number of active sites. The presence of nitrate ions promotes exposure to abundant Bi(110) and Bi(015), whereas only the Bi(012) plane forms in Bi2O3 during electrolysis. In-situ ATR FTIR results indicate that both BON and Bi2O3 follow the same pathway for formate formation. Nevertheless, the high-index planes (015) cause the Bi derived from BON to remain in an electron defect state, which increases the adsorption of *CO2. In addition, Bi(110) plane has effectively lower the energy barriers for *OCHO production than Bi(012) plane. The Bi(015) and Bi(110) planes enhance the adsorption of *CO2 intermediates and reduce the energy barrier for *OCHO formation, respectively, which contributes to the improved ECO2RR activity of BON.

Engineering hydrophobicity and high-index planes of gold nanostructures for highly selective electrochemical CO2 reduction to CO and efficient CO2 capture

In current study, we demonstrate a strategy for improving the catalytic performance of gold (Au) for carbon dioxide reduction reaction (CO2RR), specifically enhancing selectivity for CO over hydrogen evolution reaction (HER) and increasing low-level CO2 capture efficiency. This involved controlling nanostructures without any further modification. Au nanostructures having four different morphologies (i.e., degree of roughness) were fabricated via electrodeposition at varied deposition potential, resulting in different intrinsic surface hydrophobicity and exposure of high-index planes depending on the actual morphology. The roughest Au, with its combination of the most hydrophobic feature and abundant high-index planes, generated greater partial current density (jCO) and faradaic efficiency for CO (FECO) than the other Au deposits within a tested potential region: The roughest Au showed 6-fold higher FECO (95.8 %) and 327-fold higher jCO (normalized to electrode geometric surface area) at −0.75 VRHE compared to the smoothest Au. Moreover, the roughest Au exhibited excellent CO2 capture ability even at low CO2 concentration, confirmed with scanning electrochemical microscopy. These improvement at hierarchical Au for CO2RR could be ascribed to two factors. Firstly, the morphology-driven hydrophobicity provides an optimal gas–liquid-solid triple-phase interfaces, increasing the local CO2 concentration near the Au catalyst surface due to its superb CO2 capture ability. Secondly, the abundant high-index planes serve as stable active sites for CO2RR, expediting the reaction rates. Remarkably, Au with the highest hydrophobicity and enriched high-index planes, even without any chemical modification, showed excellent CO2RR catalytic performance comparable to or even better than the other previously reported Au-based catalysts.

Fabrication of self-standing large (111) single crystal diamond using bulk growth of (100) CVD diamond and lift-off process

Diamond (111) plane is superior in impurity doping and quantum spin control to (100) plane, however, there are many technical issues in mass production of the substrate, such as a smaller seed substrate size, low removal rate of polishing, and low growth rate. In this study, a large (111) single crystal diamond substrate of 7 mm × 6 mm was fabricated by growing and processing bulk (100) CVD single crystal. Furthermore, using this as a seed substrate, a (111) self-standing plate was fabricated using the lift-off method. The FWHM of the X-ray rocking curve was 46 arcsec and that of the Raman peak was 2 cm−1. This method can be applied to fabrication of any high index plane such as (113) and can be utilized to fabrication of substrate for electronic and quantum devices, device processing to fabricate vertical structure.

Strain-induced specific orbital control in a Heusler alloy-based interfacial multiferroics

For the development of spintronic devices, the control of magnetization by a low electric field is necessary. The microscopic origin of manipulating spins relies on the control of orbital magnetic moments (morb) by strain; this is essential for the high performance magnetoelectric (ME) effect. Herein, electric-field induced X-ray magnetic circular dichroism (XMCD) is used to determine the changes in morb by piezoelectric strain and clarify the relationship between the strain and morb in an interfacial multiferroics system with a significant ME effect; the system consists of the Heusler alloy Co2FeSi on a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrate. Element-specific investigations of the orbital states by operando XMCD and the local environment via extended X-ray absorption fine structure (EXAFS) analysis show that the modulation of only the Fe sites in Co2FeSi primarily contributes to the giant ME effect. The density functional theory calculations corroborate this finding, and the growth of the high index (422) plane in Co2FeSi results in a giant ME effect. These findings elucidate the element-specific orbital control using reversible strain, called the ‘orbital elastic effect,’ and can provide guidelines for material designs with a giant ME effect.

Sketching Precursor Evolution to Delineate Growth Pathways for Anatase (TiO2) Crystal Design.

Engineering advanced functional materials such as Anatase crystals through the molecular tuning of crystal facets is the current enigma of interest pertinent to solving the structure-property-performance triad. Developing optimal shapes and sizes of crystallite necessitates exploring the nanoscopic growth mechanism via precursor tracking. Here, the tapestry of particles varying in dimensionality (0D-3D), sizes (8-3000nm), and morphology (aggregated to highly faceted crystals) is generated. To decipher and subsequently modulate the crystallization pathways, high-resolution microscopy (high-resolution transmission electron microscopy(HRTEM) and field emission scanning electron microscopy(FESEM)) is used to sketch time-stamped particle evolution. Interestingly, the studies provide evidence for 4-distinct mechanisms where nanoparticles/nanosheets play direct and/or indirect roles in crystallization through multi-stage aggregation (primary, secondary, and tertiary) beginning with similar growth solutions. The four distinct pathways elucidate bulk particle formation via non-classical routes of crystallization including nanosheet alignment and aggregation, nanocrystallite formation and fusion, nanobeads formation and attachment, and direct nanosheet incorporation in bulk crystals. Notably, the direct evidence of flexible-partially-ordered nanosheets being subsumed along the contours of bulk crystals is captured. These novel syntheses generated uniquely faceted particles with high-indexed surface planes such as (004), (200), and (105), amenable to photocatalytic applications.

In-situ study on factors impeding dislocation motion in Fe9Cr1.5W0.4Si F/M steel during high temperature heating

Ferritic/martensitic (F/M) steels are promised candidate materials for the lead-cooled fast neutron reactor. However, their poor high temperature performance limits the highest in-core temperature, decreasing the reactor economics. High dislocation mobility directly related to the low strength of F/M steels but the underlying mechanisms remain unexplored. Here, in-situ heating was performed on irradiated Fe9Cr1.5W0.4Si ferritic martensitic steel in the temperature range of 873–923 K, and the interaction between dislocation lines and obstacles was investigated to reveal the mechanism that led to easier dislocation gliding. Dislocations tended to glide in several planes at the same time and only glided as a whole in one plane occasionally. It was discovered that dislocations usually glided in high index planes such as {123} planes. When moving dislocations intersected with forest dislocations, a new mechanism was found where the segments for different dislocations with the same Burgers vector could exchange, which was important for the moving dislocation to cut through the forest dislocations without decreasing their mobility. The reactions between dislocations and <100> loops included absorption, break away and rebound. Meanwhile, statistical results indicated that the highest ratio was about 48% for the case where <100> loops were restored and dislocations broke away, demonstrating that the <100> loops were not strong obstacles when interacting with moving dislocations at high temperature.

Nontypical Wulff-Shape Silicon Nanosheets with High Catalytic Activity.

Nanostructured silicon with an equilibrium shape has exhibited hydrogen evolution reaction activity mainly owing to its high surface area, which is distinct from that of bulk silicon. Such a Wulff shape of silicon favors low-surface-energy planes, resulting in silicon being an anisotropic and predictably faceted solid in which certain planes are favored, but this limits further improvement of the catalytic activity. Here, we introduce nanoporous silicon nanosheets that possess high-surface-energy crystal planes, leading to an unconventional Wulff shape that bolsters the catalytic activity. The high-index plane, uncommonly seen in the Wulff shape of bulk Si, has a band structure optimally aligned with the redox potential necessary for hydrogen generation, resulting in an apparent quantum yield (AQY) of 12.1% at a 400 nm wavelength. The enhanced light absorption in nanoporous silicon nanosheets also contributes to the high photocatalytic activity. Collectively, the strategy of making crystals with nontypical Wulff shapes can provide a route toward various classes of photocatalysts for hydrogen production.

Tunning the bandgap of MnO2 homojunction by building active high-index facet to achieve rapid electron transfer for enhanced photocatalytic sterilization

Photocatalysis has been a research hotspot in recent years, and the design and modification of photocatalysts have been the key points. Common methods for designing photocatalysts, including constructing heterojunctions and homojunctions, have been developed on the basis of heterojunctions. In this study, two homojunctions of manganese dioxide (MnO2), including a high-index crystal plane homojunction and a general homojunction, are prepared using a stepwise hydrothermal method. Using a capping agent, the high-index crystal surface of the MnO2 is exposed. It is found that the electron transport efficiency between the two components of the homojunction with high-index planes is higher and the adsorption capacity of the oxygen is stronger, which leads to higher photocatalytic efficiency. In addition, the newly designed high-index homojunction is used for the treatment of bacterial infections, and it kills Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) at rates of 99.95% ± 0.04% and 99.31% ± 0.25%, respectively. It also has excellent therapeutic effects on mouse wounds, which implies superb practical application value. This work provides a new strategy for the improved design of homojunctions and the application of photocatalytic materials.

Facet effect of MnCo2O4 nanocrystals for enhanced oxygen reduction reaction in alkaline medium

Understanding the mechanism of the four-electron transfer oxygen reduction reaction (ORR) and the structure–activity relationship of spinel oxide remains a challenge. Two bimetallic manganese-cobalt spinel oxide supported on carbon nanotube (MnCo2O4/CNT) composite materials with different crystal planes exposed are synthesized in this paper by adding unequal amounts of ammonia during the hydrothermal process. Physical characterization results indicate that the exposed surfaces of the two materials (MnCo2O4/CNT-100, MnCo2O4/CNT-800) are (001) and (112), respectively. Electrochemical tests demonstrate that the MnCo2O4/CNT-800 composite material exposed to the (112) crystal plane exhibit higher ORR catalytic activity in alkaline electrolyte, with a half-wave potential of 0.79 V and a limiting current density of 5.15 mA cm−2. The outstanding activity is attributed to the greater specific surface area, the exposure of high-index crystal plane and the high-valence metal sites on the surface. Density functional theory (DFT) calculations reveal that the active sites on the (112) crystal plane have improved adsorption and ORR thermodynamics. This work provides a strategy for developing the advanced bimetallic spinel electrocatalysts by adjusting the exposed plane.

Interface structure between Nb thin film and MgO(112) substrate: A first-principles prediction

The crystal orientation of ceramic substrates is an important factor affecting the interface structure of metal/ceramic composite materials. However, there is little information about the interface composed of metal films and ceramic substrates with a high-index plane. In this work, we predicted the interface structure between a Nb film and a MgO(112) substrate by calculating the interface separation works of different interface models by using the first-principles calculation method. The results showed that the preferred growth direction is Nb [120], and that the value of the interface separation work is 0.35 eV/Å2. The lattice mismatch between the film and substrate is less than 3%, implying that a coherent interface type is highly realizable in Nb/MgO(112). Furthermore, we analyzed the interface structures of Nb/MgO(100), Nb/MgO(110), Nb/MgO(111), and Nb/MgO(112) and found that the unique atomic configuration of the MgO substrate is the main factor determining the preferred interface structure of Nb/MgO.

Improved electrocatalytic hydrogen evolution characteristics in Mn-doped MoS2 nanosheets grown under a non-equilibrium condition

Two-dimensional (2D) monolayer pristine MoS2 transition metal dichalcogenide (TMDC) is the most investigated material due to its potential applications as a non-precious electrocatalyst for the hydrogen evolution reaction (HER). However, the active edge sites created by sulfur non-stoichiometry and a defect-engineering by selective doping play a vital role in activating inert basal planes and enhancing the HER activity. Herein we report the synthesis of highly disordered Mn-doped 2D-MoS2 nanospheres by a simple hydrothermal route under a non-equilibrium growth condition. Excess sulfur content in the precursor and electron-rich atmosphere created by Mn-doping results in an increased domain-based defects in the lattice that enhances the number of exposed edge sites, and also exposing more catalytically active high-index planes. Thereby improving its physicochemical properties. The developed electrode shows a low overpotential of 186 mV at a current density of 10 mA/cm2 and a low Tafel slope of 79.9mV/dec in acidic electrolytes. In addition, Density Functional Theory based calculation shows that Mn-doping in non-stoichiometric MoS2 enhances the electronic properties and its role in facilitating hydrogen adsorption and desorption processes with free energy close to that of benchmark Pt is established.

De-Alloying Synthesis of Mesoporous Pt-Ti-Ce Hydrogen Evolution Nanocatalysts with Exposed High-Index Crystal Planes

De-Alloying Synthesis of Mesoporous Pt-Ti-Ce Hydrogen Evolution Nanocatalysts with Exposed High-Index Crystal Planes

Structure sensitivity in gas sorption and conversion on metal-organic frameworks

Many catalytic processes depend on the sorption and conversion of gaseous molecules on the surface of (porous) functional materials. These events often preferentially occur on specific, undercoordinated, external surface sites. Here we show the combination of in situ Photo-induced Force Microscopy (PiFM) with Density Functional Theory (DFT) calculations to study the site-specific sorption and conversion of formaldehyde on the external surfaces of well-defined faceted ZIF-8 microcrystals with nanoscale resolution. We observed preferential adsorption of formaldehyde on high index planes. Moreover, in situ PiFM allowed us to visualize unsaturated nanodomains within extended external crystal planes, showing enhanced sorption behavior on the nanoscale. Additionally, on defective ZIF-8 crystals, structure sensitive conversion of formaldehyde through a methoxy- and a formate mechanism mediated by Lewis acidity was found. Strikingly, sorption and conversion were influenced more by the external surface termination than by the concentration of defects. DFT calculations showed that this is due to the presence of specific atomic arrangements on high-index crystal surfaces. With this research, we showcase the high potential of in situ PiFM for structure sensitivity studies on porous functional materials.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications.

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

A flexible and self-supported nanoporous gold wire electrode with a seamless structure for electrochemical ascorbic acid sensor

A flexible and self-supported nanoporous gold (S/NP-Au) has been produced using a simple, green, and quick approach for the electrochemical detection of l-ascorbic acid (AA). The dealloying process was used to create the main porous gold wire, and then electrochemical anodizing was adopted to construct the fine structure for nanoporous electrode. Furthermore, followed by chemical reduction with the enediol group in AA, the surface of S/NP-Au wire changed from a laminated to a scattered structure, and the preferred Au (2 0 0) high-index plane was investigated. As a result of synergistic electrocatalytic activity of Au wire skeleton towards AA, amperometric AA electrochemical sensors based on the S/NP-Au wire electrodes exhibit linear detection ranges with ultrahigh sensitivities at a low potential of 0.20 V (vs Ag. AgCl). The detection range of 0.3 μM–923.3 μM with a short response time of less than 1 s gives rise to ultralow detection limit of 26.3 nM (S/N = 3). The excellent characteristics of this sensor demonstrates it is a useful tool for accurate determination of AA in commercially available beverages such as water-soluble beverages with recoveries of 97.35 % to 110.7 %. The S/NP-Au electrode is a promising material for non-enzymatic AA detection.

Directional growth of quasi-2D Cu2O monocrystals on rGO membranes in aqueous environments.

The preparation technology of unconventional low-dimensional Cu2O monocrystals, which exhibit specific crystal planes and present significantly unique interfacial and physicochemical properties, is attracting increasing attention and interest. Herein, by integrating a high-temperature oxidation process under vacuum and a pure-water incubation process under ambient conditions, we propose the self-assembled growth and synthesis of quasi-two-dimensional Cu2O monocrystals on reduced graphene oxide (rGO) membranes. The prepared Cu2O crystals have a single (110) crystal plane, regular rectangular morphology, and potentially well conductivity. Experimental and theoretical results suggest that this assembly is attributed to the pre-nucleation clusters aggregation and directional attachment of Cu and O on the rGO membranes in aqueous environment and cation-π interactions between the (110) crystal plane of Cu2O and rGO surface. Our findings offer a potential avenue for the discovery and design of advanced low-dimensional single-crystal materials with specific interfacial properties in a pure aqueous environment.

Effects of Hydrophobic Species on the Oxygen Reduction Reaction on the High-Index Planes of Pt3Fe

Pt3Fe(111), Pt3Fe(775) = 7(111)–(111), and Pt3Fe(544) = 9(111)–(100) electrodes show the highest activity in the low-index planes, n(111)–(111), and n(111)–(100) series of Pt3Fe, respectively. The surfaces of these electrodes were modified with hydrophobic species such as THA+, melamine, and ionic liquid ([MTBD][beti]), and the effects on the oxygen reduction reaction (ORR) were studied. All the hydrophobic species improved the ORR activity on all the electrodes examined. The ORR activity of Pt3Fe(111) in 0.1 M HClO4 containing 0.1 μM melamine was 2.1 times higher than that of Pt3Fe(111) without melamine, giving 39 times higher activity than that of bare Pt(111). The durability was improved on all the electrodes examined in melamine-containing solution.

Kinetic influences on void formation in epitaxially regrown GaAs-Based PCSELs

We report an investigation into the formation of crystallographic voids during the metalorganic vapour phase epitaxial regrowth of GaAs photonic crystal structures. We employ a combination of cross-sectional scanning electron microscopy and scanning transmission electron microscopy to study structures regrown with AlAs, AlGaAs and GaAs. The change in regrowth material allows the effect of adatom diffusion kinetics on the void structure to be assessed. Whilst complete grating infill is observed for GaAs, void formation is promoted for Al-containing materials, with void size increasing with Al mole fraction, in line with reduced adatom mobility. In the case of both AlAs and AlGaAs-regrown structures, a degree of asymmetry is observed in the shape of the voids within the plane of the photonic crystal. These differences are attributed to variations in group-III adatom surface mobility and the polarities of high-index crystal planes along orthogonal crystal directions. Two growth regimes of stable and dynamic faceting are observed in cross-sections containing crystal planes with A- and B-type polarities, respectively.