Single-crystalline Nanoplates Research Articles

Elucidating the Geometric Active Sites for Oxygen Evolution Reaction on Crystalline Iron-Substituted Cobalt Hydroxide Nanoplates.

Transition-metal (oxy)hydroxides are among the most active and studied catalysts for the oxygen evolution reaction in alkaline electrolytes. However, the geometric distribution of active sites is still elusive. Here, using the well-defined crystalline iron-substituted cobalt hydroxide as a model catalyst, we reported the scanning electrochemical cell microscopy (SECCM) study of single-crystalline nanoplates, where the oxygen evolution reaction at individual nanoplates was isolated and evaluated independently. With integrated prior- and post-SECCM scanning electron microscopy of the catalyst morphology, correlated structure-activity information of individual electrocatalysts was obtained. Our result reveals that while the active sites are largely located at the edges of the pristine Co(OH)2 nanoplates, the Fe lattice incorporation significantly promotes the basal plane activities. Our approach of correlative imaging provides new insights into the effect of iron incorporation on active site distribution across nano-electrocatalysts.

Lead-Free Bi3.15Nd0.85Ti3O12 Nanoplates Filler-Elastomeric Polymer Composite Films for Flexible Piezoelectric Energy Harvesting.

Nowadays, wearable and flexible nanogenerators are of great importance for portable personal electronics. A flexible piezoelectric energy harvester (f-PEH) based on Bi3.15Nd0.85Ti3O12 single crystalline nanoplates (BNdT NPs) and polydimethylsiloxane (PDMS) elastomeric polymer was fabricated, and high piezoelectric energy harvesting performance was achieved. The piezoelectric output performance is highly dependent on the mass ratio of the BNdT NPs in the PDMS matrix. The as-prepared f-PEH with 12.5 wt% BNdT NPs presents the highest output voltage of 10 V, a peak-peak short-circuit current of 1 μA, and a power of 1.92 μW under tapping mode of 6.5 N at 2.7 Hz, which can light up four commercial light emitting diodes without the energy storage process. The f-PEHs can be used to harvest daily life energy and generate a voltage of 2–6 V in harvesting the mechanical energy of mouse clicking or foot stepping. These results demonstrate the potential application of the lead-free BNdT NPs based f-PEHs in powering wearable electronics

Mobility-Fluctuation-Controlled Linear Positive Magnetoresistance in 2D Semiconductor Bi2O2Se Nanoplates.

Linear magnetoresistance is generally observed in polycrystalline zero-gap semimetals and polycrystalline Dirac semimetals with ultrahigh carrier mobility. We report the observation of positive and linear magnetoresistance in a single-crystalline semiconductor Bi2O2Se grown by chemical vapor deposition. Both Se-poor and Se-rich Bi2O2Se single-crystalline nanoplates display a linear magnetoresistance at high fields. The Se-poor Bi2O2Se exhibits a typical 2D conduction feature with a small effective mass of 0.032m0. The average transport Hall mobility, which is lower than 5500 cm2 V-1 s-1, is significantly reduced, compared with the ultrahigh quantum mobility as high as 16260 cm2 V-1 s-1. More interestingly, the pronounced Shubnikov-de Hass oscillations can be clearly observed from the very large and nearly linear magnetoresistance (>500% at 14 T and 2 K) in Se-poor Bi2O2Se. A close analysis of the results reveals that the large and linear magnetoresistance observed can be ascribed to the spatial mobility fluctuation, which is strongly supported by Fermi energy inhomogeneity in the nanoplate samples detected using an electrostatic force microscopy images and multiple frequencies in a Shubnikov-de Hass oscillation. On the contrary, the Se-rich Bi2O2Se exhibits a transport mobility (<300 cm2 V-1 s-1) much smaller than that observed in Se-poor samples and shows a much smaller linear magnetoresistance ratio (less than 150% at 14 T and 2 K). More strikingly, no Shubnikov-de Hass oscillations can be observed. Therefore, the linear magnetoresistance in Se-rich Bi2O2Se is governed by the average mobility rather than the mobility fluctuation.

Nonlinear static bending of single-crystalline circular nanoplates with cubic material anisotropy

In this work, a model is presented for nonlinear static bending of single circular nanoplates with cubic material anisotropy. The material anisotropy is modeled based on Zener ratio for which some new functions are presented to get closer formulations. The Ritz and Galerkin weighted residual methods are used to solve the derived nonlinear differential equation using different deflection surfaces defining two integral functions for material anisotropy in polar coordinate. The results show that the deflection surface remains approximately axisymmetric even at extreme material anisotropy levels similar to orthotropic materials. This is verified by FEM too. The comprehensive results are presented and discussed for the mostly used materials at MEMS/NEMS technology including Ag, Au, Al, Si, Ni, Mo, Cu and W single-crystalline nanoplates. It is observed that the size scale effects related to material surface stresses are greater for BCC nanoplates in comparison with FCC ones. Moreover, the Poisson’s ratio in [100] direction plays an essential role in the problem which is evaluated carefully. Finally, the effective Young’s modulus of the nanoplates with 10–80 nm of thickness is compared by the experiments for Ag nanowires using a correction factor due to lack of direct experiments for nanoplates.

Coupling Piezocatalysis and Photocatalysis in Bi4NbO8X (X = Cl, Br) Polar Single Crystals

AbstractReactive oxygen species (ROS) as green oxidants are of great importance for environmental and biological applications. Photocatalysis is one of the major routes for ROS evolution, which is seriously restricted by rapid charge recombination. Herein, piezocatalysis and photocatalysis (i.e., piezo–photocatalysis) are coupled to efficiently produce superoxide radicals (•O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH) via oxygen reduction reaction (ORR), by using Bi4NbO8X (X = Cl, Br) single crystalline nanoplates. Significantly, the piezo‐photocatalytic process leads to the highest ORR performance of the Bi4NbO8Br nanoplates, exhibiting •O2−, H2O2, and •OH evolution rates of 98.7, 792, and 33.2 µmol g−1 h−1, respectively. The formation of a polarized electric field and band bending allows directional separation of charge carriers, promoting the catalytic activity. Furthermore, the reductive active sites are found enriched on all the facets in the piezo–photocatalytic process, also contributing to the ORR. By piezo–photodeposition of Pt to artificially plant reductive reactive sites, the Bi4NbO8Br plates demonstrate largely enhanced photocatalytic H2 production activity with a rate of 203.7 µmol g−1 h−1. The present work advances piezo–photocatalysis as a new route for ROS generation, but also discloses the potential of piezo–photocatalytic active sites enriching for H2 evolution.

Precisely-controlled, a few layers of iron titanate inverse opal structure for enhanced photoelectrochemical water splitting

Iron titanate (Fe2TiO5) is a promising photoanode material due to a narrow band gap, appropriate band edges, robustness and abundance. However, its performance is limited because of its low conductivity and short hole diffusion length. Precisely controlled, a few Fe2TiO5 layers of inverse opal structure (IOS) is fabricated via a layer-by-layer self-assembly and then treated by hybrid microwave annealing to produce a highly crystalline, yet IOS morphology-preserved Fe2TiO5 photoanode film for solar water splitting. The highly transparent Fe2TiO5 IOS film shows a greatly enhanced visible light harvesting, higher density of catalytically more active crystal planes, and many single crystalline nanoplates grown on the IOS architecture, relative to a reference planar film prepared under similar conditions. As a result, the optimized ‘exactly’ three Fe2TiO5 layers IOS electrode with a sacrificial gallium oxide underlayer and a ternary (Ni2CoFe)OOH co-catalyst records 2.08 mA cm−2 at 1.23 VRHE under 1 sun (100 mW cm−2) irradiation, which is the highest photocurrent density produced by Fe2TiO5 photoanode up to date.

Catalysis of hydrogen evolution reaction by Ni12P5 single crystalline nanoplates and spherical nanoparticles

Ni12P5 nanoplates composed of the {2̄ 1 1} surface showed higher hydrogen evolution activity than Ni12P5 nanoparticles.

Ultrathin Ni12P5 nanoplates for supercapacitor applications

Ultrathin single crystalline nanoplates of Ni12P5 are synthesized via a facile, template-free, wet chemical method. The thickness is about 6 nm with sizes tunable from 5 to 50 nm. The exposed plate surface is formed of {2¯11} lattice plane. Benefitting from the high electrical conductivity and the two dimensional (2D) nanostructures, the Ni12P5 nanoplates exhibit excellent supercapacitor properties. The specific capacity is about 697 C/g at the current density of 1 A/g. Even at 20 A/g, it is measured as 446 C/g, with 64.0% retention indicating an outstanding rate capability. The charge storage mechanisms include a battery-type behavior related to the bulk redox processes and a double-layer capacitance arising from the 2D geometric morphology. In particular, the morphological effects accounts for about 63% of the total charge storage effects at the voltage sweep rate of 2 mV/s in the cyclic voltammetry measurement, and is even higher percentage-wise at a higher sweep rate. This is, by far, the best performance with facile synthesis techniques for single crystalline nickel phosphides.

Thermoelectric Performance: Enhancement of Thermoelectric Performance in CuSbSe2 Nanoplate‐Based Pellets by Texture Engineering and Carrier Concentration Optimization (Small 50/2018)

In article number 1803092, Qingyu Yan, Mercouri G. Kanatzidis, and co-workers develop a bottom-up self-assembly process to prepare CuSbSe2-PtTe2 based pellets with highly oriented single-crystalline nanoplates, which results in an orientation factor of ≈0.8 for (00l) facets. The texture engineering and carrier concentration optimization enable an ≈500% enhanced ZT value (0.50 at 673 K) for CuSbSe2-2.0 mol% PtTe2 compared to pure CuSbSe2.

Enhancement of Thermoelectric Performance in CuSbSe2 Nanoplate‐Based Pellets by Texture Engineering and Carrier Concentration Optimization

This work reports the thermoelectric properties of the CuSbSe2 -x mol% PtTe2 (x = 0, 0.5, 1.0, 1.5, and 2.0) pellets composed of highly oriented single crystalline nanoplates. CuSbSe2 -PtTe2 single crystalline nanoplates are prepared by a wet-chemical process, and the pellets are prepared through a bottom-up self-assembly of the CuSbSe2 -PtTe2 nanoplates and spark plasma sintering (SPS) process. X-ray diffraction and field emission scanning electron microscopic analyses show a highly textured nature with an orientation factor of ≈0.8 for (00l) facets along the primary surface of the pellets (in-plane, perpendicular to the SPS pressure). By this way, bulk-single-crystal-like electrical and thermal transport properties with a strong anisotropy are obtained, which results in an effective optimization on thermoelectric performance. The maximum in-plane thermoelectric figure-of-merit ZT value reaches 0.50 at 673 K for CuSbSe2 -2.0 mol% PtTe2 pellet, which is about five times higher than the in-plane ZT (0.10) for pure CuSbSe2 .

Facile one pot synthesis of novel Hg2+ doped PbI2 nanostructures for optoelectronic and radiation shielding applications

Facile one pot synthesis of pure and Hg2+ (= 0.101 nm) doped PbI2 (Pb2+ = 0.133 nm) single crystalline nanoplates (NPs), nanosheets (NSs) and nanorods (NRs) were achieved through chemical route at room temperature. The single phase and high quality of the synthesized NPs, NSs and NRs was proved by X-ray diffraction and FT-Raman spectroscopic analyses. The lattice constants, crystallite size, lattice strain, dislocation density were calculated. The crystallite size was calculated to be in the range of 16–22 nm. The Hg doping in PbI2 was approved by energy dispersive X-ray spectroscopy (EDXS) and its homogeneous distribution was confirmed by scanning electron microscopy (SEM) mapping. The morphology of pure and doped synthesized nanostructures was observed to be single crystalline NPs, NSs and NRs of nanoscale thicknesses. The optical band gap was calculated from Tauc's plot and found to be in the range of 3.27–3.20 eV. The value of dielectric constant was improved from 20 to 25 and also ac electrical conductivity due to Hg2+ doping. The radiation parameters such as linear absorption coefficient, half value layer, tenth value layer and mean free path were calculated and a remarkable enhancement was observed due to Hg2+ doping. These parameters confirm that the nanostructures are highly sensitive to 214Am 59.5KeV γ-ray. The facilely synthesized nanostructures of PbI2 with enhanced properties due to Hg2+ doping makes them more suitable for nanoelectronics and room temperature radiation detector applications.

Intrinsic multiferroics in an individual single-crystalline Bi5Fe0.9Co0.1Ti3O15 nanoplate

In recent years, much attention has been paid to layer-structured Bi4Bim-3Fem-3-xMxTi3O3m+3 (BFMTO, M = Co, Mn) compounds due to their potential as high temperature single phase multiferroic materials. However, BFMTO single crystals have been rarely reported in the past, though they are better candidates for studying the corresponding intrinsic multiferroics as well as the platform for making future devices, due to their structural complexity and difficulties in fabrication. In this article, Bi5Fe0.9Co0.1Ti3O15 single-crystalline nanoplates were synthesized by the hydrothermal method. The ferromagnetic domain structure of the nanoplate was investigated by electron holography. Denser phase contours were observed and the closed magnetic flux lines indicated a significant magnetic interaction between the neighboring nanoplates, which proved the ferromagnetic nature of the sample. Furthermore, M-H loops of the sample were also measured, in which the ferromagnetic Curie temperature reached ∼730.2 K. Besides, ferroelectric domains were also detected by using a piezoresponse force microscope. All the above-mentioned results indicate the first verification of the room temperature (RT) multiferroic behaviour in such single crystals, which will be useful for both future devices and understanding the underlining physics.

Tracking the morphology and phase transformations of anodic iron oxide nanotubes using X-ray spectroscopy

X-ray spectroscopic techniques have been employed to investigate highly ordered iron oxide nanotubes (NTs) prepared by iron anodization in a fluorine-containing electrolyte followed with annealing at elevated temperatures. NTs undergo morphology and phase evolutions from amorphous NTs to single crystalline nanoplates, then nanoflakes, and finally to a polycrystalline film. X-ray diffraction and X-ray absorption near edge structure have been used for the investigation. We show that fluorine incorporation can be used as an effective morphology tailoring tool for the engineering of efficient iron oxide nanostructures.

Stereo-epitaxial growth of single-crystal Ni nanowires and nanoplates from aligned seed crystals.

Epitaxially grown anisotropic Ni nanostructures are promising building blocks for the development of miniaturized and stereo-integrated data storage kits because they can store multiple magnetic domain walls (DWs). Here, we report stereo-epitaxially grown single-crystalline Ni nanowires (NWs) and nanoplates, and their magnetic properties. Vertical and inclined Ni NWs were grown at the center and edge regions of c-cut sapphire substrates, respectively. Vertical Ni nanoplates were grown on r-cut sapphire substrates. The morphology and growth direction of Ni nanostructures can be steered by seed crystals. Cubic Ni seeds grow into vertical Ni NWs, tetrahedral Ni seeds grow into inclined Ni NWs, and triangular Ni seeds grow into vertical Ni nanoplates. The shapes of the Ni seeds are determined by the interfacial energy between the bottom plane of the seeds and the substrates. The as-synthesized Ni NWs and nanoplates have blocking temperature values greater than 300 K at 500 Oe, verifying that these Ni nanostructures can form large magnetic DWs with high magnetic anisotropy properties. We anticipate that epitaxially grown Ni NWs and nanoplates will be used in various types of 3-dimensional magnetic devices.

Synthesis and Photovoltaic Properties of Cd3As2 Faceted Nanoplates and Nano-Octahedrons

Recent theoretical predictions and angle-resolved photoemission spectroscopy measurements have shown that single crystal Cd3As2 is a three-dimensional topological Dirac semimetal possessing linear dispersions along all three momentum directions. Nanoscale topological Dirac semimetal structures have a large surface-to-volume ratio and provide a platform to explore its topological surface states. Here we report the synthesis of high quality Cd3As2 single crystalline nanoplates and nano-octahedrons via a vapor–solid growth mechanism. Triangular and hexagonal nanoplates with lateral dimensions ranging from several hundred nanometers to tens of micrometers are obtained. The top facets are (112), consistent with the natural cleavage plane of Cd3As2 single crystal. The synthesized Cd3As2 nano-octahedrons are enclosed by the {112} facets. A photovoltaic effect is demonstrated from a Cd3As2 nanoplate/metal electrode interface, suggesting potential applications in self-powered photodetection.

Synthesis and magnetic properties of the chromium-doped iron sulfide Fe1-xCrxS single crystalline nanoplates with a NiAs crystal structure.

Single crystalline iron sulfide nanoparticles doped with chromium Fe1-xCrxS (0 ≤x≤ 0.15) have been successfully prepared by a thermal decomposition method. The particles are self-organized into the single crystalline plates with the accurate hexagonal shape and dimensions up to 1 μ in plane and about 30-40 nm in thickness. The samples have the NiAs-type crystal structure (P63/mmc) at all Cr concentrations up to x = 0.15. Fe(57)-Mössbauer spectroscopy data reveal four nonequivalent iron sites in these nanocrystals related to the different number of cation vacancies in neighboring of the iron atoms. A 2C-type superstructure or a mixture of 2C and 3C superstructures of vacancy ordering can appear in these samples. It was established that in the Fe1-xCrxS series chromium prefers to replace iron in the cation layers containing vacancies at 0.00 < x < 0.10 and Cr atoms occupy both iron and vacant sites at x > 0.10. The specific magnetic properties, which can be tuned by chromium doping, enable potential applications of these nanoparticles in technical devices using the material with thermally activated magnetic memory, for example, switches or storages.

Improved pseudocapacitive performance of well-defined WO3−x nanoplates

We demonstrate the well-defined tungsten suboxide nanoplates for pseudocapacitors via a low-temperature reduction reaction under hydrogen gas atmosphere. The as-prepared WO3−x reduced at 500°C using WO3 nanoplates (500-WO3−x) shows a pure monoclinic structure and single crystalline nanoplates. The 500-WO3−x exhibits much improved pseudocapacitive performance due to W5+ and W4+ oxidation states obtained by a reduction process and improved electrical conductivity.

Synthesis and characterization of 3D Cu0.45Mn0.55O2 nanoflowers with novel photoluminescence and magnetic properties

In this paper, three-dimensional (3D) Cu 0.45 Mn 0.55 O 2 nanoflowers self-assembled by interconnecting dense stacked single-crystalline nanoplates have been prepared using the template-free hydrothermal growth method. The morphology, phase structure and composition of the as-prepared nanomaterial were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED) and energy-dispersive X-ray spectroscopy (EDX). FESEM and TEM analyses show that the size of 3D Cu 0.45 Mn 0.55 O 2 nanoflowers is in the range of 1–1.5 μm and the thickness of interconnected nanoplates is about 40 nm on the average. The photoluminescence (PL) spectra of the as-prepared Cu 0.45 Mn 0.55 O 2 nanostructures at room temperature exhibits prominent emission bands located in red–violet spectral region. Moreover, magnetic investigations revealed the weak ferromagnetic behavior of the as-prepared Cu 0.45 Mn 0.55 O 2 nanoflowers and reported for the first time using vibrating sample magnetometer (VSM).

Self-supported construction of 3D CdMoO4 hierarchical structures from nanoplates with enhanced photocatalytic properties

Three-dimensional (3D) CdMoO4 hierarchical structures constructed by single-crystalline nanoplates were prepared by a facile hydrothermal route.

Room-Temperature Synthesis of Flower-Like BiOX (X═Cl, Br, I) Hierarchical Structures and Their Visible-Light Photocatalytic Activity

A simple method for facile synthesis of three-dimensional (3D) bismuth oxyhalide (BiOX, X═Cl, Br, I) hierarchical structures at room temperature has been developed. Under the influence of L-lysine surfactant, the bismuth and halogen (Cl, Br, I) sources hydrolyze and self-assemble into flower-like hierarchical architectures within 10 min. The resulted materials were characterized by XRD, FESEM, TEM, UV-vis DRS, and N2 adsorption-desorption techniques. We found that l-lysine is indispensable for their formation and the amount of HX has great effect on the final morphology. The BiOX (X═Cl, Br, I) hierarchical architectures are composed of single-crystalline nanoplates. We propose an amino-and-carboxyl structure-directing mechanism for the formation of the hierarchical structures. To evaluate the photocatalytic activity of the as-prepared materials, rhodamine-B was employed as a probe dye for degradation under visible light. All of the BiOX (X═Cl, Br, I) with 3D architectures show higher photocatalytic activities than their sheet-like counterparts. The superior activity is ascribed to the better light-harvesting capacity of the 3D hierarchical structures. The adopted method can be applied for large-scale generation of novel structures of similar kinds in a facile manner.