Thin Nanoplates Research Articles

Controlling wave-vector of propagating surface plasmon polaritons on single-crystalline gold nanoplates.

Surface plasmon polaritons (SPPs) propagating at metal nanostructures play an important role in breaking the diffraction limit. Chemically synthesized single-crystalline metal nanoplates with atomically flat surfaces provide favorable features compared with traditional polycrystalline metal films. The excitation and propagation of leaky SPPs on micrometer sized (10–20 μm) and thin (30 nm) gold nanoplates are investigated utilizing leakage radiation microscopy. By varying polarization and excitation positions of incident light on apexes of nanoplates, wave-vector (including propagation constant and propagation direction) distributions of leaky SPPs in Fourier planes can be controlled, indicating tunable SPP propagation. These results hold promise for potential development of chemically synthesized single-crystalline metal nanoplates as plasmonic platforms in future applications.

Porous Two-Dimensional Nanosheets Converted from Layered Double Hydroxides and Their Applications in Electrocatalytic Water Splitting

Porous materials are of particular interest due to their high surface area and rich edge sites, which are favorable for applications such as catalysis. Although there are well-established strategies for synthesizing porous metal oxides (e.g., by annealing the corresponding metal hydroxides), facile and scalable routes to porous metal hydroxides and metal chalcogenides are lacking. Here, we report a simple and general strategy to synthesize porous nanosheets of metal hydroxides by selectively etching layered double hydroxide (LDH) nanoplate precursors that contain amphoteric metal and to further convert them into porous metal chalcogenides by a solution method. Using NiGa LDH as an example, we show that the thin nanoplates with high surface accessibility facilitate the topotactic conversion of NiGa LDH to β-Ni(OH)2 and further to NiSe2 with porous texture while preserving the sheet-like morphology. The converted β-Ni(OH)2 and NiSe2 are highly active for electrocatalytic oxygen evolution reaction and hydrog...

Controlled synthesis of layered double hydroxide nanoplates driven by screw dislocations.

Layered double hydroxides (LDHs) are a family of two-dimensional (2D) materials with layered crystal structures that have found many applications. Common strategies to synthesize LDHs lead to a wide variety of morphologies, from discrete 2D nanosheets to nanoflowers. Here, we report a study of carefully controlled LDH nanoplate syntheses using zinc aluminum (ZnAl) and cobalt aluminum (CoAl) LDHs as examples and reveal their crystal growth to be driven by screw dislocations. By controlling and maintaining a low precursor supersaturation using a continuous flow reactor, individual LDH nanoplates with well-defined morphologies were synthesized on alumina-coated substrates, instead of the nanoflowers that result from uncontrolled overgrowth. The dislocation-driven growth was further established for LDH nanoplates directly synthesized using the respective metal salt precursors. Atomic force microscopy revealed screw dislocation growth spirals, and under transmission electron microscopy, thin CoAl LDH nanoplates displayed complex contrast contours indicative of strong lattice strain caused by dislocations. These results suggest the dislocation-driven mechanism is generally responsible for the growth of 2D LDH nanostructures, and likely other materials with layered crystal structures, which could help the rational synthesis of well-defined 2D nanomaterials with improved properties.

ELECTROCHEMICAL RESPONSE OF 70Co–30Ni HIGHLY BRANCHED 3D-DENDRITIC STRUCTURES FOR CHARGE STORAGE ELECTRODES

ABSTRACT A 70Co–30Ni dendritic alloy was produced on stainless steel by pulse electrodeposition in the cathodic domain, and oxidized by potential cycling. X-ray diffraction (XRD) identified the presence of two phases and scanning electron microscopy (SEM) evidenced an open 3D highly branched dendritic morphology. After potential cycling in 1 M KOH, SEM and X-ray photoelectron spectroscopy (XPS) revealed, respectively, the presence of thin nanoplates, composed of Co and Ni oxi-hydroxides and hydroxides over the original dendritic film. Cyclic voltammetry tests showd the presence of redox peaks assigned to the oxidation and reduction of Ni and Co centres in the surface film. Charge/discharge measurements revealed capacity values of 121 mAh g−1 at 1 mA cm−2. The capacity retention under 8000 cycles was above 70%, stating the good reversibility of these redox materials and its suitability to be used as charge storage electrodes. Electrochemical impedance spectroscopy (EIS) spectra, taken under different applied bias, showed that the capacitance increased when the electrode was fully oxidized and decreased when the electrode was reduced, reflecting different states-of-charge of the electrode.

Roles of MoS2 and Graphene as Cocatalysts in the Enhanced Visible‐Light Photocatalytic H2 Production Activity of Multiarmed CdS Nanorods

AbstractThe incorporation of cocatalysts into semiconductors is proved to be an effective approach to improving the efficiency of the photocatalytic H2 production. Noble metals such as Pt have been widely used as cocatalysts and can significantly improve the performance of photocatalytic H2 production. However, owing to the high cost and low abundance, the use of Pt in practical applications is restricted. Herein, we report two well‐known 2 D layered materials, MoS2 and graphene, as highly active cocatalysts for H2 production in CdS‐based photocatalytic systems. The CdS–MoS2 and CdS‐MoS2–graphene nanocomposites were prepared by using a facile two‐step solvothermal method, and the morphologies of CdS and MoS2 can be well controlled. The as‐prepared binary CdS–MoS2 nanocomposite exhibits the enhanced visible‐light photocatalytic activity for H2 production in lactic acid aqueous solution compared with a CdS–graphene nanocomposite and a conventional platinized CdS photocatalyst. Moreover, the ternary CdS–MoS2–graphene nanocomposite achieves the highest visible‐light photocatalytic H2 production activity of 621.3 μmol h−1 and the apparent quantum efficiency of 54.4 % at λ=420 nm. The enhanced photocatalytic activity of the CdS–MoS2–graphene nanocomposite can be primarily attributed to the positive synergistic effect between graphene sheets and thin MoS2 nanoplates. The graphene sheets can accelerate the efficient electron transfer from CdS nanorods to the active edge sites of MoS2 nanoplates, and the nanosized MoS2 can facilitate the photogenerated electrons participating in the photocatalytic H2 production. The mechanisms for improving the photocatalytic performance of the MoS2‐ and/or graphene‐modified CdS nanocomposites were proposed by using the electrochemical analysis and photoluminescence measurement.

In situ catalytic synthesis of high-graphitized carbon-coated LiFePO4 nanoplates for superior Li-ion battery cathodes.

The low electronic conductivity and one-dimensional diffusion channel along the b axis for Li ions are two major obstacles to achieving high power density of LiFePO4 material. Coating carbon with excellent conductivity on the tailored LiFePO4 nanoparticles therefore plays an important role for efficient charge and mass transport within this material. We report here the in situ catalytic synthesis of high-graphitized carbon-coated LiFePO4 nanoplates with highly oriented (010) facets by introducing ferrocene as a catalyst during thermal treatment. The as-obtained material exhibits superior performances for Li-ion batteries at high rate (100 C) and low temperature (-20 °C), mainly because of fast electron transport through the graphitic carbon layer and efficient Li(+)-ion diffusion through the thin nanoplates.

Rational design of Bi2Te3 polycrystalline whiskers for thermoelectric applications.

Bi2Te3 polycrystalline whiskers consisting of interconnected nanoplates have been synthesized through chemical transformation from In2Te3 polycrystalline whisker templates assembled by nanoparticles. The synthesized Bi2Te3 whiskers preserve the original one-dimensional morphology of the In2Te3, while the In2Te3 nanoparticles can be transformed into the Bi2Te3 thin nanoplates, accompanied by the formation of high-density interfaces between nanoplates. The hot-pressed nanostructures consolidated from Bi2Te3 polycrystalline whiskers at 400 °C demonstrate a promising figure of merit (ZT) of 0.71 at 400 K, which can be attributed to their low thermal conductivity and relatively high electrical conductivity. The small nanoparticles inherited from the polycrystalline whiskers and high-density nanoparticle interfaces in the hot-pressed nanostructures contribute to the significant reduction of thermal conductivity. This study provides a rational chemical transformation approach to design and synthesize polycrystalline microstructures for enhanced thermoelectric performances.

Optical transmission enhancement through chemically tuned two-dimensional bismuth chalcogenide nanoplates.

Layer-structured two-dimensional nanomaterials are a family of materials with strong covalent bonding within layers and weak van der Waals interaction between layers, whose vertical thickness can be thinned down to few nanometer and even single atomic layer. Bismuth chalcogenides are examples of such two-dimensional materials. Here, we present our discovery of significant enhancement of light transmission through thin nanoplates of layered bismuth chalcogenides by intercalation of copper atoms, which is on the contrary to most bulk materials in which doping reduces the light transmission. This surprising behaviour results from two mechanisms: chemical tuning effect of substantial reduction of material absorption after intercalation and nanophotonic effect of zero-wave anti-reflection unique to ultra-small thickness of nanoplates. We demonstrate that the synergy of these two effects in two-dimensional nanostructures can be exploited for various optoelectronic applications including transparent electrode. The intercalation mechanism allows potential dynamic tuning capability.

Laser induced oxidation and optical properties of stoichiometric and non-stoichiometric Bi2Te3 nanoplates

Bi-Te nanoplates (NPs) grown by a low pressure vapor transport method have been studied by Raman spectroscopy, atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDS), and Auger electron spectroscopy (AES). We find that the surface of relatively thick (more than tens of nanometers) Bi2Te3 NPs is oxidized in the air and forms a bump under heating with moderate laser power, as revealed by the emergence of Raman lines characteristic of Bi2O3 and TeO2 and characterization by AFM and EDS. Further increase of laser power burns holes on the surface of the NPs. Thin (thicknesses less than 20 nm) NPs with stoichiometry different from Bi2Te3 were also studied. Raman lines from non-stoichiometric NPs are different from those of stoichiometric ones and display characteristic changes with the increase of Bi concentration. Thin NPs with the same thickness but different stoichiometries show different color contrast compared to the substrate in the optical image. This indicates that the optical absorption coefficient in thin Bi-Te NPs strongly depends on their stoichiometry.

Mild temperature synthesis of gold nanoplates using polyethyleneimine and their improved surface enhanced Raman signal

This study explores the facile controlled-synthesis and localized surface plasmonic properties of Au nanoplates. Au nanoplates were synthesized via a reaction of HAuCl4 with branched polyethyleneimine (BPEI) in the presence of urea at a reaction temperature as low as 30 °C. Structural characterizations revealed that the synthesized Au nanoplates had an average lateral size of around 2–8 μm and a thickness of around 40 nm, plus they were highly crystalline in spite of the low reaction temperature. Studies of the growth factors for Au nanoplates showed that the PEI morphology, molar ratio of BPEI/HAuCl4, pH of the reaction solution, and concentration of urea all played important roles in the formation of thin Au nanoplates. With a low BPEI/HAuCl4 ratio or under acidic conditions, thick Au plates were synthesized, whereas Au nanoparticles around 10–20 nm were observed with a high BPEI/HAuCl4 ratio or under basic conditions. When the synthesis was conducted in the absence of urea, thick Au nanoplates were synthesized, indicating that urea can serve as a capping agent for thin Au nanoplates. The resulting Au nanoplates also exhibited an enhanced surface-enhanced Raman scattering (SERS) signal when compared with Au nanoparticles due to their sharp corners and edges.

Formation dynamics of CoSi2thin nanoplates arrays studied by GISAXS in situ

During the last decades an increasing demand for the development of new methods of preparation of nano-composite materials suited for technological applications has been observed [1]. The interest on these nanomaterials is related to the fact that many of their properties can be varied in a continuous way by changing size, shape and/or spatial ordering. Silicides of transition metals such as CoSi2 are of great interest because of the possibilities that they open to applications as a contact material for microelectronic devices [2]. A simple method for obtaining buried arrays of CoSi2 plates coherently embedded in a Si host lattice was described in a previous study [3]. Grazing-incidence small-angle X-ray "GISAXS" and transmission electron microscopy "TEM" results indicated that the nanoplates exhibit a hexagonal lateral shape and a remarkable uniform thickness. The lattice of each CoSi2 nanoplates was shown to be coherent with the host Si lattice, and parallel to one of the four planes belonging to the Si(111) crystallographic planes family. In this work we present a diffusion dynamics study of Co into Si single crystal lattice using in situ GISAXS setup designed ad-hoc. The Co atoms were initially embedded in a SiO2 thin film deposited on Si(001) substrates subjected to a isothermal treatment during 1 hour at several temperatures between 650-850 oC, The diffused Co react with Si atoms and form CoSi2 nanoplates. GISAXS intensity was modeled assuming that the total scattering intensity is the sum of the intensity produced by a set of spatially uncorrelated and spherical Co nanoparticles – embedded in the SiO2 layer - plus the intensity coming from the hexagonal nanoplates parallel to the different planes of the Si(111) family.

Cobalt vanadium oxide thin nanoplates: primary electrochemical capacitor application.

Co3V2O8 thin nanoplates are firstly described as a kind of electrode material for supercapacitors. More importantly, from electrochemical measurements, the obtained Co3V2O8 nanoplate electrode shows a good specific capacitance (0.5 A g−1, 739 F g−1) and cycling stability (704 F g−1 retained after 2000 cycles). This study essentially offers a new kind of metal vanadium oxides as electrochemical active material for the development of supercapacitors.

Investigating Bulk Waves in Orthotropic Rectangular Nanoplates Based on Three Dimensional Elasticity Theory and Nonlocal Elasticity Theory

The propagation of bulk waves in rectangular nanoplates is studied on the basis of nonlocal three-dimensional elasticity theory. The nonlocal theory applies to both thin and thick rectangular orthotropic nanoplates. The dispersion relation for the waves is derived analytically. Our results are checked against data for macroplates. The influence of nonlocality and other parameters on the wave frequency and phase velocity is discussed.

Synthesis, characterization and electrostatic properties of WS2 nanostructures

We report the direct growth of atomically thin WS2 nanoplates and nanofilms on the SiO2/Si (300 nm) substrate by vapor phase deposition method without any catalyst. The WS2 nanostructures were systematically characterized by optical microscopy, scanning electron microscopy, Raman microscopy and atomic force microscopy. We found that growth time and growth temperature play important roles in the morphology of WS2 nanostructures. Moreover, by using Kelvin probe force microscopy, we found that the WS2 nanoplates exhibit uniform surface and charge distributions less than 10 mV fluctuations. Our results may apply to the study of other transition metal dichalcogenides by vapor phase deposition method.

Mo doping-enhanced dye absorption of Bi2Se3 nanoflowers

A simple solvothermal approach is explored to prepare Bi2−xMoxSe3 nanostructures by employing N,N-dimethylformamide (DMF) as the solvent. Mo plays an important role in the assembly of the Bi2−xMoxSe3 nanostructures from nanoplates to nanoflowers. Structural and morphological studies indicate that the resulting products are large specific surface area single-crystalline Bi2−xMoxSe3 nanoflowers self-assembled from thin nanoplates during the reaction process. The absorption properties of the as-prepared samples are investigated with Rhodamine B (RhB) as dye, and it is found that the Bi1.85Mo0.15Se3 nanoflowers show an optimal adsorption capacity, implying that Mo doping not only changes the morphologies of the nanostructures but also enhances their absorption behaviors.

Size-Dependent Behavior of Piezoelectric Circular Ultrathin Films With Consideration of Surface Effects for NEMS Applications

In this paper, size-dependent electromechanical behavior of circular nanoplates made of piezoelectric materials is studied with consideration of materials surface properties. Gurtin-Murdoch theory for solid surfaces is used to generalize the classical plate model through an analytical method. Closed-form solutions based on Bessel functions with modified arguments are given for some normalized parameters that represent different physical aspects of the problem. In addition to general parametric analysis and for more exploration, ZnO nanoplates are also examined as pointing up case studies. It is shown that external electric loading can control the size-dependent behavior of piezoelectric nanoplates without any requirement for high-precision devices to be applied. This concept is more observable in thinner nanoplates with considerable size-dependent behaviors. Next, it is shown that surface residual stresses can make the piezoelectric nanoplates with especial geometries to get self-unstable. The numerical results illustrate a contradiction at macroscale which can be used for measurement of surface residual stresses without coping with difficulties of nanoscale experimental setups. An inverse formulation is also proposed for verification of the results with relevant experiments confirming capability of the presented procedure in size-dependent analysis of nanostructures.

Wet chemical growth of ultra-long ZnO nanoplates and their optical property

A simple wet chemical method has been successfully used to fabricate very thin and ultra long ZnO nanoplates. Well crystalline ZnO nanoplates were formed as revealed from the X-ray diffraction pattern, field emission scanning electron microscopy and transmission electron microscopic images. The nanoplates are stacked together due to electrostatic interaction between various polar facets of ZnO nanocrystals. FTIR spectrum revealed the Zn–O stretching band at 501cm−1. The nanoplates exhibit excitonic UV emission at ∼383. This UV emission is superimposed with the shallow level emission at ∼438nm.

Microwave hydrothermal synthesis and optical properties of flower-like Bi2MoO6 crystallites

Abstract Flower-like Bi 2 MoO 6 crystallites were successfully synthesized by the microwave hydrothermal process using Bi(NO 3 ) 3 ·5H 2 O and Na 2 MoO 4 ·2H 2 O as source materials and adding hexamethylene tetramine (HMT) as a template. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were used to characterize the products. Ultraviolet–visible (UV–vis) spectroscopy was employed to study the optical properties of Bi 2 MoO 6 . Results show that the product morphology is flower-like on adding the template. These flower-like Bi 2 MoO 6 crystallites are a self-assembly of many thin nanoplates. HMT plays an important role in the formation of the flower-like morphology. UV–vis absorption spectra of all the Bi 2 MoO 6 samples show strong photoabsorption properties from the ultraviolet region to the visible-light region with wavelength shorter than 500 nm. The band gap of flower-like Bi 2 MoO 6 crystallites displays a slight red-shift compared with the Bi 2 MoO 6 plate-like structures.

A Size-Dependent Continuum Model for Nanoscale Circular Plates

Nanoscale circular plates are encountered in several nanotechnology-based devices such as nanoelectromechanical systems. Structures are size dependent at nanoscale due to surface energy effects. It is possible to capture such size dependence through special continuum models. In this paper, the Gurtin-Murdoch continuum theory is applied to develop a new continuum mechanics model for static deformation of thin and thick circular nanoplates. The relevant governing equations are established from basic principles. It is shown that the governing equations possess a closed-form analytical solution that makes the current approach suitable for device analysis and design. A series of closed-form analytical solutions is presented for static bending of thin and thick plates under common static loading (uniformly distributed and center point) and boundary conditions (simply supported and clamped edges). The analytical solution for a thin plate supported by a linear elastic substrate is also presented. Deflection profiles of selected silicon and aluminum plates are presented and compared with the classical plate theory results to examine the salient features of mechanical response and influence of surface elastic moduli, surface residual stress, and boundary conditions.

Observation of infrared-active modes in Raman scattering from topological insulator nanoplates

Two infrared (IR)-active vibrational modes, observed at 93 and 113 cm−1 in Raman scattering, are evidence of an inversion symmetry breakdown in thin (∼10 nm) nanoplates of topological insulator Bi2Te3 as-grown on SiO2. Both Raman and IR modes are preserved after typical device fabrication processes. In nanoplates transferred to another SiO2 substrate via contact printing, however, the IR modes are absent, and the Raman spectra are similar to those from bulk samples. The differences between as-grown and transferred nanoplates may result from nanoplate–substrate interactions.