Electrochemical growth of ZnO nanoplates

ZnO films were grown on polycrystalline Zn foil by cathodic electrodeposition in an aqueous zinc chloride/calcium chloride solution at 80?°C. Variation in the electrochemical parameters resulted in a variation in growth morphology from 1D (nanorods), 2D ('nanoplates') to 3D crystal growth. An as-received or mechanically polished substrate proved the most suitable substrate finish and allowed more highly aligned, dense structures to be grown; in contrast, electropolished substrates formed inhomogeneous deposits. Substrate annealing gave rise to large homogenous areas of nanorod deposition. Two-dimensional sheet growth was found to occur in conjunction with nanorods under specific electrochemical conditions. Hexagonal 'plates' approximately 50?nm in thickness and several microns in diameter were formed normal to the substrate.     

Molecular beam epitaxy growth of free-standing plane-parallel InAs nanoplates

Free-standing nanostructures such as suspended carbon nanotubes, graphene layers, III-V nanorod photonic crystals and three-dimensional structures have recently attracted attention because they could form the basis of devices with unique electronic, optoelectronic and electromechanical characteristics. Here we report the growth by molecular beam epitaxy of free-standing nanoplates of InAs that are close to being atomically plane. The structural and transport properties of these semiconducting nanoplates have been examined with scanning electron microscopy, transmission electron microscopy, X-ray diffraction and low-temperature electron transport measurements. The carrier density of the nanoplates can be reduced to zero by applying a voltage to a nearby gate electrode, creating a new type of suspended quantum well that can be used to explore low-dimensional electron transport. The electronic and optical properties of such systems also make them potentially attractive for photovoltaic and sensing applications.     

Te-seeded growth of few-quintuple layer Bi2Te3 nanoplates

We report on a Te-seeded epitaxial growth of ultrathin Bi2Te3 nanoplates （down to three quintuple layers （QL）） with large planar sizes （up to tens of micrometers） through vapor transport. Optical contrast has been systematically investigated for the as-grown Bi2Te3 nanoplates on the SiO2/Si substrates, experimentally and computationally. The high and distinct optical contrast provides a fast and convenient method for the thickness determination of few-QL Bi2Te3 nanoplates. By aberration-corrected scanning transmission electron microscopy, a hexagonal crystalline structure has been identified for the Te seeds, which form naturally during the growth process and initiate an epitaxial growth of the rhombohedral- structured Bi2Te3 nanoplates. The epitaxial relationship between Te and Bi2T% is identified to be perfect along both in-plane and out-of-plane directions of the layered nanoplate. Similar growth mechanism might be expected for other bismuth chalcogenide layered materials.     

Predicting the growth of two-dimensional nanostructures

The ability to predict the morphology of crystals formed by chemical reactions is of fundamental importance for the shape-controlled synthesis of nanostructures. Based on the atomistic mechanism for crystal growth under different driving forces, we have developed morphology diagrams to predict regimes for the growth of two-dimensional crystals. By using controlled reactions for crystal growth in the absence of surfactants/capping agents, we demonstrate the validity of this approach for the formation of 2D structures of Au, Ag, Pt and?Pd.     

微波法合成金纳米片

采用微波加热法,氯金酸为前驱物,乙二醇作为溶剂和还原剂,聚乙烯吡咯烷酮(PVP)作为晶面生长控制剂,葡萄糖作为辅助还原剂调控合适的还原速度合成出了边长为微米级的单晶金纳米片。采用粉末X射线衍射,扫描电子显微镜,透射电子显微镜表征了产物的成分,形貌以及晶体结构。结果表明金纳米片为面心立方单晶,边长为2～3μm,厚度为50～100nm,具有独特的(±011)上、下面。分别考察了PVP和葡萄糖添加对形成金纳米片的影响,PVP沉积在晶种{011}面上和合适的还原速度是形成金纳米片的关键。     

CO2 electrochemical sensor based on two-dimensional MoTe2 nanoplates: the effect of annealing,Mo and Te concentrations

Journal of Materials Science: Materials in Electronics - The two-dimensional materials are promising candidates for gas-sensing applications due to their unique properties as well as binary...     

Grain growth in porous two-dimensional nanocrystalline materials

Grain growth in two-dimensional polycrystals with mobile pores at the grain boundary triple junctions is considered. The kinetics of grain and pore growth are determined under the assumption that pore sintering and pore mobility are controlled by grain boundary and surface diffusion, respectively. It is shown that a polycrystal can achieve full density in the course of grain growth only when the initial pore size is below a certain critical value which depends on kinetic parameters, interfacial energies, and initial grain size. Larger pores grow without limits with the growing grains, and the corresponding grain growth exponent depends on kinetic parameters and lies between 2 and 4. It is shown that for a polycrystal with subcritical pores the average grain size increases linearly with time during the initial stages of growth, in agreement with recent experimental data on grain growth in thin Cu films and in bulk nanocrystalline Fe.     

Controllable preparation of SnO2 nanoplates and nanoparticles via hydrothermal oxidation of SnS2 nanoplates

A facile hydrothermal oxidation route has been proposed for the controllable preparation of SnO₂ nanoplates and nanoparticles, using the home-made SnS₂ nanoplates as a precursor. It was found that the temperature played an important role in the microstructures of the obtained products. While nanoplates of tetragonal phase SnO₂ were synthesized via hydrothermal treatment of the SnS₂ nanoplates in 15 vol.% H₂O₂ aqueous solution at 180 °C for 24 h, only nanoparticles of tetragonal phase SnO₂ could be obtained via hydrothermal treatment of the SnS₂ nanoplates in 15 vol.% H₂O₂ aqueous solution at 200 °C for 24 h. The as-prepared products were characterized by means of X-ray diffraction, field emission scanning electron microscope, and Raman spectra, and their possible formation mechanisms were also discussed.     

Magnetism in dopant-free ZnO nanoplates

It is known that bulk ZnO is a nonmagnetic material. However, the electronic band structure of ZnO is severely distorted when the ZnO is in the shape of a very thin plate with its dimension along the c-axis reduced to a few nanometers while keeping the bulk scale sizes in the other two dimensions. We found that the chemically synthesized ZnO nanoplates exhibit magnetism even at room temperature. First-principles calculations show a growing asymmetry in the spin distribution within the distorted bands formed from Zn (3d) and O (2p) orbitals with the reduction of thickness of the ZnO nanoplates, which is suggested to be responsible for the observed magnetism. In contrast, reducing the dimension along the a- or b-axes of a ZnO crystal does not yield any magnetism for ZnO nanowires that grow along c-axis, suggesting that the internal electric field produced by the large {0001} polar surfaces of the nanoplates may be responsible for the distorted electronic band structures of thin ZnO nanoplates.     

Facile synthesis of bimetallic nanoplates consisting of Pd cores and Pt shells through seeded epitaxial growth

Pd-Pt core-shell nanoplates with hexagonal and triangular shapes were synthesized through the heterogeneous, epitaxial growth of Pt on Pd nanoplates. The Pd nanoplates were synthesized by reducing Na2PdCl4 precursor with PVP as a reducing agent, which then served as seeds for the nucleation of Pt atoms formed by reducing H2PtCl6 with citric acid. Characterization of the as-prepared Pd-Pt nanoplates by scanning transmission electron microscopy and high-resolution transmission electron microscopy reveals that a thin, uniform Pt shell was formed around the Pd nanoplate, demonstrating the layer-by-layer epitaxial growth of Pt on Pd surface in this approach. The close lattice match between Pd and Pt (lattice mismatch of only 0.77%) and the slow reduction rate associated with the mild reducing power of citric acid play key roles in achieving the epitaxial growth of Pt shells on Pd nanoplates.     

Time-resolved photodynamics of triangular-shaped silver nanoplates

We measured the ultrafast response of triangular silver nanoparticles upon femtosecond excitation of their plasmon resonance. After a fast electron relaxation, the signature of a bimodal mechanical vibration of the particle is apparent as a spectral modulation. We identify the two lowest frequency, totally symmetric vibrations of the particle as responsible for this modulation, through their influence on the plasmon peak position and width, in full agreement with the results of a variational elastodynamic model that is also presented. From the analysis of the phase we conclude that thermal expansion and electron pressure, respectively, are responsible for the excitation of the two vibrations.     

Large-scale preparation of single-crystalline gold nanoplates

A thermal process has been demonstrated for the large-scale preparation of single-crystalline gold nanoplates with several micrometers in size, carried out by heating a salicylic acid-HAuCl₄ aqueous solution at 100 °C in the presence of poly(diallyldimethylammonium chloride) (PDDA). It is found that such nanoplates are single-crystalline gold with a preferential growth direction along the {111} plane and PDDA is crucial to the formation of such nanoplates. The possible formation mechanism of gold nanoplate is also discussed.     

Chord intercepts in a two-dimensional cell growth model

Nuclei are Poisson-distributed within a plane. Out of the nuclei, grains begin to grow instantaneously, circularly and at a constant rate. The forming microstructure at each fraction transformed, consisting of grains and untransformed regions, is characterized in this work by use of a straight line (Rosiwal's line), which passes arbitrarily through the plane. Along this line we obtain chord intercepts of grains and of untransformed regions of different lengths, independent of the position of the straight line. The distributions of these lengths are essentially determined by the distribution of the nuclei and from the conditions of growth. From these assumptions we derive, by use of probability theory, the distributions of the chord intercepts. In Part 1, only the distribution density of the chord intercept of the untransformed regions is studied. From these results several other statistical quantities of the microstructure are also deduced.     

Chord intercepts in a two-dimensional cell growth model

A foil of polypropylene is heat-treated in such a manner that a growing 2D cell-model is formed. A Rosiwal's line is placed into the totally primarily crystallized foil. The nucleus-coordinates of grains intercepting Rosiwal's line are measured. From these effective nuclei we determine at fraction transformedF = 1/4, 1/2 and 3/4 the distributions of grain-lengths and melt-lengths. Further we determine properties which are derived from the chord intercepts at a given F. Experimentally we find that the values (Poisson distribution of nuclei, chord intercepts, etc.) are in good agreement with the growing 2D cell-model.     

Electromechanical responses of piezoelectric nanoplates with flexoelectricity

Flexoelectricity, representing the coupling between electrical polarizations and strain gradients, should be taken into account in the analysis of electromechanical responses of nanostructures where large strain gradients are expected. In this paper, we will explore the influence of flexoelectricity on the electromechanical coupling behavior of a simply supported piezoelectric nanoplate by using the Kirchhoff plate theory. The governing equations and corresponding boundary conditions are deduced from Hamilton’s principle, and the analytical solutions are obtained for the deflection and natural frequency. The results indicate that the deflections predicted by the present model are smaller than those calculated by the classical one which only considers piezoelectricity, while the frequencies exhibit the opposite trend. In addition, the flexoelectric effect is more prominent for thinner plates; the differences of the deflections or frequencies between the two models are gradually diminishing with an increase in the plate thickness. The current work may contribute to the understanding of the higher-order electromechanical coupling mechanism. Moreover, the modified plate model can be utilized to accurately design novel piezoelectric nanoplate-based sensors in nanoelectromechanical systems.     

Lateral epitaxial growth of two-dimensional heterostructure linked by gold adatoms

Lateral two-dimensional(2D)heterostructures have great potential for device engineering at the atomistic scale.Their production is hindered by difficulties in obtaining atomically sharp interface free from intermixture.Here we report the continuous construction of a lateral heterostructure using blue phosphorene and tetrafluoro-tetracyanoquinodimethane(F₄TCNQ)as the building blocks.The lateral heterostructure is achieved by linking the semiconducting F₄TCNQ-Au metal organic framework and the metallic blue phosphorene-Au network via Au adatoms.The structural and electronic properties of the heterostructure have been investigated by means of scanning tunneling microscopy and spectroscopy(STM/S),complemented by density functional theory(DFT)calculations,demonstrating a structurally and electrically abrupt interface.Our approach offers the possibility of high flexibility and control that can be extended to other metal-organic species and 2D materials,establishing a foundation for the development of atomically thin in-plane superlattice and devices.     

Nonlocal free vibration of orthotropic non-prismatic skew nanoplates

The free vibration of orthotropic non-prismatic skew nanoplate based on the first-order shear deformation theory (FSDT) in conjunction with Eringen’s nonlocal elasticity theory is presented. As a simple, accurate and low computational effort numerical method, the differential quadrature method (DQM) is employed to solve the related differential equations. For this purpose, after deriving the equations of motion and the related boundary conditions, they are transformed from skewed physical domain to rectangular computational domain of DQM and accordingly discretized. After validating the formulation and method of solution, the effects of nonlocal parameter in combination with geometrical parameters and boundary conditions on the natural frequencies of the orthotropic skew nanoplates are investigated.     

Hydrothermal synthesis and optical properties of CuS nanoplates

CuS nanoplates have been successfully prepared in the presence of cation surfactant cetyltrimethylammonium bromide (CTAB) by hydrothermally treating the solution of CuCl₂·2H₂O and Na₂S·9H₂O at 180 °C for 24 h. The as-prepared CuS nanoplates are of hexagonal phase and are single crystal. The thickness and edge length of the nanoplates are about 15 nm and 60 nm, respectively. The products was characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, photoluminescence measurements and ultraviolet-visible light spectrophotometer. The influences of synthetic parameters, such as reaction time and CTAB, on the morphologies of the products have been investigated.     

Growth aspects of photochemically synthesized silver triangular nanoplates

Aspects of the growth mechanism of silver triangular nanoplates by photochemical synthesis were addressed by detailed characterization using ultraviolet-visible spectroscopy, electron microscopies, and atomic force microscopy. The quantitative characterization of their size and thickness during the reaction showed that both increase with time as well as the aspect ratio. Samples irradiated by different wavelengths showed that the size of the nanoplates can be controlled by the incident wavelength and it is responsible for the increase of the aspect ratio, but the thickness seems to be determined by the conditions of the initial seeds. It was also found that irradiation with wavelength out of resonance with the surface plasmon of the initial seeds leads to a slower kinetics. The results suggested that rational exploration of the synthesis parameter such as the type of the initial seeds in combination with the wavelength irradiation may lead to a broader type of particles already obtained by this method.