Growth Mechanism Of Nanostructures Research Articles

Tungsten nanostructure growth by sputtering and redeposition in BCA-MD-KMC hybrid simulation

The formation mechanism of fibrous tungsten nanostructures, fuzz, induced by helium plasma irradiation on tungsten materials has been investigated. We have developed a BCA-MD-KMC hybrid simulation, which solves the injection process of helium atoms by the Binary Collision Approximation (BCA) method, the diffusion process of helium atoms in tungsten materials by the Kinetic Monte-Carlo (KMC) method, and the deformation of tungsten materials due to helium bubbles by the Molecular Dynamics (MD) method. In addition, the model used to calculate the recoiling of tungsten atoms in BCA was improved to account for the reduced binding energy of tungsten atoms on rough surfaces. Using the hybrid simulation, the height of the nanostructures reached about 50 nm. The main mechanism of nanostructure growth was that sputtering and redeposition caused transport of tungsten atoms perpendicular to the surface. The present simulation was able to represent not only the dependence that the nanostructure height increases in proportion to the square root of the helium fluence, but also the existence of incubation fluence before the growth starts.

Crystal side facet-tuning of GaN nanowires and nanofins grown by molecular beam epitaxy

GaN nanostructures are promising for a broad range of applications due to their 3D structure, thereby exposing non-polar crystal surfaces. The nature of the exposed crystal facets, i.e., whether they are a-, m-plane, or of mixed orientation, impacts the stability and performance of GaN nanostructure-based devices. In this context, it is of great interest to control the formation of well-defined side facets. Here, we show that we can control the crystal facet formation at the nanowire sidewalls by tuning the III–V ratio during selective area growth by molecular beam epitaxy. Especially, the N flux serves as a tool for controlling the growth kinetics. In addition, we demonstrate the growth of GaN nanofins with either a- or m-plane side facets. Based on our observations, we present the underlying nanostructure growth mechanisms. Low temperature photoluminescence measurements show a correlation of the formation of structural defects like stacking faults with the growth kinetics. This article demonstrates the controlled selective epitaxy of GaN nanostructures with defined crystal side facets on large-scale available AlN substrates.

Growth mechanism study of silver nanostructures in a limited volume

Recently, high attention has been paid to template synthesis as a method for obtaining nanostructures with predetermined shapes and sizes. This is an obvious approach, in which the size and shape of the pores limit the geometry of the nanostructures formed inside them. As a result, nanostructures completely repeat the shape of the template pores. However, in some cases, the morphology of the resulting structures may differ from the shape of the template, and often these differences are not explained. This is a gap in fundamental knowledge on the mechanism of nanostructure growth in a limited template pore volume. In this work, we partially solve this problem. Using silver as an example, it is shown that by changing only the pore volume, without changing other chemical kinetic conditions, it is possible to controllably create nanostructures with complex geometry. Possible morphologies of nanostructures, such as crystallites, dendrites and “sunflower-like" structures, formed at critical pore diameters, have been identified. The main points inherent to the formation of silver nanostructures in the pores of the SiO2/Si template using the electroless galvanic displacement method were highlighted. The growth mechanism of silver nanostructures in a limited pore volume has been studied and discussed in details.

Influence of solvent molecular geometry on the growth of nanostructures

Solvent properties such as surface tension, dielectric constant, and viscosity have been extensively studied over more than 150 years to understand their influence on the growth kinetics of nanostructures. Interestingly, these nanoparticles-based studies have missed the influence of solvent molecular geometry. Herein, by synthesizing ZnO nanorods on a highly conductive nitrogen incorporated graphene oxide (N-GO) substrate, we present the first study showing the influence of solvent molecular geometry on the growth mechanism of nanostructures. The solvents such as water (N-GO-ZnO-W) allow a large number of functional atoms along a, b and c-axis to coordinate in all possible directions with the metal ions of wurtzite hexagonal crystal system of ZnO and thus leads to lower aspect ratio nanorods. On the contrary, the unavailability of binding sites along a-axis for solvents such as ethanol (N-GO-ZnO-E) provides a size-limiting effect and leads to preferred growth along b and c-axis, thus generating ZnO nanorods with a higher aspect ratio. The study shows that the number of interacting atoms, carbon chain length and the solvent molecular geometry influence the aspect ratio and therefore a solvent could be used to tune the nanostructures morphology and hence the performance of devices based on them.

Electrocrystallization of Ni nanocones from chloride-based bath using crystal modifier by electrochemical methods

The early stages of nucleation and growth of nanostructures can control the shape and final size of the fabricated nanostructure. Therefore, the study of the nucleation and growth mechanism of nanostructures is of great importance. The purpose of this study is to investigate the nucleation and growth mechanism of nickel nanocones from a chloride-based bath containing ethylene ammonium dichloride as a crystal modifier. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry tests were employed to investigate the nucleation and growth mechanism and also the mechanism of crystal modifier performance on the growth of nanocones. Electrochemical studies revealed that the deposition of Ni nanocones occurs as nucleation and growth, and the growth of Ni nanocones can be considered as a competitive growth between two-dimensional and three-dimensional growth. By increasing the concentration of crystal modifier in the coating bath, the growth rate accelerates in the vertical direction, leading to enhance in three-dimensional growth. In general, according to the results of this study, the growth of nickel nanocones can be attributed to the synergistic effect between crystal modifiers and growth caused by screw dislocation.

In Situ Probing of the Particle-Mediated Mechanism of WO3 -Networked Structures Grown inside Confined Mesoporous Channels.

Nanocasting, using ordered mesoporous silica or carbon as a hard template, has enormous potential for preparing novel mesoporous materials with new structures and compositions. Although a variety of mesoporous materials have been synthesized in recent years, the growth mechanism of nanostructures in a confined space, such as mesoporous channels, is not well understood, which hampers the controlled synthesis and further application of mesoporous materials. Here, the nucleation and growth of WO3 -networked mesostructures within an ordered mesoporous matrix, using an in situ transmission electron microscopy heating technique and in situ synchrotron small-angle X-ray scattering spectroscopy, are probed. It is found that the formation of WO3 mesostructures involves a particle-mediated transformation and coalescence mechanism. The liquid-like particle-mediated aggregation and mesoscale transformation process can occur in ≈10 nm confined mesoporous channels, which is completely unexpected. The detailed mechanistic study will be of great help for experimental design and to exploit a variety of mesoporous materials for diverse applications, such as catalysis, absorption, separation, energy storage, biomedicine, and nanooptics.

Synthesis of flake-like bismuth tungstate (Bi2WO6) for photocatalytic degradation of coomassie brilliant blue (CBB)

Bismuth tungstate (Bi2WO6) flake-like nanostructures with zigzag periphery and 30–40nm thickness in high yield were produced by facile and efficient modified hydrothermal technique. The as-synthesized nanostructures were characterized by X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Bi2WO6 nanostructures were investigated as visible light photocatalyst to degrade model dye coomassie brilliant blue (CBB). The role of hydrogen peroxide (H2O2) used as initiator was also studied by varying concentrations during photocatalysis. It was observed that photocatalytic activity significantly enhanced for lower initiator concentrations. The growth mechanism for nanostructures was also discussed briefly.

Chemical Vapor Deposition Synthesis of Novel Indium Oxide Nanostructures in Strongly Reducing Growth Ambient

The current study reports some interesting growth of novel In2O3 nanostructures using ambient-controlled chemical vapor deposition technique in the presence of a strongly reducing hydrazine ambient. The experiments are systematically carried out by keeping either of the carrier gas flow rate or the source temperature constant, and varying the other. For each of the depositions, the growth is studied at three different locations downstream. In this paper, we report the growth of some novel nanostructures including nanodonuts, nanomushrooms, standing nanorods and long nanowires using ambient controlled chemical vapor deposition technique. Further, the nanostructures are characterized through scanning electron microscopy, transmission electron microscopy and x-ray diffraction. First, the growth of nanowires, octahedral and nanorods were verified to occur in oxidizing, inert and reducing ambient, respectively. However, a systematic variation of experimental parameters shows that different kinds of nanostructures can be obtained using highly reducing hydrazine ambient. Further, simultaneous growth of octahedral along with nanomushrooms and the hexagonal tip of the standing nanorods provides some insight into the growth mechanisms of these novel nanostructures. Possible growth mechanisms of the nanostructures are also discussed in detail.

Step-Flow Growth of Bi2Te3 Nanobelts

Understanding the growth mechanism of nanostructures is key to tailoring their properties. Many compounds form nanowires following the vapor–liquid–solid (VLS) growth mechanism, and the growth of Bi2Te3 nanobelts was also explained following the VLS route. Here, we present another growth mechanism of Bi2Te3 nano- and submicron belts and ribbons. The samples were grown by physical vapor transport from Bi2Te3 precursors using TiO2 nanoparticles as a catalyst and analyzed by scanning electron microscopy and scanning transmission electron microscopy. The growth starts from a Te-rich cluster and proceeds via a thin, tip-catalyzed primary layer growing in the [110] direction. The primary layer serves as a support for subsequent step-flow growth. The precursor predominantly absorbs on the substrate and reaches the belt by migration from the base to the tip. Terrace edges pose energy barriers that enhance the growth rate of secondary layers compared to the primary layer. Broadening of the sidewalls is commonly ob...

Sulfur in oleylamine as a powerful and versatile etchant for oxide, sulfide, and metal colloidal nanoparticles

Understanding of crystal growth is essential to the design of materials with improved properties. Unfortunately, still very little is understood about the basic growth mechanisms of nanostructures, even in the most established colloidal synthetic routes. Etching is one of the most important mechanisms to consider during particle growth, but it is rarely considered in the syntheses of oxide or chalcogenide nanostructures. Here, we report that the most common precursor for the synthesis of sulfide nanostructures – the mixture of sulfur and oleylamine – acts as a very powerful etchant for oxide, chalcogenide, and metal nanostructures. Specifically, we discuss its effect on several nanoparticle compositions (PbS, Cu2S, Fe3O4, and Au) and compare it to control conditions in which only oleylamine is present. Our experiments suggest that the etching results from the evolution of H2S from the sulfur–oleylamine precursor. We predict that the simultaneous role of this precursor as both etchant and ligand stabilizer will make it a useful tool for the chemical post‐processing (e.g., size reduction, focusing of size distributions, faceting) of nanocrystal dispersions.

Self-organization of TiO2 nanotubes in mono-, di- and tri-ethylene glycol electrolytes

Self-organization of TiO2 nanotubes was studied by means of titanium anodizing in electrolytes containing 1, 2 and 3 oxyethylene units in the organic chain of solvent molecule, named mono-, di-, and tri-ethylene glycols. A fundamentally different nanostructures were formed in mono- and di-electrolytes in view of their self-organization; close pack nanotubes are formed in mono-electrolyte, whereas nanotubes with large spaceing in-between are formed in di-electrolyte. The analysis of the tube bottoms and dimples formed in substrate shows formation of conical-type (alumina like) and frustum-type dimples in mono- and di-electrolytes, respectively. We discuss on the formation of frustum-type dimples with the size corresponding to the space in-between the nanotubes and link their formation to the mechanism of nanostructure growth.

Inverted Wedding Cake Growth Operated by the Ehrlich–Schwoebel Barrier in Two‐Dimensional Nanocrystal Evolution

AbstractWedding cake growth is a layer‐by‐layer growth model commonly observed in epitaxial growth of metal films, featured by repeated nucleation of new atomic layers on the topmost surface owing to the confinement of the Ehrlich–Schwoebel (ES) barrier. Herein, we report an inverted wedding cake growth phenomenon observed in two‐dimensional nanostructure evolution. Through a dynamically controlled vapor–solid deposition process of ZnO, a unique basin‐shaped crown was formed on the tip of each nanowire, featured with concentric steps. The atomic steps were nucleated along the edge and propagated toward the center. This is an opposite growth behavior compared to the conventional wedding cake growth, and is thus denoted as inverted wedding cake growth. Through the relation between the crown expansion rate and the temperature, the ES barrier of ZnO was determined to be 0.88 eV. The discovery of inverted wedding cake growth provided insight into the developing nanostructure growth mechanisms.

Inverted Wedding Cake Growth Operated by the Ehrlich-Schwoebel Barrier in Two-Dimensional Nanocrystal Evolution.

Wedding cake growth is a layer-by-layer growth model commonly observed in epitaxial growth of metal films, featured by repeated nucleation of new atomic layers on the topmost surface owing to the confinement of the Ehrlich-Schwoebel (ES) barrier. Herein, we report an inverted wedding cake growth phenomenon observed in two-dimensional nanostructure evolution. Through a dynamically controlled vapor-solid deposition process of ZnO, a unique basin-shaped crown was formed on the tip of each nanowire, featured with concentric steps. The atomic steps were nucleated along the edge and propagated toward the center. This is an opposite growth behavior compared to the conventional wedding cake growth, and is thus denoted as inverted wedding cake growth. Through the relation between the crown expansion rate and the temperature, the ES barrier of ZnO was determined to be 0.88 eV. The discovery of inverted wedding cake growth provided insight into the developing nanostructure growth mechanisms.

ChemInform Abstract: Review on Nanomaterials Synthesized by Vapor Transport Method: Growth and Their Related Applications

AbstractReview: 88 refs.

High-fidelity visualization of formation of volume nanogratings in porous glass by femtosecond laser irradiation

Formation of self-organized nanogratings in bulk glasses with femtosecond laser pulses is one of the most intriguing phenomena in the interactions of light with transparent materials. With the feature sizes far beyond the optical diffraction limit, these nanostructures have found widespread applications in nanophotonics and nanofluidics. The physics of the phenomenon is still far from being fully understood, largely because of the lack of a technique for noninvasively visualizing the formation of the nanogratings embedded within bulk glasses. Here, we access the snapshots of morphologies in the laser-affected regions in a porous glass that reveal the evolution of the formation of nanogratings with an increasing number of laser pulses. Combined with further theoretical analyses, our observation provides important clues that suggest that excitation of standing plasma waves at the interfaces between areas modified and unmodified by the femtosecond laser irradiation plays a crucial role in promoting the growth of periodic nanogratings. The proposed universal nanostructure growth mechanism involving laser-induced plasma wave formation at the interfaces of the seed structures may tie together many previous observations, meanwhile linking the in-volume nanograting formation to previously discovered mechanisms for surface nanoripple formation.

Triblock copolymer-assisted construction of 20 nm-sized ytterbium-doped TiO2 hollow nanostructures for enhanced solar energy utilization efficiency

Rare-earth doped titania single-crystalline hollow nanoparticles of 20 nm are constructed via a simple sol-gel process. Amphiphilic ABA tri-block copolymers played a key role in assisting the formation of hollow structure, for which a hollow nanostructure growth mechanism is proposed. By introducing rare earth into the synthesis process, the as-prepared nanoparticles exhibit near-infrared light absorption properties. Photo-decomposition efficiency of Orange II azo dye can be successfully evaluated when using Yb3+-doped TiO2 hollow nanoparticles as photocatalysts; it is more than two times higher than the pure TiO2 hollow nanoparticles. The hollow nanostructured Yb3+-doped TiO2 samples are exploited as photoanodes in N719-sensitized solar cells and prove able to improve the photoelectric conversion efficiency by measuring the solar cell parameters of dye-sensitized solar cells (DSSCs) under simulative sunlight.

Morphology dependent nanosecond and ultrafast optical power limiting of CdO nanomorphotypes

Morphology dependent nonlinear optical power limiting of CdO nanomorphotypes.

In situ growth mechanism and the thermodynamic functions of zinc oxide nano-arrays and hierarchical structure

We report the one-step synthesis of zinc oxide nanomaterials with arrays and hierarchical structure at room temperature. The zinc oxide nanomaterials can be synthesized via a simple method without catalyst. Furthermore, we explained the growth mechanisms of the two systems. In situ growth experiment provided the information of thermodynamics and kinetics, and based on that, growth mechanism was given a further explanation via the curve of in situ growth. Moreover, the relations between thermodynamic functions and the potential difference can be established by the electrochemical method. Take bulk zinc oxide reference. The thermodynamic functions of nano zinc oxide such as standard molar entropy, standard molar Gibbs free energy of formation, and standard molar enthalpy of formation can be calculated. The change rules of thermodynamic functions at different reaction times evidenced the growth mechanism more deeply. This work may contribute to the analysis of growth mechanism for nanostructures and obtain the thermodynamic functions of nanomaterials.

Controlled reshaping and plasmon tuning mechanism of gold nanostars

Anisotropic multi-branched gold nanoparticles exhibit intense localized electromagnetic fields at their tips/edges and hence have attracted significant attention in surface enhanced Raman scattering (SERS), as well as in bio-sensing applications. Our quest for such complex hyper-branching in gold nanostructures has revealed that even the addition of a simple base (like NaOH) to the precursor reaction mixture enhances the fine tuning/reshaping of the 3D star/flower-like gold nanostars with controlled precision right from the nucleation stage. With increasing the basicity of the reaction mixture, the two strongly localized surface plasmon resonance (LSPR) peaks of the gold nanostars essentially merge into a broad singular peak, effectively indicating the steady transition from (non)planar structures to conventional spheroidal nanostructures, as confirmed by the transmission electron microscopy (TEM) measurements. Such pH induced size/shape transitions of gold nanostructures were monitored kinetically in detail through correlated molecular spectroscopic measurements nuclear magnetic resonance, fourier transformation infrared spectroscopy and X-ray photoelectron spectroscopy (NMR, FTIR and XPS), for the first time to the best of our knowledge, which ascertains a rational paradigm in better understanding the complex polyvinylpyrrolidone (PVP) functionality for its simultaneous reducing, as well as stabilizing action, in precisely controlling the anisotropic gold nanostructure growth mechanism and further exploiting this functionality in utilizing these as-formed extremely stable colloidal gold dispersions for various specific plasmonic applications.

Growth mechanism of ZnO nanostructures in wet-oxidation process

Zinc (Zn) thin films were prepared by direct current magnetron sputtering as precursors with different deposition times. Zinc oxide (ZnO) nanostructures such as nanowires, nanobelts and nanoblades were then synthesized from the Zn precursors by wet-oxidation process. The microstructures of the Zn precursor and ZnO nanostructures have been studied by scanning electronic microscopy and X-ray diffractometry. The optoelectronic properties were analyzed by photoluminescence measurement. It was found that the Zn precursor film with a porous top layer consisting of well-crystallized Zn grains is an essential for formation of ZnO nanowires. Along with time dependence study and temperature dependence studies, the ZnO nanostructure growth mechanisms during the wet-oxidation process are proposed: water vapor has a major influence on the initial stage, and the final dimensions of the nanostructure are controlled by the vapor–solid process.