Narrow Results

The grown cross traces on the top surface of single-domain YBCO bulk sample with c-axis normal to the top surface has been clearly revealed. It is found that there are many fish-scale like YBCO layers, which are well connected each other. The c-axis is normal to the top surface of the sample, which indicates that YBCO crystal starts to grow from the center to the edge along a(or b) axis in all the four regions divided by across traces, and forms a 90° angle when the four regions meet each other, The clear traces observed is just because of the slightly difference in height between adjacent regions. A simple model has been afforded to explain the growth mechanism of single-domain YBCO bulks with c-axis normal to the top surface.

A two-step anodization method has been used to produce patterned arrays of TiO₂ on the surface of Ti sheet. Hexagonal ripples were created on Ti substrate after removing the TiO₂ layer produced by first-step anodization. The shallow concaves were served as an ideal position for the subsequent step anodization due to their low electrical resistance, resulting in novel hierarchical nanostructures with small pits inside the original ripples. The mechanism of morphology evolution during patterned anodization was studied through changing the anodizing voltages and duration time. This work provides a new idea for controlling nanostructures and thus tailoring the photocatalytic property and wettability of anodic TiO₂.

Two dimensional (2D) materials are widely attracting the interest of researchers due to their unique crystal structure and diverse properties. In the present work, tungsten disulfide (WS${}_2)$ nanorods were synthesized by a simple method of pulsed laser ablation in liquid (PLAL) environment. The prepared WS₂ are analyzed by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), UV-visible spectroscopy (UV-vis) and Raman spectroscopy to confirm the surface morphology, phase and structure. A possible growth mechanism of WS₂ is proposed. This study indicates new door for the preparation of 2D materials with specific morphology.

$\alpha$-Si₃N₄ nanowires were formed by a simple chemical vapor deposition (CVD) method using Si and SiO₂ as raw materials without the addition of metal catalyst. The effect of reaction temperature on the phase composition and morphologies of the nanowires were analyzed by XRD and SEM. The experimental results indicate that a suitable reaction temperature is essential for the final products. At 1400${}^{\circ }$C, small amount of target products were obtained, and some irregular particles were attached on the surfaces of nanowires. When the temperature increased to 1450${}^{\circ }$C, the nanowires were mainly composed of $\alpha$-Si₃N₄ phase, they had smooth surfaces with diameters fluctuating from 50 to 200 nm and lengths from hundreds to thousands of microns. At further high reaction temperature (1500${}^{\circ }$C), $\beta$-Si₃N₄ phase was observed and the nanowires had larger diameters, this was negative for obtaining purity $\alpha$-Si₃N₄ nanowires. The growth process of $\alpha$-Si₃N₄ nanowires was dominantly governed by the vapor–solid mechanism.

3C-SiC nanowires were synthesized using Si, SiO₂, and active carbon as raw materials at different reaction temperatures without additional metal catalysts. The influence of reaction temperature on the phase assemblage and morphologies of the products were investigated by XRD and SEM. The experimental results indicate that a suitable reaction temperature is essential for the final products. When the reaction temperature was not high enough (1400 and 1450^∘C), the raw materials were not reacted completely, and a small amount of targeted nanowires were formed. When reaction temperature increased to 1500^∘C, the nanowires were mainly composed of 3C-SiC phase, and they were straight, curved, and needle-shaped. The straight nanowires ranged from several to tens of microns, but the diameters were not uniform. The vapor-solid mechanism dominantly governed the formation of SiC nanowires.

This paper describes a simple approach for creating silver (Ag) nanocubes using pulsed laser ablation in a liquid medium. The development of nanocubical formations of Ag obtained by laser ablation using Nd: YAG laser was conducted for 5, 10, 15, and 20min. The surface morphological analysis was performed using field-emission scanning electron microscopy (FESEM) to show the formation of silver nanocubes with edge lengths ranging from 150nm to 250nm. The UV-visible spectroscopy demonstrates that the concentration of Ag nanostructures, evidenced by the characteristic localized surface plasmon resonance band near 400nm in the colloidal solution containing Ag nanoparticles, increased with the increasing laser ablation duration from 5min to 20min. The growth mechanism for Ag nanocubes can be easily understood with the change in laser ablation time from 5 to 10, 15, and then 20min. The Ag sheets with no specific shape start to develop after 5 min of laser ablation, and after 10min, larger particles form. Then, after 15min, a small number of cube-like nanostructures with rough and uneven edges was obtained. At the end of 20min, a complete cubic formed with fine and distinct edges and a very large amount of nanocubes. The elemental silver signal was present in Ag nanocubes, as revealed by the energy-dispersive X-ray spectroscopy (EDS) spectra. The produced Ag nanocubes may be used to construct two-dimensional nanocomposites with practical applications in the electrical, optoelectronic, electrochemical, and biological areas.

We performed local density functional calculations for the electronic structure of short carbon nanobells. The calculated local density of states of the nanobells revealed field emission characteristics that agree with experimental observations. We also performed total energy calculations to study the structural stability and a related possible growth mechanism of the nanobells. In the nitrogen-doped carbon nanobells, nitrogen atoms that are attracted to the open-edge sites of the carbon nanobells appear to stop the growth of the nanostructures.

Hydrothermal method was chosen as a convenient method to fabricate zinc selenide (ZnSe) nanoparticle materials. The prepared nanospheres were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), where its different properties were observed using UV–visible spectroscopy and LCR meter. It was found that the pure ZnSe nanoparticles have a Zinc blende structure with crystallite size 10.91 nm and in a spherical form with average diameter of 35 nm (before sonication) and 18 nm (after sonication) with wide band gap of 4.28 eV. It was observed that there is inverse relation of frequency with dielectric constant and dielectric loss while AC conductivity grows up by increasing frequency. Such nanostructures were determined to be effectively used in optoelectronic devices as UV detector and in those devices where high-dielectric constant materials are required.

Carbon nanotubes (CNTs) as interconnects in integrated circuits (ICs) which are vertically aligned in growth with high tube density and long tube length are required. In this paper, we present a method to improve the height of CNTs. High-resolution transmission electron microscopic (TEM) images confirm CNTs top growth mode. By cutting and modifying the top of CNTs, the influences of different radii of apertures on interconnect resistance were studied. According to the analysis, we proposed a novel growth mechanism to improve growth height of CNTs interconnection structure and the top contact resistances of pre-cutting and post-cutting CNTs interconnection structure were forecasted. The result demonstrates that the electronic performances of the post-cutting CNTs interconnection structure with platinum (Pt)-protected layer are better than the ones of pre-cutting CNTs interconnection structure. The resistivity of the post-cutting CNTs interconnection structure with Pt-protected layer is $81.2\mathrm{\text{m}}\mathrm{\Omega }\cdot \mathrm{\text{cm}}$, which is much less than that of post-cutting CNTs interconnect structure $508.8\mathrm{\text{m}}\mathrm{\Omega }\cdot \mathrm{\text{cm}}$. In what follows, the resistance of the contacted area of pre-cutting CNTs interconnection structure is 31 $\mathrm{\Omega }$, which is much less than that of post-cutting CNTs interconnection structure 439 $\mathrm{\Omega }$. This constitutes a significant step to realize longer CNTs interconnects with complementary metal oxide semiconductor (CMOS) contact modules.

In this study, we focus on the oxidation behavior of the oxide scale with Platinum (Pt) on free standing NiCoCrAlY coating in air with water vapor at high temperature. The Pt layer is deposited on the NiCoCrAlY coating surface by electroplating, and then heat treatment at 1000${}^{\circ }$C with Argon (Ar) protection. Cycle oxidation of the oxide scale with Pt is conducted in air and air with water vapor at 1050${}^{\circ }$C. The results indicated that the spinels (NiCr₂O₄) are formed on the surface of the alumina scale in air and air with water vapor. However, this kind of spinel is inhibited in the air with water vapor and the scale on the coatings with Pt presents a good adherence during oxidation process. The thermal stress and crack initiation and propagation will be discussed.

In the present study, the individual growth process of an organism has been shown with the help of a mathematical model. The surplus energy production rate, i.e. intake rate minus metabolic cost, plays a crucial role in controlling the growth rate. Considering the existence of an optimum mass, which maximizes the surplus energy, it has been found that the scaling exponent for the metabolic cost has to be greater than the exponent for the intake rate. On the basis of the consideration that the system always generates some surplus energy, a relationship among the empirical constants has been established. The growth is found to continue with an ever decreasing rate. When the system attains its optimum mass, the growth rate is found to be the maximum. The mass variation with time has been graphically shown using the expression obtained by solving a differential equation involving surplus energy. Using figures, the dependence of mass variation upon various scaling parameters, has been thoroughly discussed. As mass increases, the surplus energy production rate per unit mass is found to decrease and this may be the probable reason for the smaller number of organisms with larger mass. As the scaling exponent regarding intake increases, the maximum attainable mass increases along with an increase in the time required for its attainment.

We have grown thin layers of γ′Fe₄N on Cu(100) substrates by molecular beam epitaxy in a flow of atomic nitrogen, delivered by a radio-frequency (RF) plasma source. This nitride phase is a ferromagnetic metallic conductor and has interesting properties for device applications. In addition it has an intriguing growth mechanism. In earlier work we found that pure crystalline layers can be grown at substrate temperatures higher than 250°C, with excess nitrogen and in the presence of hydrogen.¹ To gain insight into the growth mechanism, we studied the structure and composition with scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and X-ray diffraction (XRD). This was done for a coverage range of Fe₄N on Cu(100) between 0.5 and 30 monolayers (ML) equivalent of Fe, deposited at 400°C, or at 300°C in one case. Here a preliminary account of this study is presented. We found that at sub-ML coverage, first "depressed" (with respect to the Cu surface) islands of Fe–N are formed. Then, on top of these islands a second layer is growing. Subsequently the space between the islands is filled up by a Fe–N layer growing directly on Cu. This gives rise to a smooth surface with patches differing in height by only 0.5 Å. The following layers grow by step-flow growth. The smooth terraces still show patches with a 0.5 Å height difference. The phase is γ′Fe₄N with a distorted (p4g-like) structure as observed with LEED and STM, where a p(2 × 2) symmetry is seen. The c(2 × 2) symmetry expected for γ′Fe₄N is observed after growing 30 ML or more. A model for the growth mechanism based on our observations is proposed.

The microstructure of dendritic titanium carbides fabricated by laser surface alloying of pure titanium with graphite powder is investigated using electron probe microanalyzer (EPMA) and high-resolution transmission electron microscope (HRTEM). The growth mechanism of TiC crystals is that crystal grows by the model of continuous growth at the beginning of solidification and then the crystal surfaces that are suited to lateral growth develop fully by the model of spiral growth. So, the final morphology of dendritic TiC looks like it is composed of tiny crystal grains in a linear arrangement.

Growth mechanisms and defects formation of the manganese mercury thiocyanate (MMTC) crystal have been investigated by atomic force microscopy (AFM). Both screw dislocation controlled growth and 2D nucleation growth occur on the {110} faces. Stacking faults are observed among dislocation hillocks and the formation of them probably results from the different crystallization orientations of different spirals. Hollow channels are found around the nucleation islands and the formation of them is due to the instability of the interface generated by the rapid nucleation and growth speeds.

ZnO nanoneedle arrays were obtained from the transformation of ZnC₂O₄ precipitate, which was synthesized via electrodeposited method at room temperature. The diameter of those grown ZnO nanoneedles is about 80 nm. The XRD pattern and the HRTEM image indicate that the grown ZnO nanoneedles have the preferential growth toward (101) direction. The possible growth mechanism of the ZnC₂O₄ nanoneedle arrays is proposed and is different from the traditional V-L-S and V-S models. The study on the PL spectrum of those ZnO nanoneedles shows the near band-edge emission band (379 nm) and the green emission band (510 nm). Especially, a red shift of the green emission band emerges with the increase of the annealing temperature and time.

A quantitatively kinetic model has been established to address the self-assembly of the ring shaped nanostructures upon the droplet epitaxy via kinetic Monte Carlo simulations. The theoretical predictions about the temperature and As flux dependences of the self-assembly of the ring shaped nanostructures were in well agreement with recent experiments. It was found that the morphological evolution of the ring shaped nanostructures was attributed to the cooperation of the enhanced diffusion barriers of free Ga atoms in the inner ring region and the effects of the surface reconstruction around the Ga droplets during the arsenization step.

Gold atomic aggregates are fabricated by vapor-depositing Au atoms onto a silicone oil surface and the microstructure evolution is investigated by atomic force microscopy (AFM) observation. It is found that the Au aggregates are composed of Au circular nanoparticles with diameter around 45 nm, which is independent with the nominal film thickness d. As d increases from 1 nm to 15 nm, the height of the nanoparticles increases from 15 nm to 25 nm, indicating the geometric shape of the Au nanoparticles evolves from plateau to spherical. Furthermore, the roughness analysis shows that the mean surface roughness increases linearly with d in the range of 1 nm–15 nm, which is quite different from the findings in Ag system. The anomalous microstructure evolution of Au aggregates suggests that the growth of Au aggregates may be dominated by the shadowing effect.

Single crystal graphene has been getting lots of attention due to the lack of grain boundaries which ensures its distinguished intrinsic properties and good performance in graphene-based devices. Hence, the realization of single crystal graphene growth with tunable size and high crystallinity will be of great importance in commercial production and widespread applications. Recently, numerous studies have focussed on the controlled single crystal graphene growth, and great advancements have been made in the synthesis of large-sized single-crystal graphene (LSSG) by chemical vapor deposition (CVD). In this review, current developments of CVD-grown LSSG and its future prospects are presented and discussed. We emphasize on growth methods and growth mechanisms over transition-metal Cu and Cu alloys for deeper insights in control of size and crystallinity.

A kind of coral-like melamine formaldehyde resins/carbon nanotubes (MF/CNTs) composite particles were prepared via in situ polymerization, which showed good thermal stability under 450${}^{\circ }$C. To illustrate the mechanism of the polymer growth process, silica/CNTs were also prepared via the same method to achieve a contrast. Generally, two models were used to illustrate silica growth mechanism, the monomer addition one and the controlled aggregation one. We preferred that the monomer addition model could explain the growth of the novel coral-like MF/CNTs particles.

In this work, the growth mechanism of nickel-plated coating on primer-modified poly(ethylene terephthalate) (PET) sheets was investigated systematically. Results showed the surface structure of primer-modified PET sheets would chemisorb Sn and Pd, which are used as the catalyst for the electroless nickel plating. Nickel particles were formed on the plated PET surface. The crystal preferential orientation transformed from (200) plane to (111) plane and nickel particles grew with the increase of thickness of plated coating. The growth of nickel particles mainly included lateral growth and vertical growth. Cracks and then shed were formed in the nickel coating when the thickness exceeded about 228nm.