Simulation research on surface growth process of positive and negative frequency detuning chromium atom lithographic gratings

Chromium atom photolithography gratings are a promising technology for the development of nanoscale length standard substances due to their high accuracy,uniformity,and consistency.However,the inherent difference between the interaction of positive and negative frequency detuning standing wave field and the atoms can cause a difference in the adjacent peak-to-valley heights of the grating in positive and negative frequency detuning chromium atom lithography,which greatly reduces its accuracy.In this study,we performed a controlled variable growth simulation using the semi-classical theoretical model and Monte Carlo method with trajectory tracking and ballistic deposition methods to investigate the influence of key experimental parameters on the surface growth process of positive and negative frequency detuning atomic lithography gratings.We established a theoretical model based on simulation results and summarized empirical equations to guide the selection of experimental parameters.Our simulations achieved uniform positive and negative frequency detuning atomic lithography gratings with a period of 1/4 of the wavelength corresponding to the atomic transition frequency,and adjacent peak-to-valley heights differing by no more than 2 nm,providing an important theoretical reference for the controllable fabrication of these gratings.

Preparation of iridium nano-and submicroparticles on solid substrates by direct surface growth and drop-drying assembly

Iridium nanoparticles (IrNPs) and submicroparticles (IrSMPs) with different shapes were synthesized and assembled on indium thin oxide (ITO) and Si substrates using two different methods: direct surface growth and drop-drying assembly. The obtained IrNPs and IrSMPs were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The IrSMPs (or IrNPs) with disc-like shape and irregular shapes were obtained on ITO substrate by direct surface growth method using polyvinylpyrrolidone (PVP) and sodium citrate as different stabilizers, respectively. The reaction time and the injection temperature of reducing agent are found to have great effect on the size and morphology of the surface-grown Ir particles. The disc-like, ellipsoidal, and spherical IrSMPs (or IrNPs) were also synthesized in homogeneous solution in the presence of H3BO3 and Na2B4O7 as assistant-stabilizer. These IrNPs and IrSMPs were used as building blocks to construct nanoparticle assemblies by using a simple drop-drying method. Uniform IrNP and IrSMP assemblies were successfully prepared on Si and ITO substrates, indicating that the drop-drying method is efficient for the preparation of not only nanoparticle assemblies but also submicroparticle assemblies.

Turning weak into strong: on the CTAB-induced active surface growth

Discovering new methods and principles in the inequivalent growth of equivalent facets is of great significance for going beyond symmetrical nanocrystals and for out-of-box exploration. In this work, we demonstrate that a middle ground exists between the traditional weak ligands and the strong ligands with unusual growth modes. By modifying the seed concentration during the growth of pentagonal Au nanorods, the typical weak ligand cetyltrimethylammonium bromide(CTAB) is made strong, leading to notches of restricted growth and even the active surface growth mode. In-depth investigation in the link between growth kinetics and ligand packing reveals the principle of their interplay —— that the on-off dynamics of the ligands only allows for a certain limit of materials deposition rate. Beyond this limit, the growth materials build up and are then diverted elsewhere, leading to inequivalent growth. The fact that a freshly grown surface has few ligands promotes the active surface growth, focusing the growth materials onto a few sites. We believe that the knowhow of interfering ligand packing via growth kinetics would offer a powerful tool of synthetic control, where the facet-and curvature-dependent ligand packing is expected to be useful synthetic handles.

Evidence for the anomalous scaling behaviour of the molecular-beam epitaxy growth equation

According to the scaling idea of local slope, we investigate numerically and analytically anomalous dynamic scaling behaviour of （1＋ 1）-dimensional growth equation for molecular-beam epitaxy. The growth model includes the linear molecular-beam epitaxy （LMBE） and the nonlinear Lai-Das Sarma-Villain （LDV） equations. The anomalous scaling exponents in both the LMBE and the LDV equations are obtained, respectively. Numerical results are consistent with the corresponding analytical predictions.

A Two-Step Growth Curve: Approach to the von Bertalanffy and Gompertz Equations

Many curves have been proposed and debated to model individual growth of marine invertebrates. Broadly, they fall into two classes, first order (e.g. von Bertalanffy) and sigmoidal (e.g. Gompertz). We provide an innovative approach which demonstrates that the growth curves are not mutually exclusive but that either may arise from a simple three-stage growth model with two steps (k1 and k2) depending on the ratio of the growth parameters . The new approach predicts sigmoidal growth when is close to 1, but if either growth from stage A to stage B or B to C is fast relative to the other, the slower of the two steps becomes the growth limiting step and the model reduces to first order growth. The resulting curves indicate that there is a substantial difference in the estimated size at time t during the period of active growth. This novel two-step rate model generates a growth surface that allows for changes in the rate parameters over time as reflected in the new parameter n(t) = k1(t) - k2(t). The added degree of freedom brings about individual growth trajectories across the growth surface that is not easily mapped using conventional growth modeling techniques. This two (or more) stage growth model yields a growth surface that allows for a wide range of growth trajectories, accommodating staged growth, growth lags, as well as indeterminate growth and can help resolve debates as to which growth curves should be used to model animal growth. This flexibility can improve estimates of growth parameters used in population models influencing model outcomes and ultimately management decisions.=

Revisiting the Seasonal Evolution of the Indian Ocean Dipole from the Perspective of Process-Based Decomposition

The seasonal phase-locking feature of the Indian Ocean Dipole(IOD)is well documented.However,the seasonality ten-dency of sea surface temperature anomalies(SSTAs)during the development of the IOD has not been widely investigated.The SSTA tendencies over the two centers of the IOD peak in September-October-November are of different monthly amplitudes.The SSTA tendency over the west pole is small before June-July-August but dramatically increases in July-August-September.Meanwhile,the SSTA tendency over the east pole gradually increases before June-July-August and decreases since then.The growth rate attribution of the SSTAs is achieved by examining the roles of radiative and non-radiative air-sea coupled thermodynamic processes through the climate feedback-response analysis method(CFRAM).The CFRAM results indicate that oceanic dynamic processes largely contribute to the total SSTA tendency for initiating and fueling the IOD SSTAs,similar to previous studies.However,these results cannot ex-plain the monthly amplitudes of SSTA tendency.Four negative feedback processes(cloud radiative feedback,atmospheric dynamic processes,surface sensible,and latent heat flux)together play a damping role opposite to the SSTA tendency.Nevertheless,the sea surface temperature-water vapor feedback shows positive feedback.Specifically,variations in SSTAs can change water vapor con-centrations through evaporation,resulting in anomalous longwave radiation that amplifies the initial SSTAs through positive feedback.The effect of water vapor feedback is well in-phase with the monthly amplitudes of SSTA tendency,suggesting that the water vapor feedback might modulate the seasonally dependent SSTA tendency during the development of the IOD.

Broadening of Cr nanostructures in laser-focused atomic deposition

This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition. The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width at half maximum as approximately 95 nm. Surface growth in laser-focused Cr atomic deposition is modeled and studied by kinetic Monte Carlo simulation including two events： the one is that atom trajectories in laser standing wave are simulated with the semiclassical equations of motion to obtain the deposition position; the other is that adatom diffuses by considering two major diffusion processes, namely, terrace diffusion and step-edge descending. Comparing with experimental results （Anderson W R, Bradley C C, McClelland J J and Celotta R J 1999 Phys. Rev. A 59 2476）, it finds that the simulated trend of dependence on feature width is in agreement with the power of standing wave, the other two simulated trends are the same in the initial stage. These results demonstrate that some surface diffusion processes play important role in feature width broadening. Numerical result also shows that high incoming beam flux of atoms deposited redounds to decrease the distance between adatoms which can diffuse to minimize the feature width and enhance the contrast.

STUDY ON THE SURFACE CRACK GROWTH BEHAVIOR IN 14MnNbq BRIDGE STEEL

Three-dimensional crack closure correction methods are investigated in this paper.The fatigue crack growth tests of surface cracks in 14MnNbq steel for bridge plate subjected to tensile and bending loadings are systematically conducted.The experimentally measured fatigue crack growth rates of surface cracks are compared with those of through-thickness cracks in detail.It is found that the crack growth rates of surface cracks are lower than those of through-thickness cracks.In order to correct their differences in fatigue crack growth rates, a dimensionless crack closure correction model is proposed.Although this correction model is determined only by the experimental data of surface cracks under tensile loading with a constant ratio R=0.05, it can correlate the surface crack growth rates with reasonable accuracy under tensile and bending loadings with various stress ratios ranging from 0 to 0.5.Furthermore, predictions of fatigue life and crack aspect ratio for surface cracks are discussed, and the predicted results are also compared with those obtained from other prediction approaches.Comparison results show that the proposed crack closure correction model gives better prediction of fatigue life than other models.

Formation Mechanism and Template-free Synthesis of Hierarchical m-ZrO_2 Nanorods by Hydrothermal Method

Here, a new idea was proposed for template-free synthesis of hierarchical m-ZrO2 nanorods and ＂their＂ possible formation mechanism based on a series of chemical reactions by simple hydrothermal method. The traditional preparation methods of hierarchical ZrO2 nanorods involved inexpensive equipment, complicated process, and high production cost. The as-synthesized products composed of many nanorods with 180-200 nm in diameter and 5-7 μm in length. The fi nal product after annealing involved hierarchical monoclinic ZrO2（m-ZrO2） nanorods, namely, the big nanorod was made up of many small nanorods with 40-50 nm in diameter and 500-600 nm in length. The experimental results were useful in understanding the chemical properties of ZrB2 and ZrO2 and the design of the derivatives for m-ZrO2 nanomaterials.

ATOMIC FORCE MICROSCOPY OBSERVATION OF MAGNETRON SPUTTERED ALUMINUM－SILICON ALLOY FILMS

wo different surface morphology characteristics of magnetron sputtered aluminumsilicon(Al-Si)alloy films deposited at 0 and 200℃ were observed by atomic force microscopy(AFM).One is irregularly shaped grains put togther on a plane.The other is irregularly shaped grains Piled up in space. Nanometer-sized particles with heights from 1.6 to 2.9 nm were first observed. On the basis of these observations the growth mechanism of magnetron sputtered films is discussed.

Role of Catalysts in the Surface Synthesis of Single-Walled Carbon Nanotubes

We demonstrate the role of catalysts in the surface growth of single-walled carbon nanotubes(SWNTs)by reviewing recent progress in the surface synthesis of SWNTs.Three effects of catalysts on surface synthesis are studied:type of catalyst,the relationship between the size of catalyst particles and carbon feeding rates,and interactions between catalysts and substrates.Understanding of the role of catalysts will contribute to our ability to control the synthesis of SWNTs on various substrates and facilitate the fabrication of nanotube-based devices.

Prediction of Dendrite Orientation and Stray Grain Distribution in Laser Surface-melted Single Crystal Superalloy

A vectorization analysis technique for crystal growth and microstructure development in single-crystal weld was developed in our previous work. Based on the vectorization method, crystal growth and stray grain distribution in laser surface remelting of single crystal superalloy CMSX-4 were investigated in com- bination of simulations with experimental observations. The energy distribution of laser was taken into consideration in this research. The experimental results demonstrate that the simulation model applies well in the prediction of dendrite growth direction. Moreover, the prediction of stray grain distribution works well except for the region of dendrites growing along the [100] direction.

Interaction of straight chain alcohol vapors with self-assembled MOF film by surface plasmon resonance sensing and imaging

Interaction of straight chain alcohol vapors with MOF-199-functionalized films was studied by SPR. The signals had linear relationships with the concentration of alcohols over a wide range from 0 to 70% （v/v） and were reversible in proportional to the chain length, with R2 all above 0.99.

Growth of CdS crystals by the physical vapor transport method

Based on the physical vapor transport （PVT） method, the growth of large-size CdS crystals inside a vertical semi-closed tube is studied. Firstly, in order to ensure 1D diffusion-advection transport, multi-thin tubes are used in the growth tube. The XRD spectra of the CdS crystal grown in this configuration indicates that the crystal quality has clearly been improved, where the FWHM is 58.5 arcsec. Secondly, theoretical and experimental growth rates under different total pressures are compared; the results show that the experiential growth rate equation is valid for our semi-tube growth, and it could be used to estimate the growth rate and maximum growth time under different total pressures.

Partial Regularity of Suitable Weak Solutions of the Model Arising in Amorphous Molecular Beam Epitaxy

In this paper,we are concerned with the precise relationship between the Hausdorff dimension of possible singular point set S of suitable weak solutions and the parameterαin the nonlinear term in the following parabolic equationh_(t)+h_(xxxx)+∂_(xx)|h_(x)|^(α)=f.It is shown that when 5/3≤α<7/3,the 3α-5/α−1-dimensional parabolic Hausdorff measure of S is zero,which generalizes the recent corresponding work of Ozánski and Robinson in[SIAM J.Math.Anal.,51,228–255(2019)]forα=2 and f=0.The same result is valid for a 3D modified Navier–Stokes system.

SOOT PARTICLES ANALYSIS IN LAMINAR PREMIXED PROPANE/OXYGEN(C_(3)H_(8)/O_(2))FLAMES USING PUBLISHED MEASUREMENT DATA

A laminar premixed Propane/Air flame with a fuel equivalence ratio of 2.1 was employed for analysis of soot particles. Zeroth-order lognormal distributions (ZOLD) were used in the analysis of experimental distribution phe-nomena at different residence times during soot formation in the flame. Rayleigh抯 theory and Mie抯 scattering theory were combined with agglomerate analysis using scattering and extinction data to determine the following soot charac-teristics: agglomerate parameters, volumetric fractions, mass flow rates and surface growth rate. Soot density meas-urements were carried out to determine density variations at different stages of growth. The measured results show that for long residence times the soot clearly crystallizes with higher density (up to 1.8 g.cm-3). The increases of soot volu-metric fraction and mass flow rate indicate that the surface growth rate of soot particles exceeds the oxidation rates in the flame studied. The data obtained in this work would be used to study soot oxidation rate under flaming condition.

Promoting the Na^(+)-storage of NiCo_(2)S_(4) hollow nanospheres by surfacing Ni-B nanoflakes

Sodium ion battery(SIB)is considered as the potential alternative for next generation energy system to succeed the lithium ion battery(LIB)due to the low price and vast abundance of Na resource.Ternary metal sulfide is identified as an impo rtant redox conversion type of negative electrode for SIB.In this study,amorphous nickel boride(Ni-B)nanoflakes are introduced into the hollow Ni-Co sulfide nanospheres by a facile in situ solution growth route to promote the electrochemical performance of Na^(+)-storage.Electrochemical measurements demonstrate that the Ni-B component could effectively improve the redox kinetics of the conversion reaction and structural stability during long-term Na^(+)insertion/extraction.For example,the NiCo_(2)S_(4)@Ni-B composites display a high reversible capacity of 251.9 mA h g^(-1)at the current density of 1.0 A g^(-1)after 200 cycles,much higher than that of bare NiCo_(2)S_(4)(37.4 mA h g^(-1)at 1.0 A g^(-1)after 200 cycles).As a consequence,these results demonstrate a new sight to explore heterostructures of mixed metal-sulfides electrode materials with superior Na^(+)-storage performances.