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The silicon core and carbon mantle particles were produced by using the advanced carbon coating method which enables direct covering with the carbon layer using an electron microscope. The growth of SiC crystal was observed upon h...
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The silicon core and carbon mantle particles were produced by using the advanced carbon coating method which enables direct covering with the carbon layer using an electron microscope. The growth of SiC crystal was observed upon heating at 500℃ in vacuum. The growth process of SiC on both the carbon layer and silicon particles was directly observed by in situ observation. The inward movement of carbon into silicon began at the twinned part. The growth rate of SiC on the carbon mantle layer was estimated from in situ images and found to be 8 times faster than the growth rate of silicon carbide in silicon particles.
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Using the phase-field crystal method, we investigated the bcc {1 1 0} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. S...
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Using the phase-field crystal method, we investigated the bcc {1 1 0} vicinal surface growth from melts at the atomic scale with emphasis on the growth kinetics of two growth modes: step flow growth and island growth on terrace. Simulation results show that, for step flow growth, with the decrease of terrace width, the competition for feeding atoms between neighboring steps causes growth rate vs. step density to deviate from a linear relationship, and finally converge to a finite value. The step crystal direction also strongly influences the growth kinetics: vicinal surface with steps along the closest packed direction— [111] grows slower than that with [001] step. For island growth on terrace, the growth exponent of each layer in multi-layer island gradually transits from 1/2 for the top layer to 1/3 for the bottom layer, which demonstrates the transition from global diffusion controlled growth for top layer to surface diffusion controlled growth for bottom layer. The growth mechanism selection map with respect to terrace width and supersaturation is summarized and atom attaching rates of different growth mechanisms are also compared.
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Al:ZnO layers, with low and high Al content, 0.2% and 2.1% cat. respectively, have been prepared using the RF magnetron sputtering technique. Noticeable differences in the optical and electrical properties have been detected in th...
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Al:ZnO layers, with low and high Al content, 0.2% and 2.1% cat. respectively, have been prepared using the RF magnetron sputtering technique. Noticeable differences in the optical and electrical properties have been detected in these films. With doping, the resistivity decreases and the band-gap increases. The alterations in the films crystalline structure are explained in terms of the nanostructural changes induced by Al substitutional doping, such as a higher concentration of edge dislocation defects and a higher rotation of crystalline nano-domains in the plane of the films (normal to the preferential orientation c-axis) for the high content Al:ZnO layer. A complete description of such effects has been accomplished using several characterization techniques, such as X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The combination of these techniques provides an exhaustive understanding of the films nanostructure.
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The properties of nanostructured A16061 foils, produced by melt spinning technique at a cooling rate of about 10~7 K/s, were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction p...
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The properties of nanostructured A16061 foils, produced by melt spinning technique at a cooling rate of about 10~7 K/s, were investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction pattern (XRD) and microhardness testing. The properties of nanostructured foils were then compared with those of direct-chill (DC) casting. The results show that the formation of nanoparticles of Mg_2Si (about 50 nm in radius), the nanograins of about 61.8 nm and the ultra-fine dendrites, having a nanoarm spacing about 80-100 nm, can significantly refine the structure and, in turn, enhance the properties of nanostructured foils comparing to the DC cast ones. Besides, the produced nanodendrites can extremely lead to structure homogeneity.
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Density functional theory (DFT) calculations have been performed to study the adsorption of hydrogen on the surface of pristine and nickel decorated Al12N12 and Al12P12 nano-cages. Decoration of nickel on the surface of nano-cages...
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Density functional theory (DFT) calculations have been performed to study the adsorption of hydrogen on the surface of pristine and nickel decorated Al12N12 and Al12P12 nano-cages. Decoration of nickel on the surface of nano-cages delivers four distinct geometries. Hydrogen adsorption is studied on the surface of Ni-decorated Al12X12 (X = N, P) in these four geometries (named as P1, P2, P3, and P4). Calculations reveal very weak physisorption of H-2 on pristine nano-cages while significant enhancement in its adsorption properties is found upon using Ni-X12Y12 nano-cages. The hydrogen adsorption on Ni-Al12N12 nano-cage is in order of P2 > P3 > P4 > P1, whereas the order of adsorption energies on Ni-Al12P12 is P2 > P1 > P3 > P4. Ni complexation with Al12N12 shows considerably higher potential for H-2 adsorption compared to Al12P12. We used natural bond orbital (NBO), molecular dipole moment, density of states (DOS) and frontier molecular orbitals analyses to observe the changes in the electronic structure of Ni-Al12X12 nano-cages on adsorption of H-2. (C) 2016 Elsevier Ltd. All rights reserved.
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Vapor-liquid-solid (VLS)-grown nanowires are promising building blocks for next-generation devices because of their unique characteristics. Although Au is a widely used catalyst with the largest operable parameter window for Si na...
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Vapor-liquid-solid (VLS)-grown nanowires are promising building blocks for next-generation devices because of their unique characteristics. Although Au is a widely used catalyst with the largest operable parameter window for Si nanowire growth by the VLS method, Au catalyst droplets diffuse at a high migration velocity over a Si substrate surface and agglomerate at relatively low temperature, thus degrading the uniformity of Au catalyst droplets and Si nanowires. Our aim is to improve the controllability of nanowire growth, positioning, and diameter, which are essential attributes for practical applications. To accomplish this, a diffusion barrier layer was inserted between the catalyst and substrate. Length and diameter uniformity were considerably improved for nanowires grown together with the formation of a silicide layer as a diffusion barrier.
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Nucleation of amorphous calcium phosphate (ACP) and its phase transformation with a decrease in solution pH were investigated at a constant temperature of 32 ℃. A solution containing a mixture of CaCl_2 and KH_2PO_4 was prepared ...
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Nucleation of amorphous calcium phosphate (ACP) and its phase transformation with a decrease in solution pH were investigated at a constant temperature of 32 ℃. A solution containing a mixture of CaCl_2 and KH_2PO_4 was prepared (initial pH =7.7), and a drop was sampled at a constant interval to observe the morphological evolution of the precipitates that formed in the solution. A gel-like solution structure formed immediately after mixing and contained a small amount of sea-urchin-like ACP spherulites (3-20 um in size). These spherulites consisted of 1.5-10-um-long flexible needles that formed simultaneously with numerous ACP spherical particles. They first transformed into p-tri calcium phosphate-like material (called "pseudo p-TCP") and then into single crystals of octacalcium phosphate (OCP) without dissolution. The flexible needles in the spherulites changed into blade springs, then into flexible plates, and finally into rigid plates during the transformation. The OCP structure appeared in the pseudo P-TCP plates and gradually substituted for the P-TCP structure over time. The macroscopic spherulite morphology of the initial ACP remained unchanged during the phase transformation, suggesting that OCP is a pseudomorph of ACP. This feature was observed only when the ACP spherulites formed in the initial solution. Fiber-like aggregates consisting of P-TCP single crystals nucleated around the ACP spherical particles and grew over time. They survived until the final stage of the reaction, and OCP polycrystals formed in the mixture of p-TCP and ACP spheres. The OCP polycrystals gradually substituted for the ACP spheres without phase transformation of P-TCP into OCP.
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The reaction mechanisms between Al and Fe_3O_4powders were investi-gated. Differential thermal analysis revealed that a two-step displacementreaction between Al and Fe_3O_4took place during sintering. Initially, theFe_3O_4was conv...
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The reaction mechanisms between Al and Fe_3O_4powders were investi-gated. Differential thermal analysis revealed that a two-step displacementreaction between Al and Fe_3O_4took place during sintering. Initially, theFe_3O_4was converted to amorphous FeO at～720°C and some of the Al wasoxidized to amorphous Al_2O_3. In the final stage, when temperaturereached ～840°C, crystalline Al_2O_3particles were produced in the moltenAl-Fe liquid. The effects of cooling rate on the microstructures werestudied. When the Al-Fe liquid was furnace-cooled to room temperature,proeutectic Al_3Fe plates, plate-like divorced eutectic Al_and 2O_3particles were in situ formed in the Al(Fe) matrix. While quenching from700°C, nanometer-sized Al dendrites and Al-Al_6Fe eutectic lamellae wereproduced in the Al matrix. However, when it was rapidly quenched from900°C, the size of the proeutectic Al_3Fe phases was further reduced andAl_6Fe nanorods were found in the Al-Al_eutectics. A model wasproposed to describe the transformation of the Al-Fe intermetallics duringsolidification.
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Light confinement induced by spontaneous near?surface resonance is inherentlydetermined by the location and geometry of metallic nanostructures (NSs),offering a facile and effective approach to break through the limitation of thel...
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Light confinement induced by spontaneous near?surface resonance is inherentlydetermined by the location and geometry of metallic nanostructures (NSs),offering a facile and effective approach to break through the limitation of thelight?mater interaction within the photoactive layers. Here, we demonstratehigh?performance Al NS/ZnO quantum dots (Al/ZnO) heterostructure UVphotodetectors with controllable morphologies of the self?assembled Al NSs.The Al/ZnO heterostructures exhibit a superior light utilization than the ZnO/Al heterostructures, and a strong morphological dependence of the Al NSs onthe optical properties of the heterostructures. The inter?diffusion of Al atomsinto ZnO matrixes is of a great benefit for the carrier transportation. Consequently, the optimal photocurrent of the Al/ZnO heterostruc?ture photodetectors is significantly increased by 275 times to ~ 1.065?mA compared to that of the pristine ZnO device, and an outstandingphotoresponsivity of 11.98?A?W ?1 is correspondingly achieved under 6.9?mW?cm ?2 UV light illumination at 10?V bias. In addition, arelatively fast response is similarly witnessed with the Al/ZnO devices, paving a path to fabricate the high?performance UV photodetec?tors for applications.
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The mechanical alloying (MA) process was applied to synthesize nanostructured Al-Zn-Mg-Cu alloy powder and its composite with 3 wt.% Al2O3 particles. Both the alloy and the composite powders were produced by simultaneous milling o...
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The mechanical alloying (MA) process was applied to synthesize nanostructured Al-Zn-Mg-Cu alloy powder and its composite with 3 wt.% Al2O3 particles. Both the alloy and the composite powders were produced by simultaneous milling of the constituents for different milling times (0 50 hours), with fixed milling technical parameters. The produced powders were characterized by the X-ray diffraction (XRD) analysis to detect the generated phases. Also, a scanning electron microscope (SEM) and a transmission electron microscope (TEM) were used to observe the morphologies and measure the crystallite size of the powders, respectively. It was found that during the production of the composite powder, the size of Al2O3 particle changed which led to unexpected outcomes. In the alloy state, the average particle size and the crystallite size were lower and the microhardness values were higher than those in the composite powder. Also, the steady state was achieved after a shorter MA time in the alloy state compared to the composite state. The major reason for these results was the changes of alumina particle size in the composite powders at the first stages of the MA process due to consuming a noticeable amount of energy, which made them ineffective. In addition, the compressibility in the composite powders was lower than that of the alloy powders due to the presence of alumina particles. Moreover, in both powders, the compressibility decreased with increasing the MA time because of the increased work hardening and the reduced flow properties.
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