Nanoscale Layers Research Articles

Hydrogen isotope permeability of reduced activation ferritic/martensitic steel CLF-1 corroded by Li4SiO4

In a solid tritium breeding blanket, Li4SiO4 is in contact with reduced activation ferritic/martensitic (RAFM) steel at high temperatures for years and forms a corrosion layer. The effects of the corrosion layer on the hydrogen isotope permeability of a RAFM steel CLF-1 were thus investigated. X-ray diffraction, secondary ion mass spectroscopy and spherical aberration corrected transmission electron microscopy demonstrated the formation of a three-layered corrosion product, comprising a middle layer of LiFeO2 and an inner layer of LiCrO2. Li4SiO4 powder with the (104) crystal plane orientation was adsorbed on the outermost surface of the CLF-1, forming a nanoscale layer with a thickness of ∼150 nm. Deuterium permeation tests show that the deuterium permeability of the corroded samples was two orders of magnitude higher than that of the blank substrate that was pre-heated for 30 days, but one order of magnitude lower than that of the blank substrate that was not preheated. The CLF-1 corroded for 10 days exhibited the highest deuterium permeation flux. There was a decrease in the deuterium permeability of the steel that corroded for 15 and 30 days; thus, there was a decrease in the permeability with an increase in the corrosion period. By the weighting method and TEM analysis, a cracking and reoxidation process was proposed to explain the decreasing deuterium permeability of CLF-1 during corrosion by Li4SiO4. Our study provides a promising approach for preventing tritium permeation.

On the metallurgical joining mechanism during ultrasonic spot welding of NiTi using a Cu interlayer

Ultrasonic spot welding of NiTi shape memory alloy with Cu interlayer was performed to understand the metallurgical joining mechanism at the materials’ interface. Dynamic recrystallization of the Cu foil and high strain rate of the process induced a nano-scale transition layer composed of NiTiCu phase. The formation of this new phase occurs due to the frictional heating and shear deformation that is imposed by the ultrasonic vibration and contributes to the metallurgical bonding between the parent materials. Mechanical tension tests revealed that the joint with Cu interlayer presents enhanced strength.

Boosting high-voltage cyclic stability of nickel-rich layered cathodes in full-cell by metallurgy-inspired coating strategy

Increasing the cutoff voltage is an effective way to boost the energy density of lithium ion full-cells which use the layered nickel-rich oxides. However, the practical application of nickel-rich cathode is severely hindered by the structural degradation and grave capacity loss. Herein, we find that the deterioration of full-cell capacity retention is correlated with the lithium loss in the anode solid electrolyte interphase (SEI) especially at high voltage. The Ni and Mn ions dissolved from the cathode deposit in the anode SEI triggers lithium trapping, and consequently expedites the consumption of cyclical lithium ions. Be based on this finding, an innovative metallurgy-inspired approach of creating a uniform hydroxide layer on the cathode surface and inhibiting separate nucleation of hydroxide that employ carbon dioxide as acidic inducing precipitant, is introduced. Finally, the ultra-thin Al2O3-encapsulated cathodes are obtained after annealing process. Benefiting from the prominent physical-chemical protection function of nanoscale oxide layer, the developed cathode exhibits outstanding cycle durability in full-cell with a capacity retention of ~80% after 800 cycles at 25 °C. Notably, the modified full-cell possesses well thermal stability go through nail penetration test. This work offers an industrial-scale coating paradigm toward high performance nickel-rich cathode for application in full-cells.

In-situ Polymerization of exfoliated structure PA6/organo-clay nanocomposites

Abstract Montmorillonite (MMT) was modified with cetyl trimethyl ammonium bromide (CTAB) to obtain organomontmorillonite (OMMT) by stirring and pulsed ultrasonic mixing. Polyamide 6 (PA6)/OMMT nanocomposites were then prepared via in-situ polymerization.The resulting OMMT and PA6/OMMT nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results suggested that the OMMT interlayer distance was greatly increased to 3.13 nm due to CTAB being inter-calated into the MMT galleries. The OMMT interlayer distance was further enlarged to 10-20 nm during the polymerization process. The OMMT layers were exfoliated into nanoscale layers and uniformly dispersed in the molten ∈-caprolactam and PA6 matrix, and exfoliated structure nanocomposites were formed.

Ultra-broadband photon harvesting in large-area few-layer MoS2 nanostripe gratings.

Flat optics nanoarrays based on few-layer MoS2 are homogeneously fabricated over large-area (cm2) transparent templates, demonstrating effective tailoring of the photon absorption in two-dimensional (2D) transition-metal dichalcogenide (TMD) layers. The subwavelength subtractive re-shaping of the few-layer MoS2 film into a one-dimensional (1D) nanostripe array results in a pronounced photonic anomaly, tunable in a broadband spectral range by simply changing the illumination conditions (or the lattice periodicity). This scheme promotes efficient coupling of light to the 2D TMD layers via resonant interaction between the MoS2 excitons and the photonic lattice, with subsequent enhancement of absorption exceeding 400% relative to the flat layer. In parallel, an ultra-broadband absorption amplification in the whole visible spectrum is achieved, thanks to the non-resonant excitation of substrate guided modes promoted by MoS2 nanoarrays. These results highlight the potential of nanoscale re-shaped 2D TMD layers for large-area photon harvesting in layered nanophotonics, quantum technologies and new-generation photovoltaics.

In English

The present study aims to obtain the supported Ti-containing catalyst on a surface of stainless steel foil by low temperature ionic implantation method. The geometrical sizes of the implantation chamber allow one to synthesize composites with the maximum size of 30×30 cm. The shape and size of the catalysts provide an opportunity to use obtained samples for removal of harmful substances from both aqueous solutions and gas mixtures. A quantitative estimation of bond strength of the surface layer of the prepared composites was realized by the use of sclerometric method. It is shown that implantation of titanium ions on stainless steel foil provide significant increase in surface layer mechanical strength. The heat treatment of the sample leads to a decrease in this strength, but its value rests higher than that in initial support (stainless steel). The composition of samples surface and the effect of calcination temperature were determined by XRD, SAXS, SEM, AFM, and XPS. It is shown that after ionic implantation nanoscale layer of the implant on the surface of stainless steel was formed. Presence of titanium oxide, nitride and oxynitride was determined by XPS method. The high photocatalytic activity of this catalyst in the process of neutralizing benzene in aqueous solutions under irradiation with visible light, which significantly exceeds its activity under UV-radiation was shown. Increasing the calcination temperature leads to decreasing the samples activity and can be explained by the influence of the ratio between the nitride, oxynitride, and oxide phases of titanium. Exactly the presence of those phases on the surface explains its high activity in the degradation of benzene in aqueous solution under visible light irradiation. Thus, using of the obtained samples in the neutralization of aqueous benzene solutions under visible light irradiation is perspective from ecological point of view.

Structure and Dynamics of Nanoconfined Water Between Surfactant Monolayers.

The properties of nanoconfined water arise in direct response to the properties of the interfaces that confine it. A great deal of research has focused on understanding how and why the physical properties of confined water differ greatly from the bulk. In this work, we have used all-atom molecular dynamics (MD) simulations to provide a detailed description of the structural and dynamical properties of nanoconfined water between two monolayers consisting of an archetypal ionic surfactant, cetrimonium bromide (CTAB, [CH3(CH2)15N(CH3)3]+Br-). Small differences in the area per surfactant of the monolayers impart a clear effect on the intrinsic density, mobility, and ordering of the interfacial water layer confined by the monolayers. We find that as the area per surfactant within a monolayer decreases, the mobility of the interfacial water molecules decreases in response. As the monolayer packing density decreases, we find that each individual CTAB molecule has a greater effect on the ordering of water molecules in its first hydration shell. In a denser monolayer, we observe that the effect of individual CTAB molecules on the ordering of water molecules is hindered by increased competition between headgroups. Therefore, when two monolayers with different areas per surfactant are used to confine a nanoscale water layer, we observe the emergence of noncentrosymmetry.

Dielectric Properties of Pulsed Laser Deposited Nanoscale CeNi5 Thin Films

Dielectric properties of pulsed laser deposited, nanoscale CeNi5 alloy layers, on glass or SiO2 substrate are described using the complex dielectric function. The UV–Vis–NIR spectral behavior of this function is studied separately for its real part e1 (the dielectric constant or dielectric permittivity), and for its imaginary part e2 (the dielectric loss function). The layers were obtained from grinded CeNi5 bulk powder using short, modulated laser pulses. The absolute reflectance of the obtained nanoscale alloy layers was measured at the 632.8 nm wavelength of a liquid nitrogen cooled and stabilized He–Ne source. This value was further used to renormalize the relative differential reflectance spectroscopy measurements performed in the UV‒Vis‒NIR domain. The obtained absolute reflectance spectra were processed using the Kramers–Kronig formalism, so that the real and imaginary parts of the complex dielectric function could be computationally determined, also leading to the calculation of the electron loss functions –Im e–1 and –Im(1 + e)–1. The behavior of these functions near the spectral inflexion points was determined using appropriate theoretical considerations. The variation of the dielectric functions was explained, electron density of states and the shape of the energy bands were inferred. This study reveals the layer thickness and deposition substrate dependent optical and electrical properties of the produced nanoscale CeNi5 structures.

Anode Overpotential Control via Interfacial Modification: Inhibition of Lithium Plating on Graphite Anodes.

Lithium-metal deposition on graphite anodes limits the cycle life and negatively impacts safety of the current state of the art Li-ion batteries. Herein, deliberate interfacial modification of graphite electrodes via direct current (DC) magnetron sputtering of nanoscale layers of Cu and Ni is employed to increase the overpotential for Li deposition and suppress Li plating under high rate charge conditions. Due to their nanoscale, the deposited surface films have minimal impact (∼0.16% decrease) on cell level theoretical energy density. Interfacial properties of the anodes are thoroughly characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and spatially resolved mapping X-ray absorption near edge structure (XANES) spectroscopy. The spectroscopic measurements indicate that the Cu and Ni coatings form oxide upon exposure to an ambient environment, but they are reduced within the electrochemical cell and remain in a metallic state. Li plating is quantified by X-ray diffraction and associated electrochemistry measurements revealing that the surface treatment effectively reduces the quantity of the plated Li metal by ∼50% compared to untreated electrodes. These results establish an effective method using interfacial modification to achieve deliberate control of Li-metal deposition overpotential and reduction of lithium plating on graphite.

Multifunctional Nanoscale Metal-Organic Layers for Ratiometric pH and Oxygen Sensing.

As a monolayered version of nanoscale metal-organic frameworks (nMOFs), nanoscale metal-organic layers (nMOLs) represent an emerging class of highly tunable two-dimensional materials for hierarchical functionalization and with facile access to analytes. Here we report the design of the first nMOL-based biosensor for ratiometric pH and oxygen sensing in mitochondria. Cationic Hf12-Ru nMOL was solvothermally synthesized by laterally connecting Hf12 secondary building units (SBUs) with oxygen-sensitive Ru(bpy)32+-derived DBB-Ru ligands (bpy = 2,2'-bipyridine). The Hf12-Ru nMOL was then covalently functionalized with pH-sensitive fluorescein isothiocyanate and pH/oxygen-independent Rhodamine-B isothiocyanate through thiourea linkages to afford Hf12-Ru-F/R as a mitochondria-targeted ratiometric sensor for pH and O2 in live cells. High-resolution confocal microscope imaging with Hf12-Ru-F/R revealed a positive correlation between pH and local O2 concentration in mitochondria. Our work shows the potential of nMOL-based ratiometric biosensors in sensing and imaging of biologically important analytes in live cells.

Near-Equilibrium Control of Li2TiO3 Nanoscale Layer Coated on LiNi0.8Co0.1Mn0.1O2 Cathode Materials for Enhanced Electrochemical Performance.

Ni-rich layered metal oxide of LiNi0.8Co0.1Mn0.1O2 is a promising cathode material for next-generation lithium ion batteries because of its capability to deliver a high capacity; however, intrinsic problems, especially the side reactions between Ni4+ ions and the electrolyte, adversely affect its electrochemical and thermal stability. Surface coating by a protective and Li+-conducting Li2TiO3 layer is a strategic approach to remit those problems. The normal deposition strategies depend on the hydrolysis of titanium alkoxides, making it difficult to control the reaction equilibrium. Herein we report a near-equilibrium deposition tactic to achieve a uniform Li2TiO3 nanoscale layer coated on the surface of LiNi0.8Co0.1Mn0.1O2 microspheres to improve electrochemical performance and thermal stability. With pH modulation and BO33- scavenger in the (NH4)2TiF6 precursor solution, the ion product for the coating layer is controlled to be slightly bigger than its solubility product. The hydrolysis reaction chemistry can thus be manipulated at a near-equilibrium condition. Within the critical pH range of 4.8-5.2, a uniform coating layer of Li2TiO3 with the thickness of about 4 nm can be successfully deposited on the surface of the LiNi0.8Co0.1Mn0.1O2 cathode material, which greatly enhances its capacity retention to 93.5% after 200 cycles at 0.5 C. The appropriate Li2TiO3 coating can increase the mobility of Li ions and suppress the side reactions between electrolytes and cathode materials, which further makes the modified cathode display the higher peak temperature in differential scanning calorimetry analysis and capacity enhancement at 60 °C, which are related to safety concerns.

Influence of air humidity on the low-frequency capacitance of silicon MOS structures with a nanoscale oxide layer

The influence of air humidity on the low-frequency capacitance of Mо - SiO2 - NN+Si(111) structures with a donor concentration of 2∙1021 m−3 in the N silicon layer and a thin porous oxide, about 5 nm thick, has been investigated. It has been established that in weakly inverted structures the capacitance of surface states at the silicon - oxide interface to a great extent determines the structures low-frequency capacitance. Largely, these states are induced by water molecules adsorbed by a thin porous oxide layer from the air. The recharging of the surface states is carried out by minority charge carriers and is determined by the generation-recombination processes in the silicon space charge region. This allows the surface states capacitance, as well as the total structure capacitance, to linearly depend on the humidity of the surrounding gas medium. The obtained expression for calculation of the low-frequency capacitance of the studied structures adequately describes the experimental dependences and serves as a proof of the new low-frequency conductivity model proposed in the paper for such structures.

Pressure-gated capillary nanovalves based on liquid nanofilms

HypothesisNanoscale valving is essential to expand the potentiality of the nanodevices. However, it is difficult to fabricate valves with movable control elements in nanoscale systems and thus it is desirable to design a nanovalve which can manipulate opening and blocking a gate without moving parts. ExperimentsA pressure-gated capillary valve which contains a nanoscale liquid layer sandwiched between two plates with two aligned orifices was designed and the proof-of-concept demonstration was achieved by Many-body Dissipative Particle Dynamics. FindingsThe concave or convex meniscus appears naturally within the orifice of the capillary valve and can be controlled by the pressure difference between liquid and gas phases based on Young-Laplace equation and the edge effect. The closed state can be transformed into the open state (hole) when the two concave menisci are allowed to touch each other. The on/off switch is reversible by Laplace pressure manipulation and the passing and blocking of the fluid particles through the valve is verified.

Assessment of mechanical and corrosion properties of plasma oxidized medical grade NiTi wire

Nitinol is an excellent biomaterial amongst smart materials, which have shape and form memory effects and superelasticity, and is mainly used as orthodontic wire and coronary stent. One of the associated drawbacks, however, is nickel release into bloodstream, which can achieve critical levels. In this work, F2063 Nitinol wire was plasma-oxidized in order to obtain a TiO2 protective layer ranging from 50 to 80 nm, which helps blocking nickel release and enhances corrosion properties, thus avoiding or decreasing foreign body reactions. Two power sources (DC and RF) were evaluated and the resulting surfaces from plasma treated samples were characterized. According to the obtained results, tensile tests showed a slight improvement in superlastic elongation and in vitro corrosion resistance in specimens treated by plasma. The findings also suggest that RF power source is best suited to achieve a desired nano-scale layer in NiTi alloys. In this new light, plasma-assisted treatments can be performed in memory-shape alloys, aiming the obtention of a well adhered, corrosion improving and mechanical properties enhancing coating.

Water nanostructure formation on oxide probed in situ by optical resonances.

The dynamic characterization of water multilayers on oxide surfaces is hard to achieve by currently available techniques. Despite this, there is an increasing interest in the evolution of water nanostructures on oxides to fully understand the complex dynamics of ice nucleation and growth in natural and artificial environments. Here, we report the in situ detection of the dynamic evolution of nanoscale water layers on an amorphous oxide surface probed by optical resonances. In the water nanolayer growth process, we find an initial nanocluster morphology that turns into a planar layer beyond a critical thickness. In the reverse process, the planar water film converts to nanoclusters, accompanied by a transition from a planar amorphous layer to crystalline nanoclusters. Our results are explained by a simple thermodynamic model as well as kinetic considerations. Our work represents an approach to reveal the nanostructure and dynamics at the water-oxide interface using resonant light probing.

Effect of the Density of Electron Beam Energy on the Structure and Mechanical Characteristics of Surface Layers of Hypoeutectic Silumin

The structural phase states and mechanical properties of hypoeutectic silumin subjected to electron beam treatment with energy density of 10–35 J cm−2 are studied according to modern physical materials science. Treating silumin with an electron beam that has an energy density of 25 J cm−2 leads to the formation of a cellular structure in a layer that is up to 40 μm thick. The increase in the hardness of the surface layer of silumin is apparently due to the formation of a high-speed cellular crystallization structure of submicron size with nanoscale layers of the second phase distributed along the cell boundaries.

Investigation on the anticorrosion, adhesion and mechanical performance of epoxy nanocomposite coatings containing epoxy-silane treated nano-MoO3 on mild steel

The effect of introducing MoO3 (Molybdenum oxide) nanoparticle in the epoxy coating was analyzed by EIS and SECM methods in natural seawater. The aminopropyl triethoxy silane (APTES) was treated with the nanoparticle for the proper dispersion and chemical interaction of nanoparticle with the epoxy resin. The introduction of MoO3 nanoparticle in the epoxy coating enhances the charge transfer resistance (Rct) as well as the film resistance (Rf). The observation of iron dissolution and oxygen consumption was carried out by applying the appropriate SECM tip potential in the MoO3 modified nanocomposite coated steel. The epoxy and epoxy-MoO3 nanocomposite-coated samples were used to study the mechanical, adhesion and anticorrosion properties. The analysis using SEM/EDX displayed that the enriched Mo was detected in the nanocomposite coated steel. The presence of the nano level corrosion product containing Mo was confirmed by FIB-TEM analysis. The high corrosion protection properties of the epoxy based nanocomposite coating was due to the complex nanoscale layer formed and chemical interactions of epoxy resin with surface-modified nanoparticle in nanocomposites.

Nanoscale Layers Formed on the Surface of a Titanium Alloy by the Ion-Beam Mixing of Carbon with a Substrate

A complex of studies of the composition, structure, and properties of nanoscale surface layers of titanium alloy VT6 formed by the ion-beam mixing of a carbon nanofilm is conducted. It is found that ion-beam mixing in the transition layer of a film/substrate system provides conditions for the formation of titanium carbides, the content of which increases to 20 at % with an increase in the irradiation dose. After both the deposition and ion-beam mixing of a carbon film, the hyperfine surface layer of the samples mostly consists of carbon atoms in a disordered state with sp2- and sp3-hybridized C–C bonds. It is revealed that the coherent scattering region of samples decreases after ion-beam mixing; this effect can be attributed to an increase in the dislocation density and the formation of dislocation substructures. The formation of titanium carbides, a disordered carbon structure, and dislocation substructures under ion-beam mixing conditions leads to a more than twofold increase in the microhardness of the samples.

Near-Perfect Selective Photonic Crystal Emitter with Nanoscale Layers for Daytime Radiative Cooling

Radiative cooling, as a passive way to dissipate heat into outer space without any extra energy, has attracted considerable attention recently. However, the metal reflector of the conventional cool...

SBFE analysis of nano-scale elastic layer with consideration of surface energy effects

This paper presents an efficient and accurate numerical technique for determining the mechanical response of an infinite elastic layer under surface loading and surface stress effects. The governing equation of the bulk is formulated from the classical linear elasticity theory via a SBFE technique whereas that of the material surface is obtained from a complete version of Gurtin-Murdoch surface elasticity theory. By enforcing the continuity at the interface of the material surface and the bulk, it leads to a system of linear non-homogenous ordinary differential equations governing the nodal functions. A general solution of the resulting system of ODEs is constructed via standard procedures and then used together with the boundary conditions to form a system of linear algebraic equations governing nodal degrees of freedom. To investigate the accuracy and convergence of the proposed method, selected scenarios are solved and obtained numerical results are reported and discussed.