Manufacturing temperatures of severely cold-drawn hyper-eutectoid steel wires are sufficiently high to influence the mobility of dislocations and alloy elements, thereby affecting the materials' mechanical properties. Herein, we describe the evolution of microstructure and tensile strength of the as-drawn 3.45 GPa steel wire during post-deformation annealing for 30 min at 150-450 degrees C. Annealing at 150 degrees C raised the strength to 3.77 GPa by age-hardening through activation of dislocations pinning by carbon, while further temperature rising up to 450 degrees C caused a severe loss of strength. It was proved that annealing at 300 and 450 degrees C destabilizes the lamellar microstructure, promoting the formation of carbon-deficient (Fe,Mn,Cr)(3) C-type cementite particles with preferentially rounded and partially faceted hetero-interfaces. Annealing at 450 degrees C yielded the accumulation of Mn and Cr at the ferrite/particle interfaces, and their concentrations at the interfaces were dependent on the interface structure; i.e., lower concentrations at rounded interfaces (formed through capillarity-driven coarsening of the spheroidized cementite), and higher concentrations at faceted interfaces (that are initially existing in the as-drawn state). Our proof-of-principle observations, supported by thermodynamic calculations and kinetic assessments, provide a pathway for understanding the changes in microstructural and tensile properties during manufacturing of the hyper-eutectoid steel wires. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The first 3-D direct observation of clusters of Nd oxide inside silicate glasses was achieved using atom probe tomography. Three-dimensional elemental maps of major chemical elements in glasses such as Si, Al, Zn and O showed no evidence of regions that had concentrations higher than the average values, whereas the Nd aggregated into regions of high concentration. Elemental maps of Nd and Pb recorded from the glasses containing PbS QDs showed highly-concentrated areas of both elements at the same locations; this result indicates that PbS QDs formation started in association with the Nd clusters.

An array of amorphous tin oxide (a-SnOx.) nanohelixes (NHs) was fabricated on copper foil as an electrode for Na-ion batteries via the oblique angle deposition method, a solution- and surfactant-free process. The combination of the amorphous phase SnOx with a low oxidation number and its vertically aligned NH geometry with a large surface area and high porosity, which facilitate Na-ion dynamics and accommodate the volume changes, enabled a reversible capacity of up to 915 mA h g(-1) after 50 cycles, fast rate capability with 48.1% retention at 2 A g(-1), and high stability, which are superior to those of crystalline nanoparticle-based electrodes.

Order-disorder coherent interfaces determine the microstructure and mechanical properties of precipitation-hardened high-temperature alloys. The characteristics of these interfaces can be defined by a compositional width, δ, and structural width, δ′. The latter, which can be considered as the width of the ordered part of the interface, can play an important role in high-temperature mechanical behavior of precipitation-hardened alloys. This is due to the fact that diffusion in the ordered part of the interface is generally much slower than diffusion in the disordered phase, thus hindering the solid-state diffusion-based phenomena. Here, we investigate the order-disorder interface in a Ni-19Al (at.%) alloy as a model alloy for Ni-based superalloys using atomic-resolution scanning transmission electron microscopy and three-dimensional atom probe tomography. Then, we employ thermodynamic modeling to describe the interplay between the structural and compositional interface widths in binary Ni-Al and in ternary Ni-Al-Cr and Co-Al-W systems. We introduce the δ′/δ ratio as a critical parameter that varies significantly in different alloys. Our findings offer a general pathway to control the δ′/δ ratio of interfaces, which in turn affect the high-temperature properties of precipitation-hardened alloys.

The nanostructural hierarchy of gamma and gamma' phases is characterized in Ni-8.5Al-5.4Ti (at.%) alloy, after double aging treatment at 1000 and 780 degrees C for 6 and 20 h. Using electron microscopy and atom probe tomography, disordered gamma phase inside ordered gamma' precipitate was detected, which underwent plate-like growth during aging treatment. This unique hierarchical structure enabled the simultaneous study of direct (gamma' precipitates/gamma matrix) and inverse (gamma nanoparticles/gamma' precipitates) order-disorder interfaces in 6 and 20 h double-aged samples. It was found that the compositional interface width, delta, of direct interfaces decreased during aging treatment, whereas the thickness remained almost unaffected for inverse interfaces. The difference in thickening behavior is explained based on the change of the Gibbs-Thomson pressure for gamma plates embedded in gamma' and cuboidal gamma' precipitates surrounded by the gamma matrix. This inference suggests the possibility of prediction and control of delta(t) variations during heat treatment processes based on the current thermodynamic approach.

Emulating essential synaptic working principles using a single electronic device has been an important research field in recent years. However, achieving sensitivity and energy consumption comparable to biological synapses in these electronic devices is still a difficult challenge. Here, we report the fabrication of conjugated polyelectrolyte (CPE)-based artificial synapse, which emulates important synaptic functions such as paired-pulse facilitation (PPF), spike-timing dependent plasticity (STDP) and spiking rate dependent plasticity (SRDP). The device exhibits superior sensitivity to external stimuli andlow-energy consumption. Ultrahigh sensitivity and low-energy consumption are key requirements for building up brain-inspired artificial systems and efficient electronicbiological interface. The excellent synaptic performance originated from (i) a hybrid working mechanism that ensured the realization of both short-term and long-term plasticity in the same device, and (ii) the mobile-ion rich CPE thin film that mediate migration of abundant ions analogous to a synaptic cleft. Development of this type of artificial synapse is both scientifically and technologically important for construction of ultrasensitive highly-energy efficient and soft neuromorphic electronics.

The strengthening mechanism of the metallic material is related to the hindrance of the dislocation motion, and it is possible to achieve superior strength by maximizing these obstacles. In this study, the multiple strengthening mechanism-based nanostructured steel with high density of defects was fabricated using high-pressure torsion at room and elevated temperatures. By combining multiple strengthening mechanisms, we enhanced the strength of Fe-15 Mn-0.6C-1.5 Al steel to 2.6 GPa. We have found that solute segregation at grain boundaries achieves nanograined and nanotwinned structures with higher strength than the segregation-free counterparts. The importance of the use of multiple deformation mechanism suggests the development of a wide range of strong nanotwinned and nanostructured materials via severe plastic deformation process.

The present study aims at unveiling the influence of trace amounts of phosphorus on the macro-scale delamination in a ferritic steel. Two different steels with trace amounts of phosphorus were examined to reveal the cause: One was made by long-time high temperature holding to maximize the phosphorus segregation, and the other one was made by short-time high temperature holding to minimize the phosphorus segregation. The atom probe results at the grain boundaries ahead of the delamination-related cracks provide a strong evidence that phosphorus-enrichment and carbon-depletion for the long-time high temperature holding induces a larger degree of delamination as compared to the short-time high temperature holding. Reasons for the different segregation tendency were discussed by correlating the isothermal holding time at high temperature and the competitive segregation between phosphorus and carbon.

Solar-powered photoelectrochemical (PEC) water splitting has been a promising candidate for producing hydrogen in a clean and renewable way. Photoelectrodes are key components in PEC cells for efficient and stable hydrogen generation because they play crucial roles in absorption of photons, the separation and transportation of photo-generated charge carriers, as well as the chemical reactions with water. A variety of metal oxides for efficient photoelectrode have been intensively explored, but it is still challenging to find desirable materials to satisfy lots of requirements for PEC water splitting. Iron oxide (hematite, Fe2O3) has recently attracted much attention due to its earth abundance, low cost as well as desirable material properties for PEC water oxidation including narrow band gap energy of 2.0~2.2eV for visible light absorption and proper energy band alignment, etc. However, Fe2O3 has very short hole diffusion length and low carrier mobility, which causes considerable recombination of photo-generated electrons and holes. A lot of approaches such as nanostructures, heterojunction with other materials, surface modification, etc. have been reported to prevent the recombination of charge carriers and improve electrical properties of Fe2O3; however, these require complex manufacturing processes. In the present work, we found a much simpler way to improve the electrical properties of Fe2O3 film, namely defect-pairs due to co-doping. Titanium (Ti) and carbon (C) co-doped thin Fe2O3 film (i.e. (Ti,C)-Fe2O3) has been realized via a combination of simple solution-based spin-coating and tube furnace annealing process. This film turns out to lead significantly enhanced PEC performance when used as a photoanode: an impressively high photocurrent density of more than 4.5mAcm-2 was achieved at 1.23VRHE under AM1.5G solar spectrum and 1 sun illumination. This is compared to the value of Ti-doped Fe2O3 film, which is only about 2.6mAcm-2 photocurrent density at 1.23VRHE even though the optical properties of each film are similar. The origin for such substantial enhancement was revealed using a series of experimental and computational spectroscopies. X-ray absorption spectroscopy, electrochemical impedance measurements and density-functional-theory calculations both indicate that C atoms can be more deeply and heavily doped under the existence of Ti dopants in Fe2O3 film and then the defect-pairs of Ti and C increase not only charge carrier density but also electron’s mobility. An emphasis should be placed on the fact that this achievement was not assisted by co-catalysts and complex nanostructuring methods; hence even higher performance is expected when the film is further treated with extra-cares.

Solar-powered photoelectrochemical (PEC) water splitting has been a promising candidate for producing hydrogen in a clean and renewable way. Photoelectrodes are key components in PEC cells for efficient and stable hydrogen generation because they play crucial roles in absorption of photons, the separation and transportation of photo-generated charge carriers, as well as the chemical reactions with water. A variety of metal oxides for efficient photoelectrode have been intensively explored, but it is still challenging to find desirable materials to satisfy lots of requirements for PEC water splitting. Iron oxide (hematite, Fe 2 O 3 ) has recently attracted much attention due to its earth abundance, low cost as well as desirable material properties for PEC water oxidation including narrow band gap energy of 2.0~2.2eV for visible light absorption and proper energy band alignment, etc. However, Fe 2 O 3 has very short hole diffusion length and low carrier mobility, which causes considerable recombination of photo-generated electrons and holes. A lot of approaches such as nanostructures, heterojunction with other materials, surface modification, etc. have been reported to improve electrical properties of Fe 2 O 3 which unfortunately cause poor light absorption. In this study, three-dimensional tin oxide (SnO 2 ) nanohelix (NH) structures were fabricated as scaffolds for a thin Fe 2 O 3 layer on fluorine-doped SnO 2 glass substrate by oblique angle deposition method using electron beam evaporator. SnO 2 NH structures based photoelectrode can simultaneously enhance light absorption and charge separation and transport for efficient PEC water splitting by trapping the incident light through strong light scattering effect as well as by providing pathways for charge separation and transport and large surface area. In addition, SnO 2 NH structures are easy to be hybridized with Fe 2 O 3 through only simple solution-based spin-coating method due to its high porosity, aspect ratio and large surface area. Thin Fe 2 O 3 layer was coated along the surface of SnO 2 NH structures forming a type-II band hetero-junction and these Fe 2 O 3 coated SnO 2 NH are significantly desirable for efficient visible light driven water splitting by simultaneously improving light absorption, charge separation and transport. Highly efficient PEC performance of our hybridized photoelectrode (including more than 5.0mAcm -2 photocurrent density at 1.23V RHE under AM1.5G solar spectrum and 1 sun illumination which is a significantly excellent performance for Fe 2 O 3 based photoelectode) will be investigated and the advantages of three-dimensional SnO 2 NH structures as scaffolds for very thin Fe 2 O 3 layer as well as its potential for practical application will be discussed in detail based on electrochemical analysis, FEM simulation, angular-dependent reflectance, PEC analysis at different intensity of incident light, etc.

Synthesizing semiconductor nanoparticles through core/shell structuring is an effective strategy to promote the functional, physical, and kinetic performance of optoelectronic materials. However, elucidating the internal structure and related atomic distribution of core/shell structured quantum dots (QDs) in three dimensions, particularly at heterostructure interfaces, has been an overarching challenge. Herein, by applying complementary analytical techniques of electron microscopy and atom probe tomography, the dimensional, structural, topological, and compositional information on commercially available 11.8 nm-sized CdSSe/ZnS QDs were obtained. Systematic experiments at high resolution reveal the presence of a 1.8 nm-thick Cd xZn1 - xS inner shell with a composition gradient between the CdSe core and the ZnS outermost shell. More strikingly, the inner shell shows compositional variation because of competitive atomic configuration between Cd and ZnS, but it structurally retains a zinc-blende crystal structure with the core. The inner shell may grow through the decreased reactivity of S with Cd, followed by atomic diffusion-related processes. The composition-competitive gradient inner shell alleviates lattice misfit strain at heterostructure interfaces, thereby enhancing the quantum yield and photostabilty to a greater extent than those of other single-shell structures. Thus, this precise measurement approach could offer a potential pathway to develop a wide variety of three-dimensional core/shell-structured materials.

The chemical stability of Ag nanowires (NWs) can be addressed by introducing a layer of noble metal alloy, in particular Ag-Pd alloy, on the Ag NW surface. Due to the high cost of noble metals, it is practically important to use the least amount of noble metals as possible while achieving the chemical and electrical properties required for the electrode. To minimize the amount of Pd added to Ag NWs, the electrode performance should be correlated with the elemental distribution of Pd in the Ag NW. In this study, the amount of Pd deposited on Ag NWs is varied and the 3D elemental distribution of Pd is characterized using atom probe tomography (APT). The results indicate that chemical stability against oxidation can be achieved when the surface layer contains a very small amount of Pd (approximate to 5 at%), thereby maintaining the good electrical and mechanical properties of the pristine Ag NW electrode. This study demonstrates the suitability of Pd-treated Ag NWs as electrodes for electro-chemiluminescence involving corrosive oxidation reactions.

The relationships between tensile properties and precipitates of a high-strength low-alloy steel depending on the isothermal conditions were investigated. While the isothermally treated steel at 300–500 °C for 1 and 24 h had no significant difference, the steel treated at 500 for 336 h, denoted as 500–336 h, not only showed a decrease in tensile stress but also exhibited a highly increased elongation. Transmission electron microscopy and atom probe tomography were utilized to evaluate the precipitates distribution. The results showed that, in the case of 500–336 h sample, the fraction of precipitates with a radius over 10 nm is the highest and that of a few nano-sized precipitates is the lowest among all samples. It can be explained that the coarsening of originally nano-sized precipitates, occurred by diffusion of dissolved carbon in 500–336 h, mainly affects the tensile behavior.

In GaN microrods, phase separation of the AlGaN electron-blocking layer is an enormous obstacle for achieving high-efficiency light-emitting diodes, as this phenomenon negatively affects the device efficiency by inducing unwanted band-energy modulations. Here, we found that the AlGaN electron-blocking layer on each m-plane of the GaN microrod appears to be phase separated, and each electron-blocking layer has a different thickness and length. Our careful analysis based on atom probe tomography reveals that the Al distribution in AlGaN is not uniform and that Al-rich and Al-deficient regions are clearly present. In addition, the longer surface diffusion length of Ga adatoms, as compared to Al adatoms, and the different initial strain state of each m-plane in the GaN rods are deeply associated with the different growth rates and inhomogeneous Al composition of AIGaN, resulting in phase separation of the AIGaN electron blocking layer. These atomic-scale observations in the structural and chemical composition of AIGaN grown on GaN microrods could provide expanded opportunities for building a wide range of high-quality A1GaN electron-blocking layers.

Radio-frequency plasma enhanced CVD (RF-PECVD) carbon films were grown directly on 4-inch 4H-SiC substrates as a capping layer for MOSFET device applications. An approximately 50-nm-thick CVD carbon capping layer was found to reduce the surface roughness, as determined by atomic force microscopy (AFM). The secondary ion mass spectroscopy (SIMS) depth profile results revealed that carbon capping layer can suppress the dopant out-diffusion on the implanted surface after annealing even at high temperature (1700 °C) for 30 min. The calculated subthreshold swing (S) values of devices with CVD carbon capping layer and photo-resist process (base) measured at room temperature were 460 ± 50 (mV/dec) and 770 ± 70 (mV/dec), respectively. The lower value of 'S' for the device with carbon capping layer was related to the very low density of interface traps at the SiC-SiO2 interface. These results show the potential of CVD carbon as a capping layer for SiC MOSFET device applications.

In conventional light-emitting diodes the epitaxial strain and related piezoelectric polarization arising along the polar [0001] growth direction of the InGaN/GaN quantum wells (QWs) induce internal fields which adversely affect the radiative recombination of electron-hole pairs therein. Growing the quantum wells along a nonpolar orientation can, in principle, avoid this problem but seems to face with another problem associated with indium clustering. In this study, we present experimental evidence that supports the inhomogeneous distribution of indium in non-polar a-plane InGaN QWs by using dark-field inline electron holography as well as atom probe tomography measurements and discuss the possible origin by density functional theory calculation. A model non-polar a-plane QW structure with 10 nm-thick In0.1Ga0.9N double QWs was investigated and compared with the polar c-plane QWs with the same QW structure. Unlike the random distribution in the polar QWs, the indium atoms in the non-polar QW exhibit inhomogeneous distribution and show a tendency of periodic, clustering. We suggest the dipole interaction energy and the strain energy associated with indium substitution could have a substantial influence on the local composition of strained InGaN QWs and, particularly, triggers In clustering in the non-polar a-plane QW structure. Accompanying phase field modeling rationalizes that In clustering can also modify the in-plane polarization through piezoelectric effects, preventing the electrostatic potential from diverging along the in-plane polar direction. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A new method was introduced to distinguish the ferrite, bainite and martensite in transformation induced plasticity (TRIP) steel by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM).EBSD is a very powerful microstructure analysis technique at the length scales ranging from tens of nanometers to millimeters.How ever, iron BCC phases such as ferrite, bainite and martensite cannot be easily distinguished by EBSD due to their similar surface morphology and crystallographic structure.Among the various EBSD-based methodology, image quality (IQ) values, which present the perfection of a crystal lattice, was used to distinguish the iron BCC phases.IQ values are very useful tools to discern the iron BCC phases because of their different density of crystal defect and lattice distortion.However, there are still remaining problems that make the separation of bainite and martensite difficult.For instance, these phases have very similar IQ values in many cases, especially in deformed region; therefore, even though the IQ value was used, it has been difficult to distinguish the bainite and martensite.For more precise separation of bainite and martensite, IQ threshold values were determined by a correlative TEM analysis.By determining the threshold values, iron BCC phases were successfully separated.

Formamidinium (FA, CH(NH2)(2)) lead bromide perovskite (FAPbBr(3)) nanoparticles (NPs) are promising emitters due to their high stability and ability to emit pure green color in both film and solution states. Even though various types of metal halide NP emitters in solution have shown high photoluminescence quantum efficiencies (PLQEs), electroluminescence efficiencies of the light-emitting diodes (LEDs) using the NP films are still much poorer, possibly due to the insulating ligands which can impede the charge injection and transport in films. Therefore, the organic ligand of NPs should be designed to facilitate charge injection and transport in LEDs. Here, we synthesize ligand-engineered colloidal FAPbBr(3) NPs at RT and demonstrate high efficiency perovskite NP LEDs based on the FAPbBr(3) NPs. Control of ligand length reduces trap-assisted recombination of carriers at the surface traps, and thus maximizes the PLQE of FAPbBr(3) NPs. Ligand engineering can also improve the charge injection and transport capability in FAPbBr(3) NP films. With this ligand engineering method, we achieve maximum current efficiency of 9.16 cd/A in LEDs based on FAPbBr(3) NPs, which is the highest efficiency in FAPbBr(3) NP-LEDs to date. The ligand engineering method reported here can be a simple way to improve the luminescence efficiency of optoelectronic devices based on perovskite NP LEDs.

We investigated, for the first time, the conditions where a thermoplastic conductive composite can exhibit completely reversible stretchability at high elongational strains (ε = 1.8). We studied a composite of Au nanosheets and a polystyrene-block-polybutadiene-block-polystyrene block copolymer as an example. The composite had an outstandingly low sheet resistance (0.45 Ω/sq). We found that when a thin thermoplastic composite film is placed on a relatively thicker chemically cross-linked elastomer film, it can follow the reversible elastic behavior of the bottom elastomer. Such elasticity comes from the restoration of the block copolymer microstructure. The strong adhesion of the thermoplastic polymer to the metallic fillers is advantageous in the fabrication of mechanically robust, highly conductive, stretchable electrodes. The chemical stability of the Au composite was used to fabricate high luminescence, stretchable electrochemiluminescence displays with a conventional top-bottom electrode setup and with a horizontal electrode setup.

The core of mobile product is its multifunction sensor, a sensor for developing a low-cost but highly integrated as to implement a high performance as a requirement. This multi-functional composite sensor development process is made of a number of steps, and requires analysis of the issue or other defects in the process of the sensor. In the humidity sensor, we use the TEM and APT equipment to detect the distribution of elements between electrodes and the silicon oxide of the interface region in the sensor's membrane as an atomic unit. However, it is difficult to use APT analysis with the same TEM analysis sample because the TEM electron beam destroys the APT tip sample. In this study, we study conditions that can be analyzed in the same sample according to sample preparation conditions. The APT analysis region has a maximum sample diameter of 100 nm and a length of 300 nm. The sample is prepared by fixing a sample to be analyzed on a tungsten tip with a probe shape using FIB. The prepared specimens were coated with 3 nm of Ni metal to prevent sample destruction during TEM analysis. As a result, sample destruction was prevented. Finally, we develop TEM and APT simultaneous analysis techniques to overcome this problem and discuss the results.