Nano-sized Defects Research Articles

Review and Prospect of NiFe2O4-Based Materials for Li-Ion Battery

NiFe2O4 with high theoretical capacity, natural abundance as well as low cost exhibits tremendous potential as the electrode for lithium ion battery. Nevertheless, the great volume change upon the charge-discharge cycling gives rise to pulverization of NiFe2O4 electrode. The electron transport pathways are broken down, and ultimately, the cycling stability and reversible capacity fade rapidly, which restricts its commercial applications. Consequently, it is necessary to consider nano-size effect, interface property, defects and hybridization to satisfy the requirement of practical application. In this review, we comprehensively overview and analyze the latest progress in NiFe2O4-based anode, covering the representative synthesis method and advanced structure to realize improved Li+ storage performance. Furthermore, we objectively evaluate the Li+ storage performance of NiFe2O4-based anode materials and dissect the existing problems. Finally, an outlook for the development of advanced NiFe2O4-based anode materials is provided.

Structure Defects Formed upon the Hydrogenation of YBa2Cu3Oy Single Crystals

The fine structure of YBa2Cu3Oy single crystals with a different oxygen content subjected to a low-temperature hydrogenation have been investigated by transmission electron microscopy. It has been shown that as a result of the action of hydrogen at T = 150°С, a partial reduction of copper occurs, accompanied by the precipitation of Cu crystallites of ~100 nm in size and the formation of various structural defects. The geometric configuration of the precipitated crystallites has been considered. The results obtained show that hydrogenation is a method that makes it possible to control the structure by introducing nanosized inclusions and defects, which can be pinning centers of the magnetic vortices.

Influence of radiation damage on the structure and chemical durability of titanites

Previous studies on chemical durability of radioactive waste forms mainly focused on samples containing no radionuclides. We performed a hydrothermal experiment with several variably self-irradiated natural titanites and the leaching results indicate that radiation damage has some influence over chemical durability through its ability to change the microstructures of materials, including cracks, holes, interconnected amorphous clusters, and nano-sized defects. However, chemical durability is not influenced if the variation in local microstructures induced by radiation damage is insignificant.

Nano-size defect layers in arsenic-implanted and annealed HgCdTe epitaxial films studied with transmission electron microscopy

Optical reflectance and bright-field and high-resolution transmission electron microscopy studies of radiation damage induced by implantation of arsenic ions with 190 keV and 350 keV energy and 1014 cm–2 fluence in molecular-beam epitaxy-grown Hg0.7Cd0.3Te films were performed. A similarity in defect pattern formed by arsenic implantation in Hg1−xCdxTe with x ≈ 0.2 and x ≈ 0.3 straight after the implantation was observed with formation of three nano-size defect layers containing dislocation loops of vacancy- and interstitial-types, single dislocations and lattice deformations. After post-implantation arsenic activation annealing, most of these defects in our Hg0.7Cd0.3Te films, in contrast to Hg0.8Cd0.2Te films, disappeared. This effect is explained by the reduced influence of the electric field of the graded-gap surface layer on the diffusion of charged point defects under annealing.

Low-Temperature Bonding of Cu Through Self-Propagating Reaction Under Various Temperatures and Pressures

Abstract Low temperature soldering has been realized to create a strong metallurgical interconnection between Cu using the self-propagating exothermic reaction by Al–Ni NanoFoil. This technique presents a great potential for electronics integration with a significantly reduced processing temperature (at least 150 °C lower than traditional techniques) and minimal thermal effects to the components. In this study, finite element analysis was performed to predict the temperature profiles across bonding interfaces, which were subsequently correlated with the formation and quality of the bonded structures. It has been revealed that, for nonequilibrium nanosized phases and defects, their formation and distribution were primarily attributed to the solid–liquid interdiffusion and rapid solidification, under the highly transient regime due to a drastic heating/cooling (105–107 °C/s). The preheating and pressure applied to the bonding structure were clearly beneficial to improve the quality of bonding. This was achieved by the thinned solder thickness and the correspondingly improved temperature profiles that enable a sufficient wetting, filling, and interfacial reactions. Through the comparative analysis of the numerical predictions and the experimental results, the solder layers must completely melt across their thickness and have a total heat over 30 K ms on the Cu to ensure robust interconnections with a shear strength of approximately 37 ± 3 MPa and dense continuous bonding interfaces.

Microwave Response of Nanostructured High-Tc Superconductor Thin Films

A model for the microwave response of a nanostructured high-Tc superconductor (HTS) film, with implanted nanoparticles and nanorods of a dielectric material or point-like and columnar irradiation defects with a nano-sized cross-section is developed. In this case, the microwave surface resistance Rs(T,H,ω) is calculated both for the Meissner and mixed states of a superconductor film in an applied dc magnetic field. The obtained results indicate that the implantation of dielectric nanoparticles or point-like radiation defects can significantly improve superconductor characteristics at microwave frequencies. Namely, these nano-sized structural defects can decrease the surface resistance in the Meissner state and eliminate the oscillations of Abrikosov vortices and the related microwave energy losses, thus decreasing the contribution of Abrikosov vortices to the Rs value in the mixed state of a HTS film.

Enhanced flux pinning isotropy by tuned nanosized defect network in superconducting YBa2Cu3O6+x films

Striving to improve the critical current density Jc of superconducting YBa2Cu3O6+x (YBCO) thin films via enhanced vortex pinning, the interplay between film growth mechanisms and the formation of nanosized defects, both natural and artificial, is systematically studied in undoped and BaZrO3 (BZO)-doped YBCO thin films. The films were grown via pulsed laser deposition (PLD), varying the crystal grain size of the targets in addition to the dopant content. The microstructure of the PLD target has been observed to have a great impact on that of the deposited thin films, including the formation of vortex pinning centers, which has direct implications on the superconducting performance, especially on the isotropy of flux pinning properties. Based on experimentally measured angular dependencies of Jc, coupled with a molecular dynamics (MD) simulation of flux pinning in the YBCO films, we present a quantitative model of how the splay and fragmentation of BZO nanorods artifically introduced into the YBCO film matrix explain the majority of the observed critical current anisotropy.

Ion Irradiation Enhanced Helium Atoms Re-Solution and the Related Hardening in Hastelloy N Alloy

Transmission electron microscopy (TEM) and nanoindentation were performed in Hastelloy N alloy with three kinds of irradiation mode: single He ions, He + Xe (3 dpa) ions and He + Xe (10 dpa) ions. TEM results showed the presence of nano-sized irradiation-damage defects, such as helium bubbles, xenon bubbles, dislocation loops and precipitates. It was found that the helium bubble can grow up via absorbing vacancies, and the helium bubble shrinkage will be also occurred due to the helium atoms re-solution. In the case of He + Xe (3 dpa) ions irradiation, the helium bubble growth via absorbing vacancies induced by subsequent Xe ion irradiation was more noticeable. As for the sample irradiated by He + Xe (10 dpa) ions, the ion irradiation enhanced helium atoms re-solution played an important role. Moreover, the helium atoms were more easily dissolved from small helium bubbles and the mechanisms behind them have also been shed light on. In addition, the dispersed barrier hardening and strengthening superposition models were used to predict the nanohardness increments produced by the different irradiation defects. The nanohardness increments measured by nanoindentation for irradiated samples were basically consistent with the calculated nanohardness increments. Both the ballistic recoil re-solution and the damage assisted re-solution make it easier for helium atoms to dissolve from small helium bubbles.

Scaling laws and stability of nano-sized defect clusters in niobium via atomistic simulations and statistical analysis

The predictions of scaling laws for the structure and properties of defect clusters are generally limited to small defect clusters in their ground-state configurations. We investigated the size and geometrical configuration dependence of nano-sized defect clusters in niobium (Nb) using molecular dynamics. We studied the structure and stability of large clusters of size up to fifty defects for vacancies and one hundred defects for interstitials, as well as the role of helium and metastable configurations on the stability of these clusters. We compared three different interatomic potentials in order to determine the relative stability of these clusters as a function of their size and geometrical configurations. Additionally, we conducted a statistical analysis to predict the formation and binding energies of interstitial clusters as a function of both their size and configuration. We find that the size dependence of vacancy and interstitial clusters can be approximated by functional forms that account for bulk and surface effects as well as some considerations of elastic interactions. We also find that helium and metastable configurations can make vacancy and interstitial clusters thermally stable depending on the configuration. Our parameterized functional forms for the formation and binding energies are valid for a very broad range of defect sizes and configurations making it possible to be used directly in a coarse-grained modeling strategy such as Monte Carlo, cluster dynamics or dislocation dynamics which look at defect accumulation and evolution in microstructures.

Chemical Enhancement of Irreversible Electroporation: A Review and Future Suggestions.

Irreversible electroporation has raised great interest in the past decade as a means of destroying cancers in a way that does not involve heat. Irreversible electroporation is a novel ablation technology that uses short high-voltage electrical pulses to enhance the permeability of tumor cell membranes and generate irreversible nano-sized structural defects or pores, thus leading to cell death. Irreversible electroporation has many advantages over thermal therapies due to its nonthermal mechanism: (1) reduced risk of injury to surrounding organs and (2) no “heat-sink” effect due to nearby blood vessels. However, so far, it has been difficult for irreversible electroporation to completely ablate large tumors (eg, >3 cm in diameter). In order to overcome this problem, many preclinical and clinical studies have been performed to improve the efficacy of IRE in the treatment of large size of tumors through a chemical perspective. Due to the distribution of electric field, irreversible electroporation region, reversible electroporation region, and intact region can be found in the treatment of irreversible electroporation. Thus, 2 types of chemical enhancements of irreversible electroporation were discussed in the article, such as the reversible electroporation region enhanced and the irreversible electroporation region enhanced. Specifically, the state-of-the-art results regarding the following approaches that have the potential to be used in the enhancement of irreversible electroporation were systematically reviewed in the article, including (1) combination with cytotoxic drugs, (2) calcium electroporation, (3) modification of cell membrane, and (4) modification of the tumor cell microenvironment. In the end, we concluded with 4 issues that should be addressed in the future for improving irreversible electroporation further in a chemical way.

Leakage evolution and atomic-scale changes in Pd-based membranes induced by long-term hydrogen permeation

The long-term operation of a ceramic-supported 5 μm-thick Pd membrane at 450 °C and 27 bar with a feed representing steam-methane-reforming conditions has been monitored over a period of 100 days. Subsequently, a thorough characterisation of the exposed membrane has been performed to investigate leakage behavior and microstructural changes to the membrane occurring during the long-term membrane operation. Initially, a H2 permeance of 2.8·10−4 mol m−2 s−1 Pa−0.5 and a H2 permeate purity of 99.8% have been obtained. During continuous operation over 100 days, however, a slow but gradual decrease in H2 purity has been observed at a close-to-constant H2 permeance. Post-process leakage behavior has indicated that the increase in leakage is mainly caused by an increase in the Knudsen flow contribution, reflecting an increase in either the amount or size of nano-sized defects. A rising water test shows that these nano-sized defects are almost evenly distributed over the membrane length. Observation of the membrane cross-section revealed the formation of cavities that grew to sizes up to tens of nanometers, as a result of molecular recombination of hydrogen at low-energy sites such as dislocation walls and high-angle grain boundaries. The spherical shapes of the bubbles point to these being energetically favorable, which may be consistent with comparably high surface tensions. Therefore, the cavities observed are believed to be filled with hydrogen and stabilized by an internal pressure, that effectively counteracts the strong effect of surface energy at these small scales. The cavities may represent the origin of pinhole formation, and the atomic mechanisms behind the observed behavior are discussed and directions for enhancing the microstructural stability of Pd-based membranes are pointed out.

Controlled defects to link wetting properties to surface heterogeneity.

Small-scale heterogeneities have long been understood to give rise to contact angle hysteresis. More recently, the question of how they influence contact line dynamics has generated interest. Models that express the hysteresis or dynamics in terms of defect properties exist but have yet to be conclusively tested by experiment. Here we produce heterogeneous surfaces and thoroughly characterize individual defects. Precise dynamical measurements allow us to conclude that there is no evidence of a thermally activated dynamics due to their presence, but that the hysteresis scales with their concentration and the square of their height, as predicted by some simple models.

New model of the pinning potential barrier in layered HTc superconductors

New model of the pinning potential barrier in multilayered HTc superconductors is presented, based on geometrical approach to the capturing interaction of pancake-type vortices with nano-sized defects. Using the above model the transport current flow phenomena in these materials, especially the current–voltage characteristics and critical current density, have been considered. Details of theoretical analysis are given, including the derivation of basic mathematical equations describing the potential barrier as a function of transport current intensity and the initial position of captured pancake vortex. Computer simulation has been performed of the influence of transport current amplitude on the potential barrier height for various sizes of pinning centers and initial pancake vortex position as well as the influence of fast neutrons irradiation creating nano-sized defects on critical current of HTc layered superconductor.

Analysis of electric current flow through the HTc multilayered superconductors

Issue of the flow of the transport current through multilayered high-temperature superconductors is considered, depending on the direction of the electric current towards the surface of the superconducting CuO2 layers. For configuration of the current flow inside of the layers and for perpendicular magnetic field, it will be considered the current limitations connected with interaction of pancake type vortices with nano-sized defects, created among other during fast neutrons irradiation. So it makes this issue associated with work of nuclear energy devices, like tokamak ITER, LHC and actually developed accelerator Nuclotron-NICA, as well as cryocables. Phenomenological analysis of the pinning potential barrier formation will be in the paper given, which determines critical current flow inside the plane. Comparison of theoretical model with experimental data will be presented too as well as influence of fast neutrons irradiation dose on critical current calculated. For current direction perpendicular to superconducting planes the current-voltage characteristics are calculated basing on model assuming formation of long intrinsic Josephson's junctions in layered HTc superconductors.

Resistive transition and flux flow mechanism in CoFe2O4 nanoparticles added Cu0.5Tl0.5Ba2Ca2Cu3O10−δ superconductor

(CoFe2O4)x/Cu0.5Tl0.5Ba2Ca2Cu3O10−δ {(CoFe2O4)x/CuTl-1223}; (0 ≤ x ≤ 2) nanoparticles-superconductor composites were synthesized by solid–state reaction technique and dissipative mechanism was investigated by infield measurements and analysis. Activation energy {Uo(H)} was calculated from Arrhenius plots of infield resistivity measurements. The infield resistive properties of superconductors depend upon the fluxoid motion, which causes resistive transition broadening by shifting Tc (0) towards lower temperature values. The enhancement of transition broadening is attributed to spread of upper critical field in vortex state and dissipation process with applied magnetic field. Addition of magnetic CoFe2O4 nanoparticles reduces the fluxoid motion by introducing nano-sized defects in the host CuTl-1223 superconducting matrix, which act as effective flux pinning centers. An overall increase in the activation energy Uo(H) has been observed with increasing contents of magnetic CoFe2O4 nanoparticles, which elucidate the enhanced flux pinning with increasing CoFe2O4 magnetic nanoparticles content up to x = 1.5 wt. % in CuTl-1223 superconducting matrix.

Dislocation depinning from nano-sized irradiation defects in a bcc iron model

At the atomic level, irradiation hardening of a body-centered-cubic (bcc) crystal of iron is investigated through the study of a dislocation interaction with nano-sized obstacles of various types, i.e. nano-voids, dislocation loops with 〈100〉 and 1/2〈111〉 Burgers vectors, and C15 clusters. The dislocation pinning is common to every type of cluster excepted for loops with 1/2〈111〉 Burgers vector, the mobility of which allows them to glide along with dislocation, thence yielding a minor contribution to hardening. At bypassing of anchoring clusters, the dislocation is found to yield a pair of jogs throughout a process of local climb due to the absorption of vacancies or of self-interstitial atoms that form the clusters. In order to rationalize our simulation results, we have employed an analytical theory proposed by Bacon and Scattergood (1982) which is extended phenomenologically to treat all anchoring defects, including C15 clusters and 〈100〉 loops. For small clusters, below 17 elementary defects, the simulation results deviate from the analytical predictions, and the different types of cluster correspond to different pinning strengths amongst those of C15 clusters appear to be the largest, emphasizing a possible important contribution to irradiation hardening in iron based alloys.

Optimizing Flux Pinning of <inline-formula> <tex-math notation="TeX">$\hbox{YBa}_{2}\hbox{Cu}_{3}\hbox{\rm O}_{7\hbox{-}{\delta}} $</tex-math></inline-formula> (YBCO) Thin Films With Unique Large Nanoparticle Size and High Concentration of <inline-formula> <tex-math notation="TeX">$\hbox{\rm Y}_{2}\hbox{BaCuO}_{5}$</tex-math></inline-formula> (Y211) Additions

Addition of second-phase nanosize defects to YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) superconductor thin films is known to enhance flux pinning and increase current densities (Jc). The addition of Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> BaCuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> (Y211) was previously studied in (Y211/ YBCO)N multilayer structures and in Y211 + YBCO films deposited from pie-shaped targets. This research systematically studies the effect of Y211 addition in thin films deposited by pulsed laser deposition from YBCO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Y211 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (x = 0-15 vol.%) single targets, at temperatures of 785°C-840°C. Interestingly, the resulting size of Y211 particles is 20-40 nm, in contrast to 10-15 nm in previous studies of Y211 and 5-10 nm for other second-phase defect additions, and the number density is reduced. A slight increase of J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (H, T) was achieved, compared with previous optimization studies. Results and comparisons of flux pinning, intrinsic stresses imaged by TEM, current densities, critical temperatures, and microstructures will be presented. The overall low intrinsic stress on YBCO from Y211 lattice mismatch is smaller than previously studied second-phase defect additions known, which is hypothesized to be the driving force in achieving the unusually large second-phase nanoparticle size and volume fraction thus far in YBCO thin films.

Transport, resealing, and re-poration dynamics of two-pulse electroporation-mediated molecular delivery

Electroporation is of interest for many drug-delivery and gene-therapy applications. Prior studies have shown that a two-pulse-electroporation protocol consisting of a short-duration, high-voltage first pulse followed by a longer, low-voltage second pulse can increase delivery efficiency and preserve viability. In this work the effects of the field strength of the first and second pulses and the inter-pulse delay time on the delivery of two different-sized Fluorescein–Dextran (FD) conjugates are investigated. A series of two-pulse-electroporation experiments were performed on 3T3-mouse fibroblast cells, with an alternating-current first pulse to permeabilize the cell, followed by a direct-current second pulse. The protocols were rationally designed to best separate the mechanisms of permeabilization and electrophoretic transport. The results showed that the delivery of FD varied strongly with the strength of the first pulse and the size of the target molecule. The delivered FD concentration also decreased linearly with the logarithm of the inter-pulse delay. The data indicate that membrane resealing after electropermeabilization occurs rapidly, but that a non-negligible fraction of the pores can be reopened by the second pulse for delay times on the order of hundreds of seconds. The role of the second pulse is hypothesized to be more than just electrophoresis, with a minimum threshold field strength required to reopen nano-sized pores or defects remaining from the first pulse. These results suggest that membrane electroporation, sealing, and re-poration is a complex process that has both short-term and long-term components, which may in part explain the wide variation in membrane-resealing times reported in the literature.

Investigation on the flux pinning force and flux pinning mechanism in Ba1-xKxFe2As2 single crystal with Tc = 38.5 K

The discovery of superconductivity in iron-based superconductors by Professor Hosono in Japan in 2008 has triggered off an enormous group of researches the world wide. The iron-based superconductors are regarded as another kind of high-Tc superconductors, which possess lots of merits, such as very high upper critical field (Hc2), high critical current density (Jc), and small crystal anisotropy (), are promising for high field applications. Ba1-xKxFe2As2, as a typical FeAs-122 superconductor, is focused on by both theoretical physicists and material scientists since its discovery. In this paper, we first successfully fabricate Ba1-xKxFe2As2 single crystal. It has an onset transition temperature up to 38.5 K, while its zero resistivity temperature reaches 37.2 K. Both the R-T and M-T data of it show very sharp superconducting transition, and its critical current density at 5 K and self field is over 106 Acm-2 and almost field independent. The flux pinning force and the relative pinning mechanisms in Ba1-xKxFe2As2 are discussed by analyzing the data obtained from the measurements about the R-T and M-H under different conditions. Results indicate that the Ba1- xKxFe2As2 superconductors have very strong intrinsic vortex pinning force, and the vortex potentials (U0) under 9 T field are 5800 K and 8100 K for the H//c and H//ab, respectively. Furthermore, the vortex pinning mechanism is also investigated by analyzing the relationship Jc-B. According to the present results, the flux pinning mechanism should be (l) pinning because of the change of mean free path for electrons induced by nano-size crystallographic defects in Ba1-xKxFe2As2.

In Situ AFM and Electrochemical Study of a Waterborne Acrylic Composite Coating with CeO2 Nanoparticles for Corrosion Protection of Carbon Steel

The corrosion protection of a waterborne acrylic composite coating with 1 wt% ceria nanoparticles (CeNP) coated on carbon steel in 3 wt% NaCl solution was investigated by ex-situ and in situ as well as electrochemical atomic force microscopy (AFM) observations, combined with open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) measurements. The synthesized CeNP were stabilized by acetic acid. The transmission electron microscopy characterization showed fine nano-size of as-synthesized CeNP, the ex-situ AFM imaging revealed uniform dispersion of the CeNP in the composite coating and greatly reduced nano-sized pinholes in the coating. The in situ and electrochemical (EC) AFM investigations indicate release of some CeNP and aggregates from the coating surface and then precipitation of some particles and cerium-compounds during the exposure. The OCP and EIS results demonstrated that the addition of 1 wt% CeNP leads to a significantly improved long term barrier type corrosion protection of the waterborne acrylic composite coating for carbon steel in 3 wt% NaCl solution. The beneficial effect of the CeNP is attributed to the blocking of nano-sized defects and inhibition by the cerium compounds originated from the acetic acid stabilized CeNP.