Tens Of Nanometers Research Articles

Effect of metastable precipitate phase transformation on reheat cracking in SS347H welding

Reheat cracking occurred in the welded heat affected zone (HAZ) of the SS347H tube during high temperature applications of approximately 600 °C. The reheat cracks occur when the inside of the grain is strengthened, causing grain boundary embrittlement. In this study, the intra-granular strengthening phase transformation of the HAZ causing the reheat crack was analyzed using TEM.The hardness of SS 347H HAZ with cracks is measured to be 221HV on average, which is about 25HV higher than 196HV of HAZ without cracks. This intra-granular strengthening is due to the formation of intra-granular precipitate phases. The precipitated phase is ultimately NbC, but undergoes an intermediate phase transformation due to diffusion of Nb and C components. The phase transformation consists of the following steps: “(i) SA (solution annealing), (ii) Zone A, (iii) Zone B, and (iv) NbC precipitation.”This is a process in which Nb/C components diffuse and segregate at the reheating temperature from a solid solution state of Nb/C components, and NbC with a size of several tens of nanometers is precipitated. As metastable phases, Zones A and B exist in the intermediate process of precipitation, which is the strengthening stage where intra-granular hardness is maximized. Zone A and B in the pre-precipitation stage means that a new lattice plane is formed as the segregation of component elements forms coherency with the matrix. The relationship between the base and new lattice planes is confirmed by Double Diffraction in the TEM diffraction diagram.The root cause of reheat cracking in SS 347H HAZ is believed to be the intra-granular strengthening phase caused by zone A and zone B as a metastable phase transformation in an intermediate stage before NbC precipitation. In order to suppress reheat cracking, it is desirable to precipitate stable NbC from the metastable phases of Zones A and Zone B through stabilization heat treatment.

Study on the properties of deuterium ions in a composite cathode vacuum arc discharge

A vacuum arc discharge with a metal-deuteride cathode can generate a supersonic deuterium ion jet, which finds important applications in vacuum arc ion sources. In this study, a 1D3V spherical particle-in-cell direct simulation Monte Carlo cathode spot model with a titanium-deuteride cathode is developed to investigate the ionization and acceleration of deuterium ions from vacuum breakdown to the steady-arc stage. The effects of cathode deuteration concentration on the deuterium ion fraction and kinetic energy are also analyzed. The results show that the released deuterium atoms start to be ionized at around tens of nanometers from the cathode and then become fully ionized at about 0.4μm as the cathode potential drop gradually builds up. The proportion of deuterium ions in the plasma is slightly higher than the proportion of deuterium atoms in the cathode material. Velocity separation of deuterium and titanium ions occurs due to the acceleration of the electric field during the vacuum breakdown stage; however, the predominant ion–ion Coulomb collisions wipe out this separation in the steady-arc stage. Shifting the deuterium atom concentration in the cathode under a constant arc burning voltage produces an approximately equal current density, and increases the velocities of all ion species. A higher ion kinetic energy is gained by reducing the ohmic heating dissipation, facilitated by the lower plasma resistivity under the increased deuterium ion density.

Formation of low-dimensional nanopit structures on atomically flat surfaces of diamond (111) by nickel nanoparticles

Diamond nanoprocessing technologies are essential for the development of diamond-based devices. However, the existing etching processes damage the diamond crystal, adversely affecting the characteristics of the corresponding device. Herein, we focused on the Ni–C solid-solution reaction as a nondamaging fabrication method. Ni films (10, 3, and 1 nm) were deposited on atomically flat surfaces (AFSs) of diamond (111) and annealed under H2 gas flow. The Ni film aggregated into particles, and as the particle size decreased, Ni particles moved around, etching the diamond surface. Interestingly, when the diameter of the Ni nanoparticles was less than a few tens of nanometers, they dug one-dimensional (1D) nanopits with a linear trench shape on diamond AFS. We discuss the mechanism for the formation of these 1D nanopits in detail from the perspective of the etching-morphology dependence on the annealing time, Ni thickness, and gas atmosphere. The results of this study will improve our understanding of the Ni–C solid-solution reaction at the nanoscale and promote the development of damage-free nanofabrication techniques for diamond-based device applications.

Simultaneous improvement of strength and ductility in a P-doped CrCoNi medium-entropy alloy

A newly developed P-doped CrCoNi medium-entropy alloy (MEA) provides both higher yield strength and larger uniform elongation than the conventional CrCoNi MEA, even superior tensile ductility to the other-element-doped CrCoNi MEAs at similar yield strength levels. P segregation at grain boundaries (GBs) and dissolution inside grain interiors, together with the related lower stacking fault energy (SFE) are found in the P-doped CrCoNi MEA. Higher hetero-deformation-induced (HDI) hardening rate is observed in the P-doped CrCoNi MEA due to the grain-to-grain plastic deformation and the dynamic structural refinement by high-density stacking fault-walls (SFWs). The enhanced yield strength in the P-doped CoCrNi MEA can be attributed to the strong substitutional solid-solution strengthening by severer lattice distortion and the GB strengthening by phosphorus segregation at GBs. During the tensile deformation, the multiple SFW frames inundated with massive multi-orientational tiny planar stacking faults (SFs) between them, rather than deformation twins, are observed to induce dynamic structural refinement for forming parallelepiped domains in the P-doped CoCrNi MEA, due to the lower SFE and even lower atomically-local SFE. These nano-sized domains with domain boundary spacing at tens of nanometers can block dislocation movement for strengthening on one hand, and can accumulate defects in the interiors of domains for exceptionally high hardening rate on the other hand.

Research Progress and Development Trends of L Band Fiber Lasers

Fiber lasers have developed rapidly in recent years and play an important role in many fields. The L band refers to a wavelength range in fiber optic communications, usually between 1570 nanometers and 1625 nanometers. At present, research on L-band fiber lasers mainly focuses on improving their output power, enhancing spectral purity, and reducing costs. In this article, the author discusses the research progress and development trends based on the development of fiber lasers in the 1570 nm to 1650 nm band at home and abroad. Through investigation and research, it can be concluded that after 30 years of rapid development of single-frequency fiber lasers, the average power is hundreds of watts, the peak power is several kilowatts, the laser line width is 100 Hz, the intensity noise is close to the quantum noise limit, and the wavelength tuning range is tens of nanometers. Despite great progress, there are still some deficiencies in basic research and applied technology that need more development.

Results of round robin form measurements of optical aspheres and freeform surfaces

High-quality aspherical and freeform surfaces are in high demand, and the high-accuracy form measurement of such surfaces is a challenging task. To explore the current status of form measurement systems for complex surfaces such as aspheres and freeforms, interlaboratory comparison measurements are performed. This study presents the pseudonymized results obtained using three different surfaces (metal asphere, glass asphere, toroidal surface) in a total of six different round robins. These results were taken from a total of 13 different measurement instruments based on 9 different measurement principles and operated at 12 different laboratories. They were analyzed using a sophisticated procedure that was first developed in 2018 and then refined and tested on simulated data in 2022 to address the challenges of such a comparison at this level of accuracy. In the current study, we applied these refined methods to data acquired from tactile and optical point measurements as well as from optical areal measurements. As there are no absolutely measured and very well characterized reference standard aspherical and freeform surfaces available at the accuracy level of a few tens of nanometers root-mean-square, the approximated true forms of the surfaces were derived from the measurements and indicate the manufacturing accuracy of the surface forms. Then, the measurement’s differences to the approximated true forms were analyzed, which directly indicate the systematic measurement errors of the instruments. By also comparing the approximated true forms from the two different round robins for each surface, additional insights into the reliability and stability of these so-called virtual reference topographies were gained.

Surfactant-mediated gelation by 12-hydroxyoctadecanoic acid in a nonionic surfactant system

In this study, we present a hydrogel fabrication utilizing a water-insoluble, low-molecular-weight organogelator by the surfactant-mediated gelation (SMG). Specifically, we employed a nonionic surfactant (poly(oxyethylene) sorbitan monooleate, Tween 80) and an organogelator (12-hydroxyoctadecanoic acid, 12-HOA) to produce hydrogels. Gelation experiments conducted at varying concentrations of surfactant and gelator demonstrated successful hydrogel formation in the water/Tween 80/12-HOA system. Moreover, we observed a significant dependence of surfactant concentration on gelation ability. The sol-gel transition temperature was found to be influenced by both the gelator and surfactant concentrations. Optical and electron microscopy analyses revealed that the SMG hydrogels comprised an entangled network of fibers with micrometer-scale widths, formed as bundles of submicron-wide fibers, and further composed of fine fibers measuring several tens of nanometers in width. These fine fibers exhibited a left-handed helical structure. Small- and wide-angle X-ray scattering corroborated the presence of a lamellar structure within the fine fibers, displaying a triclinic subcell morphology. The coexistence of micelles with the fiber network was confirmed through small-angle neutron scattering and UV–vis spectroscopy. Furthermore, dynamic viscoelasticity tests demonstrated that the SMG hydrogels exhibited typical solid-like properties indicative of gel behavior.

Slow precipitate coarsening kinetics in extremely fine nanograined Ni-Cr alloys

Grain boundaries significantly influence the nucleation and growth of precipitates in supersaturated solid solutions. However, due to the inherent instability of grain boundaries in nanograined metals, the precipitation process usually occurs concurrently with grain growth during thermal annealing, making it difficult to reveal the grain size effect on the precipitate coarsening behavior. In this study, nanograined Ni-48 Cr (at.%) supersaturated alloys with grain sizes ranging from about 85 nm to 10 nm were fabricated by plastic deformation, in which the relaxed grain boundaries led to the extremely fine nanograined structure having good thermal stability. During the high-temperature annealing process, nanoscale Cr particles were precipitated from the nanograined matrix, forming a nanograined dual-phase structure. The growth kinetics of the Cr precipitates in the extremely fine nanograined structures are different from the larger grain size samples, showing a trend that the smaller the as-deformed grain size, the slower the precipitate coarsening rate. Detailed microstructural characterization and kinetic analysis indicate that the extremely fine nanograined structure may change the rate-limiting process for precipitate coarsening from lattice diffusion to grain boundary diffusion as grain size is refined to about a few tens nanometers, which leads to a slow coarsening rate. The nanograined dual-phase Ni-Cr alloy of the annealed 10 nm sample shows the highest strength among these samples as well as excellent thermal stability, which provides guidance for the design of high-performance alloys.

Variation of (001) surface structures of strontium titanate single crystals caused by flash event under direct/alternative current electric fields

Flash events, which are electric power spikes occurring under an electric field and temperature above the threshold, can significantly accelerate mass diffusion over short periods of time. This study investigated the surface structure of the (001) surface of strontium titanate single-crystal treated by flash events caused by direct current (DC) and alternating current (AC) electric fields from a viewpoint of surface-related mass diffusion. The surface structuring caused by flash events was significantly different among DC and AC electric fields. The DC-flash event destabilized surface steps, causing them to wander and form surface mounds with a height of several tens of nanometers. In addition, numerous two-dimensional (2D) nuclei with a size of several nanometers are formed on the terraces. In contrast, the AC-flash event stabilized surface steps without the formation of surface mounds, causing them nearly straight with uniform terrace width at approximately 500 nm. 2D nuclei with a size of a few 10 nm were formed at the step edges with round shapes. Both methods were confirmed as evidenced by the formation of two-dimensional nuclei on the surface after the flash events, to enhance surface-related mass diffusion.

Identification of chemical transformations in enamel apatite during the development of fissure caries at the nanoscale by means of synchrotron infrared nanospectroscopy: A pilot study

The spectral data sets obtained in our work using classical micro Fourier transform infrared spectroscopy (μFTIR) and modern broadband synchrotron infrared nanospectroscopy (SINS) methods, as well as their analysis and comparison with the known μFTIR spectroscopic results, provide new fundamental information on the mechanisms of pathological processes development in the carious fissure region of a human tooth at the level of enamel apatite crystallites (nano level). The infrared vibration signatures detected in our nanoscale study allowed us to establish gradient changes in chemical composition (phase transformations) occurring within the enamel roads at the level of apatite nanocrystals forming a prism, also to estimate changes in the crystallinity coefficient and the proportion of acid phosphates, as well as the depth of bacteria metabolism products (acid invasion). The results of the comparative study of this technique demonstrate that the combination of s-SNOM, IR spectroscopy and synchrotron broadband source in the SINS method provides excellent chemical sensitivity, sufficient for the providing of chemical identification of phase transformations with enhanced spatial resolution of ∼25 nm and the depth of useful signal output of several tens of nanometers. These advantages of SINS claim to be an advanced approach for investigations of objects of biological nature at a qualitatively new level.

Enhancing Transparency in Non-Cubic Calcium Phosphate Ceramics: Effect of Starting Powder, LiF Doping, and Spark Plasma Sintering Parameters

Our objective is to achieve a new good-quality and mechanically durable high-transparency material that, when activated by rare earth ions, can be used as laser sources, scintillators, or phosphors. The best functional transparent ceramics are formed from high-symmetry systems, mainly cubic. Considering hexagonal hydroxyapatite, which shows anisotropy, the particle size of the initial powder is extremely important and should be of the order of several tens of nanometers. In this work, transparent micro-crystalline ceramics of non-cubic Ca10(PO4)6(OH)2 calcium phosphate were fabricated via Spark Plasma Sintering (SPS) from two types of nanopowders i.e., commercially available (COM. HA) and laboratory-made (LAB. HA) via the hydrothermal (HT) protocol. Our study centered on examining how the quality of sintered bodies is affected by the following parameters: the addition of LiF sintering agent, the temperature during the SPS process, and the quality of the starting nanopowders. The phase purity, microstructure, and optical transmittance of the ceramics were investigated to determine suitable sintering conditions. The best optical ceramics were obtained from LAB. HA nanopowder with the addition of 0.25 wt.% of LiF sintered at 1000 °C and 1050 °C.

Thermal stability of refined Al6(Fe, Mn) phase formed in laser powder bed fusion process

The addition of Mn in Al–Fe alloys stabilizes the Al6Fe metastable phase (orthorhombic structure, oC28) owing to the partial occupation of Fe sublattice sites by Mn atoms (formation of Al6(Fe, Mn) phase), thereby achieving superior high-temperature strength of Al–Fe–Mn ternary alloys that are manufactured via laser powder bed fusion (L-PBF) process. This study aimed to fundamentally understand the thermal stability of the refined Al6(Fe, Mn) phase formed in the L-PBF fabricated Al–2.5%Fe–2%Mn alloy in terms of a thermodynamic approach and the kinetics of morphological changes in the Al6(Fe, Mn) phase at elevated temperatures ranging from 200 to 500 ℃. The L-PBF processed samples showed a high hardness of approximately 125 HV due to the formation of numerous dispersoids of the Al6(Fe, Mn) phase with sizes of several tens of nanometers in the α-Al matrix containing concentrated solute elements of Fe and Mn. The hardness and microstructure were almost unchanged even after exposure to a high temperature of 200 ℃ for an extended period of 1000 h. Upon exposure to 300 ℃, nucleation and growth of the Al6(Fe, Mn) phase occurred locally, particularly at grain boundaries in the α-Al matrix. Such a local growth contributed to a reduction in hardness upon thermal exposure. Simultaneously, numerous nanoscale precipitates were formed in the α-Al matrix, resulting in a suppressed reduction in hardness. Contrary to the result of the thermodynamic calculations, the θ-Al13Fe4 phase was scarcely found even after long-term exposure to 500 ℃. The θ-phase formation was accompanied by the dissolution of the refined Al6Fe metastable phase for strengthening, which significantly reduced the hardness during thermal exposure. The suppressed θ-phase formation could be associated with the thermodynamically stable Al6(Fe, Mn) phase developed during the L-PBF process, which predominantly contributed to the high microstructural stability of the L-PBF fabricated Al–Fe–Mn alloy at elevated temperatures.

Unlocking the performance evolution of GdBCO coated conductors irradiated by deuterium plasma

REBa2Cu3O7-δ (REBCO, RE: rare earth) coated conductors (CCs) can generate a powerful magnetic field and are optimal for sustaining the reaction in fusion devices. However, the REBCO CCs will inevitably be exposed to neutron radiation during device operation. Transmutation produces gas atoms such as hydrogen will affect their properties. In this paper, GdBCO CCs were irradiated by 20 eV deuterium plasma. It was found that the irradiation introduced smaller (2–4 nm) pinning sites that formed a mixed pinning landscape with rare earth oxides (tens of nanometres) in the pristine samples, leading to an improved vortex pinning. At an irradiation fluence of 5.0 × 1018 D cm−2, the J c values of the samples irradiated by deuterium can maintain the best enhancement of in-field performance at 4.2 K. Excess irradiation results in a decrease in J c, a broadening of the superconducting transition width, and an enhanced disorder in GdBCO. This study provides some valuable insights for potential changes in the properties of REBCO CCs irradiated in fusion devices.

Van der Waals Epitaxy of Weyl-Semimetal Td-WTe2.

Epitaxial growth of WTe2 offers significant advantages, including the production of high-quality films, possible long-range in-plane ordering, and precise control over layer thicknesses. However, the mean island size of WTe2 grown by molecular beam epitaxy (MBE) in the literature is only a few tens of nanometers, which is not suitable for the implementation of devices at large lateral scales. Here we report the growth of Td -WTe2 ultrathin films by MBE on monolayer (ML) graphene, reaching a mean flake size of ≃110 nm, which is, on overage, more than three times larger than previous results. WTe2 films thicker than 5 nm have been successfully synthesized and exhibit the expected Td phase atomic structure. We rationalize the epitaxial growth of Td-WTe2 and propose a simple model to estimate the mean flake size as a function of growth parameters that can be applied to other transition metal dichalcogenides (TMDCs). Based on nucleation theory and the Kolmogorov-Johnson-Meh-Avrami (KJMA) equation, our analytical model supports experimental data showing a critical coverage of 0.13 ML above which WTe2 nucleation becomes negligible. The quality of monolayer WTe2 films is demonstrated by electronic band structure analysis using angle-resolved photoemission spectroscopy (ARPES), which is in agreement with first-principles calculations performed on free-standing WTe2 and previous reports. We found electron pockets at the Fermi level, indicating a n-type doping of WTe2 with an electron density of n = 2.0 ± 0.5 × 1012 cm-2 for each electron pocket.

Molecular dynamics simulations of interfacial resistance of gases transport through MOF HKUST-1

The mass transfer resistances of CH4 and CO2 transport through MOF HKUST-1 were intensively studied by molecular simulations. The corrected diffusivities increase as thickness increases in finite HKUST-1, and converge to the maximum in infinite crystalline. The interfacial resistance plays an essential role in total one, and weakens as HKUST-1 thickness increases. Under the same conditions, CO2 molecules suffer from stronger transport resistance than CH4 counterparts due to enhanced energy barriers, larger molecular weight, stronger interactions and freedom degree loss. The transport resistances decrease with loadings, opposite to trend of gas–gas interactions. The collisions of CH4 and CO2 molecules at high loadings are inclined to specular reflection, and enhance molecular collision, resulting in stronger permeability. Compared to CH4, CO2 exhibits 40% higher interface resistance under identical loading conditions. Such similar quantitative relationship also appears on critical membrane thickness, both of which are on the order of several tens of nanometers.

The effect of viscosity on the self-similar growth of conic cusps on the surface of a conducting liquid in an electric field: Limiting cone angle

The dynamics of the formation of conic cusps on an initially smooth surface of a perfectly conducting liquid (liquid metal) in an external electric field is analytically studied. When the singularity is formed, the apex curvature radius of the accelerating protrusion, local electric field strength, and fluid velocity become infinite in a finite time. It has been demonstrated that two scales with different types of fluid behavior can be distinguished in this process. At the nanoscale (the curvature radius of the conic apex is tens of nanometers or less; the electric field strength at the apex is about 108 V/cm and higher), viscous effects play a decisive role, and a cone with the limiting opening angle of 33.1° is formed. On the macroscopic scale (the local field strength is less than 108 V/cm for liquid metals), the ideal fluid approximation is applicable, and a cone of the opening angle 98.6° (Taylor's angle) develops. In both cases, self-similar fluid flow regimes are realized, for which the spatial scale decreases with time following the power law (t0 – t)2/3, where t0 is the blowup time. In this process, the Weber number remains practically unchanged and, according to our estimates, approximately equal to 102; at the same time, the Reynolds number decreases as (t0 – t)1/3.

A plasmonic metasurface reveals differential motility of breast cancer cell lines at initial phase of adhesion

A plasmonic metasurface composed of a self-assembled monolayer of gold nanoparticles allows for fluorescence imaging with high spatial resolution, owing to the collective excitation of localized surface plasmon resonance. Taking advantage of fluorescence imaging confined to the nano-interface, we examined actin organization in breast cancer cell lines with different metastatic potentials during cell adhesion. Live-cell fluorescence imaging confined within tens of nanometers from the substrate shows a high actin density spanning < 1 μm from the cell edge. Live-cell imaging revealed that the breast cancer cell lines exhibited different actin patterns during the initial phase of cell adhesion (∼ 1 h). Non-tumorous MCF10A cells exhibited symmetric actin localization at the cell edge, whereas highly metastatic MDA-MB-231 cells showed asymmetric actin localization, demonstrating rapid polarization of MDA-MB-231 cells upon adhesion. The rapid actin organization observed by our plasmonic metasurface-based fluorescence imaging provides information on how quickly cancer cells sense the underlying substrate.

Impact of airborne iron oxide nanoparticles on Tillandsia usneoides as a model plant to assess pollution in heavy traffic areas

Due to the increasing evidence of widespread sub-micron pollutants in the atmosphere, the impact of airborne nanoparticles is a subject of great relevance. In particular, the smallest particles are considered the most active and dangerous, having a higher surface/volume ratio. Here we tested the effect of iron oxide (Fe3O4) nanoparticles (IONPs) with different mean diameter and size distribution on the model plant Tillandsia usneoides.Strands were placed in home-built closed boxes and exposed to levels of airborne IONPs reported for the roadside air, i.e. in the order of 107 - 108 items m−2. Plant growth and other morpho-physiological parameters were monitored for two weeks, showing that exposure to IONPs significantly reduced the length increment of the treated strands with respect to controls. A dose-dependence of this impairing effect was found only for particles with mean size of a few tens of nanometers. These were also proved to be the most toxic at the highest concentration tested. The IONP-induced hamper in growth was correlated with altered concentration of macro- and micronutrients in the plant, while no significant variation in photosynthetic activity was detected in treated samples. Microscopy investigation showed that IONPs could adhere to the plant surface and were preferentially located on the trichome wings.Our results report, for the first time, evidence of the negative effects of airborne IONP pollution on plant health, thus raising concerns about related environmental risks.Future research should be devoted to other plant species and pollutants to assess the impact of airborne pollution on plants and devise suitable attenuation practices.

Observations of specimen morphology effects on near-zone-axis convergent-beam electron diffraction patterns.

This work presents observations of symmetry breakages in the intensity distributions of near-zone-axis convergent-beam electron diffraction (CBED) patterns that can only be explained by the symmetry of the specimen and not the symmetry of the unit cell describing the atomic structure of the material. The specimen is an aluminium-copper-tin alloy containing voids many tens of nanometres in size within continuous single crystals of the aluminium host matrix. Several CBED patterns where the incident beam enters and exits parallel void facets without the incident beam being perpendicular to these facets are examined. The symmetries in their intensity distributions are explained by the specimen morphology alone using a geometric argument based on the multislice theory. This work shows that it is possible to deduce nanoscale morphological information about the specimen in the direction of the electron beam - the elusive third dimension in transmission electron microscopy - from the inspection of CBED patterns.

Thermal conductivity of nanocrystalline alumina films fabricated by aerosol deposition

Films fabricated by aerosol deposition (AD) are expected to be used as electrical insulating coatings. High thermal conductivity is required in addition to electrical insulation properties for electrical insulation substrate applications, but the thermal conductivity of AD films has not been reported. AD films are nanocrystalline films consisting of crystals several tens of nanometers in size, and it is unclear what effect the small particle size has on thermal conductivity. In this study, the thermal conductivity of an AD alumina film was measured by the light flash method as 15–31 W m−1 K−1 at room temperature and was large despite the particle size of several tens of nanometers. Analysis was performed using a model of grain size effects on thermal conductivity.