Designing order–disorder transformation in high-entropy ferritic steels

Order–disorder transformations hold an essential place in chemically complex high-entropy ferritic steels (HEFSs) due to their critical technological application. The chemical inhomogeneity arising from mixing of multi-principal elements of varying chemistry can drive property altering changes at the atomic scale, in particular short-range order. Using density-functional theory-based linear-response theory, we predict the effect of compositional tuning on the order–disorder transformation in ferritic steels—focusing on Cr–Ni–Al–Ti–Fe HEFSs. We show that Ti content in Cr–Ni–Al–Ti–Fe solid solutions can be tuned to modify short-range order that changes the order–disorder path from BCC-B2 (Ti atomic-fraction = 0) to BCC-B2-L21 (Ti atomic-fraction > 0) consistent with existing experiments. Our study suggests that tuning degree of SRO through compositional variation can be used as an effective means to optimize phase selection in technologically useful alloys. Graphic abstract

Tunable Planar Hall Effect in (Ga,Mn)(Bi,As) Epitaxial Layers

We have thoroughly investigated the planar Hall effect (PHE) in the epitaxial layers of the quaternary compound (Ga,Mn)(Bi,As). The addition of a small amount of heavy Bi atoms to the prototype dilute ferromagnetic semiconductor (Ga,Mn)As enhances significantly the spin–orbit coupling strength in its valence band, which essentially modifies certain magnetoelectric properties of the material. Our investigations demonstrate that an addition of just 1% Bi atomic fraction, substituting As atoms in the (Ga,Mn)As crystal lattice, causes an increase in the PHE magnitude by a factor of 2.5. Moreover, Bi incorporation into the layers strongly enhances their coercive fields and uniaxial magneto-crystalline anisotropy between the in-plane ⟨110⟩ crystallographic directions in the layers grown under a compressive misfit strain. The displayed two-state behaviour of the PHE resistivity at zero magnetic field, which may be tuned by the control of applied field orientation, could be useful for application in spintronic devices, such as nonvolatile memory elements.

Enhancing CO2 Conversion to CO over Plasma-Deposited Composites Based on Mixed Co and Fe Oxides

The hydrogenation of CO2 to produce CO and H2O, known as reverse-water-gas shift reaction (RWGS) is considered to be an important CO2 valorization pathway. This work is aimed at proposing the thin-film catalysts based on iron and cobalt oxides for this purpose. A series of Fe–Co nanocomposites were prepared by the plasma-enhanced chemical vapor deposition (PECVD) from organic cobalt and iron precursors on a wire-mesh support. The catalysts were characterized by SEM/EDX, XPS, XRD, and Raman spectroscopy and studied for hydrogenation of CO2 in a tubular reactor operating in the temperature range of 250–400 °C and atmospheric pressure. The Co-based catalyst, containing crystalline CoO phase, exhibited high activity toward CH4, while the Fe-based catalyst, containing crystalline Fe2O3/Fe3O4 phases, was less active and converted CO2 mainly into CO. Regarding the Fe–Co nanocomposites (incl. Fe2O3/Fe3O4 and CoO), even a small fraction of iron dramatically inhibited the production of methane. With increasing the atomic fraction of iron in the Fe–Co systems, the efficiency of the RWGS reaction at 400 °C increased up to 95% selectivity to CO and 30% conversion of CO2, which significantly exceeded the conversion for pure iron–based films (approx. 9%). The superior performance of the Fe–Co nanocomposites compared to “pure” Co and Fe–based films was proposed to be explained by assuming changes in the electronic structure of the catalyst resulting from the formation of p–n junctions between nanoparticles of cobalt and iron oxides.

Four-Period Vertically Stacked SiGe/Si Channel FinFET Fabrication and Its Electrical Characteristics

In this paper, to solve the epitaxial thickness limit and the high interface trap density of SiGe channel Fin field effect transistor (FinFET), a four-period vertically stacked SiGe/Si channel FinFET is presented. A high crystal quality of four-period stacked SiGe/Si multilayer epitaxial grown with the thickness of each SiGe layer less than 10 nm is realized on a Si substrate without any structural defect impact by optimizing its epitaxial grown process. Meanwhile, the Ge atomic fraction of the SiGe layers is very uniform and its SiGe/Si interfaces are sharp. Then, a vertical profile of the stacked SiGe/Si Fin is achieved with HBr/O2/He plasma by optimizing its bias voltage and O2 flow. After the four-period vertically stacked SiGe/Si Fin structure is introduced, its FinFET device is successfully fabricated under the same fabrication process as the conventional SiGe FinFET. And it attains better drive current Ion, subthreshold slope (SS) and Ion/Ioff ratio electrical performance compared with the conventional SiGe channel FinFET, whose Fin height of SiGe channel is almost equal to total thickness of SiGe in the four-period stacked SiGe/Si channel FinFET. This may be attributed to that the four-period stacked SiGe/Si Fin structure has larger effective channel width (Weff) and may maintain a better quality and surface interfacial performance during the whole fabrication process. Moreover, Si channel of the stacked SiGe/Si channel turning on first also may have contribution to its better electrical properties. This four-period vertically stacked SiGe/Si channel FinFET device has been demonstrated to be a practical candidate for the future technology nodes.

Design and characterization of novel zirconium-based amorphous alloys containing scandium for biomedical application

In this work, (Zr55Cu30Al10Ni5)100−xScx (x = 0, 0.5, 1.0, and 1.5) amorphous alloys were fabricated through steel die casting. The effects of scandium on the properties of zirconium-based amorphous alloys have been studied. The results show that the glass-forming ability of amorphous alloys increases at first and then decreases with the increase of Sc content. The highest glass-forming ability is obtained when the atomic fraction of Sc is 0.5%, which enables the production of 2-mm-thick amorphous alloy ingots. Meanwhile, the thermal stability and mechanical properties of the alloy are optimised with the atomic fraction of Sc of 1.0%. In addition, by adding an appropriate amount of Sc, the corrosion resistance of Zr–Cu–Al–Ni alloys is enhanced, particularly in the acid solution. The lowest average corrosion rate for samples in acid solution is obtained with the alloy containing atomic fraction of Sc of 1.0%. Therefore, results of this study indicate that the Zr-based amorphous alloy containing scandium has the potential for manufacturing fracture internal fixation or surgical devices.

Investigation of Gama Ray Shielding Properties of the (Al:Si) and (Al+Na):Si doped International Simple Glasses (ISG) using Phy-X/PSD and SRIM Software’s

In this investigation, the gamma photon shielding properties for the (Al:Si) and (Al + Na):Si dopped ISG glasses were investigated by using Photon Shielding and Dosimetry (Phy-X / PSD) software for the selected energy range. The obtained results showed that the highest MAC value belong to ISG-A00N glass. It was seen that the MAC values which were examined at all energies changed in harmony with WinXCom. Substituting an atomic fraction of (Al:Si) with (Al + Na):Si resulted in a reduction of the total atomic cross-section of the glass, which lowered the mass attenuation coefficient (MAC). In this study, computations were made for glasses with SiO2, Al2O3, B2O3, Na2O, CaO and ZrO2 content given with ISG-C, ISG-A00, ISG-A12, ISG-A22, ISG-A00N, ISG-A11N, ISG-A18N and ISG-A23N codes. MAC, LAC, HVL, TVL, Zeff, Neff, Ceff Zeq, EBF, EABF and FNRCS calculations were applied to assess the radiation protection parameters by using Phy-X/PSD software. In addition, MSP and PR values were calculated by using the SRIM code. In fact, each obtained parameter provides us very important information on radiation protection, and these methods are frequently used in the literature. ISG-A00N glasses were observed to have the highest attenuation coefficient. Thus, the MAC value gradually decreased as the Al, Na and Si contents increased. Likewise, the HVL, TVL and MFP values changed coherent with this. Moreover, Zeff and Neff values were seen in the ISG-A00N sample to take the maximum values to each other inversely. The most effective glass sample was seen as ISG-A00N glass at the mean free path penetration power of MSP and PR values. When all the results were evaluated, ISG-A00N glass which has the highest Si and Ca contents and density was found to be the glass with the best radiation shielding feature. It is also noteworthy that this glass does not contain any Al component. As the results of the investigation, it was found out that a very small doped of the Si increases the radiation shielding feature on the glass. It was seen that the ISG-A23N had the lowest ∑R value. The obtained results revealed that the ISG-A00N > ISG-A00 > ISG-C > ISG-A12 > ISG-A11N > ISG-A22 > ISG-A18N > ISG-A23N samples, in ascending order that attenuators for low energy radiations.

Fabrication of Compact Magnesium Disk by Spark Plasma Sintering

Fabrication of pure magnesium (Mg) disk was performed by powder metallurgy with the compaction method of spark plasma sintering (SPS). The effect of mechanical milling time on the microstructure, density, and porosity of the disk specimen was investigated. At an identical temperature, the 4 and 5 h milled specimens exhibited a nearly overlapped displacement curves during SPS, and a higher value indicating a higher densification degree than that of the 3 h milling powder. In agreement, the specimen density increased consecutively from 1.76 to 1.77 and 1.80 g/cm3 for the milling time of 3, 4, and 5 h. However, the porosity increased from 1.21% to 1.49% when the milling time increased from 3 to 4 h and further to 3.44% for 5 h milled specimens. The microstructure observation revealed that the average grain size decreased, and the pores became smaller and elongated with increasing milling time. The number of pores was higher with the gain fraction of grain boundaries. The 3 h milled specimen contained the highest atomic fraction of oxygen (21.9 at%) than that of the 4 and 5 h milled specimens (5.6 at% and 7.9 at%). The optimum milling time for obtaining high density and low porosity of pure Mg disk was 4 h.

Synthesizing of Novel Bulk (Zr67Cu33)100−xWx(x; 5–30 at%) Glassy Alloys by Spark Plasma Sintering of Mechanically Alloyed Powders

Metallic glassy alloys with their short-range order have received considerable attention since their discovery in 1960’s. The worldwide interest in metallic glassy alloys is attributed to their unique mechanical, physical, and chemical properties, which cannot be found together in long-range order alloys of the same compositions. Traditional preparation methods of metallic glasses, such as rapid solidification of melts, always restrict the formation of glassy alloys with large atomic fraction (above 3–5 at%) of high melting point metals (Ta, Mo, W). In this study, (Zr67Cu33)100−xWx(x; 5–30 at%) metallic glassy alloys were fabricated through a mechanical alloying approach, which starts from the elemental powders. This system shows excellent glass forming ability in a wide range of W (0 ≤ x ≥ 30 at%). We have proposed a spark plasma sintering technique to prepare nearly full-dense large sized (20 × 20 mm) bulk metallic glassy alloys. The as-consolidated bulk metallic glassy alloys were seen to possess high thermal stability when compared with the other metallic glassy systems. This is implied by their high glass transition temperature (722–735 K), wide range of supercooled liquid region (39 K to over 100 K), and high values of crystallization temperature (761 K to 823 K). In addition, the fabricated ternary systems have revealed high microhardness values.

Angular momentum-related probe of cold gas deficiencies

ABSTRACT Recent studies of neutral atomic hydrogen (H i) in nearby galaxies found that all field disc galaxies are H i saturated, in that they carry roughly as much H i as permitted before this gas becomes gravitationally unstable. By taking this H i saturation for granted, the atomic gas fraction fatm of galactic discs can be predicted as a function of the stability parameter q = jσ/(GM), where M and j are the baryonic mass and specific angular momentum of the disc and σ is the H i velocity dispersion (Obreschkow et al. 2016). The log-ratio Δfq between this predictor and the observed atomic fraction can be seen as a physically motivated ‘H i deficiency’. While field disc galaxies have Δfq ≈ 0, objects subject to environmental removal of H i are expected to have Δfq > 0. Within this framework, we revisit the H i deficiencies of satellite galaxies in the Virgo cluster and in clusters of the EAGLE simulation. We find that observed and simulated cluster galaxies are H i deficient and that Δfq slightly increases when getting closer to the cluster centres. The Δfq values are similar to traditional H i deficiency estimators, but Δfq is more directly comparable between observations and simulations than morphology-based–deficiency estimators. By tracking the simulated H i deficient cluster galaxies back in time, we confirm that Δfq ≈ 0 until the galaxies first enter a halo with $M_{\rm halo}\gt 10^{13}\rm M_{\odot }$, at which moment they quickly lose H i by environmental effects. Finally, we use the simulation to investigate the links between Δfq and quenching of star formation.

Cosmic-rays, gas, and dust in nearby anticentre clouds

Aim. H I 21-cm and 12CO 2.6-mm line emissions trace the atomic and molecular gas phases, respectively, but they miss most of the opaque H I and diffuse H2 present in the dark neutral medium (DNM) at the transition between the H I-bright and CO-bright regions. Jointly probing H I, CO, and DNM gas, we aim to constrain the threshold of the H I–H2 transition in visual extinction, AV, and in total hydrogen column densities, NHtot. We also aim to measure gas mass fractions in the different phases and to test their relation to cloud properties. Methods. We have used dust optical depth measurements at 353 GHz, γ-ray maps at GeV energies, and H I and CO line data to trace the gas column densities and map the DNM in nearby clouds toward the Galactic anticentre and Chamaeleon regions. We have selected a subset of 15 individual clouds, from diffuse to star-forming structures, in order to study the different phases across each cloud and to probe changes from cloud to cloud. Results. The atomic fraction of the total hydrogen column density is observed to decrease in the (0.6–1) × 1021 cm−2 range in NHtot (AV ≈ 0.4 mag) because of the formation of H2 molecules. The onset of detectable CO intensities varies by only a factor of 4 from cloud to cloud, between 0.6 × 1021 cm−2 and 2.5 × 1021 cm−2 in total gas column density. We observe larger H2 column densities than linearly inferred from the CO intensities at AV > 3 mag because of the large CO optical thickness; the additional H2 mass in this regime represents on average 20% of the CO-inferred molecular mass. In the DNM envelopes, we find that the fraction of diffuse CO-dark H2 in the molecular column densities decreases with increasing AV in a cloud. For a half molecular DNM, the fraction decreases from more than 80% at 0.4 mag to less than 20% beyond 2 mag. In mass, the DNM fraction varies with the cloud properties. Clouds with low peak CO intensities exhibit large CO-dark H2 fractions in molecular mass, in particular the diffuse clouds lying at high altitude above the Galactic plane. The mass present in the DNM envelopes appears to scale with the molecular mass seen in CO as MHDNM = 62 ± 7 MH2CO0.51 ± 0.02 across two decades in mass. Conclusions. The phase transitions in these clouds show both common trends and environmental differences. These findings will help support the theoretical modelling of H2 formation and the precise tracing of H2 in the interstellar medium.