Wide Region Research Articles

Phase transformation mechanisms occurring during spark plasma sintering elaboration of new duplex composite stainless steels

This study focuses on the elaboration of duplex stainless steels (DSS) from powder mixtures using spark plasma sintering (SPS). Different mass fractions of an austenitic 316L powder and a ferritic 410L one were blended and then sintered by SPS. Microstructural characterizations of the sintered samples obtained from different powder mixtures were performed. They were coupled with marking experiments of the powder particles’ surface. The results showed the formation of martensite within the ferritic powder and at the austenite/ferrite interfaces, following two different mechanisms. In addition, it was found that the width of the martensitic regions is mainly influenced by the diffusion of Cr and Ni from the austenitic to the ferritic powder during sintering. The characterizations revealed that the originality of this approach lies in the particular microstructure obtained after sintering. The characteristic size of the ferritic and austenitic domains in the final material is that of the initial powder particles (up to some hundred microns). Moreover, each domain is formed by equiaxed and isotropic grains, having a size ranging from some microns to some tens of microns. This particular microstructure justifies the use of the term “composite duplex stainless steels” (COMPLEX) for this kind of new DSS.

Bending performance and failure mechanisms of composite sandwich structures with 3D printed hybrid triply periodic minimal surface cores

In this paper, a novel hybrid triply periodic minimal surface (TPMS) core with a nonlinear transition region was designed by combining two types of TPMS (Diamond and Schwarz P) structures using the sigmoid function. The width of the transition region was precisely regulated by adjusting the gradient control parameter r in the sigmoid function. Composite sandwich structures (CSS) were fabricated by bonding two carbon fiber reinforced polymer (CFRP) face sheets to a 3D printed polylactic acid (PLA) core. The bending performance and failure mechanisms of the CSSs with the hybrid TPMS cores were analyzed through three-point bending tests and finite element analysis (FEA). The results indicate that as r increases, the transition region of the hybrid TPMS cores becomes narrower, leading to a gradual decrease in bending strength, bending stiffness, and core shear stress. The failure process of the CSSs in the experiment aligns well with the FEA results. Through comparative analysis of the stiffness-to-weight and strength-to-weight ratios of the CSSs with the native TPMS cores, the hybrid TPMS cores with a wider transition region enhance the structural efficiency of the CSSs, while those with a narrower transition region negatively impact the performance of the CSSs.

Solid solutions in EuSc3(BO3)4-GdSc3(BO3)4 system: Phase diagram, synthesis, crystal growth, structure and luminescence

Solid solutions based on (Eu,Gd)Sc3(BO3)4 (C2/c) and Gd0.25Sc0.75BO3 (R3¯) in the EuSc3(BO3)4-GdSc3(BO3)4 system were studied. Synthesis at 1250 °C provides wide homogeneity regions which are stable at room temperature. Melt-solution crystallization of both compounds from LiBO2-LiF flux was shown. All the obtained samples have luminescence characteristic of Eu3+ with a largest peak at 615 nm corresponding to the 5D0 → 7F2 transition. In this series the luminescence intensity monotonically increases with an increase of Eu content. The largest quantum yield of luminescence (53 %) in the EuSc3(BO3)4-GdSc3(BO3)4 system is demonstrated by EuSc3(BO3)4 sample.

The effect of Fe solute atom on interface structure and deformation behavior of Cu/FexNi1-x layered composites by molecular dynamics

Molecular dynamics investigated the effect of Fe solute atom on interface structure and deformation behavior of Cu/FexNi1-x layered composites. Ultimate stress first increases, then decreases, and then increases again with the increase of Fe content. When Fe content is between 20 % and 30 %, ultimate stress reaches the maximum value, which is 15.2 % higher than that of Cu/Ni. As the Fe content increases, stress concentration region on interface shifts from Cu layer to FexNi1-x layer, then to Cu layer, initial dislocation nucleation source on interface transfers from triangular node on Cu side to misfit dislocation line on FexNi1-x side, then to strip region on Cu side, and plastic deformation mechanism of FexNi1-x layer changes from slip of leading and trailing dislocations to slip of partial dislocations, then to slip of perfect dislocations. When Fe content is low, dislocation density rapidly increases to its peak, then decreases, and finally fluctuates around certain value, especially in the Fe30Ni70 layer where the dislocation density decreases to very low value, and interface morphology presents wavy. However, when Fe content is high, dislocation density slowly increases to its peak and then fluctuates around the peak, and interface morphology presents flat. Shear strain width of interface region decreases as Fe content increases, which indicates the interface of Cu/FexNi1-x with low Fe content has good plastic harmonized deformation ability.

Tunable terahertz filter based on graphene photonic crystals with defective layers

In this paper, we design a high-precision tunable terahertz filter by using transfer matrix method. The filter structure mainly consists of graphene embedded photonic crystals (GPCs). The front part of the GPCs contains artificial synthetic material and air layer, the back part of the GPCs is composed by and periodic stack of isotropic dielectric slabs (MgF2) embedded with graphene sheets, where air defect layer is located in the middle of the GPC as a central layer. Our simulation reveals that graphene layer and air defective layer strongly affect the filter performance. And we can get a relatively pure transmission peak in a wide frequency region. Additionally, the influence of incidence angle of terahertz wave, thickness of air layer, the unit number of front periodic structure and chemical potential of the graphene sheets can also modulate the function of the filter. And the filter has strong stability when the temperature changes from 150 K to 350 K.The results indicate that single channel, dual and multiple channels filter in a narrow frequency can be obtained by optimizing the structure parameter.

Phytoliths in bamboos from eastern and north-eastern India: Implications in distinguishing different ecoclimatic conditions and in deciphering Late Holocene climate variability

To develop a phytolith (biogenic silica) reference and to understand the eco-climatic indicative values of some grass silica short cells (GSSCs) occurring in the bamboos (Bambusoideae grasses), one of the chief floral components of eastern and north-eastern parts of India, we studied 44 modern bambusoid grasses and 26 surface soils from different eco-climatic zones covering both the plains and mountainous regions. Of the diverse phytoliths retrieved from the bamboos, Saddle tall and Saddle collapsed were the most abundant types (except in Yushania maling) and these types were also common in surface soil phytolith assemblages of the eastern and north-eastern parts of India. To assess the environmental sensitivity of most consistent morphotypes, we categorized two commonly occurring GSSC morphotypes namely Saddle tall into three groups based on their length and Saddle collapsed into two groups based on their length to width ratio respectively. Pearson’s correlation analysis, principal component analysis (PCA), and redundancy analysis (RDA) were used to understand if these morphotypes could distinguish different eco-climatic conditions. Variability of Saddle tall and Saddle collapsed types (both morphometric and abundance) in bamboos growing in these parts of India is a function of mean precipitation of the wettest quarter (MPWeQ) and mean temperature of the driest quarter (MTDQ). The present results served as a baseline for reevaluating the interpretations of a Late-Holocene fossil phytolith record from the eastern Himalaya further validating the potential of Saddle tall and Saddle collapsed types in reconstructing past climate variability in a wide geographical region.

Width of the quasi-perpendicular bow shock region at Mars

Width of the quasi-perpendicular bow shock region at Mars

Anchored Weakly‐Solvated Electrolytes for High‐Voltage and Low‐Temperature Lithium‐ion Batteries

AbstractElectrolytes endowed with high oxidation/reduction interfacial stability, fast Li‐ion desolvation process and decent ionic conductivity over wide temperature region are known critical for low temperature and fast‐charging performance of energy‐dense batteries, yet these characteristics are rarely satisfied simultaneously. Here, we report anchored weakly‐solvated electrolytes (AWSEs), that are designed by extending the chain length of polyoxymethylene ether electrolyte solvent, can achieve the above merits at moderate salt concentrations. The −O−CH2−O− segment in solvent enables the weak four‐membered ring Li+ coordination structure and the increased number of segments can anchor the solvent by Li+ without largely sacrificing the ionic dissociation ability. Therefore, the single salt/single solvent AWSEs enable solvent co‐intercalation‐free behavior towards graphite (Gr) anode and high oxidation stability towards high‐nickel cathode (LiNi0.8Co0.1Mn0.1O2‐NCM811), as well as the formation of inorganic rich electrode/electrolyte interphase on both of them due to the anion‐rich solvation shells. The capacity retention of Gr||NCM811 Ah‐class pouch cell can reach 70.85 % for 1000 cycles at room‐temperature and 75.86 % for 400 cycles at −20 °C. This work points out a promising path toward the molecular design of electrolyte solvents for high‐energy/power battery systems that are adaptive for extreme conditions.

Anchored Weakly-Solvated Electrolytes for High-Voltage and Low-Temperature Lithium-ion Batteries.

Electrolytes endowed with high oxidation/reduction interfacial stability, fast Li-ion desolvation process and decent ionic conductivity over wide temperature region are known critical for low temperature and fast-charging performance of energy-dense batteries, yet these characteristics are rarely satisfied simultaneously. Here, we report anchored weakly-solvated electrolytes (AWSEs), that are designed by extending the chain length of polyoxymethylene ether electrolyte solvent, can achieve the above merits at moderate salt concentrations. The -O-CH2-O- segment in solvent enables the weak four-membered ring Li+ coordination structure and the increased number of segments can anchor the solvent by Li+ without largely sacrificing the ionic dissociation ability. Therefore, the single salt/single solvent AWSEs enable solvent co-intercalation-free behavior towards graphite (Gr) anode and high oxidation stability towards high-nickel cathode (LiNi0.8Co0.1Mn0.1O2-NCM811), as well as the formation of inorganic rich electrode/electrolyte interphase on both of them due to the anion-rich solvation shells. The capacity retention of Gr||NCM811 Ah-class pouch cell can reach 70.85 % for 1000 cycles at room-temperature and 75.86 % for 400 cycles at -20 °C. This work points out a promising path toward the molecular design of electrolyte solvents for high-energy/power battery systems that are adaptive for extreme conditions.

Electronic band structure and optical properties of BGaAsBi/GaAs using 16 band kp Hamiltonian

The numerical simulations of optical and electronic properties of BGaAsBi/GaAs quantum wells (QWs) are obtained by diagonalizing the 16-band kp Hamiltonian with distinct boron and bismuth compositions that exhibit multifaceted potential in 1.3–1.5 μm. It has been observed that under strain-relaxed conditions for a doping concentration of 12.5 % (B, Bi), the anticipated values of spin-orbit (SO) coupling energy (ΔSO) and the bandgap (Eg) are 302 meV and 0.952 eV, respectively. Additionally, strain interaction on band structure decreases the band gap from (Eg = 0.92eV–0.85eV), increasing dopant concentration from 8 % to 12.5 %. The consequence of incorporating both Bi and B impurity is a reduction in electron effective mass of BGaAsBi by ∼1.3 times concerning the host GaAs, enhancing the optical properties of BGaAsBi/GaAs quantum-confined heterostructures. Moreover, an increase in well-width introduced a red shift and reduced the peak amplitude of the gain spectra. In addition, for solar cell application, the onset of the fundamental absorption edge is depicted at an energy of about 0.96 eV. For laser applications, the optimum threshold current density and quality factor of BGaAsBi/GaAs quantum well achieved at room temperature are 1089 A/cm2 and 3653, respectively, at well width (w = 2.0 nm), cavity length (L = 0.5 mm), and average thickness of the active region (d = 45 nm). The variation in power density is studied with injected current density, while the quality factor is calculated with well width. The outcomes could be beneficial for future use in optical devices.

Zinc Oxide/Polypyrrole particle-decorated rod structure for NO2 detection at low temperature

In this study, Zinc oxide (ZnO) nanoparticles with a size of about 50 - 70 nm were green-synthesized using tea leaves and ZnO/Polypyrrole (ZnO/Ppy) nanocomposites were obtained by ultrasonic-assisted chemical polymerization method using pyrrole monomer and the nanoparticles. The characterization of the materials is conducted using several analytical techniques, including Field Emission Scanning Electron Microscopy (FESEM) and X-Ray Diffraction (XRD) and Ultraviolet visible spectrum (UV-Vis). The synthesized PPy material exhibits have a rod-shaped structure, diameter ranging from 100 to 200 nm. The ZnO/PPy nanocomposite system, consisting of PPy rods surrounded by ZnO particles. The gas sensing characteristics of the materials have also been investigated by measuring their sensitivity, response time, and stability to NO2 at low temperature and different humidity. Notably, the material exhibits considerable sensitivity to NO2 gas at low temperatures and the parameters related to response and recovery times are relatively rapid. Furthermore, a potential gas-sensing mechanism based on changes in the width of the depletion region is proposed.

Junction Piezotronic Transistor Arrays Based on Patterned ZnO Nanowires for High-Resolution Tactile and Photo Mapping.

Recently, a great deal of interest has been focused on developing sensors that can measure both pressure and light. However, traditional sensors are difficult to integrate into silicon (Si)-based integrated circuits. Therefore, it is particularly important to design a sensor that operates on a new principle. In this paper, junction piezotronic transistor (JPT) arrays based on zinc oxide (ZnO) nanowire are demonstrated. And the JPT arrays show high spatial resolution pressure and light mapping with 195 dpi. Because ZnO nanowires are arranged vertically above the p-type Si channel's center of the transistor, the width of the heterojunction depletion region is constricted by the positive piezoelectric potential generated by strained ZnO. In addition, photogenerated charge carriers can be created in the Si channel when JPT is stimulated by light, which increases its electrical conductivity. Consequently, the external pressure and light distribution information can be obtained from the variation in the output current of the device. The prepared JPT arrays can be compatible with Si transistors, which make them highly competitive and make it possible to incorporate both pressure and light sensors into large integrated circuits. This work will contribute to many applications, such as intelligent clothing, human-computer interaction, and electronic skin.

High Defect Tolerance in Heavy‐Band Thermoelectrics

AbstractThe insensitivity of thermoelectric (TE) performance to defects and impurities induced by off‐stoichiometry or low‐purity raw elements is crucial for the low‐cost mass production of highly efficient TE materials. Here it is demonstrated that heavy‐band TE materials with high optimized carrier concentration can exhibit a high tolerance against the off‐stoichiometry in their composition. Using the heavy‐band half‐Heusler compounds as examples, it is found that for ZrNiSn with optimal carrier concentration, the off‐stoichiometry of the nominal composition in between ±5% only results in a fluctuation of its peak zT value less than 10%. A composition‐zT phase diagram is thus established, guiding the exploration of a wide nominal composition region with peak zT values exceeding 1.0. The high defect tolerance observed in heavy‐band TE materials enables the achievement of high TE performance using low‐purity raw elements. As demonstrated in several systems, including n‐type ZrNi(Sn, Sb), (Zr, Nb)CoSb, and p‐type ZrCo(Sb, Sn), comparable zT values are attained when utilizing low‐purity raw elements (≈99.5%), instead of the high‐purity ones (99.95–99.999%), leading to substantial cost saving. These findings highlight the importance of understanding defect tolerance in TE materials, which could offer an additional advantage for their practical applications.

Syndiotactic chiral metastructure with local resonance for low-frequency vibration isolation

Isolating low-frequency vibrations is a challenge in engineering due to their long wavelength. The bandgap within inertial amplification metastructures has proven to be an effective solution for isolating low-frequency vibrations. In this study, a chiral local resonator is proposed and integrated into a syndiotactic chiral inertial amplification metastructure (SCM) to create a low-frequency bandgap. Under equal mass and stiffness conditions, SCM-CR exhibits a bandgap starting frequency 32.3 % lower than that of traditional metastructures with traditional local resonators (TM-TR), and the normalized width of the bandgap is 31.7 % wider than TM-TR. The low-frequency bandgap is attributed to the presence of chiral local resonators. The inertial amplification effect induced by the chiral structure results in a resonance frequency lower than that of local resonators with equivalent mass and stiffness. Within the low-frequency bandgap, the transmission of the SCM-CR proposed in this study exhibits double attenuation notches over a specific number of periods, leading to the normalized width of the deep attenuation region 45.8 % broader than that of traditional metastructures with chiral local resonators (TM-CR). The tunability of the bandgap has also been investigated. Experimental results verified the double attenuation notches and the tunability of the bandgap. This work provides a promising solution for low-frequency vibration isolation.

Research of single-event burnout in vertical Ga2O3 FinFET by low carrier lifetime control

This paper presents the 2D simulations of single-event burnout (SEB) in vertical enhancement-mode gallium oxide (Ga2O3) fin-shaped channels field-effect transistor (FinFET) by low carrier lifetime control (LCLC) method. The correctness of the structure parameters and simulated physical models are verified by the basic electrical characteristics in experiments. The SEB simulations show that the most sensitive region to heavy ion is the narrow channel region. The SEB failure is due to the diffusion of a large number of electron–hole pairs induced by heavy ion into a strong electric field region, resulting in a large transient current density to cause the thermal failure. Afterwards, the influences of the narrow channel region width on basic characteristics and SEB performance are discussed. Then, the SEB hardening mechanism of LCLC is studied that the electric field peak in the top of the structure can be effectively reduced, and the transient current caused by second avalanche is restrained. In addition, the basic characteristics with LCLC are proved to be hardly influenced in Ga2O3 FinFET. Finally, the carrier lifetime value and local control region are studied that the SEB hardening performance can be significantly improved by a large enough control area with a low carrier lifetime.

Polymer physics models reveal structural folding features of single-molecule gene chromatin conformations.

Here, we employ polymer physics models of chromatin to investigate the 3D folding of a 2Mb wide genomic region encompassing the human LTN1 gene, a crucial DNA locus involved in key cellular functions. Through extensive Molecular Dynamics simulations, we reconstruct in-silico the ensemble of single-molecule LTN1 3D structures, which we benchmark against recent in-situ Hi-C 2.0 data. The model-derived single molecules are then used to predict structural folding features at the single-cell level, providing testable predictions for super-resolution microscopy experiments.

Rapid-scan broadband frequency-domain terahertz spectroscopy via dynamic optical phase lock

Frequency-domain terahertz (THz) spectroscopy using photomixing devices has unique advantages such as high dynamic range and high spectral resolution. Thus, many applications for solid-state and gas-phase spectroscopy have been proposed. In this study, we developed a feedback controlled technique to dynamically compensate for the optical phase accompanied by frequency sweep, enabling both fast and high-resolution data acquisition across a wide frequency region. From gas-phase THz spectroscopy measurements of dilute acetonitrile gas in a wide frequency range up to 1.1 THz, fine structures with linewidths less than 10 MHz were clearly resolved, while the data acquisition rate was improved by two orders compared to the previously reported value.

Tunable thermal expansion via the magnetic phase competition in kagome magnets

Negative thermal expansion materials can solve the challenge of mismatched coefficients of thermal expansion of components in precision instruments, thereby improving the thermal shock resistance of devices. The adjustment of negative thermal expansion performance can improve the universality of its application. In this work, tunable thermal expansion has been achieved in Hf1−xTaxFe2 kagome magnets via magnetic phase competition. The transition from ferromagnetism to antiferromagnetism results in a sharp volume shrinkage of Hf0.83Ta0.17Fe2 within a narrow temperature range of 190–230 K, which limits its practical application. As the Ta content decreases, the ferromagnetic ground state becomes more robust and eventually suppresses the antiferromagnetism completely, achieving a negative thermal expansion in Hf0.88Ta0.12Fe2 caused by the ferromagnetic to paramagnetic transition over a wide temperature region and containing room temperature (αV = −37.63 × 10−6 K−1, 250–350 K). This work realizes the regulation of negative thermal expansion through magnetic phase competition, which provides guidance for the regulation of thermal expansion of magnetic materials in the future.

Enhanced CHF of pool boiling and its predictive correlation for heterogeneous distributed composite microstructured surfaces with microcavities on micro-pin-fins

In the present study, several heterogeneous distributed composite microstructured surfaces (HDCMs) with different geometry parameters were prepared. The effect of the widths of the composite microstructured region, the widths of the smooth channels, the pitch of the micro-pin-fins, and the porosity of the surfaces on the pool boiling performance in HFE-7100 was examined under different liquid subcoolings. During the experiments, the three-phase contact lines of bubbles can be restricted by composite microstructured regions. Thus, reasonable geometry parameters can further enhance the liquid supply, promoting pool boiling heat transfer performance. The maximum critical heat flux of the HDCM is 14.1 % higher than that of the uniformly distributed composite microstructured surface (UDCM). Considering the effects of subcooled Jakob number (Jasub), composite microstructured region density number (SD), capillary resistance number (CR), and porosity (φ) on the critical heat flux (CHF) of HDCMs, an empirical correlation predicted the CHF for DCMs with different geometry parameters was proposed. The prediction results meet well with the experimental data, with an error within ±15 %.

A thermal fluid dynamic model for the melt region during the laser powder bed fusion of polyamide 11 (PA11)

Studying the physical characteristics of the melt region in polymer-based laser powder bed fusion (PBF-LB/P) offers good comprehension that is essential for quality control, process optimization, understanding of material behavior, and preserving process consistency. Among the few numerical modelling investigations of PBF-LB/P, this study focuses on 3D multiphysics simulation of melt pool morphologies, beginning with powder bed preparation incorporating the actual particle size distribution using the discrete element method (DEM). A thermal fluid dynamic numerical model is then developed based on the finite volume method (FVM) using Flow-3D Weld to simulate PBF-LB while using polyamide 11 (PA11) as the primary material. The cooling after sintering plays a crucial role for the formation of the melt region due to the high viscosity of the polymer material effectively resulting in creeping flow. Here, we propose a model for both sintering as well as the subsequent cooling step, a two-step model capable of simulating the finished structure accurately with relatively low computational resources. The model's accuracy is verified through a mesh dependency analysis and its predictive power via validation against internal single-track experiments providing dimension data on the melt region width and depth. The simulation results allow for a detailed exploration of the effects of laser settings on melt region morphologies and the occurrence of defects. The model's scope is further extended to multi-track simulation, revealing the connection between surface roughness and laser settings. In general, this study provides significant contributions to the comprehension of PBF-LB/P methodologies which in turn can be used for further process improvement.