Ultrahigh breakdown current density of van der Waals One Dimensional PdBr2\mathrm{PdBr_2}

One-dimensional (1D) van der Waals (vdW) materials offer nearly defect-free strands as channel material in the field-effect transistor (FET) devices and probably, a better interconnect than conventional copper with higher current density and resistance to electro-migration with sustainable down-scaling. We report a new halide based "truly" 1D few-chain atomic thread, PdBr$_2$, isolable from its bulk which crystallizes in a monoclinic space group C2/c. Liquid phase exfoliated nanowires with mean length (20$\pm$1)$\mu$m transferred onto SiO$_2$/Si wafer with a maximum aspect ratio of 5000 confirms the lower cleavage energy perpendicular to chain direction. Moreover, an isolated nanowire can also sustain current density of 200 MA/cm$^\mathrm{2}$ which is atleast one-order higher than typical copper interconnects. However, local transport measurement via conducting atomic force microscopy (CAFM) tip along the cross direction of the single chain records a much lower current density due to the anisotropic electronic band structure. While 1D nature of the nanoobject can be linked with non-trivial collective quantum behavior, vdW nature could be beneficial for the new pathways in interconnect fabrication strategy with better control of placement in an integrated circuit (IC)

Spin-crossover assisted metallization of few-layer FePS3_3 at 1.45 GPa

Magnetic insulators in reduced dimension are the ideal model systems to study spin-crossover(SCO) induced cooperative behavior under pressure. Similar to the external perturbations like light illumination or temperature, external pressure may provide new pathway to accelerate giant lattice collapse,and subsequently Mott transition in van der Waals (vdW) materials with diminishing effect of the third dimension. Here, we investigate room-temperature layer-dependent SCO and insulator-metal transition in vdW magnet,FePS3, under high pressure using micro-Raman scattering.Experimentally obtained spectra, in agreement with the computed Raman modes, indicates evidence of IMT of FePS3 started off with a spin-state transition from a high (S=2) to low spin state (S=0) with a thickness dependent critical pressure (P_c) which reduces to 1.45 GPa in 3-layer flakes compared to 10.8 GPa for the bulk counterpart. Additionally, a broad Raman mode (P*) emerges between 310 cm^{-1} and 370 cm^{-1} at elevated pressure for three different thicknesses of FePS3 flakes (3-100 layers), also corroborated with computational results which suggests the pressure dependent decrease of metal-ligand bond distance(Fe-S) with lowering of magnetic moment in FePS3. Phenomenologically, our results in few-layer flakes with strong structural anisotropy which enhances the in-plane strain with applied pressure can be understood by adopting Hubbard model and considering the spectral-range (bandwidth W) as a function of layer numbers and pressure with a power-law scaling. Reduction of the critical pressure for phase transition in few-layer vdW magnets to 1-2 GPa marks the possibility of using nano-enclosure fit for use in device electronics where the pressure is induced due to interfacial adhesion, like in vdW heterostructure or molecules trapped between layers,and thereby,avoiding the conventional use of diamond anvil cell

Proximitized spin-phonon coupling in topological insulator due to two-dimensional antiferromagnet

Induced magnetic order in a topological insulator (TI) can be realized either by depositing magnetic adatoms on the surface of a TI or engineering the interface with epitaxial thin film or stacked assembly of two-dimensional (2D) van der Waals (vdW) materials. Herein, we report the observation of spin-phonon coupling in the otherwise non-magnetic TI Bi$_\mathrm{2}$Te$_\mathrm{3}$, due to the proximity of FePS$_\mathrm{3}$ (an antiferromagnet (AFM), $T_\mathrm{N}$ $\sim$ 120 K), in a vdW heterostructure framework. Temperature-dependent Raman spectroscopic studies reveal deviation from the usual phonon anharmonicity at/below 60 K in the peak position (self-energy) and linewidth (lifetime) of the characteristic phonon modes of Bi$_{2}$Te$_{3}$ (106 cm$^{-1}$ and 138 cm$^{-1}$) in the stacked heterostructure. The Ginzburg-Landau (GL) formalism, where the respective phonon frequencies of Bi$_{2}$Te$_{3}$ couple to phonons of similar frequencies of FePS$_3$ in the AFM phase, has been adopted to understand the origin of the hybrid magneto-elastic modes. At the same time, the reduction of characteristic $T_\mathrm{N}$ of FePS$_3$ from 120 K in isolated flakes to 65 K in the heterostructure, possibly due to the interfacial strain, which leads to smaller Fe-S-Fe bond angles as corroborated by computational studies using density functional theory (DFT). Besides, our data suggest a double softening of phonon modes of Bi$_\mathrm{2}$Te$_\mathrm{3}$ (at 30 K and 60 K), which in turn, demonstrates Raman scattering as a possible probe for delineating the magnetic ordering in bulk and surface of a hybrid topological insulator

MnOx supported on a TiO2@SBA-15 nanoreactor used as an efficient catalyst for one-pot synthesis of imine by oxidative coupling of benzyl alcohol and aniline under atmospheric air

In the present study, a mesoporous silica (SBA-15) encapsulated TiO2 nanoreactor is used as a support for MnOx and this MnOx/TiO2@SBA-15 acts as a catalyst for the one-pot synthesis of imine by oxidative coupling between benzyl alcohol and aniline in the presence of atmospheric air. To understand the properties, the catalysts were characterized by several analytical techniques, namely, N2 adsorption–desorption isotherm, small angle X-ray scattering (SAXS), wide angle X-ray diffraction, high resolution transmission electron microscopy (HRTEM), H2-temperature programmed reduction (H2-TPR), O2-temperature programmed oxidation (O2-TPO) and NH3-temperature programmed desorption (NH3-TPD). The pore encapsulation process by SBA-15 causes TiO2 to be in a highly dispersed state, and this highly dispersed TiO2 makes maximum contact with the MnOx species as well as the reactant molecules. The reaction was carried out at atmospheric pressure with equimolar amounts of substrates without additives in the presence of atmospheric air. The yield and selectivity of imines vary with the MnOx and TiO2 loading. The 7.5 wt% MnOx loaded TiO2@SBA-15 (5 wt% TiO2) nanoreactor showed the highest catalytic activity. With the increase in weak acid sites and the oxygen activation ability of the prepared catalyst, the conversion and selectivity of the desired product reached 96% and 97%, respectively. The investigation of the reaction mechanism suggests that there is a synergistic effect between highly dispersed TiO2 and MnOx, which improves the reactant conversion and the selectivity of the desired product (N-benzylideneaniline) and also the prepared catalyst shows excellent recyclability up to the 10th cycle. The recyclability and hot filtration study confirms the true heterogeneity of the prepared catalyst during imine synthesis. The heterogeneity of the prepared catalyst, the avoidance of any noble metal and the utilization of air as an oxidizing agent represent an efficient, green reaction pathway for imine synthesis

Characterization of lignite deposits of Barmer Basin, Rajasthan: insights from mineralogical and elemental analysis

The geochemistry of fly ash produced from the combustion of coal at thermal power plants presents a significant challenge for disposal and environmental impact due to its complex mineralogical and elemental composition. The objective of this study was to investigate the mineralogical and elemental distribution of thirty lignite samples from the Barmer Basin using advanced techniques such as X-ray diffraction (XRD), X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analysis revealed the presence of minerals such as haematite (Fe2O3), nepheline, anhydrite, magnesite, andalusite, spinel and anatase. Other minor minerals included albite, siderite, periclase, calcite, mayenite, hauyne, pyrite, cristobalite, quartz, nosean and kaolinite. XRF analysis demonstrated that the most abundant elements in the Barmer Basin lignite ash were iron oxide (Fe2O3), sulphur oxide (SO3), calcium oxide (CaO), and quartz (SiO2) followed by minor traces of toxic oxides (SrO, V2O5, NiO, Cr2O3, Co2O3, CuO) that are known to have adverse effects on human health and the environment. The rare earth element (REE) composition showed higher concentrations of Tb, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc at the Giral and lower concentrations at Sonari mine. The Barmer lignites recorded higher concentration of trace elements such as V, Cr, Co, Ni, Cu and Sr while lower concentration of Rb, Cs, Ba, Pb, As, Th and U were observed within optimal range. The study findings revealed the predominant mineral concentration, elemental makeup, trace elements and rare earth elements associated with lignite reserves in the Barmer Basin

Optimization of Amylase Production from B. amyloliquefaciens

Demand for microbial amylase production persists because of its immense importance in wide spectrum industries. The present work has been initiated with a goal of optimization of solid state fermentation condition for amylase using agroindustrial waste and microbial strain like B. amyloliquefaciens (MTCC 1270). In an aim to improve the productivity of amylase, fermentation has been carried out in the presence of calcium (Ca+2), Nitrate (NO3−), and chloride ions (Cl−) as well as in the presence of D-inositol and mannitol. Amylase needs calcium ion for the preservation of its structure, activity and stability that proves beneficial also for amylase production using solid state fermentation. The inclusion of ions and sugars in the SSF media is promising which can be explained by the protection offered by them against thermal decay of amylase at various incubation periods at 37°C

Anisotropic magnetodielectric coupling in layered antiferromagnetic FePS 3

We report anisotropic magnetodielectric coupling in layered van der Waals antiferromagnetic FePS3 (Néel temperature TN∼ 120 K) with perpendicular anisotropy. Above TN, while the dielectric response function along the c axis shows frequency-dependent relaxations, in-plane data is frequency independent and reveals a deviation from phonon-anharmonicity in the ordered state, thereby implying a connection to spin-phonon coupling known to be indicative of onset of magnetic ordering. At low temperature (below 40 K), atypical anomaly in the dielectric constant is corroborated with temperature-dependent dc and ac susceptibility. The magnetodielectric response across this anomaly differs significantly for both in-plane and out-of-plane cases. We have explained this in terms of preferential orientation of magnetic antiferromagnetic zigzag alignment, implied by the in-plane structural anisotropy as confirmed by ab initio calculations. Controlling the relative strength of magnetodielectric coupling with magnetic anisotropy opens a strategy for tracking subtle modifications of structures, such as in-plane anisotropy, with potential applications for spintronic technologies

Emergence of a Non-van der Waals Magnetic Phase in a van der Waals Ferromagnet

International audienceManipulation of long-range order in two-dimensional (2D) van der Waals (vdW) magnetic materials (e.g., CrI$_3$, CrSiTe$_3$ etc.), exfoliated in few-atomic layer, can be achieved via application of electric field, mechanical-constraint, interface engineering, or even by chemical substitution/doping. Usually, active surface oxidation due to the exposure in the ambient condition and hydrolysis in the presence of water/moisture causes degradation in magnetic nanosheets which, in turn, affects the nanoelectronic/spintronic device performance. Counterintuitively, our current study reveals that exposure to the air at ambient atmosphere results in advent of a stable nonlayered secondary ferromagnetic phase in the form of Cr$_2$Te$_3$ (T$_{C2}$~ 160 K) in the parent vdW magnetic semiconductor Cr$_2$Ge$_2$Te$_6$ (T$_{C1}$~ 69 K). In addition, the magnetic anisotropy energy (MAE) enhances in the hybrid by an order from the weakly anisotropic pristine Cr$_2$Ge$_2$Te$_6$ crystal, increasing the stability of the FM ground state with time. Comparing with the freshly prepared Cr$_2$Ge$_2$Te$_6$, the coexistence of the two ferromagnetic phases in the time elapsed bulk crystal is confirmed through systematic investigation of crystal structure along with detailed dc/ac magnetic susceptibility, specific heat, and magnetotransport measurement. To capture the concurrence of the two ferromagnetic phases in a single material, Ginzburg-Landau theory with two independent order parameters (as magnetization) with a coupling term can be introduced. In contrast to rather common poor environmental stability of the vdW magnets, our results open possibilities of finding air-stable novel materials having multiple magnetic phases