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Two-dimensional ferroelectric materials are beneficial for power-efficient memory devices and transistor applications. Here, we predict out-of-plane ferroelectricity in a new family of buckled metal oxide (MO; M: Ge, Sn, Pb) monolayers with significant spontaneous polarization. Additionally, these monolayers have a narrow valence band, which is energetically separated from the rest of the low-lying valence bands. Such a unique band structure limits the long thermal tail of the hot carriers, mitigating subthreshold thermionic leakage and allowing field-effect transistors (FETs) to function beyond the bounds imposed on conventional FETs by thermodynamics. Our quantum transport simulations reveal that the FETs based on these MO monolayers exhibit a large ON/OFF ratio with an average subthreshold swing of less than 60 mV/decade at room temperature, even for short gate lengths. Our work motivates further exploration of the MO monolayers for developing advanced, high-performance memory and logic devices. [ABSTRACT FROM AUTHOR]

The doping influenced carrier dynamics to maneuvering n-type to p-type semiconducting gold cluster assembly have been assessed. The resonance photoemission spectroscopic measurements corroborate an incremental rise in the density of states at the valence edge, the overlap of valence states due to doping, and the presence of distinct spin–orbit splitting and coupling in manganese-doping (Au7Mn) compared to gold clusters (Au8), originating from the relativistic effect resulted in a semiconducting property. The work function dependent current–voltage characteristics in metal–semiconductor configuration show Ohmic and Schottky behaviors assorting p-type carriers in Au7Mn in contrast to the n-type Au8 and are presenting an atomic cluster based fast electronic device. [ABSTRACT FROM AUTHOR]

The high-entropy alloy with composition AlCoCrFeNi2.1, additively manufactured with the laser powder-bed fusion technique, has a far-from-equilibrium BCC/FCC eutectic nanolamellar structure. We studied the high-pressure response of this alloy under both static compression and high-strain rate shock compression. The response to static compression using a diamond anvil cell was studied at pressures up to 302 GPa with synchrotron x-ray diffraction at the advanced photon source. The high-pressure FCC-only phase of the EHEA previously observed by Pope et al. [AIP Adv. 13, 035124 (2023)] is found to be stable up to the highest pressure achieved in this study with a volume compression of V/V0 = 0.587 at ambient temperature. The shock experiments were performed by using GEKKO XII lasers at the Institute of Laser Engineering, Osaka University. The principal Hugoniot equation-of-state of the EHEA was measured up to a pressure of 515 GPa and a compression of V/V0 = 0.613. Additionally, the thermal equation of state of the EHEA was measured up to 6.2 GPa and 1623 K using a large-volume Paris–Edinburgh cell to obtain the temperature dependence of bulk modulus and thermal expansion coefficients. The melting temperature for EHEA AlCoCrFeNi2.1 at a pressure of 5.6 GPa was measured to be 1648 ± 25 K. These results can be used to refine stochastic (or special) quasi-random structure (SQS) models for high-pressure high-temperature behavior of high-entropy alloys. [ABSTRACT FROM AUTHOR]

Transition-metal and rare-earth borides are of considerable interest due to their electronic, mechanical, and magnetic properties as well as their structural stability under extreme conditions. Here, we report on a series of high-pressure Raman and x-ray diffraction experiments on the cubic rare-earth hexaboride EuB6 to an ultrahigh pressure of 187 GPa in a diamond anvil cell. In EuB6, divalent europium ions occupy the corners of the cubic structure, which encloses a rigid boron-bonded cage. So far, no structural phase transitions have been reported, while the nanoindentation studies indicate amorphization in nanoscale shear bands during plastic deformation. Our x-ray diffraction studies have revealed that the ambient cubic phase of EuB6 shows broadening and splitting of diffraction peaks starting at 72 GPa and the broadening continuing to 187 GPa. The high-pressure phase is recovered on decompression, and the Raman spectroscopy of the recovered sample from 187 GPa shows a downward frequency shift and broadening of T2g, Eg, and A1g modes of boron octahedron. The density functional theory simulations of EuB6 at 100 GPa have identified five possible lowest energy crystal structures. The experimental x-ray diffraction data at high pressures is compared with the theoretical predictions and the role of structural distortions induced by shear stresses is also discussed. [ABSTRACT FROM AUTHOR]

2D ferroelectric materials are promising for designing low-dimensional memory devices. Here, we explore strain-tunable ferroelectric properties of group-IV monochalcogenides MX (M = Ge , Sn; X = S , Se) and their potential application in lateral field tunnel junction devices. We find that these monolayers have in-plane ferroelectricity, with their ferroelectric parameters being on par with other known 2D ferroelectric materials. Among SnSe, SnS, GeSe, and GeS, we find that GeS has the best ferroelectric parameters for device applications, which can be improved further by applying uniaxial tensile strain. We use the calculated ferroelectric properties of these materials to study the tunneling electroresistance (TER) of a 4 nm device based on a lateral ferroelectric tunnel junction. We find a substantial TER ratio of 10 3 – 10 5 in the devices based on these materials, which can be further improved up to a factor of 40 on the application of tensile strain. [ABSTRACT FROM AUTHOR]

Tantalum (Ta) is a metal that has useful properties that make it useful in extreme environments. It is, therefore, important to understand how Ta performs in such extreme conditions by accurately measuring its properties. In this work, the yield strength of tantalum has been measured at pressures up to 276 GPa using axial and radial x-ray diffraction (XRD) methods in diamond anvil cells (DACs). We measured strength using XRD in a radial DAC to 50 GPa, in an axial DAC to 60 GPa using diamonds with standard flat culets, and in a final experiment to 276 GPa using toroidal diamond anvils. The radial XRD data were refined using the Material Analysis Using Diffraction Rietveld software package to extract lattice strain and the yield strength. The axial data were refined using the General Structure Analysis System II and a linewidth method was used to calculate the yield strength. The yield strength measured near ambient pressure was found to be 0.5 GPa and increased with a pressure of up to 50 GPa, where the yield strength plateaued at a value of 2.4 GPa. At pressures above 60 GPa, the strength increased again to a maximum value of 9 GPa at the highest pressure of 276 GPa. The data from the three experiments show good agreement between the methods and previously reported experimental data. This agreement illustrates the value of axial diffraction data for material strength determination and allows for measurements at multi-hundreds of GPa using toroidal DACs. [ABSTRACT FROM AUTHOR]

Shear strength measurements have been carried out on rhenium diboride, ReB2, to a pressure of 74 GPa using a Radial X-ray Diffraction (R-XRD) technique in a diamond anvil cell using platinum as an internal x-ray pressure standard. The R-XRD result has provided a unique insight into the deformation of hexagonal crystal lattice under non-hydrostatic compression and variation of shear strength with increasing pressure. From R-XRD data, we have estimated hydrostatic component of compression to determine an equation of state of rhenium diboride yielding a bulk modulus of K0 = 366 ± 25 GPa with a pressure derivative K 0 ′ = 4.3 ± 0.5 in good agreement with hydrostatic density functional theory calculations. The average lower bound of shear strength (τ) from various diffraction planes was then calculated using the measured interplanar d-spacing (dm) and hydrostatic component of d-spacing (dp) to be shown to approach 6.7 ± 0.4 GPa at 70 GPa. Our results show that the anisotropic compression effects observed in ReB2 under hydrostatic compression are correlated to electronic structure changes under compression as predicted by theoretical calculations. [ABSTRACT FROM AUTHOR]

The effect of ion irradiation on the proximity effect in YBa2Cu3O7−δ/La0.67Sr0.33MnO3 and YBa2Cu3O7−δ/SrTiO3/La0.67Sr0.33MnO3 heterostructures has been investigated using spin-polarized neutron reflectivity experiments. We demonstrate that the magnetization in the ferromagnetic (La0.67Sr0.33MnO3) layer at the interface is correlated with the suppression of the superconductivity in the YBa2Cu3O7−δ layer after irradiation, while the layer structure of the heterostructures remains intact. The evolution of the magnetization of the interfacial ferromagnetic layer studied as a function of temperature for both the irradiated heterostructures shows the absence of the proximity effect observed in the un-irradiated samples. The absence of a proximity effect is attributed to the suppression of the superconductivity, as seen in macroscopic magnetization measurements of the heterostructures after ion irradiation. [ABSTRACT FROM AUTHOR]

We report on the large-area and high-quality growth of single- to few-monolayer thick MoS2 thin films on oxidized Si (100) substrates via the pulsed laser deposition method. Our Raman, x-ray photoelectron spectroscopic, and FE-SEM measurements confirmed that atomically thin MoS2 layers are highly uniform and are stoichiometric. We found a type-I band alignment at the MoS2/SiO2 heterointerfaces through photoemission spectroscopic valence-band measurements. The valence- and conduction band offset (VBO and CBO) at the 1L MoS2/SiO2 interface was observed to be 3.91 and 2.96 ± 0.05 eV, respectively. The values of VBO and CBO increase up to 4.15 and 3.56 ± 0.05 eV, respectively, with an increase in the MoS2 layer number. This observation can be attributed to the shift of the Mo-4dz2 orbitals due to interlayer coupling for thicker MoS2 films, reducing its bandgap, resulting in an increment in VBO and CBO values. [ABSTRACT FROM AUTHOR]

We have investigated the structural, electronic, optical, and transport properties of 2D halide perovskite MAZX3 (MA = CH3NH3; Z = Pb, Sn; and X = Cl, Br, I) using density functional theory. The result suggests that as the atomic radius of halogen increases from Cl to I, the respective lattice constant increases, with a decrease in the bandgap. The bandgap of MAPbX3 is higher than that of MASnX3. The optical properties show that MAPbX3 has a higher static dielectric constant as compared to MASnX3. The optical activities of MAPbX3 and MASnX3 are in the visible region as well as the high ultraviolet region with a high absorption coefficient of 105 cm-1. Furthermore, we found that the carrier mobility of 2D perovskite is higher than the experimental value of bulk systems. The 2D MAPbCl3, MAPbBr3, and MASnCl3 show higher carrier mobility compared to the bulk system. In our outcome, lead-free MASnBr3 shows a higher efficiency of 28.62%, as compared to the 28.21% of MAPbI3. Our results could lead experimentalists to develop these materials for optoelectronics and solar cell device applications. [ABSTRACT FROM AUTHOR]

Antiferromagnetic coupling between rare-earth (RE) and transition metals (TM) gives rise to various magnetic ground states in RE/TM heterostructures. Interface structure and morphology tend to play important roles in defining the magnetic properties of heterostructures of these materials. Using spin-dependent polarized neutron reflectivity (PNR), we found a distinct magnetic structure for RE/TM (Gd/Co) multilayers having different interface morphologies. Two Gd/Co multilayers, each consisting of eight bilayers of Gd and Co, were grown at different argon pressures to accomplish variation in the interface morphology. The Gd/Co multilayer, which is grown at a lower argon pressure, exhibits lower intermixing/interdiffusion at the interfaces and shows asymmetric magnetic hysteresis loops below the compensation temperature (Tcomp ∼ 140 K) and antisymmetric magnetoresistance at Tcomp. The other multilayer, grown at two different argon pressures for the top and bottom four bilayers, shows a double hysteresis loop with an exchange-bias-like shift to the field axis at temperatures above Tcomp (∼150 K). From PNR measurements across Tcomp, these behaviors were attributed to interface dependent magnetic helical structures. The PNR results indicate the formation of a twisted helical magnetic structure with planar 2π domain walls and the evolution of magnetic inhomogeneities below Tcomp. The interface dependent twisted helical magnetic structures and the development of highly correlated magnetic inhomogeneities may find applications in all-spin-based technologies. [ABSTRACT FROM AUTHOR]

In the present work, we have systematically investigated the structural, electronic, vibrational, and H2 storage properties of a layered 2H boron sulfide (2H-BS) monolayer using spin-polarized density functional theory (DFT). The pristine BS monolayer shows semiconducting behavior with an indirect bandgap of 2.83 eV. Spin-polarized DFT with van der Waals correction suggests that the pristine BS monolayer has weak binding strength with H2 molecules, but the binding energy can be significantly improved by alkali metal functionalization. A system energy study indicates the strong bonding of alkali metals with the BS monolayer. The Bader charge analysis also concludes that a considerable charge is transferred from the metal to the BS monolayer surface, which was further confirmed by the iso-surface charge density profile. All functionalized alkali metals form cations that can bond multiple H2 molecules with sufficient binding energies, which are excellent for H2 storage applications. An ideal range of adsorption energy and practicable desorption temperature promises the ability of the alkali metal functionalized BS monolayer as an efficient material for hydrogen storage. [ABSTRACT FROM AUTHOR]

In recent work, we have investigated the electronic and optical properties of pristine and functionalized Si2BN quantum dots (QDs) using first-principles calculations. Due to the edge functionalization, Si2BN QDs have binding energies of −0.96 eV and −2.08 eV per hydrogen atom for the adsorption of single and double hydrogen atoms, respectively. These results reveal the stability and the bonding nature of hydrogen at the edges of Si2BN QD. In particular, the charge transfer between hydrogen and other atoms is explicitly increased. The electronic band structure of pristine Si2BN QD shows a metallic behavior with a finite number of electronic states in the density of states at the Fermi level. The frequency-dependent optical properties, such as refractive index, extinction coefficient, absorption coefficient, electron energy loss spectra, and reflectivity, are computed for both the parallel and perpendicular components of electric field polarization. The higher absorption was found in the infrared regime. The present study shows that the functionalization of Si2BN QD by two hydrogen atoms is energetically stable. It offers a promising application of Si2BN QD, which can be used in optical nanodevices such as photodetectors and biomedical imagination. [ABSTRACT FROM AUTHOR]

The rotating magnetocaloric effect is of recent interest in the magnetic refrigeration technique, in which the cooling effect is attained by rotating the anisotropic magnetocaloric material from one orientation to the other in a fixed magnetic field. In this work, we report the anisotropic magnetocaloric properties of single crystals of the ferromagnetic Weyl semimetal Co 3 Sn 2 S 2 for magnetic field H along the c-axis (H ∥ c) and magnetic field H along the ab-plane (H ∥ a b). We observed a significant (factor of 2) difference between the magnetocaloric effect measured in both orientations. The rotating magnetocaloric effect has been extracted by taking the difference of the magnetic entropy change (Δ S M) for fields applied in the two crystallographic orientations. Scaling analysis of Δ S M , the rescaled Δ S M (T , H) vs reduced temperature θ curves collapse onto a single universal curve, indicates that the transition from paramagnetic to ferromagnetic phases at 174 K is a second-order magnetic phase transition. Furthermore, using the power law dependence of Δ S M and relative cooling power RCP, the critical exponents β and γ are calculated, which are consistent with the recent critical behavior study on polycrystalline samples of this compound [Yan et al., Solid State Commun. 281, 57 (2018)]. [ABSTRACT FROM AUTHOR]

We have deposited LaNiO3 thin films on LaAlO3 (001), SrTiO3 (001), and Si (001) substrates using the pulsed laser deposition technique. Depositions were carried out at various substrate temperatures ranging from 0 to 800 °C. The effects of lattice mismatch and structural disorder on the transport properties of films deposited on various substrates and at different substrate temperatures are reported. X-ray diffraction confirms a highly c-axis oriented growth of LaNiO3 films on all the substrates at substrate temperatures of 600 and 800 °C, while at lower substrate temperatures deposited films are amorphous. Emergence of a new Raman mode indicates symmetry lowering in all the deposited crystalline films. Hardening of the Eg(3) (∼400 cm−1) mode is also observed with the rise of in-plane compressive strain. Resistivity curves for films on Si show a semiconducting behaviour and follow a variable range hopping mechanism. Crystalline films on LaAlO3 and SrTiO3 exhibit a metallic character along with a low-temperature resistivity upturn, which is attributed to the contribution of self-localization to resistivity at low temperatures as indicated by magnetotransport measurements. [ABSTRACT FROM AUTHOR]

The honeycomb lattice iridate Na2IrO3 shows frustrated magnetism and can potentially display Kitaev-like exchange interactions. Recently, it was shown that the electronic properties of the surface of crystalline Na2IrO3 can be tuned by Ar plasma treatment in a controlled manner, leading to various phases of matter ranging from a fully gapped to a metallic surface, where the possibility of a charge-density wave like transition has been suggested. Here, through direct imaging with an atomic force microscope (AFM) in air, we show that the surface of crystalline Na2IrO3 evolves rapidly as elemental Na effuses out of the interleave planes to the surface and undergoes sublimation, thereby disappearing from the surface gradually over time. Using conductive AFM, we recorded a series of topographs and surface current maps simultaneously and found that the modification of the surface leads to change in the electronic properties in a dynamic fashion until the whole system reaches a dynamic equilibrium. These observations are important in the context of the exotic electronic and magnetic properties that the surface of Na2IrO3 displays. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

The honeycomb lattice iridate Na2IrO3 shows frustrated magnetism and can potentially display Kitaev-like exchange interactions. Recently, it was shown that the electronic properties of the surface of crystalline Na2IrO3 can be tuned by Ar plasma treatment in a controlled manner, leading to various phases of matter ranging from a fully gapped to a metallic surface, where the possibility of a charge-density wave like transition has been suggested. Here, through direct imaging with an atomic force microscope (AFM) in air, we show that the surface of crystalline Na2IrO3 evolves rapidly as elemental Na effuses out of the interleave planes to the surface and undergoes sublimation, thereby disappearing from the surface gradually over time. Using conductive AFM, we recorded a series of topographs and surface current maps simultaneously and found that the modification of the surface leads to change in the electronic properties in a dynamic fashion until the whole system reaches a dynamic equilibrium. These observations are important in the context of the exotic electronic and magnetic properties that the surface of Na2IrO3 displays. [ABSTRACT FROM AUTHOR]

Changes in bulk crystallization behavior following devitrification at high pressure are investigated for a Fe78B13Si9 composition metallic glass using in-situ energy dispersive x-ray powder diffraction. Crystallization with time was evaluated for a series of measurements to a maximum pressure of 5.63 ± 0.15 GPa for the Fe78B13Si9 glass. Pressure was found to strongly affect onset bulk crystallization temperature Tx. Crystallization at each pressure was found to progress in two stages. In the first stage, α-Fe precipitates and in the second Fe2B forms while α-Fe continues to crystallize. Complementary high pressure room temperature studies were conducted. [ABSTRACT FROM AUTHOR]

The giant optical activity of chiral metamaterials (CMMs) holds great potential for tailoring the polarization state of an electromagnetic (EM) wave. In controlling the polarization state, the aspect of asymmetric transmission (AT), where a medium allows the EM radiation to pass through in one direction while restricting it in the opposite direction, adds additional degrees of freedom such as one-way channelling functionality. In this work, a CMM formed by a pair of mutually twisted slanted complementary metal strips is realized for broadband AT accompanied with crosspolarization (CP) conversion for linearly polarized EM waves. Numerically, the proposed ultrathin (~λ/42) CMM shows broadband AT from 8.58 GHz to 9.73 GHz (bandwidth of 1.15 GHz) accompanied with CP transmission magnitude greater than 0.9. The transmission and reflection spectra reveal the origin of the asymmetric transmission as the direction sensitive cross polarization conversion and anisotropic electric coupling occurring in the structure which is then elaborated with the surface current analysis and electric field distribution within the structure. An experiment is carried out to verify the broadband AT based CP conversion of the proposed CMM at microwave frequencies, and a reliable agreement between numerical and experimental results is obtained. Being ultra-thin, the reported broadband AT based CP conversion of the proposed CMM is useful for controlling radiation patterns in non-reciprocal EM devices and communication networks. [ABSTRACT FROM AUTHOR]

High temperature superconductors have created exciting opportunities for switchable metamaterial and plasmonic devices operating at terahertz frequencies. In recent times, there have been several demonstrations using superconducting metamaterials, such as thermal, electrical, magnetic, and optical switching. Here, we explore the impact of conductivity on terahertz metamaterial resonators with different resonance line shapes. Lorentzian and Fano line shaped resonators show different levels of enhancement in the quality factor and resonance intensity for metallic, superconductor, and perfect electric conductors, due to the interplay between the radiative and the non-radiative loss mechanisms in a metamaterial array. [ABSTRACT FROM AUTHOR]

The toroidal dipole moment, a localized electromagnetic excitation of torus magnetic fields, has been observed experimentally in metamaterials. However, the metamaterial based toroidal moment was restricted at higher frequencies by the complex three-dimensional structure. Recently, it has been shown that toroidal moment could also be excited in a planar metamaterial structure. Here, we use asymmetric Fano resonators to illustrate theoretically and experimentally the underlying physics of the toroidal coupling in an array of planar metamaterials. It is observed that the antiparallel magnetic moment configuration shows toroidal excitation with higher quality (Q) factor Fano resonance, while the parallel magnetic moment shows relatively lower Q factor resonance. Moreover, the electric and toroidal dipole interferes destructively to give rise to an anapole excitation. The magnetic dipole-dipole interaction is employed to understand the differences between the toroidal and magnetic Fano resonances. We further study the impact of intra unit-cell coupling between the Fano resonator pairs in the mirrored and non-mirrored arrangements. The numerical and theoretical approach for modelling the near-field effects and experimental demonstration of toroidal and magnetic Fano resonances in planar systems are particularly promising for tailoring the loss in metamaterials across a broad range of the electromagnetic spectrum. [ABSTRACT FROM AUTHOR]

The direct and indirect valleys in Germanium (Ge) are separated by a very small offset, which opens up the prospect of direct tunneling in the ⌈ valley of an extended Ge source tunnel field effect transistor (TFET). We explore the impact of thickness scaling of extended Ge source lateral TFET on the band to band tunneling (BTBT) current. The Ge source is extended inside the gate by 2 nm to confine the tunneling in Ge only. We observe that as the thickness is scaled, the band alignment at the Si/Ge heterojunction changes significantly, which results in an increase in Ge to Si BTBT current. Based on density functional calculations, we first obtain the band structure parameters (bandgap, effective masses, etc.) for the Ge and Si slabs of varying thickness, and these are then used to obtain the thickness dependent Kane's BTBT tunneling parameters. We find that electrostatics improves as the thickness is reduced in the ultra-thin Ge film (≤10 nm). The ON current degrades as we scale down in thickness; however, the subthreshold slope (SSAVG) improves remarkably with thickness scaling due to subsurface BTBT. We predict that 8 nm thin devices offer the best option for optimized ON current and SSAVG. [ABSTRACT FROM AUTHOR]

The effect of strain on the metal-insulator transition (MIT) of the epitaxial NdNiO3 film on the c-axis oriented LaAlO3 single crystal, grown by pulsed laser deposition, has been investigated. Swift heavy ion irradiation was used to vary the strain state of the deposited film. X-ray diffraction confirmed a systematic fluence dependent rise in the in-plane compressive strain, while maintaining the epitaxy of the film. This in-plane compressive strain has been found to reduce the MIT temperature, which finally disappeared for the highest fluence of the irradiation. This is also corroborated with the Raman spectroscopy measurements which suggest that the ion irradiation induced stress is responsible for the suppression of the metal-insulator transition. [ABSTRACT FROM AUTHOR]

We report temperature (RT-150K) and field dependent low frequency noise measurements on Ge n-FETs. Specifically, we delineate the temperature, field, and interfacial layer (GeON vs. GeO2) dependence of the gate overdrive index (β) on corresponding changes in volume interface trap density (Nit) and mobility (μ). For Nit < 1 x 1020 cm-3 eV-1, the dominant noise mechanism, number or mobility fluctuation, depends on the change in μ, but for Nit > 1 x 1020 cm-3eV-1 near the conduction band edge, changes in l as well as Nit determine the noise mechanism. Finally, we show that the β values of Ge n-FETs are significantly different from conventional Si transistors as well as Ge p-FETs at RT and 150 K due to much higher Nit and/or μ values of the Ge n-FETs. [ABSTRACT FROM AUTHOR]

Researchers analysed the effects of using different gas phase precursors for the growth of diamond films on Ti-6Al-4V alloy. Film quality and hardness were high, but adhesion was poor, using 2% CH4 in H2 gas mixtures. A change to an initial 5% saturation followed by a 2% saturation caused an improvement in adhesion quality but a slight decline in hardness. CO/H2 mixtures, which were were rich in CO, produced good adherence but poor hardness and low growth rates.

We studied the resistive memory switching in pulsed laser deposited amorphous LaHoO3 (a-LHO) thin films for non-volatile resistive random access memory applications. Nonpolar resistive switching (RS) was achieved in Pt/a-LHO/Pt memory cells with all four possible RS modes (i.e., positive unipolar, positive bipolar, negative unipolar, and negative bipolar) having high RON/ROFF ratios (in the range of ~104-105) and non-overlapping switching voltages (set voltage, VON~±63.6-4.2V and reset voltage, VOFF~±1.3-1.6V) with a small variation of about 65-8%. Temperature dependent current-voltage (I-V) characteristics indicated the metallic conduction in low resistance states (LRS). We believe that the formation (set) and rupture (reset) of mixed conducting filaments formed out of oxygen vacancies and metallic Ho atoms could be responsible for the change in the resistance states of the memory cell. Detailed analysis of I-V characteristics further corroborated the formation of conductive nanofilaments based on metal-like (Ohmic) conduction in LRS. Simmons-Schottky emission was found to be the dominant charge transport mechanism in the high resistance state. [ABSTRACT FROM AUTHOR]

A systematic study on structural, microstructural, optical, dielectric, and electrical properties of phase-pure silicon-modified SrTiO3 polycrystalline electroceramics synthesized using high energy solid state reaction techniques is presented. The asymmetry and splitting in the x-ray diffractometer spectra and the observation of first order transverse optical TO2 and longitudinal optical LO4 modes in Raman spectra (nominally forbidden) revealed the distortion in the cubic lattice as a result of breaking of inversion symmetry due to doping. A bandgap Eg of 3.27?eV was determined for the sample by diffuse reflectance spectroscopy. A high dielectric constant of ~400 and very low dielectric loss of ~0.03 were obtained at 100?kHz near ambient conditions. The temperature dependence of the dielectric data displayed features of high temperature relaxor ferroelectric behavior as evidence of existence of polar nano-regions. The ac conductivity as a function of frequency showed features typical of universal dynamic response and obeyed a power law σac = σdc + Aσn . The temperature dependent dc conductivity followed an Arrhenius relation with activation energy of 123?meV in the 200-500?K temperature range. The linear dielectric response of Pt/SrSi0.03Ti0.97O3/Pt dielectric capacitors was well characterized. The measured leakage current was exceptionally low, 13?nA/cm2 at 8.7?kV/cm, revealing an interface blocked bulk conduction mechanism. [ABSTRACT FROM AUTHOR]

High-pressure synchrotron based angle dispersive x-ray diffraction (ADXRD) studies were carried out on SmGdO3 (SGO) up to 25.7 GPa at room temperature. ADXRD results indicated a reversible pressure-induced phase transition from ambient monoclinic to hexagonal phase at ∼8.9 GPa. The observed pressure-volume data were fitted with the third order Birch-Murnaghan equation of state yielding zero pressure bulk modulus Bo=132(22) and 177(9) GPa for monoclinic (B-type) and hexagonal (A-type) phases, respectively. Pressure dependent micro-Raman spectroscopy further confirmed the monoclinic to hexagonal phase transition at about 5.24 GPa. The mode Grüneisen parameters and pressure coefficients for different Raman modes corresponding to each individual phases of SGO were calculated using pressure dependent Raman mode analysis. [ABSTRACT FROM AUTHOR]

Amorphous YCrO3 (YCO) films were prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition in order to investigate resistive switching (RS) phenomenon. The Pt/YCO/Pt device showed stable unipolar RS with resistance ratio of ∼105 between low and high resistance states, excellent endurance and retention characteristics, as well as, non-overlapping switching voltages with narrow dispersions. Based on the x-ray photoelectron spectroscopy and temperature dependent switching characteristics, observed RS was mainly ascribed to the oxygen vacancies. Moreover, current-voltage characteristics of the device in low and high resistance states were described by Ohmic and trap controlled space-charge limited conduction mechanisms, respectively. [ABSTRACT FROM AUTHOR]

Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO3 over a temperature range of 20-300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Néel transition at TN∼142 K. Magnetization isotherms recorded at 125K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below TN. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near TN. An additional phonon anomaly was identified at T*∼60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between TN and T* suggest competing WFM and AFM interactions. A close match between the phonon frequency of B3g (3)-octahedral rotation mode with the square of sublattice magnetization between TN and T* is indicative of the presence of spin-phonon coupling in multiferroic YCrO3. [ABSTRACT FROM AUTHOR]

Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO3 over a temperature range of 20-300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Néel transition at TN∼142 K. Magnetization isotherms recorded at 125K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below TN. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near TN. An additional phonon anomaly was identified at T*∼60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between TN and T* suggest competing WFM and AFM interactions. A close match between the phonon frequency of B3g (3)-octahedral rotation mode with the square of sublattice magnetization between TN and T* is indicative of the presence of spin-phonon coupling in multiferroic YCrO3. [ABSTRACT FROM AUTHOR]

Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO3 over a temperature range of 20-300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Néel transition at TN~142 K. Magnetization isotherms recorded at 125K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below TN. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near TN. An additional phonon anomaly was identified at T* ~ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between TN and T* suggest competing WFM and AFM interactions. A close match between the phonon frequency of B3g (3)-octahedral rotation mode with the square of sublattice magnetization between TN and T* is indicative of the presence of spin-phonon coupling in multiferroic YCrO3. [ABSTRACT FROM AUTHOR]

Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO3 over a temperature range of 20-300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Néel transition at TN~142 K. Magnetization isotherms recorded at 125K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below TN. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near TN. An additional phonon anomaly was identified at T* ~ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between TN and T* suggest competing WFM and AFM interactions. A close match between the phonon frequency of B3g (3)-octahedral rotation mode with the square of sublattice magnetization between TN and T* is indicative of the presence of spin-phonon coupling in multiferroic YCrO3. [ABSTRACT FROM AUTHOR]

A study was conducted to investigate the influence of adding nitrogen to a high methane plasma concentration for the chemical vapor deposition of diamond films. The plasma has a high Ch4 fraction of 15% (in hydrogen) and an operating chamber pressure of 125 Torr. Film roughness, crystallinity, fracture toughness, micro-Raman spectral features and film microstructure were correlated with nitrogen concentrations in the plasma. Results are presented.

Research was conducted to describe the static pressure compression of cerium metal to 208 GPa in a diamond anvil cell at room temperature. A synchrotron x-ray source and an internal copper pressure standard were used in the energy-dispersive x-ray diffraction analyses of cerium metal to 208 GPa. Results indicate that cerium is isoelectronic and isostructural with 5 f-band metal thorium at ultrapressures.

Optical activity and cross polarization conversion (CPC) of a rotated-arm-square chiral metamaterial (CMM) is reported in this work. Proposed CMM shows strong chirality owing to the cross coupling between the induced magnetic field and incident electric field of the applied electromagnetic wave. Mechanism of CPC functionality is explained based on the surface current distribution of CMM structure. Microwave experiment is performed to reveal the CPC utility of the proposed CMM. Among various designs on the CPC converters, possibility of near 99% efficiency is revealed in the proposed CMM. [ABSTRACT FROM AUTHOR]

A study was conducted to characterize the preparation of nanostructured diamond films on Ti-6Al-4V alloy and on molybdenum utilizing a high density CH4/H2 plasma process. Experimental Results indicated that a high density plasma process for microwave plasma-assisted chemical vapor deposition supported the deposition of adhered nanostructured diamond films on Ti-6Al-4V alloy and molybdenum substrates.