Neuromorphic devices with extremely low energy consumption are greatly demanded for brain-like computing and artificial intelligence (AI). In this work, the ZnO-NiO nanocomposite as an active layer used to create artificial synaptic memristor devices with memory functions, including high ON/OFF ratios, stable and filamentary resistive switching behavior, long-term/short-term plasticity (LTP/STP), and learning-experience response. These qualities closely resemble biological learning and memory activities. Controlled production and rupture of Ag filaments result in resistive switching with a switching ratio of ∼103, making them ideal for nonvolatile memory demands. Before electroforming, the progressive conductance modulation of a Ag/ZnO/NiO/Pt/Ti/SiO2 memristor may be observed, and the working mechanism described by the subsequent development and contraction of Ag filaments induced by a redox reaction. Furthermore, the nanocomposite memristors demonstrated an exponential decay curve with a 2.26 μs decay time constant and an artificial neural network (ANN) with outstanding identification accuracy of 90.7% for handwritten digits. This work suggests that the proposed memristors (with a stable and mutifuntional responses) might enable efficient neuromorphic designs.

The development of high-performance electrostatic energy storage dielectrics is essential for various applications such as pulsed-power technologies, electric vehicles (EVs), electronic devices, and the high-temperature aviation sector. However, the usage of lead as a crucial component in conventional high-performance dielectric materials has raised severe environmental concerns. As a result of this, there is an urgent need to explore lead-free alternatives. Ferroelectric ceramics offer high energy density but lack stability at high temperatures. Here we present a lead-free (1 - x)BiFeO3-xCaTiO3 (x = 0.6, 0.7, and 0.8; BFO-CTO) ceramic capacitor with low dielectric loss, high thermal stability, and high energy density up to ∼200 °C. The introduction of CTO (x = 0.7) to the BFO matrix triggers a transition from the normal ferroelectrics to the relaxor ferroelectrics state, resulting in a high recoverable energy density of 1.18 J cm-3 at 190 °C with an ultrafast dielectric relaxation time of 44 μs. These results offer a promising, environmentally friendly, high-capacity ceramic capacitor material for high-frequency and high-temperature applications.

This research article focuses on analyzing the behavior of high-temperature dielectric relaxation and electric conduction mechanisms in Bi1-xNdxFeO3 (BNFO) samples, where the value of x varies as 0, 0.10, 0.15, and 0.2. The study’s findings indicate that all these samples exhibit two distinct dielectric transitions. The first transition occurs at a lower temperature (Ts), typically in the range of 425 to 450 K, and is characterized by a frequency-dependent shoulder. This transition is associated with the presence of polar nanoregions (PNRs). The second transition takes place within a temperature range of approximately 580 to 650 K, marking the transition from a ferroelectric to a paraelectric state at the Curie temperature (TC). Furthermore, impedance analysis of the specimens reveals a negative temperature coefficient of resistance, indicating a wide range of relaxation behavior that does not conform to the Debye-type model. Additionally, the study of conductivity provides valuable insights into the transport phenomena observed in these samples. The obtained energy storage properties of these bulk ceramics are quite significant compared to the similar systems reported in the literature.

Novel dielectrics with electrostatic energy storage capabilities attracted significant attention in recent years for high-energy storage applications due to their high-power density. The structural, electrical, and dielectric properties play a pivotal role in attaining high power densities in dielectric ceramics. Here, the authors presented the influence of CaTiO3 on the structural, electrical, and dielectric properties of BiFeO3-CaTiO3 (BFO-CTO) lead-free ceramics. (BFO)(1−x)–(CTO)x (x = 0, 0.1, 0.3, and 0.5 and 1) ceramics were fabricated from calcined powders of BFO and CTO using the microwave sintering technique. Due to the partial substitution of Ca2+ and Ti4+ into the A and B sites (of Bi3+ and Fe3+, respectively) structural phase transformation occurred from rhombohedral to orthorhombic crystal structure for x ≥ 0.3. As the CTO concentration is increased, the resistivity of BFO-CTO samples is enhanced by two orders of magnitude, from 2.21 × 103 Ω cm (x = 0) to 8.80 × 105 Ω cm (x = 0.5). The leakage current density was reduced by two orders of magnitude, from ~ 2.60 × 10–1 A cm−2 (x = 0) to ~ 2.50 × 10–3 A cm−2 (x = 0.5). The improved resistivity, reduced leakage current and enhanced dielectric properties make lead-free BFO-CTO dielectrics as an excellent alternative to existing energy storage systems.

Antiferromagnetic insulators are a ubiquitous class of magnetic materials, holding the promise of low-dissipation spin-based computing devices that can display ultra-fast switching and are robust against stray fields. However, their imperviousness to magnetic fields also makes them difficult to control in a reversible and scalable manner. Here we demonstrate a novel proof-of-principle ionic approach to control the spin reorientation (Morin) transition reversibly in the common antiferromagnetic insulator α-Fe2O3 (haematite) – now an emerging spintronic material that hosts topological antiferromagnetic spin-textures and long magnon-diffusion lengths. We use a low-temperature catalytic-spillover process involving the post-growth incorporation or removal of hydrogen from α-Fe2O3 thin films. Hydrogenation drives pronounced changes in its magnetic anisotropy, Néel vector orientation and canted magnetism via electron injection and local distortions. We explain these effects with a detailed magnetic anisotropy model and first-principles calculations. Tailoring our work for future applications, we demonstrate reversible control of the room-temperature spin-state by doping/expelling hydrogen in Rh-substituted α-Fe2O3.

Reduced graphene oxide (rGO) has attracted significant interest in an array of applications ranging from flexible optoelectronics, energy storage, sensing, and very recently as membranes for water purification. Many of these applications require a reproducible, scalable process for the growth of large-area films of high optical and electronic quality. In this work, we report a one-step scalable method for the growth of reduced-graphene-oxide-like (rGO-like) thin films via pulsed laser deposition (PLD) of sp2 carbon in an oxidizing environment. By deploying an appropriate laser beam scanning technique, we are able to deposit wafer-scale uniform rGO-like thin films with ultrasmooth surfaces (roughness <1 nm). Further, in situ control of the growth environment during the PLD process allows us to tailor its hybrid sp2-sp3 electronic structure. This enables us to control its intrinsic optoelectronic properties and helps us achieve some of the lowest extinction coefficients and refractive index values (0.358 and 1.715, respectively, at 2.236 eV) as compared to chemically grown rGO films. Additionally, the transparency and conductivity metrics of our PLD grown thin films are superior to other p-type rGO films and conducting oxides. Unlike chemical methods, our growth technique is devoid of catalysts and is carried out at lower process temperatures. This would enable the integration of these thin films with a wide range of material heterostructures via direct growth.

Understanding the interaction of water molecules with the surfaces of different materials has become an important field of research. A large body of theoretical and experimental research work has been dedicated to understanding how interfacial water interacts with the surface structure/chemistry of materials. The underlying mechanism on which many applications are based is, in fact, the interaction of materials with liquids. This necessitates further investigations on wetting dynamics of materials. Motivated by the gaps in the knowledge in this domain, we have performed a systematic study of water contact angle and surface free energy determination on less explored oxide thin-films and two-dimensional (2D) van der Waals structures ranging from exotic rare-earth oxides (REOs) to graphene, MoS2, WS2 and their hetero-structures. Besides these macroscale measurements, we also show an atomic scale approach to locally probe the wetting properties of materials.

Oxide multilayer hetero-structure of BaFeO3-KTa0.47Nb0.53O3 have been grown using the pulsed laser deposition and the ex situ annealed in a flowing oxygen atmosphere. The multilayer has been characterized using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Magnetic properties have been studied via SQUID measurements. Magnetization in the multilayer structure shows significant improvement compared to previous measurements of bare BaFeO3. Measuring magnetization as a function of temperature and fitting the resulting M–T curves to Bloch's 3/2 law, yields an estimated Curie temperature (TC) of around 425 K and a P factor of around 1.5, consistent with magnetization from a three dimensional crystal structure. In spite of using a room temperature ferroelectric KTa0.47Nb0.53O3 composition, no evidence of ferroelectricity was observed in multi-layer structure.

High quality epitaxial Ba2FeMoO6 thin films and Ba2FeMoO6-(BaxSr1-x)TiO3 bi-layer (BL) and superlattice (SL) structures were grown via pulsed laser deposition under low oxygen pressure, and their structural, magnetic, and magneto-transport properties were examined. Superlattice and bi-layer structures were confirmed by X-ray diffraction patterns. Low temperature magnetic measurement shows that the saturation magnetization (MS) is significantly higher for SLs and almost similar or lower for BLs, when compared to phase pure Ba2FeMoO6 thin films. The variation of the coercive field (HC) follows exact opposite trend, where BL samples have higher HC and SL samples have lower HC than pure Ba2FeMoO6 thin films. Also, a significant decrease of the Curie temperature is found in both BL and SL structures compared to pure Ba2FeMoO6 thin films. Negative magneto-resistance is seen in all the BL and SL structures as well as in pure Ba2FeMoO6 thin films. In contrast to the magnetic properties, the magneto-transport properties do not show much variation with induced strain.

Superlattice (SL) structures of Ba2FeMoO6/Ba0.5Sr0.5TiO3 were grown via pulsed laser deposition on high quality ultra-smooth SrTiO3 substrates. N number of ferroelectric Ba0.5Sr0.5TiO3 layers were grown on five layers of ferromagnetic Ba2FeMoO6 and their structural, magnetic, transport, and magneto-transport properties were examined, focusing on the effects of superlattice periodicity of Ba0.5Sr0.5TiO3 layers. XRD analysis of SLs proved their layered superlattice structure. Magnetic study of the SLs showed increment of saturation magnetization and decrease of Curie temperature when compared to magnetization of pure Ba2FeMoO6 thin film. Magneto-transport measurement showed the presence of negative magneto-resistance in all superlattice samples, similar to magneto-transport behavior of pure Ba2FeMoO6 thin film. Hall measurement and transport study showed a consistent increment of anomalous Hall effect and temperature dependent conductivity, respectively, with the number of Ba0.5Sr0.5TiO3 layers.

In this manuscript, we demonstrate a method based on atomic force microscopy which enables local probing of surface wettability. The maximum pull-off force, obtained from force spectroscopy shows a remarkable correlation with the macroscopically observed water contact angle, measured over a wide variety of surfaces starting from hydrophilic, all the way through to hydrophobic ones. This relationship, consequently, facilitates the establishment of a universal behaviour. The adhesion forces scale with the polar component of surface energy. However, no such relation could be established with the dispersive component. Hence, we postulate that the force(s) which enable us to correlate the force spectroscopy data measured on the nanoscale to the macroscopic contact angle are primarily arising from electrostatic-dipole-dipole interactions at the solid-liquid interface. London forces play less of a role. This effect in is line with density functional theory (DFT) calculations suggesting a higher degree of hydroxylation of hydrophilic surfaces. This result shows that molecular simulations and measurements on an atomic scale can be extrapolated to macroscopic surface wetting problems.

Epitaxial Ba2FeMoO6 thin films were grown via pulsed laser deposition under low oxygen pressure and their structural, chemical, and magnetic properties were examined, focusing on the effects of oxygen pressure. The chemical disorder, off-stoichiometry in B site cations (Fe and Mo) increased with increasing oxygen pressure and thus magnetic properties were degraded. Interestingly, in contrast, negative magneto-resistance, which is the characteristics of this double perovskite material, was enhanced with increasing oxygen pressure. It is believed that phase segregation of highly disordered thin films is responsible for the increased magneto-resistance of thin films grown at high oxygen pressure. The anomalous Hall effect, which behaves hole-like, was also observed due to spin-polarized itinerant electrons under low magnetic field below 1T and the ordinary electron-like Hall effect was dominant at higher magnetic fields.

We provide experimental evidence for the existence of ferromagnetism in bilayers of Pd/C60 which is supported by theoretical calculations based on density functional theory (DFT). The observed ferromagnetism is surprising as C60 and Pd films are both non-ferromagnetic in the non-interacting limit. Magnetization (M) versus applied field (H) data acquired at different temperatures (T) show magnetic hysteresis with typical coercive fields (Hc) on the order of 50 Oe. From the temperature-dependent magnetization M(T) we extract a Curie temperature (TC≥550K) using Bloch-like power law extrapolations to high temperatures. Using DFT calculations we investigated all plausible scenarios for the interaction between the C 60 molecules and the Pd slabs, Pd single atoms and Pd clusters. DFT shows that while the C60 molecules are nonmagnetic, Pd films have a degenerate ground state that, subject to a weak perturbation, can become ferromagnetic. Calculations also show that the interaction of C60 molecules with excess Pd atoms and with sharp edges of a Pd slab is the most likely configuration that render the system ferromagnetic. Interestingly, the calculated charge transfer (0.016 e per surface Pd atom, 0.064 e per Pd for intimate contact region) between C60 and Pd does not appear to play an important role. © 2013 Elsevier B.V.

Temperature-dependent transport measurements on ultrathin antiferromagnetic Mn films reveal a heretofore unknown nonuniversal weak-localization correction to the conductivity which extends to disorder strengths greater than 100kΩ per square. The inelastic scattering of electrons off of gapped antiferromagnetic spin waves gives rise to an inelastic scattering length which is short enough to place the system in the three-dimensional regime. The extracted fitting parameters provide estimates of the energy gap (Δ≈16K) and Heisenberg exchange constant (J≈1000K).

A facile synthesis of 3-6 nm, water dispersible, near-infrared (NIR) emitting, quantum dots (QDs) magnetically doped with Fe is presented. Doping of alloyed CdTeS nanocrystals with Fe was achieved in situ using a simple hydrothermal method. The magnetic quantum dots (MQDs) were capped with N-acetyl-cysteine (NAC) ligands, containing thiol and carboxylic acid functional groups to provide stable aqueous dispersion. The optical and magnetic properties of the Fe doped MQDs were characterized using several techniques. The synthesized MQDs are tuned to emit in the vis-NIR (530-738 nm) wavelength regime and have high quantum yields (67.5-10%). NIR emitting (738 nm) MQDs having 5.6 atomic% Fe content exhibited saturation magnetization of 85 emu per g [Fe] at room temperature. Proton transverse relaxivity of the Fe doped MQDs (738 nm) at 4.7 T was determined to be 3.6 mM^-1 s^-1. The functional evaluation of NIR MQDs has been demonstrated using phantom and in vitro studies. These water dispersible, NIR emitting and MR contrast producing Fe doped CdTeS MQDs, in an unagglomerated form, have the potential to act as multimodal contrast agents for tracking live cells. © The Royal Society of Chemistry.

Epitaxial ruthenium dioxide (Ru O2) chromium dioxide (Cr O2) thin film heterostructures have been grown on (100) -TiO2 substrates by chemical vapor deposition. Both current-in-plane (CIP) and current-perpendicular-to-plane (CPP) giant magnetoresistive stacks were fabricated with either Co or another epitaxial Cr O2 layer as the top electrode. The Cr2 O3 barrier, which forms naturally on Cr O2 surfaces, is no longer present after the Ru O2 deposition, resulting in a highly conductive interface that has a resistance at least four orders of magnitude lower. However, only very limited magnetoresistance (MR) was observed. Such low MR is due to the appearance of a chemically and magnetically disordered layer at the Cr O2 and Ru O2 interfaces when Cr2 O3 is transformed into rutile structures during its intermixing with Ru O2. © 2005 American Institute of Physics.

Highly strained semiconductors grow epitaxially on mismatched substrates in the Stranski-Krastanow growth mode, wherein islands are formed after a few monolayers of layer-by-layer growth. Elastic relaxation on the facet edges, renormalization of the surface energy of the facets, and interaction between neighboring islands via the substrate are the driving forces for self-organized growth. The dimensions of the defect-free islands are of the order B, the de Broglie wavelength, and provide three-dimensional quantum confinement of carriers. Self-organized In(Ga)As/GaAs quantum dots, or quantum boxes, are grown bMEy molecular beam expitaxy (MBE) or metal-organic vapor phase epitaxy (MOVPE) on GaAs, InP, and other substrates and are being incorporated in microelectronic and opto-electronic devices. The use of strain to produce self-organized quantum dots has now become a well-accepted approach and is widely used in III-V semiconductors and other material systems. Much progress has been made in the area of growth, where focus has been on size control, and on optical characterization, where the goal has been the application to lasers and detectors. The unique carrier dynamics in the dots, characterized by femtosecond pump-probe spectroscopy, has led to novel device applications. This article reviews the growth and electronic properties of InGaAs quantum dots and the characteristics of interband and intersublevel lasers and detectors and modulation devices.

We studied a bilayer system consisting of a two-dimensional electron gas in a GaAs/AlGaAs heterostructure and a thin superconducting Al film. Drag measurements were made by passing current through the two-dimensional electron gas layer and measuring the voltage induced in the superconducting layer. Unexplained peaks in drag voltage near the transition region were seen in previous similar experiments. We also detected a draglike voltage peak in the transition region. The signal is found to be nonintrinsic and due to radio frequency interference. The extremely nonlinear impedance of the Al in the transition region allows the interference to couple in this manner. We show a simplified analysis of the measurement system that reproduces the main features of our results.

A study was performed on tunnel injection quantum dot lasers. The small-signal modulation characteristics of quantum dot lasers wherein electrons were injected into quantum dots by phonon assisted tunelling was reported. It was found that tunneling is a viable option for injecting electrons in quantum dot lasers.

We report experimental studies of temperature-dependent Auger recombination coefficients in self-assembled quantum dots. The results are based on a study of temperature-dependent large signal modulation experiments made on self-organized In0.4Ga0.6As/GaAs quantum dot lasers. The Auger coefficient decreases from ∼ 8 × 10-29 cm6/s at 100 K to ∼ 4 × 10-29 cm6/s at 300 K. This behavior, which is different from results in other higher-dimensional systems, is explained in terms of the temperature dependence of electron-hole scattering in the dots and contribution from higher lying states in the dot and adjoining layers. © 2001 American Institute of Physics.