Reversible phase transformation of correlated oxides by field‐driven ionic process present opportunity to efficiently transduce between ionic transfer and electrical currents in insertion‐based ...reconfigurable transistors. However, the switching rate of insertion transistors is fundamentally limited by the slow rate of ionic insertion into the lattices of correlated oxides. Here, it is demonstrated that preformed oxygen vacancies in VO2−δ lattices strongly accelerate proton insertion by low gate voltage in synaptic transistors. As the degree of oxygen deficiency δ increases in VO2−δ transistors, the steepness of phase transformation and transconductance increase during the voltage sweep at the expense of the channel current modulation. Theoretical and experimental analyses reveal that the accelerated of H+ kinetics in the VO2−δ lattice occurs because immobile oxygen vacancies reduce the energy barrier to H+ migration. In an electronic synapse, this facile H+ migration in VO2−δ lattices renders “inscribed” memory by positioning the H+ neurotransmitter far from the electrolyte/VO2−δ interface. This discovery suggests a strategy to improve the learning and memory processes of artificial synaptic devices by controlling the density of intrinsic defects in the lattice framework to achieve efficient ion exchange.
The switching rate of insertion transistors is limited by the slow rate of ionic insertion into a channel layer. Here, it is demonstrated that preformed oxygen vacancies in VO2−δ lattices accelerate proton insertion by gate voltage in synaptic transistors. It suggests a strategy to improve the memory processes of artificial synapses by controlling the density of defects in the lattice framework.
Abstract
Spinodal decomposition, the spontaneous phase separation process of periodic lamellae at the nanometer scale, of correlated oxide ((Ti, V)O
2
) systems offers a sophisticated route to ...achieve a new class of mesoscale structures in the form of self-assembled superlattices for possible applications using steep metal–insulator transitions. Here, we achieve the tunable self-assembly of (Ti, V)O
2
superlattices with steep transitions (Δ
T
MI
< 5 K) by spinodal decomposition with accurate control of the growth parameters without conventional layer-by-layer growth. Abrupt compositional modulation with alternating Ti-rich and V-rich layers spontaneously occurs along the growth direction because in-plane lattice mismatch is smaller in this direction than in other directions. An increase in the film growth rate thickens periodic alternating lamellae; the phase separation can be kinetically enhanced by adatom impingement during two-dimensional growth, demonstrating that the interplay between mass transport and uphill diffusion yields highly periodic (Ti, V)O
2
superlattices with tunable lamellar periods. Our results for creating correlated (Ti, V)O
2
oxide superlattices provide a new bottom-up strategy to design rutile oxide tunable nanostructures and present opportunities to design new material platforms for electronic and photonic applications with correlated oxide systems.
The perfect (111)-oriented CoFe2O4 thin films were grown on Pt(111)/Si substrate by pulsed laser deposition technique at substrate temperature of 600°C. The optimum oxygen pressure was found to be ...10mTorr based on structural and magnetic properties. The film grown at 10mTorr has the highest (111)-orientation degree and magnetization. The films are under in-plane tensile stress due to the residual thermal strain which is thickness-dependent. It was found that the (111)-oriented CoFe2O4 thin film demonstrates the strong in-plane magnetic anisotropy which results from orientation as well as the stress-induced magnetic anisotropy.
•The perfect (111)-oriented CoFe2O4 thin film was achieved on Pt(111)/Si by PLD technique.•(111)-oriented CoFe2O4 films were obtained at high temperature and at various thicknesses.•CoFe2O4 thin film grown at 10mTorr has the highest (111)-orientation degree and magnetization.•The (111)-oriented CoFe2O4 thin film demonstrates the strong in-plane magnetic anisotropy.
Designing energy-efficient artificial synapses with adaptive and programmable electronic signals is essential to effectively mimic synaptic functions for brain-inspired computing systems. Here, we ...report all-solid-state three-terminal artificial synapses that exploit proton-doped metal–insulator transition in a correlated oxide NdNiO3 (NNO) channel by proton (H+) injection/extraction in response to gate voltage. Gate voltage reversibly controls the H+ concentration in the NNO channel with facile H+ transport from a H+-containing porous silica electrolyte. Gate-induced H+ intercalation in the NNO gives rise to nonvolatile multilevel analogue states due to H+-induced conductance modulation, accompanied by significant modulation of the out-of-plane lattice parameters. This correlated transistor operated by a proton pump shows synaptic characteristics such as long-term potentiation and depression, with nonvolatile and distinct multilevel conductance switching by a low voltage pulse (≥ 50 mV), with high energy efficiency (∼1 pJ) and tolerance to heat (≤150 °C). These results will guide the development of scalable, thermally-stable solid-state electronic synapses that operate at low voltage.
We propose the novel strategy for indirect-to-direct band gap transition of gallium oxide-based semiconductors for ultraviolet lighting device through first-principles calculations using a screened ...hybrid functional. Our calculations show that the tuning of electronic band gap of α-Ga2O3 is straightforward by adding dopants, which mimics alloy-like system. In order to put the band gap in the energy range of ultraviolet light, Group-III (In, Tl) at the Ga site and Group-V (N, P) or Group-VI (S, Se) at the O site are examined. We find that the most of doped Ga2O3 possess direct or nearly direct band gaps lying in the ultraviolet energy that is essential for optoelectronic devices.
•Ga2O3-based systems for ultraviolet optoelectronic applications is proposed through first-principles calculations.•Bandgap can be tuned to cover the energy of deep ultraviolet and ultraviolet light.•High content of cation and anion dopant leads to indirect-to-direct bandgap transition.
We report on tunneling measurements that reveal the evolution of the quasiparticle state density in two rare earth perovskite nickelates, NdNiO{sub 3} and LaNiO{sub 3}, that are close to a bandwidth ...controlled metal to insulator transition. We measure the opening of a sharp gap of ∼30 meV in NdNiO{sub 3} in its insulating ground state. LaNiO{sub 3}, which remains a correlated metal at all practical temperatures, exhibits a pseudogap of the same order. The results point to both types of gaps arising from a common origin, namely, a quantum critical point associated with the T = 0 K metal-insulator transition. The results support theoretical models of the quantum phase transition in terms of spin and charge instabilities of an itinerant Fermi surface.
The perfect (111)-oriented Co0.8Fe2.2O4 thin films are grown on Pt(111)/Si substrate using pulsed laser deposition technique at substrate temperature of 600°C and laser pulse rate of 5 and 10Hz. The ...Fe K-edge X-ray absorption near edge structure analyses revealed that Fe in Co0.8Fe2.2O4 films deposited at both 5 and 10Hz exists in Fe3+ state leading to the actual composition of Co0.8Fe2.2O4+δ. In order to study the effect of film thickness on the magnetic properties, the film thickness was increased by increase in the pulse rate as well as the time of deposition during pulsed laser deposition process. It was found that by increase of the film thickness, the saturation magnetization and squareness will be generally increased. In the films with same thickness, those which deposited at higher pulse rate have a higher coercivity. In the films deposited at same pulse rate (10Hz) and different time of deposition, the saturation magnetization, coercivity, and squareness were increased by increasing the thickness, but the coercivity will be decreased with further increasing the thickness due to the relaxation of residual stresses.
•The film deposited at higher pulse rate has a higher coercivity.•The thinner films (less than 75nm thick) showed a constricted magnetization curve.•The coercivity as well as squareness increased by increasing the thickness.•By further increasing the thickness, the coercivity decreased.
Hydrogen, the smallest and the lightest atomic element, is reversibly incorporated into interstitial sites in vanadium dioxide (VO2), a correlated oxide with a 3d(1) electronic configuration, and ...induces electronic phase modulation. It is widely reported that low hydrogen concentrations stabilize the metallic phase, but the understanding of hydrogen in the high doping regime is limited. Here, we demonstrate that as many as two hydrogen atoms can be incorporated into each VO2 unit cell, and that hydrogen is reversibly absorbed into, and released from, VO2 without destroying its lattice framework. This hydrogenation process allows us to elucidate electronic phase modulation of vanadium oxyhydride, demonstrating two-step insulator (VO2)-metal (HxVO2)-insulator (HVO2) phase modulation during inter-integer d-band filling. Our finding suggests the possibility of reversible and dynamic control of topotactic phase modulation in VO2 and opens up the potential application in proton-based Mottronics and novel hydrogen storage.
Bi(III)‐based oxides are emerging as important semiconductors for future electronic applications. Through hybrid density functional theory calculations and defect analysis, we demonstrate that ...ABi(III)O2 (A = Na or K) is a promising wide‐band‐gap bipolar semiconductor. Our calculations predict ABiO2 to have a large band gap of 1.97 eV for NaBiO2 and 2.77 eV for KBiO2. Unlike widely‐used oxide semiconductors such as In2O3 and ZnO, the spatially extended cation states (Bi 6s) of ABiO2 significantly contribute to the valence band maximum, enhancing p‐type dopability. We indeed show that potential acceptors, such as SrBi, produce shallow levels. In addition, n‐type doping is found to be possible through the extrinsic doping of heterovalent elements such as Te and F. The band‐structure analysis reveals that ABiO2 has small effective masses for electrons and holes (< 1m0 where m0 is the electron rest mass), indicating favorable electron and hole transport properties.
Abstract Bi(III)‐based oxides are emerging as important semiconductors for future electronic applications. Through hybrid density functional theory calculations and defect analysis, we demonstrate ...that A Bi(III)O 2 ( A = Na or K) is a promising wide‐band‐gap bipolar semiconductor. Our calculations predict A BiO 2 to have a large band gap of 1.97 eV for NaBiO 2 and 2.77 eV for KBiO 2 . Unlike widely‐used oxide semiconductors such as In 2 O 3 and ZnO, the spatially extended cation states (Bi 6s) of A BiO 2 significantly contribute to the valence band maximum, enhancing p‐type dopability. We indeed show that potential acceptors, such as Sr Bi , produce shallow levels. In addition, n‐type doping is found to be possible through the extrinsic doping of heterovalent elements such as Te and F. The band‐structure analysis reveals that A BiO 2 has small effective masses for electrons and holes (< 1 m 0 where m 0 is the electron rest mass), indicating favorable electron and hole transport properties.
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