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\nImpact of StatementAs miniaturization of semiconductor memory devices is reaching its physical and technological limits, there is a demand for memory technologies that operate on new principles. Atomic switches are nanoionic devices that show repeatable resistive switching between high-resistance and low-resistance states under bias voltage applications, based on the transport of metal ions and redox reactions in solids. Their essential structure consists of an ion conductor sandwiched between electrochemically active and inert electrodes. This review focuses on the resistive switching mechanism of atomic switches that utilize a solid polymer electrolyte (SPE) as the ion conductor. Owing to the superior properties of polymer materials such as mechanical flexibility, compatibility with various substrates, and low fabrication costs, SPE-based atomic switches are a promising candidate for the next-generation of volatile and nonvolatile memories. Herein, we describe their operating mechanisms and key factors for controlling the device performance with different polymer matrices. In particular, the effects of moisture absorption in the polymer matrix on the resistive switching behavior are addressed in detail. As potential applications, atomic switches with inkjet-printed SPE and quantum conductance behavior are described. SPE-based atomic switches also have great potential in use for neuromorphic devices. The development of these devices will be enhanced using nanoarchitectonics concepts, which integrates functional materials and devices.This article reviews a series of works starting with the author’s 2011 paper on solid polymer electrolyte-based atomic switches, and describes the current status and future prospects for this technology. [ABSTRACT FROM AUTHOR]

The process dependence of the mixed ionic-electronic conductivity of sintered octadecylamine-encapsulated silver sulfide nanoparticle thin films has been studied and correlated with the film structure. Although grain growth begins around 120 °C, there is no significant electrical conductivity until 350 °C and mixed conductivity until 400 °C, when the nanoparticle encapsulant evaporates. Higher temperatures decompose the silver sulfide. In lateral structures, no filaments form until sintering at 400 °C. The process dependence of mixed ionic electronic conducting properties may provide a method for engineering materials for use in electrochemical metallization resistive random access memories. [ABSTRACT FROM AUTHOR]

Silver-iodide (AgI)-based superionic conductors are attracting widespread interest for their potential applications in electrochemical devices such as sensors and batteries. A new kind of nanocomposite with highly ordered AgI nanowires embedded in an anodic-aluminum-oxide (AAO) membrane was fabricated by low-temperature step-electrochemical growth. Structural evolution, phase transition, and ionic conductivity were investigated by x-ray diffraction, differential scanning calorimetry, and impedance measurements. The phase transition from β/γ-AgI phase to α-AgI phase occurred at temperature of 168 °C, that is, higher than that of reported bulk AgI (147 °C); abnormally, the α to β/γ phase-transition temperature on cooling was also depressed as large hysteresis formed. The high-temperature phase, namely, α-AgI, remained at temperatures as low as 80 °C. The initial highly oriented-growth AgI nanowire disappeared after undergoing heating and cooling processes and a mixture of polycrystalline β/γ-AgI and amorphouslike interface phases formed. The cooled AgI-AAO composite displayed ionic conductivity in the order of 10-2 S cm-1 at room temperature. This array-structured nanocomposite of AgI-AAO may be further developed for usage as a new type of battery, i.e., “nanobatteries” and “nanosensors” with individual AgI nanowires as basic elements. [ABSTRACT FROM AUTHOR]

We examined the structural and electrical properties of silver sulfide films as a function of the sulfurization time of 70-nm-thick Ag films. Variations in the sulfurization time caused variations in the Ag/S atomic percentage ratio of the silver sulfide films, and as-grown films with various compositions, such as S-rich (Ag/S=1.59), stoichiometric (Ag/S=2), and Ag-rich (Ag/S=2.16) films were formed. Amongst the various as-grown films, Ag ions existed in the most polarizable environment in the Ag-rich films. All the films existed in the acanthite α-phase, and the sulfurization conditions did not cause any drastic change in the preferred orientation of this phase. The resistivity of these films strongly depended on the Ag/S ratio. While the resistivity of stoichiometric or S-rich films was about 107–108 Ω cm, excess Ag of the Ag-rich film caused a decrease in the resistivity by four orders of magnitude. The Ag/S ratio also played a significant role in our observation of the change in resistance within the films from high- to low-resistance state and vice versa with the reversal of the bias polarity of the film. Distinct switching of the resistance was observed only for the Ag-rich film. We also examined the effects of post-deposition annealing (PDA) of various films at 190 °C. PDA caused the formation of Ag-rich films (Ag/S=2.12–2.17) in all cases, and Ag ions existed in a more polarizable environment in all the films as compared with stoichiometric film. All the annealed films contained mixed acanthite α-phase and argentite β-phase. Furthermore, all the films had low resistivities of about 0.01–0.02 Ω cm, which indicated that the coexisting metallic argentite β-phase of the films significantly improved the conductivity of the films as compared to the as-grown film with similar Ag/S ratio. Clear switching behavior of the resistance could be observed within all the annealed films, thereby indicating that excess Ag in the silver sulfide films is a requirement for observation of such a phenomenon. [ABSTRACT FROM AUTHOR]

The chemical etching properties of ferroelectric LiTaO3 crystal in near-stoichiometric compositions were quantitatively investigated with various ratios of HF and HNO3 acid mixtures by scanning force microscopy in the nanoscale range. Along with congruent LiTaO3 crystal, the -Z surfaces of near-stoichiometric LiTaO3 crystal were etched preferentially with pure HF acid and mixtures of HF and HNO3 acids. The etching rates on the -Z surface of near-stoichiometric LiTaO3 crystal were slower than that of congruent LiTaO3 crystal. The roughness (peak to peak) of etched surfaces were about 2 nm after being etched in all ratios of HF and HNO3 acids to a 70-nm etch depth. The temperature dependence of the etch rate followed the Arrhenius law. By taking advantage of the chemical preferential etching properties, precision surface structures could be fabricated on near-stoichiometric LiTaO3 crystal. [ABSTRACT FROM AUTHOR]

Domain patterning thin ferroelectric films creates nonlinear optical devices. Unfortunately, pinholes cause conventional electrical domain-poling methods to short circuit when used on thin film. We have applied a focused ion beam (FIB) to pattern the ferroelectric domains of LiNbO3 single crystalline films with thicknesses of 800 nm–2 μm. FIB can fabricate domains 100 times faster than a scanning probe microscope and can be applied to irregular surface structures. Furthermore, FIB is compatible with semiconductor device processing techniques, which paves the way for monolithic nonlinear photonic integrated circuits in ferroelectrics. [ABSTRACT FROM AUTHOR]

Abstract: Theoretical impedance relationships in a limiting process with non-steady-state surface diffusion were derived based on the interfacial conductivity concept at the interface between an oxygen ion conductor and a metallic electrode. While the non-steady-state surface diffusion of adsorbed neutral oxygen on the metallic electrode could be described by Fick's second law, approximated and equivalent equations to the Warburg impedance and Gerischer impedance were derived according to the boundary conditions and occurrence of dissipation by the chemical reaction. The diffusion related to the electrochemical impedance signal is not the diffusion of the oxygen ions. In addition, it is not necessary to assume an electrochemical potential gradient or profile of the free electrons in the metallic electrode. The relationships obtained in this paper indicate that electrochemical potential measured by an instrument is clearly defined by the electrochemical potential of free electrons at the triple phase boundary. The meaning of the equivalent electrical circuits corresponding to the impedance spectra is reconsidered from the view points of the interfacial conductivity concept. [Copyright &y& Elsevier]

A compact neuromorphic nanodevice with inherent learning and memory properties emulating those of biological synapses is the key to developing artificial neural networks rivaling their biological counterparts. Experimental results showed that memorization with a wide time scale from volatile to permanent can be achieved in a WO3−x-based nanoionics device and can be precisely and cumulatively controlled by adjusting the device’s resistance state and input pulse parameters such as the amplitude, interval, and number. This control is analogous to biological synaptic plasticity including short-term plasticity, long-term potentiation, transition from short-term memory to long-term memory, forgetting processes for short- and long-term memory, learning speed, and learning history. A compact WO3−x-based nanoionics device with a simple stacked layer structure should thus be a promising candidate for use as an inorganic synapse in artificial neural networks due to its striking resemblance to the biological synapse. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the effect of subgrain boundaries on periodic domain-inverted structures with a period of ∼30μm in near-stoichiometric LiTaO3 (SLT) crystals and found that they negligibly affected the structures. Using SLT crystals having subgrain boundaries and a quasi-phase matching technique, we fabricated a 2-mm-thick, 60-mm-long periodically poled SLT frequency converter with a domain-inverted structure with a 30.5-μm period and demonstrated optical parametric oscillation. [Copyright &y& Elsevier]

Abstract: The development of nanometer-scale devices operating under a new principle that could overcome the limitations of current semiconductor devices has attracted interest in recent years. We propose that nanoionic devices that operate by controlling the local transport of ions are promising in this regard. It is possible to control the local transport of ions using the solid electrochemical properties of ionic and electronic mixed conductors. As an example of this concept, here, we report a method of controlling the transport of silver ions of the mixed-conductor silver sulfide (Ag2S) crystal and basic research on nanoionic devices based on this mixed conductor. These devices show unique functions such as atom deposition, resistance switching, and quantum point contact switching. The switches operate through the formation and dissolution of an atomic bridge between the electrodes, and the behavior is realized by control of the local solid-state electrochemical reaction. Potential nanoionic devices utilizing the unique functions and characters that do not exist in conventional semiconductor devices are discussed. [Copyright &y& Elsevier]

Abstract: Metal chalcogenide-based mixed ionic–electronic conductors such as Ag2S and Cu2S can be specifically architected for application in nanoelectronic devices. We present a template-confined synthesis of metal chalcogenide (e.g., Ag2S, Cu2S) nanowires for mixed conductor-based nanoelectronics. First, the metal nanowire array was electroplated into pores of a porous alumina membrane. Anodic polarization was then used to transform the metal into the metal sulfide in aqueous hydrosulfide (HS−) solutions. The as-synthesized mixed conductors'' hetero-nanowire array was characterized by X-ray diffraction and electron microscopy. Electronic transport measurements show non-linear and reproducible electrical switching characteristics. The high and low resistance states can be reversibly changed by altering the polarity of the applied voltage between the bottom and top electrodes. The electrical-switching behavior is attributed to electric-field-induced accumulation and dissolution of metallic conducting pathways inside the mixed conductors'' nanowires. [Copyright &y& Elsevier]

Abstract: Patterned ferroelectric domains and domain selective etching of the patterned domains can provide ferroelectrics-based photonic crystals. In this paper, electron-beam has been applied to switch domains in LiNbO3 (LN) and LiTaO3 (LT) crystals. The complex dynamics of interaction of beam electrons with the crystals has been highlighted. Based on this research, an improved e-beam domain patterning technique utilizing resist covering is successfully applied to switch domains in a z-cut 1mol% MgO-doped stoichiometric LN at room temperature. [Copyright &y& Elsevier]

We have investigated microscale to nanoscale ferroelectric domain and surface engineering of a near-stoichiometric LiNbO[SUB3] crystal by using scanning force microscopy. The single crystals LiNbO[SUB3] fixed on metal substrates were polished to a 5 μm thickness. Artificial patterns of inverted-domain structures were fabricated in the samples, where polarization directions of the domains were switched by scanning the samples with a conductive cantilever while applying voltages. Furthermore, the negatively polarized surfaces in the patterns were preferentially etched in HF solution. As a result, cavity and mound-shaped surfaces were fabricated; these structures could be used to create functional templates and devices. [ABSTRACT FROM AUTHOR]

(a) Schematic illustration of the synthesis process of LSM, (b) top view of model structure. • The LSM are prepared by simple one-step topological reaction. • The LSM with two-dimensional structure has an ultrathin thickness of 20 nm. • The LSM has a large specific surface area and abundant pore sizes. • The LSM displays good specific capacity and cycling stability comparing with common Si material. The structure fracture of silicon electrodes due to the volume change during Si-Li alloying reactions greatly hinders their practical applications. Herein a layered Si material (LSM) was prepared by a simple one-step topological reaction and used as an effective LIBs anode. The layered structure has abundant gaps and pores to accelerate ion transportation. Microstructure measurements demonstrate the formation of an amorphous lithiation product but not Si-Li alloys. As a result, the LSM anode shows higher specific capacity and a much better cycling performance than common bulk Si anode. Thus, the LSM could be alternative high-performance Si anode in LIBs. [ABSTRACT FROM AUTHOR]

We examined the structural and electrical properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and mixed roxbyite-covellite phases were formed with increasing sulfurization time. The Cu/S atomic percentage ratio of the films decreased with increasing sulfurization time, and films with various compositions such as Cu-rich and stoichiometric copper sulfide with underlying unreacted Cu as well as pure stoichiometric and S-rich copper sulfide were obtained. The surface morphology and the electrical resistivity of the films depended on the chemical phase and composition of the films. The resistivity decreased with increasing Cu deficiency in the films. Distinct switching of the resistance from high to low-state, and vice versa, with the reversal of the bias polarity of the film was observed only for the mixed metallic Cu-chalcocite phased film with underlying Cu. However, the chalcocite film with underlying Cu exhibited a semiconducting behavior. This indicated that excess Cu within the chalcocite film is required for the observation of the switching behavior of the resistance. [ABSTRACT FROM AUTHOR]

The stability of periodically poled domain structures in near-stoichiometric lithium tantalite, LiTaO3, (SLT) crystals exhibiting a low coercive field has become an important issue in the use of quasiphase-matching (QPM) devices. Temperature-induced backswitching in inverted domain structures in a 1.0 mol % MgO-doped SLT-QPM device with a QPM period of 6.1 μm used for the second harmonic generation of 488-nm-wavelength light was investigated using scanning force microscopy. It was revealed that backswitching consistently occurred due to heat treatment and that the amount was dependent on the temperature history. We propose an effective method of suppressing backswitching in the inverted domain structures of SLT-QPM devices on the basis of systematically analyzing the backswitching phenomena. [ABSTRACT FROM AUTHOR]

An all-solid-state electric-double-layer transistor (EDLT) with a Gd-doped CeO2 (GDC) oxide ion conductor/SrTiO3 (STO) insulator structure has been developed. At 473 K, the drain current of the EDLT was well controlled, from less than nA order to μA order, by electrostatic carrier doping at the GDC/STO interface due to oxide ion (O2-) migration in the GDC, in contrast to an inactiveness at room temperature. The EDL capacitance at the interface, measured with an ac impedance spectroscopy, was 14 μF cm-2, higher than that reported for a microporous-SiO2 EDLT and comparable to that of an ionic-liquid-gated EDLT. [ABSTRACT FROM AUTHOR]

Solid‐state batteries (SSBs) that use solid electrolytes instead of flammable liquid electrolytes have the potential to generate higher specific capacity and offer better safety. Magnesium (Mg) based SSBs with Mg metal anodes are considered to be one of the most promising energy storage candidates, because it gives high theoretical volumetric capacities of 3830 mAh cm−3. Here, we demonstrate an atomic layer deposition (ALD) process with a double nitrogen plasma process that successfully produces nitrogen‐incorporated magnesium phosphorus oxynitride (MgPON) solid‐state electrolyte (SSE) thin films at a low deposition temperature of 125 °C. The ALD MgPON SSEs exhibit an ionic conductivity of 0.36 and 1.2 μS cm−1 at 450 and 500 °C, respectively. The proposed ALD strategy shows the ability of conformal deposition nitrogen‐doped SSEs on pattered substrates and is attractive for using nitride ion‐conducing films as protective or wetting interlayers in solid‐state Mg and Li batteries. [ABSTRACT FROM AUTHOR]

Solid‐state batteries (SSBs) that use solid electrolytes instead of flammable liquid electrolytes have the potential to generate higher specific capacity and offer better safety. Magnesium (Mg) based SSBs with Mg metal anodes are considered to be one of the most promising energy storage candidates, because it gives high theoretical volumetric capacities of 3830 mAh cm−3. Here, we demonstrate an atomic layer deposition (ALD) process with a double nitrogen plasma process that successfully produces nitrogen‐incorporated magnesium phosphorus oxynitride (MgPON) solid‐state electrolyte (SSE) thin films at a low deposition temperature of 125 °C. The ALD MgPON SSEs exhibit an ionic conductivity of 0.36 and 1.2 μS cm−1 at 450 and 500 °C, respectively. The proposed ALD strategy shows the ability of conformal deposition nitrogen‐doped SSEs on pattered substrates and is attractive for using nitride ion‐conducing films as protective or wetting interlayers in solid‐state Mg and Li batteries. [ABSTRACT FROM AUTHOR]

Bipolar resistance switching (BRS) behavior and the effects of atmosphere (air, vacuum, O2 gas, or N2 gas) on BRS behavior occurred in the top and bottom interfaces in the M(top electrode)/WO3-x/Pt(bottom electrode) (M = Pt, Au) devices were investigated. Stable BRS only can be obtained in the interface with Pt electrode. And, the top Pt/WO3-x interface exhibited stable BRS only in an oxygen-rich atmosphere (air and O2 gas). In contrast, the bottom WO3-x/Pt interface showed stable BRS under any atmosphere. Based on the x-ray photoelectron spectroscopy measurement on Pt, Au/WO3-x interfaces, it is identified that the oxygen migration process during resistance switching mainly occurs between the Pt/WO3-x interface and Pt electrode. [ABSTRACT FROM AUTHOR]

Electric double layer effect in solid electrochemical systems is a key topic in energy storage applications. In this review, we outline recent investigations on the electric double layer effect of solid electrolyte interfaces by utilizing a semiconducting diamond surface as a probe of electrical charges at the solid/solid interfaces. Hall measurements with various solid electrolyte-based transistors evidenced that the electric double-layer effect strongly depends on the properties of the electrolyte and the very thin region from the interface. The unveiled features of the electric double layer at solid electrolyte interfaces are quantitatively discussed from the viewpoint of charge density and charging-discharging rate. Furthermore, applications of the unique switching response of the electric double layer transistors to neuromorphic computing are also demonstrated. [ABSTRACT FROM AUTHOR]

Atomic switches are nanoionic devices that control the diffusion of metal cations and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge, which is a conductive path between two electrodes in the on-state. In contrast to conventional semiconductor devices, atomic switches can provide a highly conductive channel even if their size is of nanometer order. In addition to their small size and low on-resistance, their nonvolatility has enabled the development of new types of programmable devices, which may achieve all the required functions on a single chip. Three-terminal atomic switches have also been developed, in which the formation and annihilation of a metal atomic bridge between a source electrode and a drain electrode are controlled by a third (gate) electrode. Three-terminal atomic switches are expected to enhance the development of new types of logic circuits, such as nonvolatile logic. The recent development of atomic switches that use a metal oxide as the ionic conductive material has enabled the integration of atomic switches with complementary metal-oxide-semiconductor (CMOS) devices, which will facilitate the commercialization of atomic switches. The novel characteristics of atomic switches, such as their learning and photosensing abilities, are also introduced in the latter part of this review. [ABSTRACT FROM AUTHOR]

We examined the structural properties of copper sulfide films as a function of the sulfurization time of 70-nm-thick Cu films. Copper sulfide films with various phases such as mixed metallic Cu-chalcocite, chalcocite, roxbyite, and covellite phases were formed with increasing sulfurization time. To evaluate the structural stability of various films, all the films were exposed to the ambient atmosphere for the same amount of time. Although the phase structure and stoichiometry of the films were maintained at a greater depth, the near-surface region of the films was oxidized and covered with overlayers of oxide, hydroxide, and/or sulfate species due to the exposure and reaction with the ambient atmosphere. The oxygen uptake and its reactivity with the copper sulfide film surfaces were enhanced with increasing sulfur content of the films. In addition, the type of divalent state of copper formed on the film surfaces depended on the phase structure, composition, and stoichiometry of the films. [ABSTRACT FROM AUTHOR]

Surface engineering at the nanoscale level of lithium niobate crystals is performed by scanning probe microscopy and is theoretically analyzed by the structural property and the chemical bonding structure. The present work shows that -Z surface of lithium niobate crystals may be well fabricated by precisely artificial patterns, which has potential applications in future nanodevices. [ABSTRACT FROM AUTHOR]

The electric double layer (EDL) effect at solid electrolyte/electrode interfaces has been a key topic in many energy and nanoelectronics applications (e.g., all-solid-state Li+ batteries and memristors). However, its characterization remains difficult in comparison with liquid electrolytes. Herein, we use a novel method to show that the EDL effect, and its suppression at solid electrolyte/electronic material interfaces, can be characterized on the basis of the electric conduction characteristics of hydrogenated diamond(H-diamond)-based EDL transistors (EDLTs). Whereas H-diamond-based EDLT with a Li-Si-Zr-O Li+ solid electrolyte showed EDL-induced hole density modulation over a range of up to three orders of magnitude, EDLT with a Li-La-Ti-O (LLTO) Li+ solid electrolyte showed negligible enhancement, which indicates strong suppression of the EDL effect. Such suppression is attributed to charge neutralization in the LLTO, which is due to variation in the valence state of the Ti ions present. The method described is useful for quantitatively evaluating the EDL effect in various solid electrolytes. The effect of the electric double layer with solid electrolytes remains hard to characterize. In this study, the authors show how to evaluate the electric double layer effect with various lithium solid electrolytes using a hydrogenated diamond-based transistor. [ABSTRACT FROM AUTHOR]

Photorefractive damage at λ=532 nm and green-light-induced infrared absorption (GRIIRA) of near-stoichiometric LiTaO 3 (SLT) single crystals were investigated. The SLT crystal even without MgO doping showed high photorefractive damage resistance and suppressed GRIIRA. In addition, a small amount of MgO doped into the SLT crystal almost eliminated the photorefractive damage and GRIIRA. A 3-mm-thick periodically poled SLT (PPSLT) and a 1-mm-thick periodically poled MgO-doped SLT (PPMgSLT) were successfully fabricated and their optical parametric oscillation (OPO) performances were investigated. [ABSTRACT FROM AUTHOR]

Atomic switch, operating by forming and dissolving a metal-protrusion in a nanogap, shows an exponentially large bias dependence and a faster switching with increasing temperature and decreasing off-resistance. These major characteristics are explained with a simple model where the electrochemical potential at the subsurface of solid-electrolyte electrode determines the precipitation rate of metal atoms and the electric-field in the nanogap strongly affects the formation of metal-protrusion. Theoretically calculated switching time, based on this model, well reproduced the measured properties of a Cu2S-based atomic switch as a function of bias, temperature and off-resistance, providing a significant physical insight into the mechanism. [ABSTRACT FROM AUTHOR]

The structures of inverted nanodomains in LiNbO3 crystals were investigated using atomic force microscopy (AFM) combined with piezoresponse force microscopy and atomic force acoustic microscopy. The acoustic and AFM topographic images reflected in domain structures with polarization orientation revealed that unexpected antiparallel domains randomly exist in inverted nanodomains in congruent LiNbO3 but not in near-stoichiometric one. The Gibbs free energy change ΔG associating with the internal field Eint in congruent LiNbO3 was discussed. We propose that nonstoichiometric defects, which caused Eint during polarization reversal, play a key role in formation of antiparallel domains in congruent LiNbO3 crystals. [ABSTRACT FROM AUTHOR]

Metallic nanoparticle deposition from an aqueous solution onto the +Z surfaces of LiNbO3 nanodomain patterns has been demonstrated. The distribution of the selectively deposited Ag particles was uniform and their sizes were 2–10 nm both in the diameter and height. The authors have inferred the mechanism by which the photovoltaic effect causes Ag particles to be deposited selectively on the +Z surfaces. The photovoltaic current density and the ferroelectric crystal thickness are found to be fundamental parameters of the photocatalytic deposition. [ABSTRACT FROM AUTHOR]

Graphene materials have attracted significant research interest as anodes in lithium-ion batteries (LIBs). However, their low volumetric capacity and high working voltage limit the energy density and thus hinder their practical applications. In this research, monolayer graphene and MoS 2 were prepared by controlled CVD growth processes. Graphene/MoS 2 alternately stacked structure (GMASS) was subsequently fabricated by alternately stacking graphene and MoS 2 monolayers layer by layer. When evaluated as an anode for LIB, GMASS demonstrates an obviously reduced working voltage compared to monolayer graphene electrodes (1.31 V vs. 1.46 V). And its volumetric capacity is much higher than that of an average graphite anode (1260 mAh cm−3 vs. 461 mAh cm−3). This fundamental research could promote the development of graphene/MoS 2 heterostructures for high-energy LIBs. Image 1 • Graphene/MoS 2 alternately stacked structure (GMASS) was fabricated. • GMASS demonstrates an obviously reduced working voltage. • GMASS shows a higher volumetric capacity comparing with graphite anode. [ABSTRACT FROM AUTHOR]

The stability of domains engineered in near-stoichiometric and congruent composition LiTaO3 crystals was investigated after heat treatment using scanning force microscopy. Piezoresponse images of the domains showed that the heat treatment had induced backswitching in the near-stoichiometric crystals and that the degree of backswitching depended on the domain structure and heating temperature. No backswitching was observed in the congruent composition crystals after the same heat treatment. The thermal stability of engineered LiTaO3 domains thus depends on the number of nonstoichiometric defects, the domain wall energy, and the pyroelectric effect. [ABSTRACT FROM AUTHOR]

The surface potential imaging of nanoscale domains engineered on near-stoichiometric LiNbO3 (SLN) crystals was investigated using Kelvin probe-based, electrostatic force microscopy. The surface potential image reflected in the domain structure was clearly obtained using heat treatment in vacuum due to the decreases in spontaneous polarization and screening charge adsorption. In-vacuum observation revealed that the surface potential contrast and polarity of nanoscale engineered domains can be repeatedly changed by switching the temperature between 298 and 393 K, demonstrating the controllability of the spontaneous polarization distribution in SLN crystals. [ABSTRACT FROM AUTHOR]

A general and straightforward strategy was developed for fabricating transition metal carbide (TMC)/carbon (C) core/shell nanospheres (NSs) by laser ablation of transition metals in acetone/ethanol liquid. Various TMC/C core/shell NSs such as TaC/C, NbC/C, HfC/C, and MoC/C core/shell NSs were successfully fabricated, highlighting the generality of this method. Crucially, this approach is green, facile, catalyst-free, and especially can be operated under ambient environments. Interestingly, all of the as-synthesized TMCs in the NS cores showed a cubic phase and structures similar to that of NaCl-type. The cores were further encapsulated by amorphous carbon shell with different thickness. As an example of the functional properties of these compound materials, the TaC/C core/shell NSs obtained were investigated as a supercapacitor electrode, which showed a large specific capacitance, excellent rate capability and remarkable cycling ability, revealing that the NSs could be used as new electrode materials for electrochemical energy storage. The photoluminescence of TaC/C core/shell NSs exhibited strong emission under the specific excitation wavelength at room temperature, showing potential biomedical applications due to the good biocompatibility of carbon shell. Besides, the basic physical and chemical reactions involved in the unique formation mechanism under highly nonequilibrium states induced by ultrafast laser ablation were discussed. [ABSTRACT FROM AUTHOR]

Abstract: A hard X-ray photoelectron spectroscopy (HX-PES) has been employed in order to investigate electrochemical polarization at carbon/amorphous tantalum oxide thin film hetero-interface. In situ HX-PES observation of Ta 4f and O 1s spectra has revealed parallel chemical shift of the core levels within the redox window width of 2.4eV, indicating Fermi level shifts due to the redox state modulation mediated by protonation and deprotonation under applied dc bias voltage. In addition to protons, oxide ions are suggested to take part in the redox state variation especially under a larger applied electric field. The results have been discussed in framework of solid state electrochemistry and Pourbaix-type E-pO diagram to indicate electrochemical stability domains of solid oxide systems is proposed. [Copyright &y& Elsevier]

In situ hard x-ray photoemission spectroscopy (HX-PES) and soft x-ray absorption spectroscopy (SX-XAS) have been employed to investigate a local redox reaction at the carbon/Gd-doped CeO2 (GDC) thin film heterointerface under applied dc bias. In HX-PES, Ce3d and O1s core levels show a parallel chemical shift as large as 3.2 eV, corresponding to the redox window where ionic conductivity is predominant. The window width is equal to the energy gap between donor and acceptor levels of the GDC electrolyte. The Ce M-edge SX-XAS spectra also show a considerable increase of Ce3+ satellite peak intensity, corresponding to electrochemical reduction by oxide ion migration. In addition to the reversible redox reaction, two distinct phenomena by the electrochemical transport of oxide ions are observed as an irreversible reduction of the entire oxide film by O2 evolution from the GDC film to the gas phase, as well as a vigorous precipitation of oxygen gas at the bottom electrode to lift off the GDC film. These in situ spectroscopic observations describe well the electrochemical polarization behavior of a metal/GDC/metal capacitor-like two-electrode cell at room temperature. [ABSTRACT FROM AUTHOR]

Scandium (Sc) and yttrium (Y) co-doped ZrO2 (ScYSZ) thin films were prepared on a SiO2-Si substrate via pulsed laser deposition (PLD) method. In order to obtain good quality thin films with the desired microstructure, various oxygen partial pressures ( P O 2 ) from 0.01 Pa to 10 Pa and substrate temperatures (Ts) from 25 °C to 800 °C were investigated. X-ray diffraction (XRD) patterns results showed that amorphous ScYSZ thin films were formed at room substrate temperature while cubic polycrystalline thin films were obtained at higher substrate temperatures (Ts = 200 °C, 400 °C, 600 °C, 800 °C). Raman spectra revealed a distinct Raman shift at around 600 cm−1 supporting a cubic phase. However, a transition from cubic to tetragonal phase can be observed with increasing oxygen partial pressure. Photoemission spectroscopy (PES) spectra suggested supporting analysis that more oxygen vacancies in the lattice can be observed for samples deposited at lower oxygen partial pressures resulting in a cubic structure with higher dopant cation binding energies as compared to the tetragonal structure observed at higher oxygen partial pressure. On the other hand, dense morphologies can be obtained at lower   P O 2 (0.01 Pa and 0.1 Pa) while more porous morphologies can be obtained at higher P O 2 (1.0 Pa and 10 Pa). [ABSTRACT FROM AUTHOR]

[Display omitted] • In situ hard X-ray photoelectron spectroscopy was performed to investigate the origin of irreversibility in electrochromic Li x WO 3 thin films. • The appearance of irreversibility was observed in Li x WO 3 during operation. • Reversible/irreversible components generated during operation were distinguished and evaluated quantitatively. Three kinds of components are known in the insertion of Li+ into electrochromic WO 3 (Li x WO 3): (i) reversible Li+, (ii) irreversible Li 2 WO 4 formation and (iii) irreversible Li+ trapping. To develop Li x WO 3 -based electrochromic devices, in situ hard X-ray photoelectron spectroscopy (HAXPES), in situ Raman spectroscopy and electrochemical measurements were performed. In situ HAXPES can quantitatively distinguish (i) reversible Li+ and (iii) irreversible Li+ trapping as the variation in the oxidation state of the W ion whereas the electrochemical measurements can evaluate (i) reversible Li+ and the sum of (ii) irreversible Li 2 WO 4 formation and (iii) irreversible Li+ trapping. Furthermore, in situ Raman spectroscopy detected the enhancement of crystallinity due to Li+ insertion with high sensitivity. The combination of the in situ HAXPES and the electrochemical measurements enables the separation and quantitative evaluation of (i), (ii) and (iii). The inserted Li+ conversion ratios of (i) reversible Li+, (ii) irreversible Li 2 WO 4 formation and (iii) irreversible Li+ trapping to the entire inserted Li+ were clarified. (i.e. , 41.4 %, 50.9 %, and 7.7 %, respectively). [ABSTRACT FROM AUTHOR]

Quantized conductance was observed in a cation-migration-based resistive switching memory cell with a simple metal–insulator–metal (MIM) structure using a thin Ta2O5 layer. The observed conductance changes are attributed to the formation and dissolution of a metal filament with an atomic point contact of different integer multiples in the Ta2O5 layer. The results demonstrate that atomic point contacts can be realized in an oxide-based MIM structure that functions as a nanogap-based atomic switch (Terabe et al 2005 Nature433 47). By applying consecutive voltage pulses at periodic intervals of different times, we also observed an effect analogous to the long-term potentiation of biological synapses, which shows that the oxide-based atomic switch has potential for use as an essential building block of neural computing systems. [ABSTRACT FROM AUTHOR]

Memory is believed to occur in the human brain as a result of two types of synaptic plasticity: short-term plasticity (STP) and long-term potentiation (LTP; refs , , , ). In neuromorphic engineering, emulation of known neural behaviour has proven to be difficult to implement in software because of the highly complex interconnected nature of thought processes. Here we report the discovery of a Ag2S inorganic synapse, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time. The structure known as an atomic switch, operating at critical voltages, stores information as STP with a spontaneous decay of conductance level in response to intermittent input stimuli, whereas frequent stimulation results in a transition to LTP. The Ag2S inorganic synapse has interesting characteristics with analogies to an individual biological synapse, and achieves dynamic memorization in a single device without the need of external preprogramming. A psychological model related to the process of memorizing and forgetting is also demonstrated using the inorganic synapses. Our Ag2S element indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory. [ABSTRACT FROM AUTHOR]

We propose a three-terminal nanometer metal switch that utilizes a solid electrolyte where a nanoscale metal filament is stretched and retracted. Its operating principle is based on electrochemical reaction and ion migration in the electrolyte. The fabricated device is composed of a solid electrolyte layer (CuS), a gate (Cu), a source (Cu), and a drain (Pt). After the Cu filament is formed between the source and the drain by applying the drain voltage, repeatable on/off switching in the drain current is obtained by controlling the gate voltage. The on/off current ratio can be as high as 10, and the programmable cycle is around 50. Each state can be kept for up to 40 days. Since the gate is separated from the current path, the switching current can be reduced to 10 μA, which is two orders of magnitude smaller than that of a two-terminal switch. In this paper, we present the operating principle and electrical characteristics of the three-terminal switches, and discuss how suitable they are for reconfigurable circuits. © 2011 Wiley Periodicals, Inc. Electron Comm Jpn, 94(4): 55-61, 2011; Published online in Wiley Online Library (). DOI 10.1002/ecj.10214 [ABSTRACT FROM AUTHOR]

We demonstrate memristive operations using gap-type AgS atomic switches, in which the growth and shrinkage of an Ag protrusion are controlled by using solid-electrochemical reactions. In addition to conventional memristive operations such as those proposed and demonstrated by resistive random-access memories (ReRAMs) using metal oxide compounds, gap-type AgS atomic switches also show new types of memristive operations by storing information from input signals without changing their output until a sufficient number of signals are inputted. The new types of memristive operations resemble the learning process seen in neuroplasticity, where changes occur in the organization of the human brain as a result of experience. [ABSTRACT FROM AUTHOR]

A novel solid-electrolyte nonvolatile switch that we previously developed for programmable large-scale-integration circuits turns on or off when a conducting Cu budge is formed or dissolved in the solid electrolyte. Cu+ ion migration and an electrochemical reaction are involved in the switching process. For logic applications, we need to adjust its turn-on voltage (VON), which was too small to maintain the conductance state during logic operations. In this paper, we clarified that VON is mainly affected by the rate of Cu+ ion migration in the solid electrolyte. Considering the relationship between the migration rate and VON, we replaced the former electrolyte, Cu2-αS, with Ta2O5, which enabled us to appropriately adjust VON with a smaller Cu+ ion diffusion coefficient. [ABSTRACT FROM AUTHOR]

We have investigated solid electrolyte switches that utilize electrochemical reactions (deposition and dissolution) of metallic ions. The switch turns off or on when a metallic bridge electrochemically forms or dissolves in the solid electrolyte. Each state is nonvolatile and the switching is repeatable up to 105 cycles. The promising application is a programmable switch in a field programmable logic because of its small size (<30 nm) and low ON resistance (<100Ω). This paper discusses the electrical characteristics, operation principle, and applications of the solid electrolyte switch. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(1): 68–73, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20542 [ABSTRACT FROM AUTHOR]

The domain switching at the nanoscale is studied at both −Z and +Z surfaces of a lithium niobate crystal. A remarkable difference between both surfaces is experimentally observed by scanning probe microscopy, and is theoretically analyzed by the structural property and the chemical bonding structure of the lithium niobate crystal. The domain switching at the −Z surface is much easier and more stable than that at the +Z surface, which makes lithium niobate crystals have potential applications in the future domain engineering, especially at the nanoscale level. [Copyright &y& Elsevier]

The authors examined the electronic transport of a solid electrolyte resistive switch. Using element analysis and the temperature dependence of its electronic transport, they deduced that the conductive path is composed of Cu metal precipitated in the solid electrolyte film by an electrochemical reaction. Furthermore, they observed Coulomb blockade phenomena at 4 K when the switch was in the off state. Their observations and experimental results suggest that the metallic conductive path consists of metallic islands separated by tunneling barriers and that switching between the on and off states originates from modulation in the tunneling barriers. [ABSTRACT FROM AUTHOR]

Nanosized inverted domain dots in ferroelectric materials have potential applications in ultrahigh-density rewritable data storage systems. Here, a data storage system based on scanning nonlinear dielectric microscopy and thin films of ferroelectric single-crystal lithium tantalite is presented. Through domain engineering, nanosized inverted domain dots have been successfully formed at a data density of 1.50 Tbit/in.². Nanosized inverted domain dots in ferroelectric materials have potential applications in ultrahigh-density rewritable data storage systems. Here, a data storage system based on scanning nonlinear dielectric microscopy and thin films of ferroelectric single-crystal lithium tantalite is presented. Through domain engineering, nanosized inverted domain dots have been successfully formed at a data density of 1.50 Tbit/in.². [ABSTRACT FROM AUTHOR]

Epitaxial Ca1-xSrxVO3 (0 ≦ x ≦ 1) thin films were grown on (100)-oriented SrTiO3 substrates by using the pulsed laser deposition technique. In contrast to the previous report that metal-insulator transition (MIT) in Ca1-xSrxVO3 (CSVO) was achieved only for extremely thin films (several nm thick), MIT was observed at 39, 72, and 113 K for films with a thickness of 50 nm. The electronic structure was investigated by hard and soft X-ray photoemission spectroscopy (HX-PES and SX-PES). The difference between these PES results was significant due to the variation in an escape depth of photoelectrons of PES. While HX-PES showed that the V 2p3/2 spectra consisted of four peaks (V5+, V4+, V3+, and V2+/1+), SX-PES showed only three peaks (V5+, V4+, and V3+). This difference can be caused by a strain from the substrate, which leads to the chemical disorder (V5+, V4+, V3+, and V2+/1+). The thin film near the substrate is affected by the strain. The positive magnetoresistance is attributed to the effect of electron-electron interactions in the disorder system. Therefore, the emergence of MIT can be explained by the electron-electron interactions from the chemical disorder due to the strain. [ABSTRACT FROM AUTHOR]