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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]

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]

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]

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]

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]

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]

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]