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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 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]