Search

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]

Memorization caused by the change in conductance in a Ag2S gap-type atomic switch was investigated as a function of the amplitude and width of input voltage pulses (Vin). The conductance changed little for the first few Vin, but the information of the input was stored as a redistribution of Ag-ions in the Ag2S, indicating the formation of sensory memory. After a certain number of Vin, the conductance increased abruptly followed by a gradual decrease, indicating the formation of short-term memory (STM). We found that the probability of STM formation depends strongly on the amplitude and width of Vin, which resembles the learning behavior of the human brain. [ABSTRACT FROM AUTHOR]

Atomic structures of a Si (111) surface are dynamically observed at a 2 s/frame velocity over a scanning field about 150 Å×150 Å using a fast scanning tunneling microscope (FSTM). A FSTM has been developed and it features a compensation method for probe tip servo position error in the constant current mode. The compensation value is derived from the ratio of tunnel current fluctuation and tunnel current (Δ I/I) in differential-type tunnel current equation. The FSTM provides first dynamic observation of a residual gas molecule adsorption on atomic defects in 7×7 Si adatom reconstructions using a video tape recorder. In addition, a thermal drift of about 10 Å /s, about 30 min after direct electric flash heating of the sample for Si surface cleaning, can be easily observed. [ABSTRACT FROM AUTHOR]

A new type of microscope, which is based upon both a scanning tunneling microscope (STM) and a technique for detecting acoustic waves, is described. An acoustic wave generated in a STM’s sample, by vibration of its tip, is detected by a piezoelectric transducer coupled to the sample. The amplitude of the acoustic wave corresponds to the strength of the force interaction between the tip and the sample, and is sensitive to tip-sample spacing. We have been successful in keeping the spacing constant by using a new feedback loop that holds this amplitude constant without tunneling. This method enhances the features of the STM without reducing its functions and enables simultaneous use of both force interactions and tunneling current to investigate the properties of samples. Topographies taken by the new feedback system and tunneling current images are shown. [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]

Presents a study which investigated natural oxide growth on silicon facets using an atomic force microscope with current measurement. Experimental details; Results and discussion; Conclusion.

A fast scanning tunneling microscope (FSTM) is developed using a new method of compensating for the probe tip servo error in constant current mode. The compensation value is derived from the ratio of tunnel current fluctuation to tunnel current (ΔI/I) in a differential tunnel current equation. Dynamic video images of Si(111) adatomic structures taken using the FSTM prove that this method is effective for fast scanning. [ABSTRACT FROM AUTHOR]

The gap-type atomic switch is a novel neuromorphic device that possesses functions such as analog changes in resistance and short-term/long-term memory-based learning. However, it is difficult to integrate conventional gap-type atomic switches that use a vacuum gap and Ag2+δS, which has restricted their practical use. In this study, we developed a new, easy to fabricate gap-type atomic switch that incorporates a molecular layer as a gap and Ta2O5 as an ionic transfer material. This molecular gap-type atomic switch operates in a manner that is similar to conventional vacuum gap-type atomic switches. We also demonstrate stochastic operations using the aforementioned molecular gap-type atomic switches. These results indicate a higher potential for the practical use of gap-type atomic switches. [ABSTRACT FROM AUTHOR]

Nonvolatile three-terminal operation is demonstrated using a Pt/Ta2O5-x/Pt, Pt structure, by controlling oxygen vacancy drift to make/annihilate a conductive channel between a source and a drain. The as-fabricated device is in an off-state. Application of a positive gate bias moves oxygen vacancies in a Ta2O5-x layer towards a channel region, making the channel region conductive. The conductive channel remains even after unloading the gate bias. Application of a negative gate bias, which moves the oxygen vacancies back towards the gate electrode, is required to turn off the device. The device shows a high ON/OFF ratio of up to 106. [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]

Diffusivity of Cu in amorphous (a-) Ta2O5 is increased by low temperature annealing above 350 °C but the increase is suppressed by adding SiO2 to Ta2O5. To clarify the reasons, we investigated the structural difference between a-Ta2O5 and a-SiO2–Ta2O5. The results show that the low temperature annealing does not cause polycrystallization of Ta2O5 but purges weakly bonded oxygen atoms from the bulk and decreases the film density. Adding SiO2 to Ta2O5 is shown to increase the coordination number of Ta–O, which results in the improved thermal stability. [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]

Proposes a just-on-surface magnetic force microscope for advanced spatial resolution of the magnetic stray field image. Resolution images provided; Ability to observe a localized surface magnetic stray field caused by magnetization; Comparison with the conventional magnetic force microscope.

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]