Lilan Zou

CoNi2S4 Nanosheet Arrays Supported on Nickel Foams with Ultrahigh Capacitance for Aqueous Asymmetric Supercapacitor Applications

We report that CoNi2S4 nanosheet arrays exhibit ultrahigh specific capacitance of 2906 F g(-1) and areal capacitance of 6.39 F cm(-2) at a current density of 5 mA cm(-2), as well as good rate capability and cycling stability, and superior electrochemical performances with an energy density of 33.9 Wh kg(-1) at a power density of 409 W kg(-1) have been achieved in an assembled aqueous asymmetric supercapacitor. The CoNi2S4 nanosheet arrays were in situ grown on nickel foams by a facile two-step hydrothermal method. The formation mechanism of the CoNi2S4 nanosheet arrays was based on an anion-exchange reaction involving the pseudo Kirkendall effect. The two aqueous asymmetric supercapacitors in series using the CoNi2S4 nanosheet arrays as the positive electrodes can power four 3-mm-diameter red-light-emitting diodes. The outstanding supercapacitive performance of CoNi2S4 nanosheet arrays can be attributed to ravine-like nanosheet architectures with good mechanical and electrical contact, low crystallinity and good wettability without an annealing process, rich redox reactions, as well as high conductivity and transport rate for both electrolyte ions and electrons. Our results demonstrate that CoNi2S4 nanosheet arrays are promising electrode materials for supercapacitor applications.

Highly uniform resistive switching properties of amorphous InGaZnO thin films prepared by a low temperature photochemical solution deposition method.

We report on highly uniform resistive switching properties of amorphous InGaZnO (a-IGZO) thin films. The thin films were fabricated by a low temperature photochemical solution deposition method, a simple process combining chemical solution deposition and ultraviolet (UV) irradiation treatment. The a-IGZO based resistive switching devices exhibit long retention, good endurance, uniform switching voltages, and stable distribution of low and high resistance states. Electrical conduction mechanisms were also discussed on the basis of the current-voltage characteristics and their temperature dependence. The excellent resistive switching properties can be attributed to the reduction of organic- and hydrogen-based elements and the formation of enhanced metal-oxide bonding and metal-hydroxide bonding networks by hydrogen bonding due to UV irradiation, based on Fourier-transform-infrared spectroscopy, X-ray photoelectron spectroscopy, and Field emission scanning electron microscopy analysis of the thin films. This study suggests that a-IGZO thin films have potential applications in resistive random access memory and the low temperature photochemical solution deposition method can find the opportunity for further achieving system on panel applications if the a-IGZO resistive switching cells were integrated with a-IGZO thin film transistors.

Resistive switching properties and physical mechanism of cobalt ferrite thin films

We report reproducible resistive switching performance and relevant physical mechanism of sandwiched Pt/CoFe2O4/Pt structures in which the CoFe2O4 thin films were fabricated by a chemical solution deposition method. Uniform switching voltages, good endurance, and long retention have been demonstrated in the Pt/CoFe2O4/Pt memory cells. On the basis of the analysis of current-voltage characteristic and its temperature dependence, we suggest that the carriers transport through the conducting filaments in low resistance state with Ohmic conduction behavior, and the Schottky emission and Poole-Frenkel emission dominate the conduction mechanism in high resistance state. From resistance-temperature dependence of resistance states, we believe that the physical origin of the resistive switching refers to the formation and rupture of the oxygen vacancies related filaments. The nanostructured CoFe2O4 thin films can find applications in resistive random access memory.

Multilevel resistive switching effect in sillenite structure Bi12TiO20 thin films

Multilevel resistive switching effect has been demonstrated in Pt/Bi12TiO20/Pt structures, in which the sillenite structure Bi12TiO20 thin films were prepared by a chemical solution deposition method. The non-volatile multilevel resistive switching can be easily realized by changing either the compliance current during set process or reset voltage during reset process. The Pt/Bi12TiO20/Pt devices show excellent switching parameters such as reproducible switching effect, low set/reset voltage, high cell yield, good endurance, and long retention time (up to 104 s). The dominated conduction mechanisms were Ohmic conduction in low resistance state (LRS) and lower voltage region of high resistance state (HRS), and Schottky emission in higher voltage region of HRS. In the reset process, the switching from LRS to HRS consists of two parts: an abrupt transition due to thermal effect and a gradual transition owing to electric field-induced migration of oxygen vacancies. On the basis of the measurements of the resi...

Uniform bipolar resistive switching properties with self-compliance effect of Pt/TiO2/p-Si devices

We report uniform bipolar resistive switching characteristic with self-compliance effect of Pt/TiO2/p-Si devices in which TiO2 thin films were prepared directly on p-Si substrates by chemical solution deposition method. The resistive switching parameters of the Pt/TiO2/p-Si cell obtained, such as distribution of threshold voltages, retention time, as well as resistance variation of high resistance state (HRS) and low resistance state (LRS), were investigated, and the conduction mechanisms of HRS and LRS were analyzed. The conductive mechanism at LRS and low voltage region of HRS was dominated by Ohmic law. At the high voltage region of HRS, the conductive mechanism followed the space charge limited current theory. The resistive switching phenomenon can be explained by electron trapping and de-trapping process, in which the defects (most probably oxygen vacancies) act as electron traps. Our study suggests that using p-type silicon as bottom electrode can provide a simple method for fabricating a resistive ...

Tuning bipolar resistive switching by forming defect dipoles in A-site-deficient perovskite calcium titanate thin films

If we intentionally make the A-site in an ABO3 perovskite structure deficient, it is possible to tune the resistive switching effect by forming defect dipoles. In this study, an A-site-deficient calcium titanate (Ca0.95TiO3, CTO) thin film was fabricated on a Pt/Ti/SiO2/Si substrate as an active layer for resistive random-access memory. The Pt/CTO/Pt device exhibited stable bipolar resistive switching performance with good endurance and long retention. The resistive switching may be attributable to the formation and rupture of the conduction filaments due to the O vacancies and defect dipoles resulting from the interaction between the Ca and O vacancies.