Dongqing Liu

Analog Memristors Based on Thickening/Thinning of Ag Nanofilaments in Amorphous Manganite Thin Films

We developed an analog memristor based on the thickening/thinning of Ag nanofilaments in amorphous La(1-x)Sr(x)MnO3 (a-LSMO) thin films. The Ag/a-LSMO/Pt memristor exhibited excellent pinched hysteresis loops under high-excitation frequency, and the areas enclosed by the pinched hysteresis loops shrank with increasing excitation frequency, which is a characteristic typical of a memristor. The memristor also showed continuously tunable synapselike resistance and stable endurance. The a-LSMO thin films in the memristor acted as a solid electrolyte for Ag(+) cations, and only the Ag/a-LSMO/Pt memristor electroformed with a larger current compliance easily exhibited high-frequency pinched hysteresis loops. On the basis of the electrochemical metallization (ECM) theory and electrical transport models of quantum wires and nanowires, we concluded that the memristance is ultimately determined by the amount of charge supplied by the external current. The state equations of the memristor were established, and charge was the state variable. This study provides a new analog memristor based on metal nanofilaments thickening/thinning in ECM cells, which can be extended to other resistive switching materials. The new memristor may enable the development of beyond von Neumann computers.

Nonvolatile bipolar resistive switching in amorphous Sr-doped LaMnO3 thin films deposited by radio frequency magnetron sputtering

Amorphous Sr-doped LaMnO3 (a-LSMO) thin films were deposited on Pt/Ti/SiO2/Si substrate by radio frequency magnetron sputtering. The Ag/a-LSMO/Pt device exhibited reversible bipolar resistive switching over 100 cycles with a resistance ratio (high resistance state to low resistance state) of over 4 orders of magnitude and stable retention for over 104 s at room temperature. Analysis indicates that the resistive switching originates from the formation/rupture of Ag nanofilaments in the a-LSMO thin films acting as solid electrolytes. The device showed potential for multibit storage as well as low power consumption applications.

Diode-like volatile resistive switching properties in amorphous Sr-doped LaMnO3 thin films under lower current compliance

Amorphous Sr-doped LaMnO3 (a-LSMO) thin films can exhibit diode-like volatile resistive switching (RS) properties under lower compliance current (CC). The Ag/a-LSMO/Pt cell exhibits stable volatile RS cycles up to 100 times with rectification ratio above 102. The volatility depends strongly on the temperature as well as the CC-controlled dimension of the Ag nanofilament forming in a-LSMO. The conductive atomic force microscopy current-mapping images confirm the instability of conducting nanofilaments forming under lower CC. The volatile RS behaviors could be explained by the Rayleigh instability of the Ag nanofilament, together with the diffusion of Ag atoms to the a-LSMO matrix. The diode-like volatile RS properties have great application potential in the beyond von-Neumann computers.

Infrared thermochromic properties of VO2 thin films prepared through aqueous sol-gel process

The stoichiometric vanadium(IV) oxide thin films were obtained by controlling the temperature, time and pressure of annealing. The thermochromic phase transition and the IR thermochromic property of 400 nm and 900 nm VO2 thin films in the 7.5 μm-14 μm region were discussed. The derived VO2 thin film samples were characterized by Raman, XRD, XPS, AFM, SEM, and DSC. The resistance and infrared emissivity of VO2 thin films under different temperature were measured, and the thermal images of films were obtained using infrared imager. The results show that the VO2 thin film annealed at 550 °C for 10 hours through aqueous sol-gel process is pure and uniform. The 900 nm VO2 thin film exhibits better IR thermochromic property than the 400 nm VO2 thin film. The resistance of 900 nm VO2 film can change by 4 orders of magnitude and the emissivity can change by 0.6 during the phase transition, suggesting the outstanding IR thermochromic property. The derived VO2 thin film can control its infrared radiation intensity and lower its apparent temperature actively when the real temperature increases, which may be applied in the field of energy saving, thermal control and camouflage.

Infrared thermochromic properties of monoclinic VO2 nanopowders using a malic acid-assisted hydrothermal method for adaptive camouflage

Monoclinic VO2 nanopowders were synthesized using a malic acid-assisted hydrothermal method. The derived VO2 nanopowders were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy. The phase transition properties of the monoclinic VO2 nanopowders were studied using differential scanning calorimetry, which displayed an obvious phase transition at 67.2 °C with a narrow thermal hysteresis width of 4.9 °C. Also, the resistance–temperature relationship and the thermal infrared images in the waveband 7.5–13 μm were analyzed. The results showed that the VO2 samples have excellent electrical properties with resistance changes as large as two orders of magnitude. The VO2 nanopowders obtained can control their infrared radiation intensity actively and lower their radiation temperature. Furthermore, the stability of the VO2 nanopowders was investigated. The results showed that the VO2 nanopowders have good thermal stability, oxidation resistance below 375 °C in an air atmosphere and humidity resistance, which has great application prospects in adaptive infrared camouflage technology.

Memristive Properties of Transparent

Amorphous La1-xSrxMnO3 (a-LSMO) thin films were deposited on indium tin oxide (ITO) glass at room temperature by radio frequency magnetron sputtering. The transmittance of a-LSMO (10 nm)/ITO/glass is 75% at 600 nm, which is promising for transparent memristors. The Ag/a-LSMO (10 nm)/ITO/glass memristor exhibits nonvolatile bipolar resistive switching properties with a resistance ratio , stable write/erase endurance , and long retention. The memristor can exhibit pinched hysteresis loops under high-frequency voltage excitations. These memristive properties are ascribed to diameter changes of the Ag nanofilament in the a-LSMO.

({\rm La},\,{\rm Sr}){\rm MnO}_{3}

A forefront and efficient inkjet printing technology is developed for vanadium dioxide (VO2). The inkjet-printed VO2 films exhibit a solar modulating ability of 15.31% with comparable visible transmittance. Their excellent performance has been further confirmed using a smart window model. Patterned VO2 films were also prepared via inkjet printing technology.

Thin Films Deposited on ITO Glass at Room Temperature

Paraffin microemulsions are multifunctional thermal fluid consisting of water as the continuous phase and paraffin as the dispersed phase. They can store or transfer a large amount of thermal energy by using the latent heat capacity of the paraffin during the phase transition as well as the sensible heat capacity of water. In this study, hexadecane O/W microemulsions were emulsified by an ionic surfactant SDS and a co-surfactant butanol. The phase behavior, effective stability, droplet size and thermophysical properties, such as latent heat and dynamic viscosity, were investigated experimentally. The results showed the prepared microemulsion with 30 wt.% hexadecane has expected high heat capacity about 93.4 J/g and low viscosity about 21 mpa·s. The average droplet size is 73 nm. The results indicate that they have potential applications in thermal energy storage and transfer.