Changle Chen

Photoresponsive character of double-doped La2∕3(Ca1∕3Sr2∕3)1∕3MnO3 film

The transient resistance change induced by modulated laser pulse has been observed in the double-doped perovskite La2∕3(Ca1∕3Sr2∕3)1∕3MnO3 thin film prepared by rf magnetron sputtering method. The time response character of photoinduced voltage signal is independent of the bias current, but its photoinduced relative change in resistance is nonlinearly dependent on the bias current. All the phenomena in the perovskite film is explained by the double exchange model and the small polaron theory. This is very important in the practical application of a colossal magnetoresistance photoelectric switch.

Photoinduced effect in charge-ordering La0.5Ca0.5MnO3 film

Charge-ordered La0.5Ca0.5MnO3 film has been deposited on (100)-LaAlO3 substrate using rf magnetron sputtering method. X-ray diffraction analysis shows that the bulk has orthorhombic structure and the film has the better epitaxial character. The charge-ordering transition temperature is about 280 K by fitting the resistance-temperature curve using the variable-range hopping model. The decrease in the resistance of the film irradiated by the laser is caused by the delocalization effect of the correlated electron system. The photoinduced relaxation exhibits different processes when the laser is on and off, which can be attributed to thermal fluctuation.

Degenerate seaweed to tilted dendrite transition and their growth dynamics in directional solidification of non-axially oriented crystals: a phase-field study.

We report the results of a phase-field study of degenerate seaweed to tilted dendrite transition and their growth dynamics during directional solidification of a binary alloy. Morphological selection maps in the planes of (G, Vp) and (ε4, Vp) show that lower pulling velocity, weaker anisotropic strength and higher thermal gradient can enhance the formation of the degenerate seaweed. The tip undercooling shows oscillations in seaweed growth, but it keeps at a constant value in dendritic growth. The M-S instability on the tips and the surface tension anisotropy of the solid-liquid interface are responsible for the formation of the degenerate seaweed. It is evidenced that the place where the interfacial instability occurs determines the morphological transition. The transient transition from degenerate seaweed to tilted dendrite shows that dendrites are dynamically preferred over seaweed. For the tilted dendritic arrays with a large tilted angle, primary spacing is investigated by comparing predicted results with the classical scaling power law, and the growth direction is found to be less sensitive to the pulling velocity and the primary spacing. Furthermore, the effect of the initial interface wavelength on the morphological transition is investigated to perform the history dependence of morphological selection.

Dielectric behavior of hexagonal and orthorhombic YFeO3 prepared by modified sol-gel method

Polycrystalline YFeO3 ceramic powders were synthesized by modified polyacrylamide sol-gel method. X-ray diffraction analysis demonstrated that the crystal structures of YFeO3 could be controlled from hexagonal phase (h-YFeO3) to orthorhombic phase (o-YFeO3) through the calcined temperature. Temperature-dependent dielectric constants (εr) and losses (tanδ) show that strong frequency dispersion phenomena occur in whole measuring temperature. Both the h-YFeO3 and o-YFeO3 exhibit dielectric relaxation behavior at Tu2009<u2009250xa0K and at Tu2009>u2009340xa0K, which could be attributed to thermal activation. Whereas, only h-YFeO3 shows an anomaly dielectric peak at Tmu2009=u2009297xa0K fitted with Curie-Weiss law and modified Curie-Weiss law, indicating a possible P63mc-P63cm transition with slightly diffuse characteristics.

Switching behavior of oxygen-deficient La0.6Ca0.4MnO3−δ thin films

Photoinduced switching of resistance by several orders of magnitude is observed in oxygen-deficient La0.6Ca0.4MnO3−δ thin films deposited on Si substrates. The magnitude of the transient photoconductivity could attain 95.9% at room temperature under 532nm cw laser illumination at laser intensity of 142mW∕cm2. The switching has a fast photoresponse effect on a nanosecond time scale when irradiated by a 532nm laser pulse of 7ns duration. The photocurrent and photoresponse times depend on the laser intensity and the applied electric field. These results can be important for practical applications in the manganite-based optical devices.

Photoinduced effect on carrier transport properties in La0.7Sr0.3MnO3/Si heterostructure

The photoinduced effect on carrier transport properties has been investigated in the La0.7Sr0.3MnO3/Si heterostructure prepared by the pulsed laser deposition method. A giant photoinduced relative change in the resistance of about 6783% in the current-perpendicular-to-plane (CPP) geometry of the heterostructure has been observed when it is irradiated by a 532 nm laser at T = 270 K. The rising time of about 100 µs in the CPP geometry of the heterostructure under modulated laser irradiation of 200 µs duration seems to be independent of temperature. This provides an innovation for potential application in functional optical and electrical devices.

The electric transport properties of Al-doped ZnO/BiFeO3/ITO glass heterostructure

BiFeO3 (BFO) and 4 wt. % Al-doped ZnO (ZAO) layers were grown on indium tin oxide (ITO) glass substrate using a pulsed laser deposition (PLD) method. I–V curves of the ZAO/BFO/ITO glass structure were investigated over the temperature range from 60 to 240 K. Analysis of the leakage current demonstrates that Poole–Frenkel emission is the dominant mechanism in our sample. The relations between resistance and temperature at positive and negative bias voltages are different, and the difference arises from the ferroelectric switching in BFO and the interfacial depletion layer between the semiconducting and the ferroelectric layers. Magnetoresistance (MR) effect is observed and the negative MR is related to the electron spin-dependent scattering and the interface resistance of the heterostructure.

Structural Stability, Electronic and Magnetic Properties of Cu Adsorption on Defected Graphene: A First Principles Study

Structural stabilities, electronic structures, and magnetic properties of Cu atom adsorption on pure, B(N)-doped and single-vacancy graphene have been studied using the first-principle method. It was found that the electronic property of graphene can be tuned by B or N doping. B-doped and N-doped graphene turned into a p-type and n-type semiconductor with a band gap of 0.2xa0eV, respectively. Total energy calculation results demonstrated the most stable site for the Cu atom adsorption on pure, B-doped and N-doped graphene is the top, bridge, and hollow site, respectively. B doping and vacancy both enhance the adsorption capacity for the Cu atom, while N doping weakens the capacity. Furthermore, B and N atoms do not induce magnetism in graphene, while the magnetic moment is induced when Cu is adsorbed on the graphene sheet, which is mainly caused by the unsaturated s-electrons of the Cu atom.

Self-powered ultraviolet photovoltaic effects based on metal/SrTiO3 Schottky junctions

Self-powered ultraviolet photovoltaic effects have been investigated in metal/SrTiO3 Schottky junctions. The absorption edge of the SrTiO3 single crystal is about 389 nm. The peak photovoltage of the Pt/SrTiO3 junction is about 0.50 V at when it is illuminated by a KrF excimer laser with a wavelength of 248 nm. The peak photovoltages decrease with increasing the temperature due to the strong thermal fluctuation. Moreover, the peak photovoltages almost linearly increase with an increase in the power density of the laser at . The experimental results reveal it may be useful for self-powered ultraviolet detecting sensitive devices.

Polarization Switching and Photoinduced Dielectric and Ferroelectric Properties in YMnO3/La0.67Sr0.33MnO3 Heterostructure

YMnO3/La0.67Sr0.33MnO3 heterostructure was fabricated on SrTiO3 (110) substrate by pulse laser deposition technology. The photoinduced resistance is markedly decreased in the low temperature region (20-300 K), especially arresting at the TC of o-YMnO3 (∼30 K), the TN of o-YMnO3 (∼40 K), and the TN of h-YMnO3 (∼80 K). The variance tendency of the dielectric constant anomaly near the TN of o-YMnO3 progressively decreases as the frequency increases, while the anomaly near the TN of h-YMnO3 is not observed in the same frequency region. Additionally, the dielectric constant is suppressed under photo excitation, and the variation increases with the rise in temperature and frequency. A distinct photoinduced suppression in the ferroelectric hysteresis loops is observed, maybe the trapping of photoinduced electrons to incur the reorientation of domain or increase the leakage current density. The obvious polarization switching in phase and amplitude images are observed when poling at ±8 V DC bias by the piezoresponse force microscopy technique at room temperature.