In this letter, we report the related transport properties of (La1-yPry)0.5Sr0.5MnO3 (y = 0.1, 0.2, 0.3, 0.4 and 0.5) films prepared by pulsed laser deposition. The transport properties of the films with different fields applied, such as optical field, magnetic field and strain field, were investigated. The results show that the resistance increases and the metal–insulator transition temperature shifts to lower temperature with the increasing of Pr doping. However, the film with the doping amount of 0.5 exhibits an insulation characteristic, and showed transient photoconductivity effect, with a relative change of photo-resistance of 7.2% at low temperature. Otherwise, a negative magneto-resistance of 54% was observed at 80 K and 1 T magnetic field. Further, by using an external electric field to modulate the films grown on the PbMg1/3Nb2/3O3-PbTiO3 substrate, it was found that the electric field reduced the resistance and had a faking effect on the relative change of the photo-resistance. It is mainly attributed to the influence of the external field on lattice distortion and charge carrier delocalization.

The subthreshold swing (SS) of a field-effect transistor (FET) is given by the body factor multiplied by the transport factor and has a limit of $60\text{ mV} \cdot ^{-1}$ at room temperature in the case of the MOSFET. To break this SS limit, the negative-capacitance FET (NC-FET) lowers the body factor by using a ferroelectric film in the gate stack, whereas the cold source FET (CS-FET) and the Dirac source FET (DS-FET) lower the transport factor by introducing an electronic bandgap or manipulating the density of states in the injecting source. In this work, we theoretically and computationally investigate the possibility of FETs with both NC and CS/DS so that both the body and transport factors are lowered simultaneously. The new device physics of the negative-capacitance CS-FET (NCCS-FET) is numerically investigated for 2-D monolayer black phosphorus (ML-BP) FETs with the Hf 0.5 Zr 0.5 O 3 ferroelectric material in the gate stack. The device characteristics of six different FETs, the conventional MOSFET, CS-FET, DS-FET, NC-FET, NCCS-FET, and NCDS-FET are calculated and compared. Overall, the NCCS-FET achieves an average SS of $30.1\text{ mV} \cdot ^{-1}$ and a minimum SS as low as $7.21\text{ mV} \cdot ^{-1}$ ; its O N–O FF ratio is about four orders of magnitude higher than that of a conventional MOSFET. The combined effects of NC and CS more efficiently decrease power dissipation.

Organic-inorganic perovskites have attracted increasing attention in recent years owing to their excellent optoelectronic properties and photovoltaic performance. In this work, the prototypical hybrid perovskite CH3NH3PbI3 is turned into a ferromagnetic material by doping Mn, which enables simultaneous control of both charge and spin of electrons. The room-temperature ferromagnetism originates from the double exchange interaction between Mn2+-I--Mn3+ ions. Furthermore, it is discovered that the magnetic field can effectively modulate the photovoltaic properties of Mn-doped perovskite films. The photocurrent of Mn-doped perovskite solar cells increases by 0.5 % under a magnetic field of 1 T, whereas the photocurrent of undoped perovskite decreases by 3.3 %. These findings underscore the potential of Mn-doped perovskites as novel solution-processed ferromagnetic material and promote their application in multifunctional photo-electric-magnetic devices.

The polarization and dielectric properties in a BaTiO3/La0.67Sr0.33MnO3 (BTO/LSMO) heterojunction with external magnetic field are investigated in the temperature range from 20 to 300 K. Excited by magnetic field under an intensity of 0.8 T, the saturation polarization is enhanced by a maximum value of 21.5% at 220 K, and the coercive electric field is decreased by a peak rate of 10.5% at 200 K. There also exists a significant magneto-induced variation of dielectric property around the temperature range of 200-220 K. The maximum changing rate of the dielectric constant and dielectric loss reaches 23.6% and 17.9%, respectively. The temperature range with the above maximum magnetoelectric coupling effect is consistent with the metal-insulator transition temperature of the LSMO layer. The magneto-induced polarization and dielectric performance change may result from the charge-based coupling through the BTO/LSMO interface.

The photoresponsive characteristics of SrTiO 3 -based oxide heterointerfaces at different thicknesses and strains are investigated. In addition to the typical persistent photoconductivity, the transient photoconductivity is observed at the heterointerfaces below the critical thickness. More intriguingly, it shows a transition from the transient photoconductivity to the persistent photoconductivity for the interfaces at the critical thickness with enhancing temperatures, which is related to the dominant role of thermal energy. Moreover, larger strain at the LaAlO 3 /SrTiO 3 interfaces produces a roughly greater photoinduced change in the resistance than the strain-relaxed (La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 )O 3 /SrTiO 3 interfaces. Our results provide deeper insight into the photoresponsive properties and intrinsic mechanisms of two-dimensional electron gas at complex oxide interfaces.

The Ba0.85Ca0.15Zr0.1Ti0.9O3/La0.67Sr0.33MnO3 (BCZT/LSMO) heterostructures were deposited on LaAlO3 (111) substrates through radio-frequency magnetron sputtering technique. Dielectric behaviors as a function of frequency, temperature and magnetic field were investigated. The frequency dependence of dielectric permittivity exhibited apparent relaxation behavior. The corresponding activation energy estimated from Arrhenius plot was 2 meV. Abnormal point at 120 K was detected from the real part of dielectric permittivity vs temperature plot and magnetodielectricity (MD) vs temperature plot simultaneously, which refer to rhombohedral to orthorhombic phase transition in BCZT. A maximum of 20 percent was obtained in MD-temperature pattern, indicating obvious magneto-electric (ME) coupling. The dielectric permittivity relaxation phenomena as well as magnetodielectric effect can be ascribed to the role of space charges, which arise at interface of BCZT and LSMO owing to lattice mismatch. The dependence of magneto-dielectric on temperature results from the variation of lattice mismatch degree induced by phase transition of BCZT.

Magnetic two-dimensional electron gases at the oxide interfaces are always one of the key issues in spintronics, giving rise to intriguing magnetotransport properties. However, reports about magnetic two-dimensional electron gases remain elusive. Here, we obtain the magnetic order of LaAlO3/SrTiO3 systems by introducing magnetic dopants at the La site. The transport properties with a characteristic of metallic behavior at the interfaces are investigated. More significantly, magnetic-doped samples exhibit obvious magnetic hysteresis loops and the mobility is enhanced. Meanwhile, the photoresponsive experiments are realized by irradiating all samples with a 360 nm light. Compared to magnetism, the effects of dopants on photoresponsive and relaxation properties are negligible because the behavior originates from SrTiO3 substrates. This work paves a way for revealing and better controlling the magnetic properties of oxide heterointerfaces.

Using a pulsed laser deposition method, the electron-doped La0.85Hf0.15MnO3 (LHMO) film with the thickness of 90 nm was epitaxially grown on LaAlO3 (001) single crystal substrate. The structural, magnetic and electrical transport properties of the film have been studied comprehensively. The X-ray diffraction patterns confirm that LHMO film is of single phase, good quality and c axis orientation. The film undergoes a ferromagnetic-like ordering to paramagnetic states at T C =280 K. Moreover, a spin glass behavior observed in the film may be attributed to the strain effects. Using the percolation theory, we have analyzed the resistivity data ρ (T) of the film and given an excellent fit in the whole temperature range. Particularly, large temperature coefficient of resistance of 11.27% K− 1 has been discovered near sub-room-temperature, indicating that LHMO film could be useful for bolometric applications.

In this paper, [(La 0.9 Sr 0.1 MnO 3 ) n /(Pa 0.9 Ca 0.1 MnO 3 ) n /(La 0.9 Sb 0.1 MnO 3 ) n ] m superlattices films have been deposited on (001) Nb:SrTiO 3 substrates by a laser molecular-beam epitaxy technology. Expected ferroelectricity arise at well-defined tricolor superlattice at low temperature, composed of transition metal manganite, which is absent in the single-phase compounds. Furthermore, the ferroelectric properties of the superlattices are enhanced by increasing the periodicity m, which may be attributed to the accumulation of the polarization induced by the frustration. As for the magnetic hysteresis loop characteristics of the multilayer structures, the saturation magnetization and magnetic coercivity of films present definitely a strong periodic dependence. It also indicates that the frustration may exist in the tricolor superlattice. Our results further verify the previous theoretical research of generating multiferroics experimentally paving a way for designing or developing the novel magnetoelectric devices based on manganite ferromagnets.

In this paper, we perform the quantitative phase-field simulations based on the surface morphology and growth regime of the hexagonal GaN spiral structure. We investigate the highly anisotropic energy, the deposition rate and the kinetic attachment and detachment effects. A regularized equation including the modified gradient coefficient is employed to study the anisotropic effect. Results show that the highly anisotropic energy modulates the equilibrium state by changing the local curvature of the tip step and thus leading to the changed spiral spacing. Under the weak anisotropy, the spiral spacing and morphology keep stable with the increase of the anisotropic strength. In the case of facet anisotropy, however, the larger anisotropic strength facilitates the spiral growth due to the local interfacial instability caused by increasing the supersaturation for the tip step. As to the effect of deposition, the deposition rate imposes the reaction on the curvature of interface due to the variations of supersaturation and step velocity. The larger rate of deposition enables the shorter spacing for both anisotropic and isotropic spirals. We carry out a convergence study of spiral spacing with respect to the step width to estimate the precision of the phase-field simulation. Results show that the larger deposition rate and the higher anisotropy give rise to the lower convergence of the spiral model. Moreover, we find that the kinetic attachment affects the instinct regime of spiral growth by changing the step spacing and the scaling exponents of spiral spacing versus deposition rate. The anisotropic spiral exhibits the more significant hexagonal structure and the lower value of step velocity by reducing the value of kinetic coefficient. The scaling exponent decreases with anisotropy increasing, but it increases with kinetic effect strengthening. The highly anisotropic energy contributes to weakening the sensitivity of the spiral spacing to the kinetic effect.

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.

In this paper, we introduce different forms of mobility into a quantitative phase-field model to produce arbitrary Ehrlich-Schwoebel (ES) effects. Convergence studies were carried out in the one-side step-flow model, which showed that the original mobility not only induces the ES effect, but also leads to larger numerical instability with increase of the step width. Thus, another modified form of the ES barrier is proposed, and is found to be more suitable for large-scale simulations. Model applications were performed on the wedding-cake structure, coarsening and coalescence of islands and spiral growth. The results show that the ES barrier exhibits more significant kinetic effects at the larger deposition rates by limiting motions of atoms on upper steps, leading to aggregation on the top layers, as well as the roughening of growing surfaces.

In this letter, we perform the phase-field simulations to investigate nucleation regime of submonolayer growth via a quantified nucleation term. Results show that the nucleation related kinetic coefficients have changed the density of islands and critical sizes to modulate the nucleation regime. The scaling behavior of the island density can be agreed with the classical theory only when effects of modulations have been quantified. We expect to produce the quantitative descriptions of nucleation for submonolayer growth in phase-field models.

In this paper we report the leakage current,ferroelectric and piezoelectric properties of the YFe O3film with hexagonal structure,which was fabricated on Si（111）substrate by a simple sol-gel method.The leakage current test shows good characteristics as the leakage current density is 5.4×10-6A/cm2under 5 V.The dominant leakage mechanism is found to be an Ohmic behavior at low electric field and space-charge-limited conduction at high electric field region.The P–E measurements show ferroelectric hysteresis loops with small remnant polarization and coercive field at room temperature.The distinct and switchable domain structures on the nanometer scale are observed by piezoresponse force microscopy,which testifies to the ferroelectricity of the YFe O3film further.

La-doped BaSnO3 is regarded as a very essential material to construct transparent perovskite devices due to its super high electrical mobility in perovskite transparent conducting oxides. For understanding the high electrical mobility, the effective mass of the carrier in La-doped BaSnO3 is a critical factor and should be determined. In this work, the performances of epitaxial La-doped BaSnO3 thin films grown on (LaAlO3)0.3 (SrAl0.5Ta0.5O3)0.7 (001) substrate by radio-frequency (RF) magnetron sputtering technique are investigated. The electrical properties (resistivity, carrier density, mobility and Seebeck coefficient) and the optical transmittance are analyzed. In addition, it is proved from both the Hall effect and thermoelectric power measurements that the La-doped BaSnO3 thin films are n-type degenerate semiconductor. At 300 K, the resistivity, carrier density, mobility and Seebeck coefficient are 0.987 mΩ·cm, 2.584×1020 cm-3, 24.49 cm2·V-1·s-1 and 45.71 μV/K, respectively. The electron effective mass ～ 0.31m0 (m0, the free electron mass) is extracted by combining the Seebeck coefficient and carrier density. Ba0.99La0.01SnO3 (BLSO) thin film exhibits a high optical transmittance of 73% in the visible spectral region. In order to derive the band-gap energy, the complex dielectric constant, and the film thickness, the transmittance spectrum is simulated based on the dielectric model comprising the band-gap transition (O'Leary-Johnson-Lim model) and free electron excitation (Drude-Lorentz model). The band-gap energy, exponential band tail and thickness of the BLSO thin film are 3.43 eV, 0.27 eV and 781.2 nm, respectively. Wavelength-dependence of complex dielectric function of the BLSO thin film is also obtained from the fitted line. Additionally, the parameters (optical carrier density and mobility) resulting from the optical measurement are in agreement with the results from the electrical measurement, which supports the calculated electron effective mass aforementioned.

Hexagonal YMnO3 is a special kind of multiferroics which shows unique advantages in magneto-electric field due to its low permittivity and only c-axis polarization. However, its ferroelectric properties, especially domain structures, have not been intensively investigated. In this study, YMnO3 film about 270 nm in thickness is prepared on Si(100) substrate by sol-gel spin coating. Structure and morphology of the film are characterized by grazing incidence X-ray diffraction and atomic force microscopy. Domain structure and its reversal behavior on a nanoscale are examined by piezoresponse force microscopy (PFM). The leakage current and ferroelectric property are also investigated. The results show that the film displays a hexagonal perovskite structure with good crystallinity and has smooth surface with a root-mean-square roughness of 7.209 nm. PFM images and typical local piezoresponse loops reveal the good piezoelectric and ferroelectric properties of the YMnO3 film at room temperature. Meanwhile, the offsets of amplitude loop and phase loop are observed due to the internal electric field. Leakage current density of YMnO3 film is lower than 10-6 A·cm-2, so saturated hysteresis loop can be obtained.

Using piezoresponse force microscopy (PFM), we mainly studied the piezoelectric, ferroelectric properties of YMnO3 thin film deposited on ZnO:Al/Al2O3 substrate by pulsed laser deposition. X-ray diffraction measurement indicated that YMnO3 film and ZnO:Al bottom electrode exhibit (000l) preferred orientation. The leakage currents of the YMnO3 film are related with temperature. The resistivity of the film at 40kV/cm is about 2.3×107Ωcm at room temperature (300K). Piezoresponse force microscopy images and local piezoresponse loops reveal the piezoelectric and ferroelectric properties of the YMnO3 film at room temperature. Polarizations (P) versus electric field (E) measurements further testify the ferroelectricity of the YMnO3 film.

Epitaxial La2/3Sr1/3MnO3(LSMO), BaTiO3(BTO), Bi4Ti3O12(BIT) were successively deposited on LaAlO3(100) substrate by pulsed laser molecular beam epitaxial technique(MBE). Structure, surface morphology, domain structure, local switching spectroscopy and ferroelectric hysteresis loop of films were investigated by X-ray diffraction(XRD), piezoelectric force microscopy(PFM) and ferroelectric instrument, respectively. The results indicate that prepared BIT/BTO ferroelectric composite films are preferential orientation along the c axis, and the PFM phase loop with the domain switching characteristic and amplitude-voltage butterfly loop demonstrate that the films possess good ferroelectric behavior. The remnant polarization(2Pr) of BIT/BTO composite film is(2.6±0.1)×10–6 C/cm2 under applying voltage of 8 V, whereas the 2Pr of BIT film and BTO film are only(1.1±0.1)×10–6 C/cm2 and(0.3±0.1)×10–6 C/cm2, respectively. Such improvement of ferroelectric properties in composite film could be attributed to interface effect and crystal structure distortion.