Gotowa bibliografia na temat „Polarization switching barrier”

Ferroelectric tunnel junctions (FTJs) are promising candidates for the next-generation memory technologies. The electroresistance mechanism, however, has been reported not only from the polarization-modulation of barrier profiles. Electrical migration of charged defects has also been observed as a possible origin for the resistive switching. Here, we achieve two kinds of electroresistance behaviors in Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions by introducing oxygen vacancies in the Pb(Zr,Ti)O3 barrier. The oxygen vacancies are observed by x-ray photoelectron spectroscopy, and their effects on the widely adopted piezoresponse force microscopy characterizations of ultrathin ferroelectric films have been analyzed by AC voltage-dependent hysteresis loops. For the Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 device that is modulated by the polarization reversal, a counterclockwise resistance–voltage ( R– V) relationship is observed due to the tunneling between high and low barriers, whereas the R– V hysteresis loop is changed to clockwise with the existence of oxygen vacancies, in which conductive filaments are formed in the Pb(Zr,Ti)O3 barrier. However, such an ionic electroresistance is not stable during repetitive switching. Further investigation on memristive behaviors is, thus, performed on the ferroelectric-controlled Pt/Pb(Zr,Ti)O3/(La,Sr)MnO3 tunnel junctions. An excellent linearity is achieved in continuous resistance change owing to the nucleation-limited-switching mode of domain switching in the Pb(Zr,Ti)O3 barrier, giving rise to spike-timing-dependent plasticity behaviors for the Hebbian rule of learning and memory. These results provide insight into the distinguishing of ferroelectric and ionic contributions in electroresistance of FTJ devices, facilitating deep understanding of nonvolatile resistive memories.

Taking account the presence of external magnetic field, we study the conductance properties in spin field-effect transistors (SFET). It is shown that the conductance of the SFET exhibits an excellent magnetic switching characteristic for high potential barriers, and it is more and more pronounced with the potential barrier strength increasing. According to the effect, we can switch the SFET on or off by tuning the strength of the magnetic field. We also study how the conductance of the SFET is manipulated by spin–orbit coupling strength and spin polarization in source and drain.

Based on density-functional calculations, we have studied possible ferroelectric switching path in monodomain single crystal of rhombohedral BiFeO3 , a prototypical multiferroic compound. By carefully studying the behaviors of FeO6 corner-sharing double-tetrahedrons, we find abrupt changes in total energy and oxygen atomic positions, and therefore polarizations, occur in the ferroelectric switching path of rhombohedral BiFeO3 . Detailed analyses suggest that such behavior might be caused by the frustrated magnetic ordering in the paraelectric phase of rhombohedral BiFeO3 , where three O atoms and the Bi atom are in the same plane perpendicular to the polarization direction. This is supported by the fact that the ferroelectric switching for paramagnetic BiFeO3 is smooth and has a much lower energy barrier than that of antiferromagnetic BiFeO3 .

Generating and manipulating valley polarization in a controlled method is significant. The inherently broken centrosymmetry of the buckled honeycomb structures gives it both ferroelectricity and valley degree of freedom, which provides an opportunity to realize electrically controlled valley polarization. In the first step, we explored the origin of buckling. The hexagonal structure is polar due to buckling of the surface, but the degree of buckling and the energy barrier to switching electric polarization are determined not solely by the chemical composition. We combined the electronegativity difference, bond length and the distribution of charge density to describe quantificationally the polarity of chemical bonds. It shows the characteristics of relatively long bond-length but relatively small electronegativity-difference. For exploring the ferroelectricity of buckling structures and the behavior of ferroelectric (FE) control of the valley degree of freedom, the [Formula: see text]-GaP is used as a model system to elucidate the strain effect on FE behavior and the magnetic proximity effect on the polarization and switching of valley. We found that the spontaneous polarization is positively correlated with the electronegativity difference within a certain range, and the compression strain can effectively manipulate spontaneous polarization and switch barrier. A combination of the magnetic proximity effect and the inversion of electric polarization can generate and switch valley polarization effectively.

we report reproducible resistive switching performance and relevant physical mechanism of Pt/La0.7Sr0.3MnO3/Nb0.05Bi0.95FeO3/Nb:SrTiO3 ferroelectric heterostructure which was fabricated by pulsed laser deposition. This device exhibits a nonvolatile resistive switching with a resistance ratio of up to 60 under 2V/-3V pulse voltages at room temperature. Low voltage readout, reliable resistance switching reproducibility and good time retention, indicating promise for non-destructive readout nonvolatile memories. In this metal/p-semiconductor/ferroelectric/n-semiconductor heterostructure, the mechanism of resistive switching behavior would be attributed to the ferroelectric polarization enhanced field-induced charge redistribution at the semiconductor/ferroelectric interface, resulting in the modulation of the interface barrier height. Keywords: Resistive switching, Ferroelectric resistive switching, Ferroelectric field effect.

The polarization switching pathway plays a key role in deciding the magnitudes of the spontaneous polarization and the coercive electric field, which can be used to realize controllable ferroelectric properties. In this paper, by first-principles calculations, we reveal how the spontaneous polarization ( Ps) and the switching barrier ( Eb) of orthorhombic HfO2 ( o-HfO2) respond to various lattice strains depending on two kinds of switching pathways, i.e., the shift-across (SA) pathway and the shift-inside pathway. It is revealed that the existence of the two pathways is most likely dependent on the interface termination of o-HfO2, and the SA pathway exhibits higher critical values of both Ps and Eb. By applying lattice strains on o-HfO2 (001) and (010) planes, a ferroelectric–paraelectric phase transition from the polar Pca21 to the nonpolar Pbcn can be observed. Importantly, the variation trends of Ps and Eb under the same lattice strains are found to be highly different depending on the switching pathways. However, by carefully designing the interfacial tail atoms, strain engineering can efficiently improve Eb and Ps for both pathways in o-HfO2 films. Our work uncovers the mechanisms of the switching pathways and opens a new avenue for preparing high-performance ferroelectric devices using strain engineering.

We have studied the field cycling behavior of microscopic TiN/Hf0.5Zr0.5O2/TiN ferroelectric capacitors using synchrotron-based soft x-ray photoemission electron microscopy. The oxygen vacancy ([Formula: see text]) concentration near the top TiN/Hf0.5Zr0.5O2 interface is estimated from the reduction of Hf4+ to Hf3+ as measured in the Hf 4f core level spectra. The [Formula: see text] concentration increases with field cycling and redistributes under the effect of the internal field due to the polarization. Upward pointing polarization slightly depletes the concentration near the top interface, whereas downward polarization causes [Formula: see text] drift toward the top interface. The [Formula: see text] redistribution after wake-up is consistent with shifts in the I–V switching peak. The Schottky barrier height for electrons decreases systematically with cycling in polarization states, reflecting the overall increase in [Formula: see text].

Ferroelectric thin-film bilayers of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT)/PbZr0.52Ti0.48O3 (PZT) were grown on a flexible substrate of mica using pulsed laser deposition. Growth of the bilayer was induced with a thin film of LaNiO3 (LNO) single crystal, which was deposited on a mica substrate through van der Waals epitaxy. The LNO thin film also serves as the electrode for the bilayer device. The growth of the LNO thin film along the [Formula: see text] orientation adopts a “Stranski–Krastanov” mechanism, governed by the relaxation of elastic energy between LNO/mica. Compared with the single layers of PMN-PT or PZT, or the bilayer of PZT/PMN-PT, the PMN-PT/PZT bilayer exhibits enhanced ferroelectric properties, with remnant polarization up to 72 μC/cm2. In addition, polarization in the PMN-PT/PZT bilayer exhibits excellent resistance against mechanical bending fatigue over 108 switching cycles. Such improved performances are ascribed to spontaneous polarizations enhanced by the residual stress at the PMN-PT/PZT heterointerface, increased interfacial potential barrier against leakage, and suppressed diffusion of Nb or Mg across the interface.

The monolayers of early transition metal carbides and carbonitrides named MXenes are exfoliated from the corresponding bulk MAX phases (Mn+1AXn, M = early transition metal, A = group IIIA or IVA element and X = carbon and/or nitrogen), where MX layers are interleaved with “A” atoms. The selective etching of the A element from the MAX phases using the aqueous solution of HF as the etchant causes functionalization of the surface of MXenes, which are represented by Mn+1XnT2, (T=F, O, H and/or OH). According to experimental reports, the uncontrolled, non-uniform and mixed functionalization of MXene cause the biggest challenge in the isolation of pristine MXene. Using the first-principles calculations, we have carried out a comprehensive study for isolating pristine MXene using Nb4AlC3 MAX phase. The calculated bond-dissociation energy (BDE), density of states (DOS) and electron localization function (ELF) show that the presence of LiF instead of commonly used HF in MAX phase facilitates the isolation of pristine Nb4C3 MXene. Almost all of the MXenes are non-uniformly functionalized therefore, to get an ordered functionalization of MXene, the role of chemical potentials of all the constituents need to be determined. We extended our study and carried out a comprehensive investigation of exfoliation process of Ti3AlC2 to Ti3C2 MXene via HF insertion. Spontaneous dissociation of HF and subsequent termination of edge Ti atoms by H/F weakens Al−MXene bonds. A consequent opening of interlayer gap allows further insertion of HF that leads to the formation of AlF3 and H2, which eventually come out of the MAX, leaving behind functionalized MXene. Thermodynamic analysis shows that depending upon the chemical potentials, along with full F-termination, mixed and non-uniform functionalization of MXene can also be stabilized. Unlike other functional groups, O-termination opens the band gap in otherwise metallic MXenes. We showed that depending upon the position of the O atoms, two phases namely BB′ and CB are possible. Using the insights from charge transfer, DOS, and ELF, the stability of BB′ and CB phases is explored as a function of M atom in MXene. Further, due to the absence of inversion symmetry, the CB phase of Sc2CO2 MXene possess intrinsic dipoles. A monolayer having both ferroelectric and new-unreported antiferroelectric low-energy configurations is obtained for the first time. The reasonable polarization switching barrier ensures the potential of this material for nonvolatile memory applications. Furthermore, as we go from the monolayer to bilayer, interestingly, the transition from insulator to a nondegenerate 2D electron/hole gas system takes place. As there are various choices of functional groups available, an enormous number of MXene can be generated. Characterizing all with the conventional methods would be very time-consuming and inefficient. Hence, we utilized the machine-learning (ML) based approach to predict the various properties in an accelerated manner. A total of 23,870 MXenes are generated and stored in a functional materials database named “aNANt”. Using ML based classification model, the metal-semiconductor classification is carried out with an accuracy of 99%. Further, the Gaussian process-based regression model is developed to predict the band gap of these MXenes with GW level accuracy. The application of ML based approach is extended to accurately position the GW band edges at an absolute scale, which are predicted with a minimal root mean square error of 0.12 eV

A strictly non-block matrix switch is a basic component in photonic space-division and time-division switching systems. A polarization dependent 8×8 LiNbO3 matrix switch has recently been reported1,2). However, maintaining polarization dependency for such switches, when insisting upon using polarization maintaining fibers or polarization controllers, seems to be a serious technical barrier for pratical use.

Nonlinear self-switching is an important step toward all-optical signal processing and passive mode-locking of lasers. In nonlinear self-switching, the power-dependent coupling of energy between two channels is caused by the imbalance of nonlinear gain/absorption and/or refractive-index between the two channels. In this paper, we report the experimental results of nonlinear polarization switching in an InGaAs/GaAs single quantum well(QW) GRINSCH optical amplifier. The amplifier consists of a 10 nm InGaAs well. On either side of the well, it includes a 40 nm GaAs barrier, an about 200 nm graded-index separate confinement layer with AlxGa1-xAs (x drops from 0.4 to 0), and an Al0.4Ga0.6As p/n type cladding. It lased at the threshold current 120 mA with 20 % duty cycle at 974 nm. The amplifier had a length about 300 μm and a ridge 50 μm wide for lateral guiding. The electro-luminescence in the TE (TM) mode was centered near 975 (940) nm, indicating the relative energy state of the heavy and light hole subbands. In the experiment, we used a Ti:Sapphire laser (Mirra 900) for femtosecond and cw optical signals. After the signals passed through the amplifier, their polarization status and power distributions between the TE and TM directions were recorded, as shown in Fig. 1.