RESUMO
Dislocations often exhibit unique physical properties distinct from those of the bulk material. However, functional applications of dislocations are challenging due to difficulties in the construction of high-performance devices of dislocations. Here we demonstrate unidirectional single-dislocation Schottky diode arrays in a Fe2O3 thin film on Nb-doped SrTiO3 substrates. Conductivity measurements using conductive atomic force microscopy indicate that a net current will flow through individual dislocation Schottky diodes under forward bias and disappear under reverse bias. Under cyclic bias voltages, the single-dislocation Schottky diodes exhibit a distinct resistive switching behavior containing low-resistance and high-resistance states with a high resistance ratio of â¼103. A combined study of transmission electron microscopy and first-principles calculations reveals that the Fe2O3 dislocations comprise mixed Fe2+ and Fe3+ ions due to O deficiency and exhibit a one-dimensional electrical conductivity. The single-dislocation Schottky diodes may find applications for developing ultrahigh-density electronic and memory devices.
RESUMO
Ferroelectricity and electrical conductivity are two fundamentally incompatible properties that are difficult to simultaneously achieve in a material. Here, we combine these two contradictory properties by embedding conducting SrNbO3 micro/nanopillars into a ferroelectric SrNbO3.5 (i.e., Sr2Nb2O7) thin film. The high-Tc ferroelectric SrNbO3.5 thin film is epitaxially grown on a LaAlO3 substrate by pulsed laser deposition. The conducting SrNbO3 micro/nanopillars are introduced into the film via an electron-irradiation-induced SrNbO3.5-to-SrNbO3 phase transformation triggered by a focused electron beam. The sizes and distribution of the SrNbO3 micro/nanopillars can be accurately controlled through artificial manipulation of the electron-irradiation-induced SrNbO3.5-to-SrNbO3 phase transformation. The ferroelectric SrNbO3/SrNbO3.5 thin film with an in-plane polarization exhibits an electrical conductivity in the out-of-plane direction. Such conducting ferroelectric thin films may lead to the discovery of plentiful physical phenomena and have great potential for pyroelectric, photoelectric, and multiferroic applications.
RESUMO
Domain walls affect significantly ferroelectric and magnetic properties of magnetoelectric multiferroics. The stereotype is that the ferroelectric polarization will reduce at the domain walls due to the incomplete shielding of depolarization field or the effects of gradient energy. By combining transmission electron microscopy and first-principles calculations, we demonstrate that the ferroelectric polarization of tail-to-tail 180° domain walls in ε-Fe2O3 is regulated by the bound charge density. A huge enhancement (43%) of ferroelectric polarization is observed in the type I domain wall with a low bound charge density, while the ferroelectric polarization is reduced to almost zero at the type II domain wall with a high bound charge density. The magnetic coupling across the type I and type II ferroelectric domain walls are antiferromagnetic and ferromagnetic, respectively. Revealing mechanisms for enhancing ferroelectric polarization and magnetic behaviors at ferroelectric domain walls may promote the fundamental research and potential applications of magnetoelectric multiferroics.
RESUMO
Incoherent interfaces with large mismatches usually exhibit very weak interfacial interactions so that they rarely generate intriguing interfacial properties. Here we demonstrate unexpected strong interfacial interactions at the incoherent AlN/Al2O3 (0001) interface with a large mismatch by combining transmission electron microscopy, first-principles calculations, and cathodoluminescence spectroscopy. It is revealed that strong interfacial interactions have significantly tailored the interfacial atomic structure and electronic properties. Misfit dislocation networks and stacking faults are formed at this interface, which is rarely observed at other incoherent interfaces. The band gap of the interface reduces significantly to ~ 3.9 eV due to the competition between the elongated Al-N and Al-O bonds across the interface. Thus this incoherent interface can generate a very strong interfacial ultraviolet light emission. Our findings suggest that incoherent interfaces can exhibit strong interfacial interactions and unique interfacial properties, thereby opening an avenue for the development of related heterojunction materials and devices.
RESUMO
ε-Fe2O3 has attracted intense interest in the field of magnetoelectric materials due to its promising physical properties. The epitaxial growth of ε-Fe2O3 thin films is challenging since it is a metastable phase of iron oxide. In this study, ε-Fe2O3 (001) thin films are epitaxially grown on SrTiO3 (111) substrates by pulsed laser deposition (PLD). The crystal structure, valence state, and microstructure of the ε-Fe2O3 thin films are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. It is revealed that the oxygen pressure, deposition and annealing temperatures, and laser beam energy affect significantly the epitaxial growth of ε-Fe2O3 thin films. The orientation relationship between films and substrates is ε-Fe2O3 (001)[010] // SrTiO3 (111)[1¯10]. The magnetic hysteresis loops tested by a superconducting quantum interference device and UV-Vis reflection spectra suggest that the ε-Fe2O3 thin film with thickness of â¼ 20 nm has a strong magnetic anisotropy, a coercivity of 600 Oe, and an indirect band gap of 3.26 eV.
RESUMO
Crystal defects play an important role in the degradation and failure of semiconductor materials and devices. Direct determination of band gap of defects is a critical step for clarifying how the defects affect the physical properties of semiconductors. Here, high-quality aluminum nitride (AlN) thin films were grown epitaxially on single-crystal Al2O3 substrates via pulsed laser deposition. The atomic structure and band gap of three types of inversion domain boundaries (IDBs) in AlN were determined using aberration-corrected transmission electron microscopy and atomic-resolution valence electron energy-loss spectroscopy. It was found that the band gap of all of the IDBs reduces evidently compared to that of the bulk AlN. The maximum band gap reduction of the IDBs is 1.0 eV. First-principles calculations revealed that the band gap reduction of the IDBs is mainly due to the rise of pz orbital at the valence band maximum, which originates from the elongated Al-N bonds along the [0001] direction at the IDBs. The successful band gap determination of defects paves an avenue for quantitatively evaluating the effect of defects on the performance of semiconductor materials and devices.