LaNiO3 ultrathin films were deposited on (001) SrTiO3 substrates by pulsed laser deposition. Transport properties of these LaNiO3 films were studied as a function of film thickness. A metal-insulator transition is observed as the film thickness is less than a critical value, 5 unit cells (u.c.). This transition is due to a thickness-driven carrier localization. The critical thickness can be influenced by inserting a 2 u.c.-thick SrTiO3 underlayer between the LaNiO3 film and the substrate. SrTiO3 underlayers, deposited under a low O2 pressure, may keep the 5 u.c. LaNiO3 film metallic. However, the critical thickness of LaNiO3 with a SrTiO3 underlayer post-annealed in O2 at 950 °C is still 5 unit cells. It is proposed that electrons transferred to the LaNiO3 film, induced by oxygen vacancy doping in the underlayer, reduce the critical thickness for carrier localization.

LaAlO3 ultrathin films, 10 unit cells in thickness, have been deposited epitaxially on TiO2-terminated (001) SrTiO3 substrates with various O2 pressures. Electromechanical response from the LaAlO3/SrTiO3 heterostructures is studied using combined piezoresponse force microscopy, electrostatic force microscopy, and scanning Kelvin probe microscopy. Oxygen vacancies are found to be responsible for the observed piezoelectric response but only for samples deposited with an oxygen pressure lower than 10–5 mbar. However, ambient humidity is demonstrated to have a significant effect on the electromechanical response. The observations are discussed in terms of modulations on the intrinsic electrostriction in LAO/STO by an electric field induced by nonuniform distribution of either oxygen vacancies in the bulk or ionic adsorbates on the surface of LAO.Keywords: electromechanical response; piezoresponse force microscopy; surface adsorbate; surface and interface; two-dimentional electron gas;

•We prepared Fe:SrTiO3/Nb:SrTiO3 epitaxial homojunctions.•We found peculiar rectifying characteristics in the above junction.•We explained this by the temperature-dependent epsilon of SrTiO3.Fe-doped SrTiO3 (Fe:STO) thin films have been deposited epitaxially on Nb-doped SrTiO3 (Nb:STO) substrates to form a homojunction. Rectifying characteristics of the Fe:STO/Nb:STO homojunction are studied as a function of temperature. The current under reverse bias is observed to increase dramatically with decreasing temperature. This increased reverse current is ascribed to direct tunneling from the valence band of Fe:STO into the conduction band of Nb:STO, by taking into account the temperature and bias dependence of the dielectric constant of SrTiO3.

Ferroelectric \(\hbox {BiFeO}_3\) (BFO) thin films were deposited on (001) \(\hbox {SrTiO}_3\) substrates buffered with \(\hbox {La}_{0.7}\hbox {Sr}_{0.3}\hbox {MnO}_3\) (LSMO) electrodes. Bipolar resistive switching in Pt/BFO/LSMO heterostructures were observed with high stability and long retention. However, transport characteristics of Pt/BFO/LSMO is highly asymmetric and pronounced resistive switching can only be observed by applying negative reading pulses on the Pt top electrodes, i.e. when the Pt/BFO Schottky barrier is reverse-biased. This resistive switching is discussed in terms of a modulation on the Pt/BFO interface Schottky barrier by the polarization switching in ferroelectric BFO. Comparative studies on Pt/BFO/\(\hbox {SrRuO}_3\) and Pt/BFO/\(\hbox {LaNiO}_3\) heterostructures reveal that the work function of the electrode materials and the formation of Schottky barriers are significant to the observed resistive switching behaviors.

AbstractThe effects of Pr substitution on the structures, magnetism and electrical properties of Bi(Fe0.95Mn0.05)O3 films are investigated systematically. X-ray diffraction and Raman spectra results confirm that a phase transition from rhombohedral to tetragonal structure occurs at about 15% Pr substitution. The X-ray photoelectron spectroscopy reveals that Fe2+ in the films can be suppressed by Pr substitution. Enhanced ferromagnetism at room temperature is observed near the phase boundary composition. The increased remanent magnetization in the 15% Pr-substituted film can be understood by taking into account both the modification of the short-range canted G-type antiferromagnetic order at phase boundaries and the suppression of long-range incommensurate spin cycloid of BiFeO3 due to Pr substitution. Meanwhile, large ferroelectric remanent polarization of un-doped BFO can be maintained when Pr concentration is less than 20%. With 15% Pr substitution, the film shows a large remanent polarization of 62 μC/cm2 and a reduced coercive field of 217 kV/cm. These results demonstrate that doped BFO films with compositions near phase boundary may be promising candidates for multifunctional applications due to the simultaneous exhibition of enhanced ferromagnetism and superior ferroelectric properties.Highlights► The effects of Pr substitution on multiferroicity of BiFeO3 films are studied. ► A phase transition from R3c to P 4mm occurs around 15% Pr substitution. ► Enhanced ferromagnetism is observed near the phase boundary composition. ► Large ferroelectric remanent polarization can be also achieved at the phase boundary.

The effects of Pr substitution on the structure and magnetism of Bi(Fe0.95Mn0.05)O3 powders are investigated systemically. X-ray diffraction and Raman spectra results confirm a phase transition from rhombohedral to tetragonal structure with increasing Pr concentration and the phase boundary occurs at 14% Pr substitution. At the phase boundary composition, enhanced room temperature ferromagnetism has been observed with a remanent magnetization about 0.260 emu/g. The increased magnetization can be understood considering both the modification of the short-range canted G-type antiferromagnetic order at phase boundaries and the suppression of long-range incommensurate spin cycloid of BiFeO3 by Pr substitution.

(1−x%)(Na0.5Bi0.5)TiO3–x%SrTiO3 (NBTSx) thin films were deposited on Pt/TiO2/SiO2/Si substrates by a spin-on sol–gel method and rapid thermal annealing. The stock solutions were prepared using sodium acetate, bismuth acetate, strontium acetate, and titanium n-butoxide as precursors, ethanol, and acetic acid as solvents and acetylacetone as the chelating agent. The thermal treatment conditions were determined by thermal analyses of the dry gel powders derived from the stock solutions. Structure and dielectric tunable properties of the films were studied as functions of Sr concentration. NBTSx films exhibit the perovskite structure of a pseudo-cubic symmetry with the lattice parameters increasing with increasing Sr concentration. It was found that the substitution of Sr in Na0.5Bi0.5TiO3 may greatly reduce the dielectric loss while decrease the tunability at the same time. The best figure of merit was achieved in NBTS80 films. The results were discussed and compared with related materials.

Faceted single-crystalline ZnO tubes were synthesized by a simple soft solution method at 65 °° C. These tubes are of several micrometers in length and several hundred nanometers in diameter, with bell-mouths on each end. Structural characterizations using electron spectroscopy revealed that these hexagonal ZnO tubes were along [0 0 0 1] direction and side-enclosed by {011¯0} facets. The growth of ZnO in hydrothermal condition and the formation of this unusual bell-mouthed structure were discussed on the basis of the observation of ring-shaped nano-crystallites upon decreasing the time for growth.