Search

We report on the synthesis of ultra-thin films of highly distorted EuNiO3 (ENO) grown by interrupted pulse laser epitaxy on YAlO3 perovskite (YAP) substrates. Samples were then investigated with reflection high energy electron diffraction, atomic force microscopy, x-ray diffraction, reciprocal space mapping, and x-ray absorption spectroscopy. Combined, the measurements revealed the samples exhibited high structural and electronic quality that is of critical importance to the observed electronic and magnetic properties of the rare-earth nickelates. Growth of ultra-thin films of this highly distorted nickelate system in precisely controlled environments provides the ability to thoroughly investigate electronic phases with decoupled metal-to-insulator/charge-order and anti-ferromagnetic transitions. [ABSTRACT FROM AUTHOR]

We have deposited NdNi1−xMnxO3 (0 ⩽ x ⩽ 0.10) thin films on two different substrates, YAlO3 (1 0 0) and NdGaO3 (0 0 1), respectively, to explore the effects of Mn-doping with compressive and tensile strain. These films show metal–insulator transitions, except for two films with x = 0.10. The Hall coefficient measurements show that the majority of charge carriers are holes in these films. Increasing Mn-doping linearly decreases the temperature coefficient of resistance in the conducting temperature-region. The resistivity increases systematically with increasing Mn-doping in the films with tensile strain, whereas it non-monotonically decreases with doping in thin films with compressive strain. This study reveals competition and combination of different effects of the Mn-doping and of the strain, where the competition and the combination depend on the temperature-region and the type of strain. In addition to the effects of electronic configuration of Mn ions on the free carrier concentration, we find that the effects of Mn-doping on the resistivity are also mediated by the structure, and moulded under the influence of strain. The effects of Mn-doping and strain are distinguished and explained here. [ABSTRACT FROM AUTHOR]

Electron and spin dynamics of strongly correlated NdNiO3 are investigated across the metal–insulator transition with ultrafast optical spectroscopy at different temperatures, pump laser fluences, and laser polarizations. Transient differential reflectivity measurements on the insulating phase NdNiO3 show two characteristic electronic decay processes. The slow decay process, strongly dependent on coherent phonon excitation, is attributed to the electron–phonon interaction, while the fast decay process, to the electron-spin interaction. The temporal evolution of Kerr rotation reveals that net spin polarization can be induced by circularly polarized light in insulating NdNiO3 via electron excitation from the Ni t to e orbital, and two net spin polarizations with opposite directions are observed given the antiferromagnetic ordering in insulating NdNiO3. At the insulator-to-metal transition, the transient differential reflectivity reverses its sign; the metallic phase NdNiO3 also shows two characteristic electronic decay processes, a typical metallic decay processes and a slow decay process; the slow decay process is attributed to the interaction between electrons and the low frequency coherent phonons (2.45 THz). Our experiments demonstrate that the phase transition involves several processes upon continuous heating: the electron-spin interaction disappears at 9 K below the transition temperature; at the transition temperature, NdNiO3 transitions into the metallic phase and the antiferromagnetic ordering transitions into the paramagnetic ordering; at the transition temperature, the structure of NdNiO3 changes from a monoclinic structure () to a high temperature orthorhombic () structure. Such a structure change results in the change in phonon vibrations, and subsequently, leads to the disappearance of the electron–phonon interactions due to the insulating phase NdNiO3 and the emergence of other types of electron–phonon interactions due to the metallic phase. [ABSTRACT FROM AUTHOR]

The bulk rhombohedral LaNiO3 is a unique member of the rare-earth nickelate RNiO3 family devoid of any phase transition down to low temperatures, in addition, it lies in the proximity of quantum critical point. In this paper, we show that the bi-axial strain induces pronounced disparity both in static and dynamic transport when measured across two in-plane crystal axes of an orthorhombic LaNiO3 thin film. A maximum in-plane transport anisotropy of 50% at 30 K is observed in dc conductivity when measured across [1 0 0]o and [0 1 0]o directions. Similar in-plane dynamic transport anisotropy i.e. dissimilar disorder strengths appear across two orthogonal axes in oxygen deficient film. In oxygen stoichiometric film too, a pure Drude-type THz conductivity transforms to a near Drude-type across in-plane orientations. This unique in-plane transport anisotropy, unveiled in a broad range of dc to THz frequencies, underlines a strong structure-property relation and emphasizes the need to engineer the charge transport along appropriate crystal axis for evaluating the application potential of rare earth nickelates. [ABSTRACT FROM AUTHOR]

We report a detailed study of the structural and magnetic properties of pulse laser deposition grown superlattices (SLs) comprising of metallic ferromagnet La0.7Sr0.3MnO3 (LSMO) and paramagnet LaNiO3 (LNO) with the stacking order [(LSMO)d/(LNO)t]15 (d  =  3.3 nm, t  =  1.5 nm, 3 nm, 5 nm) on (1 1 1) and (0 0 1)  −  oriented SrTiO3 (STO) single crystal substrates. The x-ray reflectivity data and diffraction of SLs reveal the well-defined smooth and periodic nature of the SLs. The reciprocal space mapping provides the evidence of coherently strained epitaxial layers of the perovskite structures with long-range periodicity. The [(LSMO)3.3/(LNO)3]15 SL on STO (1 1 1) exhibits a positive exchange-bias effect, which indicates the induced-magnetization with interface driven antiferromagnetic coupling in (1 1 1)-stacking. The robust magnetic ordering was observed for a SL grown on (1 1 1)-oriented STO as compared to the (0 0 1) stacked SLs. Beyond 1.5 nm thickness of LaNiO3, all of the above anomalous magnetic characteristics of SLs seizes away. The interface induced magnetism in the LNO layers was discussed using the temperature and magnetic field dependence of magnetization measurements. [ABSTRACT FROM AUTHOR]

High-quality epitaxial LaMnO3/LaAlO3 superlattices (SLs) with (0 0 1), (0 1 1), and (1 1 1) out-of-plane orientation were grown by pulsed laser deposition. This SL material was predicted theoretically as a Chern insulator for realizing the quantum anomalous Hall effect. In our investigations, a paramagnetic-ferromagnetic phase transition is found with decreasing temperature around 100 K, indicating a controllable ferroic order at low temperatures. Electrical transport measurements reveal a thermally activated single-gap behavior with a fitted band gap of 436 meV for the (1 1 1)-oriented SL. With that, the results prove the predictions of a ferromagnetic background in the SLs, and of a gapped band structure. [ABSTRACT FROM AUTHOR]

We present a direct method to measure the oxygen stoichiometry in an oxide film with an accuracy of about 2%. It is based on a combination of 18O annealing and high mass resolution secondary ion mass spectroscopy. Calibration has been done on a LaNiO3 film whose electrical properties dependence on oxygen stoichiometry are well documented. The method is illustrated with a series of LaNiO3 films grown on SrTiO3 substrates prepared with different oxygen stoichiometries. The large influence of the surface state on oxygen exchange is evidenced in films grown on different substrate orientations or coated with a thin layer of LaAlO3. Oxygen surface exchange and bulk diffusion is then discussed for both LaNiO3 and SrVO3 films. [ABSTRACT FROM AUTHOR]

Because of the observation of half-metallicity in graphitic carbon nitride C4N3 (g-C4N3), extensive research has recently been focused on this compound. Using density-functional calculations, herein diverse electronic properties of g-C4N3 were engineered by applying biaxial compressive strain. The calculated results demonstrate that g-C4N3 preserves ferromagnetic half-metallicity when the strain is lower than  −2%, accompanied by a decrease of the half-metallic gap. When the compressive strain ranges from  −5 to  −3%, the compound turns into nonmagnetic metal. By increasing the strain on the end, it becomes a nonmagnetic semiconductor. Further investigations show that all nonmagnetic semiconductors possess a direct band gap with a value of around 1.6 eV. This fact indicates that g-C4N3 can be applied in spintronic or photovoltaic fields under a strain environment. [ABSTRACT FROM AUTHOR]

Epitaxial PrNiO3 (PNO) thin films were grown on single-crystal LaAlO3, (LaAlO3)0.3(SrAlTaO6)0.7, and SrTiO3 substrates, respectively, by the polymer-assisted deposition method. It is found that compared with that of PNO bulk, the c-axis parameter of PNO film increases under compressive strain and decreases under tensile strain. Moreover, under tensile strain, the c-axis first decreases and then increases. All the PNO films exhibit metal–insulator (MI) transition with a thermal hysteresis in the temperature-dependent resistivity. At room temperature, the resistivity of the PNO films shows an increasing trend with the lattice mismatch strain changing from compressive to tensile. The MI transition temperature TMI of the PNO films under both compressive and tensile strains is lower than that of PNO bulk. However, the trend of TMI dependent on the lattice mismatch between the film and the substrate under tensile strain is decreasing. The conduction mechanism fits very well with the Mott’s variable range hopping (VRH) model in temperatures below 35 K. It is suggested that strain relaxation increases with the strain increasing from compressive to tensile, which results in the increase of oxygen vacancies compensated by more Ni2+ changed from Ni3+ in the film. The competing and joint effects of the bending of the Ni–O–Ni bond angle, the elongation of the Ni–O bond length, and the change of Ni valence dominate the transport properties of the PNO films. [ABSTRACT FROM AUTHOR]

We used molecular beam epitaxy (MBE) growth to control the density of oxygen vacancy-related (VO-R) defects at (Ba,Sr)TiO3/SrTiO3 heterojunctions along with depth-resolved cathodoluminescence spectroscopy (DRCLS), surface photovoltage spectroscopy and positron annihilation spectroscopy (PAS) to identify their optical signature, energy levels and spatial distribution. We grew (Ba,Sr)TiO3 epilayers on SrTiO3 using oxygen plasma-assisted MBE under a range of oxygen pressures and temperatures designed to control oxygen extraction from the SrTiO3 substrate that feeds the (Ba,Sr)TiO3 epilayer growth and generates oxygen vacancies. DRCLS and PAS identify a 2.95 eV optical emission with VO-R defect—valence band transitions that peak below the heterointerface and their interplay with 1.8 and 2.3 eV cation vacancies versus growth conditions. These studies reveal that native defects accumulate near SrTiO3/(Ba,Sr)TiO3 interfaces and are sensitive to growth conditions. [ABSTRACT FROM AUTHOR]

The PDF file provided contains web links to all articles in this volume [ABSTRACT FROM AUTHOR]

Depth-resolved cathodoluminescence spectroscopy (DRCLS) has developed over the past few decades into a powerful technique for characterizing electronic properties of advanced materials structures and devices on a nanoscale. The lateral and depth-resolved capabilities of DRCLS enable researchers to probe native defects, impurities, chemical changes and local band structure inside state-of-the-art device structures on an unprecedented scale. A key strength of DRCLS is its ability to distinguish electronic features at buried interfaces within multilayer device structures, interfaces whose microscopic physical features can determine macroscopic electronic properties. This review provides a general overview of DRCLS and illustrates the wide array of applications now available using this technique. [ABSTRACT FROM AUTHOR]