DataSheet1_Asymmetric Interfacial Intermixing Associated Magnetic Coupling in LaMnO3/LaFeO3 Heterostructures.docx

The structural and magnetic properties of LaMnO3/LaFeO3 (LMO/LFO) heterostructures are characterized using a combination of scanning transmission electron microscopy, electron energy-loss spectroscopy, bulk magnetometry, and resonant x-ray reflectivity. Unlike the relatively abrupt interface when LMO is deposited on top of LFO, the interface with reversed growth order shows significant cation intermixing of Mn3+ and Fe3+, spreading ∼8 unit cells across the interface. The asymmetric interfacial chemical profiles result in distinct magnetic properties. The bilayer with abrupt interface shows a single magnetic hysteresis loop with strongly enhanced coercivity, as compared to the LMO plain film. However, the bilayer with intermixed interface shows a step-like hysteresis loop, associated with the separate switching of the “clean” and intermixed LMO sublayers. Our study illustrates the key role of interfacial chemical profile in determining the functional properties of oxide heterostructures.</p

Electronic and Chemical Properties of Nickel Oxide Thin Films and the Intrinsic Defects Compensation Mechanism

Although largely studied, contradictory results on nickel oxide (NiO) properties can be found in the literature. We herein propose a comprehensive study that aims at leveling contradictions related to NiO materials with a focus on its conductivity, surface properties, and the intrinsic charge defects compensation mechanism with regards to the conditions preparation. The experiments were performed by in situ photoelectron spectroscopy, electron energy loss spectroscopy, and optical as well as electrical measurements on polycrystalline NiO thin films prepared under various preparation conditions by reactive sputtering. The results show that surface and bulk properties were strongly related to the deposition temperature with in particular the observation of Fermi level pinning, high work function, and unstable oxygen-rich grain boundaries for the thin films produced at room temperature but not at high temperature (>200 °C). Finally, this study provides substantial information about surface and bulk NiO properties enabling to unveil the origin of the high electrical conductivity of room temperature NiO thin films and also for supporting a general electronic charge compensation mechanism of intrinsic defects according to the deposition temperature

Stabilizing Perovskite Pb(Mg_0.33Nb_0.67)O₃–PbTiO₃ Thin Films by Fast Deposition and Tensile Mismatched Growth Template

Because of its low hysteresis, high dielectric constant, and strong piezoelectric response, Pb­(Mg1/3Nb2/3)­O3–PbTiO3 (PMN–PT) thin films have attracted considerable attention for the application in PiezoMEMS, field-effect transistors, and energy harvesting and storage devices. However, it remains a great challenge to fabricate phase-pure, pyrochlore-free PMN–PT thin films. In this study, we demonstrate that a high deposition rate, combined with a tensile mismatched template layer can stabilize the perovskite phase of PMN–PT films and prevent the nucleation of passive pyrochlore phases. We observed that an accelerated deposition rate promoted mixing of the B-site cation and facilitated relaxation of the compressively strained PMN–PT on the SrTiO3 (STO) substrate in the initial growth layer, which apparently suppressed the initial formation of pyrochlore phases. By employing La-doped-BaSnO3 (LBSO) as the tensile mismatched buffer layer, 750 nm thick phase-pure perovskite PMN–PT films were synthesized. The resulting PMN–PT films exhibited excellent crystalline quality close to that of the STO substrate

Chemical Structure of Nitrogen-Doped Graphene with Single Platinum Atoms and Atomic Clusters as a Platform for the PEMFC Electrode

A platform for producing stabilized Pt atoms and clusters through the combination of an N-doped graphene support and atomic layer deposition (ALD) for the Pt catalysts was investigated using transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). It was determined, using imaging and spectroscopy techniques, that a wide range of N-dopant types entered the graphene lattice through covalent bonds without largely damaging its structure. Additionally and most notably, Pt atoms and atomic clusters formed in the absence of nanoparticles. This work provides a new strategy for experimentally producing stable atomic and subnanometer cluster catalysts, which can greatly assist the proton exchange membrane fuel cell (PEMFC) development by producing the ultimate surface area to volume ratio catalyst

Structure–Property Relations of Methylamine Vapor Treated Hybrid Perovskite CH₃NH₃PbI₃ Films and Solar Cells

The power conversion efficiency of halide perovskite solar cells is heavily dependent on the perovskite layer being sufficiently smooth and pinhole-free. It has been shown that these features can be obtained even when starting out from rough and discontinuous perovskite film by briefly exposing the film to methylamine (MA) vapor. The exact underlying physical mechanisms of this phenomenon are, however, still unclear. By investigating smooth, MA treated films based on very rough and discontinuous reference films of methylammonium triiode (MAPbI₃) and considering their morphology, crystalline features, local conductive properties, and charge carrier lifetime, we unraveled the relation between their characteristic physical qualities and their performance in corresponding solar cells. We discovered that the extensive improvement in photovoltaic performance upon MA treatment is a consequence of the induced morphological enhancement of the perovskite layer together with improved electron injection into TiO₂, which in fact compensates for an otherwise compromised bulk electronic quality simultaneously caused by the MA treatment

Crystal Structure and Luminescent Properties of R_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ (R = Gd, Sm) Red Phosphors

The R2(MoO4)3 (R = rare earth elements) molybdates doped with Eu3+ cations are interesting red-emitting materials for display and solid-state lighting applications. The structure and luminescent properties of the R2–xEux(MoO4)3 (R = Gd, Sm) solid solutions have been investigated as a function of chemical composition and preparation conditions. Monoclinic (α) and orthorhombic (β′) R2–xEux(MoO4)3 (R = Gd, Sm; 0 ≤ x ≤ 2) modifications were prepared by solid-state reaction, and their structures were investigated using synchrotron powder X-ray diffraction and transmission electron microscopy. The pure orthorhombic β′-phases could be synthesized only by quenching from high temperature to room temperature for Gd2–xEux(MoO4)3 in the Eu3+-rich part (x > 1) and for all Sm2–xEux(MoO4)3 solid solutions. The transformation from the α-phase to the β′-phase results in a notable increase (∼24%) of the unit cell volume for all R2–xEux(MoO4)3 (R = Sm, Gd) solid solutions. The luminescent properties of all R2–xEux(MoO4)3 (R = Gd, Sm; 0 ≤ x ≤ 2) solid solutions were measured, and their optical properties were related to their structural properties. All R2–xEux(MoO4)3 (R = Gd, Sm; 0 ≤ x ≤ 2) phosphors emit intense red light dominated by the 5D0→​7F2 transition at ∼616 nm. However, a change in the multiplet splitting is observed when switching from the monoclinic to the orthorhombic structure, as a consequence of the change in coordination polyhedron of the luminescent ion from RO8 to RO7 for the α- and β′-modification, respectively. The Gd2–xEux(MoO4)3 solid solutions are the most efficient emitters in the range of 0 x < 1.5, but their emission intensity is comparable to or even significantly lower than that of Sm2–xEux(MoO4)3 for higher Eu3+ concentrations (1.5 ≤ x ≤ 1.75). Electron energy loss spectroscopy (EELS) measurements revealed the influence of the structure and element content on the number and positions of bands in the ultraviolet–visible–infrared regions of the EELS spectrum

KEu(MoO₄)₂: Polymorphism, Structures, and Luminescent Properties

In this paper, with the example of two different polymorphs of KEu­(MoO₄)₂, the influence of the ordering of the <i>A</i>-cations on the luminescent properties in scheelite related compounds (<i>A</i>′,<i>A</i>″)_<i>n</i>[(<i>B</i>′,<i>B</i>″)­O₄]_<i>m</i> is investigated. The polymorphs were synthesized using a solid state method. The study confirmed the existence of only two polymorphic forms at annealing temperature range 923–1203 K and ambient pressure: a low temperature anorthic α-phase and a monoclinic high temperature β-phase with an incommensurately modulated structure. The structures of both polymorphs were solved using transmission electron microscopy and refined from synchrotron powder X-ray diffraction data. The monoclinic β-KEu­(MoO₄)₂ has a (3+1)-dimensional incommensurately modulated structure (superspace group <i>I</i>2<i>/b</i>(αβ0)­00, <i>a</i> = 5.52645(4) Å, <i>b</i> = 5.28277(4) Å, <i>c</i> = 11.73797(8) Å, γ = 91.2189(4)^o, <b>q</b> = 0.56821(2)<b>a</b>*–0.12388­(3)<b>b</b>*), whereas the anorthic α-phase is (3+1)-dimensional commensurately modulated (superspace group <i>I</i>1̅(αβγ)­0, <i>a</i> = 5.58727(22) Å, <i>b</i> = 5.29188(18)­Å, <i>c</i> = 11.7120(4) Å, α = 90.485(3)^o, β = 88.074(3)^o, γ = 91.0270(23)^o, <b>q</b> = 1/2<b>a</b>* + 1/2<b>c</b>*). In both cases the modulation arises due to Eu/K cation ordering at the <i>A</i> site: the formation of a 2-dimensional Eu³⁺ network is characteristic for the α-phase, while a 3-dimensional Eu³⁺-framework is observed for the <i>β-</i>phase structure. The luminescent properties of KEu­(MoO₄)₂ samples prepared under different annealing conditions were measured, and the relation between their optical properties and their structures is discussed

Alternating Superconducting and Charge Density Wave Monolayers within Bulk 6R-TaS₂

Van der Waals (vdW) heterostructures continue to attract intense interest as a route of designing materials with novel properties that cannot be found in nature. Unfortunately, this approach is currently limited to only a few layers that can be stacked on top of each other. Here, we report a bulk vdW material consisting of superconducting 1H TaS2 monolayers interlayered with 1T TaS2 monolayers displaying charge density waves (CDW). This bulk vdW heterostructure is created by phase transition of 1T-TaS2 to 6R at 800 °C in an inert atmosphere. Its superconducting transition (Tc) is found at 2.6 K, exceeding the Tc of the bulk 2H phase. Using first-principles calculations, we argue that the coexistence of superconductivity and CDW within 6R-TaS2 stems from amalgamation of the properties of adjacent 1H and 1T monolayers, where the former dominates the superconducting state and the latter the CDW behavior

Co-Rich ZnCoO Nanoparticles Embedded in Wurtzite Zn_1–<i>x</i>Co_<i>x</i>O Thin Films: Possible Origin of Superconductivity

Co-rich ZnCoO nanoparticles embedded in wurtzite Zn_0.7Co_0.3O thin films are grown by pulsed laser deposition on a Si substrate. Local superconductivity with an onset <i>T</i>_c at 5.9 K is demonstrated in the hybrid system. The unexpected superconductivity probably results from Co³⁺ in the Co-rich ZnCoO nanoparticles or from the interface between the Co-rich nanoparticles and the Zn_0.7Co_0.3O matrix

Crystal Structure and Luminescent Properties of R_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ (R = Gd, Sm) Red Phosphors

The R₂(MoO₄)₃ (R = rare earth elements) molybdates doped with Eu³⁺ cations are interesting red-emitting materials for display and solid-state lighting applications. The structure and luminescent properties of the R_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ (R = Gd, Sm) solid solutions have been investigated as a function of chemical composition and preparation conditions. Monoclinic (α) and orthorhombic (β′) R_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ (R = Gd, Sm; 0 ≤ <i>x</i> ≤ 2) modifications were prepared by solid-state reaction, and their structures were investigated using synchrotron powder X-ray diffraction and transmission electron microscopy. The pure orthorhombic β′-phases could be synthesized only by quenching from high temperature to room temperature for Gd_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ in the Eu³⁺-rich part (<i>x</i> > 1) and for all Sm_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ solid solutions. The transformation from the α-phase to the β′-phase results in a notable increase (∼24%) of the unit cell volume for all R_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ (R = Sm, Gd) solid solutions. The luminescent properties of all R_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ (R = Gd, Sm; 0 ≤ <i>x</i> ≤ 2) solid solutions were measured, and their optical properties were related to their structural properties. All R_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ (R = Gd, Sm; 0 ≤ <i>x</i> ≤ 2) phosphors emit intense red light dominated by the ⁵D₀→​⁷F₂ transition at ∼616 nm. However, a change in the multiplet splitting is observed when switching from the monoclinic to the orthorhombic structure, as a consequence of the change in coordination polyhedron of the luminescent ion from RO₈ to RO₇ for the α- and β′-modification, respectively. The Gd_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ solid solutions are the most efficient emitters in the range of 0 < <i>x</i> < 1.5, but their emission intensity is comparable to or even significantly lower than that of Sm_2–<i>x</i>Eu_<i>x</i>(MoO₄)₃ for higher Eu³⁺ concentrations (1.5 ≤ <i>x</i> ≤ 1.75). Electron energy loss spectroscopy (EELS) measurements revealed the influence of the structure and element content on the number and positions of bands in the ultraviolet–visible–infrared regions of the EELS spectrum