Journal: Communications Materials

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Publisher

Nature

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ISSN

2662-4443

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2020 - 20268
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Publications1 - 8 of 8
  • Sub-unit cell engineering of CrVO3 superlattice thin films
    Item type: Journal Article
    Bellani, Claudio; Mellaerts, Simon; Hsu, Wei-Fan; et al. (2026)
    Communications Materials
    Ordered corundum oxides introduce new prospects in the field of functional oxides thin films, complementing the more widely studied class of ABO3 perovskites. In this work, we take advantage of the layer-by-layer growth regime to fabricate epitaxial CrVO3 superlattice thin films with atomic-scale accuracy on the periodic arrangement of chromium and vanadium layers. By means of X-ray diffraction, scanning transmission electron microscopy and Raman spectroscopy, we confirm the thickness control in the sub-unit cell scale, alternating 3, 2 or 1 single atomic layers of Cr2O3 and V2O3. We stabilize the ilmenite phase of CrVO3 (space group R3¯) and compare the functional properties of the thin film with those calculated by density functional theory. This approach to the growth of ordered corundum oxides opens the path towards the stabilization of complex oxides with tailored properties by varying the composition and the superlattice period, ultimately broadening the family of functional rhombohedral oxides.
  • Cathodic protection mechanism of iron and steel in porous media
    Item type: Journal Article
    Martinelli-Orlando, Federico; Mundra, Shishir; Angst, Ueli (2024)
    Communications Materials
    Cathodic protection was introduced two centuries ago and since has found widespread application in protecting structures such as pipelines, offshore installations, and bridges from corrosion. Despite its extensive use, the fundamental working mechanism of cathodic protection remains debated, particularly for metals in porous media such as soil. Here, we use in-situ and ex-situ characterisation techniques coupled with electrochemical measurements to characterise the spatio-temporal changes occurring at the steel-electrolyte interface. We show that upon cathodic protection, the interfacial electrolyte undergoes alkalinisation and deoxygenation, and that depending on polarisation conditions, an iron oxide film can simultaneously form on the steel surface. We further demonstrate that these changes in interfacial electrolyte chemistry and steel surface state result in altered anodic and cathodic reactions and their kinetics. We propose a mechanism of cathodic protection that integrates previous theories, based on both concentration and activation polarisation, complimentarily. We discuss the implications of this study in enhancing corrosion protection technologies and the safe, economical, and environmentally friendly operation of critical steel-based infrastructures.
  • Making EuO multiferroic by epitaxial strain engineering
    Item type: Journal Article
    Goian, Veronica; Held, Rainer; Bousquet, Eric; et al. (2020)
    Communications Materials
    Multiferroics are materials exhibiting the coexistence of ferroelectricity and ideally ferromagnetism. Unfortunately, most known magnetoelectric multiferroics combine ferroelectricity with antiferromagnetism or with weak ferromagnetism. Here, following previous theoretical predictions, we provide clear experimental indications that ferroelectricity can be induced by epitaxial tensile strain in the ferromagnetic simple binary oxide EuO. We investigate the ferroelectric phase transition using infrared reflectance spectroscopy, finding that the frequency of the soft optical phonon reduces with increasing tensile strain and decreasing temperature. We observe such a soft mode anomaly at 100 K in (EuO)2/(BaO)2 superlattices grown epitaxially on (LaAlO3)0.29-(SrAl1/2Ta1/2O3)0.71 substrates, which is a typical signature for a displacive ferroelectric phase transition. The EuO in this superlattice is nominally subjected to 6.4% biaxial tensile strain, i.e., 50% more than believed needed from previously published calculations. We interpret our results with new first-principles density functional calculations using a hybrid functional, which provides a better quantitative agreement with experiment than the previously used local-density approximation and generalized gradient approximation functionals.
  • High performance ultra-thin lithium metal anode enabled by vacuum thermal evaporation
    Item type: Journal Article
    Rospars, Nicolas; Srout, Mohammed; Fu, Chengyin; et al. (2024)
    Communications Materials
    The passivation layer that naturally forms on the lithium metal surface contributes to dendrite formation in lithium metal batteries by affecting lithium nucleation uniformity during charging. Herein, we propose using vacuum thermal evaporation to produce a high-performance ultra-thin lithium metal anode (≤25 µm) with a native layer much thinner than that of extruded lithium. The evaporated lithium metal shows significantly reduced charge-transfer resistance, resulting in uniform and dense lithium plating in both carbonate and ether electrolytes. This study reveals that the evaporated lithium metal outperforms the extruded version in ether electrolyte and with LiFePO4 cathodes, showing a 30% increase in cycle life. Additionally, when paired with LiNi0.6Mn0.2Co0.2O2 cathodes in carbonate electrolyte, the evaporated anode’s cycle life is tripled compared to the extruded lithium metal. This demonstrates that vacuum thermal evaporation is a viable method for producing ultra-thin lithium metal anodes that prevent dendrite growth due to their excellent surface condition. (Figure presented.)
  • Millimeter-wave to near-terahertz sensors based on reversible insulator-to-metal transition in VO2
    Item type: Journal Article
    Qaderi, Fatemeh; Rosca, Teodor; Burla, Maurizio; et al. (2023)
    Communications Materials
    In the quest for low power bio-inspired spiking sensors, functional oxides like vanadium dioxide are expected to enable future energy efficient sensing. Here, we report uncooled millimeter-wave spiking detectors based on the sensitivity of insulator-to-metal transition threshold voltage to the incident wave. The detection concept is demonstrated through actuation of biased VO2 switches encapsulated in a pair of coupled antennas by interrupting coplanar waveguides for broadband measurements, on silicon substrates. Ultimately, we propose an electromagnetic-wave-sensitive voltage-controlled spike generator based on VO2 switches in an astable spiking circuit. The fabricated sensors show responsivities of around 66.3 MHz.W−1 at 1 μW, with a low noise equivalent power of 5 nW.Hz−0.5 at room temperature, for a footprint of 2.5 × 10−5 mm2. The responsivity in static characterizations is 76 kV.W−1. Based on experimental statistical data measured on robust fabricated devices, we discuss stochastic behavior and noise limits of VO2 -based spiking sensors applicable for wave power sensing in mm-wave and sub-terahertz range.
  • Static magnetic order with strong quantum fluctuations in spin-1/2 honeycomb magnet Na₂Co₂TeO₆
    Item type: Journal Article
    Jiao, Jinlong; Li, Xiyang; Lin, Gaoting; et al. (2024)
    Communications Materials
    Kitaev interactions, arising from the interplay of frustration and bond anisotropy, can lead to strong quantum fluctuations and, in an ideal case, to a quantum-spin-liquid state. However, in many nonideal materials, spurious non-Kitaev interactions typically promote a zigzag antiferromagnetic order in the d-orbital transition-metal compounds. Here, by combining neutron scattering with muon-spin rotation and relaxation techniques, we provide mechanism insights into the exotic properties of Na2Co2TeO6, a candidate material of the Kitaev model. Below TN, the zero-field muon-spin relaxation rate becomes almost constant (~0.45 μs−1). We attribute this temperature-independent relaxation rate to the strong quantum fluctuations, as well as to the frustrated Kitaev interactions. As the magnetic field increases, neutron scattering data indicate a broader spin-wave excitation at the K-point. Therefore, quantum fluctuations seem not only robust but are even enhanced by the applied magnetic field. Our findings provide valuable hints for understanding the onset of the quantum-spin-liquid state in Kitaev materials.
  • Three-dimensional imaging of topologically protected strings in a multiferroic nanocrystal
    Item type: Journal Article
    Najeeb, Mansoor A.; Serban, David; Porter, Daniel G.; et al. (2025)
    Communications Materials
    Multiferroic materials can host a plethora of intriguing phenomena due to the presence of multiple ferroic properties that break both spatial inversion symmetry and time reversal symmetry at an observable scale. Hexagonal manganite multiferroics are of particular interest as the properties of their symmetry-lowering phase transition can be described by a Mexican-hat-like potential energy surface. The early universe is proposed to have undergone a symmetry-lowering phase transition that is described by a similar Mexican-hat-like potential that gives rise to the formation of one-dimensional topologically protected defects known as cosmic strings. According to the Kibble-Zurek mechanism, hexagonal manganite multiferroics can host the crystallographic equivalent of cosmic strings and can therefore serve as a testing ground for exploration of concepts in cosmology. To date, however, direct imaging of 1D topological defects in a condensed matter material system has not been achieved. Here we report on robust three-dimensional imaging of topologically protected strings in a single hexagonal manganite nanocrystal, enabled by advances in experimental techniques. Our findings reveal multiferroic strings with a preferred phase vortex winding direction and average separation of similar to 93 nm.
  • High harmonic spectroscopy reveals anisotropy of the charge-density-wave phase transition in TiSe₂
    Item type: Journal Article
    Tyulnev, Igor; Zhang, Lin; Vamos, Lenard; et al. (2025)
    Communications Materials
    Charge density waves (CDW) appear as periodic lattice deformations which arise from electron-phonon and excitonic correlations and provide a path towards the study of condensate phases at high temperatures. While characterization of this correlated phase is well established via real or reciprocal space techniques, for systems where the mechanisms interplay, a macroscopic approach becomes necessary. Here, we demonstrate the application of polarization-resolved high-harmonic generation (HHG) spectroscopy to investigate the correlated CDW phase and transitions in TiSe2. Unlike previous studies focusing on static crystallographic properties, the research examines the dynamic reordering that occurs within the CDW as the material is cooled from room temperature to 14 K. By linking ultrafast field-driven dynamics to the material's potential landscape, the study demonstrates HHG's unique sensitivity to highly correlated phases and their strength. The findings reveal an anisotropic component below the CDW transition temperature, providing insights into the nature of this phase. The investigation highlights the interplay between linear and nonlinear optical responses and their departure from simple perturbative dynamics, offering a fresh perspective on correlated quantum phases in condensed matter systems.
Publications1 - 8 of 8