Huairuo Zhang

Two-dimensional Cu nanostructures containing noncanonical face-centered cubic/hexagonal close-packed (fcc/hcp) heterophase boundaries are attractive for CO2 electroreduction but remain difficult to prepare by wet-chemical methods. Here, we report a high-temperature solution reduction route to Cu nanodisks with a thickness of 26.5 ± 2.3 nm and a diameter of 85.6 ± 3.7 nm. Transmission electron microscopy reveals abundant fcc/2H and fcc/4H interfaces on the nanodisk side surfaces, where the 2H and 4H polytypes exhibit AB and ABCB stacking, respectively. In CO2-saturated 0.1 M KHCO3, the nanodisks achieve a methane Faradaic efficiency of 60.4% at −1.25 V vs the reversible hydrogen electrode and outperform fcc Cu nanoparticle and microsheet controls tested at the same catalyst loading. Density functional theory calculations indicate that the free-energy penalty for forming the *CHO intermediate is smaller on the fcc/2H and fcc/4H models than on fcc Cu. These results support a thermodynamic contribution of heterophase interfaces to the observed methane selectivity; the calculations do not establish a reduction in kinetic activation barriers. This solution-phase route therefore provides access to phase-engineered Cu nanodisks and enables structure−property relationships relevant to CO2-to-CH4 electrocatalysis.

The interplay of superconductivity, band topology, and spontaneous time-reversal-symmetry breaking (TRSB) is expected to enable topological superconducting boundary states. Intriguingly, the iron-chalcogenide superconductor FeTe 0.55 Se 0.45 exhibits spontaneous magnetization in the superconducting state, motivating its use as a single-material platform in which three ingredients coexist. Here, we report evidence for a nontrivial, boundary-mediated superconducting transport response in exfoliated Fe(Te,Se) devices, exhibiting long-range nonlocality and strongly suppressed thermal broadening. Polar Kerr measurements establish that TRSB emerges below T Kerr < T c and coexists with superconductivity across multiple Fe(Te,Se) compositions studied here, providing an independent symmetry-breaking scale that can be directly compared with transport. To reliably access boundary transport, we engineer crystallographically sharp, continuous edges and implement side-surface-dominant contacts, as validated by contact-size analysis and cross-sectional imaging. Under these conditions, topological FeTe 0.55 Se 0.45 exhibits an anomalous conductance plateau that is absent in topologically trivial FeTe 0.40 Se 0.60 and Fe 1.02 Te 0.55 Se 0.45 under comparable measurements. This plateau requires both the source and drain to be attached to uninterrupted sharp edges, persists over micrometer-scale separations far exceeding the bulk coherence length, has markedly reduced thermal decoherence, and collapses when the drain is moved to the top surface. Its temperature evolution is governed by TRSB: The plateau shows minimal thermal broadening below T Kerr * and disappears near T Kerr rather than T c . Collectively, the doping selectivity, TRSB correlation, edge-geometry requirement, and long-range nonlocal nature establish experimentally grounded criteria for identifying boundary-mediated superconducting transport in FeTe 0.55 Se 0.45 and motivate further phase-sensitive and theoretical work to determine its microscopic origin.

Multiferroics host simultaneous and coupled ferroic orders, allowing disparate external stimuli to induce abrupt transformations in their structures and properties. Creating multiferroicity in two-dimensional (2D) van der Waals (vdW) platforms would add the elements of strong quantum confinement, enhanced quasiparticle excitations, and wide tunability to the capabilities of these systems. In this work, we constructed vdW heterostructures of ferromagnetic triiron gallium ditelluride (Fe ₃ GaTe ₂ ) and ferroelectric copper indium thiophosphate (CuInP ₂ S ₆ ) to integrate their respective orders. We observed strong interferroic coupling at room temperature by demonstrating ferroelectrically reconfigurable magnetic anisotropy of 2D Fe ₃ GaTe ₂ . The interferroic magnetoelectricity diminished with increasing Fe ₃ GaTe ₂ thickness, revealing the interfacial nature of heterostructure multiferroicity. Our discovery of all-vdW heterostructure multiferroicity opens the door to the artificial assembly of vdW layers for designer 2D multiferroics.

We have fabricated all-thin-film solid oxide fuel cell (SOFC) heterostructures and investigated the transport properties of Sm0.2Ce0.8O2−δ (SDC20) in an out-of-plane measurement geometry. The SOFC heterostructures, consisting of a bottom SrRuO3 or Ba0.93La0.07SnO3 electrode and an SDC20 electrolyte, were fabricated on SrTiO3 (001) substrates via pulsed laser deposition. The hetero-epitaxial nature and atomically sharp interfaces between the electrolyte and the electrode were confirmed by x-ray diffraction and high-resolution scanning transmission electron microscopy. Out-of-plane electrochemical impedance spectroscopy measurements indicate that the electrochemical properties of the SDC20 thin films are quantitatively consistent with those of bulk SDC20 in a wide temperature range from 350 to 550 °C. Our results demonstrate that all-thin-film heterostructures can serve as a platform for direct investigation of intrinsic transport properties of electrochemical materials.

Achieving low contact resistance in p-type transistors remains a critical challenge when using transition-metal dichalcogenides (TMDs) as channel materials. Deposition of high work function contact metals at elevated temperatures often causes defects or strain at the metal/channel interface, which in turn can result in an increased contact resistance. Metallic two-dimensional (2D) materials offer a promising solution in this context due to their low-temperature contact formation and atomically flat surfaces. However, experimental progress has been slow in part due to the rather large bandgap of monolayer WSe ₂ . Here, we report a novel approach, using metallic layered Nb _0.3 W _0.7 Se ₂ as a contact for monolayer and bilayer WSe ₂ transistors with channel lengths down to 100 nm. Combined with ultra-scaled gate dielectrics with an effective oxide thickness (EOT) of 1.3nm, the resulting 2D/2D contacted FETs exhibit high on-current densities of up to 375 µA/µm and 1.1 mA/µm on monolayer and bilayer WSe ₂ channel, respectively. This method also enables the fabrication of 2D/2D contacted monolayer WSe ₂ devices achieving subthreshold swings as small as 88 mV/dec.

Broadband absorption in the visible spectrum is essential in optoelectronic applications that involve power conversion such as photovoltaics and photocatalysis. Most ultrathin broadband absorbers use parasitic plasmonic structures that maximize absorption using surface plasmons and/or Fabry-Perot cavities, which limits the weight efficiency of the device. Here, we show the theoretical and experimental realization of an unpatterned/planar semiconductor thin-film absorber based on monolayer transition-metal dichalcogenides. We experimentally demonstrate an average total absorption in the visible range (450-700 nm) of >70% using 300 W g^-1 may be achieved in a photovoltaic cell based on this metamaterial absorber.

Solid-state magneto-ionic (MI) effects have shown promise for energy-efficient nanoelectronics, where ionic migration may be used to achieve atomic-scale control of interfaces in magnetic nanostructures. To date, magneto-ionics have been mostly explored in oxygen-based systems [1-4], while there is a surge of interest in alternative ionic systems due to their different ionic migration mechanisms and characteristics [5-7]. We have recently demonstrated effective MI control of magnetic functionalities using a variety of ionic species, particularly nitrogen. In nitride-based Ta/CoFe/MnN/Ta films, the chemically induced MI effect is combined with the electric field driving of nitrogen to electrically manipulate exchange bias [8]. Upon field-cooling the heterostructure, ionic diffusion of nitrogen from MnN into the Ta layers occurs. A significant exchange bias is observed, which can be further enhanced by ~ 20% after voltage conditioning (Figs. 1a-1e). This enhancement can be reversed by voltage conditioning with an opposite polarity. Nitrogen migration within the MnN layer and into the Ta capping layer causes the enhancement in exchange bias, which is observed in polarized neutron reflectometry studies. We have also achieved all-nitride-based magneto-ionic systems [9]. Thin films of (001)-ordered Mn₄N are grown by sputtering Mn onto Mn₃N₂ seed layer on Si (100) substrate. Nitrogen ion migration across the Mn₃N₂ /Mn layers leads to a continuous evolution of the layers to Mn₃N₂ /Mn₄N, Mn₂N/Mn₄N, and eventually Mn₄N alone (Figs. 1f-1g). Furthermore, we have demonstrated MI control of the exchange bias effect in an all-nitride Mn₄N/MnN_x system, where the field-trained exchange field can be varied up to ten times by introducing or extracting nitrogen from the nitride system. This is achieved by adjusting the nitrogen gas partial pressure during deposition or varying annealing temperature after deposition. These effects demonstrate contrasts with oxygen-based MI effects in terms of operating principles, switching speed, and reversibility. Such MI systems are valuable platforms to gain quantitative understanding at buried interfaces. They also offer potentials for device applications based on electric modulation of magnetic functionalities. This work has been supported in part by the NSF (ECCS-2151809, DMR-2005108, DMR-1828420), SRC/NIST SMART Center, and KAUST. [1] U. Bauer et al., Nat. Mater. 14, 174 (2015). [2] C. Bi et al., Phys. Rev. Lett. 113, 267202 (2014). [3] D. A. Gilbert et al., Nat. Commun. 7, 11050 (2016). [4] G. Chen et al., Sci. Adv. 6, eaba4924 (2020). [5] A. J. Tan et al., Nat. Mater. 18, 35 (2019). [6] G. Chen et al., Phys. Rev. X 11, 021015 (2021). [7] J. de Rojas et al., Nat. Commun. 11, 5871 (2020). [8] C. J. Jensen et al., ACS Nano 17, 6745 (2023). [9] Z. J. Chen et al., Appl. Phys. Lett. 123, 082403 (2023). Figure 1

Spiking neural networks (SNNs) with phase change memory (PCM) devices are promising for in-memory computing, but their performance is often constrained by the abrupt depression (conductance decrease) of PCM synapses. Here, we report an energy-efficient SNN using Ge ₄ Sb ₆ Te ₇ (GST467) as the phase-change material in a single device per synapse with identical pulses, and find > 2× reduction of inference energy in such SNNs compared to SNNs using two conventional PCMs per synapse. We leverage the unique gradual potentiation and depression characteristics of Ge ₄ Sb ₆ Te ₇ in a behavioral model and train a two-layer SNN to demonstrate both pattern and online learning. We also uncover the trade-offs between energy consumption and SNN recognition rate considering resistance drift and conductance ranges of the synapses, providing a design guideline for future energy-efficient PCM-based SNN.

The vast high entropy alloy (HEA) composition space is promising for discovery of new material phases with unique properties. This study explores the potential to achieve rare‐earth‐free high magnetic anisotropy materials in single‐phase HEA thin films. Thin films of FeCoNiMnCu sputtered on thermally oxidized Si/SiO₂ substrates at room temperature are magnetically soft, with a coercivity on the order of 10 Oe. After post‐deposition rapid thermal annealing (RTA), the films exhibit a single face‐centered‐cubic phase, with an almost 40‐fold increase in coercivity. Inclusion of 50 at.% Pt in the film leads to ordering of a single L1₀ high entropy intermetallic phase after RTA, along with high magnetic anisotropy and 3 orders of magnitude coercivity increase. These results demonstrate a promising HEA approach to achieve high magnetic anisotropy materials using RTA.