Ferroelectric memristors represent a promising new generation of devices that have a wide range of applications in memory, digital information processing, and neuromorphic computing. Recently, van der Waals ferroelectric In2Se3 with unique interlinked out‐of‐plane and in‐plane polarizations has enabled multidirectional resistance switching, providing unprecedented flexibility in planar and vertical device integrations. However, the operating mechanisms of these devices have remained unclear. Here, through the demonstration of van der Waals In2Se3‐based planar ferroelectric memristors with the device resistance continuously tunable over three orders of magnitude, and by correlating device resistance states, ferroelectric domain configurations, and surface electric potential, the studies reveal that the resistive switching is controlled by the multidomain formations and the associated energy barriers between domains, as opposed to the commonly assumed Schottky barrier modulations at the metal‐ferroelectric interface. The findings reveal new device physics through elucidating the microscopic operating mechanisms of this new generation of devices, and provide a critical guide for future device development and integration efforts.

Two-dimensional (2D) van der Waals materials and related heterostructures have shown a wide variety of novel electronic and optoelectronic properties. However, a key challenge in fully realizing their potential is a general lack of manufacturing techniques capable of producing desired heterostructures at a large scale. Here, we demonstrate a highly scalable direct-laser-writing approach to fabricating in-plane heterostructures in two-dimensional In2Se3 nanolayers. This approach derives from an optically activated solid–solid phase transition that leads to significant changes in local properties (semiconducting vs metal-like), while preserving the single crystallinity of the local lattice, leading to well-defined heterointerfaces and demonstrating a scalable path to large-area device manufacturing. Carrier transport across in-plane heterojunction nanoscale devices fabricated by this technique exhibits asymmetric diode behaviors supported by the presence of interface energy barriers as revealed by Kelvin probe force microscopy. Scanning photocurrent microscopy shows short-circuit photocurrent in these devices, demonstrating their potential applications in efficient photodetection and photovoltaics. Our numerical modeling of the device characteristics reveals space-charge-limited and injection-limited conduction as the carrier transport mechanisms, in contrast to the standard diode model.

Transition metal and rare earth cations are important fission products present in used nuclear fuel, which in high concentrations tend to precipitate crystalline phases in vitreous nuclear waste forms. Two phases of particular interest are powellite (CaMoO 4) and oxyapatite (Ca 2 RE 8 (SiO 4) 6 O 2). The glass compositional dependencies controlling crystallization of these phases on cooling from the melt are poorly understood. In the present study, the effect of rare earth identity and modifier cation field strength on powellite and apatite crystallization were studied in a model MoO 3-containing alkali/alkaline-earth aluminoborosilicate glass with focus on (1) influence of rare earth cation size (for RE 3+ : Ce, La, Nd, Sm, Er, Yb) and (2) influence of non-framework cations (RE 3+ , Mo 6+ , Na + , Ca 2+). Quenched glasses and glass-ceramics (obtained by slow cooling) were characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray absorption (XAS), and electron probe microanalysis (EPMA). All samples were X-ray amorphous upon quenching, except the Ce-containing composition which crystallized ceria (CeO 2), and the sample devoid of any rare earth cations which crystallized powellite (CaMoO 4). On heat treatment, powellite and oxyapatite crystallized in the majority of the samples with the former crystallizing in the volume, while the latter on the surface. The EPMA results confirmed a small concentration of boron in the oxyapatite crystal structure. RE cations were incorporated in the glass, as well as in powellite, oxyapatite, and in the case of Yb 3+ , keiviite (Yb 2 Si 2 O 7). Raman spectroscopy showed that the primary vibration band for molybdate MoO 4 2in the glasses was strongly affected by the ionic field strength of the modifying cations (alkali, alkaline earth, and RE), suggesting their proximity to the MoO 4 2ions in the glass, though the MoO bond length and coordination according to XAS suggested little local change.

Exciton localization in transition-metal dichalcogenide monolayers is behind a variety of interesting phenomena and applications, including broad-spectrum solar cells and single-photon emissions. Strain fields at the periphery of topographically distinct features such as nanoscopic bubbles were recently associated with localized charge-neutral excitons. Here, we use tip-enhanced photoluminescence (PL) to visualize excitons in WSe2/MoSe2 heterobilayers (HBL). We find strong optical emission from charged excitons, particularly positively charged trions, in HBL supported by interlayer charge transfer. Our results reveal strong trion confinement, with a localization length scale comparable to the trion size, at the apex region inside individual nanoscopic bubbles. Nano-PL mapping also shows sub-10-nm spatial variations in the localized trion emission spectra, which stem from atomic-scale potential energy fluctuations. These findings demonstrate the possibility of confining charged exciton complexes that are electrically tunable, opening up further opportunities to probe many-body exciton physics and to explore additional possible sites for strong exciton localization that can lead to quantum emission.

We interrogate para-mercaptobenzoic acid (MBA) molecules chemisorbed onto plasmonic silver nanocubes through tip-enhanced Raman (TER) spectral nanoimaging. Through a detailed examination of the spectra, aided by correlation analysis and density functional theory calculations, we find that MBA chemisorbs onto the plasmonic particles with at least two distinct configurations: S-and CO 2bound. High spatial resolution TER mapping allows us to distinguish between the distinct adsorption geometries with a pixel-limited (<5 nm) spatial resolution under ambient laboratory conditions.