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Memristor devices fabricated using the chalcogenide Ge 2 Te 3 phase change thin films in a metal-insulator-metal structure are characterized using thermal and electrical stimuli in this study. Once the thermal and electrical stimuli are applied, cross-sectional transmission electron microscopy (TEM) and X-ray energy-dispersive spectroscopy (XEDS) analyses are performed to determine structural and compositional changes in the devices. Electrical measurements on these devices showed a need for increasing compliance current between cycles to initiate switching from low resistance state (LRS) to high resistance state (HRS). The measured resistance in HRS also exhibited a steady decrease with increase in the compliance current. High resolution TEM studies on devices in HRS showed the presence of residual crystalline phase at the top-electrode/dielectric interface, which may explain the observed dependence on compliance current. XEDS study revealed diffusion related processes at dielectric-electrode interface characterized, by the separation of Ge 2 Te 3 into Ge- and Te- enriched interfacial layers. This was also accompanied by spikes in O level at these regions. Furthermore, in-situ heating experiments on as-grown thin films revealed a deleterious effect of Ti adhesive layer, wherein the in-diffusion of Ti leads to further degradation of the dielectric layer. This experimental physics-based study shows that the large HRS/LRS ratio below the current compliance limit of 1 mA and the ability to control the HRS and LRS by varying the compliance current are attractive for memristor and neuromorphic computing applications. 

Bimetallic nanoparticles remain a promising avenue to achieve highly reactive catalysts. In this contribution, we demonstrate the use of a photoswitchable peptide for the production of PdAu bimetallic nanoparticles at a variety of Pd : Au ratios. Using this peptide, the biomolecular overlayer structure can be switched between two different conformations ( cis vs. trans ) via light irradiation, thus accessing two different surface structures. The composition and arrangement of the materials was fully characterized, including atomic-level analyses, after which the reactivity of the bimetallic materials was explored using the reduction of 4-nitrophenol as a model system. Using these materials, it was demonstrated that the reactivity was maximized for the particles prepared at a Pd : Au ratio of 1 : 3 and with the peptide in the cis conformation. Such results present routes to a new generation of catalysts that could be remotely activated for on/off reactivity as a function of the ligand overlayer conformation. 

Abstract Crystalline solids exhibiting glass-like thermal conductivity have attracted substantial attention both for fundamental interest and applications such as thermoelectrics. In most crystals, the competition of phonon scattering by anharmonic interactions and crystalline imperfections leads to a non-monotonic trend of thermal conductivity with temperature. Defect-free crystals that exhibit the glassy trend of low thermal conductivity with a monotonic increase with temperature are desirable because they are intrinsically thermally insulating while retaining useful properties of perfect crystals. However, this behavior is rare, and its microscopic origin remains unclear. Here, we report the observation of ultralow and glass-like thermal conductivity in a hexagonal perovskite chalcogenide single crystal, BaTiS 3 , despite its highly symmetric and simple primitive cell. Elastic and inelastic scattering measurements reveal the quantum mechanical origin of this unusual trend. A two-level atomic tunneling system exists in a shallow double-well potential of the Ti atom and is of sufficiently high frequency to scatter heat-carrying phonons up to room temperature. While atomic tunneling has been invoked to explain the low-temperature thermal conductivity of solids for decades, our study establishes the presence of sub-THz frequency tunneling systems even in high-quality, electrically insulating single crystals, leading to anomalous transport properties well above cryogenic temperatures. 

Combining topological insulators (TIs) and magnetic materials in heterostructures is crucial for advancing spin‐based electronics. Magnetic insulators (MIs) can be deposited on TIs using the spin‐spray process, which is a unique nonvacuum, low‐temperature growth process. TIs have highly reactive surfaces that oxidize upon exposure to atmosphere, making it challenging to grow spin‐spray ferrites on TIs. In this work, it is demonstrated that a thin titanium capping layer on TI, followed by oxidation in atmosphere to produce a thin TiO_xinterfacial layer, protects the TI surface, without significantly compromising spin transport from the magnetic material across the TiO_xto the TI surface states. First, it is demonstrated that in Bi₂Te₃/TiO_x/Ni₈₀Fe₂₀heterostructures, TiO_xprovides an excellent barrier against diffusion of magnetic species, yet maintains a large spin‐pumping effect. Second, the TiO_xis also used as a protective capping layer on Bi₂Te₃, followed by the spin‐spray growth of the MI, Ni_xZn_yFe₂O₄(NZFO). For the thinnest TiO_xbarriers, Bi₂Te₃/TiO_x/NZFO samples have antiferromagnetic (AFM) disordered interfacial layer because of diffusion. With increasing TiO_xbarrier thickness, the diffusion is reduced, but still maintains strong interfacial magnetic exchange‐interaction. These experimental results demonstrate a novel method of low‐temperature growth of magnetic insulators on TIs enabled by interface engineering.