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The rapid development of brain‐inspired computing requires new artificial components and architectures for its hardware implementation. In this regard, memristive devices emerged as potential candidates for artificial synapses because of their ability to emulate the plasticity of the biological synapses. In this work, the synaptic behavior of the TiN/La2NiO4+δ/Pt memristive devices based on thermally annealed La2NiO4+δ films is thoroughly investigated. Using electron energy loss spectroscopy (EELS), it is shown that post‐deposition annealing using inert (Ar) or oxidizing (O2) atmospheres affects the interstitial oxygen content (δ) in the La2NiO4+δ films. Electrical characterization shows that both devices exhibit long‐term potentiation/depression (LTP/LTD) and spike‐timing‐dependent plasticity (STDP). At the same time, the Ar annealed TiN/La2NiO4+δ/Pt device demonstrates filamentary‐like behavior, fast switching, and low energy consumption. On the other hand, the O2 annealed TiN/La2NiO4+δ/Pt devices are forming‐free, exhibiting interfacial‐like resistive switching with slower kinetics. Finally, the simulation tools show that spiking neural network (SNN) architectures with weight updates based on the experimental data achieve high inference accuracy in the digit recognition task, which proves the potential of TiN/La2NiO4+δ/Pt devices for artificial synapse applications. [ABSTRACT FROM AUTHOR]

Scanning transmission electron microscopy (STEM) techniques are used to improve the understanding of out‐of‐plane oriented Sb2Te3 thin films deposited by sputtering on SiO2 and Si substrates. Nanobeam precession electron diffraction, energy‐dispersive X‐ray spectroscopy, and high‐angle‐annular dark‐field imaging show that the presence of 1–2 atomic planes of Te on top of the substrate is a crucial factor for successful growth of such films, which can be achieved by optimizing cosputtering of Te and Sb2Te3 targets. The formation of an actual van der Waals (vdW) gap between the substrate and the first Sb2Te3 quintuple layer allows for vdW epitaxy. This gap is larger than those separating Te planes in the pseudo‐2D Sb2Te3 structure. HAADF image analysis provides detailed information on the atomic arrangement such as interplanar distances, vdW gaps, and Debye–Waller coefficients, all these with a few pm precision. For the anisotropic atomic displacements, a new methodology is introduced based on the statistical analysis of atomic column positions that provides information on the low‐frequency phonon modes. Ab initio calculations are used to support our results. Overall, this study provides quantitative STEM tools particularly well suited for nonperiodic pseudo‐2D materials, such as Sb2Te3/GeTe superlattices. [ABSTRACT FROM AUTHOR]

The development of innovative heterostructures made of ZnO nanowires is of great interest for enhancing the performances of many devices in the fields of optoelectronics, photovoltaics, and energy harvesting. We report an original fabrication process to form ZnO/ZnGa2O4 core–shell nanowire heterostructures in the framework of the wet chemistry techniques. The process involves the partial chemical conversion of ZnO nanowires grown via chemical bath deposition into ZnO/ZnGa2O4 core–shell nanowire heterostructures with a high interface quality following their immersion in an aqueous solution containing gallium nitrate heated at a low temperature. The double-step process describing the partial chemical conversion relies on successive dissolution and reaction mechanisms. The present finding offers the possibility to fabricate ZnO/ZnGa2O4 core–shell nanowire heterostructures at low temperatures and over a wide variety of substrates with a large surface area, which is attractive for nanostructured solar cells, deep-UV photodetectors, and piezoelectric devices. [ABSTRACT FROM AUTHOR]

Transparent electrodes based on emerging nanomaterials like silver nanowire (AgNW) networks have been extensively investigated in the past few years. Thanks to their superior flexibility and versatility in terms of fabrication and device integration, they present an excellent alternative to indium tin oxide. However, the lack of thermal, electrical, and chemical stability requires the encapsulation of the AgNW. This has been performed using thin metal oxide films, graphene, or organic protective coatings. Despite the very promising properties of such nanocomposite approaches and the performance enhancement, more investigation is needed to minimize the loss of optical transmittance upon coating and achieve superior electrical, thermal, and mechanical stability. In the present work, the encapsulation of AgNW networks with aluminum nitride (AlN) coatings is reported for the first time, and it is compared to AgNW/Al2O3 nanocomposites. Thanks to the low thicknesses (<20 nm) and the wide band gap of AlN, the optical transparency is not impacted. Furthermore, the nanocomposite networks demonstrate no failure under electrical and thermal stress conditions (up to 21 V and 400 °C respectively), in contrast to the AgNW/Al2O3 nanocomposites, which fail after 15 V and 350 °C. In addition, microscratch tests reveal the remarkable mechanical robustness of the nanocomposites, and the electrical stability is further confirmed under accelerated environmental tests, coupled with ex situ characterization by SEM and XPS. The results reported in the present work show that AgNW/AlN electrodes are outstanding candidates for high-performance transparent electrodes. [ABSTRACT FROM AUTHOR]

Valence change memories, in which internal redox reactions control the change in resistance are promising candidates for resistive random access memories (ReRAMs) and neuromorphic computing elements. In this context, La2NiO4+δ (L2NO4), a mixed ionic‐electronic conducting oxide, well known for its highly mobile oxygen interstitial ions, emerges as a potential switching material for novel L2NO4‐based memristive devices. However, their integration in complementary metal oxide semiconductor (CMOS) technology still has to be demonstrated, as the major focus of previous studies has been carried out on epitaxial films grown on single crystals. In this work, the optimization of the deposition temperature and precursor solution composition is presented, allowing to obtain high‐quality polycrystalline L2NO4 thin films grown by metal organic chemical vapor deposition on a platinized silicon substrate, and to use these films to build memristive devices in vertical configuration with Ti top electrodes. A bipolar analog‐type transition in resistance can be achieved in Ti/L2NO4/Pt memristive devices. While the "forming" process required for the devices based on nonoptimized L2NO4 thin films is considered as a drawback, the Ti/optimized L2NO4/Pt devices are forming‐free and exhibit a good cyclability. These results prove the switching response of L2NO4‐based devices in a vertical configuration for the first time. [ABSTRACT FROM AUTHOR]

Interface‐type valence change memories (VCMs) are exciting candidates for multilevel storage in resistive random access memories (RRAM) and as artificial synapses for neuromorphic computing. Several materials have been proposed as VCM candidates and, depending on the materials and electrodes of choice, different switching mechanisms take place leading to the change in resistance. Here, the focus is on La0.8Sr0.2MnO3–δ (LSM) perovskite and, particularly, the role of its nanostructure on the memristive device performance. The nanostructural details of the layers are modified by growing LSM epitaxial thin films on different substrates, i.e., SrTiO3 (STO) and LaAlO3 (LAO), by metal‐organic chemical vapor deposition (MOCVD). An interface‐type memristive response is observed using Ti as active electrode and Pt as inert electrode. The modifications in the nanostructure of LSM (strain and dislocations) determine the memristive performance, leading to differences in cycle to cycle reproducibility and multilevel capabilities by the modification of the LSM's oxygen migration properties. The results show that nanostructure engineering is a promising approach for optimizing the performance of memristive devices, an approach which can also be extended and applied to other nanoionic electrochemical devices. [ABSTRACT FROM AUTHOR]