The ability for artificially reproducing human brain type signals’ processing is one of the main challenges in modern information technology, being one of the milestones for developing global communicating networks and artificial intelligence. Electronic devices termed memristors have been proposed as effective artificial synapses able to emulate the plasticity of biological counterparts. Here we report for the first time a single crystalline nanowire based model system capable of combining all memristive functions – non-volatile bipolar memory, multilevel switching, selector and synaptic operations imitating Ca2+ dynamics of biological synapses. Besides underlying common electrochemical fundamentals of biological and artificial redox-based synapses, a detailed analysis of the memristive mechanism revealed the importance of surfaces and interfaces in crystalline materials. Our work demonstrates the realization of self-assembled, self-limited devices feasible for implementation via bottom up approach, as an attractive solution for the ultimate system miniaturization needed for the hardware realization of brain-inspired systems.

High-quality, 25 nm octahedral-shaped Fe3O4 magnetite nanocrystals are epitaxially grown on 9 nm Au seed nanoparticles using a modified wet-chemical synthesis. These Fe3O4-Au Janus nanoparticles exhibit bulk-like magnetic properties. Due to their high magnetization and octahedral shape, the hybrids show superior in vitro and in vivo T2 relaxivity for magnetic resonance imaging as compared to other types of Fe3O4-Au hybrids and commercial contrast agents. The nanoparticles provide two functional surfaces for theranostic applications. For the first time, Fe3O4-Au hybrids are conjugated with two fluorescent dyes or the combination of drug and dye allowing the simultaneous tracking of the nanoparticle vehicle and the drug cargo in vitro and in vivo. The delivery to tumors and payload release are demonstrated in real time by intravital microscopy. Replacing the dyes by cell-specific molecules and drugs makes the Fe3O4-Au hybrids a unique all-in-one platform for theranostics.

Laser ablation in liquids (LAL) has emerged as a versatile approach for the synthesis of alloy particles and oxide nanomaterials. However, complex chemical reactions often take place during synthesis due to inevitable atomization and ionization of the target materials and decomposition/hydrolysis of solvent/solution molecules, making it difficult to understand the particle formation mechanisms. In this paper, a possible route for the formation of FeMn alloy nanoparticles as well as MnOx nanoparticles, ‐sheets, and ‐fibers by LAL is presented. The observed structural, compositional, and morphological variations are clarified by transmission electron microscopy (TEM). The studies suggest that a reaction between Mn atoms and Fe ions followed by surface oxidation result in nonstoichiometric synthesis of Fe‐rich FeMn@FeMn2O4 core–shell alloy particles. Interestingly, a phase transformation from Mn3O4 to Mn2O3 and finally to Ramsdellite γ‐MnO2 is accompanied by a morphology change from nanosheets to nanofibers in gradually increasing oxidizing environments. High‐resolution TEM images reveal that the particle‐attachment mechanism dominates the growth of different manganese oxides.

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Compound semiconducting nanowires are promising building blocks for several nanoelectronic devices yet the inability to reliably control their growth morphology is a major challenge. Here, we report the Au-catalyzed vapor-liquid-solid (VLS) growth of GaN nanowires with controlled growth direction, surface polarity and surface roughness. We develop a theoretical model that relates the growth form to the kinetic frustration induced by variations in the V(N)/III(Ga) ratio across the growing nanowire front. The model predictions are validated by the trends in the asgrown morphologies induced by systematic variations in the catalyst particle size and processing conditions. The principles of shape selection highlighted by our study pave the way for morphological control of technologically relevant compound semiconductor nanowires. arXiv:1305.3936v1 [cond-mat.mes-hall]