Here we synthesize 2-ethylhexyl, 2-hexyldecyl, 2-[2-(2-methoxyethoxy)ethoxy]ethyl, oleyl and n-octadecyl phosphonic acid and use them to functionalize CdSe and HfO2 nanocrystals. In contrast to branched carboxylic acids, post-synthetic surface functionalization of CdSe and HfO2 nanocrystals is readily achieved with branched phosphonic acids. Phosphonic acid capped HfO2 nanocrystals are subsequently evaluated as memristor using conductive atomic force microscopy (c-AFM). We find that 2-ethylhexyl phosphonic acid is a superior ligand, combining a high colloidal stability with a compact ligand shell that results in a record-low operating voltage that is promising for application in flexible electronics.
Microbially produced electrically conductive protein filaments are of interest because they can function as conduits for long-range biological electron transfer. They also show promise as sustainably produced electronic materials. Until now, microbially produced conductive protein filaments have been reported only for bacteria. We report here that the archaellum ofMethanospirillum hungateiis electrically conductive. This is the first demonstration that electrically conductive protein filaments have evolved inArchaea. Furthermore, the structure of theM. hungateiarchaellum was previously determined (N. Poweleit, P. Ge, H. N. Nguyen, R. R. O. Loo, et al., Nat Microbiol 2:16222, 2016,https://doi.org/10.1038/nmicrobiol.2016.222). Thus, the archaellum ofM. hungateiis the first microbially produced electrically conductive protein filament for which a structure is known. We analyzed the previously published structure and identified a core of tightly packed phenylalanines that is one likely route for electron conductance. The availability of theM. hungateiarchaellum structure is expected to substantially advance mechanistic evaluation of long-range electron transport in microbially produced electrically conductive filaments and to aid in the design of “green” electronic materials that can be microbially produced with renewable feedstocks.IMPORTANCEMicrobially produced electrically conductive protein filaments are a revolutionary, sustainably produced, electronic material with broad potential applications. The design of new protein nanowires based on the knownM. hungateiarchaellum structure could be a major advance over the current empirical design of synthetic protein nanowires from electrically conductive bacterial pili. An understanding of the diversity of outer-surface protein structures capable of electron transfer is important for developing models for microbial electrical communication with other cells and minerals in natural anaerobic environments. Extracellular electron exchange is also essential in engineered environments such as bioelectrochemical devices and anaerobic digesters converting wastes to methane. The finding that the archaellum ofM. hungateiis electrically conductive suggests that some archaea might be able to make long-range electrical connections with their external environment.
13Here we report that the archaellum of Methanospirillum hungatei is electrically 14 conductive. Our analysis of the previously published archaellum structure suggests 15 that a core of tightly packed phenylalanines is one likely route for electron 16 conductance. This is the first demonstration that electrically conductive protein 17 filaments (e-PFs) have evolved in Archaea and is the first e-PF for which a structure 18 is known, facilitating mechanistic evaluation of long-range electron transport in e-19PFs. 20 21 22
Successful synthesis of ordered porous, multi-component complex materials requires a series of coordinated processes, typically including fabrication of a master template, deposition of materials within the pores to form a negative structure, and a third deposition or etching process to create the final, functional template. Translating the utility and the simplicity of the ordered nanoporous geometry of binary oxide templates to those comprising complex functional oxides used in energy, electronic, and biology applications has been met with numerous critical challenges. This review surveys the current state of commonly used complex material nanoporous template synthesis techniques derived from the base anodic aluminum oxide (AAO) geometry.
Recent advances in memristive nanocrystal assemblies leverage controllable colloidal chemistry to induce a broad range of defect-mediated electrochemical reactions, switching phenomena, and modulate active parameters. The sample geometry of virtually all resistive switching studies involves thin film layers comprising monomodal diameter nanocrystals. Here we explore the evolution of bipolar and threshold resistive switching across highly-ordered, solution-processed nanoribbon assemblies and mixtures comprising BaZrO3 (BZO) and SrZrO3(SZO) nanocrystals. The effects of nanocrystal size, packing density, and A-site substitution on operating voltage (VSET; VTH) and switching mechanism were studied through a systematic comparison of nanoribbon heterogeneity (i.e., BZO-BZO vs. BZO-SZO) and monomodal vs bimodal size distributions (i.e., small-small; small-large). Analysis of the current-voltage response confirm that tip-induced, trap-mediated space-charge-limited current and trap-assisted tunneling processes drive the low resistance and high resistance states, respectively. Our results demonstrate that both smaller nanocrystals and heavier alkaline earth substitution decrease the onset voltage and improve stability and state retention of monomodal assemblies and bimodal nanocrystal mixtures, thus providing a base correlation that informs fabrication of solution-processed, memristive nanocrystal assemblies.
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