Addressable Direct-Write Nanoscale Filament Formation and Dissolution by Nanoparticle-Mediated Bipolar Electrochemistry

Abstract

Nanoscale conductive filaments, usually associated with resistive memory or memristor technology, may also be used for chemical sensing and nanophotonic applications; however, realistic implementation of the technology requires precise knowledge of the conditions that control the formation and dissolution of filaments. Here we describe and characterize an addressable direct-write nanoelectrochemical approach to achieve repeatable formation/dissolution of Ag filaments across a ∼100 nm poly(ethylene oxide) (PEO) film containing either Ag alone or Ag together with 50 nm Ag-nanoparticles acting as bipolar electrodes. Using a conductive AFM tip, formation occurs when the PEO film is subjected to a forward bias, and dissolution occurs under reverse bias. Formation-dissolution kinetics were studied for three film compositions: Ag|PEO-Ag, Ag|poly(ethylene glycol) monolayer-PEO-Ag, and Ag|poly(ethylene glycol) monolayer-PEO-Ag/Ag-nanoparticle. Statistical analysis shows that the distribution of formation times exhibits Gaussian behavior, and the fastest average initial formation time occurs for the Ag|PEO-Ag system. In contrast, formation in the presence of Ag nanoparticles likely proceeds by a noncontact bipolar electrochemical mechanism, exhibiting the slowest initial filament formation. Dissolution times are log-normal for all three systems, and repeated reformation of filaments from previously formed structures is characterized by rapid regrowth. The direct-write bipolar electrochemical deposition/dissolution strategy developed here presents an approach to reconfigurable, noncontact in situ wiring of nanoparticle arrays-thereby enabling applications where actively controlled connectivity of nanoparticle arrays is used to manipulate nanoelectronic and nanophotonic behavior. The system further allows for facile manipulation of experimental conditions while simultaneously characterizing surface conditions and filament formation/dissolution kinetics.

Direct‐Write Formation and Dissolution of Silver Nanofilaments in Ionic Liquid‐Polymer Electrolyte Composites

“…The formation time distributions are normal, Figure 3a,c, while the dissolution events show a log normal distribution, Figure 3b,d. These are the same types of distributions reported for filaments formed in PEO-based electrolytes, [5] and the different distributions suggest that the underlying formation and dissolution mechanisms are fundamentally different. This difference is reasonable, because it takes longer to form a filament for the first time, that is, the formation step, than it does to break the filament.…”

“…In addition, SPEs have recently been used for memory devices based on resistive switching, in which conductive filaments formed and dissolved in response to an external electric field are used to achieve on and off states typically separated by several orders of magnitude in resistance. The formation of metal filaments through polymer electrolytes has been demonstrated previously for polyethylene oxide (PEO)‐based electrolytes, including our group's recent report on silver filament formation kinetics through PEO …”

“…We use the AFM to characterize the mechanical properties of PEGDA/IL/silver hexafluorophosphate (AgPF 6 ) electrolyte films, create Ag nanofilaments through the films via electrodeposition, and correlate the filament formation/dissolution kinetics with the mechanical properties of the polymer composite. PeakForce Quantitative Nanomechanical Mapping (PF‐QNM) is used to map the Young's modulus, while a conductive AFM is used to form and dissolve the Ag filaments electrochemically . The location of the AFM tip is controlled over the x – y plane to enable the direct‐write fabrication of filaments in a predefined grid pattern.…”

“…PeakForce Quantitative Nanomechanical Mapping (PF-QNM) is used to map the Young's modulus, while a conductive AFM is used to form and dissolve the Ag filaments electrochemically. [5,18] The location of the AFM tip is controlled over the x-y plane to enable the direct-write fabrication of filaments in a predefined grid pattern. As shown in Figure 1c, the conductive AFM tip operates as a mobile top electrode, while an Ag thin film below the electrolyte functions as a sacrificial counterelectrode.…”

“…The formation of metal filaments through polymer electrolytes has been demonstrated previously for polyethylene oxide (PEO)-based electrolytes, [4] including our group's recent report on silver filament formation kinetics through PEO. [5] In addition to batteries and memory, SPEs can potentially form the basis for a new class of metamaterials with reconfigurable optical properties. A metamaterial can be formed by embedding metal nanoparticles (NPs) in a well-defined array within a dielectric, in which the optical properties are tuned by adjusting the spacing of the NPs to interact with electromagnetic radiation over a designed wavelength range.…”