This study presents the direct measurement of proton transport along filamentous Desulfobulbaceae, or cable bacteria. Cable bacteria are filamentous multicellular microorganisms that have garnered much interest due to their ability to serve as electrical conduits, transferring electrons over several millimeters. Our results indicate that cable bacteria can also function as protonic conduits because they contain proton wires that transport protons at distances >100 µm. We find that protonic conductivity (σP) along cable bacteria varies between samples and is measured as high as 114 ± 28 µS cm-1 at 25 °C and 70% relative humidity (RH). For cable bacteria, the protonic conductance (GP) and σP are dependent upon the RH, increasing by as much as 26-fold between 60% and 80% RH. This observation implies that proton transport occurs via the Grotthuss mechanism along water associated with cable bacteria, forming proton wires. In order to determine σP and GP along cable bacteria, we implemented a protocol using a modified transfer-printing technique to deposit either palladium interdigitated protodes (IDP), palladium transfer length method (TLM) protodes, or gold interdigitated electrodes (IDE) on top of cable bacteria. Due to the relatively mild nature of the transfer-printing technique, this method should be applicable to a broad array of biological samples and curved materials. The observation of protonic conductivity in cable bacteria presents possibilities for investigating the importance of long-distance proton transport in microbial ecosystems and to potentially build biotic or biomimetic scaffolds to interface with materials via proton-mediated gateways or channels.

We have developed a specialized adapter to enable a field-directed sputter sharpening (FDSS) of SPM tips in a commonly used ultrahigh vacuum scanning tunneling microscope (STM). The adapter is for a Scienta Omicron low-temperature STM system equipped with a typical Ar+ sputtering source in an adjoining sample preparation chamber. It interfaces directly with the Omicron transfer plate and tip holder, thereby allowing the FDSS technique to be implemented with minimal additional hardware. We have used C60 molecules to benchmark the performance of the in situ sharpening of electrochemically etched W tips, showing nearly an order of magnitude reduction in the apparent tip diameter. The design of the FDSS adapter presented in this paper enables in situ tip sharpening and demonstrates that the FDSS technique can be applied to produce tips suitable for high-asperity molecules.

Nickel ditelluride is an unusual member of the transition metal dichalcogenide family which has garnered interest due to potential valley spin-polarized surface states near the Fermi level and the presence of Dirac nodes in its electronic band structure. In this work, exfoliation of bulk nickel ditelluride is performed under ultra-high vacuum in order to generate a clean surface for scanning tunneling microscopy and spectroscopy at 4.8 K. Multiple features in the observed electronic density of states are observed in the vicinity of the Fermi level and compared to calculated band structures to elucidate their origins. Our results are consistent with the presence of the spin-polarized surface states, yet indicate trivial states, which are close to the Fermi level, can interfere with their potential utility in spintronic applications.

Previous gate-dependent conductance measurements of metallic carbon nanotubes have revealed unexplainable conductance suppressions, occurring at two different gate voltages. These were previously attributed to the gate-dependency of contact resistance. Our gate-dependent conductivity measurements on a metallic nanotube with known chirality show that these bimodal conductance suppressions are the manifestations of Wigner cusps, often seen in atomic and nuclear physics experiments.

Here we report how two-dimensional crystal (2DC) overlayers influence the recrystallization of relatively thick metal films and the subsequent synergetic benefits this provides for coupling surface plasmon-polaritons (SPPs) to photon emission in 2D semiconductors. We show that annealing 2DC/Au films on SiO 2 results in a reverse epitaxial process where initially nanocrystalline Au films gain texture, crystallographically orient with the 2D crystal overlayer, and form an oriented porous metallic network (OPEN) structure in which the 2DC can suspend above or coat the inside of the metal pores. Both laser excitation and exciton recombination in the 2DC semiconductor launch propagating SPPs in the OPEN film. Energy in-/out- coupling occurs at metal pore sites, alleviating the need for dielectric spacers between the metal and 2DC layer. At low temperatures, single-photon emitters (SPEs) are present across an OPEN-WSe 2 film, and we demonstrate remote SPP-mediated excitation of SPEs at a distance of 17 μm.

Recent studies have shown that MoS2 can undergo a structural phase transition from the 2H to 1T' phase on Au substrates at moderate temperatures. Here, we use ultraviolet and x-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopy, and scanning tunneling microscopy/spectroscopy to probe the impact of annealing exfoliated, monolayer MoS2 on Au. Our results across multiple length scales indicate that 2H-MoS2 becomes hybridized with Au upon thermal annealing without inducing the 1T' structural phase and the bandgap can be modulated to zero width depending on the degree of hybridization. These results can be used to control the resistance of metal-MoS2 contacts at the atomic scale without introduction of defects or structural phase

Scanning tunneling microscopy and spectroscopy (STM/STS) are used to electronically switch atomically-thin memristors, referred to as “atomristors”, based on a graphene/molybdenum disulfide (MoS_2)/Au heterostructure. A gold-assisted exfoliation method was used to produce near-millimeter (mm) scale MoS_2 on Au thin-film substrates, followed by transfer of a separately exfoliated graphene top layer. Our results reveal that it is possible to switch the conductivity of a graphene/MoS_2/Au memristor stack using an STM tip. These results provide a path to further studies of atomically-thin memristors fabricated from heterostructures of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs).

Advancing electronic devices that interface with biology will require a thorough understanding of the electrochemical pathways that transduce electronic currents into the ionic currents.