High-Hole-Mobility Fiber Organic Electrochemical Transistors for Next-Generation Adaptive Neuromorphic Bio-Hybrid Technologies.

The latest developments in fiber design and materials science are paving the way for fibers to evolve from parts in passive components to functional parts in active fabrics. Designing conformable, organic electrochemical transistor (OECT) structures using poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) fibers has excellent potential for low-cost wearable bioelectronics, bio-hybrid devices, and adaptive neuromorphic technologies. However, to achieve high-performance, stable devices from PEDOT:PSS fibers, approaches are required to form electrodes on fibers with small diameters and poor wettability, that leads to irregular coatings. Additionally, PEDOT:PSS-fiber fabrication needs to move away from small batch processing to roll-to-roll or continuous processing. Here, it is shown that synergistic effects from a superior electrode/organic interface, and exceptional fiber alignment from continuous processing, enable PEDOT:PSS fiber-OECTs with stable contacts, high µC* product (1570.5 F cm-1 V-1 s-1 ), and high hole mobility over 45 cm2 V-1 s-1 . Fiber-electrochemical neuromorphic organic devices (fiber-ENODes) are developed to demonstrate that the high mobility fibers are promising building blocks for future bio-hybrid technologies. The fiber-ENODes demonstrate synaptic weight update in response to dopamine, as well as a form factor closely matching the neuronal axon terminal.

Desorption from Hot Scandate Cathodes: Effects on Vacuum Device Interior Surfaces after Long-Term Operation.

Scandate cathodes have exhibited superior emission properties compared to current state-of-the-art "M-type" thermionic cathodes. However, their integration into vacuum devices is limited in part by a lack of knowledge regarding their functional lifespan and behavior during operation. Here, we consider thermal desorption from scandate cathodes by examining the distribution of material deposited on interior surfaces of a sealed vacuum device after ~26,000 h of cathode operation. XPS, EDS, and TEM analyses indicate that on the order of 1 wt.% of the initial impregnate is desorbed during a cathode's lifetime, Ca does not desorb uniformly with time, and little to no Sc desorbs from the cathode surfaces (or does so at an undetectable rate). Findings from this first-ever study of a scandate cathode after extremely long-time operation yield insight into the utility of scandate cathodes as components in vacuum devices and suggest possible effects on device performance due to deposition of desorption products on interior device surfaces.

Synthesis of Catalytic Nanoporous Metallic Thin Films on Polymer Membranes.

Composite membranes were produced with a metallic thin film forming the upper layer of the composite on a porous polymer support. Commercially available membranes were used as supports with both micron and nanometer scale pores. Alloy films of ~110 nm thickness were deposited via magnetron sputtering to produce the top layer of the composite. Dealloying the film with sulfuric acid allowed the creation of a nanoporous film structure with a ligament size of 7.7 ± 2.5 nm. Resulting composite membranes were permeable to water at all stages of production, and a UF PSf membrane with 90 nm of nanoporous Fe/Pd on top showed a flux of 183 LHM/bar. The films were evaluated for dechlorination of toxic polychlorinated biphenyls from water. At a loading of 6.6 mg/L of Pd attached to 13.2 cm2 support in a 2.5 ppm PCB-1 solution with 1.5 ppm dissolved H2, over 90% of PCB-1 was removed from solution in 30 minutes, which produced the expected product biphenyl from the dechlorination reaction.

In situ indentation of nanoporous gold thin films in the transmission electron microscope.

The mechanical behavior of nanoporous gold was investigated during in situ nanoindentation in the transmission electron microscope. Thin films of nanoporous gold, with ligaments and pores of the order of 10-nm diameter, offer a highly constrained geometry for deformation and thus provide an opportunity to study the role of defects such as dislocations in the plasticity of nanomaterials. Films ranging in thickness from 75 to 300 nm were indented, while the motion of dislocations and deformation of ligaments were observed in situ. Dislocations were generated and moved along ligament axes, after which they interacted with other dislocations in the nodes of the porous network. For thicker films, the load-displacement curves exhibited load drops at regular intervals. The question of whether the spacing of these load drops was related to the collapse of pores in the nanoporous films or due to bursts of plasticity within the ligaments was investigated. Additionally, the effect of the indenter displacement rate on the mechanical response of these gold films with nanoscale porosity was investigated. Indentation rates were varied from 1.5 to 30 nm/s. There appears to be a kinetic factor related to dislocation nucleation, where slower displacement rates cause load drops to occur at shorter distance intervals and over longer time intervals.

Observation of giant diffusivity along dislocation cores.

Diffusion of atoms in a crystalline lattice is a thermally activated process that can be strongly accelerated by defects such as grain boundaries or dislocations. When carried by dislocations, this elemental mechanism is known as "pipe diffusion." Pipe diffusion has been used to explain abnormal diffusion, Cottrell atmospheres, and dislocation-precipitate interactions during creep, although this rests more on conjecture than on direct demonstration. The motion of dislocations between silicon nanoprecipitates in an aluminum thin film was recently observed and controlled via in situ transmission electron microscopy. We observed the pipe diffusion phenomenon and measured the diffusivity along a single dislocation line. It is found that dislocations accelerate the diffusion of impurities by almost three orders of magnitude as compared with bulk diffusion.