Conductivity Modulation of Gold Thin Film at Room Temperature via All-Solid-State Electric-Double-Layer Gating Accelerated by Nonlinear Ionic Transport

Dynamic Response of Ion Transport in Nanoconfined Electrolytes

Ion transport in nanoconfined electrolytes exhibits nonlinear effects caused by large driving forces and pronounced boundary effects. An improved understanding of these impacts is urgently needed to guide the design of key components of the electrochemical energy systems. Herein, we employ a nonlinear Poisson-Nernst-Planck theory to describe ion transport in nanoconfined electrolytes coupled with two sets of boundary conditions to mimic different cell configurations in experiments. A peculiar nonmonotonic charging behavior is discovered when the electrolyte is placed between a blocking electrode and an electrolyte reservoir, while normal monotonic behaviors are seen when the electrolyte is placed between two blocking electrodes. We reveal that impedance shapes depend on the definition of surface charge and the electrode potential. Particularly, an additional arc can emerge in the intermediate-frequency range at potentials away from the potential of zero charge. The obtained insights are instrumental to experimental characterization of ion transport in nanoconfined electrolytes.

Emulation of Synaptic Plasticity on a Cobalt-Based Synaptic Transistor for Neuromorphic Computing

Neuromorphic computing (NC), which emulates neural activities of the human brain, is considered for the low-power implementation of artificial intelligence. Toward realizing NC, fabrication, and investigations of hardware elements─such as synaptic devices and neurons─are crucial. Electrolyte gating has been widely used for conductance modulation by massive carrier injections and has proven to be an effective way of emulating biological synapses. Synaptic devices, in the form of synaptic transistors, have been studied using various materials. Despite the remarkable progress, the study of metallic channel-based synaptic transistors remains massively unexplored. Here, we demonstrated a three-terminal electrolyte gating-modulated synaptic transistor based on a metallic cobalt thin film to emulate biological synapses. We have realized gating-controlled, non-volatile, and distinct multilevel conductance states in the proposed device. The essential synaptic functions demonstrating both short-term and long-term plasticity have been emulated in the synaptic device. A transition from short-term to long-term memory has been realized by tuning the gate pulse parameters, such as amplitude and duration. The crucial cognitive behavior, including learning, forgetting, and re-learning, has been emulated, showing a resemblance to the human brain. Beyond that, dynamic filtering behavior has been experimentally implemented in the synaptic device. These results provide an insight into the design of metallic channel-based synaptic transistors for NC.

Ionically Connected Floating Electrodes for Long-Distance (>1 mm) Coplanar-Gating Graphene Transistors

Exploiting the long-range polarizability of an electrolyte based on ion migration, electric double-layer transistors (EDLTs) can be constructed in an unconventional configuration; here, the gate electrode is placed coplanarly with the device channel. In this paper, we demonstrate the influence of the distance factors of the electrolyte layer on the operation of EDLTs with a coplanar gate. As the promptness of the electric double-layer formation depends on the distance between the channel and the gate, the dynamic characteristics of a remote-gated transistor degrade with long distances. To suppress this degradation, we suggest using multiple coplanar floating gates bridged through ionic dielectric layers. Unlike remotely gated EDLTs that utilize a single extended electrolyte layer, the devices with multiple segmented electrolyte layers operate effectively even when they are gated from a distance longer than 1 mm.

Pulse Dynamics of Electric Double Layer Formation on All-Solid-State Graphene Field-Effect Transistors

Electric double layer (EDL) dynamics in graphene field-effect transistors (FETs) gated with polyethylene oxide (PEO)-based electrolytes are studied by molecular dynamics (MD) simulations from picoseconds to nanoseconds and experimentally from microseconds to milliseconds. Under an applied field of approximately mV/nm, EDL formation on graphene FETs gated with PEO:CsClO₄ occurs on the timescale of microseconds at room temperature and strengthens within 1 ms to a sheet carrier density of n_S ≈ 10¹³ cm^-2. Stronger EDLs (i.e., larger n_S) are induced experimentally by pulsing with applied voltages exceeding the electrochemical window of the electrolyte; electrochemistry is avoided using short pulses of a few milliseconds. Dynamics on picosecond to nanosecond timescales are accessed using MD simulations of PEO:LiClO₄ between graphene electrodes with field strengths of hundreds of mV/nm which is 100× larger than experiment. At 100 mV/nm, EDL formation initiates in sub-nanoseconds achieving charge densities up to 6 × 10¹³ cm^-2 within 3 nanoseconds. The modeling shows that under sufficiently high electric fields, EDLs with densities ∼10¹³ cm^-2 can form within a nanosecond, which is a timescale relevant for high-performance electronics such as EDL transistors (EDLTs). Moreover, the combination of experiment and modeling shows that the timescale for EDL formation ( n_S = 10¹³ to 10¹⁴ cm^-2) can be tuned by 9 orders of magnitude by adjusting the field strength by only 3 orders of magnitude.

Humidity-insensitive temperature sensor based on a quartz capillary anti-resonant reflection optical waveguide

A compact, humidity-insensitive, fiber optic temperature sensor based on a quartz capillary, antiresonant reflecting optical waveguide was proposed and experimentally demonstrated. The transmission spectral responses of the proposed sensor were experimentally investigated regarding temperature variation and environmental humidity. Resonant dips exhibited temperature sensitivity as large as 201 pm/°C from -30 to 45 °C in a humid environment. By coating a sufficiently thick gold film onto the sensor surface, the humidity cross-sensitivity issue was effectively resolved. This proposed sensor was anticipated to find potential applications in humid environments, and moreover, immunity to humidity-sensitivity ensures its applicability in marine environments.

Effect of oxygen vacancy segregation in Au or Pt/oxide hetero-interfaces on electronic structures

We investigated the effects of oxygen vacancy segregation on electronic structures in the vicinity of hetero-interfaces between noble metals (Au and Pt) and yttria stabilized zirconia by performing first-principles calculations and Bader analysis.