Heat-Driven Iontronic Nanotransistors

InAs Nanowire-Based Twin Electrical Sensors Enabling Simultaneous Gas Detection

Epitaxially grown InAs NWs are relevant for electrical sensing applications due to the Fermi level pinning at the NW surface and are highly sensitive to the surrounding environment. While a single NW growth batch consists of millions of virtually identical replicas of the same NW, real samples display subtle differences in NW size, shape, and structure, which may affect detection performance. Here, electrical gas detection is investigated in two nominally identical or twin devices fabricated starting from the same NW growth batch. Two individual wurtzite InAs NWs are placed onto a fabrication substrate at a 2 μm distance with a 90° relative orientation, each NW is electrically contacted, and the nanodevices are exposed to humidity and NO2 flux diluted in synthetic air. Electrical signal versus time is measured simultaneously in each nanodevice upon exposure to different gases and concentrations. The observed detection limit is 2 ppm for NO2 and 20% for relative humidity. Correlation analysis methods are exploited by calculating autocorrelation and cross-correlation functions for the experimental signal pairs, indicating lack of cross-correlation in the signal noise of the two nanodevices, suggesting that signal differences between the twins could be ascribed mainly to nonidealities in the fabrication protocol and nanoscopic differences in the two nanostructures, rather than to different environmental conditions. While InAs nanowires are used here as demonstrators of simultaneous gas sensing, the approach is general and virtually applies to any nanoscale material suitable for the realization of two-terminal electronic devices.

Electrochemical Control of the Ultrafast Lattice Response of a Layered Semimetal

The unique layer-stacking in two-dimensional (2D) van der Waals materials facilitates the formation of nearly degenerate phases of matter and opens novel routes for the design of low-power, reconfigurable functional materials. Electrochemical ion intercalation between stacked layers offers a promising approach to stabilize bulk metastable phases and to explore the effects of extreme carrier doping and strain. However, in situ characterization methods to study the structural evolution and dynamical functional properties of these intercalated materials remains limited. Here a novel experimental platform is presented capable of simultaneously performing electrochemical lithium-ion intercalation and multimodal ultrafast characterization of the lattice using both electron diffraction and nonlinear optical techniques. Using the layered semimetal WTe2 as a model system, the interlayer shear phonon mode that modulates stacking between 2Dlayers is probed, showing that small amounts of lithiation enhance the amplitude and lifetime of the phonon, contrary to expectations. This results from the dynamically fluctuating and anharmonic structure between nearly degenerate phases at room temperature, which can be stabilized by electronic carriers accompanying the inserted lithium ions. At high lithiation, the Td' structure emerges and quenches the phonon response. This work defines new approaches for using electrochemistry to engineer the dynamic structure of 2D materials.

Impact of surface charge density modulation on ion transport in heterogeneous nanochannels

The PNP nanotransistor, consisting of emitter, base, and collector regions, exhibits distinct behavior based on surface charge densities and various electrolyte concentrations. In this study, we investigated the impact of surface charge density on ion transport behavior within PNP nanotransistors at different electrolyte concentrations and applied voltages. We employed a finite-element method to obtain steady-state solutions for the Poisson-Nernst-Planck and Navier-Stokes equations. The ions form a depletion region, influencing the ionic current, and we analyze the influence of surface charge density on the depth of this depletion region. Our findings demonstrate that an increase in surface charge density results in a deeper depletion zone, leading to a reduction in ionic current. However, at very low electrolyte concentrations, an optimal surface charge density causes the ion current to reach its lowest value, subsequently increasing with further increments in surface charge density. As such, atV app = + 1 V andC 0 = 1 mM , the ionic current increases by 25% when the surface charge density rises from 5 to 20  mC . m - 2 , whereas atC 0 = 10 mM , the ionic current decreases by 65% with the same increase in surface charge density. This study provides valuable insights into the behavior of PNP nanotransistors and their potential applications in nanoelectronic devices.

Editorial: focus on waste-heat harvesting via thermoelectric conversion: materials, devices and systems for sustainable energy technologies

The focus collection 'Waste-heat harvestingviathermoelectric conversion: Materials, devices and systems for sustainable energy technologies' collates several research articles and a Roadmap highlighting the most recent advances in the field of thermoelectricity from the viewpoint of both basic and applied research, with a special eye on the work of the Italian community.