Charge state-dependent ion condensation near conjugated polymer backbones

Materials Horizons · 2025-11-17 · 2 citations

Despite the technological appeal of polymeric organic mixed ionic/electronic conductors (OMIECs) for diverse applications, a deep understanding of the fundamentals of mixed charge transport in these materials, especially regarding the complex interplay between polymer, ion and solvent structure in determining transport, is lacking. Herein, extensive molecular dynamics (MD) simulations of a model OMIEC representing various electrochemically gated states are reported that reveal charge state-dependent counterion condensation. X-ray diffraction simulations based on the MD data predict a measurable change in the scattering intensity at the counterion absorption edge, indicative of counterion repositioning with charging. We leverage an operando resonant X-ray scattering technique to experimentally corroborate the simulated scattering and report excellent agreement between predicted and experimental data, confirming that counterions preferentially reside in the lamellar mid-plane of crystallites at low doping, and near the polymer backbone at higher doping. Driving forces for ion type-dependent spatial repositioning and implications thereof are discussed.

Ultrahigh-Responsivity Near-Infrared Printed Photodetectors Based on Megasonically Processed RuCl₃ Nanosheets

Nano Letters · 2025-04-07 · 1 citations

Electronic structure modification via intercalative electron-doping of α-RuCl3, a two-dimensional (2D) transition metal halide, imparts unique optoelectronic properties such as near-infrared (NIR) absorption. While bulk-scale RuCl3 nanosheet production has been established using conventional liquid phase exfoliation, printed devices compatible with scalable manufacturing remain unexplored. Here, we demonstrate fully aerosol-jet-printed (AJP) NIR photodetectors based on megasonically processed RuCl3 nanosheets. The NIR photoresponse is enhanced by intercalation-based electron-doping in two stages: primary electrochemical intercalation of bulk RuCl3 crystals with quaternary ammonium bromides followed by megasonic exfoliation and secondary intercalation with polyvinylpyrrolidone. The degree of doping is controlled by the starting size of the primary intercalant, as larger primary intercalants ultimately enable greater secondary intercalation and electron-doping. In this manner, the combination of two-step intercalative doping and megasonic processing results in fully printed photodetectors with NIR responsivity of 244 mA/W at 1550 nm, outperforming previous reports by more than an order of magnitude.

Facet-Dependent Doping and Dopant-Dependent Faceting in Si-Doped GaAsSb Nanowires

Crystal Growth & Design · 2025-12-19

In this work, we correlate the spatial distributions of Si, Sb, and rotational twins in Si-doped GaAs1–xSbx nanowires. GaAs1–xSbx nanowires were grown epitaxially on Si(111) substrates by tuning process conditions to achieve repeated nucleation of rotational twins and growth along the [111]B direction; dilute Sb and Si fluxes were chosen to create a sufficient twin density to achieve a high yield while avoiding the growth of the wurtzite phase. While the impact of Si and Sb on twin density and nanowire growth rate has been previously reported, the facet-dependent incorporation of these species has not been established. Scanning transmission electron microscopy was used to confirm that Sb incorporates preferentially on the (111)B facets relative to {1̅1̅0} facets prior to nucleation of a rotational twin. With periodic twinning, this facet dependence leads to alternating regions of enriched and depleted Sb concentrations attributed to a growth rate-dependent Sb–As-exchange mechanism. Atom probe tomography measurements establish that while Si doping is not perturbed by twinning on (111)B facets, Si and Sb concentrations are anticorrelated for growth on non-(111)B facets. Density functional theory calculations underpin a thermodynamic model that explains the observed anisotropies in the dopant incorporation.

Robust interpretation of electrochemical impedance spectra using numerical complex analysis

PubMed · 2025-10-03

Electrochemical Impedance Spectroscopy (EIS) is a noninvasive technique widely used for understanding charge transfer and charge transport processes in electrochemical systems and devices. Standard approaches for the interpretation of EIS data involve starting with a hypothetical circuit model for the physical processes in the device based on experience/intuition and then fitting the EIS data to this circuit model. This work explores a mathematical approach for extracting key characteristic features from EIS data by relying on fundamental principles of complex analysis. These characteristic features can suggest the presence of inductors and constant phase elements (nonideal capacitors) from impedance data and enable us to answer questions about the identifiability and nonuniqueness of equivalent circuit models. In certain scenarios such as models with only resistors and capacitors, we are able to enumerate all possible families of circuit models. Finally, we apply the mathematical framework presented here to real-world electrochemical systems and highlight results using impedance measurements from a lithium-ion battery coin cell.

Author response for "Charge state-dependent ion condensation near conjugated polymer backbones"

2025-11-06

In Situ TBCl Etching and Selective-Area Growth and Doping of GaN

˜The œMaterials Research Society series · 2025-01-01

Ultra‐Flexible Pixelated Perovskite Photodetectors Enabled by Honeycomb Polymer Grids for High‐Resolution Imaging

Advanced Materials · 2025-03-17 · 17 citations

Abstract A nature‐inspired fabrication method based on a photolithography‐free flexible polymer grid is reported for high‐resolution pixelation of perovskite photodiode arrays with exceptional mechanical ductility and a morphology resembling that of natural compound eyes. The resulting pixelated perovskite photosensitive layer has a ≈1 µm pixel size with 2000 Pixels per inch (PPI) resolution when fully assembled as a photodetector array, delivering a detectivity of >10 13 Jones while providing cross‐talk free imaging. Using a polymer grid effectively releases stress on the perovskite platform, greatly increasing the mechanical agility of the otherwise brittle perovskite film. This novel fabrication methodology and device design offer new possibilities for applications in robotics, biomedical imaging, and virtual and augmented reality.

Resistive Switching in α-In₂Se₃ Lateral Field-Effect Transistors

ACS Nano · 2025-04-11 · 6 citations

Ferroelectric semiconducting field-effect transistors (FeS-FETs) based on two-dimensional materials exhibit nonvolatile resistive switching, making them promising candidates for next-generation memory and neuromorphic computing. However, the mechanisms governing resistive switching in α-In2Se3 lateral devices remain unresolved, particularly regarding the relative contributions of channel and contact resistance. In this study, Kelvin probe force microscopy (KPFM) was employed to spatially resolve the gate-poling-dependent contact and channel resistances in α-In2Se3 FeS-FETs, while scanning photocurrent microscopy (SPCM) was used to quantify changes in effective Schottky barrier height at the metal contacts. Both contact and channel resistances were found to increase (decrease) with positive (negative) poling, with the contact resistance modulation correlating with changes in Schottky barrier height. Control experiments on as-exfoliated multidomain flakes confirmed that spontaneous polarization influences both channel and contact resistances. However, typical clockwise resistive switching characteristics can be observed even in the absence of detectable ferroelectric polarization switching. Furthermore, typical gate-poling conditions lead to the formation of stacking defects observed by ex situ high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The observed defects can impede domain wall motion, providing a rationale for the lack of an abrupt switching threshold and a possible mechanism of coupling in-plane fields to out-of-plane polarization. We conclude that resistive switching in α-In2Se3 lateral channel devices is often influenced by both reversible polarization switching and irreversible defect formation, highlighting the need for improved domain wall control and defect mitigation strategies to enhance FeS-FET performance for reliable memory applications.

What Complex Analysis Can Tell Us about Electrochemical Impedance Spectroscopy

ECS Meeting Abstracts · 2025-11-24

Electrochemical Impedance Spectroscopy (EIS) is a standard non-invasive technique widely used to understand electronic and ionic transport mechanisms in diverse material systems. There have been several approaches, particularly using machine learning, to classify and categorize the complex-valued data that is produced through EIS. Existing approaches typically have been optimized to specific materials systems, thus lacking general applicability of the classification framework. In this work, we describe a novel mathematical framework that allows us to discover key features within the EIS data. This framework builds on the fundamental principles of complex analysis and recent advances in numerical rational function approximation, to extract key mathematical properties of material systems directly from their EIS data, without relying on the knowledge of equivalent circuit models. We look at ways to ascertain the presence of imperfect capacitors i.e constant phase elements and Warburg elements. We explore questions about the identifiability and uniqueness of equivalent circuit models that can produce the EIS impedance data. We highlight results using both synthetic data and experimental data. The experimental data we analyze is obtained from diverse material systems including Lithium ion batteries and electrodes coated with a conjugated polymer. We also compare our results with those obtained by standard machine learning approaches and highlight the complementary insights that our mathematical framework can provide.