Conduction Mechanism Research Articles

Charge transport mechanism in [GeOx](z)[SiO2](1-z) based MIS structures

The mechanisms of conductivity in metal–insulator–semiconductor (MIS) structures based on [GeOx](z)[SiO2](1-z) films (0.25 ≤ z ≤ 1) fabricated by co-evaporation of germanium oxide and silicon oxide powders in vacuum and deposition on a p+-type silicon substrate are studied. Indium tin oxide deposited by magnetron method is used as the top electrode. According to IR spectroscopy, Ge–O, Si–O, and Ge–O–Si bonds are detected in the films, while no features related to the presence of germanium clusters are found in the Raman spectra. The current–voltage characteristics (I–V curves) are measured at different temperatures and analyzed by applying the eight most common models of charge transport in MIS structures. It is found that the experimental I–V curves are most accurately approximated in the space charge limited current model, and the parameters of the charge traps are determined within this model.

Shot Noise in a Metal Close to the Mott Transition.

SrIrO3 is a metallic complex oxide with unusual electronic and magnetic properties believed to originate from electron correlations due to its proximity to the Mott metal-insulator transition. However, the nature of its electronic state and the mechanism of metallic conduction remain poorly understood. We demonstrate that the shot noise produced by nanoscale SrIrO3 junctions is strongly suppressed, inconsistent with diffusive quasiparticle transport. Analysis of thermal effects and scaling with the junction length reveals that conduction is mediated by collective hopping of electrons almost localized by correlations. Our results provide insight into the non-Fermi liquid state close to the Mott transition and advance shot noise measurements as a powerful technique for the study of quantum materials.

Piezotronic Strain Sensor with Uniform and Switchable Sensitivity by Conductivity Transformation

Piezotronic strain sensors that convert mechanical deformation into electrical signals are becoming increasingly important in artificial intelligence, human-machine interfaces, and robotic technologies. These applications require piezotronic sensor with the integration of high-sensitivity, high-stability, and versatile-functionality, which are limited by the single conductivity mechanism. In this study, we propose a piezotronic strain sensor with uniform and switchable sensitivity in a short channel field effect junction.The strain-induced piezo-potential can be used to switch the conductivity between Schottky and Ohmic regime, leading to an exponential (linear) piezotronic modulation in Schottky (Ohmic) conductivity elucidated by Fermi occupation theory. Local gauge factor reaches a high value of 1330 in Schottky conductivity and a low value of 320 in Ohmic regime, yielding a higher ratio of 4.2. The stable conductivity makes these high and low sensitivity uniform over a wide strain range. This study gives a deep insight into the correlation of strain-sensing performance and conductive mechanism in piezotronic sensors, and offers a new avenue to develop multifunctional and high-sensitivity sensors.

Reconstruction of LATP-LT composite solid electrolyte and analysis of Li+ conduction mechanism using 3D CT

Li1+xAlxTi2-x(PO4)3 (LATP) is a highly promising solid-state electrolyte, known for its high lithium-ion conductivity and stability at room temperature. This study successfully prepared LATP-LT composite solid-state electrolytes by combining LATP with Li2O-TeO2 (LT) glass, utilizing the molten state of the glass at high temperatures. The investigation focused on the effects of different ratios and sintering conditions on the performance of the LATP-LT composites. Results indicate that an appropriate amount of LT enhances the material's sinterability, facilitating continuous lithium-ion conductivity while inhibiting the diffusion of lithium dendrites within the pores. The LATP-LT composite solid electrolyte achieved an ionic conductivity of 1.81×10-4 S/cm at room temperature. Thus, selecting an optimal concentration of LT can serve as a breakthrough in the development of all-solid-state lithium-ion batteries, advancing the field of solid-state electrolytes.

Effect of temperature and frequency on the dielectric behaviour of cellulose nanocrystals

Nanocellulose is a promising material for advanced applications due to its renewable nature, non-toxicity, eco-friendliness, mechanical strength and other unique properties. This study investigates the dielectric properties of cellulose nanocrystals (CNCs) derived from wastepaper through acid hydrolysis, across a temperature range of 30°C to 100°C and a frequency range of 1 Hz to 10 MHz. Using theoretical models such as the modified Cole-Cole model, Jonscher's universal dielectric response (UDR) model and modified Kohlrausch-Williams-Watts (KWW) model, a detailed analysis is performed. The results indicate that the dielectric properties depend on temperature, with the frequency dispersion of the real (ε′) and imaginary parts (ε″) of the dielectric permittivity fitting the modified Cole-Cole equation. These values show an initial increase up to 70°C (ε′∼ 6000 and dielectric loss <1) followed by a decrease at higher temperatures, which is linked to the hydroxyl groups. A temperature dependence is also observed in space charge conductivity, free charge conductivity and relaxation time. Non-Debye type behaviour is attributed to asymmetrical features in the electric modulus spectra, as explained by the modified KWW model at various temperatures. The frequency variation of AC conductivity adheres to Jonscher’s power law and the temperature variation of the frequency exponent (0≤ s ≤1) indicates a correlated barrier hopping conduction mechanism for charge carriers. Overall, these findings highlight CNCs as excellent candidate for antistatic applications, demonstrating conductivity ranging from 10−5 to10−9 Scm−1. The results also suggest CNCs can be used in energy storage applications due to their outstanding dielectric properties and low dielectric loss (<1).

Synergy of hierarchical structures and multiple conduction mechanisms for designing ultra-wide linear range pressure sensors

Synergy of hierarchical structures and multiple conduction mechanisms for designing ultra-wide linear range pressure sensors

Dragonfly wings-inspired, anti-freezing, ultra-stretchable, and transparent nano-structure sodium alginate-based hydrogel for non-delayed wearable sensing at low-temperatures.

Conductive hydrogels are regarded as an optimal flexible electronic material. Nevertheless, simultaneously achieving excellent mechanical and conductive properties in hydrogels necessitates attention. The high mechanical properties of hydrogels were achieved by employing a strategy that involves constructing a nano-structure network inspired by the highly ordered structure of dragonfly wings. The conductivity and anti-freezing of the hydrogel were enhanced through the construction of a conductive mechanism, achieved by combining ions with nano-particles. The hydrogel exhibits outstanding properties, including anti-freezing, ultra-stretchable (6000%), impressive conductivity (16.2Sm-1), a transparency level of up to 91.2%, and excellent sensitivity in strain sensors. Regulation of the hydrogel matrix's topology and the formation of bionic nano-structures synergistically establish the hydrogel's ultra-stretching and energy dissipation mechanism. The high conductivity of the hydrogel is achieved by constructing a synergistic conduction pathway, which incorporates nano-particles and ions. Under the stretching-induced effect of hydrogel, it facilitates a more efficient path for conduction, thereby enhancing its conductivity and sensing sensitivity under significant strains. Subsequently, this hydrogel was successfully applied to wearable sensor technology, demonstrating surprisingly remarkably prompt non-delayed sensing performance even at low-temperatures. It presents abundant opportunities for expanding the application of hydrogels in flexible electronics.

Microscopic insights into UiO-66@proton exchange composite membrane by molecular dynamics simulation

UiO-66 as one of the known metal-organic frameworks (MOFs) has been recognized as highly promising dopants for enhancing the proton conductivity of proton exchange membrane (PEM) owing to the large pore volume and structure tunability. Despite the numerous experimental reports on MOF-doped PEMs, their increased proton conductivity is commonly ascribed to enhanced water uptake. The underlying mechanisms from a microscopic perspective remain elusive. Therefore, this work explores the microstructure and water diffusion dynamics within composite membranes to decipher their mechanisms involved in proton conductivity using molecular dynamics (MD) simulations. Four types of composite membranes based on two representative MOFs i.e. UiO-66 and UiO-66-NH2 and two PEMs including Nafion and Dow, respectively, were taken into account. It is revealed that the UiO-66-NH2 doped Nafion composite membrane exhibits the highest water uptake among the four composite membranes resulting from the super hydrophilicity of UiO-66-NH2. Besides, the more concentrated distribution of sulfonic groups near the water-PEM interface and the higher interface roughness of UiO-66-NH2 doped Nafion lead to more water molecules surrounding its sulfonic groups that are favorable for the proton dissociation from sulfonic groups. Furthermore, the increased water channel connectivity of MOF-doped membranes that promotes proton transport through water via the Grotthuss mechanism demonstrates one of the mechanisms for increased proton conductivity. On the other hand, although the reduced lifetime of the hydrogen bond network and the enhanced water diffusion coefficient within MOF-doped membranes manifest the favorable proton transfer via the Vehicle mechanism. Overall, UiO-66-NH2 doped Nafion membranes exhibiting the highest water channel connectivity and water diffusion coefficients demonstrate the greatest potential of UiO-66-NH2 doping in advancing the proton conductivity. These findings provided microscopic insights into understanding the improved proton conductivity mechanism of MOF doped PEMs, and the approaches developed in this work may be extended to other composite membranes.

Photocurrent in PZT/TiOx composite film prepared via self-assembly of perovskite matrix and ALD of titania

A novel approach for the preparation of ferroelectric composite films has been successfully developed by combining sol–gel evaporation-induced self-assembly (EISA) of porous lead zirconate titanate (PZT) films with atomic layer deposition (ALD) of titania. The EISA process, which utilizes a Brij-type surfactant, facilitates the formation of large columnar perovskite grains with narrow (∼20 nm) interconnected pores. ALD, employing the thermal reaction of titanium isopropoxide with water, ensures uniform titania growth within the pores throughout the film thickness, as demonstrated by transmission electron microscopy and ellipsometric porosimetry. The resulting PZT-TiOx composite films exhibit a pronounced photovoltaic current under visible light illumination, attributed to electron excitation from the valence band to Ti3+ states, followed by movement via a hopping conduction mechanism. The photocurrent value varies with the direction of polarization. This behavior presents a potential method for controlling photoconductivity through polarization, with possible applications in electronic and photonic devices.

Unveiling exceptional conduction mechanism and high proton conductivity in amorphous electrolyte for advanced ceramic fuel cells

The requirement of high ion conductive material working at low temperatures is highly demanding in fuel cells. This study explains a groundbreaking advancement in ceramic fuel cells by exploring the potential of amorphous Sm0.3Al0.7-oxide and the proton conduction mechanism of amorphous oxides. Opposite to conventional crystalline electrolytes, amorphous electrolytes showed superior ion conduction. To study the detailed mechanism of ion conduction, amorphous Sm0.3Al0.7-oxide was selected which exhibited an exceptional proton conductivity of 0.17 S/cm and a power density of 1100 mW/cm2 at 550 °C, significantly surpassing traditional electrolyte materials. Using advance characterization techniques, a new approach has been proposed to provide the reasons for the high conductivity of amorphous materials, which entails a complete mechanism that describes how disordered structure and disoriented grain boundaries facilitate efficient proton conduction by reducing energy barriers and enhancing ionic mobility. Also, it has been described how the high enthalpy and the high energy state of amorphous materials are suitable for enhancing proton conduction. This study aims to clarify why amorphous materials are promising candidates for future fuel cell applications, facilitating significant advancements in SOFC and PCFC technologies and paving the way for more efficient and sustainable energy solutions.

Facile Hydrothermal Synthesis and Resistive Switching Mechanism of the α-Fe2O3 Memristor

Among the transition metal oxides, hematite (α-Fe2O3) has been widely used in the preparation of memristors because of its excellent physical and chemical properties. In this paper, α-Fe2O3 nanowire arrays with a preferred orientation along the [110] direction were prepared by a facile hydrothermal method and annealing treatment on the FTO substrate, and then α-Fe2O3 nanowire array-based Au/α-Fe2O3/FTO memristors were obtained by plating the Au electrodes on the as-prepared α-Fe2O3 nanowire arrays. The as-prepared α-Fe2O3 nanowire array-based Au/α-Fe2O3/FTO memristors have demonstrated stable nonvolatile bipolar resistive switching behaviors with a high resistive switching ratio of about two orders of magnitude, good resistance retention (up to 103 s), and ultralow set voltage (Vset = +2.63 V) and reset voltage (Vreset = −2 V). In addition, the space charge-limited conduction (SCLC) mechanism has been proposed to be in the high resistance state, and the formation and destruction of the conductive channels modulated by oxygen vacancies have been suggested to be responsible for the nonvolatile resistive switching behaviors of the Au/α-Fe2O3/FTO memristors. Our results show the potential of the Au/α-Fe2O3/FTO memristors in nonvolatile memory applications.

Exploring the synaptic response of reactive Mn electrodes based TiO2 resistive switches

Mn/TiO2/Mn devices, prepared by reactive sputtering and photolithography techniques, were characterized by analyzing their current–voltage (I-V) dependence, non-volatile memory properties, and artificial synapse behavior. The detailed study of its I-V characteristics allowed for highlighting the main conduction mechanisms involved in the electrical transport through the Mn-TiO2 junctions and determining an equivalent circuit model. These results show that the oxidation of metallic Mn electrodes and the application of electrical pulses produce a complex scenario associated with a highly inhomogeneous oxygen vacancy distribution. The resistance hysteresis switching loops were determined, as well as the synaptic-like weight depreciation and potentiation, revealing a linear dependence of the reset voltage as a function of the amplitude of the set voltage and a quasi-linear variation of the conductance with the number of applied pulses. Simulations based on spiking neural network architecture, considering different updates of the synaptic weights, were trained to learn handwriting patterns. Notably, those based on the linear learning rule of the Mn/TiO2/Mn devices outperformed others with increasing non-linear behavior, demonstrating both high recognition and noise tolerance factors, further highlighting the robustness of this approach.

Main Heat Transfer Mechanisms in Hot Stamping Processes: a Review

Objectives: The article reviews heat transfer mechanisms in the hot stamping process, highlighting models to calculate the interfacial heat transfer coefficient (IHTC), crucial for optimizing the cooling and quality of formed products. Theoretical Framework: In hot stamping of high-strength steels, the IHTC is affected by variables such as contact pressure, roughness and temperature. Cooling efficiency directly impacts the temperature distribution and martensitic microstructure of the material, essential for structural strength. Method: The review compares IHTC calculation methods, such as inverse heat conduction analysis and Newton's law of cooling, detailing the convection, radiation and conduction mechanisms at each stage of the process: transfer, positioning and forming. Results and Discussion: The inverse heat conduction analysis proved to be the most accurate for determining the IHTC, compared to the finite element method (FEM). The study suggests that efficient cooling channels and high conductivity materials in the matrix reduce cooling time and improve the quality of the final product. Research Implications: Findings provide a basis for improving thermal management in hot stamping, reducing cycle time and increasing productivity. Originality/Value: This work contributes a comprehensive reference on IHTC, assisting researchers and engineers in optimizing heat transfer and production efficiency in the manufacture of automotive components.

High Proton Conductivity of Acid Impregnated COFs Stabilized by Post-Oxidation.

The investigation of proton conduction processes within artificial nanopores using phosphoric acid (H3PO4) and sulfuric acid (H2SO4) not only sheds light on the mechanisms of proton conduction for these strong acids in confined environments, while also provides critical insights into the proper understanding of biological transmembrane proton transport. However, the synthesis of stable and acid-resistant host frameworks is yet a major challenges. By following that, the present study is conducted with the aim of improving the chemical stability of an imine-based COF (CPOF-10) by converting it into an amide-linked COF (CPOF-11) via a post-oxidative approach. In which, the integration of an appropriate amount of imidazole groups into the framework facilitates the efficient impregnation of liquid proton-conducting acids. The obtained results indicate the ten times greater proton conductivity of H3PO4@CPOF-11 than that of H3PO4@CPOF-10, thereby, successfully achieving 8.63 × 10-2 S cm-1 at 160°C, under nitrogen (N2) atmosphere. Moreover, the highly stable CPOF-11 tolerated H2SO4 doping, delivering a high proton conductivity of up to 1.70 × 10-1 S cm-1 at 140°C, with a significantly low activation energy of 0.05 eV. To the best of the knowledge, this activation energy (0.05 eV) of H2SO4@CPOF-11 is found to be one of the lowest value among all the reported proton-conducting materials. Thus, this study will provide new understanding for the fabrication of advanced porous organic materials in fuel cells application.

Investigation of the Optical, Electric Properties, and Conduction Mechanism of the Cubic Spinel LiMn2O4

Investigation of the Optical, Electric Properties, and Conduction Mechanism of the Cubic Spinel LiMn₂O₄

Printed High-Entropy Prussian Blue Analogs for Advanced Non-Volatile Memristive Devices.

Non-volatile memristors dynamically switch between high (HRS) and low resistance states (LRS) in response to electrical stimuli, essential for electronic memories, neuromorphic computing, and artificial intelligence. High-entropy Prussian blue analogs (HE-PBAs) are promising insertion-type battery materials due to their diverse composition, high structural integrity, and favorable ionic conductivity. This work proposes a non-volatile, bipolar memristor based on HE-PBA. The device, featuring an active layer of HE-PBA sandwiched between Ag and ITO electrodes, is fabricated by inkjet printing and microplotting. The conduction mechanism of the Ag/HE-PBA/ITO device is systematically investigated. The results indicate that the transition between HRS and LRS is driven by an insulating-metallic transition, triggered by extraction/insertion of highly mobile Na+ ions upon application of an electric field. The memristor operates through a low-energy process akin to Na+ shuttling in Na-ion batteries rather than depending on formation/rupture of Ag filaments. Notably, it showcases promising characteristics, including non-volatility, self-compliance, and forming-free behavior, and further exhibits low operation voltage (VSET = -0.26 V, VRESET = 0.36 V), low power consumption (PSET = 26 µW, PRESET = 8.0 µW), and a high ROFF/RON ratio of 104. This underscores the potential of high-entropy insertion materials for developing printed memristors with distinct operation mechanisms.

Conceptualizing Surface-Like Diffusion for Ultrafast Ionic Conduction in Solid-State Materials.

Surface-like diffusion is a recently proposed concept to explain the mechanism of ultrafast ionic conduction in high-rate oxide (e. g., niobium oxides and their alloys with TiO2 and WO3) and framework materials (e. g., Prussian blue analogs). This perspective seeks to illustrate the structural origin, theoretical foundation, and experimental evidences of surface-like diffusion. Unlike classical lattice diffusion, which typically involves ionic hopping between adjacent interstitial sites in solids, surface-like diffusion occurs when ions-that are significantly smaller than the interstitials-migrate along the off-center path in the diffusion channel. This mechanism results in an exceptionally low activation energy (Ea) down to 0.2 eV, which is crucial for achieving high-rate performance in electrochemical devices such as lithium-ion and sodium-ion batteries. This concept review also discusses the criteria to identify materials with potential surface-like diffusion and outlines theoretical and experimental tools to capture such phenomenon. Several candidates for further investigation are proposed based on the current understanding of the mechanism.

Thermal management of NEPCM during freezing considering conduction mechanism

Thermal management of NEPCM during freezing considering conduction mechanism

Coexistence of analog and digital resistive switching behaviors in TiN/SiNx resistive random access memory device

The digital–analog hybrid resistive random access memory can not only be used in computing in memory integrated circuits but also adapt to various requirements, such as achieving lower integration complexity. In this work, resistive memory devices with Ta/SiNx/TiN/Pt structures were fabricated, which exhibit a gradual analog or abrupt digital resistive state (DRS) characteristic depending on the different applied voltage range. The experimental results indicate that different RS switching of these devices is due to the change in the conductive mechanism in the SiNx/TiN double-layer structure. The Schottky barrier at the SiNx/TiN interface is the cause of analog resistive state characteristics under low sweeping voltage, while the formation/rupture of the conductive filaments formed under large voltage is the reason for the device to exhibit DRS characteristics.

Piezoresistive, Piezocapacitive and Memcapacitive Silk Fibroin-Based Cement Mortars.

Water-stable proteins may offer a new field of applications in smart materials for buildings and infrastructures where hydraulic reactions are involved. In this study, cement mortars modified through water-soluble silk fibroin (SF) are proposed. Water-soluble SF obtained by redissolving SF films in phosphate buffer solution (PBS) showed the formation of a gel with the β sheet features of silk II. Electrical measurements of SF indicate that calcium ions are primarily involved in the conductivity mechanism. By exploiting the water solubility properties of silk II and Ca2+ ion transport phenomena as well as their trapping effect on water molecules, SF provides piezoresistive and piezocapacitive properties to cement mortars, thus enabling self-sensing of mechanical strain, which is quite attractive in structural health monitoring applications. The SF/cement-based composite introduces a capacitive gauge factor which surpasses the traditional resistive gauge factor reported in the literature by threefold. Cyclic voltammetry measurements demonstrated that the SF/cement mortars possessed memcapacitive behavior for positive potentials near +5 V, which was attributed to an interfacial charge build-up modulated by the SF concentration and the working electrode. Electrical square-biphasic excitation combined with cyclic compressive loads revealed memristive behavior during the unloading stages. These findings, along with the availability and sustainability of SF, pave the way for the design of novel multifunctional materials, particularly for applications in masonry and concrete structures.