Electron Transport Characteristics Research Articles

Automated Scanning Dielectric Microscopy Toolbox for Operando Nanoscale Electrical Characterization of Electrolyte‐Gated Organic Transistors

AbstractElectrolyte‐gated organic transistors (EGOTs) leveraging organic semiconductors' electronic and ionic transport characteristics are the key enablers for many biosensing and bioelectronic applications that can selectively sense, record, and monitor different biological and biochemical processes at the nanoscale and translate them into macroscopic electrical signals. Understanding such transduction mechanisms requires multiscale characterization tools to comprehensively probe local electrical properties and link them with device behavior across various bias points. Here, an automated scanning dielectric microscopy toolbox is demonstrated that performs operando in‐liquid scanning dielectric microscopy measurements on functional EGOTs and carries out extensive data analysis to unravel the evolution of local electrical properties in minute detail. This paper emphasizes critical experimental considerations permitting standardized, accurate, and reproducible data acquisition. The developed approach is validated with EGOTs based on blends of organic small molecule semiconductor and insulating polymer that work as accumulation‐mode field‐effect transistors. Furthermore, the degradation of local electrical characteristics at high gate voltages is probed, which is apparently driven by the destruction of local crystalline order due to undesirable electrochemical swelling of the organic semiconducting material near the source electrode edge. The developed approach paves the way for systematic probing of EGOT‐based technologies for targeted optimization and fundamental understanding.

Research on the robust electrical contact properties and favorable transport characteristics of two-dimensional WB4/MoSi2N4 van der Waals heterostructures

Ensuring optimal interface contact performance is crucial for achieving low-resistance ohmic contact in the design of two-dimensional (2D) electronic devices. In this study, we systematically investigate the contact properties of van der Waals (vdW) heterojunctions formed by compositing the semi-metal WB4 with Dirac cones and the semiconductor MoSi2N4 through first-principles calculations. A thorough investigation has been carried out on the electronic structure and transport characteristics at the interface. Our research findings indicate that the WB4/MoSi2N4 combination demonstrates robust ohmic contact performance, maintaining ohmic or near-ohmic p-type Schottky contacts over a wide range when exposed to electric field, varying layer spacing, and biaxial strain. This unique characteristic is associated with the Fermi level pinning (FLP), where there are gap states present at the interface. Here, the FLP plays a positive role in maintaining ohmic contact. In addition, different derivatives of MoSi2N4 are combined with WB4 to create heterostructures and study the changes in contact performance. Our research shows that the robust ohmic contact of WB4/MoSi2N4 will have excellent prospects for application in future electronic devices.

Ultrathin 2D Alloyed Cu−Ga−Zn−S Curved Nanobelts for Boosting Visible‐Light Photocatalytic Hydrogen Evolution

Abstract2D semiconductor nanomaterials have received significant attention as photocatalysts for solar‐to‐hydrogen conversion due to their robust light absorption capacity, large specific surface area, and superior electron transport characteristics. Nevertheless, it is challenging to develop 2D quaternary copper‐based sulfides (QCSs) with functional integration of conducive structural features for photocatalysis from multiple elements and intricate control conditions. Herein, ultrathin 2D alloyed Cu−Ga−Zn−S (CGZS) curved nanobelts (NBs) are fabricated by using a facile one‐pot colloidal method. Subsequently, the derived Cu31S16‐CGZS Janus heterostructures are designed by increasing Cu concentrations. The formation mechanism of 2D curved alloys and Janus heterostructures is systematically investigated. Without cocatalysts, curved alloyed CGZS NBs demonstrated superior photocatalytic activities of 1264.2 µmol g−1 h−1 compared to Janus heterostructured Cu31S16−CGZS (463.1 µmol g−1 h−1) under visible light (> 400 nm). Experimental and theoretical results unveiled that the improved photocatalytic activities of curved CGZS NBs can be attributed to enhanced charge–carrier separation efficiency resulting from high crystallinity and ultrathin 2D structure, abundant active sites from curved structure, high‐active (0001) crystal facet with the lowest reaction Gibbs energy, work function, and metal‐like properties. This work offers new insights into functional integration into ultrathin 2D QCSs with enhanced visible‐light photocatalytic performance.

Pressure influenced electronic phase transition, mechanical, optoelectronic, and transport characteristics of double perovskite Rb2AgSbCl6: A first-principles investigation

In this work, we used density functional theory (DFT) simulations to investigate the structural, elastic, electronic, optical, and transport characteristics of pressure-induced Rb2AgSbCl6. By calculating the octahedral and the tolerance factors, the phase stability has been verified. The calculated formation energy and Gibbs free energy values have demonstrated the thermodynamic stability of the material. The outcomes of the mechanical behavior analysis revealed that the pressure-driven Rb2AgSbCl6 is mechanically stable and sustains ductility as well as anisotropy. Additionally, as the pressure is increased from 0 GPa to 100 GPa, the band gap has been reduced from 2.64 eV to 0 eV. The hydrostatic pressure of 100 GPa was the critical pressure at which the material revealed a metallic nature. The optical properties such as absorbance and optical conductivity shift towards lower energy and comparatively higher at increased pressure with minimal energy loss. The thermoelectric characteristics are examined utilizing the BoltzTraP code at different pressures. The figure of merit (ZT) value was increased from 0.76 to 0.80 with the increase in pressure at room temperature. These characteristics render pressure-influenced Rb2AgSbCl6 favorable candidates for utilization in solar cells as well as thermoelectric devices.

2D Janus Polarization Functioned by Mechanical Force.

2Dpolarization materials have emerged as promising candidates for meeting the demands of device miniaturization, attributed to their unique electronic configurations and transport characteristics. Although the existing inherent and sliding mechanisms are increasingly investigated in recent years, strategies for inducing 2D polarization with innovative mechanisms remain rare. This study introduces a novel 2D Janus state by modulating the puckered structure. Combining scanning probe microscopy, transmission electron microscopy, and density functional theory calculations, this work realizes force-triggered out-of-plane and in-plane dipoles with distorted smaller warping in GeSe. The Janus state is preserved after removing the external mechanical perturbation, which could be switched by modulating the sliding direction. This work offers a versatile method to break the space inversion symmetry in a 2D system to trigger polarization in the atomic scale, which may open an innovative insight into configuring novel 2D polarization materials.

Exploring the effects of mono-bromination on hole-electron transport and distribution in dibenzofuran and dibenzothiophene isomers: a first-principles study.

This study delves into hole-electron transport and distribution properties inherent in mono-brominated dibenzofuran (DBF) and dibenzothiophene (DBT) isomers. As determined by frontier molecular orbitals, all brominated structures have narrower bandgaps than their primary structures. The TD-DFT calculation showed that 2BDBT had the highest absorption wavelength of all molecules at 315.35nm. Notably, the study unveils remarkably low electron and hole reorganization energies due to bromine substitution in DBF and DBT molecules. Specifically, the 4BDBF has the lowest hole reorganization energy of all DBF configurations, 0.229eV. In addition, 3BDBF has 0.226eV less electron reorganization energy than all other molecules. Compared to DBT, 3BDBT has the lowest electron reorganization energy of 0.254eV. Overall, this research sheds significant light on the fundamental electronic and hole transport characteristics of bromine-substituted DBF and DBT isomers, highlighting their promising role in polymer design as donors/acceptors for advanced organic electronic applications. Molecular structures were optimized using Density Functional Theory (DFT) B3LYP/6-311 + + G (d, p) level of theory, and the study further elucidates these molecules' energy levels and absorption spectra through Time-Dependent Density Functional Theory TD-DFT; these calculations were performed using Gaussian 09W software package. The key parameters such as reorganization energies, Electron Localization Function map, Laplacian Bond Order, and NCI-RDG were meticulously examined for the molecules with the results of DFT calculations were analyzed and displayed by utilizing the software packages VMD 1.9.4 and Multiwfn 3.8, aiming to comprehend their charge transport and distribution properties.

Impact of Halide Ion Occupancy on Thermodynamic, Mechanical, Electro-optic, and Electron Transport Characteristics of Rb2CuAsX6 (X = F, Cl, Br) Double Perovskites Using Density Functional Theory

Impact of Halide Ion Occupancy on Thermodynamic, Mechanical, Electro-optic, and Electron Transport Characteristics of Rb2CuAsX6 (X = F, Cl, Br) Double Perovskites Using Density Functional Theory

Characterizing Local Electronic States of Twin Boundaries in Copper.

Grain boundaries (GBs) and twin boundaries (TBs) in copper (Cu) are two major planar defects that influence electrical conductivity due to their complex electron transport characteristics, involving electron scattering and electron concentration. Understanding their local electronic states is crucial for the design of future conductor materials. In this study, we characterized electron behaviors at TBs and GBs within one Cu grain using atomic force microscopy. Our findings revealed that, compared with GBs, TBs exhibit better current transport capability (direct-current mode) and larger electromagnetic loss (high-frequency microwave mode). Both kelvin probe force microscopy and theoretical analysis suggested that TBs with smaller lattice disorder possess lower density of states at the Fermi level. The reduced density of states may result in decreased electron scattering and a lower electron concentration at TBs. The latter can be highlighted by the high-frequency skinning effect, manifested as larger electromagnetic loss and weaker high-frequency conductivity.

Ultralow Glassy Thermal Conductivity and Controllable, Promising Thermoelectric Properties in Crystalline o-CsCu5S3.

We thoroughly investigated the anharmonic lattice dynamics and microscopic mechanisms of the thermal and electronic transport characteristics in orthorhombic o-CsCu5S3 at the atomic level. Taking into account the phonon energy shifts and the wave-like tunneling phonon channel, we predict an ultralow κL of 0.42 w/mK at 300 K with an extremely weak temperature dependence following ∼T-0.33. These findings agree well with experimental values along with the parallel to the Bridgman growth direction. The κL in o-CsCu5S3 is suppressed down to the amorphous limit, primarily due to the unconventional Cu-S bonding induced by the p-d hybridization antibonding state coupled with the stochastic oscillation of Cs atoms. The nonstandard temperature dependence of κL can be traced back to the critical or dominant role of wave-like tunneling of phonon contributions in thermal transport. Moreover, the p-d hybridization of Cu(3)-S bonding results in the formation of a valence band with "pudding-mold" and high-degeneracy valleys, ensuring highly efficient electron transport characteristics. By properly adjusting the carrier concentration, excellent thermoelectric performance is achieved with a maximum thermoelectric conversion efficiency of 18.4% observed at 800 K in p-type o-CsCu5S3. Our work not only elucidates the anomalous electronic and thermal transport behavior in the copper-based chalcogenide o-CsCu5S3 but also provides insights for manipulating its thermal and electronic properties for potential thermoelectric applications.

Biaxila strain modulated high anisotropic gas-sensing performance of C5N-based two-dimensional devices: A first-principles study

Two-dimensional carbon nitride materials have been widely used in many applications such as device fabrication, gas adsorption and separation due to their abundant element resources, high physicochemical stability and excellent electronic properties. In this paper, density functional theory and non-equilibrium Green's function method are used to study the electronic structure, transport characteristics and gas sensitivity of C5N-based structures. The results show that the electron transport exhibits obvious anisotropy, in which the electron transport in the armchair direction is more conductive than that in the zigzag direction. It is worth noting that the negative differential resistance effect exists in both directions. Furthermore, the transport and sensing characteristics of inorganic molecules (NO, CO, NO2, SO2, and NH3) adsorbed on the C5N monolayer are studied. The results show that CO, SO2 and NH3 exist on the surface of C5N in the form of physical adsorption, while NO and NO2 adhere to the surface of C5N in the form of chemical adsorption. The designed C5N gas sensor exhibits high sensitivity to NO and NO2 molecules, reaching 81 % sensitivity to NO2 at a 0.1 V bias voltage. Finally, the effect of strain on the adsorption properties of gas sensing devices is studied. Studies have shown that the application of -4 % strain in the armchair direction significantly increases the current of NO and NO2, significantly improving the performance of the gas sensor. Whether strain is applied to the device or gas adsorption, C5N materials always maintain significant anisotropy. This study shows that C5N is a highly anisotropic and sensitive two-dimensional material, which has broad application potential in the field of electronic properties and gas sensing.

Study on the conductivity of metal-based epitaxial graphene with vacancy defects and anharmonic effects

Metal-based epitaxial graphene exhibits extremely high conductivity at room temperature, making the study of its conductance crucial for understanding electron transport mechanisms in two-dimensional materials. In this paper, we applied solid-state physics theories and methods to investigate factors influencing the conductivity of metal-based epitaxial graphene. We considered the variation of conductivity and its temperature stability coefficient with temperature, taking into account the anharmonic vibrations of atoms, and explored the impact of anharmonic effects on conductivity. Using copper-based graphene as an example, we established relationships between temperature and several key parameters: electronic conductivity (σe), conductivity contributed by electron–phonon interactions (σp), conductivity contributed by vacancy defects (σn), and total conductivity (σ), along with its temperature stability coefficient (ασ). All research results were obtained within the temperature range of 300 K to 1200 K. The study reveals that σ decreases nonlinearly as temperature increases, with a magnitude on the order of (Ω ∙ m)-1, which is approximately equal to σp. The conductivity of copper-based epitaxial graphene is found to be greater than that of lithium-based epitaxial graphene. The anharmonic effects of atomic vibrations increase σ, and this increase is more pronounced at higher temperatures. The temperature stability coefficient ασ rapidly decreases with increasing temperature before tending to a constant, indicating that conductivity exhibits better temperature stability at higher temperatures. This paper provides theoretical guidance for understanding electron transport characteristics of metal-based epitaxial graphene and contributes to the design and application of high-performance electronic devices.

Electronic transport properties of WS2 using ensemble Monte Carlo method

The electronic transport characteristics of tungsten disulfide (WS2) sheets are studied using the ensemble Monte Carlo technique in the presence of intrinsic scattering mechanisms only. The transport properties of the material are obtained in a two-valley model where intra- and inter-valley scatterings are considered in K and Q valleys. The velocity overshoot effect is observed for some applied field values. Negative differential phenomena are seen for some values of the energy difference between K and Q valleys ( ΔEKQ ), therefore ΔEKQ and the effective mass of carriers in the Q valley has a critical role in the transport and mobility characteristics of WS2. The mobility of carriers is calculated as a function of temperature and the results are compatible with some existing theoretical and experimental predictions.

Transport properties and electronic phase transitions in two-dimensional tellurium at high pressure

Utilizing in situ Raman spectroscopy, resistivity, and Hall-effect measurements, we conducted an extensive investigation on the continuous electronic phase transitions and transport properties of two-dimensional (2D) tellurium (Te) under high pressure at room and low temperature (80–300 K). The distinguishable decrease in the A1 Raman mode's full width at half maximum in the trigonal phase (Te-I) indicated an electronic phase transition at 2.2 GPa. The following Hall-effect experiments located the Lifshitz transition and the semiconductor-semimetal transition at 0.9 and 1.9 GPa, respectively, and the semiconductor-semimetal transition was also confirmed by resistivity variation through temperature. The charge carrier types of the Te changed from hole to electron during the phase transition from Te-I to Te-II (triclinic phase) at low temperature, while the transport parameters remained almost unchanged during the phase transition from Te-II to Te-III (monoclinic phase). The results offered complete and thorough electronic phase transitions and transport characteristics of 2D Te, hence great advancing the potential application of Te in electronic devices.

Growth and Electrical Characterization of Hybrid Core/Shell InAs/CdSe Nanowires.

Core-only InAs nanowires (NWs) remain of continuing interest for application in modern optical and electrical devices. In this paper, we utilize the II-VI semiconductor CdSe as a shell for III-V InAs NWs to protect the electron transport channel in the InAs core from surface effects. This unique material configuration offers both a small lattice mismatch between InAs and CdSe and a pronounced electronic confinement in the core with type-I band alignment at the interface between both materials. Under optimized growth conditions, a smooth interface between the core and shell is obtained. Atom probe tomography (APT) measurements confirm substantial diffusion of In into the shell, forming a remote n-type doping of CdSe. Moreover, field-effect transistors (FETs) are fabricated, and the electron transport characteristics in these devices is investigated. Finally, band structure simulations are performed and confirm the presence of an electron transport channel in the InAs core that, at higher gate voltages, extends into the CdSe shell region. These results provide a promising basis toward the application of hybrid III-V/II-VI core/shell nanowires in modern electronics.

Ternary composite WS2/GO/Au synthesized from laser ablation and hydrothermal method for photo- and electro-chemical degradation of methylene blue dye

Photocatalysts based on two-dimensional (2D) material with full optical absorption in the visible region have gained a lot of interest as a potential method for the degradation of pollutants, but there are very few single materials that can fulfill this requirement. In this research, we are suggesting the formation of WS2/GO/Au ternary composite prepared by WS2 and GO using nanosecond laser ablation followed by adding Au using the hydrothermal method. Ultraviolet-visible (UV–Vis), Raman, x-ray diffraction (XRD) spectroscopies, and field emission scanning electron microscopy (FE-SEM) were used to investigate the microstructure, morphology, and spectroscopic properties of the samples that had been produced. The UV–Vis spectra suggest the formation of a ternary composite, and FE-SEM shows morphology as Au nanoparticles with a size ranging from 20 to 30 nm are perfectly mixed with WS2 nanosheets, which can be seen on GO sheets. SEM-Energy dispersive x-ray spectroscopic (EDS) images indicate the availability of all elements in prepared samples and the formation of a ternary composite of WS2/GO/Au. XRD and Raman spectroscopy confirm the crystalline nature of AuNPs and WS2 and suggest the transformation of GO into rGO. The prepared pristine (WS2), binary (WS2/GO), and ternary composite show the capability for methylene blue degradation under UV-light irradiation as 41.85 %, 48.26 %, and 83.17 %, while electrocatalytic degradation gives 99 % for WS2/GO/Au respectively. The improved photocatalytic activity by the multicomponent has been demonstrated by nanostructured catalysts with specific morphology due to their exceptional electron transport characteristics. The WS2/GO/Au composite is anticipated to be an encouraging photoelectric material for experimental study in the research area of photocatalysis.

Axially Chiral Organic Semiconductors for Visible-Blind UV-Selective Circularly Polarized Light Detection.

Technologies that detect circularly polarized light (CPL), particularly in the UV region, have significant potential for various applications, including bioimaging and optical communication. However, a major challenge in directly sensing CPL arises from the conflicting requirements of planar structures for efficient charge transport and distorted structures for effective interaction with CPL. Here, a novel design of an axially chiral n-type organic semiconductor is presented to surmount the challenge, in which a binaphthyl group results in a high dissymmetry factor at the molecular level, while maintaining excellent electron-transporting characteristics through the naphthalene diimide group. Experimental and computational methods reveal different stacking behaviors in homochiral and heterochiral assemblies, yielding different structures: Nanowires and nanoparticles, respectively. Especially, the homochiral assemblies exhibit effective π-π stacking between naphthalene diimides despite axial chirality. Thus, phototransistors fabricated using enantiomers exhibit a high maximum electron mobility of 0.22 cm2 V-1 s-1 and a detectivity of 3.9 ×1012 Jones, alongside the CPL distinguishing ability with a dissymmetry factor of responsivity of 0.05. Furthermore, the material possesses a wide bandgap, contributing to its excellent visible-blind UV-selective detection. These findings highlight the new strategy for compact CPL detectors, coupled with the demonstration of less-explored n-type and UV region phototransistors.

Synthesis and characterization of Mo-doped PbS thin films for enhancing the photocatalytic hydrogen production

Photocatalytic hydrogen production has gained considerable attention as a sustainable method for renewable energy production. Lead sulfide (PbS) compound has significant reserves and a suitable bandgap for the production of hydrogen gas via the water photo-splitting process. However, the charge recombination effect of the charge carriers severely limits their potential use in solar water splitting. Herein, the photoelectrodes of PbS were fabricated through the chemical bath deposition method and then doped with different Mo concentrations to optimize the hydrogen photo-production activity. Both structural and performance characterizations of the photoelectrodes have been carried out using various characterization techniques. The photoelectrochemical (PEC) performance of molybdenum (Mo)-doped PbS photoelectrodes exhibits a significant increase in the photocurrent density with the optimum photocurrent density of 1.2 mA/cm2 obtained at 0.8 % Mo doping atomic ratio which was twelve times higher than that of a pure PbS photoelectrode. The doping of Mo induces the electron-hole separation yield which results in improved electron transport characteristics. The Mo doping was as act as a donor site that increased the PbS film conductivity. The newly optimized Mo–PbS was used as a promising photoelectrode supported on commercial glass using the optimum Mo-doped PbS photoelectrode, the photoelectrochemical (PEC) hydrogen production rate was reached 122 μmol/h cm2 during the solar water splitting process and the conversion efficiency of the incident photon-to-current (IPCE) value was 7.0 % at 390 nm monochromatic exposure. Moreover, the stability of the optimum electrode was evaluated as a function of the number of runs and exposure time in addition to the electrochemical impedance study.

Electronic transport characteristics and nanodevice designs for β-HfNCl monolayer

The mechanical properties, electronic structure, electric transport and optoelectronic properties of a recently predicted wide bandgap semiconductor β-HfNCl monolayer are systematically studied by means of first-principles calculations. β-HfNCl monolayer is isotropic in mechanical properties, whose calculated Young’s modulus, shear modulus, and layer modulus of β-HfNCl monolayer are 128.9–129.2, 44.28, and 119.46 N m−1, respectively. An appropriate tensile strain (i.e., beyond 3 %) can induce a transition from indirect bandgap to direct bandgap. In addition, we construct several conceptual nanodevice structures based on β-HfNCl monolayer, such as pn-junction diodes, pin-junction field-effect transistors (FETs) and phototransistors. The electronic transport results reveal that the pn-junction diodes have obvious rectification effect and strong electric anisotropy. Their rectification ratios and electric anisotropy ratio (η) can reach up to 106 and 3.69, respectively. The FETs have an obvious field-effect behavior with a slightly lower rectification ratio (105). Moreover, we investigate the photoelectric response of the phototransistors of β-HfNCl monolayer under the illumination of light. They have a strong response to the light whose energy is larger than the violet light, indicating that the β-HfNCl monolayer can be a platform to detect the ultraviolet light. These findings provide crucial insights into the potential applications of β-HfNCl monolayer in electronic and optoelectronic devices.

Temperature dependent electron transport and interface state studies on Ni/n-Si/Al/Ag lateral Schottky junction

We investigate in this work,the electron transport characteristics across Ni/n-Si Schottky junctions from temperature dependent current–voltage (I-V-T) and capacitance–voltage (C-V-T) studies. Barrier height obtained from I–V measurements exhibited upsurge with increasing temperature, whereas, the ideality factor decreases with increasing temperature within the range of 300K–400K. To analyze electron transport mechanism, possibilities of Thermionic Field Emission and Generation-Recombination have been investigated over the temperature range, and, it has been observed that due to less characteristic energy at discussed temperature range; these effects have a minor contribution to electron transport. To account for the temperature-dependent properties and lateral barrier inhomogeneity, a double Gaussian spatial distribution of the potential barrier has been observed from conventional and modified Richardson plots. The density of Interface states at different energy levels from the conduction band has also been studied.

Electron transport characteristics in water under electrostrictive effect

The transport characteristics of electrons are crucial for the generation and development of pulse discharge in water. In this work, we develop a physical model of electron transport that consides elastic and inelastic collision cross sections. The purpose of this study is to investigate frequency variations of elastic collisions, ionization and excitation collisions with different initial electron energy values, and to explore the characteristic of electron energy loss in water. The Monte Carlo method is employed to track structure characteristics of electron transmission and scattering under varying energy values. The results show that the electrons of lower energy (~20 eV) are significantly impacted by the water molecule scattering, hence their transmission capacities are weakened. When the incident energy of electron reaches 100 eV, the scattering deviation distance is roughly equivalent to the transmission depth, about 6–8 nm, and the maximum deviation angle <i>θ</i><sub>shift</sub> ~ 60°. When the electron incident energy is in a range of 10–1000 eV, the number of elastic collisions is much greater than the number of excitation and ionization collisions, and the number of ionization collisions and excitation collisions increases significantly with the increase of electron energy. The higher the electron incident energy, the greater the energy loss is. However, the energy loss decreases sharply with the extension of penetration distance. For the ionization collision, the average ionization energy loss, <i>W</i>, decreases rapidly with the increase of electron energy, and ultimately maintains at a level of 20–30 eV, which is consistent with the experimental results reported.