Field-effect Charge Research Articles

Pyrazinoquinoxaline derivatives for flexible electronic devices: effect of the mechanical properties of the crystals on device durability.

Understanding the interplay between the molecular structure and material properties of emerging p-type organic semiconductors marks a significant stride in the advancement of molecular electronics. Among the array of promising materials, mechanically flexible single crystals of π-conjugated molecules stand out due to their potential for cutting-edge applications in organic electronics. Notably, derivatives of pyrazinoquinoxaline (PQ) are recognized as versatile building blocks for constructing π-conjugated systems, showcasing good semiconductor performance in organic field-effect transistors (OFETs). In this study, we present an exploration into the p-type charge transport and mechanical characteristics of two newly synthesized PQ derivatives: 5,10-diphenyl-2,3,7,8-tetra(thiophen-2-yl)pyrazino[2,3-g]quinoxaline (DPTTQ) and 2,3,5,7,8,10-hexa(thiophen-2-yl)pyrazino[2,3-g]quinoxaline (HTPQ). HTPQ crystals exhibit flexural behaviour under applied stress, effortlessly returning to their initial configuration upon relaxation. Conversely, two polymorphic forms of DPTTQ crystals display brittle fracture when subjected to a similar stress. Specifically, DPTTQ molecules adopt a β-sheet packing, while HTPQ presents a γ-packing with a corrugated arrangement. Field-effect charge transport measurements reveal p-type charge transport in both DPTTQ and HTPQ, with HTPQ showcasing hole mobility up to 0.01 cm2 V-1 s-1, while DPTTQ exhibits mobility that is at least one order of magnitude lower. This variance in the field effect mobility can be directly correlated to the difference in crystal packing, highlighting a clear structure-property correlation. Moreover, taking advantage of the flexural nature of the HTPQ crystals, we fabricated durable electronic devices, which retain their conductivity for over 60 cycles of strain, indicating the efficacy of our chemical design in demonstrating high-performance flexible devices. These findings underscore the promise of semiconducting organics with γ-packing for achieving both better mobility and elasticity for integration into organic electronic devices.

Physical Factors Governing the Shape of the Miram Curve Knee in Thermionic Emission

In a current density versus temperature (J-T) (Miram) curve in thermionic electron emission, experimental measurements demonstrate there is a smooth transition between the exponential region and the saturated emission regions, which is sometimes referred to as the "roll-off" or "Miram curve knee". The shape of the Miram curve knee is an important figure of merit for thermionic vacuum cathodes. Specifically, cathodes with a sharp Miram curve knee at low temperature with a flat saturated emission current are typically preferred. Our previous work on modeling nonuniform thermionic emission revealed that the space charge effect and patch field effect are key pieces of physics which impact the shape of the Miram curve knee. This work provides a more complete understanding of the physical factors connecting these physical effects and their relative impact on the shape of the knee, including the smoothness, the temperature, and the flatness of the saturated emission current density. For our analyses, we use a periodic, equal-width striped ("zebra crossing") work function distribution as a model system and illustrate how the space charge and patch field effects restrict the emission current density near the Miram curve knee. The results indicate there are three main physical parameters which significantly impact the shape of the Miram curve. Such physical knowledge directly connects the patch size, work function values, anode-cathode voltage, and anode-cathode gap distance to the shape of the Miram curve, providing new understanding and a guide to the design of thermionic cathodes used as electron sources in vacuum electronic devices (VEDs).

Interface based field effect configuration and charge conduction mechanisms for manganite thin film heterostructures

Control over the movements of free charge carriers across any manganite based interface can functionalize the device for spintronic applications.

Electromagnetic and Electrostatic Particle-in-Cell Simulations for Multipactor in Parallel-Plate Waveguide

This article introduced a multipactor threshold criterion based on collision and emission currents, and the simulation results were compared using a traditional method. The impact of macroparticle weight on multipactor saturation was studied using electromagnetic particle-in-cell (EM-PIC) simulations of CST Particle Studio. It was found that the simulation results converged when the macroparticle weight was less than 106. A model calculating accumulated charge on the dielectric surface was proposed and validated against theoretical calculations. The dynamic evolution of multipactor in dielectric-loaded parallel-plate waveguide was analyzed, and predictions were validated against results from the existing model. Finally, the effect of surface charge fields and space charge effect on the multipactor mechanism was studied. The results showed that the multipactor could be suppressed when the ratio of the number of accumulated electrons on the dielectric surface to the saturation electron population was greater than 3.96.

Beyond the two-dimensional field-effect charge transport paradigm in molecular thin film transistors

Beyond the two-dimensional field-effect charge transport paradigm in molecular thin film transistors

In situ triggering metallicity in 3D graphene via constructing wrinkle configuration

Freestanding 3D graphene with a controllable electronic state is quite desirable for high-power all-carbon electronics. Although field-effect doping and charge doping have been demonstrated to manipulate the electronic properties of graphene derivatives, using these strategies to achieve nanoscale control remains a challenge. Herein, we developed a strategy for in situ triggering metallicity in semiconductor 3D graphene films (GFs) by building 1D wrinkles. Moreover, the controllable engineering of wrinkles represents a feasible way to realize the manipulation of 1D metallic states with characteristic width ranging from nanoscale to mesoscale. The global metallicity is achieved in GFs by constructing wrinkle percolation networks. The idea of in situ triggering metallicity in semiconducting graphene demonstrates potential application in high-power nanoelectronics. A striking case is that in situ constructing 1D metallic wrinkle provides a promising candidate as the metallic wire interconnects in all-carbon electronics.

ADVANCED COMPUTING TOPOLOGICAL AND DYNAMICAL INVARIANTS OF RELATIVISTIC BACKWARD-WAVE TUBE TIME SERIES IN CHAOTIC AND HYPERCHAOTIC REGIMES

The advanced results of computing the dynamical and topological invariants (correlation dimensions values, embedding, Kaplan-York dimensions, Lyapunov’s exponents, Kolmogorov entropy etc) of the dynamics time series of the relativistic backward-wave tube with accounting for dissipation and space charge field and other effects are presented for chaotic and hyperchaotic regimes. It is solved a system of equations for unidimensional relativistic electron phase and field unidimensional complex amplitude. The data obtained make more exact earlier presented preliminary data for dynamical and topological invariants of the relativistic backward-wave tube dynamics in chaotic regimes and allow to describe a scenario of transition to chaos in temporal dynamics.

Multi-State Heterojunction Transistors Based on Field-Effect Tunneling-Transport Transitions.

A monolithic ternary logic transistor based on a vertically stacked double n-type semiconductor heterostructure is presented. Incorporation of the organic heterostructure into the conventional metal-oxide-semiconductor field-effect transistor (MOSFET) architecture induces the generation of stable multiple logic states in the device; these states can be further optimized to be equiprobable and distinctive, which are the most desirable and requisite properties for multivalued logic devices. A systematic investigation reveals that the electrical properties of the device are governed by not only the conventional field-effect charge transport but also the field-effect charge tunneling at the heterointerfaces, and thus, an intermediate state can be finely tuned by independently controlling the transition between the onsets of these two mechanisms. The achieved device performance agrees with the results of a numerical simulation based on a pseudo-metal-insulator-metal model; the obtained findings therefore provide rational criteria for material selection in a simple energetic perspective. The operation of various ternary logic circuits based on the optimized multistate heterojunction transistors, including the NMIN and NMAX gates, is also demonstrated.

Multifunctional full-visible-spectrum optoelectronics based on a van der Waals heterostructure

Multifunctional devices are expected to allow development of low-cost, highly integrated, and energy-efficient electronics for the internet of things (IoT) era. Here, we demonstrate an all-two-dimensional ReSe2/h-BN/graphene heterostructure (ReSe2 HS) consisting of a vertically coupled ReSe2 field-effect transistor and charge storage component, which possesses multifunctional characteristics for use in electronics and optoelectronics. As an electrically controlled non-volatile memory (NVM), the ReSe2 HS delivers high-performance multilevel data storage with a readout on/off current ratio exceeding 105 and excellent durability (>104 s) at an ultralow Vds of 50 mV, which benefits to the development of power saving devices. The ReSe2 HS design and high-photoresponsivity ReSe2 channel also achieve an energy efficient optical NVM with full-visible-spectrum distinction. Besides, the ReSe2 HS displays unique ambipolarity to operate as either an inverter or frequency doubler. We further propose a power-free ReSe2 HS optical memory matrix to simplify imaging systems. The ReSe2 HS shows promise for use in light-programmable information storage systems and neuromorphic computation with low power consumption.

ХАОТИЧНА ДИНАМІКА РЕЛЯТИВІСТСЬКОЇ ЛАМПИ ЗВЕРНЕНОЇ ХВИЛІ З УРАХУВАННЯМ ВПЛИВУ ПОЛЯ ПРОСТОРОВОГО ЗАРЯДУ ТА ДИСИПАЦІЇ: НОВІ ЕФЕКТИ

We have performed an advanced modelling nonlinear dynamics elements for relativistic backward-wave tube (RBWT) with accounting for dissipation and space charge field effects etc. The temporal dependences of the normalized field amplitude (power) in a wide range of variation of the controlling parameters (electric length of an interaction space N, bifurcation parameter L and relativistic factor g0) are computed. The dynamic and topological invariants of the RBWT dynamics in auto-modulation and chaotic regimes such as correlation dimensions values, embedding, Kaplan-York dimensions, Lyapunov’s exponents, Kolmogorov entropy etc are calculated. It has been discovered the "beak" effect on the plane of parameters: bifurcation Piers-like parameter L – relativistic factor g0.

Field-Effect Charge Transport in Doped Polymer Semiconductor-Insulator Alternating Bulk Junctions with Ultrathin Transport Layers.

Conjugated-polymer field-effect transistors are attractive for flexible electronics. However, relatively high chemical doping (oxidation) concentration of p-type polymer semiconductors is usually not compatible with good transistor performance, due to poor switching-off capability and short-channel performance. Here, we propose a combined simulation and experimental investigation on charge transport in a semiconductor-insulator alternating bulk junction composed of repeating semiconductor and insulator regions, which shows better transistor performance at higher doping levels, as compared with traditional planar transistors. Moreover, the doped semiconductor transport layers in the junction should be less than 2 nm thick to ensure sufficient pinch-off capability. Using some semiconductors including poly(3-hexylthiophene), we utilize a fast solvent evaporation approach to obtain semiconductor-insulator alternating bulk junctions with ultrathin (thickness < 2 nm) semiconductor crystallites and with vertical gradients of both morphology and electronic properties. Doping with a concentration of up to 1019 cm-3 simultaneously induces the improvement of field-effect mobility, on/off ratio, and subthreshold swing, which leads to long-term (>1 year) stability, without lowering the short-channel performance. Moreover, these heterojunctions are optically transparent, nearly colorless, and flexible, thus could be exploited for wide electronic and photonic applications.

Chalcogen Bridged Thieno- and Selenopheno[2,3-d:5,4-d′]bisthiazole and Their Diketopyrrolopyrrole Based Low-Bandgap Copolymers

We report the synthesis and characterization of four novel small bandgap copolymers incorporating the electron-deficient thieno[2,3-d:5,4-d′]bisthiazole and selenopheno[2,3-d:5,4-d′]bisthiazole building blocks with a series of electron-deficient diketopyrrolopyrole units. The four resultant copolymers were synthesized via palladium Stille cross-coupling reaction, and their optical, thermal stability, electrochemical, and field-effect charge transport properties were investigated. All copolymers showed low optical bandgaps (1.53–1.56 eV); in addition, X-ray diffraction on solution-cast films revealed that the selenium-containing copolymers exhibit higher crystallinity compared to their thiophene counterparts.

Meta-screening and permanence of polar distortion in metallized ferroelectrics

Ferroelectric materials are characterized by a spontaneous polar distortion. The behavior of such distortion in the presence of free charge is the key to the physics of metallized ferroelectrics in particular, and of structurally polar metals more generally. Using first-principles simulations, here we show that a polar distortion resists metallization and the attendant suppression of long-range dipolar interactions in the vast majority of a sample of 11 representative ferroelectrics. We identify a meta-screening effect, occurring in the doped compounds as a consequence of the charge rearrangements associated to electrostatic screening, as the main factor determining the survival of a noncentrosymmetric phase. Our findings advance greatly our understanding of the essentials of structurally polar metals, and offer guidelines on the behavior of ferroelectrics upon field-effect charge injection or proximity to conductive device elements.

Tuning polymorphism in 2,3-thienoimide capped oligothiophene based field-effect transistors by implementing vacuum and solution deposition methods

The impact of the processing method in controlling the polymorphism and field-effect charge mobility of 2,3-thienoimide-based oligothiophenes semiconductors was investigated.

Two color laser self focusing and terahertz generation in multi-ion species plasma

An analytical formalism of self focusing of two co-propagating laser beams, fundamental ω1 and close to second harmonic ω2≈2ω1, in a multi-ion species plasma and resonant terahertz radiation generation has been developed. The nonlinearity arises due to ponderomotive force on electrons by both the beams and subsequent ambipolar redistribution of the plasma. The ions of higher charged state are strongly depleted from the axial region due to space charge field effects and electron charge is largely compensated by the ions of lower charge. When the power of the strong beam equals the critical power for its self-guiding, the plasma provides an oscillatory waveguide for the weak beam; the weak beam shrinks and rebounds when its frequency is lower than that of the strong beam, and it swallows and rebounds when the frequency is higher. When both beams are strong the nonlinearities have cumulative effect on both the beams. The cross coupling of the beams gives rise to nonlinear current giving rise to terahertz radiation at ω=ω2−2ω1 frequency. An axial density ripple aids phase matching and gives rise to higher power conversion efficiency. Self focusing leads to enhancement in conversion efficiency.

Metallopolyyne polymers containing naphthalene diimide-oligothiophene moieties and their applications in organic field-effect transistors

Two novel platinum(II) donor-acceptor (D-A) naphthalene diimide (NDI)-based copolymers have been designed and synthesized. The effects of thiophene numbers on the thermal, optical, electronic and charge transport properties of the polymers have been investigated. These solution processable polymers exhibit p-channel field-effect charge transport characteristics, unlike other organic NDI-based polymeric analogues. All the results indicated that they have potential applications in high-performance organic field-effect transistors (OFETs).

Reversible Plastic Deformation of Polymer Blends as a Means to Achieve Stretchable Organic Transistors.

Intrinsically stretchable semiconductors will facilitate the realization of seamlessly integrated stretchable electronics. However, to date demonstrations of intrinsically stretchable semiconductors have been limited. In this study, a new approach to achieve intrinsically stretchable semiconductors is introduced by blending a rigid high-performance donor-acceptor polymer semiconductor poly[4(4,4dihexadecyl4Hcyclopenta [1,2b:5,4b' ] dithiopen2yl) alt [1,2,5] thiadiazolo [3,4c] pyridine] (PCDTPT) with a ductile polymer semiconductor poly(3hexylthiophene) (P3HT). Under large tensile strains of up to 75%, the polymers are shown to orient in the direction of strain, and when the strain is reduced, the polymers reversibly deform. During cyclic strain, the local packing order of the polymers is shown to be remarkably stable. The saturated field effect charge mobility is shown to be consistently above 0.04 cm2 V-1s-1 for up to 100 strain cycles with strain ranging from 10% to 75% when the film is printed onto a rigid test bed. At the 75% strain state, the charge mobility is consistently above 0.15 cm2 V-1s-1. Ultimately, the polymer blend process introduced here results in an excellent combination of device performance and stretchability providing an effective approach to achieve intrinsically stretchable semiconductors.

Image Charge and Electric Field Effects on Hydrogen-like Impurity-bound Polaron Energies and Oscillator Strengths in a Quantum Dot

By using Landau–Pekar variational method, the ground and the first excited state energies and the transition frequencies between the ground and the first excited states of a hydrogen-like impurity-bound polaron in a spherical quantum dot (QD) have been studied by taking into account the image charge effect (ICE). We employ the dielectric continuum model to describe the phonon confinement effects. The oscillator strengths (OSs) of transitions from the 1s-like state to excited states of 2s, 2px, and 2pz symmetries are calculated as functions of the applied electric field and strength of the confinement potential. We have shown that with and without image charge effect, the increase of the strength of the parabolic confinement potential leads to the increase of the oscillator strengths of 1s − 2px and 1s − 2pz transitions. This indicates that the energy differences between 1s- and 2px- as well as 1s- and 2pz-like states have a dominant role determining the oscillator strength. Although there is almost no difference in the oscillator strengths for transitions 1s − 2px and 1s −2pz when the image charge effect is not taken into account, it becomes significant with the image charge effect.

Nanoscale Charge Percolation Analysis in Polymer-Sorted (7,5) Single-Walled Carbon Nanotube Networks.

The current percolation in polymer-sorted semiconducting (7,5) single-walled carbon nanotube (SWNT) networks, processed from solution, is investigated using a combination of electrical field-effect measurements, atomic force microscopy (AFM), and conductive AFM (C-AFM) techniques. From AFM measurements, the nanotube length in the as-processed (7,5) SWNTs network is found to range from ≈100 to ≈1500 nm, with a SWNT surface density well above the percolation threshold and a maximum surface coverage ≈58%. Analysis of the field-effect charge transport measurements in the SWNT network using a 2D homogeneous random-network stick-percolation model yields an exponent coefficient for the transistors OFF currents of 16.3. This value is indicative of an almost ideal random network containing only a small concentration of metallic SWNTs. Complementary C-AFM measurements on the other hand enable visualization of current percolation pathways in the xy plane and reveal the isotropic nature of the as-spun (7,5) SWNT networks. This work demonstrates the tremendous potential of combining advanced scanning probe techniques with field-effect charge transport measurements for quantification of key network parameters including current percolation, metallic nanotubes content, surface coverage, and degree of SWNT alignment. Most importantly, the proposed approach is general and applicable to other nanoscale networks, including metallic nanowires as well as hybrid nanocomposites.

Negative DC corona inception in coaxial cylinders under variable atmospheric conditions: A comparison with positive corona

Characteristics of negative DC corona threshold inception in the coaxial cylindrical electrode arrangement are investigated based on experimental data and computations on avalanche growth considering a field and atmospheric conditions dependent photoelectron emission coefficient. A transition region between glow and streamer regimes of inception of the self-sustained corona discharge could be identified on the basis of space charge field effects on avalanche growth. Approximate expressions are introduced for satisfactorily estimating the negative corona inception field strength as interactively affected by conductor radius and atmospheric conditions. Polarity effects on corona inception characteristics are elucidated. The establishment of the glow corona generally occurs up to larger conductors for negative than positive corona; the opposite may also apply depending on atmospheric conditions. The inception field strength as well as its dependence on atmospheric conditions differs only slightly between negative and positive streamer corona; a critical avalanche number per unit length of ∼108 cm−1 is required for both negative and positive streamer formation.