Symmetric Electron Research Articles

Ambipolar organic thin film transistors prepared with a one step solution technique

One of the most challenging problems limiting the development of the technology of organic electronics is a lack of simple, solution based, techniques for producing organic thin film transistors (OTFTs) with ambipolar characteristics. In this work, a simple method of manufacturing ambipolar OTFTs, based on a zone-casting technique, is presented. This technique was used to prepare thin and highly oriented films from a combination of the p-type organic semiconductor, TIPS-Pentacene, with one of the two naphthalene bisimide derivatives, both exhibiting electron conductivity. The OTFTs produced with such active layers display ambipolar properties with symmetric characteristics and electron and hole mobility in the best case amounting to: μe=1.5×10−2 and μh=1.1×10−2cm2V−1s−1, respectively.

A cylindrically symmetric "micro-Mott" electron polarimeter.

A small, novel, cylindrically symmetric Mott electron polarimeter is described. The effective Sherman function, Seff, or analyzing power, for 20 kV Au target bias with a 1.3 keV energy loss window is 0.16 ± 0.01, where uncertainty in the measurement is due primarily to uncertainty in the incident electron polarization. For an energy loss window of 0.5 keV, Seff reaches its maximum value of 0.24 ± 0.02. The device's maximum efficiency, I/Io, defined as the detected count rate divided by the incident particle rate, is 3.7 ± 0.2 × 10(-4) at 20 keV. The figure-of-merit of the device, η, is defined as Seff (2)IIo and equals 9.0 ± 1.6 × 10(-6). Potential sources of false asymmetries due to detector electronic asymmetry and beam misalignment have been investigated. The new polarimeter's performance is compared to published results for similar compact retarding-field Mott polarimeters, and it is concluded that this device has a relatively large Seff and low efficiency. SIMION(®) electron trajectory simulations and Sherman function calculations are presented to explain the differences in performance between this device and previous designs. This design has an Seff that is insensitive to spatial beam fluctuations and, for an energy loss window >0.5 keV, negligible background due to spurious ion and X-ray production at the target.

Generation and Formation of Axially Symmetrical Tubular Electron Beam in a Cold Metal Secondary-Emission Cathode Magnetron Gun—Part I: Experiment

Generation and Formation of Axially Symmetrical Tubular Electron Beam in a Cold Metal Secondary-Emission Cathode Magnetron Gun—Part I: Experiment

Generation and Formation of Axially Symmetrical Tubular Electron Beam in a Cold Metal Secondary-Emission Cathode Magnetron Gun—Part II: Computer Modeling

This paper presents the computer modeling results, explaining the generation mechanism of periodical electron bunches in a cold cathode metal secondary-emission magnetron gun and describes a scenario of the secondary-emission electron multiplication at the front and droop portions of the anode voltage pulse. An analytical model for analyzing the kinematical characteristics of the formed electron cloud and a self-consistent numerical mathematical model on the basis of the particle-in-cell method for studying the collective electron processes have been developed. The general stages of forming the electron beam in the cold cathode secondary-emission magnetron gun are shown. It is shown that an efficiency of secondary-electron multiplication depends on the shape and parameters of the high-voltage pulse. The obtained results of the computer modeling are in good agreement with the experimental data.

Collective scattering of an incident monochromatic circularly polarized wave in an unmagnetized non-equilibrium plasma

Collective scattering of an incident monochromatic circularly polarized electromagnetic wave in an unmagnetized non-equilibrium plasma is investigated. The wave equation of the scattered waves are numerically solved by giving wave spectra of the incident electromagnetic wave and a variety of longitudinal fluctuations of a plasma. In addition to the well known symmetric ion and electron features of frequency spectrum in an equilibrium plasma, some asymmetries are found in a frequency spectrum when anisotropic longitudinal wave propagation or the effect of the presence of a beam mode are taken into account.

电子、质子和氢原子—微观粒子内部结构解析

本文以双波包双原点粒子模型[1]为基础，结合四维x空间和四维E空间概念对电子、质子和氢原子内部结构进行了讨论。描绘出了电子、质子的形象和内部结构特点，从而使微观粒子波函数、自旋、粒子振荡态、不确定性原理等现代物理概念展现了易于理解的图景。通过比较电子在四维x空间和质子在四维E空间的运动，提出了与电子单极子大对称的质子单极子就是磁单极子，进而对氢原子内电磁相互作用、强相互作用和物质原子的结构因果有了一种新的解读。这种从新的角度对基本粒子的审视，不同于数学推演对微观物质的抽象描述，但它更直观简洁且优美清晰。 In this paper, based on the double wave packet double origin particle model [1], the internal structure of electron, proton and hydrogen atom is discussed by combining the four-dimensional space and four-dimensional space concept. This paper describes the image and the internal structure of the electron and proton, so the concepts of the modern physics of the micro-particles wave function, spin physics, particle oscillation state, the uncertainty principle, etc., show the easily understood pictures. By comparing the movement of electron in four-dimensional x space and proton in four dimensional E space, it is proposed that the proton monopole with large symmetrical electron monopole is magnetic monopole. Then there is a new interpretation of the electro- magnetic interaction, strong interaction and the structure of the material atoms in the hydrogen atom. This review of elementary particles from a new angle, is different from the mathematical derivation of micro material abstract description, but it’s more intuitive, beautiful, concise, and clear.

Kinetic approach to deriving the envelope equation for a relativistic electron beam propagating in the ion focusing regime in the presence of an ion channel with an arbitrary radial profile

Kinetic methods are applied to derive the transport equations, the virial equations, the dynamic-equilibrium equation, and the envelope equation for an axially symmetric paraxial relativistic electron beam propagating in the ion focusing regime in the presence of an ion plasma channel with a radial density profile differing significantly from the corresponding profile of the beam current density. The resultant equations contain the terms that take into account this difference. In addition, the equations obtained account for the case when the electron component of the background plasma is only partially removed from the beam region.

Impact of Asymmetric Configurations on the Heterogate Germanium Electron–Hole Bilayer Tunnel FET Including Quantum Confinement

We investigate the effect of asymmetric configurations on the heterogate germanium electron–hole bilayer tunnel FET (TFET) and assess the improvement that they provide in terms of boosting the typically very low ON-current levels of TFET devices in the presence of field-induced quantum confinement. We show that when a very strong inversion for holes is induced at the bottom of the channel, the formation of the inversion layer for electrons is shifted to higher gate voltages, which in turn enhances the electrostatic control of the band bending at the top of the channel. As a result, the pinning of the quantized energy subbands is prevented for a wider range of gate voltages, and this allows vertical band-to-band tunneling distances to be further reduced compared with the conventional symmetric electron–hole bilayer configurations.

High-performance n-type black phosphorus transistors with type control via thickness and contact-metal engineering.

Recent work has demonstrated excellent p-type field-effect switching in exfoliated black phosphorus, but type control has remained elusive. Here, we report unipolar n-type black phosphorus transistors with switching polarity control via contact-metal engineering and flake thickness, combined with oxygen and moisture-free fabrication. With aluminium contacts to black phosphorus, a unipolar to ambipolar transition occurs as flake thickness increases from 3 to 13 nm. The 13-nm aluminium-contacted flake displays graphene-like symmetric hole and electron mobilities up to 950 cm2 V−1 s−1 at 300 K, while a 3 nm flake displays unipolar n-type switching with on/off ratios greater than 105 (107) and electron mobility of 275 (630) cm2 V−1 s−1 at 300 K (80 K). For palladium contacts, p-type behaviour dominates in thick flakes, while 2.5–7 nm flakes have symmetric ambipolar transport. These results demonstrate a leap in n-type performance and exemplify the logical switching capabilities of black phosphorus.

Transport properties of pristine few-layer black phosphorus by van der Waals passivation in an inert atmosphere.

Ultrathin black phosphorus is a two-dimensional semiconductor with a sizeable band gap. Its excellent electronic properties make it attractive for applications in transistor, logic and optoelectronic devices. However, it is also the first widely investigated two-dimensional material to undergo degradation upon exposure to ambient air. Therefore a passivation method is required to study the intrinsic material properties, understand how oxidation affects the physical properties and enable applications of phosphorene. Here we demonstrate that atomically thin graphene and hexagonal boron nitride can be used for passivation of ultrathin black phosphorus. We report that few-layer pristine black phosphorus channels passivated in an inert gas environment, without any prior exposure to air, exhibit greatly improved n-type charge transport resulting in symmetric electron and hole transconductance characteristics.

How a Redox‐Innocent Metal Promotes the Formal Reductive Elimination of Biphenyl Using Redox‐Active Ligands

One of the most compelling strategies for utilizing redox-active ligands is to perform redox events at the ligands to avoid accessing prohibitively high energy oxidation states at the metal center. This has been demonstrated experimentally in many systems, yet there is little understanding of the fundamental electronic structures involved with these transformations or how to control them. Here, the reductive elimination of biphenyl from [M(isq)2Ph2] (M = Ti, Zr, and Hf and isq = 2,4-di-tert-butyl-6-tert-butyliminosemiquinone) was studied computationally. It was found that the metal remains in the +IV oxidation state and all redox chemistry was mediated by the redox-active ligands. Two types of electron-transfer mechanisms were identified, an asymmetric unpaired electron transfer (UET) and a symmetric pairwise electron transfer (PET), the former always being lower in energy. The energetic differences between these two mechanisms were explained through simple molecular orbital theory arguments. Despite the metal's redox-inactivity, it still has a marked influence on the calculated energetics of the reaction, with the Ti systems being much more reactive than the Zr/Hf systems. This primarily originates from the shorter Ti-Ph bond, which leads to a stronger filled-filled interaction between these ligands at the reactant state. This greater reactant destabilization leads to the lower activation energies.

Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams

The high-current fast electron beams generated in high-intensity laser-solid interactions require the onset of a balancing return current in order to propagate in the target material. Such a system of counter-streaming electron currents is unstable to a variety of instabilities such as the current-filamentation instability and the two-stream instability. An experimental study aimed at investigating the role of instabilities in a system of symmetrical counter-propagating fast electron beams is presented here for the first time. The fast electron beams are generated by double-sided laser-irradiation of a layered target foil at laser intensities above 1019 W/cm2. High-resolution X-ray spectroscopy of the emission from the central Ti layer shows that locally enhanced energy deposition is indeed achieved in the case of counter-propagating fast electron beams.

Evidence that histidine forms a coordination bond to the A0A and A0B chlorophylls and a second H-bond to the A1A and A1B phylloquinones in M688HPsaA and M668HPsaB variants of Synechocystis sp. PCC 6803

The axial ligands of the acceptor chlorophylls, A0A and A0B, in Photosystem I are the Met sulfur atoms of M688PsaA and M668PsaB. To determine the role of the Met, His variants were generated in Synechocystis sp. PCC 6803. Molecular dynamics simulations on M688HPsaA show that there exist low energy conformations with the His coordinated to A0A and possibly H-bonded to A1A. Transient EPR studies on M688HPsaA indicate a more symmetrical electron spin distribution in the A1A phyllosemiquinone ring consistent with the presence of an H-bond to the C1 carbonyl. Ultrafast optical studies on the variants show that the 150fs charge separation between P700 and A0 remains unaffected. Studies on the ns timescale show that 57% of the electrons are transferred from A0A− to A1A in M688HPsaA and 48% from A0B− to A1B in M668HPsaB; the remainder recombine with P700+ with 1/e times of 25ns and 37ns, respectively. Those electrons that reach A1A and A1B in the branch carrying the mutation are not transferred to FX, but recombine with P700+ with 1/e times of ~15μs and ~5μs, respectively. Hence, the His is coordinated to A0 in all populations, but in a second population, the His may be additionally H-bonded to A1. Electron transfer from A0 to A1 occurs only in the latter, but the higher redox potentials of A0 and A1 as a result of the stronger coordination bond to A0 and the proposed second H-bond to A1 preclude electron transfer to the Fe/S clusters.

Reduced forms of the Wigner distribution function for the numerical analysis of rotationally symmetric synchrotron radiation

In an effort to provide a computationally convenient approach to the characterization of partially coherent synchrotron radiation in phase space, a thorough discussion of the minimum dimensionality of the Wigner distribution function for rotationally symmetric sources of arbitrary degrees of coherence is presented. It is found that perfectly coherent, perfectly incoherent and partially coherent sources may all be characterized by a three-dimensional reduced Wigner distribution function, and some special cases are discussed in which a two-dimensional reduced Wigner distribution function suffices. An application of the dimension-reducing formalism to the case of partially coherent radiation from a planar undulator and a circularly symmetric electron beam as can be found in linear accelerators is demonstrated. The photon distribution is convolved over a realistic electron bunch, and how the beta function, emittance and energy spread of the bunch affect the total degree of coherence of the radiation is inspected. Finally the cross spectral density is diagonalized and the eigenmodes of the partially coherent radiation are recovered.

Bulk response and grain boundary microelectrical activity of high TC BaTiO3–(Bi1/2K1/2)TiO3-based positive temperature coefficient of resistance ceramics

Abstract

Calculation of force exerted by the Ohmic plasma channel on a relativistic electron beam propagating in a dense gas-plasma medium

The problem on the interaction of an Ohmic plasma channel displaced in the transverse direction with a paraxial azimuthally symmetric relativistic electron beam propagating in a dense gas-plasma medium is considered. The formula for determining the force of the beam-plasma interaction is derived using the “hard” model of the beam and the channel in the case of an arbitrary displacement of the symmetry axis of the plasma channel relative to the corresponding axis of the beam. The forces are calculated in the Bennett and Gauss approximations for the radial profiles of the beam and the channel.

Plenary Special Lectures

The correction of the aberrations of electron lenses is the long story of many seemingly fruitless efforts to improve the resolution of electron microscopes by compensating for aberrations of round electron lenses over a period of 50 years. The problem started in 1936 when Scherzer demonstrated that the chromatic and spherical aberrations of rotationally symmetric electron lenses are unavoidable. Moreover, the coefficients of these aberrations cannot be made sufficiently small. As a result, the resolution limit of standard electron microscopes equals about one hundred times the wavelength of the electrons, whereas modern light microscopes have reached a resolution limit somewhat smaller than the wavelength. In 1947, Scherzer found an ingenious way for enabling aberration correction. He demonstrated in a famous article that it is in theory possible to eliminate chromatic and spherical aberrations by lifting any one of the constraints of his theorem, either by abandoning rotational symmetry or by introducing time-varying fields, or space charges. Moreover, he proposed a multipole corrector compensating for the spherical aberration of the objective lens.

Structural and mechanical properties of corundum and cubic (AlxCr1−x)2+yO3−y coatings grown by reactive cathodic arc evaporation in as-deposited and annealed states

Coatings of (AlxCr1−x)2+yO3−y with 0.51⩽x⩽0.84 and 0.1⩽y⩽0.5 were deposited on hard cemented carbide substrates in an industrial cathodic arc evaporation system from powder-metallurgy-prepared Cr/Al targets in pure O2 and O2+N2 atmospheres. The substrate temperature and bias in all the deposition runs were 575°C and −120V, respectively. The composition of the coatings measured by energy dispersive X-ray spectroscopy and elastic recoil detection analysis differed from that of the facing targets by up to 11%. Microstructure analyses performed by symmetrical X-ray diffraction and transmission electron microscopy showed that corundum, cubic or mixed-phase coatings formed, depending on the Cr/Al ratio of the coatings and O2 flow per active target during deposition. The corundum phase was promoted by high Cr content and high O2 flow per target, while the cubic phase was observed mostly for high Al content and low O2 flow per active target. In-situ annealing of the cubic coatings resulted in phase transformation from cubic to corundum, completed in the temperature range of 900–1100°C, while corundum coatings retained their structure in the same range of annealing temperatures. Nanoindentation hardness of the coatings with Cr/Al ratio <0.4 was 26–28GPa, regardless of the structure. Increasing the Cr content of the coatings resulted in increased hardness of 28–30GPa for corundum coatings. Wear resistance testing in a turning operation showed that coatings of Al–Cr–O have improved resistance to crater wear at the cost of flank wear compared with TiAlN coatings.

Technique of symmetric type quasi-linear electron pulse duration modulation

A novel technique of symmetric type quasi-linear electron pulse duration modulation is proposed. The salient feature from the conventional photoelectron gun is the introduction of the alternating electric field resonator. The electric field that results is synchronously controlled to generate the desired quasi-linear differential energy modulation on the electron pulse passing through. The effect resulted directly is that the leading electrons undergo negative energy modulation and decelerate, while the rear ones positive energy modulation and accelerate, which eventually leads to electron-pulse-duration modulation. The technical details are demonstrated, together with an illustration example.

Optical and electrical study of cap layer effect in QHE devices with double-2DEG

ABSTRACTIn this work we report on the characteristics of GaAs/AlGaAs heterostructures with a symmetric double two-dimensional electron gas (D-2DEG). Optical characterization was made by room temperature photoreflectance (PR) spectroscopy as well as electrical properties were determinated using the quantum Hall effect measurements at 2K. In order to study the surface effects on the conduction band profile, three samples with different GaAs cap layer thickness (25, 60 and 80 nm) were grown by the molecular beam epitaxy. Photoreflectance spectra at room temperature show the wide-period Franz-Keldysh oscillations between 1.42 and 1.70 eV originated by the surface electric field. The analysis of these oscillations shows that the surface electric field varies from 503 to 120 kV/cm whereas the thickness of the cap layer increases that was produced by the reduction of the depletion zone near the surface. Using QHE measurements we found that electron density increases if the surface electric field decreases.