К вопросу о влиянии неоднородного диэлектрического покрытия на характеристики металлической поверхности

Within the framework of the quantum-statistical functional and the Ritz method, the the problem of finding the surface energy per unit area and work function electrons of a metal flat surface with a inhomogeneous dielectric coating, taken into account in the approximation of a continuous medium. For a uniform coating, the calculated values are insensitive to the selection one-parameter functions for an electronic profile, but sensitive to the gradient series of kinetic energy non-interacting electrons. Calculations are performed for Al, Na and the comparison with the calculations by the Kohn-Shem method is made. Analytically the connection between the theory of the Ritz method for inhomogeneous coatings and calculations by the Kohn-Shem method work function of electrons for metal-dielectric nanosandwiches. As it turned out, the influence inhomogeneous coating on the characteristics of the metal surface can be scaled down to a uniform coverage case. The possibility of using the obtained results in various experimental situations are discussed.

Characterization of silicon tunnel field effect transistor based on charge plasma

The aim of the proposed paper is an analytical model and realization of the characteristics for tunnel field-effect transistor (TFET) based on charge plasma (CP). One of the most applications of the TFET device which operates based on CP technique is the biosensor. CP-TFET is to be used as an effective device to detect the uncharged molecules of the bio-sample solution. Charge plasma is one of some techniques that recently invited to induce charge carriers inside the devices. In this proposed paper we use a high work function in the source (ϕ=5.93 eV) to induce hole charges and we use a lower work function in drain (ϕ=3.90 eV) to induce electron charges. Many electrical characterizations in this paper are considered to study the performance of this device like a current drain (ID) versus voltage gate (Vgs), ION/IOFF ratio, threshold voltage (VT) transconductance (gm), and sub-threshold swing (SS). The signification of this paper comes into view enhancement the performance of the device. Results show that high dielectric (K=12), oxide thickness (Tox=1 nm), channel length (Lch=42 nm), and higher work function for the gate (ϕ=4.5 eV) tend to best charge plasma silicon tunnel field-effect transistor characterization.

STUDYING MULTILAYERED GRAPHENES BY ELECTROPHYSICAL METHODS

The paper studies multilayer graphenes in the form of free-standing films. The authors provide data about the morphology and electrical properties of films treated with plasma of various chemical composition. It is shown that it is possible to control the electrical properties of the surface and electron work function without significantly affecting its morphology. The obtained samples, combining mechanical flexibility with unreactiveness and high electrical conductivity, are promising for application in flexible charge storage devices.

INFLUENCE OF POLYMORPHIC TRANSFORMATIONS ON ANISOTROPY OF THE SURFACE ENERGY AND THE WORK FUNCTION OF THE ELECTRON OF LITHIUM

На базе электронно-статистического метода показана связь и проведена оценка поверхностной энергии и работы выхода электрона граней кристаллов лития с учетом дисперсионного, поляризационного и осцилляционного взаимодействия атомов поверхностного слоя. Считалось, что кристаллическая решетка не имеет дефектов. Модифицированы выражения поправок и аналитического соотношения, связывающего работу выхода электрона и поверхностную энергию с учетом типа кристаллической решетки и ориентации граней. Рассчитана работа выхода электрона и поверхностная энергия гладких граней при предельных температурах существования полиморфных фаз лития. Установлено влияние полиморфных превращений и температуры на анизотропию. Температурный коэффициент работы выхода электрона бездефектного кристалла положителен и составляет порядка 0,1-1 мэВ. Результаты расчетов хорошо согласуются с экспериментальными данными для поликристаллов. On the basis of the electronic-statistical method, a relationship is obtained and the surface energy and the work function of the electron of the faces of lithium crystals are estimated, taking into account the dispersion, polarization, and oscillatory interactions of the atoms of the surface layer. It was assumed that the crystal lattice has no defects. The expressions for the corrections and an analytical relationship between the work function of the electron and the surface energy are modified taking into account the type of the crystal lattice and the orientation of the faces. The work function of the electron and the surface energy of smooth faces are calculated at the limiting temperatures of the existence of polymorphic lithium phases. The influence of polymorphic transformations and temperature on the anisotropy is established. The temperature coefficient of the work function of an electron in a defect-free crystal is positive and amounts to about 0,1-1 meV. The calculation results are in good agreement with the experimental data for polycrystals.

Exploration on performance of two-dimensional GaN photocathodes with uniform-doping and variable-doping structure

In this paper, the properties of two-dimensional (2D) gallium nitride (GaN) photocathodes with a uniform doping and variable doping structure are studied by using Mg as a doping element based on first principles. The stability, bandstructure, work function, density of state and optical properties of the GaN bilayer and GaN trilayer in two-doped ways are investigated. The results show that formation energy of variable doping structure is less than that of the uniform doping structure, which means that the variable doping structure is more stable. At the same time, the formation energy increases with increase of layers. The pristine GaN bilayer has an indirect bandgap, while the doped GaN bilayer transforms into a direct bandgap. The impurity levels appear in a forbidden band of doped GaN trilayers, which is favorable for electron transition. The results of work function reveal that variable doping structure has lower vacuum barriers and more electron escape numbers, which proves that it can improve the quantum efficiency of photocathodes. Finally, the analysis of optical properties shows that the uniform doping structure has better optical properties than that of the variable doping structure.

OH binding energy as a universal descriptor of the potential of zero charge on transition metal surfaces

The potential of zero charge (U_PZC) is an important quantity of metal-water interfaces that are central in many electrochemical applications. In this work, we use ab initio molecular dynamics (AIMD) simulations to study a large number of (111), (100), (0001) and (211) and overlayers of transition metal-water interfaces in order to identify simple descriptors to predict their U_PZC. We find a good correlation between water coverage and the work function reduction Δφ which is defined by the difference of the work function in vacuum and in the presence of water. Furthermore, we determine the vacuum binding energies of H2O and *OH species as good descriptors for the prediction of water coverage and thereby of ∆φ. Our insights unify different facet geometries and mixed metal surfaces and thereby generalize recent observations. We further present a scheme to predict U_PZC based only on the *OH binding and the vacuum work function estimated from static DFT calculations. This formalism is applicable to all investigated metals and mixed metal surfaces including terrace and step geometries and does not require expensive AIMD simulations. To evaluate physical influences to U_PZC, we decompose ∆φ into its orientational (∆φ_orient) and electronic(∆φ_el) components. We find ∆φ_orient to be a facet dependent property and a major contributor to ∆φ on (211) surfaces, while ∆φ_sub strongly depends on the metal identity.