Theoretical models of Schottky-barrier height formation are reviewed. A particular emphasis is placed on the examination of how these models agree with general physical principles. New concepts on the relationship between interface dipole and chemical bond formation are analyzed, and shown to offer a coherent explanation of a wide range of experimental data.

Recent advances in Schottky barrier concepts

Premises of creation of Internet portal designed to provide access to participants of educational and scientific process for the joint creation, consolidation, concentration and rapid spreading of educational and scientific information resources in its own depository are considered. CMS-based portal content management systems’ potentiality is investigated. Architecture for Internet portal of MES of Ukraine’s information resources is offered.

Створення порталу інформаційно-довідкових ресурсів міністерства освіти і науки україни

The formation of the Schottky barrier height (SBH) is a complex problem because of the dependence of the SBH on the atomic structure of the metal-semiconductor (MS) interface. Existing models of the SBH are too simple to realistically treat the chemistry exhibited at MS interfaces. This article points out, through examination of available experimental and theoretical results, that a comprehensive, quantum-mechanics-based picture of SBH formation can already be constructed, although no simple equations can emerge, which are applicable for all MS interfaces. Important concepts and principles in physics and chemistry that govern the formation of the SBH are described in detail, from which the experimental and theoretical results for individual MS interfaces can be understood. Strategies used and results obtained from recent investigations to systematically modify the SBH are also examined from the perspective of the physical and chemical principles of the MS interface.

The physics and chemistry of the Schottky barrier height

Experimental studies of the superconductive properties of fullerides are briefly reviewed. Theoretical calculations of the electron-phonon coupling, in particular for the intramolecular phonons, are discussed extensively. The calculations are compared with coupling constants deduced from a number of different experimental techniques. It is discussed why ${\mathrm{A}}_{3}$${\mathrm{C}}_{60}$ are not Mott-Hubbard insulators, in spite of the large Coulomb interaction. Estimates of the Coulomb pseudopotential ${\mathrm{\ensuremath{\mu}}}^{\mathrm{*}}$, describing the effect of the Coulomb repulsion on the superconductivity, as well as possible electronic mechanisms for the superconductivity, are reviewed. The calculation of various properties within the Migdal-Eliashberg theory and attempts to go beyond this theory are described.

/pdf/superconductivity-in-fullerides-1l7z4d92t8.pdf

Superconductivity in fullerides

The outstanding properties of SiO2, which include high resistivity, excellent dielectric strength, a large band gap, a high melting point, and a native, low defect density interface with Si, are in large part responsible for enabling the microelectronics revolution. The Si/SiO2 interface, which forms the heart of the modern metal–oxide–semiconductor field effect transistor, the building block of the integrated circuit, is arguably the worlds most economically and technologically important materials interface. This article summarizes recent progress and current scientific understanding of ultrathin (<4 nm) SiO2 and Si–O–N (silicon oxynitride) gate dielectrics on Si based devices. We will emphasize an understanding of the limits of these gate dielectrics, i.e., how their continuously shrinking thickness, dictated by integrated circuit device scaling, results in physical and electrical property changes that impose limits on their usefulness. We observe, in conclusion, that although Si microelectronic devices...

Ultrathin (<4 nm) SiO2 and Si-O-N gate dielectric layers for silicon microelectronics: Understanding the processing, structure, and physical and electrical limits

THE discovery1 of superconductivity, with a transition temperature Tc of 18 K, in potassium-doped C60 was followed by the synthesis of other superconducting M3C60 phases: Rb3C60 (Tc = 28K and 30 K; refs 2, 3), CsRb2C60 (Tc = 31K; ref. 4) and Cs2RbC60 (Tc = 33 K; ref. 4). A monotonic relationship is observed5 between Tc and lattice constant a0 for these face-centred cubic M3C0 compounds, all of which have a0 values larger than that of pure C60. Here we study this relationship over a wider range using mixed alkali compounds incorporating sodium (Na2MC60, where M is K, Rb or Cs) and lithium (Li2CsC60). The Na2MC60 compounds have face-centred cubic structures and are superconducting, with Tc = 12 K (M = Cs), 2.5 K (M = Rb) and 2.5 K (M = K); these Tcs are lower than those predicted on the basis of high-pressure studies6–8. This departure from the previous relationship between Tc and a0 for lattice parameters smaller than that of pristine C60 may provide new insights into what controls superconductivity in these materials.

Superconductivity in sodium-and lithium-containing alkali-metal fullerides

The crystal structure of superconducting Na2CsC60 was studied by high-resolution powder neutron diffraction between 1.6 and 425 K. Contrary to the literature, the structure at low temperatures is primitive cubic [See equation in the PDF file], isostructural with pristine C60. Anticlockwise rotation of the C60 units by 98° about [111] allows simultaneous optimization of C60-C60 and alkali-fulleride interactions. Optimal Na+-C603- coordination is achieved with each sodium ion located above one hexagon face and three hexagon-hexagon fusions of neighboring fulleride ions (coordination number 12). Reduction of the C60 molecule lengthens the hexagon-hexagon fusions and shortens the pentagon-hexagon fusions (to ∼1.43 angstroms). On heating, Na2CsC60 undergoes a phase transition to a face-centered-cubic [See equation in the PDF file] phase, best modeled as containing quasi-spherical C603- ions. The modified structure and intermolecular potential provide an additional dimension to the behavior of superconducting fullerides and should sensitively affect their electronic and conducting properties.

https://science.sciencemag.org/content/sci/263/5149/950.full.pdf

Crystal structure, bonding, and phase transition of the superconducting Na2CsC60 fulleride

THE surprisingly high transition temperatures (Tc) for superconductivity in alkali-meta-doped C60 has spurred wide interest in understanding its mechanism1–6. Recently the increase in Tc with lattice constant was demonstrated for these materials6, and was interpreted as resulting from the corresponding increase in the density of states at the Fermi level. According to the standard (BCS) theory of superconductivity, the other important factor controlling Tc is the phonon that mediates electron pairing. To test whether this factor plays a part for the C60 superconductors, we prepared C60 containing various amounts of 13C, which we then doped with rubidium to give Rb3C60. Measurements of diamagnetic shielding and Meissner effect show that Tc decreases as the 13C content increases, as expected within the context of BCS-like phonon-mediated pairing; but the dependence on the mass is stronger than for most electron-phonon superconductors where Tcm−α with α ≤0.5. Instead, the exponent a has the remarkably large value of 1.4±0.5. Regardless of the interpretation of this value, it is clear that phonons have an important role in the origin of superconductivity in doped C60.

Isotope effect on superconductivity in Rb3C60

Reflection ellipsometry is applied to characterize the molecular orientation of rubbed polyimide films for liquid crystal display devices Thickness, dielectric constants and tilt angle of the principal dielectric axis of the molecularly oriented upper layer and thickness of the random layer in rubbed polyimide films can be determined by analyzing the anisotropic polarization of reflected light

https://iopscience.iop.org/article/10.1143/JJAP.35.5873/pdf

Ichiro Hirosawa

Papers

Superconductivity in sodium-and lithium-containing alkali-metal fullerides

Crystal structure, bonding, and phase transition of the superconducting Na2CsC60 fulleride

Isotope effect on superconductivity in Rb3C60

Method of Characterizing Rubbed Polyimide Film for Liquid Crystal Display Devices Using Reflection Ellipsometry

Structure and superconductivity of C60 fullerides