Mechanical properties of nanocrystalline materials

Processes of severe plastic deformation (SPD) are defined as metal forming processes in which a very large plastic strain is imposed on a bulk process in order to make an ultra-fine grained metal The objective of the SPD processes for creating ultra-fine grained metal is to produce lightweight parts by using high strength metal for the safety and reliability of micro-parts and for environmental harmony In this keynote paper, the fabrication process of equal channel angular pressing (ECAP), accumulative roll-bonding (ARB), high pressure torsion (HPT), and others are introduced, and the properties of metals processed by the SPD processes are shown Moreover, the combined processes developed recently are also explained Finally, the applications of the ultra-fine grained (UFG) metals are discussed

Severe Plastic Deformation (SPD) Processes for Metals

Since the first days of high-Tc superconductivity, the materials science and the physics of grain boundaries in superconducting compounds have developed into fascinating fields of research. Unique electronic properties, different from those of the grain boundaries in conventional metallic superconductors, have made grain boundaries formed by high-Tc cuprates important tools for basic science. They are moreover a key issue for electronic and large-scale applications of high-Tc superconductivity. The aim of this review is to give a summary of this broad and dynamic field. Starting with an introduction to grain boundaries and a discussion of the techniques established to prepare them individually and in a well-defined manner, the authors present their structure and transport properties. These provide the basis for a survey of the theoretical models developed to describe grain-boundary behavior. Following these discussions, the enormous impact of grain boundaries on fundamental studies is reviewed, as well as high-power and electronic device applications.

/pdf/grain-boundaries-in-high-t-c-superconductors-2widq11ljn.pdf

Grain boundaries in high- T c superconductors

Grain Boundary Complexions

Current issues in recrystallization: A review

A brief review of the theoretical state of the art in the field of semiconductor interfaces is presented. Itis shown that the important factor controlling the different semiconductor barrier heights is the densityof states associated with the semiconductor dangling-bonds. Passivated semiconductor surfaces presentsaturated dangling-bonds and have modified barrier heights. Results for hydrogen-passivated GaAs(11O)-surfaces are presented; it is shown that the Schottky-barrier height formed by the deposition of a K-layeris sustantially changed by the hydrogen-passivation. 1 INTRODUCTION Interfaces of crystalline materials are at the heart of different devices, and their understanding is basic toan appropriate design of many microelectronic systems. In this regard, semiconductors and their interfaceswith other semiconductors or metals have received the major attention1 , and we shall concentrate ourdiscussion in this paper on analyzing their basic electronic properties and their relation to the formationof different barriers.There are, basically, two kinds of semiconductor contacts: metal- semiconductor2'3 and semiconductor-semiconductor interfaces4. A great deal of the recent research in this field has been addressed to under-standing how their different barrier heights depend on the properties of the crystals forming the contact5.Fig.1 shows the main parameters defining each barrier: (a) for a metal semiconductor interface,

Interfaces in crystalline materials

We present a theory for the scanning tunneling microscope (STM) current based on a Keldysh Green function formalism. In our formalism, we solve self-consistently an ab initio linear combination of atomic orbitals Hamiltonian within a local density formalism. Total energy calculations for xenon deposited on metal surfaces are performed to obtain the equilibrium position, and the Green functions needed to compute the current are obtained at the same time. Structural and nonstructural effects that can influence the correct interpretation of experimental STM results are studied. We find good agreement between our calculations and experimental images taken under highly controlled conditions, and we conclude that STM images should be analyzed by comparing iteratively the theory and the experiment, much in the same way as it is usually done for other surface sensitive techniques like low-energy electron diffraction, photoelectron diffraction, surface-extended x-ray-absorption fine structure spectroscopy, etc. \textcopyright{} 1996 The American Physical Society.

Theory of the scanning tunneling microscope: Xe on Ni and Al.

Systematic theoretical studies of the Schottky barrier control by passivating atomic intralayers

Schottky barrier formation for passivated semiconductor surfaces

A discussion is presented on the semiconductor interface barrier formation. Schottky barriers and heterojunction band offsets are analysed by means of the intrinsic and extrinsic charge neutrality levels. These levels are shown to be controlled by the interface geometry and its local chemistry. The chemical properties and the charge neutrality levels of different Schottky barriers are presented. Heterojunction band offsets are also analysed and are shown to depend on the electronegativity of the metal intralayers deposited at the interface: more electronegative metal atoms tend to reduce the hetero junction band offsets.

http://rsta.royalsocietypublishing.org/content/roypta/344/1673/567.full.pdf

R. Saiz-Pardo

Papers

Interfaces in crystalline materials

Theory of the scanning tunneling microscope: Xe on Ni and Al.

Systematic theoretical studies of the Schottky barrier control by passivating atomic intralayers

Schottky barrier formation for passivated semiconductor surfaces

Electron States at Semiconductor Interfaces: The Intrinsic and Extrinsic Charge Neutrality Levels