Ab initio calculations of thermomechanical properties and electronic structure of vitreloy Z r41.2 T i13.8 C u12.5 N i10 B e22.5

The thermomechanical properties and electronic structure of vitreloy (Zr41.2Ti13.8Cu12.5Ni10Be22.5) are investigated using accurate ab initio molecular dynamic (AIMD) simulations and ab initio calculations. The structure of the model with 512 atoms is validated by comparison to the experimental data with calculated thermomechanical properties in good agreement with the existing measurements. Detailed calculation of the electronic structure and bonding at the density functional level is obtained. It is revealed that the traditional definition of bond length in metallic glasses has a limited interpretation, and any theory based on geometrical consideration of their values for discussion on the structural units in metallic glasses has similarly limited applications. On the other hand, we advocate the use of a quantum mechanical based metric, the total bond order density (TBOD), and their partial components or PBOD as valuable parameters to characterize the interatomic bonding in multicomponent glasses such as vitreloy

Mo-Si-B-Based Coatings for Ceramic Base Substrates

Alumina-containing coatings based on molybdenum (Mo), silicon (Si), and boron (B) ("MoSiB coatings") that form protective, oxidation-resistant scales on ceramic substrate at high temperatures are provided. The protective scales comprise an aluminoborosilicate glass, and may additionally contain molybdenum. Two-stage deposition methods for forming the coatings are also provided

Elastic and electronic properties of Ti2Al(CxN1−x) solid solutions

The elastic coefficients and mechanical properties (bulk modulus, shear modulus, Young\u27s modulus and Poisson\u27s ratio) of Ti2Al(CxN1−x) continuous solid solutions for x from 0 to 1 are calculated using ab initio DFT methods on 4×4×1 supercell models. It is shown that the properties of these solid solutions do not vary linearly with x. Although the lattice constant c is almost constant for x≤0.5, a increases linearly. For x\u3e0.5, c starts to increase with x while the rate of increase in a slows down. For x between 0.5 and 0.85, the elastic coefficients and the mechanical parameters show interesting dependence on x and crossovers, signifying the complex interplay in the structure and properties in Ti2Al(CxN1−x) solid solutions. The nonlinear variations in mechanical properties are explained in terms of subtle difference in the electronic structure and bonding between nitrides and carbides in complex MAX phase compounds

In situ atomic layer deposition and electron tunneling characterization of monolayer Al 2 O 3 on Fe for magnetic tunnel junctions

Magnetic tunnel junctions (MTJs), formed through sandwiching an ultrathin insulating film (so-called tunnel barrier or TB), with ferromagnetic metal electrodes, are fundamental building blocks in magnetoresistive random access memory (MRAM), spintronics, etc. The current MTJ technology employs physical vapor deposition (PVD) to fabricate either amorphous AlOx or epitaxial MgO TBs of thickness around 1 nm or larger to avoid leakage caused by defects in TBs. Motivated by the fundamental limitation in PVD in, and the need for atomically thin and defect-free TBs in MTJs, this work explores atomic layer deposition (ALD) of 1-6 Å thick Al 2 O 3 TBs both directly on Fe films and with an ultrathin Al wetting layer. In situ characterization of the ALD Al 2 O 3 TB was carried out using scanning tunneling spectroscopy (STS). Despite a moderate decrease in TB height E b with reducing Al wetting layer thicknesses, a remarkable E b of ∼1.25 eV was obtained on 1 Å thick ALD Al 2 O 3 TB grown directly on an Fe electrode, which is more than twice of that of thermal AlOx TB (∼0.6 eV). Achieving such an atomically thin low-defect TB represents a major step towards improving spin current tunneling in MTJs

Atomically Thin Al2O3 Films for Tunnel Junctions

Metal-insulator-metal tunnel junctions are common throughout the microelectronics industry. The industry standard AlOx tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically thin barriers demanded for enhanced quantum coherence. In this work, we employ in situ scanning tunneling spectroscopy along with molecular-dynamics simulations to understand and control the growth of atomically thin Al2O3 tunnel barriers using atomic-layer deposition. We find that a carefully tuned initial H2O pulse hydroxylated the Al surface and enabled the creation of an atomically thin Al2O3 tunnel barrier with a high-quality M−I interface and a significantly enhanced barrier height compared to thermal AlOx. These properties, corroborated by fabricated Josephson junctions, show that atomic-layer deposition Al2O3 is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next generation of metal-insulator-metal tunnel junctions

Atomically Thin Al2 O3 Films for Tunnel Junctions

Metal-insulator-metal tunnel junctions are common throughout the microelectronics industry. The industry standard AlOx tunnel barrier, formed through oxygen diffusion into an Al wetting layer, is plagued by internal defects and pinholes which prevent the realization of atomically thin barriers demanded for enhanced quantum coherence. In this work, we employ in situ scanning tunneling spectroscopy along with molecular-dynamics simulations to understand and control the growth of atomically thin Al2O3 tunnel barriers using atomic-layer deposition. We find that a carefully tuned initial H2O pulse hydroxylated the Al surface and enabled the creation of an atomically thin Al2O3 tunnel barrier with a high-quality M-I interface and a significantly enhanced barrier height compared to thermal AlOx. These properties, corroborated by fabricated Josephson junctions, show that atomic-layer deposition Al2O3 is a dense, leak-free tunnel barrier with a low defect density which can be a key component for the next generation of metal-insulator-metal tunnel junctions

Superconductivity in Mo5SiB2

In the MoSi binary system, Mo5Si3 crystallizes in the W5Si3 (T1 phase) structure type. However, when boron replaces silicon in this compound, a structural transition occurs from the W5Si3 prototype structure to the Cr5B 3 prototype structure (T2 phase) at the composition Mo5SiB2. Mo5SiB2 has received much attention in the literature as a candidate for structural application in high-temperature turbines, but its electronic and magnetic behavior has not been explored. In this work, we show that Mo5SiB2 is a bulk superconducting material with critical temperature close to 5.8 K. The specific-heat, resistivity and magnetization measurements reveal that this material is a conventional type II BCS superconductor. © 2011 Elsevier Ltd. All rights reserved