Modeling the Effects of Varying the Ti Concentration on the Mechanical Properties of Cu-Ti Alloys.

The mechanical properties of CuTi alloys have been characterized extensively through experimental studies. However, a detailed understanding of why the strength of Cu increases after a small fraction of Ti atoms are added to the alloy is still missing. In this work, we address this question using density functional theory (DFT) and molecular dynamics (MD) simulations with the modified embedded atom method (MEAM) interatomic potentials.

On the Structure of Oxygen Deficient Amorphous Oxide Films.

Understanding defects in amorphous oxide films and heterostructures is vital to improving performance of microelectronic devices, thin-film transistors, and electrocatalysis. However, to what extent the structure and properties of point defects in amorphous solids are similar to those in the crystalline phase are still debated. The validity of this analogy and the experimental and theoretical evidence of the effects of oxygen deficiency in amorphous oxide films are critically discussed.

Structure and Migration Mechanisms of Small Vacancy Clusters in Cu: A Combined EAM and DFT Study.

Voids in face-centered cubic (fcc) metals are commonly assumed to form via the aggregation of vacancies; however, the mechanisms of vacancy clustering and diffusion are not fully understood. In this study, we use computational modeling to provide a detailed insight into the structures and formation energies of primary vacancy clusters, mechanisms and barriers for their migration in bulk copper, and how these properties are affected at simple grain boundaries. The calculations were carried out using embedded atom method (EAM) potentials and density functional theory (DFT) and employed the site-occupation disorder code (SOD), the activation relaxation technique nouveau (ARTn) and the knowledge led master code (KLMC).

Thermodynamic analysis of the interaction between metal vacancies and hydrogen in bulk Cu.

Using grand canonical thermodynamic analysis with inputs from DFT calculations we calculated equilibrium molar fractions of copper vacancies (V), H interstitials (H) and their complexes in bulk Cu in a wide range of temperature and hydrogen pressure values. The results show that the equilibrium molar fractions of both V and H are low in most conditions of interest, in good agreement with available experimental data. Although H-V complexes have significantly lower formation energies than the isolated defects, the low molar fraction of H is predicted to have little impact on the rise in vacancy molar fraction for external hydrogen pressures below 100 bar.

Difference in Structure and Electronic Properties of Oxygen Vacancies in -Quartz and -Cristobalite Phases of SiO.

α-cristobalite (α-C) is a polymorph of silica, mainly found in space exploration and geochemistry research. Due to similar densities, α-C is often used as a proxy for amorphous SiO2, particularly in computer simulations of SiO2 surfaces and interfaces. However, little is known about the properties of α-C and its basic oxygen defects.

Carboxylate Adsorption on Rutile TiO(100): Role of Coulomb Repulsion, Relaxation, and Steric Hindrance.

Understanding the adsorption and photoactivity of acetic acid and trimethyl acetic acid on TiO surfaces is important for improving the performance of photocatalysts and dye-sensitized solar cells. Here we present a structural study of adsorption on rutile TiO(100)-1 × 1 and -1 × 3 using Scanning Tunnelling Microscopy and Density Functional Theory calculations. Exposure of both terminations to acetic acid gives rise to a ×2 periodicity in the [001] direction (i.

Inverse Perovskite Oxysilicides and Oxygermanides as Candidates for Nontoxic Infrared Semiconductor and Their Chemical Bonding Nature.

We have synthesized inverse-perovskite-type oxysilicides and oxygermanides represented by SiO and GeO ( = Ca and Sr) and studied their characteristics in the search for nontoxic narrow band gap semiconductors. These compounds exhibit a sharp absorption edge around 0.9 eV and a luminescence peak in the same energy range.

Properties of intrinsic point defects and dimers in hexagonal boron nitride.

Hexagonal boron nitride (hBN) is a wide gap 2D layered material with good insulating properties. Intrinsic point defects in hBN play an important role in its applications as a dielectric in 2D electronic devices. However, the electronic properties of these defects are still poorly understood.

Modeling of Diffusion and Incorporation of Interstitial Oxygen Ions at the TiN/SiO Interface.

Silica-based resistive random access memory devices have become an active research area due to complementary metal-oxide-semiconductor compatibility and recent dramatic increases in their performance and endurance. In spite of both experimental and theoretical insights gained into the electroforming process, many atomistic aspects of the set and reset operation of these devices are still poorly understood. Recently a mechanism of electroforming process based on the formation of neutral oxygen vacancies (V) and interstitial O ions (O) facilitated by electron injection into the oxide has been proposed.

The role of surface reduction in the formation of Ti interstitials.

Density functional theory simulations are used to investigate the formation and mobility of Ti interstitial ions, Ti, at the (110) surface of rutile TiO. Interstitials were found to be favoured in the second layer below the surface plane, where they induce electron polaron states at surface and subsurface lattice Ti atoms. Reduction of the surface significantly lowers the barrier for Ti formation at the surface: the barrier for formation of Ti is reduced to just ∼0.

The origin of negative charging in amorphous AlO films: the role of native defects.

Amorphous aluminum oxide AlO (a-AlO) layers grown by various deposition techniques contain a significant density of negative charges. In spite of several experimental and theoretical studies, the origin of these charges still remains unclear. We report the results of extensive density functional theory calculations of native defects-O and Al vacancies and interstitials, as well as H interstitial centers-in different charge states in both crystalline α-AlO and in a-AlO.

First principles calculations of optical properties for oxygen vacancies in binary metal oxides.

Using an advanced computational methodology implemented in CP2K, a non-local PBE0-TC-LRC density functional and the recently implemented linear response formulation of the Time-dependent Density Functional Theory equations, we test the interpretation of the optical absorption and photoluminescence signatures attributed by previous experimental and theoretical studies to O-vacancies in two widely used oxides-cubic MgO and monoclinic (m)-HfO. The results obtained in large periodic cells including up to 1000 atoms emphasize the importance of accurate predictions of defect-induced lattice distortions. They confirm that optical transitions of O-vacancies in 0, +1, and +2 charge states in MgO all have energies close to 5 eV.

Structure and properties of intrinsic and extrinsic defects in black phosphorus.

The electronic and geometric structures of a range of intrinsic and extrinsic defects in black phosphorus (BP) are calculated using Density Functional Theory (DFT) and a hybrid density functional. The results demonstrate that energy barriers to form intrinsic defects, such as Frenkel pairs and Stone-Wales type defects, exceed 3.0 eV and their equilibrium concentrations are likely to be low.

Relation between image charge and potential alignment corrections for charged defects in periodic boundary conditions.

Charged defects are often studied within the periodic density functional theory (DFT), but this introduces strong finite-size artifacts. In this work, we develop an electrostatic image interaction correction (IIC) method based on the direct solution of the Poisson equation for charge models constructed directly from DFT calculations. These IICs are found to be detail-insensitive, depending almost entirely on bulk dielectric properties.

Silicon Oxide (SiO ): A Promising Material for Resistance Switching?

Interest in resistance switching is currently growing apace. The promise of novel high-density, low-power, high-speed nonvolatile memory devices is appealing enough, but beyond that there are exciting future possibilities for applications in hardware acceleration for machine learning and artificial intelligence, and for neuromorphic computing. A very wide range of material systems exhibit resistance switching, a number of which-primarily transition metal oxides-are currently being investigated as complementary metal-oxide-semiconductor (CMOS)-compatible technologies.

Intrinsic charge trapping in amorphous oxide films: status and challenges.

We review the current understanding of intrinsic electron and hole trapping in insulating amorphous oxide films on semiconductor and metal substrates. The experimental and theoretical evidences are provided for the existence of intrinsic deep electron and hole trap states stemming from the disorder of amorphous metal oxide networks. We start from presenting the results for amorphous (a) HfO, chosen due to the availability of highest purity amorphous films, which is vital for studying their intrinsic electronic properties.

Intrinsic electron trapping in amorphous oxide.

We demonstrate that electron trapping at intrinsic precursor sites is endemic in non-glass-forming amorphous oxide films. The energy distributions of trapped electron states in ultra-pure prototype amorphous (a)-HfO insulator obtained from exhaustive photo-depopulation experiments demonstrate electron states in the energy range of 2-3 eV below the oxide conduction band. These energy distributions are compared to the results of density functional calculations of a-HfO models of realistic density.

Intrinsic Resistance Switching in Amorphous Silicon Suboxides: The Role of Columnar Microstructure.

We studied intrinsic resistance switching behaviour in sputter-deposited amorphous silicon suboxide (a-SiO ) films with varying degrees of roughness at the oxide-electrode interface. By combining electrical probing measurements, atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM), we observe that devices with rougher oxide-electrode interfaces exhibit lower electroforming voltages and more reliable switching behaviour. We show that rougher interfaces are consistent with enhanced columnar microstructure in the oxide layer.

Theoretical modeling of charge trapping in crystalline and amorphous AlO.

The characteristics of intrinsic electron and hole trapping in crystalline and amorphous AlO have been studied using density functional theory (DFT). Special attention was paid to enforcing the piece-wise linearity of the total energy with respect to electron number through the use of a range separated, hybrid functional PBE0-TC-LRC (Guidon et al 2009 J. Chem.

Diffusion and aggregation of oxygen vacancies in amorphous silica.

Using density functional theory (DFT) calculations, we investigated oxygen vacancy diffusion and aggregation in relation to dielectric breakdown in amorphous silicon dioxide (a-SiO). Our calculations indicate the existence of favourable sites for the formation of vacancy dimers and trimers in the amorphous network with maximum binding energies of approximately 0.13 eV and 0.

Influence of ions on two-dimensional and three-dimensional atomic force microscopy at fluorite-water interfaces.

Recent advancement in liquid-environment atomic force microscopy (AFM) has enabled us to visualize three-dimensional (3D) hydration structures as well as two-dimensional (2D) surface structures with subnanometer-scale resolution at solid-water interfaces. However, the influence of ions present in solution on the 2D- and 3D-AFM measurements has not been well understood. In this study, we perform atomic-scale 2D- and 3D-AFM measurements at fluorite-water interfaces in pure water and a supersaturated solution of fluorite.