Electronic materials process modeling

Summary This report focuses on current needs in the process modeling of materials used in electronic and optoelectronic device fabrication and provides specific recommendations in addressing these needs. The establishment of relationships between materials structure and processing is identified as the critical modeling need in the electronics industry. A hierarchical modeling approach is suggested aiming at the development of efficient and robust process simulators with predictive capabilities and, thus, providing modeling tools for development of optimal materials processing strategies. This approach is based on linking a variety of existing theoretical and computational methods which include: ab initio, semi-empirical, and empirical atomic-scale simulation methods for accurate calculation of materials properties and mechanistic physical understanding; microstructural-scale thermodynamic, transport, and kinetic modeling; and macroscopic process-specific process simulation. Issues of interdisciplinary communication and collaboration and exploratory research for new materials are also addressed.Providing a standard list of literature references is beyond the scope of this report. A general overview of industrial needs and technical goals is provided by Ref. 1.     

First principles prediction of structural stability,elastic, lattice dynamical and thermal properties of osmium carbides

Abstract

First principles calculations are performed to investigate the structural stability, elastic, lattice dynamical and thermal properties of osmium carbides with various crystal structures. Our calculation indicates that the I₄Te type structure is energetically the most favourable for Os₄C. Based on stress–strain relationships, elastic constants are obtained, and the relevant mechanical properties are also discussed. The phonon dispersion relation and the dynamical stability are also predicted. We have found that the predicted structures are mechanically stable as well as dynamically stable except for cubic-Os₄C. Through the quasi-harmonic Debye model, the temperature and pressure effects on the bulk modulus, thermal expansion coefficient, heat capacity, Grüneisen parameter and Debye temperature are presented.     

Development of MOE (molecular orbital calculation engine)

We are constructing the computing system, molecular orbital calculation engine (MOE), which realizes super high-performance and cost-down of molecular orbital calculations by developing the special purpose computer for high-performance molecular orbital calculations. This report describes the summary of the MOE.     

Site occupancy of Ce3+ in β-Ca2SiO4: A combined experimental and ab initio study

Low-temperature photoluminescence properties of the β-Ca_2(1−x)Ce_xNa_xSiO₄ (x = 0.0005) phosphor synthesized by a solid-state reaction method are investigated with excitation energies in the vacuum ultraviolet (VUV) to ultraviolet (UV) range. Two distinct types of emission and excitation spectra are observed, which are attributed to 4f–5d transitions of two different sets of Ce³⁺ centers. On the basis of density functional theory (DFT) calculations within the supercell model and wave function-based CASSCF/CASPT2 embedded cluster calculations, the two sets of Ce³⁺ centers are ascribed to the Ce³⁺ located on the seven-coordinated Ca1 and eight-coordinated Ca2 sites, respectively. Furthermore, from the observed relative spectral intensities, DFT total energy calculations, and comparison of experimental and calculated 4f → 5d transition energies, it is concluded that the occupation of Ce³⁺ on the Ca2 site is more energetically favorable than the occupation on the Ca1 site. Finally, the redshift of the lowest 4f → 5d transition of Ce³⁺ on the Ca2 site relative to that on the Ca1 site is discussed in terms of the changes of the 5d centroid energy and crystal-field splitting with the local coordination structure.     

Ab Initio Calculations of the Electronic Structures of Copper Pyrites CuS2, CuSe2 and CuTe2

The electronic structures of CuS2, CuSe2 and CuTe2 with pyrite structures, within the framework the density-functional theory have been investigated. The calculated results explained the recent experimental results which show that there is no clear indication of strong electron correlations in the electronic properties of Cu pyrites, due to the dominant chalcogen p character rather than d characteristic of Cu at the Fermi level.     

Electronic structure of the ladder-chain compound Sr14−xCaxCu24O41

The electronic structure of the ladder-chain compound Sr_14−xCa_xCu₂₄O₄₁ is studied by ab initio calculations within the local density approximation. The effects of Ca substitution and structure modulation on electronic structure are discussed. It is found that 0.05 holes per copper atom are on the ladder layers for fully substituted compound, Ca₁₄Cu₂₄O₄₁.     

Ab initio Calculations of the Formation Energies of Lithium Intercalations in SnSb

SnSb has attracted a great attention in recent investigations as an anode material for Li ion batteries. The formation energies and electronic properties of the Li intercalations in SnSb have been calculated within the framework of local density functional theory and the first-principles pseudopotential technique. The changes of volumes, band structures, charge density analysis and the electronic density of states for the Li intercalations are presented. The results show that the average Li intercalation formation energy per Li atom is around 2.7 eV.     

Ab initio study of magnetic coupling in aniline-based molecules: Role of Fe atoms

Our interest is the study of magnetic properties of organic compounds. We have previously reported a new class of organic magnets based on aniline and aminonaphthalenesulfonic acid. In this work, we explore theoretically a simple model based on superposed aniline molecules (radicals) and Fe atoms to determine the mechanism that stabilizes the parallel alignment of the electronic spin. Calculations were performed within the non-local spin density approximation with Becke's exchange functional and the gradient-corrected functional of Lee, Yang and Parr (BYLP) using the DMol program. The results show a high sensitivity of the magnetic properties to the oxidation state of the metal: intercalated between molecular aniline the total spins are 1, 0 and 1/2 for Fe0, FeII and FeIII, and between radicals the spins are 0, 0 and 1/2, respectively. This opens the possibility of creating molecular magnets by doping purely organic materials with transition metal atoms or ions.     

Density functional theory study of magnetic coupling between Cu atoms and aniline molecules

To study the influence of transition metal atoms on the magnetic properties of compounds based on aniline and aminonaphthalenesulfonic acid, we explore theoretically a simple model based on stacked aniline molecules (radicals) and intercalated Cu atoms. Calculations were performed within the non-local spin density approximation with Becke's exchange functional and the gradient-corrected functional of Lee, Yang and Parr (BYLP) using the DMol program. The results reveal a surprisingly strong interaction between the Cu s and d valence electrons with the molecular states, leading to a ferromagnetic coupling in the case of Cu0 and CuII with molecular aniline. In the case of aniline radicals, the coupling is ferromagnetic for Cu0 and ferrimagnetic for CuII. Stacks involving three and four aniline molecules show localization of the spin density to the molecules adjacent to the Cu atom.     

First-principles approach to the calculation of electronic spectra in clusters

We discuss a method for first-principles calculations of photoemission spectra in small clusters, going well beyond a standard density functional theory-local density approximation (DFT-LDA) approach. Starting with a DFT-LDA calculation, we evaluate self-energy contributions to the quasiparticle energies of an electron or hole in the GW scheme, where the self-energy Σ = GW is constructed from the one-particle Green's function G and the RPA screened Coulomb interaction W. The contributions of structural relaxation are taken into account. We show the importance of these effects at the example of the photoemission spectrum of SiH₄. We also briefly discuss results for longer hydrogenated silicon chains, and address the problem of optical absorption.     

Ab initio study of stacking faults and deformation mechanism in C15 Laves phases Cr2X (X = Nb,Zr, Hf)

Based on the synchroshear model, the formation of stacking fault and twinning fault in C15 Laves phases is modeled, then the generalized stacking fault energy curves and deformation mechanism in C15 Laves phases Cr₂X (X = Nb, Zr, Hf) alloys are investigated by ab initio calculations based on the density functional theory. The results demonstrate that the unstable stacking fault and twinning fault energies of C15 Laves phases Cr₂X (X = Nb, Zr, Hf) by the synchroshear are still large while the stable stacking fault and twinning fault energies are low, and the deformation modes by extended partial dislocation and twining are feasible in C15 Laves phases Cr₂X (X = Nb, Zr, Hf). Moreover, the Cr₂Nb has the largest deformation twinning tendency, followed by Cr₂Zr and Cr₂Hf. The evolution of electronic structure during the synchroshear process is further studied to unveil the intrinsic mechanism for the formation of stacking fault and twinning fault in C15 Laves phases Cr₂X (X = Nb, Zr, Hf).     

Atomistic calculations and materials informatics: A review

In recent years, there has been a large effort in the materials science community to employ materials informatics to accelerate materials discovery or to develop new understanding of materials behavior. Materials informatics methods utilize machine learning techniques to extract new knowledge or predictive models out of existing materials data. In this review, we discuss major advances in the intersection between data science and atom-scale calculations with a particular focus on studies of solid-state, inorganic materials. The examples discussed in this review cover methods for accelerating the calculation of computationally-expensive properties, identifying promising regions for materials discovery based on existing data, and extracting chemical intuition automatically from datasets. We also identify key issues in this field, such as limited distribution of software necessary to utilize these techniques, and opportunities for areas of research that would help lead to the wider adoption of materials informatics in the atomistic calculations community.     

Ab initio Calculations of Magnetic Properties of Fe16N2

Pseudo-potential and plane wave basis-set under the framework of density functional theory have been employed to study the electronic and magnetic properties of Fe162, and to have an insight look on the subject of giant magnetic moments reported in Fe16N2. After geometrical optimization, band structures and densities of states have been evaluated together with the atom resolved band populations and magnetic moments. In this paper, we report a theoretical effort to look into the various aspects of the magnetic properties of Fe16N2, including volume effect and distortion effect.     

Effect of Y and Zn substitution on elastic properties of 6H-type ABCBCB LPSO structure in Mg97Zn1Y2 alloy

Theoretical investigations of the effect of Y and Zn atom substitution on elastic properties of 6H-type ABCBCB LPSO structure in Mg₉₇Zn₁Y₂ alloy have been performed from density function theory. Elastic properties, including elastic constants and elastic modulus were investigated, and the influence of Y and Zn substitution were discussed in detail. Elastic anisotropies were analyzed by several methods, and the results show that the anisotropy in compression is almost negligible, whereas the anisotropy in shear is relatively large. Furthermore, the shear anisotropy becomes larger with Zn substitution than Y substitution. The electronic characteristics indicate that the Mg-Y and Mg-Zn bonds exhibit covalent feature due to hybridization, so the interactions of Mg with Y and Zn are enhanced.     

Theoretical studies of the pressure-induced zinc-blende to cinnabar phase transition in CdTe and thermodynamical properties of each phase

Luminescence of CdTe quantum dots embedded in ZnTe is quenched at pressure of about 4.5 GPa in the high-pressure experiments. This pressure-induced quenching is attributed to the “zinc-blende–cinnabar” phase transition in CdTe, which was confirmed by the first-principles calculations. Theoretical analysis of the pressure at which the phase transition occurs for CdTe was performed using the CASTEP module of Materials Studio package with both generalized gradient approximation (GGA) and local density approximation (LDA). The calculated phase transition pressures are equal to about 4.4 GPa and 2.6 GPa, according to the GGA and LDA calculations, respectively, which is in a good agreement with the experimental value. Theoretically estimated value of the pressure coefficient of the band-gap luminescence in zinc-blende structure is in very good agreement with that recently measured in the QDs structures. The calculated Debye temperature, elastic constants and specific heat capacity for the zinc-blend structure agree well with the experimental data; the data for the cinnabar phase are reported here for the first time to the best of the authors' knowledge.     

Electronic and optical properties of the orthorhombic compounds FeX2 (X = P,As and Sb)

First principles calculations, by means of the full-potential linearized augmented plane wave (FP-LAPW) method within the local density approximation (LDA), were carried out for the structural, electronic and optical properties of the orthorhombic compounds FeP₂, FeAs₂ and FeSb₂. The structural properties are determined through the total energy minimization and the relaxation of the internal parameters. The modified Becke–Johnson (mBJ) method is applied for the electronic structure of FeSb₂. Our LDA-calculation shows that the first two compounds are indirect-gap semiconductors, while for the third one it predicts a small hole-pocket at the R point. The mBJ gives a semiconducting state with an indirect energy gap of 0.248 eV for FeSb₂. The overall shape of the calculated imaginary parts of the dielectric tensor is similar for the three compounds. The assignment of the structures in the optical spectra and band structure transitions are investigated. The electronic dielectric constant along (0 1 0) direction is the largest for the three compounds. For FeAs₂, the calculated components of reflectivity have the same trend of variation as the measured ones in the energy range 1.54–3.1 eV.     

Identification of the partitioning characteristics of refractory elements in σ and γ phases of Ni-based single crystal superalloys based on first principles

The impurity formation energies of the σ and γ phases of Ni-based single crystal superalloys doped with W, Cr and Co in different sublattices have been investigated using first-principles based on the density functional theory. The bonding characteristics of the doped σ phase were analyzed with the valence charge densities and the density of the states. The results of the calculations indicated that the typical refractory element W, which has a large atomic size, preferentially partitions into the σ phase due to the nature of the bonding and the unique crystal structure with close-packed planes and large interstitial spaces. In addition, the site preference of refractory elements in γ phase was in the order of W, Cr and Co.