Anatoli Korkin

Structure and electronic properties of zirconium and hafnium nitrides and oxynitrides

The atomic structure, stability and electronic properties of zirconium and hafnium nitrides and oxynitrides (MN, M3N4, and M2N2O; M=Zr, Hf) have been studied using first-principles density functional theory calculations. It is found that the orthorhombic Pnam structure of M3N4, which was observed experimentally for zirconium nitride, is more stable for this stoichiometry than the cubic spinel and rock-salt-type structures. The calculated band structures and electronic densities of states demonstrate that both the MN and M3N4 phases of zirconium and hafnium nitrides in the rock-salt-type structure are characterized by metallic properties, while the orthorhombic structure of the M3N4 phase exhibits an insulating behavior in agreement with experimental observations. The formation of nitrogen vacancies in the insulating M3N4 phase converts it into the metallic MN phase. Calculations of Zr2N2O and Hf2N2O in the cubic Bixbyite-type and hexagonal P3–ml crystal structures predict that these materials are insulato...

First-principle investigation of the hydroxylation of zirconia and hafnia surfaces

First-principle calculations demonstrate that the adsorption energies of water on the (001) and (101) surfaces of tetragonal zirconia (t-ZrO2) and on the (001) surface of monoclinic zirconia and hafnia (m-ZrO2 and m-HfO2) strongly depend on the surface hydroxylation degree. It is found that the fully hydroxylated t-ZrO2(001) surface undergoes a 2×2 reconstruction. The influence of surface dipole-dipole interactions on the calculated adsorption energy is discussed.

Oxygen vacancies in tetragonal ZrO 2 : ab initio embedded cluster calculations

Formation of oxygen vacancies in bulk tetragonal ZrO2 and at its (101) and (001) surfaces was studied using ab initio embedded cluster calculations. A new technique was proposed for generating a set of point charges that represents the Coulomb field of the crystal environment both for bulk and surface cluster structures. This technique provides the rapid convergence of the calculated Madelung potential to the unique true value. The estimated bulk vacancy formation energy in tetragonal ZrO2 is 8.8 eV, while surface vacancy energy formation depends on the type of the surface and position of removed oxygen atom and varies from 8.3 to 9.3 eV. The calculated activation energy of oxygen vacancy migration in bulk ZrO2 is 1.95 eV.

On the Mechanism of Silicon Nitride Chemical Vapor Deposition from Dichlorosilane and Ammonia

Silicon nitride, Si 3N4, films have broad industrial applications, particularly in semiconductors and integrated circuit technology. 1 One common way for depositing the films is the reaction of dichlorosilane (DCS, SiH2Cl2) with ammonia (NH3). Optimization of the film deposition and properties often requires knowledge of gas-phase and surface reaction kinetics. The commonly used approach for deriving a mechanism and kinetics of chemical vapor deposition (CVD) is based on experimental results combined with reasonable assumptions. The reaction rate parameters of the resulting gas-phase reactions and semiempirical deposition reactions are then fit to experimental film growth rate data in reactor simulations. 2-5 Such an approach, although useful, has serious limitations due to the lack of understanding of the reaction mechanism on a molecular level. Fundamental understanding of deposition chemistry can aid in implementation of new technologies and in obtaining films of high quality with respect to their structure and properties. 6 A few kinetic models available in the literature for silicon nitride deposition 2-5,7 are based on different assumptions about the mechanism of gas-phase and surface reactions. Surface reactions have been treated by assuming various forms for the conversion of adsorbed gas-phase reactants and intermediates into the final Si 3N4 film without considering possible elementary reactions. In the model suggested by Peev et al. 3 a single power-law expression, rate 5 k [SiH2Cl2] 0.49 [NH3] 0.46 (Freundlich adsorpbtion isotherm), has been used to fit to experimental data and no gas-phase reactions are considered. Roenigk and Jensen 2 have included gas-phase decomposition of DCS into dichlorosililene and hydrogen into their kinetic models, Eq. 1, in order to explain film nonuniformities and growth rate changes across the wafer during low pressure CVD growth. The formation of aminochlorosilane (ACS, SiH2(Cl)NH2) via direct reaction of DCS with ammonia, Eq. 2, was also considered as an alternative. Under the low pressure conditions studied, inclusion of this bimolecular reaction “gives less quantitative agreement with experimental data” 2 SiH2Cl2 r SiCl2 1 H2

Atomistic modeling of chemical vapor deposition: silicon nitride CVD from dichlorosilane and ammonia

Abstract The mechanism and kinetics of chemical vapor deposition of silicon nitride films from SiH2Cl2 and NH3 have been studied theoretically by ab initio (MP2/MC-31G(d,p) and MP2/6-31G(d)) methods combined with the transition state and RRKM theories. Reactions involving the starting reagents and no more than one of the initial reaction products are included in the analysis. It has been found that, in the gas phase at least at T SiN surface groups. The calculated SiN bond length 1.62 A is considerably shorter than typical lengths of crystalline SiN bonds (1.74–1.76 A), and the surface atoms of these diatomic groups are significantly displaced from their bulk crystalline positions.

Theoretical ab initio Study of TiCl4 Ammonolysis: Gas Phase Reactions of TiN Chemical Vapor Deposition

Abstract The mechanism of TiCl4 ammonolysis has been studied theoretically at ab initio Hartree-Fock, B3LYP, MP2 and CCSD(T)//B3LYP levels using effective core potentials for Ti and Cl and 6-31G* basis sets for N and H. TiCl4 and products of its ammonolysis form five- and six-coordinated complexes with ammonia, which intermediate substitution of Cl atoms by NH2 groups. Transition state energies for the subsequent steps of ammonolysis decrease with increasing number of NH2 groups bound to Ti. The energy of the transition state for the first step of ammonolysis is 19 kcal mol-1 above the energy of the reactants (TiCl4+NH3) and 8 kcal mol-1 above the products (TiCl3NH2 + HCl). The following steps have transition states energetically located below the products, indicating weak hydrogen bonded complex formation as intermediate between transition state and product. A thermodynamic estimation shows the last step of ammonolysis to be endothermic, while the first three steps are exothermic if the adduct formation energy is taken into account.

Computational study of ZrSiO4 polymorphs

Using the density functional theory in a local density approximation and generalized gradient approximation (GGA) with a plane wave basis set we have revealed eight new polymorphs of ZrSiO4 within the energy range ∼1eV above the most stable zircon which have higher and lower density than experimentally known zircon and reidite. Two structures, which have both silicon and zirconium atoms sixfold coordinated, orthorhombic AlTaO4-like (alumotantite), and monoclinic PbWO4-like (raspite), have similar energies at a GGA level ∼0.35eV above reidite and density intermediate between zircon and reidite. Among two low-density structures, which can be potentially revealed experimentally in the nanocrystalline thin films, the orthorhombic CaSO4-like form has an energy similar to reidite but with much lower density.

CHIMERA: A software tool for reaction rate calculations and kinetics and thermodynamics analysis

This article presents and overviews the CHIMERA program package, which provides a user‐friendly graphical interface between quantum chemistry and chemical kinetics programs. CHIMERA facilitates calculations of rate constants for gas‐phase reactions using transition state and Rice–Ramsperger–Kassel–Marcus theories. The program includes computational modules for simulation of gas‐phase kinetics using simplified reactor models and for computation of chemical equilibria. The review includes a description of the theory implemented in the code, the program description, the general strategy of calculations using CHIMERA, and illustrative examples of the program application.

Nanotechnology for Electronics, Photonics, and Renewable Energy

Molecular Electronics: Challenges and Perspectives.- Three-Dimensional Silicon-Germanium Nanostructures for CMOS-Compatible Light Emitters.- On Application of Plasmas in Nanotechnologies.- All Carbon Nanotubes Are Not Created Equal.- Two Routes to Subcellular Sensing.- Photothermal Sensing of Chemical Vapors Using Microcantilevers.- Nanoelectronics for DNA Sensing.- Nanostructured Electrode Materials for Lithium-Ion Batteries.- Synthetic Models of Copper Proteins for Biofuel Cell Applications.

Nanotechnology for electronic materials and devices

A Hybrid Route from CMOS to Nano and Molecular Electronics.- From SOI Basics to Nano-Size MOSFETs.- Strategies of Nanoscale Semiconductor Lasers.- Silicon Nanocrystal Nonvolatile Memory.- Novel Dielectric Materials for Future Transistor Generations.- Scanning Force Microscopies for Imaging and Characterization of Nanostructured Materials.- Simulation of Nano-CMOS Devices: From Atoms to Architecture.- Lattice Polarons and Switching in Molecular Nanowires and Quantum Dots.