Native Point Defects in yttria as a High-Dielectric-Constant Gate Oxide Material: A First-Principles Study

Yttria (Y₂O₃) has become a promising gate oxide material to replace silicon dioxide in metal-oxide-semiconductor (MOS) devices. The characterization of native point defect in Y₂O₃ is essential to understand the behavior of the material. We used the first-principles pseudopotential method to study the electronic structure, defect structure and formation energy of native point defects in Y₂O₃. Vacancies, interstitials and antisites in their relevant charge states are considered. The dominant defect types are identified under different chemical potentials and different Fermi levels. Oxygen vacancies are the dominant defect types under high yttrium chemical potential condition. Lower yttrium chemical potential leads to oxygen interstitials and ultimately yttrium vacancies when Y₂O₃ is used as a high dielectric constant gate oxide material in MOS devices.Singapore-MIT Alliance (SMA

Small Polarons in Transition Metal Oxides

The formation of polarons is a pervasive phenomenon in transition metal oxide compounds, with a strong impact on the physical properties and functionalities of the hosting materials. In its original formulation the polaron problem considers a single charge carrier in a polar crystal interacting with its surrounding lattice. Depending on the spatial extension of the polaron quasiparticle, originating from the coupling between the excess charge and the phonon field, one speaks of small or large polarons. This chapter discusses the modeling of small polarons in real materials, with a particular focus on the archetypal polaron material TiO2. After an introductory part, surveying the fundamental theoretical and experimental aspects of the physics of polarons, the chapter examines how to model small polarons using first principles schemes in order to predict, understand and interpret a variety of polaron properties in bulk phases and surfaces. Following the spirit of this handbook, different types of computational procedures and prescriptions are presented with specific instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure

Investigation of the Mixing and Devolatilization Behavior in a Continuous Twin-Shaft Kneader

The technical synthesis and processing of polymer materials is the basis for major branches of the chemical industry. Well introduced for high-viscosity processes are screw extruders. However, in case of large residence times a large volume kneader is more appropriate, but the latter still requires further understanding for intensification purposes. To achieve this, silicone oil of high viscosity is used as kneading material. First, the axial mixing behavior is characterized by studying the residence time distribution. The response functions show that the classical dispersion model leads to an appropriate description of the experimental data. By means of a fast chemical reaction of second order the radial mixing behavior including transport on the molecular scale is studied. The amount of detected product is a measure for the contact-area produced by kneading and therefore for the mixing efficiency. Furthermore, the mass transfer from the silicone oil phase to the gas phase is investigated in two cases. Firstly, the transfer component is dissolved in the liquid phase and, secondly, it is dispersed in it. Both industry relevant cases are experimentally and theoretically investigated. The kneader enables high surface renewal and larger concentration gradients for the efficient mass transfer