Presentation on theme: "Chapter 1. Introduction, perspectives, and aims. On the science of simulation and modelling. Modelling at bulk, meso, and nano scale. (2 hours). Chapter."— Presentation transcript:
Chapter 1. Introduction, perspectives, and aims. On the science of simulation and modelling. Modelling at bulk, meso, and nano scale. (2 hours). Chapter 2. Experimental Techniques in Nanotechnology. Theory and Experiment: “Two faces of the same coin” (2 hours). Chapter 3. Introduction to Methods of the Classic and Quantum Mechanics. Force Fields, Semiempirical, Plane-Wave pseudpotential calculations. (2 hours) Chapter 4. Introduction to Methods and Techniques of Quantum Chemistry, Ab initio methods, and Methods based on Density Functional Theory (DFT). (4 hours) Chapter 5. Visualization codes, algorithms and programs. GAUSSIAN; CRYSTAL, and VASP. (6 hours)
. Chapter 6. Calculation of physical and chemical properties of nanomaterials. (2 hours). Chapter 7. Calculation of optical properties. Photoluminescence. (3 hours). Chapter 8. Modelization of the growth mechanism of nanomaterials. Surface Energy and Wullf architecture (3 hours) Chapter 9. Heterostructures Modeling. Simple and complex metal oxides. (2 hours) Chapter 10. Modelization of chemical reaction at surfaces. Heterogeneous catalysis. Towards an undertanding of the Nanocatalysis. (4 hours)
Chapter 9. Heterostructures Modeling. Simple and complex metal oxides. Juan Andrés y Lourdes Gracia Departamento de Química-Física y Analítica Universitat Jaume I Spain & CMDCM, Sao Carlos Brazil Sao Carlos, Novembro 2010
When two isomorphs of different materials are in epitaxial contact, an extraordinary phenomenon emerges in the interface, which cannot happen in the bulk or in the surface of an only specific material. Heterostructures sandwich-type
There is an enormous number of possible arrangements, so it would be better to investigate multicompound systems of potential interest using ab initio calculations to confirm that a given system has the desired properties before performing the experiment. ‡ ‡ (a) H. N. Lee, H. M. Christen, M. F. Chisholm, C. M. Rouleau, D. H. Lowndes, Nature 433, 395 (2005); (b) G. Rijnders, D. H. A. Blank, Nature 433, 369 (2005) The coupling between TiO 2 and SnO 2 affects the electronic structure and it could be used to control and improve the superficial physical and chemical properties of these systems. Heterostructures sandwich-type
surface core TiO 2 outer SnO 2 core SnO 2 outer TiO 2 (110)17.286.9015.956.36 (010)10.996.3811.234.46 (101)11.455.3812.004.90 (001)9.383.289.812.94 SnO 2 /TiO 2 /SnO 2 TiO 2 /SnO 2 /TiO 2 Thickness (Å) of the used models Characterization of heterostructures TiO 2 @SnO 2 J. Phys. Chem. A 112, 8943 (2008)
X´ M X E g = 2.68 eV X´ M X X´ M X E g = 3.24 eV X´ M X E g = 2.57 eV (a) (c) (e) (b) X´ M X (d) E g = 3.70 eV (110) TiO 2 (a); SnO 2 (b); SnO 2 /TiO 2 /SnO 2 (c) and TiO 2 /SnO 2 /TiO 2 (d)
(010) TiO 2 (a); SnO 2 (b); SnO 2 /TiO 2 /SnO 2 (c) and TiO 2 /SnO 2 /TiO 2 (d) X´ M X E g = 3.55 eV (a) (c) X´ M X E g = 3.46 eV (e) X´ M X (b) E g = 3.55 eV X´ M X (d) E g = 3.75 eV
X´ M X X´ M X E g = 3.22 eV (a) (c) X´ M X E g = 3.44 eV (e) X´ M X (b) E g = 2.77 eV X´ M X (d) E g = 3.70 eV (101) TiO 2 (a); SnO 2 (b); SnO 2 /TiO 2 /SnO 2 (c) and TiO 2 /SnO 2 /TiO 2 (d)
X M X X´ M X E g = 2.76 eV (a) (c) X´ M X (e) X´ M X (b) E g = 2.53 eV X´ M X (d) (001) TiO 2 (a); SnO 2 (b); SnO 2 /TiO 2 /SnO 2 (c) and TiO 2 /SnO 2 /TiO 2 (d) E g = 3.19 eV E g = 3.48 eV
Characterization of heterostructures TiO 2 @SnO 2
La parte superior de las bandas de Valencia (VB) vienen dominadas por las capas externas, esto es, por el TiO 2 y el SnO 2, respectivamente, mientras que la topología de la parte inferior de las bandas de conducción (CB) se parece a la de los cores. Hay una estabilización energética tanto de la VB como de la CB tanto en la superficie (110) como la (010) para el sistema SnO 2 /TiO 2 /SnO 2 en relación a su core TiO 2, mientras que se encuentra la tendencia opuesta para las misma superficies en el TiO 2 /SnO 2 /TiO 2 en relación a su core SnO 2 Caracterización heteroestructuras TiO 2 @SnO 2
(001) Sr Zr Ti O Perspectives Characterization of heterostructure SrZrO 3 /SrTiO 3 /SrZrO 3
Charge density PZT TiO2 ended Not shared isolines between Pb and O a toms Ionic character, interaction of atoms as punctual charges Shared isolines between Ti and O atoms with continuous electronic density Covalent contribution plane PbO plane TiO2 SITES: 8 and 18
PZT -8-18 PbO-ended: Gap: 3,62 eVPZT -5-25. PbO-ended: Gap: 3,45 eV BAND STRUTURES PbO ended GAP INDIRETO PT. PbO-ended: Gap: 3,99 eV
PZT -8-18 TiO2-ended: Gap: 4,41 eV PZT -3-23 TiO2-ended: Gap: 3.66 eV INDIRECT GAP GAP INDIRETO DIRECT GAP BAND STRUTURES TiO2 ended PT. TiO2-ended: Gap: 3,84 eV INDIRECT GAP
Two-Dimensional Confinement of 3d 1 Electrons in LaTiO 3 /LaAlO 3 Multilayers S. S. A. Seo, M. J. Han, G.W. J. Hassink, W. S. Choi, S. J. Moon, J. S. Kim, T. Susaki, Y. S. Lee, J. Yu, C. Bernhard, H.Y. Hwang, G. Rijnders, D. H. A. Blank, B. Keimer, and T.W. Noh PRL 104, 036401 (2010) We report spectroscopic ellipsometry measurements of the anisotropy of the interband transitions parallel and perpendicular to the planes of (LaTiO 3 )n(LaAlO 3 )5 multilayers with n = 1–3. These provide direct information about the electronic structure of the two-dimensional (2D) 3d 1 state of the Ti ions. In combination with local density approximation, including a Hubbard U calculation, we suggest that 2D confinement in the TiO2 slabs lifts the degeneracy of the t 2g states leaving only the planar d xy orbitals occupied. We outline that these multilayers can serve as a model system for the study of the t 2g 2D Hubbard model.
Oxygen octahedron reconstruction in the SrTiO 3 /LaAlO 3 heterointerfaces investigated using aberration-corrected ultrahigh-resolution transmission electron microscopy C. L. Jia, S. B. Mi, M. Faley, U. Poppe, J. Schubert, and K. Urban PHYSICAL REVIEW B 79, 081405 2009 We investigate the LaAlO 3 /SrTiO 3 interface by means of aberration- corrected ultrahigh-resolution transmission electron microscopy allowing us to measure the individual atomic shifts in the interface at a precision of a few picometers. We find that the oxygen octahedron rotation typical for rhombohedral LaAlO3 is across the interface and is also induced in the originally cubic SrTiO 3 layer. Octahedra distortion leads to ferroelectricitylike dipole formation in the interface which is in addition modified by cation intermixing.
Carrier-mediated magnetoelectricity in complex oxide heterostructures Increasing demands for high-density, stable nanoscale memory elements, as well as fundamental discoveries in the field of spintronics, have led to renewed interest in exploring the coupling between magnetism and electric fields. Although conventional magnetoelectric routes often result in weak responses, there is considerable current research activity focused on identifying new mechanisms for magnetoelectric coupling. Here we demonstrate a linear magnetoelectric effect that arises from a carriermediated mechanism, and is a universal feature of the interface between a dielectric and a spin-polarized metal. Using firstprinciples density functional calculations, we illustrate this effect at the SrRuO 3 /SrTiO 3 interface and describe its origin. To formally quantify the magnetic response of such an interface to an applied electric field, we introduce and define the concept of spin capacitance. In addition to its magnetoelectric and spin capacitive behaviour, the interface displays a spatial coexistence of magnetism and dielectric polarization, suggesting a route to a new type of interfacial multiferroic. J. M. RONDINELLI, M. STENGEL AND N. A. SPALDIN, Nanotechnology 3, 46 2008
Magnetoelectric effect at the SrRuO 3 /BaTiO 3 (001) interface: An ab initio study Manish K. Niranjan, J. D. Burton, J. P. Velev, S. S. Jaswal, and E. Y. Tsymbal APPLIED PHYSICS LETTERS 95, 052501 2009 Ferromagnet/ferroelectric interface materials have emerged as structures with strong magnetoelectric coupling that may exist due to unconventional physical mechanisms. Here we present a first- principles study of the magnetoelectric effect at the ferromagnet/ferroelectric SrRuO 3 /BaTiO 3 (001) interface. We find that the exchange splitting of the spin-polarized band structure, and therefore the magnetization, at the interface can be altered substantially by reversal of the ferroelectric polarization in the BaTiO 3. These magnetoelectric effects originate from the screening of polarization charges at the SrRuO 3 /BaTiO 3 interface and are consistent with the Stoner model for itinerant magnetism.
Preparation and enhanced photoluminescence property of ordered ZnO/TiO2 bottlebrush nanostructures C.W. Zou et al. / Chemical Physics Letters 476 (2009) 84–88 ZnO/TiO2 bottlebrush-like nanostructures have been prepared by a two-step process with facile hydrothermal method and magnetron sputtering technique. The bottlebrush heterostructures were formed due to the extremely low deposition rate of the magnetron sputtering process at room temperature and vapor–solid transformation mechanism dominates the TiO2 nanowires growth. This kind of bottlebrush heterostructures with a suitable length and density of covered TiO2 nanowires showed an enhanced photoluminescence property from TiO2 due to the resonant effect, which will offer great potential for photocatalysis applications.