Heterostructure Modeling in Nanotechnology: Theory & Applications

1. 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)

2. . 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)

3. 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

4. Heterostructures sandwich-type 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.

5. 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. ‡ The coupling between TiO2 and SnO2 affects the electronic structure and it could be used to control and improve the superficial physical and chemical properties of these systems. ‡ (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, Nature433, 369 (2005)

6. Characterization of heterostructures TiO2@SnO2 SnO2/TiO2/SnO2 TiO2/SnO2/TiO2 Thickness (Å) of the used models J. Phys. Chem. A 112, 8943 (2008)

7. X´ M X G (a) (b) Eg = 3.24 eV Eg = 2.68 eV G X´ M X G G X´ M X G Eg = 2.57 eV Eg = 3.70 eV (c) (d) G X´ M X G G X´ M X G (110) TiO2 (a); SnO2 (b); SnO2/TiO2/SnO2 (c) and TiO2/SnO2/TiO2(d) (e)

8. X´ M X G Eg = 3.46 eV Eg = 3.55 eV (b) (a) G X´ M X G G X´ M X G Eg = 3.55 eV Eg = 3.75 eV (c) (d) G X´ M X G G X´ M X G (010) TiO2 (a); SnO2 (b); SnO2/TiO2/SnO2 (c) and TiO2/SnO2/TiO2(d) (e)

9. X´ M X G Eg = 3.44 eV (a) Eg = 2.77 eV (b) G X´ M X G G X´ M X G Eg = 3.22 eV Eg = 3.70 eV (c) (d) G X´ M X G G X´ M X G (101) TiO2 (a); SnO2 (b); SnO2/TiO2/SnO2 (c) and TiO2/SnO2/TiO2(d) (e)

10. X´ M X G Eg = 3.19 eV (a) Eg = 2.53 eV (b) G X´ M X G G X M X G Eg = 3.48 eV Eg = 2.76 eV (c) (d) G X´ M X G G X´ M X G (001) TiO2 (a); SnO2 (b); SnO2/TiO2/SnO2 (c) and TiO2/SnO2/TiO2(d) (e)

11. Characterization of heterostructures TiO2@SnO2

12. Caracterización heteroestructuras TiO2@SnO2 La parte superior de las bandas de Valencia (VB) vienen dominadas por las capas externas, esto es, por el TiO2 y el SnO2, 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 SnO2/TiO2/SnO2 en relación a su core TiO2, mientras que se encuentra la tendencia opuesta para las misma superficies en el TiO2/SnO2/TiO2 en relación a su core SnO2

13. Perspectives • Characterization of heterostructure SrZrO3/SrTiO3/SrZrO3 Sr Zr Ti (001) O

14. PZT 40/60 (1 0 0) (PbZrO3/PbTiO3/PbZrO3) • TiO2 ended • 9 layers model • PbO ended • 11 layers model Sites: 5 - 25 Sites : 8 - 18 Sites: 10 - 20 Sites: 3 – 23

15. Charge density PZT TiO2 ended SITES: 8 and 18 • plane TiO2 • plane PbO • 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

16. BAND STRUTURES PbO ended PT . PbO-ended: Gap: 3,99 eV GAP INDIRETO PZT -8-18 PbO-ended: Gap: 3,62 eV PZT -5-25. PbO-ended: Gap: 3,45 eV GAP INDIRETO GAP INDIRETO

17. BAND STRUTURES TiO2 ended PT . TiO2-ended: Gap: 3,84 eV DIRECT GAP PZT -3-23 TiO2-ended: Gap: 3.66 eV PZT -8-18 TiO2-ended: Gap: 4,41 eV INDIRECT GAP GAP INDIRETO INDIRECT GAP

18. PT- Ti PZT-Ti- 3-23 PZT-Ti -8-18

19. Two-Dimensional Confinement of 3d1 Electrons in LaTiO3/LaAlO3 Multilayers We report spectroscopic ellipsometry measurements of the anisotropy of the interband transitions parallel and perpendicular to the planes of (LaTiO3)n(LaAlO3)5 multilayers with n = 1–3. These provide direct information about the electronic structure of the two-dimensional (2D) 3d1 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 t2g states leaving only the planar dxy orbitals occupied. We outline that these multilayers can serve as a model system for the study of the t2g 2D Hubbard model. 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)

23. Oxygen octahedron reconstruction in the SrTiO3/LaAlO3 heterointerfaces investigated using aberration-corrected ultrahigh-resolution transmission electron microscopy We investigate the LaAlO3 /SrTiO3 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 SrTiO3 layer. Octahedra distortion leads to ferroelectricitylike dipole formation in the interface which is in addition modified by cation intermixing. C. L. Jia, S. B. Mi, M. Faley, U. Poppe, J. Schubert, and K. Urban PHYSICAL REVIEW B 79, 081405 2009

27. 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 SrRuO3/SrTiO3 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

30. Magnetoelectric effect at the SrRuO3 /BaTiO3(001) interface: An ab initio study 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 SrRuO3 /BaTiO3 (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 BaTiO3. These magnetoelectric effects originate from the screening of polarization charges at the SrRuO3 /BaTiO3 interface and are consistent with the Stoner model for itinerant magnetism. Manish K. Niranjan, J. D. Burton, J. P. Velev, S. S. Jaswal, and E. Y. Tsymbal APPLIED PHYSICS LETTERS 95, 052501 2009

33. Preparation and enhanced photoluminescence property of ordered ZnO/TiO2 bottlebrush nanostructures 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. C.W. Zou et al. / Chemical Physics Letters 476 (2009) 84–88