|
 |
|
|
 |
 |
|
 |
|
 |
|
 |
|
 |
|
|
SurfInt
|
|
|
|
|
|
|
||||||||||||||||||
|
SurfInt |
||||||||||||||||||||||
|
|
|
|||||||||||||||||||||
|
|
PHYSICS AND CHEMISTRY OF SURFACES AND INTERFACES (SurfInt)
 Stefano Baroni Dario Alfe` Francesco Ancilotto Alfonso Baldereschi Nadia Bingelli Andrea Dal Corso Alberto Debernardi Pietro Decleva Xiangmei Duan Stefano Fabris Giovanna Fronzoni Ralph Gebauer Anton Kokalj Maria Peressi Giacinto Scoles Pierluigi Silvestrelli Mauro Stener Alessandro Stroppa Flavio Toigo Paolo GiannozziMain research lines:
Our purpose is to enhance basic knowledge and predictive tools in Surface Science, motivated by and usable for the design and engineering of new materials, devices, and processes. This will be achieved through the concerted effort of researchers with different backgrounds (Physics, Chemistry, Materials Engineering) and strong competence in computational techniques. While our motivation and choice of investigated systems come from the world of applied science and engineering, our approach will be mainly fundamental, focused on the atomic scale structure and dynamics of surfaces and interfaces. The detailed chemistry of solid-state surfaces determines the reactivity of many heterogeneous catalysts used in industrially relevant processes. Also, engineering complex materials and devices down to the nano-scale is strongly constrained by the properties of the intervening surfaces and interfaces, as the surface to bulk ratio increases with shrinking sizes. For these and many other reasons, solid-state surfaces are challenging systems for basic science, and an intense experimental effort is currently being devoted to the atomic-scale investigation of their properties. This involves both new microscopies and spectroscopies with atomic-scale resolution (STM/STS, AFM, etc.) and traditional spectroscopies and diffraction techniques (photo-emission, electron and neutron diffraction, etc.) benefitting from the high power and resolution of modern large-scale experimental facilities. Although the broad features of the experimental data can be often understood in terms of simple models and semi-empirical methods, modeling complex surface processes normally requires more sophisticated techniques, capable e.g., of dealing with changes of atomic coordination along chemical reaction paths. Among such techniques, the most appropriate are ab-initio methods based on density-functional theory (DFT), which are more flexible and almost as accurate as traditional quantum-chemistry methods, also thanks to ever improving new density functionals. The availability of massively parallel super-computers and of novel schemes to solve the single-particle Schrödinger equation presently make DFT applicable to system sizes up to a few hundred atoms. DFT-based applications extend nowadays to the study of dynamical properties (the Car-Parrinello method) and to the calculation of higher derivatives of the Born-Oppenheimer energy surface, necessary to calculate, e.g., vibrational frequencies (density-functional perturbation theory, DFPT). Electronic excitation processes still require adequate generalizations to be accounted for in an accurate and conceptually sound way. Time-dependent DFT (TDDFT) is among the most promising ways to do this. This technique, whose static limit is DFPT, will be used in the present activity to study photo-emission and photo-absorption, and enhanced to cope with periodic systems. Our expertise covers a broad variety of materials and properties, and, in particular, a wide and well documented experience in the numerical study of the structural, vibrational, electronic and chemical properties of metal- and semiconductor-based surfaces and interfaces. Many of us have been heavily involved in the development of new theoretical tools (such as e.g. DFPT for the study of lattice vibrations) and/or in the creation of sophisticated and flexible scientific software (such as the pseudo-potential-based PWSCF and PHONON packages, the Car-Parrinello LAUTREC code, or the LCAO-based TDDFT code). Our activity will be partly motivated by other activities in the Center (especially Nano ) and by collaborations with experimental groups. In turn, we expect to stimulate new experiments and produce basic knowledge useful to more technologically oriented activities. Synergies are foreseen with Hi-PT, especially concerning surface thermal properties, and with Hi-Corr to which we will provide motivation for the study of correlation effects in low dimensional structures. Our collaborations with experimental and/or other theoretical groups are very active, but still occasional. The creation of this CRS will provide a reference structure to consolidate these collaborations and systematically promote similar ones. Surfaces and interfaces are challenging systems both for DFT implementations (energy functionals) and for the computational methods. We expect significant progresses in these two areas, which will be of considerable interest for the other activities within the CRS and for the community outside. The IT-MC group will help us optimize, document, and disseminate the software produced within the present activity. 1 ADSORPTION, RECONSTRUCTION, AND CATALYSIS AT TRANSITION METAL SURFACES We will study the adsorption of atoms and molecules on transition metal surfaces, aiming at a microscopic understanding of the mechanisms governing heterogeneous catalysis. The main research topics will be (in parenthesis the starting projects): (i) role of steps, reconstruction, defects and promoters on the catalytic properties of surfaces (interaction of oxygen and ethylene on Ag(410) [1]); (ii) magnetic surfaces (non collinear effects on the adsorbates induced quenching of magnetism in Ni(110)[2]); (iii) vibrational and thermodynamical properties of chemisorbed system (calculation of the vibrational modes of a hydrocarbon on a transition metal surface [3], influence of thermal expansion on core-level shifts in Be(0001), vibrational broadening of Rh 3d XPS line). We will investigate some of these questions with experimental groups at ELETTRA and in Genoa with whom we are already working on the reduction of NO on Rh, and on the epoxidation of ethylene on Ag. 2 STRUCTURAL, ELECTRONIC, AND MAGNETIC PROPERTIES OF INTERFACES We aim at understanding and predicting the fundamental properties of solid/solid interfaces with special attention given to those of increasing technological interest for magneto-opto-electronic devices, starting from a wide expertise in more conventional interfaces. Synergies with line #1 and strong collaborations with experimental groups, particularly at TASC and ELETTRA, are foreseen. Collaboration with the TASC lab on cross-sectional STM is already the subject of an INFM-funded research project (PRA). Research will include: (i) vibrational and magnetic properties of semiconductor-based interfaces of interests for spintronic applications, such as MnAs on ZnSe and GaAs, NiMnSb/GaAs [4]; (ii) structural properties and electron localization at interfaces with non-crystalline materials (e.g., a-Si:H/c-Si interfaces); (iii) interface states and optical properties (e.g., reflectance anisotropy) of interfaces based on wide-gap semiconductors (e.g., GaN) of interest in visible opto-electronics and high-T/high-power electronics [5]; (iv) magnetic films and multilayers (initially: Fe on CuAu). 3 PHYSICS AND CHEMISTRY OF ORGANIC OVERLAYERS ON SEMICONDUCTOR SURFACES The fabrication of well-defined interfaces between semiconductor and organic materials will play a central role in emerging technological areas such as molecular electronics and biotechnology. Ideally organic layers chemisorbed on semiconductor surfaces should be crystalline and integrated with the existing microelectronics technology, which is mostly based on Silicon. We will study the growth of organic layers on the Si surfaces using state-of-the art ab initio techniques, integrated by large-scale modelizations based on semi-empirical potentials, with parameters derived from ab initio results. The ultimate goal will be to select from a variety of different functional groups those leading to novel physical and chemical properties of the organic-semiconductor system [6-8]. In the first 2 years we will start our research by studying the physical and chemical properties of different organic molecules chemisorbed on Si surfaces, and by formulating reliable models for the growth of organic films. 4 NUCLEATION AND GROWTH OF LOW-DIMENSIONAL INORGANIC STRUCTURES This line is devoted to the study of technologically important surface and interface processes and systems, often of biological interest, relevant to the fabrication of complex inorganic nano-structures. These include the nucleation of minerals at solid/liquid interfaces and on biological supports (biomineralisation [9]), and thin ceramic films grown on metal surfaces [10]. We shall study: (i) the chemistry of biocompatible implant surfaces (e.g., oxide or nitride coatings) relevant for tuning the nucleation and growth of bone tissue (apatites); (ii) the nucleation of metal or mineral phases on the surface of biological material, and how the material achieves control on growth; (iii) the structure and functionality of thin oxide films grown on transition metal surfaces. Each point will benefit from collaborations with the research staff of the present and other activities of the CRS, and from established collaborations with physicists, engineers, chemists, biologists and medical doctors active in the Trieste area and abroad. 5 LARGE SCALE SIMULATION OF ELECTRONIC EXCITATION AND PHOTOEMISSION We aim at simulating photo-absorption and photo-emission processes at surfaces using the the TDDFT approach, improving upon the expertise which we already have for large finite systems [11]. Applications to transition metal compounds will elucidate the electronic factors which govern the reactivity in catalytic and biological processes [12], like the activation of inert hydrocarbons by organo-metallic oxides, or the activity of the metal center in metallo-proteins. Interactions with the BioMod activity are foreseen. The fully parallel implementation of a new TDDFT algorithm will open the way of modeling surfaces using clusters of radius up to 1nm. In collaboration with Line 1 and using their expertise with DFPT we plan to implement this technique using repeated slab models and to apply it to molecules adsorbed on metal surfaces and heterogeneous catalysis. Other methodological improvements will include: TDDFT for open shells, alternative basis sets, use of the time-dependent Schrödinger equation, proper treatment of cluster termination, embedding techniques, optimal exploitation of advanced computational architectures. BIBLIOGRAPHY [1] M. Rocca et al. Phys. Rev. B 61, 231 (2000) [2] P. Morrall et al. Phys. Rev. B 64, 064407 (2001) [3] G. Held et al. Phys. Rev. Lett. 87, 216102 (2001) [4] R. Fitzgerald, Phys. Today 53, 21 (2000) [5] F.A. Ponce and D.P. Bour, Nature 386, 351 (1997) [6] Hamers et al., J. Phys. Chem. B 101, 1489 (1997) [7] J.S. Hovis et al., J. Vac. Sci. Technol. B 15, 1153 (1997) [8] R. Konecny et al., Surf. Sci. 417, 169 (1998) [9] C.A. Orme et al., Nature 411, 775 (2001) [10] I. Sebastian et al., Faraday Discuss. 144, 129 (1999) [11] H. Bachau et al., ROP, 2001, in press [12] T. Glaser et al., Acc. Chem. Res. 33, 859 |
|
|
|
||||||||||||||||||||||||||
|
|
|
INFM crs DEMOCRITOS
SISSA - Via Beirut 2-4 34014 Grignano, Trieste, ITALY Tel. +39 0403787443 Fax. +39 0403787528 |
|
|
|
webmaster: webadmin@democritos.it
|
![[X]](/immagini/busta.gif){kind=small}
