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MODELING THE WORLD OF NANOSCIENCE (NANO)
 Erio Tosatti Furio Ercolessi Santi Prestipino Giuseppe Santoro Ugo Tartaglino Malgorzata Wierzbowska Marco Bernasconi Davide Ceresoli Anna Delin Michele Fabrizio Annalisa Fasolino Eduardo Jagla Nicola Manini Daniele Passerone Bo Persson Fabien Picaud Wassila Sekkal Alexander Smogunov Ruben WethMain research lines:
The planned action of this research line will be the computational and theoretical modeling of nanoscience and nanotechnology-related physics problems, chosen among the most interesting and relevant ones. The modeling will employ all the modern methods of computational condensed matter theory at the state-of-the-art level. Simulation by classical molecular dynamics and Monte Carlo methods, one of the strong points in Trieste, is particularly suitable at the nanoscopic level. Ab initio electronic structure calculations and Car-Parrinello simulations, another strong point, will be employed when electrons are explicitly relevant. Strong electronic correlations, which develop easily at the nanoscopic level, can in addition be modeled adequately given the high level of local expertise. 1 PROPERTIES OF METAL NANOWIRES Metal nanowires are a hot experimental subject. The reasons why certain metals can yield monatomic nanowires is not well understood [1] and will be investigated, as well as those leading to chiral nanowires [2] and their consequences. The onset of dissipation in monatomic wires [3], and the possibility of nanowire magnetism, so far only hypothetical [4] offer new routes. Building on existing theoretical approaches [4,5,6,7] we wish to move on to the new problems, the goal being the full relationship between nanocontact mechanics and electrical conduction. We also aim at building a new computer code for ballistic conductance calculations in collaboration with the Milano Bicocca group (Bernasconi), and to interact strongly with the experimental groups at TASC/Elettra (Di Fabrizio, Modesti). The electronic structure expertise of the CRS SurfInt activity will be important. 2 NANOFRICTION AND ADHESION Friction involving metal is both electronic and atomic in nature. The role of electronic friction as measured by its disappearance at the superconducting transition [8] is a controversial issue [9] that can be addressed computationally. The mechanical, atomic friction is particularly interesting between incommensurate monolayers. We plan modeling and simulating that friction microscopically, both between metal monolayers, and in the more common case of inert atom or lubricant molecule layers on a metal substrate [10]. Nanoadhesion is a second promising front. The pull-off force between two bodies is dominated by the nanoscale rugosity at the interface, and new phase transitions have been identified as a function of that [11] . We expect a cooperation with the Modena surface computational group (Santoro, Bortolani), and with the Genova (Valbusa, Buatier), and Padova (Mistura) experimental groups, presently SISSA partner groups in a small-scale project INFM PRA, and to start newer ones, both at national level with Elettra groups (Carbone), and international with Nijmegen (Fasolino). A European network led by E. Meyer (Basel) is also being discussed. The local scientific mass in SISSA is presently small, and will be built up also with the help of the other components of this CRS. 3 MODELING OF FIELD-EFFECT FULLERENE AND ORGANIC MONOLAYER DEVICES Unveileing the nanoscale physics behind the spectacular field-effect monolayer devices based on fullerene, pentacene, and other organics of Batlogg, Schoen et al. [12] is an urgent open problem. The nanoscale charge distribution, the presence of the field, and the delicate low-frequency librations will need the development of specifically accurate ab-initio codes. Under the new human and computational umbrella provided by the CRS, we believe we can, based also on previous experience on organic insulator surfaces [13], accomplish that. We also plan to address superconductivity, particularly the stunning 117 K seen in positively doped fullerene [14], a problem where we have already made an entry [15,16]. Collaboration on fullerenes with the Milan groups (Manini, Bernasconi), with the Zurich experimental group (Batlogg), and with the QMC CRS research activity is envisaged and will be important. 4 SIMULATION OF THERMAL AND STRAIN-INDUCED TRANSITIONS AT SURFACES AND CLUSTERS Local strain and/or small size can drive phase transitions at crystal surfaces, including changes of reconstructions, enhanced melting and prewetting, etc. Simulation methods demonstrating size-induced premelting of clusters [17] and strain-induced surface reconstruction/deconstruction [18] are well developed and ready to be exploited. Special phenomena which await exploration in nanophysics are surface freezing, hystorically observed in the alkanes [19], and surface nonmelting, common in metals [20]: both permit the survival of small clusters in their solid form above the bulk melting point, which does not occur in ordinary circustances. Simulation studies of clusters and surfaces, made up of materials that possess surface freezing and surface nonmelting are being planned within this line. An investigation of the solid-liquid interface will also be possible. Recent applications of reaction-induced surface bending of protein-coated metal lamellae are already existent in the area of biomolecular nanomechanical systems [21] and we consider simulating them. This sub-project is entirely based on temporary investigators and postdocs, and will benefit from the long-term researcher position for its full implementation and support. External collaboration is envisaged with european (Passerone, Manno; Persson, Juelich), and extra-european groups (Jagla, Bariloche). REFERENCES [1] Common Origin for Surface Reconstruction and the Formation of Chains of Metal Atoms , R.H.M. Smit, C. Untiedt, A.I. Yanson, J.M. van Ruitenbeek, cond-mat/0106641. [2] Synthesis and characterization of helical multi-shell gold nanowires Y.Kondo and K. Takayanagi, Science 289, 606 (2000); Weird Gold Nanowires , E. Tosatti and S. Prestipino, Science 289, 561 (2000). [3] Onset of dissipation in ballistic atomic wires N. Agrait, C. Untiedt, G. Rubio-Bollinger, S. Vieira, cond-mat/0110601. [4] Selective d-state Conduction Blocking in Nickel Nanocontacts , A. Smogunov, A. Dal Corso, and E. Tosatti, cond/mat 0111376, to appear on Surface Science. [5] Structure and Evolution of a Metallic Nanowire-Tip Junction , E.A. Jagla and E. Tosatti, Phys. Rev. B 64, 205412 (2001). [6] String Tension and Stability of Magic Tip-Suspended Nanowires , E. Tosatti, S. Prestipino, S. Kostlmeier, A. Dal Corso, and F. Di Tolla, Science, 291, 288 (2001). [7] Non-crystalline structures of Ultra-Thin Unsupported Nanowires , O. Gulseren, F. Ercolessi, and E. Tosatti, Phys. Rev. Lett. 80, 3775 (1998). [8] Superconductivity-dependent sliding friction A.Dayo, W. Alnasrallah, and J. Krim, Phys. Rev. Lett. 80, 1690 (1998). [9] The Puzzling Collapse of Electronic Sliding Friction on a Superconductor Surface , B.N.J. Persson, E. Tosatti, Surface Sci. 411, L855 (1998). [10] Dynamical Phase Transitions in the Nanofriction of Kr Films on Gold , L. Bruschi, A. Carlin, and G. Mistura, Phys. Rev. Lett., to appear (2001). [11] The effect of surface roughness on the adhesion of elastic solids , B.N.J. Persson and E. Tosatti, J. Chem. Phys. 115, 5597 (2001). [12] See, e.g., Ambipolar pentacene field-effect transistors and inverters , J.H. Schoen, S. Berg, C. Kloc C, and B. Batlogg, Science 287, 1022 (2000). [13] Surface States and Negative Electron Affinity in Polyethylene , M.C. Righi, S. Scandolo, S. Serra, S. Iarlori, E. Tosatti, and G. Santoro, Phys. Rev. Letters 87, 076802-1 (2001). [14] High-temperature superconductivity in lattice-expanded C-60 J.H. Schoen, C. Kloc, B. Batlogg, Science 293, 2432 (2001). [15] Electron--vibration coupling constants in positively charged fullerene , N. Manini, A. Dal Corso, M. Fabrizio, and E.Tosatti, Phil. Mag. B 81, 793 (2001). [16] Direct Transition Between a Singlet Mott Insulator and a Superconductor , M. Capone, M. Fabrizio and E. Tosatti, Phys. Rev. Letters 86, 5361 (2001). [17] Melting of small gold particles: mechanism, and size effects , F.Ercolessi, W. Andreoni, and E. Tosatti, Phys. Rev. Lett. 66, 911 (1991); [18] Strain-driven transitions between surface reconstructions U.Tartaglino, E.Tosatti, D.Passerone, and F.Ercolessi, cond-mat/0110576. [19] Surface crystallization of liquid normal-alkanes , X. Z. Wu, E. B. Sirota, S. K. Sinha, B. M. Ocko, and M. Deutsch, Phys. Rev. Lett. 70, 958-961 (1993). [20] Anharmonicity but Absence of Surface Melting on Al(001) , A.M. Molenbroek, J.W.M. Frenken, Phys. Rev. B 50, 11132 (1994). [21] Translating biomolecular recognition into nanomechanics , J. Fritz, M.K.Baller, H.P.Lang, H.Rothuizen, P.Vettiger, E.Meyer, H.J. Guntherodt, C.Gerber, and J.K.Gimzewski, Science 288, 316 (2000). |
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