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Seminari  

Il Dipartimento di Fisica ospita Seminari di Dipartimento, Seminari organizzati dai gruppi di ricerca, e Physics Colloquia organizzati dalla Scuola di Dottorato.

I Seminari vengono inseriti nel Calendario.

Di seguito gli eventuali Seminari in programma nel mese in corso:

Seminari  
14/07/2017 Ore 11:00 - 13:00

Seminario di Dipartimento: Localisation of soft modes at the depinning transition di Alejandro B. Kolton

14 luglio 2017, ore 11, nell'aula Caldirola
Dipartimento di Fisica di Via Celoria 16

Speaker:
Alejandro B. Kolton, Condensed Matter Theory Group, Centro Atómico Bariloche (CAB) and Instituto Balseiro.
Bariloche, Argentina

The contact line of a liquid meniscus on a rough surface, vortices in a type II superconductor, domain walls in ferromagnetic or ferroelectric materials, fractures or amorphous solids under tension, friction between solids or tectonic plates, are some examples of systems that can flow only above a finite threshold drive at which a putative depinning transition takes place. The latter is usually characterized by intermittency and large avalanches of activity or “earthquakes” upon approaching the critical point. On the other hand, Anderson localization is usually associated to the specific quantum behaviour atomic or subatomic particles display in a random potential. In this talk I will show there is a nice and fruitful connexion between these two problems, for the paradigmatic case of driven elastic interfaces in random media [*].  

[*] X. Cao, S. Bouzat, A. Rosso, A. B. Kolton, arXiv:1705.10289 [cond-mat.dis-nn].

 

Info

web site of the Center for Complexity & Biosystems

Ezequiel Ferrero ezequiel.ferrero@unimi.it

07/07/2017 Ore 10:00 - 12:00

Seminario di Dipartimento: Understanding the adsorption of shuttle-cock shaped subphthalocyanine molecule on Cu(111) surface di Shashank S. Harivyasi

7 luglio 2017, ore 10, nell'aula riunioni della sezione Struttura della materia
Dipartimento di Fisica di Via Celoria 16

Speaker: Shashank S. Harivyasi, Graz University of Technology (Graz, Austria)

We know that the structure of an organic molecule plays a determining role in its adsorption on metal surface and on the subsequent interaction with it. For example, large planar molecules typically lie completely flat on most metal surfaces. However, the situation becomes more complex in case of non-planar molecules which show a varying tendency in planarization upon adsorption, depending mainly on the metal-molecule combination. Here, we try to understand these phenomena in a system that shows extreme behavior: adsorption of shuttle-cock shaped three-fold symmetric Chloroboron subphthalocyanine molecule on Cu (111) surface results in an almost complete planarization and considerable hybridization of molecular orbitals with metal electronic states, making this interface an interesting test-case for links between the two phenomena. Moreover, at sub-monolayer coverage, the adsorbed molecules aggregate into two separate phases that have different contrasts in the scanning tunneling microscopy (STM) and show different growth behavior.

In this talk, S. S. Harivyasi combines results from density-functional theory and from ultraviolet photospectroscopy & low-temperature STM to analyze the adsorption process as well as the interfacial geometry and electronic structure of the molecule onCu(111). Using DFT, we study the steps of the adsorption process by gradually increasing the van der Waals interaction (between the adsorbate and the substrate) and following the evolution of the molecule’s electronic and geometrical structure. We identify that the bonding of the molecule is a two-stage process involving Fermi-level pinning followed by a rehybridization of the molecule’s frontier orbitals. Especially the observed evolution of charge rearrangements help us to explain why we see an almost complete planarization. Further, by investigating different possible conformations and their energy costs and by comparing simulations and experiments, we deduce that the molecule on Cu(111) is susceptible to dechlorination. Since a majority but not all molecules undergo dechlorination, the overall result is a formation of the two different species that in turn lead to the formation of the two phases.

The results thus highlight the need to carefully consider what surface-mediated chemical processes might happen as well as how they happen.

 

Info
Guido Fratesi guido.fratesi@unimi.it

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