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- Almgren, Magnus, 1972, et al.
(författare)
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Mapping Systems Security Research at Chalmers
- 2011
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Ingår i: First SysSec Workshop (SysSec 2011). - 9780769545301 ; , s. 67-70
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Konferensbidrag (refereegranskat)abstract
- The department of Computer Science and Engineering at Chalmers University has a long tradition of research in systems security, including security metrics, attack detection, and mitigation. We focus on security issues arising in four specific environments: (1) backbone links, (2) sensor networks, (3) the connected car, and (4) the smart grid. In this short summary we describe recent results as well as open research questions we are exploring.
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| 3. |
- Baran, Jakub D., et al.
(författare)
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A Case of Unusually Large Density of States Changes For Physisorption - TetraPhenyl-Porphyrins on Cu(111)
- 2015
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Conformational changes caused by surface adsorption can dramatically affect a molecule’s properties. The conformational flexibility of the porphyrin family of molecules has been exploited particularly well in a number of contexts, including prototypical molecular switches. Despite this level of study, however, the exact mechanisms underpinning conformational switching are often unclear. We show that the conformation of the tetra(4-bromophenyl) porphyrin (Br4TPP) on Cu(111) depends critically on the precise adsorption site of the molecule, and that, remarkably, large conformational changes are driven entirely by van der Waals (vdW) interactions between the molecule and the substrate surface. A combination of scanning probe microscopy, low temperature single molecule manipulation, dispersion-corrected density functional theory (DFT) and molecular dynamics (MD) simulations shows that van der Waals forces dominate the adsorption of TPP molecules, causing significant distortions of the molecular architecture so that the porphyrin can adopt one of two low energy conformations. In addition, scanning probe manipulation has been used to translate and switch the Br4TPP molecule between conformations via an intermediary, ‘hybrid’ structure. We have used the generalized gradient approximation (GGA) parameterization by Perdew—Burke—Ernzerhof (PBE), and the sparse-matter optBP86b-vdW20 (vdW-DFT) exchange and correlation functional to account for the missing dispersion forces. In order to check for the presence of chemical bonding we have analyzed the molecule-surface complexes using electron localization function (ELF) and Bader charges. We find that vdW-forces alone are capable of causing large shifts in the molecular density of states, despite the complete absence of chemical interactions.
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| 6. |
- Baran, Jakub D., et al.
(författare)
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Density Functional Study of Metal-Phthalocyanines Interactions With a Silver Surface Ag(111).
- 2007
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Konferensbidrag (refereegranskat)abstract
- Metal phthalocyanines (MPc) are generally planar organic molecules comprising of a central metal atom surrounded by aromatic rings. Phthalocyanines are structurally similar to important biomolecules such as haemoglobin and chlorophyll and are commonly used in industry for pigmentation. They have been the focus of intense interest due to their electrical and (non-linear) optical properties. Deposited and/or slef-assembled on metal electrodes, phthalocyanines are attractive candidates for novel molecular sensors, memory, and light-harvesting components. Fundamental understanding of molecule-molecule and molecule-surface interaction is important when attempting to determine the charge transport characteristics of metal phthalocyanines. The most important are the interactions between first layer adsorbate molecules and the substrates, since these interactions determine the structural ordering of the organic films and therefore also have a considerable impact on the efficiency of optical, electronic, and magnetic properties of the system. To study the adsorption of metal-phthalocyanines (MPc (M=Co, Sn, Pb) on the Ag(111) surface we have performed electronic structure calculations using a cluster representation of the surface within the framework of density functional theory (DFT) [1]. Our calculations use the generalized gradient approximation (GGA) parameterization by Pedrew-Burke-Ernzerhof (PBE) for the exchange-correlation energy [2]. We have investigated bonding on three surface adsorption sites (hcp-hollow, fcc-hollow and on-top). SnPc was found to adsorb weakly to the surface, and to prefer hollow bonding rather than on-top bonding. The distance between the Sn atom and the top layer Ag-surface atoms (hcp-hollow and fcc-hollow) is consistent with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [3,4]. Adsorption of CoPc was found very site specific and to prefer the on-top binding site. The distance between the Co atom and the top layer Ag atoms is ~3 . For PbPc, successful adsorption was only obtained on the hcp-hollow site. For SnPc and PbPc binding energy is small fraction of eV, however CoPc bind much strongly to Ag(111) .For each of these systems we have found good agreement in binding geometries with experimental data
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| 7. |
- Baran, Jakub D., et al.
(författare)
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DFT Computation Of Metal-Phthalocyanines Bonded To Ag(111)
- 2007
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Konferensbidrag (refereegranskat)abstract
- To study the adsorption of metal-phthalocyanines (MPc (M=Co; Sn; Pb) on the Ag(111) surface we have performed electronic structure calculations using a cluster representation of the surface within the framework of density functional theory (DFT) [1]. Our calculations use the generalized gradient approximation (GGA) parameterization by Pedrew-Burke-Ernzerhof (PBE) for the exchange-correlation energy [2]. We have investigated bonding on three surface adsorption sites (hcp-hollow; fcc-hollow and on-top). SnPc was found to adsorb weakly to the surface (0.15 to 0.25 eV); and to prefer hollow bonding rather than on-top bonding. The distance between the Sn atom and the top layer Ag-surface atoms (hcp-hollow and fcc-hollow) is consistent with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [3;4]. CoPc is much more strongly bound to the Ag(111) surface and was found to prefer the on-top site. The calculated binding energy is 1.2 eV and the distance between the Co atom and the top layer Ag atoms is 3 (which also matched the experimental data well). For PbPc; successful adsorption was only obtained on the hcp-hollow site with a binding energy of 0.5 eV. For each of these systems we have found good agreement in binding geometries with experimental data.
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| 9. |
- Baran, Jakub D., et al.
(författare)
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Interactions of Metal-phthalocyanines MPc (M=Co; Sn; Pb) with Silver Surface Ag(111) : A Density Functional Study
- 2008
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Konferensbidrag (refereegranskat)abstract
- Deposited and/or self-assembled on metal electrodes; metal-phthalocyanine are attractive candidates for novel molecular sensors; memory; and light-harvesting components. The knowledge of the their molecular geometry and electronic structure are crucial points in order to understand their interactions with surfaces. To study the adsorption of metal-phthalocyanines (MPc (M=Co; Sn; Pb) bonded parallel on the Ag(111) surface we have performed electronic structure calculations using a cluster representation (55 and 169 silver atoms) of the surface within the framework of density functional theory (DFT) [1]. Our calculations use the generalized gradient approximation (GGA) parameterization by Pedrew-Burke-Ernzerhof (PBE) for the exchange-correlation energy [2] and multipole accelerated resolution of identity method [3]. We have investigated bonding on three surface adsorption sites (hcp-hollow; fcc-hollow and on-top). For each of these systems we have found good agreement in binding geometries with experimental data obtained by normal incidence X-ray standing wave spectroscopy (NIXSW) [4;5]. Binding energies and geometries for all systems are given. We propose flat chemisorption of respective MPcs on Ag(111).
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