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Coverage-dependent study of nickel tetraphenyl-porphyrin on Au(332) and Au(788)(Surface Science, Elsevier BV, 2022-05-03) [Article]The coverage-dependent self-assembly of Nickel-tetraphenyl porphyins on Gold vicinal surfaces was studied by scanning tunneling microscopy. On Au(788) the molecular self-assembly is square-shaped, following the molecular symmetry. On Au(332) the molecules nucleate in a parallelogram lattice for monolayer coverage and in a squared lattice for multilayer coverage. Depending on the vicinal surface the molecules adopt either a saddle shaped or a more planar conformation. The experiments demonstrate that crystallographic direction, terrace sizes and coverage are important in establishing different assembly geometries.
Comment on “Electrical Switch of Poisson’s Ratio in IV–VI Monolayers via Pseudophase Transitions”(The Journal of Physical Chemistry Letters, American Chemical Society (ACS), 2022-04-28) [Article]Significant modulation of Poisson's ratio of IV-VI semiconductor monolayers in an electric field was claimed to be discovered by first-principles calculations in The Journal of Physical Chemistry Letters, 2021, 12, 3217-3223. We show that these results are not correct because of improper modeling of the electric field.
Computational study of the potential room-temperature superconductor carbonaceous sulfur hydride(2022-03-16) [Thesis]
Advisor: Schwingenschlögl, Udo
Committee members: Fatayer, Shadi; Anthopoulos, Thomas D.; Ghaffour, NorEddineResearch in superconductivity is heading towards overcoming the limitations imposed by extreme conditions, and promising candidates in this pursuit are superconductors made from hydrides. Carbonaceous Sulfur Hydride (CSH) was reported in Nature 586, 373-377 (2020) as a room-temperature superconductor in the pressure range of 140-267 GPa; however, there is controversy in the literature regarding these results. Here, we use density functional theory to confirm the hypothesis of Nature 596, E9-E10 (2021) that a metallic path is the reason for the sharp drop in resistance interpreted in Nature 586, 373-377 (2020) as indicative of a weak type 2 superconductor. We find that the metallic behavior of CSH is dominated by sulfur p-orbitals, and not by metallization of hydrogen. If CSH would be a superconductor, the predicted Ginzburg Landau parameter would be 1356.9, reflecting an unusually strong type 2 superconductor and thus contradicting the interpretation of Nature 586, 373-377 (2020). The fact that we find no metallic states below 220 GPa casts doubts on the onset of superconductivity at 140 GPa reported in Nature 586, 373-377 (2020). Additionally, the small fraction of active hydrogen density of states at the Fermi level shows that CSH is not a high-temperature superconductor.