| 1. |
- Simonov, K. A., et al.
(author)
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Synthesis of armchair graphene nanoribbons from the 10,10′-dibromo-9,9′-bianthracene molecules on Ag(111) : The role of organometallic intermediates
- 2018
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
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Journal article (peer-reviewed)abstract
- We investigate the bottom-up growth of N = 7 armchair graphene nanoribbons (7-AGNRs) from the 10,10′-dibromo-9,9′-bianthracene (DBBA) molecules on Ag(111) with the focus on the role of the organometallic (OM) intermediates. It is demonstrated that DBBA molecules on Ag(111) are partially debrominated at room temperature and lose all bromine atoms at elevated temperatures. Similar to DBBA on Cu(111), debrominated molecules form OM chains on Ag(111). Nevertheless, in contrast with the Cu(111) substrate, formation of polyanthracene chains from OM intermediates via an Ullmann-type reaction is feasible on Ag(111). Cleavage of C-Ag bonds occurs before the thermal threshold for the surface-catalyzed activation of C-H bonds on Ag(111) is reached, while on Cu(111) activation of C-H bonds occurs in parallel with the cleavage of the stronger C-Cu bonds. Consequently, while OM intermediates obstruct the Ullmann reaction between DBBA molecules on the Cu(111) substrate, they are required for the formation of polyanthracene chains on Ag(111). If the Ullmann-type reaction on Ag(111) is inhibited, heating of the OM chains produces nanographenes instead. Heating of the polyanthracene chains produces 7-AGNRs, while heating of nanographenes causes the formation of the disordered structures with the possible admixture of short GNRs.
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| 2. |
- Svirskiy, Gleb I, et al.
(author)
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Electronic structure of nickel porphyrin NiP : Study by X-ray photoelectron and absorption spectroscopy
- 2017
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In: Physics of the Solid State. - 1063-7834. ; 59:2, s. 368-377
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Journal article (peer-reviewed)abstract
- Energy distributions and properties of the occupied and empty electronic states for a planar complex of nickel porphyrin NiP are studied by X-ray photoemission and absorption spectroscopy techniques. As a result of the analysis of the experimental spectra of valence photoemission, the nature and energy positions of the highest occupied electronic states were determined: the highest occupied state is formed mostly by atomic states of the porphine ligand; the following two states are associated with 3d states of the nickel atom. It was found that the lowest empty state is specific and is described by the σ-type b1g MO formed by empty Ni3dx2−y2-states and occupied 2p-states of lone electron pairs of nitrogen atoms. This specific nature of the lowest empty state is a consequence of the donor–acceptor chemical bond in NiP.
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| 3. |
- Krasnikov, S. A., et al.
(author)
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An X-ray absorption and photoemission study of the electronic structure of Ni porphyrins and Ni N-confused porphyrin
- 2008
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In: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 20:23, s. 1-235207
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Journal article (peer-reviewed)abstract
- Investigations of chemical bonding and electronic structure features for polycrystalline (porphyrinato)nickel (II) (NiP, the simplest Ni porphyrin), (5,10,15,20-tetraphenylporphyrinato)nickel (II) (NiTPP) and (2-aza-21-carba-5,10,15,20-tetraphenylporphyrinato)nickel (II) (N-confused NiTPP, NiNCTPP) have been performed by means of high-resolution soft x-ray absorption and x-ray photoemission spectroscopy. The Ni 2p3/2 x-ray absorption spectra show strong pi-back-bonding in these compounds leading to a high-energy shift (1.2 eV for the NiP and NiTPP) of the entire absorption structure compared to Ni metal. It has been found that the main absorption line of the Ni 2p3/2 spectrum of the NiNCTPP is shifted by an additional 0.5 eV to higher energies in comparison with those for other nickel porphyrins. This shift is evidence of stronger back-donation (metal-to-ligand charge transfer) and a smaller effective number of 3d electrons on the central Ni atom in the NiNCTPP as compared to other Ni porphyrins. The confused N atom in the NiNCTPP is of pyrrolic type (protonated nitrogen), which was confirmed by the N 1s absorption and core-level photoemission spectra.
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| 4. |
- Krasnikov, S. A., et al.
(author)
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Electronic structure of Ni(II) porphyrins and phthalocyanine studied by soft X-ray absorption spectroscopy
- 2007
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In: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 332:2-3, s. 318-324
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Journal article (peer-reviewed)abstract
- Investigations of chemical bonding and electronic structure features for polycrystalline Ni(II) phthalocyanine (NiPc), Ni(II) tetrabenzoporphyrin (NiTBP), Ni(II) 2,3,7,8,12,13,17,18-octaethylporphyrin (NiOEP), Ni(II) 5,10,15,20-tetraisobutylporphyrin (NiTiBuP), Ni(II) 5,15-diphenylporphyrin (NidPP) and Ni(II) 5,15-diisobutylporphyrin (NidiBuP) have been performed by means of high-resolution soft X-ray absorption spectroscopy. It has been found that the low-lying unoccupied electron states in nickel porphyrins are mainly generated by the NiN4 quasi-molecule: the lowest empty state is the weakly antibonding molecular orbital (MO) of sigma b(1g), symmetry with nearly pure Ni 3d(x2-y2) character, while the next empty state is the e(g) MO, which has a hybridized Ni 3d pi-N 2p pi character and reflects pi chemical bonding (pi-back-donation) between nickel and neighbouring nitrogen atoms of the pyrrole rings. The differences observed in the Ni 2p spectra of nickel porphyrins and phthalocyanines indicate a limited usefulness of the NiN4 quasi-molecule and a need for its extension to the whole porphyrin (phthalocyanine) macrocycle. As a result, the differences in the Ni 2p spectra of the complexes and in their electronic structure are associated with a torsion of the opposite pyrrole ring planes (NiOEP, NiTiBuP) and the presence of N atoms in meso positions (NiPc). These conclusions are further confirmed by a comparative analysis of the Ni 2p and N Is absorption spectra for NiPc and NiOEP. (c) 2007 Elsevier B.V. All rights reserved.
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| 5. |
- Preobrajenski, Alexei, et al.
(author)
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Adsorption-induced gap states of h-BN on metal surfaces
- 2008
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:8, s. 085421-
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Journal article (peer-reviewed)abstract
- The formation of hexagonal boron nitride (h-BN) monolayers on Ni(111), Rh(111), and Pt(111) has been studied by a combination of x-ray emission, angle-resolved valence band photoemission, and x-ray absorption in search for interface-induced gap states of h-BN. A significant density of both occupied and unoccupied gap states with N 2p and B 2p characters is observed for h-BN/Ni(111), somewhat less for h-BN/Rh(111) and still less for h-BN/Pt(111). X-ray emission shows that the h-BN monolayer is chemisorbed strongly on Ni(111) and very weakly on Pt(111). We associate the gap states of h-BN adsorbed on the transition metal surfaces with the orbital mixing and electron sharing at the interface because their density increases with the growing strength of chemisorption.
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| 6. |
- Baran, J. D., et al.
(author)
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Theoretical and experimental comparison of SnPc, PbPc, and CoPc adsorption on Ag(111)
- 2010
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In: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121 .- 1550-235X. ; 81:7
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Journal article (peer-reviewed)abstract
- A combination of normal-incidence x-ray standing-wave (NIXSW) spectroscopy, x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density-functional theory (DFT) has been used to investigate the interaction of a number of phthalocyanine molecules (specifically, SnPc, PbPc, and CoPc) with the Ag(111) surface. The metal-surface distances predicted by the DFT calculations for SnPc/Ag(111) (2.48 angstrom) and CoPc/Ag(111) (2.88 angstrom) are in good agreement with our NIXSW experimental results for these systems (2.31 +/- 0.09 and 2.90 +/- 0.05 angstrom, respectively). Good agreement is also found between calculated partial density-of-states plots and STM images of CoPc on Ag(111). Although the DFT and Pb 4f NIXSW results for the Pb-Ag(111) distance are similarly in apparently good agreement, the Pb 4f core-level data suggest that a chemical reaction between PbPc and Ag(111) occurs due to the annealing procedure used in our experiments and that the similarity of the DFT and Pb 4f NIXSW values for the Pb-Ag(111) distance is likely to be fortuitous. We interpret the Pb 4f XPS data as indicating that the Pb atom can detach from the PbPc molecule when it is adsorbed in the "Pb-down" position, leading to the formation of a Pb-Ag alloy and the concomitant reduction in Pb from a Pb2+ state (in bulklike films of PbPc) to Pb-0. In contrast to SnPc, neither PbPc nor CoPc forms a well-ordered monolayer on Ag(111) via the deposition and annealing procedures we have used. Our DFT calculations show that each of the phthalocyanine molecules donate charge to the silver surface, and that back donation from Ag to the metal atom (Co, Sn, or Pb) is only significant for CoPc.
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| 7. |
- Mazzola, F., et al.
(author)
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Graphene coatings for chemotherapy: avoiding silver-mediated degradation
- 2015
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In: 2d Materials. - : IOP Publishing. - 2053-1583. ; 2:2
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Journal article (peer-reviewed)abstract
- Chemotherapy treatment usually involves the delivery of fluorouracil (5-Fu) together with other drugs through central venous catheters. Catheters and their connectors are increasingly treated with silver or argentic alloys/compounds. Complications arising from broken catheters are common, leading to additional suffering for patients and increased medical costs. Here, we uncover a likely cause of such failure through a study of the surface chemistry relevant to chemotherapy drug delivery, i.e. between 5-Fu and silver. We show that silver catalytically decomposes 5-Fu, compromising the efficacy of the chemotherapy treatment. Furthermore, HF is released as a product, which will be damaging to both patient and catheter. We demonstrate that graphene surfaces inhibit this undesirable reaction and would offer superior performance as nanoscale coatings in cancer treatment applications.
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| 8. |
- Murphy, B. E., et al.
(author)
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Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED
- 2012
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In: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 24:4
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Journal article (peer-reviewed)abstract
- The room temperature self-assembly and ordering of (5,15-diphenylporphyrinato) nickel(II) (NiDPP) on the Ag(111) and Ag/Si(111)-(root 3 x root 3)R30 degrees surfaces have been investigated using scanning tunnelling microscopy and low-energy electron diffraction. The self-assembled structures and lattice parameters of the NiDPP monolayer are shown to be extremely dependent on the reactivity of the substrate, and probable molecular binding sites are proposed. The NiDPP overlayer on Ag(111) grows from the substrate step edges, which results in a single-domain structure. This close-packed structure has an oblique unit cell and consists of molecular rows. The molecules in adjacent rows are rotated by approximately 17 degrees with respect to each other. In turn, the NiDPP molecules form three equivalent domains on the Ag/Si(111)-(root 3 x root 3)R30 degrees surface, which follow the three-fold symmetry of the substrate. The molecules adopt one of three equivalent orientations on the surface, acting as nucleation sites for these domains, due to the stronger molecule-substrate interaction compared to the case of the Ag(111). The results are explained in terms of the substrate reactivity and the lattice mismatch between the substrate and the molecular overlayer.
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| 9. |
- Ng, May Ling, et al.
(author)
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Effect of substrate nanopatterning on the growth and structure of pentacene films
- 2010
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In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:11, s. 115449-
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Journal article (peer-reviewed)abstract
- The effect of modulating the structure of thin pentacene (C22H14) films by a nanopatterned inert substrate, known as hexagonal boron nitride nanomesh, is reported. Films of different thickness are grown and characterized by x-ray absorption, core-level photoemission, low-energy electron microscopy, microbeam low-energy electron diffraction, and scanning tunneling microscopy. Initially the pentacene molecules adsorb with the molecular plane lying flat on the substrate but they tend to flip up with increasing coverage, forming well-ordered monolayer-thick islands of upright molecules with low nucleation density. The herringbone packing of the upright molecules is observed with scanning tunneling microscopy. The electronic structure of the adsorbed molecules is very similar to that of the gas-phase pentacene, implying weak interaction with the substrate and between the molecules. The periodic corrugation of the substrate surface causes the monolayer of upright pentacene molecules to form two different coincidence superstructures. The lattice parameters of the pentacene unit cell for each of these two substrate-induced domains are determined from the microdiffraction patterns. Both domains can occur in several equivalent configurations, thus resulting in a number of twins with a typical size of a few micrometers. The first monolayer grows in a layer-by-layer mode until it is completed while the second monolayer forms diffusion-limited fractal islands. Upon annealing, the pentacene films are thermally stable up to approximately 80 degrees C and thereafter the onset of desorption is observed.
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| 10. |
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