| 1. |
- Daukiya, Lakshya, et al.
(författare)
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Covalent Functionalization by Cycloaddition Reactions of Pristine Defect-Free Graphene
- 2017
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 11:1, s. 627-634
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Tidskriftsartikel (refereegranskat)abstract
- Based on a low-temperature scanning tunneling microscopy study, we present a direct visualization of a cycloaddition reaction performed for some specific fluorinated maleimide molecules deposited on graphene. Up to now, it was widely admitted that such a cycloaddition reaction can not happen without pre-existing defects. However, our study shows that the cycloaddition reaction can be carried out on a defect-free basal graphene plane at room temperature. In the course of covalently grafting the molecules to graphene, the sp(2) conjugation of carbon atoms was broken, and local sp(3) bonds were created. The grafted molecules perturbed the graphene lattice, generating a standing-wave pattern with an anisotropy which was attributed to a (1,2) cycloaddition, as revealed by T-matrix approximation calculations. DFT calculations showed that while both (1,4) and (1,2) cycloadditions were possible on free-standing graphene, only the (1,2) cycloaddition could be obtained for graphene on SiC(0001). Globally averaging spectroscopic techniques, XPS and ARPES, were used to determine the modification in the elemental composition of the samples induced by the reaction, indicating an opening of an electronic gap in graphene.
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| 2. |
- Isvoranu, Cristina, et al.
(författare)
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Adsorption of ammonia on multilayer iron phthalocyanine.
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:11
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of ammonia on multilayers of well-ordered, flat-lying iron phthalocyanine (FePc) molecules on a Au(111) support was investigated by x-ray photoelectron spectroscopy. We find that the electron-donating ammonia molecules coordinate to the metal centers of iron phthlalocyanine. The coordination of ammonia induces changes of the electronic structure of the iron phthalocyanine layer, which, in particular, lead to a modification of the FePc valence electron spin.
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| 3. |
- Isvoranu, Cristina, et al.
(författare)
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Ammonia adsorption on iron phthalocyanine on Au(111): Influence on adsorbate-substrate coupling and molecular spin.
- 2011
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 134:11
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of ammonia on Au(111)-supported monolayers of iron phthalocyanine has been investigated by x-ray photoelectron spectroscopy, x-ray absorption spectroscopy, and density functional theory calculations. The ammonia-induced changes of the x-ray photoemission lines show that a dative bond is formed between ammonia and the iron center of the phthalocyanine molecules, and that the local spin on the iron atom is quenched. This is confirmed by density functional theory, which also shows that the bond between the iron center of the metalorganic complex and the Au(111) substrate is weakened upon adsorption of ammonia. The experimental results further show that additional adsorption sites exist for ammonia on the iron phthalocyanine monolayer.
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| 4. |
- Isvoranu, Cristina, et al.
(författare)
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Comparison of the Carbonyl and Nitrosyl Complexes Formed by Adsorption of CO and NO on Mono layers of Iron Phthalocyanine on Au(111)
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:50, s. 24718-24727
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between monolayers of iron phthalocyanine on a Au(111) support and carbon monoxide and nitric oxide is studied by X-ray photoelectron spectroscopy and density functional theory calculations. We find several carbon monoxide and nitric oxide adsorbate species, and in particular species that bind to the iron ions of the phthalocyanine compound. The formation of phthalocyanine carbonyl and nitrosyl complexes leads to a redistribution of the electrons in the iron 3d levels resulting in a change of the spin state. Further, the adsorption results in an electronic decoupling of the iron phthalocyanine adsorbates from the substrate. The extent of the spin change and adsorbate substrate decoupling depends on which ligand is used. The X-ray photoelectron spectroscopy results suggest that a covalent bond is formed between the NO and CO adsorbates and the FePc iron ion, and that the NO and CO valence states hybridize with metal ion d states. The density functional theory calculations show that CO adsorbs in a linear configuration, while NO adsorption assumes a tilted geometry.
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| 5. |
- Isvoranu, Cristina, et al.
(författare)
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Electron spectroscopy study of the initial stages of iron phthalocyanine growth on highly oriented pyrolitic graphite.
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:21
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Tidskriftsartikel (refereegranskat)abstract
- The nature of the intermolecular and substrate bonds of iron phthalocyanine adsorbed on highly oriented pyrolitic graphite has been investigated by x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. We find that the molecules grow in a highly ordered fashion with the molecules essentially plane-parallel to the surface in both the mono- and multilayers. The spectra obtained on both types of film are virtually identical, which shows that the bonds both between the adsorbate and substrate and between the molecular layers have a pure van der Waals nature. Supporting density functional theory results indicate that the layers are stabilized by weak hydrogen bonds within the molecular layers.
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| 6. |
- Isvoranu, Cristina, et al.
(författare)
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Pyridine Adsorption on Single-Layer Iron Phthalocyanine on Au(111)
- 2011
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 115:41, s. 20201-20208
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of pyridine on monolayers of well-ordered, flat-lying iron phthalocyanine molecules on Au(111) is investigated by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and density functional theory. It is found that pyridine both coordinates to the iron site of iron phthalocyanine and binds weakly to other sites. The iron coordination causes significant changes in the electronic structure of the iron phthalocyanine compound, with the implication of a change of the spin properties of the iron atoms due to the strong ligand field created by the pyridine axial ligand. Both low coverages and multilayer coverages of pyridine are considered. At low doses, the pyridine molecules are ordered, whereas in multilayers, no preferred orientation is observed. The orientation of the FePc molecules with respect to the Au(111) surface is not affected by the adsorption of pyridine.
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| 7. |
- Snezhkova, Olesia, et al.
(författare)
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Nature of the bias-dependent symmetry reduction of iron phthalocyanine on Cu(111)
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:7
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Tidskriftsartikel (refereegranskat)abstract
- Subtle changes in the geometric and electronic properties of supported molecules, with a potential impact on the functioning of molecular devices, can typically be imaged by scanning probe microscopy, but their exact origin and nature often remain unclear. Here we show explicitly that the symmetry reduction of iron phthalocyanine upon adsorption on Cu(111) can be observed not only in scanning tunneling microscopy, but also in core-level spectroscopy, and that it is related to nonisotropic charge transfer into the two principal molecular axes, but in combination with topographic influences.
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