| 1. |
- Svirskiy, G. I., et al.
(författare)
-
Comparative X-Ray Absorption Analysis of the Spectrum of Vacant Electronic States in Cobalt and Nickel Tetraphenylporphyrin Complexes
- 2018
-
Ingår i: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 60:3, s. 581-591
-
Tidskriftsartikel (refereegranskat)abstract
- The energy distributions and the properties of the lower vacant electronic states in cobalt and nickel tetraphenylporphyrin complexes CoTPP and NiTPP are studied by X-ray absorption spectroscopy. Quasimolecular analysis of the experimental absorption spectra measured in the region of the 2p and 1s ionization thresholds of complexing metal atoms, as well as the 1s thresholds of ligand atoms (nitrogen and carbon), is based on the comparison of the corresponding spectra with each other and with the spectra of the simplest nickel porphyrin NiP. It has been established that, despite a general similarity of the spectra of nitrogen and carbon in CoTPP and NiTPP, the fine structure of the 2p and 1s absorption spectra of cobalt and nickel atoms are radically different. The observed differences in the spectra of cobalt and nickel are associated with the features of the energy distribution of vacant 3d electron states. The presence in CoTPP of the partially filled valence 3db2g molecular orbital (MO) results in the appearance in the cobalt spectra of a low-energy band, which is absent in the spectrum of nickel in NiTPP and leads to a doublet structure of transitions to b1g and e g MOs due to the exchange interaction between 3d electrons in partially filled 3db2g and 3db1g or 3de g MOs. The spectrum of vacant states in CoTPP differs from that in NiTPP also due to the smaller energy distance between 3db1g and e g MOs and the different positions of nonbonding MOs with the C2p character of the porphine ligand.
|
|
| 2. |
- Svirskiy, Gleb I, et al.
(författare)
-
Electronic structure of nickel porphyrin NiP : Study by X-ray photoelectron and absorption spectroscopy
- 2017
-
Ingår i: Physics of the Solid State. - 1063-7834. ; 59:2, s. 368-377
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 3. |
- Dedkov, Y S, et al.
(författare)
-
Correlations in the electronic structure of half-metallic ferromagnetic CrO2 films: An x-ray absorption and resonant photoemission spectroscopy study
- 2005
-
Ingår i: Physical Review B (Condensed Matter and Materials Physics). - 1098-0121. ; 72:6
-
Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of high-quality CrO2(100) films was investigated by means of x-ray absorption and resonant photoemission spectroscopy at the 2p-3d excitation threshold. The obtained binding energy of the occupied Cr 3d states is in agreement with the results predicted within the local spin-density approximation using the dynamical mean-field theory [L. Craco , Phys. Rev. Lett. 90, 237203 (2003)]. The reported data support a model of CrO2 as a half-metallic ferromagnet with strong electron-correlation effects.
|
|
| 4. |
- Krasnikov, S. A., et al.
(författare)
-
An X-ray absorption and photoemission study of the electronic structure of Ni porphyrins and Ni N-confused porphyrin
- 2008
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 20:23, s. 1-235207
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 5. |
- Krasnikov, S. A., et al.
(författare)
-
Electronic structure of Ni(II) porphyrins and phthalocyanine studied by soft X-ray absorption spectroscopy
- 2007
-
Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104. ; 332:2-3, s. 318-324
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 6. |
- Preobrajenski, Alexei, et al.
(författare)
-
Adsorption-induced gap states of h-BN on metal surfaces
- 2008
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 77:8, s. 085421-
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Preobrajenski, Alexei, et al.
(författare)
-
Strong Participator Channels in the Non-Radiative Resonant Decay of B 1s Excitation in B2O3
- 2005
-
Ingår i: Physica Scripta. - 0031-8949. ; T115, s. 1071-1073
-
Tidskriftsartikel (refereegranskat)abstract
- We observe and analyze a considerable enhancement of photoelectron intensity of the valence band features in solid B2O3 upon tuning the photon energy across the B 1s → π*2pz resonance. This enhancement is an evidence of the strong 2p electron correlations in pre-edge photoionization dynamics in boron oxide. Such strength of the correlation is unusual for a solid, whose valence band is composed of only s and p electrons. We assign these effects to the considerable spatial localization of the highest occupied and lowest unoccupied electronic states of boron oxide on the BO33- quasimolecular anion, as well as to the strong 2p electron coupling between them. Solid state effects in the electronic structure and B 1s → π* decay dynamics are found to be minor, while molecular effects of the BO33- fragment are dominating.
|
|
| 11. |
- Vinogradov, A. S., et al.
(författare)
-
The hybridized M3d-F2p character of low-energy unoccupied electron states in 3d metal fluorides observed by F 1s absorption
- 2005
-
Ingår i: Physica Scripta. - 0031-8949. ; T115, s. 510-512
-
Tidskriftsartikel (refereegranskat)abstract
- The near-edge fine structure of the F 1s absorption spectra of 3d metal fluorides was studied for the first time with high energy resolution. The spectra of these, the most ionic compounds of the 3d atoms, are analyzed comparing with the F 1s absorption spectrum of the molecular TiF62− anion in solid K2TiF6. The latter spectrum was afore interpreted considering the fluorine spectra of the molecular PF6− anion in a KPF6 crystal and of the gas-phase SF6 molecule. The low-energy empty electron states in the 3d metal fluorides are shown to be formed due to covalent mixing of the metal 3d and fluorine 2p electron states.
|
|
| 12. |
- Baringhaus, J., et al.
(författare)
-
Bipolar gating of epitaxial graphene by intercalation of Ge
- 2014
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 104:26
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the ambivalent behavior of Ge intercalation is studied by means of scanning tunneling microscopy and spectroscopy as well as local 4-point probe transport measurements. In quantitative agreement with angle-resolved photoemission experiments, both p-and n-type doped graphene areas and their doping level were identified by local spectroscopy. The p-doped areas appear higher by 2 angstrom with respect to the n-doped areas suggesting incorporation of thicker Ge-layers accompanied by a modified coupling to the initial SiC-surface. Furthermore, the sheet resistance was measured on each of the patches separately. The intrinsic imbalance between the carrier types in the different areas is well reflected by the transport study. The process of intercalation does not affect the transport properties in comparison to pristine graphene pointing to a sufficient homogeneity of the decoupled graphene layer. Transport measurements across chemically gated pn-junctions reveal increased resistances, possibly due to enlarged tunneling barriers. (C) 2014 AIP Publishing LLC.
|
|
| 13. |
- Murphy, B. E., et al.
(författare)
-
Growth and ordering of Ni(II) diphenylporphyrin monolayers on Ag(111) and Ag/Si(111) studied by STM and LEED
- 2012
-
Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. - 1361-648X .- 0953-8984. ; 24:4
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 14. |
- Ng, May Ling, et al.
(författare)
-
Effect of substrate nanopatterning on the growth and structure of pentacene films
- 2010
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:11, s. 115449-
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 15. |
|
|
| 16. |
|
|
