| 1. |
- Svirskiy, G. I., et al.
(författare)
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Comparative X-Ray Absorption Analysis of the Spectrum of Vacant Electronic States in Cobalt and Nickel Tetraphenylporphyrin Complexes
- 2018
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Ingår i: Physics of the solid state. - 1063-7834 .- 1090-6460. ; 60:3, s. 581-591
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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.
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| 2. |
- Vinogradov, N. A., et al.
(författare)
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The structural evolution of graphene/Fe(110) systems upon annealing
- 2017
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Ingår i: Carbon. - : Elsevier BV. - 0008-6223 .- 1873-3891. ; 111, s. 113-120
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability and the structural evolution of graphene grown on Fe(110) has been studied upon annealing in ultra-high vacuum conditions (UHV, P <= 10(-9) mbar) and in the presence of gaseous ethylene at a pressure of similar to 10(-6) mbar by grazing incidence X-ray diffraction. It was observed that upon annealing at temperatures below 630 degrees C, graphene on Fe is thermally stable. Exposure to ethylene at these temperatures promotes the formation of graphene while inhibiting its deterioration. Annealing graphene/Fe(110) at temperatures above 630 degrees C results in a fast degradation of graphene followed by carburization of the sample, that is the irreversible formation of various iron carbides, with the most common phases being Fe3C (cementite) and Fe7C3 (Eckstrom-Adcock carbide). Annealing of the carburized sample does not result in the formation of a detectable graphitic structure.
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| 3. |
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| 4. |
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| 5. |
- Simonov, Konstantin A., et al.
(författare)
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Effect of Electron Injection in Copper-Contacted Graphene Nanoribbons
- 2016
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Ingår i: Nano Reseach. - : Springer Science and Business Media LLC. - 1998-0124 .- 1998-0000. ; 9:9, s. 2735-2746
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Tidskriftsartikel (refereegranskat)abstract
- For practical electronic device applications of graphene nanoribbons (GNRs), it is essential to have abrupt and well-defined contacts between the ribbon and the adjacent metal lead. By analogy with graphene, these contacts can induce electron or hole doping, which may significantly affect the I/V characteristics of the device. Cu is among the most popular metals of choice for contact materials. In this study, we investigate the effect of in situ intercalation of Cu on the electronic structure of atomically precise, spatially aligned armchair GNRs of width N = 7 (7-AGNRs) fabricated via a bottom-up method on the Au(788) surface. Scanning tunneling microscopy data reveal that the complete intercalation of about one monolayer of Cu under 7-AGNRs can be facilitated by gentle annealing of the sample at 80 A degrees C. Angle-resolved photoemission spectroscopy (ARPES) data clearly reflect the one-dimensional character of the 7-AGNR band dispersion before and after intercalation. Moreover, ARPES and core-level photoemission results show that intercalation of Cu leads to significant electron injection into the nanoribbons, which causes a pronounced downshift of the valence and conduction bands of the GNR with respect to the Fermi energy (Delta E similar to 0.5 eV). As demonstrated by ARPES and X-ray absorption spectroscopy measurements, the effect of Cu intercalation is restricted to n-doping only, without considerable modification of the band structure of the GNRs. Post-annealing of the 7-AGNRs/Cu/Au(788) system at 200 A degrees C activates the diffusion of Cu into Au and the formation of a Cu-rich surface Au layer. Alloying of intercalated Cu leads to the recovery of the initial position of GNR-related bands with respect to the Fermi energy (E (F)), thus, proving the tunability of the induced n-doping.
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| 6. |
- Simonov, Konstantin A., et al.
(författare)
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From Graphene Nanoribbons on Cu(111) to Nanographene on Cu(110) : Critical Role of Substrate Structure in the Bottom-Up Fabrication Strategy
- 2015
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 9:9, s. 8997-9011
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Tidskriftsartikel (refereegranskat)abstract
- Bottom-up strategies can be effectively implemented for the fabrication of atomically precise graphene nanoribbons. Recently, using 10,10'-dibromo-9,9'-bianthracene (DBBA) as a molecular precursor to grow armchair nanoribbons on Au(111) and Cu(111), we have shown that substrate activity considerably affects the dynamics of ribbon formation, nonetheless without significant modifications in the growth mechanism. In this paper we compare the on-surface reaction pathways for DBBA molecules on Cu(111) and Cu(110). Evolution of both systems has been studied via a combination of core-level X-ray spectroscopies, scanning tunneling microscopy, and theoretical calculations. Experimental and theoretical results reveal a significant increase in reactivity for the open and anisotropic Cu(110) surface in comparison with the close-packed Cu(111). This increased reactivity results in a predominance of the molecular substrate interaction over the intermolecular one, which has a critical impact on the transformations of DBBA on Cu(110). Unlike DBBA on Cu(111), the Ullmann coupling cannot be realized for DBBA/Cu(110) and the growth of nanoribbons via this mechanism is blocked. Instead, annealing of DBBA on Cu(110) at 250 degrees C results in the formation of a new structure: quasi-zero-dimensional flat nanographenes. Each nanographene unit has dehydrogenated zigzag edges bonded to the underlying Cu rows and oriented with the hydrogen-terminated armchair edge parallel to the [1-10] direction. Strong bonding of nanographene to the substrate manifests itself in a high adsorption energy of -12.7 eV and significant charge transfer of 3.46e from the copper surface. Nanographene units coordinated with bromine adatoms are able to arrange in highly regular arrays potentially suitable for nanotemplating.
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| 7. |
- Generaloy, Alexander V., et al.
(författare)
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Evolution of CuI/Graphene/Ni(111) System during Vacuum Annealing
- 2015
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:22, s. 12434-12444
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined core-level spectroscopy and low-energy electron diffraction study of the evolution of thin CuI layers on graphene/Ni(111) during annealing. It has been found that the annealing of the CuI/graphene/Ni(111) system up to 160 degrees C results in the formation of an ordered CuI overlayer with a (root 3 x root 3) R30 degrees structure on top of the graphene surface. At annealing temperatures of about 180 degrees C or higher, the CuI overlayer decomposes with a simultaneous intercalation of Cu and I atoms underneath the graphene monolayer on Ni(111). Nearly complete intercalation of graphene by Cu and I atoms can be achieved by deposition of about 20 angstrom of CuI, followed by annealing at 200 degrees C. The intercalated graphene layer is p-doped due to interfacial iodine atoms.
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| 8. |
- Mukherjee, Soham, et al.
(författare)
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Interplay between Growth Mechanism, Materials Chemistry, and Band Gap Characteristics in Sputtered Thin Films of Chalcogenide Perovskite BaZrS3
- 2023
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:22, s. 11642-11653
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Tidskriftsartikel (refereegranskat)abstract
- The prototypical chalcogenide perovskite BaZrS3, characterized by its direct band gap, exceptionally strong light-harvesting ability, and good carrier transport properties, provides fundamental prerequisites for a promising photovoltaic material. This inspired the synthesis of BaZrS3 in the form of thin films, using sputtering and rapid thermal processing, aimed at device fabrication for future optoelectronic applications. Using a combination of short- and long-range structural information from X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD), we have elucidated how, starting from a random network of Ba, Zr, and S atoms, thermal treatment induces crystallization and growth of BaZrS3 and explained its impact on the observed photoluminescence (PL) properties. We also provide a description of the electronic structure and substantiate the surface material chemistry using a combination of depth-dependent photoelectron spectroscopy (PES) using hard X-ray (HAXPES) and traditional Al K alpha radiation. From the knowledge of the optical band gap of BaZrS3 thin films, synthesized at an optimal temperature of 900 C-degrees, and our estimation of the valence band edge position with respect to the Fermi level, one may conclude that these semiconductor films are intrinsic in nature with a slight n-type character. A detailed understanding of the growth mechanism and electronic structure of BaZrS3 thin films helps pave the way toward their utilization in photovoltaic applications.
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| 9. |
- Putintseva, Yuliya A., et al.
(författare)
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Siberian larch (Larix sibirica Ledeb.) mitochondrial genome assembled using both short and long nucleotide sequence reads is currently the largest known mitogenome
- 2020
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Ingår i: BMC Genomics. - : BMC. - 1471-2164. ; 21:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Plant mitochondrial genomes (mitogenomes) can be structurally complex while their size can vary from similar to 222 Kbp inBrassica napusto 11.3 Mbp inSilene conica. To date, in comparison with the number of plant species, only a few plant mitogenomes have been sequenced and released, particularly for conifers (the Pinaceae family). Conifers cover an ancient group of land plants that includes about 600 species, and which are of great ecological and economical value. Among them, Siberian larch (Larix sibiricaLedeb.) represents one of the keystone species in Siberian boreal forests. Yet, despite its importance for evolutionary and population studies, the mitogenome of Siberian larch has not yet been assembled and studied. Results: Two sources of DNA sequences were used to search for mitochondrial DNA (mtDNA) sequences: mtDNA enriched samples and nucleotide reads generated in the de novo whole genome sequencing project, respectively. The assembly of the Siberian larch mitogenome contained nine contigs, with the shortest and the largest contigs being 24,767 bp and 4,008,762 bp, respectively. The total size of the genome was estimated at 11.7 Mbp. In total, 40 protein-coding, 34 tRNA, and 3 rRNA genes and numerous repetitive elements (REs) were annotated in this mitogenome. In total, 864 C-to-U RNA editing sites were found for 38 out of 40 protein-coding genes. The immense size of this genome, currently the largest reported, can be partly explained by variable numbers of mobile genetic elements, and introns, but unlikely by plasmid-related sequences. We found few plasmid-like insertions representing only 0.11% of the entire Siberian larch mitogenome. Conclusions: Our study showed that the size of the Siberian larch mitogenome is much larger than in other so far studied Gymnosperms, and in the same range as for the annual flowering plantSilene conica(11.3 Mbp). Similar to other species, the Siberian larch mitogenome contains relatively few genes, and despite its huge size, the repeated and low complexity regions cover only 14.46% of the mitogenome sequence.
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| 10. |
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