| 1. |
- Doyle, Catherine M., et al.
(författare)
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Surface Mediated Synthesis of 2D Covalent Organic Networks : 1,3,5-Tris(4-bromophenyl)benzene on Au(111)
- 2019
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Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 256:2
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Tidskriftsartikel (refereegranskat)abstract
- Covalent organic networks derived from surface-mediated self-assembly of 1,3,5-tris(4-bromophenyl)benzene into two-dimensional networks on Au(111) have been studied by scanning tunneling microscopy (STM) and by X-ray spectroscopic methods. High resolution soft X-ray photoemission spectroscopy (SXPS) using synchrotron radiation have been used to study the formation of the 1,3,5-tris(4-bromophenyl)benzene-derived 2D networks by observing temperature-dependent C 1s and Br 3d core level XPS spectra. X-ray absorption (XA) measurements of the formation of these 2D networks have been obtained at the C K-edge where their temperature and angular dependence are examined. The results of these XPS and XA spectroscopic measurements are compared to detailed ab initio electronic structure calculations of 1,3,5-tris(4-bromophenyl)benzene molecules to aid the interpretation of the features of these spectra.
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| 2. |
- 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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| 3. |
- Jacobse, Peter H., et al.
(författare)
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One Precursor but Two Types of Graphene Nanoribbons : On-Surface Transformations of 10,10'-Dichloro-9,9'-bianthryl on Ag(111)
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 123:14, s. 8892-8901
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Tidskriftsartikel (refereegranskat)abstract
- On-surface synthesis has emerged in the last decade as a method to create graphene nanoribbons (GNRs) with atomic precision. The underlying premise of this bottom-up strategy is that precursor molecules undergo a well-defined sequence of inter- and intramolecular reactions, leading to the formation of a single product. As such, the structure of the GNR is encoded in the precursors. However, recent examples have shown that not only the molecule, but also the coinage metal surface on which the reaction takes place, plays a decisive role in dictating the nanoribbon structure. In this work, we use scanning probe microscopy and X-ray photoelectron spectroscopy to investigate the behavior of 10,10'-dichloro-9,9'-bianthryl (DCBA) on Ag(111). Our study shows that Ag(111) can induce the formation of both seven-atom wide armchair GNRs (7-acGNRs) and 3,1-chiral GNRs (3,1-cGNRs), demonstrating that a single molecule on a single surface can react to different nanoribbon products. We additionally show that coadsorbed dibromoperylene can promote surface-assisted dehydrogenative coupling in DCBA, leading to the exclusive formation of 3,1-cGNRs.
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| 4. |
- Mazzola, F., et al.
(författare)
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Graphene coatings for chemotherapy: avoiding silver-mediated degradation
- 2015
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Ingår i: 2d Materials. - : IOP Publishing. - 2053-1583. ; 2:2
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Ng, May Ling, et al.
(författare)
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Reversible Modification of the Structural and Electronic Properties of a Boron Nitride Monolayer by CO Intercalation
- 2015
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 16:5, s. 923-927
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the reversible intercalation of CO between a hexagonal boron nitride (h-BN) monolayer and a Rh(111) substrate above a threshold CO pressure of 0.01 mbar at room temperature. The intercalation of CO results in the flattening of the originally corrugated h-BN nanomesh and an electronic decoupling of the BN layer from the Rh substrate. The intercalated CO molecules assume a coverage and adsorption site distribution comparable to that on the free Rh(111) surface at similar conditions. The pristine h-BN nanomesh is reinstated upon heating to above 625 K. These observations may open up opportunities for a reversible tuning of the electronic and structural properties of monolayer BN films.
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| 6. |
- Risinggård, Helene Kjær, et al.
(författare)
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Degradation of the chemotherapy drug 5-fluorouracil on medical-grade silver surfaces
- 2018
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332. ; 435, s. 1213-1219
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of the chemotherapy drug 5-fluorouracil by a non-pristine metal surfaces is studied. Using density functional theory, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy we show that the drug is entirely degraded by medical-grade silver surfaces, already at body temperature, and that all of the fluorine has left the molecule, presumably as HF. Remarkably, this degradation is even more severe than that reported previously for 5-fluorouracil on a pristine monocrystalline silver surface (in which case 80% of the drug reacted at body temperature) [1]. We conclude that the observed reaction is due to a reaction pathway, driven by H to F attraction between molecules on the surface, which results in the direct formation of HF; a pathway which is favoured when competing pathways involving reactive Ag surface sites are made unavailable by environmental contamination. Our measurements indicate that realistically cleaned, non-pristine silver alloys, which are typically used in medical applications, can result in severe degradation of 5-fluorouracil, with the release of HF – a finding which may have important implications for the handling of chemotherapy drugs.
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| 7. |
- Senkovskiy, Boris V., et al.
(författare)
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Semiconductor-to-Metal Transition and Quasiparticle Renormalization in Doped Graphene Nanoribbons
- 2017
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Ingår i: Advanced Electronic Materials. - : Wiley. - 2199-160X. ; 3:4
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Tidskriftsartikel (refereegranskat)abstract
- A semiconductor-to-metal transition in N = 7 armchair graphene nanoribbons causes drastic changes in its electron and phonon system. By using angle-resolved photoemission spectroscopy of lithium-doped graphene nanoribbons, a quasiparticle band gap renormalization from 2.4 to 2.1 eV is observed. Reaching high doping levels (0.05 electrons per atom), it is found that the effective mass of the conduction band carriers increases to a value equal to the free electron mass. This giant increase in the effective mass by doping is a means to enhance the density of states at the Fermi level which can have palpable impact on the transport and optical properties. Electron doping also reduces the Raman intensity by one order of magnitude, and results in relatively small (4 cm−1) hardening of the G phonon and softening of the D phonon. This suggests the importance of both lattice expansion and dynamic effects. The present work highlights that doping of a semiconducting 1D system is strikingly different from its 2D or 3D counterparts and introduces doped graphene nanoribbons as a new tunable quantum material with high potential for basic research and applications.
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| 8. |
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| 9. |
- 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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| 10. |
- 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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| 11. |
- Simonov, Konstantin, 1988-
(författare)
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Effect of Substrate on Bottom-Up Fabrication and Electronic Properties of Graphene Nanoribbons
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Taking into account the technological demand for the controlled preparation of atomically precise graphene nanoribbons (GNRs) with well-defined properties, the present thesis is focused on the investigation of the role of the underlying metal substrate in the process of building GNRs using bottom-up strategy and on the changes in the electronic structure of GNRs induced by the GNR-metal interaction. The combination of surface sensitive synchrotron-radiation-based spectroscopic techniques and scanning tunneling microscopy with in situ sample preparation allowed to trace evolution of the structural and electronic properties of the investigated systems.Significant impact of the substrate activity on the growth dynamics of armchair GNRs of width N = 7 (7-AGNRs) prepared on inert Au(111) and active Cu(111) was demonstrated. It was shown that unlike inert Au(111) substrate, the mechanism of GNRs formation on Ag(111) and Cu(111) includes the formation of organometallic intermediates based on the carbon-metal-carbon bonds. Experiments performed on Cu(111) and Cu(110), showed that a change of the balance between molecular diffusion and intermolecular interaction significantly affects the on-surface reaction mechanism making it impossible to grow GNRs on Cu(110).It was demonstrated that deposition of metals on spatially aligned GNRs prepared on stepped Au(788) substrate allows to investigate GNR-metal interaction using angle-resolved photoelectron spectroscopy. In particular intercalation of one monolayer of copper beneath 7-AGNRs leads to significant electron injection into the nanoribbons, indicating that charge doping by metal contacts must be taken into account when designing GNR/electrode systems. Alloying of intercalated copper with gold substrate upon post-annealing at 200°C leads to a recovery of the initial position of GNR-related bands with respect to the Fermi level, thus proving tunability of the induced n-doping. Contrary, changes in the electronic structure of 7-AGNRs induced by the deposition of Li are not reversible. It is demonstrated that via lithium doping 7-AGNRs can be transformed from a semiconductor into a metal state due to the partial filling of the conduction band. The band gap of Li-doped GNRs is reduced and the effective mass of the conduction band carriers is increased.
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| 12. |
- Uihlein, Johannes, et al.
(författare)
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Influence of Graphene on Charge Transfer between CoPc and Metals: The Role of Graphene-Substrate Coupling
- 2015
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 119:27, s. 15240-15247
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of cobalt phthalocyanine (CoPc) on Pt(111), graphene/Pt(111), and Au-intercalated graphene/Ni(111) is investigated by photoexcited electron spectroscopies: photoemission (XPS and UPS) and X-ray absorption spectroscopy (XAS or NEXAFS). For CoPc on Pt(111), significant changes of the shape of XPS and XAS spectra indicate a charge transfer from the metal substrate to the Co ion of CoPc. The strong interaction between CoPc and Pt(111) can be completely prevented by the insertion of a graphene buffer layer. For CoPc on graphene/Ni(111), the charge transfer is only prevented if the graphene on Ni(111) is intercalated by gold. Therefore, the disturbance of the graphene electronic structure by the interaction with underlying substrate and the corresponding charge doping of graphene has been found to affect the electronic properties of adsorbed CoPc considerably.
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| 13. |
- Vinogradov, Nikolay A., et al.
(författare)
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Single-Phase Borophene on Ir(111) : Formation, Structure, and Decoupling from the Support
- 2019
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 13:12, s. 14511-14518
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Tidskriftsartikel (refereegranskat)abstract
- Artificial two-dimensional (2D) materials, which host electronic or spatial structure and properties not typical for their bulk allotropes, can be grown epitaxially on atomically flat surfaces; the design and investigation of these materials are thus at the forefront of current research. Here we report the formation of borophene, a planar boron allotrope, on the surface of Ir(111) by exposing it to the flux of elemental boron and consequent annealing. By means of scanning tunneling microscopy and density functional theory calculations, we reveal the complex structure of this borophene, different from all planar boron allotropes reported earlier. This structure forms as a single phase on iridium substrate in a wide range of experimental conditions and may be then decoupled from the substrate via intercalation. These findings allow for production of large, defect-free borophene sheets and advance theoretical understanding of polymorphism in borophene.
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| 14. |
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