| 1. |
- Ahmad, Y., et al.
(författare)
-
NMR and NEXAFS Study of Various Graphite Fluorides
- 2013
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 117:26, s. 13564-13572
-
Tidskriftsartikel (refereegranskat)abstract
- Graphite fluorides with different structural types (CyF)(n) (y = 2.5, 2, and 1) and room temperature graphite fluorides were studied by solid state,NMR and NEXAFS. Data extracted from those two techniques are complementary, providing information about the C-F bonding and the hybridization character of the carbon atom valence states. The comparison of data obtained by different methods such as NMR, Raman, and X-ray absorption leads to similar conclusions regarding the chemical bonding in fluorographites. Several major configurations of fluorinated graphites are discussed, that is, planar sheets with mainly sp(2) hybridization in room temperature graphite fluorides and corrugated sheets with sp(3) hybridization in covalent high temperature graphite fluoride. Different references such as highly oriented pyrolytic graphite (HOPG), graphitized carbon nanodiscs (graph-CNDs) and nanodiamonds (NDs) have also been investigated for comparison.
|
|
| 2. |
- Simonov, K. A., et al.
(författare)
-
Synthesis of armchair graphene nanoribbons from the 10,10′-dibromo-9,9′-bianthracene molecules on Ag(111) : The role of organometallic intermediates
- 2018
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8:1
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 3. |
- Simonov, K. A., et al.
(författare)
-
Features of metal atom 2p excitations and electronic structure of 3d-metal phthalocyanines studied by X-ray absorption and resonant photoemission
- 2013
-
Ingår i: Applied Surface Science. - : Elsevier BV. - 1873-5584 .- 0169-4332. ; 267, s. 132-135
-
Tidskriftsartikel (refereegranskat)abstract
- The metal atom 2p core excitations in 3d-metal phthalocyanines (MPc's, M = Ni, Co, Fe) have been studied via a combination of near edge X-ray absorption fine structure (NEXAFS) and resonant photoemission (ResPE) spectroscopy. On the basis of comparison of the corresponding spectra of NiPc, CoPc and FePc it has been shown that the presence of a partly filled molecular orbital (MO) dramatically affects the formation and decay processes of the M 2p core excitation in CoPc and, to a greater extend, in FePc due to the significant 3d-3d exchange interaction. It has been found that the low-lying unoccupied electronic states of NiPc, CoPc and FePc are strongly localized within the MN4 quasi-molecule and have nearly pure 3d character. Moreover, mainly 3d metallic character of the high-lying occupied MOs of NiPc, CoPc and FePc has been proved. (C) 2012 Elsevier B. V. All rights reserved.
|
|
| 4. |
- Simonov, K. A., et al.
(författare)
-
Combined microscopic and spectroscopic insights into the on-surface synthesis of graphene nanoribbons
- 2018
-
Ingår i: Encyclopedia of Interfacial Chemistry : Surface Science and Electrochemistry - Surface Science and Electrochemistry. - 9780128097397 - 9780128098943 ; , s. 236-243
-
Bokkapitel (refereegranskat)abstract
- Graphene nanoribbons (GNR) constitute a rapidly growing class of novel fascinating materials. Controlling the properties of GNR often implies controlling their atomic structure. In order to exert this control, a bottom-up approach for the growth of GNR is commonly used. Despite its great success, a lack of mechanistic understanding of the on-surface chemical processes remains one of the main challenges hindering further progress in the GNR synthesis. The most important question is how the properties of the underlying metal substrate and the precursor molecule affect the reaction pathway. A multitechnique approach utilizing complementary microscopic and spectroscopic methods is highly efficient for revealing the details of nanostructure formation on surfaces. This article is aimed at demonstrating that this approach enables a reliable monitoring of the on-surface chemical transformations upon GNR formation, thereby opening up a route to the design of GNR with targeted structure and properties. By referring to recent examples it is shown that a combination of X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS) can provide chemical sensitivity necessary to complement structural information routinely obtained with scanning tunneling microscopy (STM). This combination of techniques is especially powerful in identifying different stages of the GNR growth processes and revealing various factors affecting reaction pathways.
|
|
| 5. |
- Simonov, K. A., et al.
(författare)
-
Controllable oxidation of h-BN monolayer on Ir(111) studied by core-level spectroscopies
- 2012
-
Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 606:3-4, s. 564-570
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of atomic oxygen adsorption on the structure and electronic properties of monolayer hexagonal boron nitride (h-BN) grown on Ir(111) has been studied using near edge X-ray absorption fine structure spectroscopy (NEXAFS), photoelectron spectroscopy (PES), and low-energy electron diffraction (LEED). It has been shown that the oxidation of the h-BN monolayer occurs through a gradual substitution of N by O in the h-BN lattice. This process leads to the formation of defect sites corresponding to three different types of the B atom environment (BN3-xOx with x=1,2,3). The oxidation of the h-BN monolayer is very different from the case of graphene on Ir(111), where adsorption of atomic oxygen results mainly in the formation of epoxy groups [J. Phys. Chem. C. 115, 9568 (2011)]. A post-annealing of the h-BN monolayer after oxygen exposure results in further destruction of the B N bonds and formation of a B2O3-like structure. (C) 2011 Elsevier B.V. All rights reserved.
|
|
| 6. |
|
|
| 7. |
- Vinogradov, Nikolay, et al.
(författare)
-
Formation and Structure of Graphene Waves on Fe(110)
- 2012
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 109:2
-
Tidskriftsartikel (refereegranskat)abstract
- A very rich Fe-C phase diagram makes the formation of graphene on iron surfaces a challenging task. Here we demonstrate that the growth of graphene on epitaxial iron films can be realized by chemical vapor deposition at relatively low temperatures, and that the formation of carbides can be avoided in excess of the carbon-containing precursors. The resulting graphene monolayer creates a novel periodically corrugated pattern on Fe(110). Using low-energy electron microscopy and scanning tunneling microscopy, we show that it is modulated in one dimension forming long waves with a period of similar to 4 nm parallel to the [001] direction of the substrate, with an additional height modulation along the wave crests. The observed topography of the graphene/Fe superstructure is well reproduced by density functional theory calculations, and found to result from a unique combination of the lattice mismatch and strong interfacial interaction, as probed by core-level photoemission and x-ray absorption spectroscopy.
|
|
| 8. |
- Sterling, Cody M., et al.
(författare)
-
Sensitivity of Nitrogen K-Edge X-ray Absorption to Halide Substitution and Thermal Fluctuations in Methylammonium Lead-Halide Perovskites
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:15, s. 8360-8368
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of hybrid perovskite materials in solar cells crucially depends on their electronic properties, and it is important to investigate contributions to the total electronic structure from specific components in the material. In a combined theoretical and experimental study of CH3NH3PbI3-methylammonium lead triiodide (MAPI)-and its bromide cousin CH3NH3PbBr3 (MAPB), we analyze nitrogen K-edge (N Is-to-2p*) X-ray absorption (XA) spectra measured in MAPI and MAPB single crystals. This permits comparison of spectral features to the local character of unoccupied molecular orbitals on the CH3NH3+ (MA(+)) counterions and allows us to investigate how thermal fluctuations, hydrogen bonding, and halide-ion substitution influence the XA spectra as a measure of the local electronic structure. In agreement with the experiment, the simulated spectra for MAPI and MAPB show close similarity, except that the MAPB spectral features are blue-shifted by +0.31 eV. The shift is shown to arise from the intrinsic difference in the electronic structure of the two halide atoms rather than from structural differences between the materials. In addition, from the spectral sampling analysis of molecular dynamics simulations, clear correlations between geometric descriptors(N-C, N-H, and H center dot center dot center dot I/Br distances) and spectral features are identified and used to explain the spectral shapes.
|
|
