| 1. |
- Caputo, Marco, et al.
(författare)
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Charge Transfer and Orbital Reconstruction at an Organic-Oxide Interface
- 2023
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Ingår i: Nano Letters. - 1530-6984. ; 23:23, s. 11211-11218
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Tidskriftsartikel (refereegranskat)abstract
- The two-dimensional electron system (2DES) located at the surface of strontium titanate (STO) and at several other STO-based interfaces has been an established platform for the study of novel physical phenomena since its discovery. Here we report how the interfacing of STO and tetracyanoquinodimethane (TCNQ) results in a charge transfer that depletes the number of free carriers at the STO surface, with a strong impact on its electronic structure. Our study paves the way for efficient tuning of the electronic properties, which promises novel applications in the framework of oxide/organic-based electronics.
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| 2. |
- Lanzilotto, Valeria, et al.
(författare)
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Tailoring surface-supported water-melamine complexes by cooperative H-bonding interactions
- 2021
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Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 3:8, s. 2359-2365
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Tidskriftsartikel (refereegranskat)abstract
- The water-splitting photo-catalysis by carbon nitride heterocycles has been the subject of recent theoretical investigations, revealing a proton-coupled electron transfer (PCET) reaction from the H-bonded water molecule to the CN-heterocycle. In this context, a detailed characterization of the water-catalyst binding configuration becomes mandatory in order to validate and possibly improve the theoretical modeling. To this aim, we built a well-defined surface-supported water/catalyst interface by adsorbing water under ultra-high vacuum (UHV) conditions on a monolayer of melamine grown on the Cu(111) surface. By combining X-ray photoemission (XPS) and absorption (NEXAFS) spectroscopy we observed that melamine adsorbed onto copper is strongly tilted off the surface, with one amino group dangling to the vacuum side. The binding energy (BE) of the corresponding N 1s component is significantly higher compared to other N 1s contributions and displays a clear shift to lower BE as water is adsorbed. This finding along with density functional theory (DFT) results reveals that two adjacent melamine molecules concurrently work for stabilizing the H-bonded water-catalyst complex: one melamine acting as a H-donor via the amino-N (NHMIDLINE HORIZONTAL ELLIPSISOHH) and another one as a H-acceptor via the triazine-N (C = NMIDLINE HORIZONTAL ELLIPSISHOH).
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| 3. |
- Grossmann, Lukas, et al.
(författare)
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Mechanistic insights into on-surface reactions from isothermal temperature-programmed X-ray photoelectron spectroscopy
- 2024
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Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372.
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Tidskriftsartikel (refereegranskat)abstract
- On-surface synthesis often proceeds under kinetic control due to the irreversibility of key reaction steps, rendering kinetic studies pivotal. The accurate quantification of reaction rates also bears potential for unveiling reaction mechanisms. Temperature-Programmed X-ray Photoelectron Spectroscopy (TP-XPS) has emerged as an analytical tool for kinetic studies with splendid chemical and sufficient temporal resolution. Here, we demonstrate that the common linear temperature ramps lead to fitting ambiguities. Moreover, pinpointing the reaction order remains intricate, although this key parameter entails information on atomistic mechanisms. Yet, TP-XPS experiments with a stepped temperature profile comprised of isothermal segments facilitate the direct quantification of rate constants from fitting time courses. Thereby, rate constants are obtained for a series of temperatures, which allows independent extraction of both activation energies and pre-exponentials from Arrhenius plots. By using two analogous doubly versus triply brominated aromatic model compounds, we found that their debromination on Ag(111) is best modeled by second-order kinetics and thus proceeds via the involvement of a second, non-obvious reactant. Accordingly, we propose that debromination is activated by surface supplied Ag adatoms. This hypothesis is supported by Density Functional Theory (DFT) calculations. We foresee auspicious prospects for this TP-XPS variant for further exploring the kinetics and mechanisms of on-surface reactions. The temporal evolution of the reactant concentrations as measured by XPS for different temperature profiles reveals that the debromination of organic molecules on Ag(111) is activated by Ag adatoms.
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| 4. |
- Ugolotti, Aldo, et al.
(författare)
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In-Plane Hydrogen Bonds and Out-of-Plane Dipolar Interactions in Self-Assembled Melem Networks
- 2023
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:23, s. 11307-11316
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Tidskriftsartikel (refereegranskat)abstract
- Melem(2,6,10-triamino-s-heptazine) is the building block of melon,a carbon nitride (CN) polymer that is proven to produce H-2 from water under visible illumination. With the aim of bringingadditional insight into the electronic structure of CN materials,we performed a spectroscopic characterization of gas-phase melem andof a melem-based self-assembled 2D H-bonded layer on Au(111) by meansof ultraviolet and X-ray photoemission spectroscopy (UPS, XPS) andnear-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Inparallel, we performed density functional theory (DFT) simulationsof the same systems to unravel the molecular charge density redistributioncaused by the in-plane H-bonds. Comparing the experimental resultswith the spectroscopic DFT simulations, we can correlate the inducedcharge accumulation on the N-amino atoms to the red-shiftof the corresponding N 1s binding energy (BE) and of the N-amino 1s -> LUMO+n transitions. Moreover, when introducing a supportingAu(111) surface in the computational simulations, we observe a molecule-substrateinteraction that almost exclusively involves the out-of-plane molecularorbitals, leaving those engaged in the in-plane H-bonded network ratherunperturbed.
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| 5. |
- Zhang, Teng, et al.
(författare)
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Clarifying the Adsorption of Triphenylamine on Au(111) : Filling the HOMO-LUMO Gap
- 2022
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:3, s. 1635-1643
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we analyze the electronic structure modifications of triphenylamine (TPA), a well-known electron donor molecule widely used in photovoltaics and optoelectronics, upon deposition on Au(111) at a monolayer coverage. A detailed study was carried out by synchrotron radiation-based photoelectron spectroscopy, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, scanning tunneling microscopy (STM), and ab initio calculations. We detect a new feature in the pre-edge energy region of the N K-edge NEXAFS spectrum that extends over 3 eV, which we assign to transitions involving new electronic states. According to our calculations, upon adsorption, a number of new unoccupied electronic states fill the energy region between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the free TPA molecule and give rise to the new feature the pre-edge region of the NEXAFS spectrum. This finding highlights the occurrence of a considerable modification of the electronic structure of TPA. The appearance of new states in the HOMO-LUMO gap of TPA when adsorbed on Au(111) has crucial implications for the design of molecular nanoelectronic devices based on similar donor systems.
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