| 1. |
- Alippi, Paola, et al.
(författare)
-
A Ru-Ru pair housed in ruthenium phthalocyanine : the role of a "cage" architecture in the molecule coupling with the Ag(111) surface
- 2017
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:2, s. 1449-1457
-
Tidskriftsartikel (refereegranskat)abstract
- A number of studies have investigated the properties of monomeric and double-decker phthalocyanines (Pcs) adsorbed on metal surfaces, in view of applications in spintronics devices. In a combined experimental and theoretical study, we consider here a different member of the Pcs family, the (RuPc)(2) dimer, whose structure is characterized by two paired up magnetic centers embedded in a double-decker architecture. For (RuPc)(2) on Ag(111), we show that this architecture works as a preserving cage by shielding the Ru-Ru pair from a direct interaction with the surface atoms. In fact, while noticeable surface-to-molecule charge transfer occurs with the ensuing quenching of the molecular magnetic moment, such phenomena occur here in the absence of a direct Ru-Ag coupling or structural rearrangement, at variance with other Pcs and thanks to the above shielding effect. These unique properties of the (RuPc)(2) architecture are expected to permit an easy control of the surface-to-molecule charge-transfer process as well as of the molecular magnetic properties, thus making the (RuPc)(2) dimer a significant paradigm for innovative "cage" structures as well as a promising candidate for applications in spintronics nano or single-molecule devices.
|
|
| 2. |
- Grossmann, Lukas, et al.
(författare)
-
Mechanistic insights into on-surface reactions from isothermal temperature-programmed X-ray photoelectron spectroscopy
- 2024
-
Ingår i: Nanoscale. - : ROYAL SOC CHEMISTRY. - 2040-3364 .- 2040-3372.
-
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.
|
|
| 3. |
- Lanzilotto, Valeria, et al.
(författare)
-
Tailoring surface-supported water-melamine complexes by cooperative H-bonding interactions
- 2021
-
Ingår i: Nanoscale Advances. - : Royal Society of Chemistry. - 2516-0230. ; 3:8, s. 2359-2365
-
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).
|
|
| 4. |
- Lisa Pinardi, Anna, et al.
(författare)
-
Tailored Formation of N-Doped Nanoarchitectures by Diffusion-Controlled on-Surface (Cyclo)-Dehydrogenation of Heteroaromatics
- 2013
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 7:4, s. 3676-3684
-
Tidskriftsartikel (refereegranskat)abstract
- Surface-assisted cyclodehydrogenation and dehydrogenative polymerization of polycyclic (hetero)aromatic hydrocarbons (PAH) are among the most important strategies for bottom-up assembly of new nanostructures from their molecular building blocks. Although diverse compounds have been formed in recent years using this methodology, a limited knowledge on the molecular machinery operating at the nanoscale has prevented a rational control of the reaction outcome. We show that the strength of the PAH-substrate interaction rules the competitive reaction pathways (cyclodehydrogenation versus dehydrogenative polymerization). By controlling the diffusion of N-heteroaromatic precursors, the on-surface dehydrogenation can lead to monomolecular triazafullerenes and diazahexabenzocoronenes (N-doped nanographene), to N-doped oligomeric or polymeric networks, or to carbonaceous monolayers. Governing the on-surface dehydrogenation process is a step forward toward the tailored fabrication of molecular 2D nanoarchitectures distinct from graphene and exhibiting new properties of fundamental and technological interest.
|
|
| 5. |
- Palacio, Irene, et al.
(författare)
-
Spectroscopic characterization of the on-surface induced (cyclo)dehydrogenation of a N-heteroaromatic compound on noble metal surfaces
- 2017
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:33, s. 22454-22461
-
Tidskriftsartikel (refereegranskat)abstract
- New nanoarchitectures can be built from polycyclic aromatic hydrocarbons (PAHs) by exploiting the capability of some metal surfaces for inducing cyclodehydrogenation reactions. This bottom-up approach allows the formation of nanostructures with a different dimensionality from the same precursor as a consequence of the diffusion and coupling of the PAHs adsorbed on the surface. In this work we present a thorough study, by means of a combination of X-ray photoemission spectroscopy, near-edge X-ray absorption fine structure and scanning tunneling microscopy with first principle calculations of the structural and chemical transformations undergone by pyridyl-substituted dibenzo[5]helicene on three coinage surfaces, namely Cu(110), Cu(111) and Au(111). Upon annealing, on-surface chemical reactions are promoted affecting the adsorbate/substrate and the molecule/molecule interactions. This thermally induced process favours the transformation from diffusing isolated molecules to polymeric nanographene chains and finally to N-doped graphene.
|
|
| 6. |
- Zhang, Teng, et al.
(författare)
-
Clarifying the Adsorption of Triphenylamine on Au(111) : Filling the HOMO-LUMO Gap
- 2022
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:3, s. 1635-1643
-
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.
|
|
| 7. |
- Zhang, Teng, 1988-
(författare)
-
Synchrotron Radiation Studies of Molecular Building Blocks for Functional Materials
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research on new materials is a primary driving force for progress in human society. One of the most significant research topic nowadays is the development of new functional materials for technological applications, like perovskite implemented in solar cells, and graphene as a representative for the new 2D materials family. It is then crucial to fully understand the functionality of such materials from a fundamental point of view, as a complementary and useful guide to develop/design new devices of improved performance and energy efficiency.In the thesis, comprehensive characterizations of molecular building blocks used in i) novel energy conversion devices (CoPc, TPA, DPTA and m-MTDATA), and ii) in 2D materials (biphenylene and melamine) have been performed by PhotoElectron Spectroscopy (PES), and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy carried out at synchrotron radiation facilities, representing effective, powerful light source dedicated to the front-line materials research of great value in both science and industry. PES and NEXAFS spectroscopy, in combination with Density Functional Theory (DFT) calculations have provided a deep understanding of the electronic structure of the investigated systems in relation to their functionality. The investigations always included the combination and comparison between experimental and theoretical results. The studied molecules were characterized as free and adsorbed on surfaces, from the simple building blocks to more complex molecular systems. The characterizations allowed us to identify the electronic structure modifications due to substitutions (Paper III), increasing complexity of the molecules (Paper V), molecule-substrate interactions (Paper I, II, IV, V) and intra-molecular H-bonding interactions (Paper VI).
|
|
