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Sökning: WFRF:(Lanzilotto Valeria)

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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.
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2.
  • Cappel, Ute B, et al. (författare)
  • Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells.
  • 2017
  • Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:40, s. 34970-34978
  • Tidskriftsartikel (refereegranskat)abstract
    • ) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.
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3.
  • Lanzilotto, Valeria, et al. (författare)
  • Spectroscopic Fingerprints of Carbon Nitride Functional Groups Locked-up in Intermolecular H-bonding Interactions
  • Ingår i: Chemistry: A European Journal. - 0947-6539 .- 1521-3765.
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated the effect of intermolecular H- bonding interactions on the local electronic structure of N- functionalities, amino group and pyridine-like N, which are characteristic of a new class of metal-free polymeric photo-catalysts named graphitic carbon nitrides, g-C3N4. Specifically, we have performed a characterization of the melamine molecule, a building block of g-C3N4, combining X-ray photoemission (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The molecule has been studied in the gas phase, as non-interacting system, and in the solid state within a hydrogen bonded network. With the support of density functional theory (DFT) simulations of the spectra, we have found that the H-bonds mainly affect the N 1s level of the amino group, leaving the N 1s level of the pyridine-like N mostly unperturbed. This fact is responsible for a reduction of the chemical shift between the two XPS N 1s levels, compared to the free melamine. Consequently, N K-edge NEXAFS resonances involving the amino N 1s level also shift to lower photon energies. Moreover, the solid state absorption spectra have shown strong modification/quenching of resonances related with transitions from the amino N 1s level towards σ*orbitals involving the -NH2 terminations. 
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4.
  • Lanzilotto, Valeria, et al. (författare)
  • Spectroscopic Fingerprints of Intermolecular H-Bonding Interactions in Carbon Nitride Model Compounds
  • 2018
  • Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 24:53, s. 14198-14206
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of intermolecular H-bonding interactions on the local electronic structure of N-containing functional groups (amino group and pyridine-like N) that are characteristic of polymeric carbon nitride materials p-CN(H), a new class of metal-free organophotocatalysts, was investigated. Specifically, the melamine molecule, a building block of p-CN(H), was characterized by X-ray photoelectron (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The molecule was studied as a noninteracting system in the gas phase and in the solid state within a H-bonded network. With the support of DFT simulations of the spectra, it was found that the H-bonds mainly affect the N1s level of the amino group, leaving the N1s level of the pyridine-like N mostly unperturbed. This is responsible for a reduction of the chemical shift between the two XPS N1s levels relative to free melamine. Consequently, N K-edge NEXAFS resonances involving the amino N1s level also shift to lower photon energies. Moreover, the solid-state absorption spectra showed significant modification/quenching of resonances related to transitions from the amino N1s level to sigma* orbitals involving the NH2 termini.
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5.
  • 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).
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6.
  • Lanzilotto, Valeria, et al. (författare)
  • The Challenge of Thermal Deposition of Coordination Compounds : Insight into the Case of an Fe-4 Single Molecule Magnet
  • 2016
  • Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 28:21, s. 7693-7702
  • Tidskriftsartikel (refereegranskat)abstract
    • Realization of well-controlled hybrid interfaces between solid surfaces and functional complex molecules can be hampered by the presence of contaminants originated by the fragmentation of fragile architectures based on the coordinative bond. Here, we present a morphological and spectroscopic analysis of submonolayer films obtained by sublimation of the [Fe-4(L)(2)(dpm)(6)] (Fe-4) single molecule magnet on different substrates. Though intact tetranuclear molecules can be transferred to surfaces, smaller molecular species are often codeposited. By comparison of substrates characterized by different reactivities, such as Au(111), Cu(100), and Cu2N, and employing a protocol of indirect exposure of the substrate, we infer that the observed fragments do not originate from the reaction of Fe-4 molecules with the surface but rather are produced during Fe-4 sublimation, which releases Fe(dpm)(3) as a very volatile compound. Fe(dpm)(3) undergoes substrate-dependent on-surface decomposition to final products that have been identified by combined STM, UPS, XPS, and DFT studies.
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7.
  • Ponzi, Aurora, et al. (författare)
  • Inequivalent Solvation Effects on the N 1s Levels of Self-Associated Melamine Molecules in Aqueous Solution
  • 2023
  • Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 127:13, s. 3016-3025
  • Tidskriftsartikel (refereegranskat)abstract
    • This work shows how the N 1s photoemission (PE) spectrum of self-associated melamine molecules in aqueous solution has been successfully rationalized using an integrated computational approach encompassing classical metadynamics simulations and quantum calculations based on density functional theory (DFT). The first approach allowed us to describe interacting melamine molecules in explicit waters and to identify dimeric configurations based on π–π and/or H-bonding interactions. Then, N 1s binding energies (BEs) and PE spectra were computed at the DFT level for all structures both in the gas phase and in an implicit solvent. While pure π-stacked dimers show gas-phase PE spectra almost identical to that of the monomer, those of the H-bonded dimers are sensibly affected by NH···NH or NH···NC interactions. Interestingly, the solvation suppresses all of the non-equivalences due to the H-bonds yielding similar PE spectra for all dimers, matching very well our measurements.
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8.
  • Schaefer, Andreas, 1981, et al. (författare)
  • Defect-Induced Water Bilayer Growth on Anatase TiO2(101)
  • 2018
  • Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 34:37, s. 10856-10864
  • Tidskriftsartikel (refereegranskat)abstract
    • Preparing an anatase TiO2(101) surface with a high density of oxygen vacancies and associated reduced Ti species in the near-surface region results in drastic changes in the water adsorption chemistry compared to adsorption on a highly stoichiometric surface. Using synchrotron radiation excited photoelectron spectroscopy, we observe a change in the water growth mode, from layer-by-layer growth on the highly stoichiometric surface to bilayer growth on the reduced surface. Furthermore, we have been able to observe Ti3+ enrichment at the surface upon water adsorption. The Ti3+ enrichment occurs concomitant with effective water dissociation into hydroxyls with a very high thermal stability. The water bilayer on the reduced surface is thermally more stable than that on the stoichiometric surface, and it is more efficient in promoting further water dissociation upon heating. The results thus show how the presence of subsurface defects can alter the wetting mechanism of an oxide surface.
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9.
  • Schaefer, Andreas, 1981, et al. (författare)
  • First layer water phases on anatase TiO2(101)
  • 2018
  • Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 674, s. 25-31
  • Tidskriftsartikel (refereegranskat)abstract
    • The anatase TiO2(101) surface and its interaction with water is an important topic in oxide surface chemistry. Firstly, it benchmarks the properties of the majority facet of TiO2 nanoparticles and, secondly, there is a controversy as to whether the water molecule adsorbs intact or deprotonates. We have addressed the adsorption of water on anatase TiO2(101) by synchrotron radiation photoelectron spectroscopy. Three two-dimensional water structures are found during growth at different temperatures: at 100 K, a metastable structure forms with no hydrogen bonding between the water molecules. In accord with prior literature, we assign this phase to chains of disordered molecules. Growth 160 K results in a metastable structure with expressed hydrogen bonding between the water molecules. At 190 K, the water molecules become disordered as the thermal energy is too high and hence the hydrogen bonds break. The result is a structure with isolated monomers. Partial dissociation is observed for all three growths, with the molecular state only slightly favored in energy (20–40 meV) over the dissociated state. Heating of a thick film leads to more dissociation compared to a bilayer, when formed at 100 K. Thus, extending the water network facilitates proton transport and hence dissociation. The results reconcile apparent conflicting experimental results previously obtained by scanning tunneling microscopy (STM) and core level photoelectron spectroscopy.
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10.
  • Teng, Zhang, et al. (författare)
  • Exploring the electronic structure of CoPc by photoemission and absorption spectroscopy
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Photoelectron spectroscopy  and X-ray absorption spectroscopy were used to investigate the occupied and empty density of states of cobalt phthalocyanine (CoPc) in the gas phase and in thin films of different thicknesses, deposited onto a Au (111) single crystal. The comparison between experimental gas phase results and density functional theory single molecule simulations confirmed that the CoPc ground state is correctly described by the 2A1g electronic configuration. Moreover, the atomic character of the highest occupied molecular orbital of CoPc was addressed by performing photon energy dependent valence photoemission spectroscopy experiments on both CoPc gas phase and film samples. Our results clearly show that the highest occupied molecular orbital is derived only from the organic ligand, with mainly contribution from the carbon atoms. Multiplet ligand field theory was employed to simulate the Co L edge X-ray absorption spectroscopy results.
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11.
  • Ugolotti, Aldo, et al. (författare)
  • In-Plane Hydrogen Bonds and Out-of-Plane Dipolar Interactions in Self-Assembled Melem Networks
  • 2023
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:23, s. 11307-11316
  • 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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12.
  • 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.
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13.
  • Zhang, Teng, et al. (författare)
  • Conclusively Addressing the CoPc Electronic Structure : A Joint Gas-Phase and Solid-State Photoemission and Absorption Spectroscopy Study
  • 2017
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 121:47, s. 26372-26378
  • Tidskriftsartikel (refereegranskat)abstract
    • The occupied and empty densities of states of cobalt phthalocyanine (CoPc) were investigated by photoelectron and X-ray absorption spectroscopies in the gas phase and in thin films deposited on a Au(111) surface. The comparison between the gas-phase results and density functional theory single-molecule simulations confirmed that the CoPc ground state is correctly described by the (2)A(1g) electronic configuration. Moreover, photon-energy-dependent valence photoemission spectra of both the gas phase and thin film confirmed the atomic character of the highest occupied molecular orbital as being derived from the organic ligand, with dominant contributions from the carbon atoms. Multiplet ligand-field theory was employed to simulate the Co L-edge X-ray absorption spectroscopy results.
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14.
  • Zhang, Teng, 1988-, et al. (författare)
  • Electronic structure modifications induced by increased molecular complexity : from triphenylamine to m-MTDATA
  • 2019
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 21:32, s. 17959-17970
  • Tidskriftsartikel (refereegranskat)abstract
    • The starburst pi-conjugated molecule 4,4 ',4 ''-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (C57H48N4, m-MTDATA), based on triphenylamine (TPA) building blocks, is widely used in optoelectronic devices due to its good electron-donor characteristics. The electronic structure of m-MTDATA was investigated for the first time in the gas phase by means of PhotoElectron Spectroscopy (PES) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The combination of Density Functional Theory (DFT) calculations with the experimental spectra provides a comprehensive description of the molecular electronic structure. Moreover, by comparing the results with previous TPA measurements, we could shed light on how the electronic structure evolves when the molecular size is increased. We found that the C 1s photoelectron spectra of m-MTDATA and TPA are similar, due to the balance of the counter-acting effects of the electronegativity of the N atoms and the delocalization of the amine lone-pair electrons. In contrast, the increased number of N atoms (i.e. N lone pairs) in m-MTDATA determines a three-peak feature in the outermost valence binding energy region with strong contributions by the N 2p(z) orbitals. We also obtained a decrease of the HOMO-LUMO gap for m-MTDATA, which points to improved electron donating properties of m-MTDATA with respect to TPA.
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15.
  • Zhang, Teng, 1988-, et al. (författare)
  • Electronic Structure Study of Free and Adsorbed m-MTDATA
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • The starburst p-conjugated molecule based on triphenylamine (TPA) building block, 4,4',4" -Tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA), is widely used in optoelectronic devices due to its electron-donating properties. The electronic structure of m-MTDATA was investigated in the gas-phase and when deposited in thin films on a Au(111) surface by means of PhotoElectron Spectroscopy (PES) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. Density Functional Theory (DFT) calculations were compared to the experimental gas-phase results, providing a comprehensive description of the molecular electronic structure. Moreover, the results were compared with previous TPA measurements, shedding light on the electronic structure modification due to the increased molecular complexity.  Similar to TPA, but more complex, the binding energy of the C 1s photoelectron line of m-MTDATA results from the balance of two counter-acting effects: (1) the electronegativity of the N atoms and (2) the delocalization of lone-pair electrons of the nitrogen. Compared to TPA, the outermost valence PE spectrum of m-MTDATA shows a 3-peak feature with N 2pz character and a lowering of the binding energy of the HOMO. When adsorbed on Au(111),  the changes observed in PES and NEXAFS spectra with respect to the free molecules,  can be explained by a significant modification of m-MTDATA molecular and electronic structure, due to the molecule-substrate interaction.
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16.
  • Zhang, Teng, 1988-, et al. (författare)
  • Lone-Pair Delocalization Effects within Electron Donor Molecules: The Case of Triphenylamine and Its Thiophene-Analog
  • 2018
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 122:31, s. 17706-17717
  • Tidskriftsartikel (refereegranskat)abstract
    • Triphenylamine (TPA) and its thiophene-analog, N,N-diphenyl-2-thiophenamine (DPTA), are both well-known as electron-donating molecules implemented in optoelectronic devices such as organic solar cells and LEDs. Comprehensive valence and core level photoelectron spectroscopy, as well as near edge X-ray absorption spectroscopy (NEXAFS), measurements have been performed on gas phase TPA and DPTA. The experimental results have been compared to density functional theory calculations, providing a detailed description of the molecular electronic structure. Specifically, the C 1s photoelectron lines of both TPA and DPTA were resolved in the different C atom contributions and their binding energies explained as the result of two counter-acting effects: (1) the electronegativity of the nitrogen atom (and sulfur atom in DPTA) and (2) the the N (and S in DPTA) lone-pair electrons. In addition, the C K-edge NEXAFS spectrum of DPTA reveals that the lowest unoccupied molecular orbital (LUMO) energy position is affected differently if the core hole site is on the phenyl compared to the thiophene ring. The electron-donating properties of these two molecules are largely explained by the significant contribution of the N lone-pair electrons (p(z)) to the highest occupied molecular orbital. The contribution to the LUMO and to the empty density of states of the sulfur of the thiophene ring in DPTA explains the better performance of donor-pi-acceptor molecules containing this moiety and implemented in photoenergy conversion devices.
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17.
  • Zhang, Teng, et al. (författare)
  • m-MTDATA on Au(111) : Spectroscopic Evidence of Molecule-Substrate Interactions
  • 2022
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:6, s. 3202-3210
  • Tidskriftsartikel (refereegranskat)abstract
    • The starburst pi-conjugated molecule based on triphenylamine (TPA) building blocks, 4,4',4 ''-tris(N-3-ethylphenyl-N-phenylamino)triphenylamine (C57H48N4, m-MTDATA), is widely used in optoelectronic devices due to its electron-donating properties. The electronic structure of m-MTDATA adsorbed on an Au(111) surface was investigated by means of photoelectron spectroscopy (PES) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results were further compared to gas-hase measurements and DFT calculations. Our results clearly indicate a significant molecule-substrate interaction that induces considerable modifications on the electronic structure of the adsorbate compared to the isolated molecule. The energy level alignment analysis shows that the HOMO-LUMO gap is filled by new interface states.
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18.
  • 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).
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19.
  • Zhang, Teng, 1988-, et al. (författare)
  • X-ray Spectroscopy Investigations of TPA/Au(111): Charge Redistribution via Core Exitation?
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • Triphenylamine (TPA) is a well-known electron donor molecule largely used in photovoltaics. In this article we analyze the electronic structure modifications due to the adsorption of the molecules at a monolayer coverage on a Au(111) surface. Only a weak interaction was observed between the TPA and the gold during the adsorption process, being impossible to get more than 1ML coverage at room temperature. The characterizations have been performed by core and valence Photoelectron Spectroscopy (PES) and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy. The results were compared with our previous investigations on free TPA, and theoretical models were used to explain the changes of the electronic structure due to the adsorption on the metallic gold surface. The calculation confirms the weak interaction between the adsorbed TPA and the Au(111), with only a slight change of the twisting angle of the TPA phenyl rings. The resulting adsorption geometry can be used to explain the broadening of the C 1s PES line with respect to the gas-phase results and the expected absence of angle dependence in the C K-edge NEXAFS. However, a significant modification was observed in the N K-edge NEXAFS spectra of TPA/Au(111), showing a new pre-edge feature due to transitions involving out-of-plane orbitals. This pre-edge feature is ascribed to the interaction between the molecules and the surface, having a different character and energy position than the pre-edge observed for free TPA. A model, considering a TPA+ cation formed by a charge redistribution process between the adsorbate and the surface valence states seems to give a qualitative explanation of this pre-edge intensity. Since our calculations predict only a weak interaction between the TPA molecules and the gold surface, we propose that such a charge redistribution happens in the core-excited state created by photon absorption.
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