On-surface polymerization is a powerful bottom-up approach that allows for the growth of covalent architectures with defined properties using the two-dimensional confinement of a highly defined ...single-crystal surface. Thermal heating is the preferred approach to initiate the reaction, often via cleavage of halogen substituents from the molecular building blocks. Light represents an alternative stimulus but has, thus far, only rarely been used. Here, we present a direct comparison of on-surface polymerization of dibromo-anthracene molecules, induced either thermally or by light, and study the differences between the two approaches. Insight is obtained by a combination of scanning tunneling microscopy, locally studying the polymer shape and size, and X-ray photoelectron spectroscopy, which identifies bond formation by averaging over large surface areas. While the polymer length increases slowly with the sample heating temperature, illumination promotes only the formation of short covalent structures, independent of the duration of light exposure. Moreover, irradiation with UV light at different sample temperatures highlights the important role of molecular diffusion across the surface.
Light is a versatile tool to remotely activate molecules adsorbed on a surface, for example, to trigger their polymerization. Here, we explore the spatial distribution of light-induced chemical ...reactions on a Au(111) surface. Specifically, the covalent on-surface polymerization of an anthracene derivative in the submonolayer coverage range is studied. Using scanning tunneling microscopy and X-ray photoemission spectroscopy, we observe a substantial increase of the local molecular coverage with the sample illumination time at the center of the laser spot. We find that the interplay between thermally induced diffusion and the reduced mobility of reaction products steers the accumulation of material. Moreover, the debromination of the adsorbed species never progresses to completion within the experiment time, despite a long irradiation of many hours.
Aerosol processing enables the preparation of hierarchical graphene nanocomposites with special crumpled morphology in high yield and in a short time. Using modular insertion of suitable precursors ...in the starting solution, it is possible to synthesize different types of graphene-based materials ranging from heteroatom-doped graphene nanoballs to hierarchical nanohybrids made up by nitrogen-doped crumpled graphene nanosacks that wrap finely dispersed MoS2 nanoparticles. These materials are carefully investigated by microscopic (SEM, standard and HR TEM), diffraction (grazing incidence X-ray diffraction (GIXRD)) and spectroscopic (high resolution photoemission, Raman and UV−visible spectroscopy) techniques, evidencing that nitrogen dopants provide anchoring sites for MoS2 nanoparticles, whereas crumpling of graphene sheets drastically limits aggregation. The activity of these materials is tested toward the photoelectrochemical production of hydrogen, obtaining that N-doped graphene/MoS2 nanohybrids are seven times more efficient with respect to single MoS2 because of the formation of local p–n MoS2/N-doped graphene nanojunctions, which allow an efficient charge carrier separation.
The intrinsic stability of the 5 V LiCoPO4–LiCo2P3O10 thin-film (carbon-free) cathode material coated with MoO3 thin layer is studied using a comprehensive synchrotron electron spectroscopy in situ ...approach combined with first-principle calculations. The atomic–molecular level study demonstrates fully reversible electronic properties of the cathode after the first electrochemical cycle. The polyanionic oxide is not involved in chemical reactions with the fluoroethylene-containing liquid electrolyte even when charged to 5.1 V vs Li+/Li. The high stability of the cathode is explained on the basis of the developed energy level model. In contrast, the chemical composition of the cathode–electrolyte interface evolves continuously by involving MoO3 in the decomposition reaction with consequent leaching of oxide from the surface. The proposed mechanisms of chemical reactions are attributed to external electrolyte oxidation via charge transfer from the relevant electron level to the MoO3 valence band state and internal electrolyte oxidation via proton transfer to the solvents. This study provides a deeper insight into the development of both a doping strategy to enhance the electronic conductivity of high-voltage cathode materials and an efficient surface coating against unfavorable interfacial chemical reactions.
The space between a metal surface and a two-dimensional cover can be regarded as a nanoreactor, where confined molecule adsorption and surface reactions may occur. In this work, we report CO ...intercalation and reactivity between a graphene-hexagonal boron nitride (h-BNG) heterostructure and Pt(111). By employing high resolution X-ray photoemission spectroscopy (XPS) we demonstrate the molecular intercalation of the full h-BNG overlayer and stabilization of a dense
23.4°-13CO layer on Pt(111) under ultra-high vacuum at room temperature. We provide experimental evidence of a weakened CO-metal bond due to the confinement effects of the 2D cover. Temperature-programmed XPS results reveal that CO desorption is kinetically delayed and occurs at a higher temperature than on bare Pt(111). Moreover, CO partially reacts with the h-BNG layer to form boron-oxide species, which affect repeated CO intercalation. Finally, we found that the properties of the system towards interaction with CO can be considerably recovered using high temperature treatment.
Molybdenum disulfide (MoS2) few-layer films have gained considerable attention for their possible applications in electronics and optics and also as a promising material for energy conversion and ...storage. Intercalating alkali metals, such as lithium, offers the opportunity to engineer the electronic properties of MoS2. However, the influence of lithium on the growth of MoS2 layers has not been fully explored. Here, we have studied how lithium affects the structural and optical properties of the MoS2 few-layer films prepared using a new method based on one-zone sulfurization with Li2S as a source of lithium. This method enables incorporation of Li into octahedral and tetrahedral sites of the already prepared MoS2 films or during MoS2 formation. Our results discover an important effect of lithium promoting the epitaxial growth and horizontal alignment of the films. Moreover, we have observed a vertical-to-horizontal reorientation in vertically aligned MoS2 films upon lithiation. The measurements show long-term stability and preserved chemical composition of the horizontally aligned Li-doped MoS2.
Anatase TiO
2
nanoparticles doped either with Li or Ni have been synthesized via hydrolysis in variable concentrations. Microstructural analysis confirms the high crystallinity of the doped ...nanoparticles with sizes around 7 nm, while compositional analysis shows low doping below 2% at. Despite the low concentration of dopants, variations in the Raman and Photoluminescence signals were observed in the doped nanoparticles, mainly due to non-stoichiometry and oxygen deficiency promoted by Li or Ni doping. Doping effects associated with Li and Ni were observed by photoelectron spectroscopy and first principle calculations, which associate the appearance of states in the valence band region to oxygen deficiency and Li or Ni doping and lower n-type character induced by Ni doping. Finally, changes in the thermally induced anatase-to-rutile transition (ART) have been also observed in the doped samples, leading to a dopant-promoted faster ART which occurs at lower temperature boosted due to the dopant effect.
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We report on the experimental investigation of single crystals of trans-RuNOPy4F(ClO4)2 (1) in its ground state (GS). The X-ray absorption spectroscopy (XAS) spectra measured at the N, O and F ...K-edges were compared to TDDFT calculations to identify and assign the absorption peaks, and to elucidate the structures of coordinated nitric oxide (NO). Based on a reasonable match of experimental and calculated spectra of GS, the N, O and F K-edges XAS spectra of Ru-ON (MS1) and Ru-η2-(NO) (MS2) isomers of 1 were calculated. According to the calculations, the energy or/and intensity of the 1 s→LUMO, LUMO+ 1 peaks of N, O or F K-edge changes significantly after GS isomerization to both MS1 and MS2. Current theoretical modeling of the NO linkage isomer in 1 is a background for the future investigation of isomerization process of NO by XAS methods. Since the investigated isomerization occurs in a variety of different nitrosyl complexes, obtained results can be extrapolated to a large family of transition metal nitrosyl compounds.
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•Multi-edge XAS spectra of a photoswitchable nitrosyl complex.•The linkage NO isomers exhibit features different from the ground state.•TDDFT calculations revealed the nature of XAS features.
On-surface synthesis of thin organic and organometallic films in a bottom-up fashion has become a promising approach for the development of new nanotechnologies. In this work we studied ...5,11-dibromotetracene (C18H10Br2) as a prototypical case of rodlike polyaromatic molecules functionalized with two bromine atoms on the sides. The adsorption and temperature-stimulated transformations of dibromotetracene assemblies on Ag(110) have been investigated by a combination of synchrotron radiation X-ray photoemission spectroscopy (XPS), near-edge X-ray absorption spectroscopy (NEXAFS), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. Upon the contact with the Ag substrate, the Br–C bonds are promptly cleaved at room temperature, and Ag-coordinated protopolymers are formed along the 001 substrate direction. The organometallic dimers and trimers remain on the surface up to 523 K. The stabilization of the protopolymers is driven by the substrate anisotropy and weak interactions with nearby Br atoms. The short oligomers formed at elevated temperatures are weakly bounded to the substrate and desorb before covalent structures can be formed.
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