1,720,986 research outputs found
On-Surface Supramolecular Networks: Structure and Dynamics of Formation in Ultra-High Vacuum and at the Solid/Liquid Interface
Full text linkOn-surface supramolecular chemistry inspired the fabrication of a large variety of atomically controlled systems and on-surface synthesis allowed the production of low-dimensional materials with atomic precision. Since numerous surface-supported nanostructures are constantly developed, their possible applications stimulate diverse areas of research such as catalysis, organic electronics, surface sensing, surface functionalization and nanopatterning.
Several protocols and interfacial approaches have been developed for the production of surface-supported supramolecular networks by self-assembly and by far, the increasing interest for nanomaterials with innovative functionalities has boosted the search in on-surface activation of chemical reaction for the covalent stabilization of more complex molecular architectures.
Photochemistry was furthered as a promising approach for this purpose and pioneering examples allowed a deeper understanding of light-induced on-surface chemical reactions. However, the search in this field is still at its birth and further research is required. The Scanning Tunneling Microscope provides the necessary resolution for this studies in various conditions, including solid/liquid or solid/air interfaces or Ultra High Vacuum (UHV).La chimica supra-molecolare di superficie ha permesso la produzione di numerose nanostrutture tramite l'utilizzo di protocolli di sintesi innovativi. In questo modo si sono ottenuti, tramite controllo strutturale a livello atomico e molecolare, numerosi materiali a ridotta dimensionalità. L'applicazione di tali scoperte si sviluppa nell'ambito della ricerca relativa alla catalisi, all'elettronica organica, alla funzionalizzazione e alla sensibilizzazione della superfici.
Poiché esistono diversi approcci per per la produzione di tali strutture, la ricerca ha spinto i propri interessi verso la nano-fabbricazione di materiali per ottenerne, sfruttando varie tecniche, di innovativi, più stabili ed efficienti.
La fotochimica di superficie in questo senso, permette di ottenere materiali molto complessi ed inoltre permette di capire i fenomeni alla base dei processi di sintesi indotta dalla luce, che ad oggi, non sono del tutto semplici da interpretare.
La microscopia a scansione di tunneling (STM) fornisce l'opportuna risoluzione spaziale per questo tipo di studi, i cui principi sono ancora oggi oggetto di dibattito
Metal-Free on-Surface Photochemical Homocoupling of Terminal Alkynes
No full textOn-surface synthesis involving the homocoupling of aryl-alkynes affords the buildup of bisacetylene derivatives directly at surfaces, which in turn may be further used as ingredients for the production of novel functional materials. Generally, homocoupling of terminal alkynes takes place by thermal activation of molecular precursors on metal surfaces. However, the interaction of alkynes with surface metal atoms often induces unwanted reaction pathways when thermal energy is provided to the system. In this contribution we report about light-induced metal-free homocoupling of terminal alkynes on highly oriented pyrolitic graphite (HOPG). The reaction occurred with high efficiency and selectivity within a self-assembled monolayer (SAM) of aryl-alkynes and led to the generation of large domains of ordered butadiynyl derivatives. Such a photochemical uncatalyzed pathway represents an original approach in the field of topological C–C coupling at the solid/liquid interface
Co3O4/TiO2 heterostructures obtained by hybrid method
No full textHigh surface-to-volume ratio Co3O4/TiO2 heterojunctionks were fabricated by combining different methods. Atomic layer deposition (ALD) and a photochemical method were used to coat polystyrene (PS) 3D-Direct Opal (3D-DO) structures on conductive ITO substrates. Firstly, 3D-DO of PS were crystallized on ITO substrates to form the high surface-to-volume ratio template via a self-assembly method. A low-temperature ALD TiO2 film was infiltrated onto the PS opal structure. Then, the PS template was removed by a thermal treatment in air at 450 8C for 5 h. Hollow anatase phase nanospheres were obtained, crystallized in a face entered cubic (FCC) lattice with the (111) plane oriented parallel to the substrate surface. Finally, the hollow TiO2 nano spheres were coated with Co3O4 via a photochemical method. This ordered 3D nanostructure with designed morphology may findapplications as surface-enhanced materials for photovoltaic
devices
DIRECT AND FULLERENE-TEMPLATED PHOTOCHEMICAL POLYMERIZATION OF FUNCTIONALIZED PORPHYRINS ON A SILVER SUBSTRATE
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Structurally Tunable Self-Assembled 2D Cocrystals of C60 and Porphyrins on the Ag (110) Surface
No full textDue to the donor–acceptor nature of their supramolecular interactions, nanostructured porphyrin-fullerene self-assembled architectures show attractive properties that can be exploited in high efficiency solar cells. In this work, we show that six different ordered bicomponent porphyrin-fullerene (C60) networks are obtained by controlling the peripheral functionalization of meso-tetraphenylporphyrins (TPP) with amino groups and the stoichiometry of their aggregates with C60 on Ag (110). Such networks can be grouped in two general classes, depending on their structural habit: the so-called “stripes” phases, formed by alternating monomolecular stripes of C60 and TPP, and the so-called “pores” phases, where a fullerene net accommodates isolated TPP molecules in nanometer-sized pores. These phases are of general interest in the field of surface-supported electron donor–acceptor systems, since they represents a rare example of fullerene-containing surface-supported bicomponent supramolecular networks where the binary nanostructures are definitely more stable thermodynamically than the two separated single-component phases, thereby resembling three-dimensional TPP/C60 cocrystals. The thermodynamic stability in an extended temperature range has profound consequences on the degree of long-range order attainable in the self-assembly process
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
An experimental and theoretical study of metallorganic coordination networks of tetrahydroxyquinone on Cu(111)
No full textThe adsorption of tetrahydroxyquinone (THQ) on the Cu(111) surface at different temperatures gives rise to different ordered structures, unveiled by density functional theory (DFT) modelling of scanning tunnelling microscopy (STM) topography and by X-ray absorption spectroscopy (XAS) measurements. After annealing, the THQ films generated tetrameric Cu clusters embedded in a metal–organic tetraoxyquinone (TOQ) network, whose electronic properties were thoroughly studied. The remarkable agreement between the STM results and periodic calculations was exploited to model C and O K-edge XA spectra recorded before (room temperature, RT) and after annealing (high temperature, HT). The subsequent analysis of the C and O TOQ@Cu(111) K-edge XA spectra provides definitive information about the structural arrangement of the TOQ@Cu(111) coordination network, confirming the complete THQ dehydrogenation upon annealing, suggested by the simulations of the STM images. The obtained information is crucial to rationalize the evolution of THQ@Cu(111) upon heating, shedding light into the potential reactivity of the HT coordination network, and, more generally, to investigate the nature and character of low-lying virtual states, the most involved states in the chemical reactions
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