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Structure and chemical characterization of novel 2D homo- and hetero-organic architectures on a gold surface: a combined STM and photoemission spectroscopies study
No full textThis work focuses on the study of the electronic and structural properties of molecular architectures at metal surfaces formed by assembly of functionalized organics, in particular amino- and/or carboxylic-functionalized molecules. Several homo- and hetero-organic architectures are characterized on a gold (111) surface by means of combined low temperature scanning tunneling microscopy (LT-STM) and X-ray spectroscopy techniques, coupled with ab initio calculations performed in collaboration with theoretical groups. The aim is to identify the role of the molecule-molecule and molecule-substrate interactions in determining the electronic and structural configuration of the investigated systems. This thesis is subdivided in two parts. In the first part we report the homo-organic assembly of a simple solvent molecule, dimethyl sulfoxide (DMSO), and two different amino-functionalized molecules. In particular, DMSO is found to form molecular complexes unexpectedly trapping gold adatoms natively available on Au(111). Although such adatoms are not visible in the STM images, comparison between experiments and theoretical calculations shows that they are crucial for the stability of the observed DMSO complexes. Then, we have studied a small aminomethyl-functionalized molecule, 1-naphthylmethylamine (NMA), forming complexes of 3 or 4 molecules, and an amino-phenyl-porphyrin forming hydrogen bonded molecular chains. In the latter two works, we have pointed out the interplay between the amino-amino and amino-gold substrate interactions which drive the formation of such complexes.
In the second part we exploit what we have learned about the amino-functionalized molecules on Au(111) to build novel hetero-organic supramolecular architectures based on the amino-carboxylic (A-C) interaction. Initially, we have studied the self-assembly of two small molecules, namely NMA and terephthalic acid (TPA, carboxylic-), whose 2D hetero-organic assembly is shown to be driven by the competition between the A-C and carboxylic-carboxylic recognition. In literature, organic templates are successfully synthesized on surfaces to build guest-host systems based on the shape matching between the host template and guest molecules. We instead exploit the competitive A-C bond to develop a novel guest-host method based on chemical affinity. By employing the monolayer of a carboxylic-functionalized porphyrin as the host template, we find that small guest aminomethyl-terminated molecules (like NMA) can be intercalated into this 2D template. These results show that the competitive A-C recognition is a powerful tool to build supramolecular assemblies
Growth of regular nanometric molecular arrays on a functional 2D template based on a chemical guest-host approach
No full textA regular 2D array of crown molecules, which would spontaneously self-assemble into disordered molecular
clusters, is obtained by exploiting a guest–host process, based on the chemical affinity between
amino and carboxylic groups on a gold surface. First a carboxylic organic template is formed, which then
serves as a host for amino-functionalized crown molecules. The amino-carboxylic interaction thereby
drives the formation of a monolayer of guest molecules, regularly distributed at the nanometer scale, preventing
their aggregation in unordered clusters observed on a bare gold surface. This method, which can
be applied to other guest molecules, represents a novel route to overcome the shape-matching requirements
of the standard guest–host architectures. Furthermore, it is intrinsically selective, due to the chemical
nature of the anchoring process
A competitive amino-carboxylic hydrogen bond on a gold surface
No full textAn amino-carboxylic motif is identified as a novel synthon in the formation of 2D hetero-organic architectures at surfaces. The well-defined interacting scheme we describe herein represents an ideal prototypical system for further investigation of the interaction at surfaces of the two functional groups
Binary Conformational Switches in a Porphyrin Chain: Tautomerization and Stereoisomerization
Full text linkIn the last decade, hydrogen (H-)tautomerization, that is, a reaction that involves simple intramolecular proton transfer, has been studied in single phthalocyanine, porphyrin, and porphycene derivatives as a prototypical single molecular conductance switch. Here, by means of low-temperature scanning tunneling microscopy and density functional theory calculations, we report a binary H-tautomerism and stereoisomeric conformational switch in (amino-functionalized) porphyrins assembled in molecular chains on a gold surface. We show that the formation of the chain is crucial for the binary tautomeric switch mechanism as the single molecule switches differently. Our findings suggest that the (amino-)functionalization of molecules can be exploited not only to drive the formation of molecular self-assemblies but also to steer their switching properties
On-surface trapping of alkali atoms by crown ethers in ultra high vacuum
No full textCrown ethers, assembled into a regular 2D array via a chemical guesthost recognition process, have been successfully employed to trap sodium atoms on a surface, under ultra- high vacuum conditions
Carbon dioxide reduction on Ir(111): Stable hydrocarbon surface species at near-ambient pressure
Full text linkStable hydrocarbon surface species in the carbon dioxide hydrogenation reaction on Ir(111) were identified by means of infrared-visible sum-frequency generation vibrational spectroscopy and X-ray photoelectron spectroscopy under near-ambient pressure conditions (0.1 mbar). By introducing gas phase binary and ternary mixtures of CO2, CO, and H2 into the reaction chamber, stable ethylidyne and ethynyl species were found at the metal surface above 425 K, in remarkable analogy with that observed during the ethylene decomposition process yielding graphene. In addition, upon increasing temperature (up to 600 K depending on the reaction conditions), vibrational and electronic spectroscopic fingerprints appeared that could be attributed to the nucleation of aromatic hydrocarbons at the edge of metastable graphenic clusters interacting with the metal surface
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
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
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