1,721,035 research outputs found
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
Study on Electronic and Spintronic Properties of Metal Halide Semiconductors
No full textMetal halide semiconductors (MHS) have gained significant attention recently due to their exceptional optoelectronic properties. The diverse chemical and structural properties make MHS a promising platform for multifunctional materials. The thesis will focus on the electronic and spintronic properties of MHS, from typical lead halide perovskite structures to lead halide coordination polymers. In Chapter 3, functional organics were designed in low-dimensional lead halide perovskites to enhance charge transportability. By incorporating a strong electron-accepting methylviologen (MV) cation, charge transfer (CT) at the organic/inorganic interface can effectively expand the absorption range and photoresponse activity. The photoinduced CT process was further characterized by transient absorption spectroscopy, which shows an ultrafast CT process within 1 ps, generating charge-separated states. This unveils the interesting photophysics of these unconventional one-dimensional (1D) perovskites with functional organic chromophores, which is promising in the application of solar cells. In Chapter 4, magnetic spins were introduced in three-dimensional CH3NH3PbCl3 (MAPbCl3) perovskite in the form of a dilute magnetic semiconductor (DMS). By co-doping of magnetic (Fe2+) and aliovalent (Bi3+) metal ions into MAPbCl3 perovskite, ferromagnetism was observed below 12 K. Magnetic ions are proposed to interact through the bound magnetic polarons to achieve ferromagnetic coupling. This work provides a new avenue for the development of solution-processable magnetic semiconductors. Chapter 5 studied the structure-property relationship in two-dimensional lead halide coordination polymers. A series of photoresponsive two-dimensional (2D) lead-halide coordination polymers with bipyridyl ethylene (bpe) ligands were synthesized, which can undergo topochemical [2+2] photocycloaddition. The chemical and structural diversity of 2D lead-halide coordination polymers allows to systematically modulate the rate of [2+2] photocycloaddition by changing the halide and bpe ligands. The photo-transformed coordination polymers with cyclobutane linkages show drastically different optical absorption and emission properties. This work presents a viable strategy to modify the structure and properties of lead-halide coordination polymers by post-synthetic modification.</p
Enantiomeric Photosynthesis of Amino Acid with Chiral CdZnS Nanostructure
No full textThis study systematically investigates the synthesis and structural evolution of chiral CdZnS nanostructures. Chirality in the urchin-like morphology is induced through interactions among cysteine, amines, and metal ions. Notably, a novel hierarchical Cd0.9Zn₀.₁S nanosphere, composed of twisted nanorods, has been successfully synthesized. This material was selected as a chiral catalyst to explore enantioselective amino acid synthesis via the chiral-induced spin selectivity (CISS) effect. While typical CO2 reduction reaction (CO2RR) products such as ethanol, acetone, and acetate were detected, amino acids were not observed. Further investigation into the overall yield and the photoelectrical properties of CdZnS is required to gain deeper insights into its CO2RR performance.</p
Multifaceted Exploration of Complex Magnetic, Optical, and Electrical Properties of Metal Halide Structures
No full textThis thesis presents a multifaceted investigation into the complex magnetic, optical, and electrical properties of rationally designed metal halide structures, leveraging strategies such as organic cation engineering, metal ion substitution, high-entropy alloying, and non-covalent interaction control. Novel Fe-Cl based layered double perovskites were synthesized, revealing long-range superexchange pathways (Fe-Cl-MI-Cl-Fe) and tunable antiferromagnetic ordering influenced by organic cations and diamagnetic MI ions, alongside modulated optical band gaps. Concurrently, extended honeycomb Cs3MFeMnCl9 (M=Na, Ag) systems, derived from bilayer triangular lattice structures, were explored; density functional theory (DFT) confirmed Mn2+ d-orbital contributions reduce band gaps, while experimental studies showed diamagnetic bridging ions modulate their robust antiferromagnetic exchange interactions. A pivotal advancement was the application of high-entropy engineering to lanthanide double perovskites, yielding materials with significantly enhanced ambient and thermal stability. These high-entropy systems exhibit versatile multifunctional photoluminescence, encompassing broadband self-trapped exciton emission, characteristic sharp Ln3+ f-f transitions, efficient NIR-II emission, and notable up-conversion luminescence, all within a single crystalline host. Furthermore, the nuanced role of halogen bonds in 2D hybrid layered (EIA)2(MA)n-1PbnI3n+1 perovskites was elucidated. Layer-thickness-dependent halogen bond strength was found to dictate organic cation conformation, leading to controlled symmetry breaking. This structural asymmetry in specific (n=2) non-centrosymmetric configurations induced Rashba band splitting, evidenced by suppressed radiative recombination and prolonged spin lifetimes, alongside a reversible bulk photovoltaic effect. Collectively, this work deepens the understanding of intricate structure-property relationships in diverse metal halide architectures and offers design principles for novel multifunctional materials.</p
Twisting Photons with Chiral Metal-Halide Perovskites
No full textOver the past few decades, metal-halide perovskites have garnered widespread research interest due to their extraordinary semiconductive properties and facile synthetic routes. In recent years, the incorporation of chiral organic cations into the perovskite lattice structure induces symmetry breaking. Thus, these perovskites crystallize in chiral space group, with helical packing pattern in the structure. It offers opportunities to precisely control the behavior (i.e. angular momentum) of photons, phonons and electrons within the perovskite. Thus, chiral perovskites exhibit attractive chiroptical and spintronic properties, which involves the polarization of light and electrons. Since chiral perovskites being reported, the unusual chiroptical and spintronic properties have been extensively investigated. However, several key questions remain unsolved. For instance, whether the genuine circular dichroism in chiral perovskite thin film is interfered by external factors during the measurement; the structure-CD relationship in chiral perovskite is still underexplored; whether magnetic doping strategy in bulk chiral perovskite will generate emerging properties; the relationship between chiroptical and spintronic properties within chiral 2D perovskites is unknown. This thesis summarizes my three PhD projects, which aim to solve the questions being aroused above. In the first project, through spectroscopic measurement and Muller matrix analysis, we discovered that the previously reported “apparent” anisotropy factor measured from circular dichroism (CD) in chiral MHS thin films is not an intrinsic chiroptical property, dimensional and zero-dimensional chiral MHS thin films. Spectroscopic methods was established to decouple the genuine CD from other spurious contributions, which allows a quantitative comparison of the intrinsic chiroptical activity across different chiral MHS. The relationship between the structure and the genuine chiroptical activity was then uncovered, which is well described by the chirality-induced spin–orbit coupling in the chiral structures. Our study unveils the macroscopic origin of chiroptical activity of chiral MHS and provides design principles for obtaining high anisotropic factors for future chiral optoelectronic applications. In the second project, we synthesized a Mn2+-doped chiral two-dimensional (2D) perovskite, We found that efficient energy transfer from the chiral host to the Mn2+ dopants was observed. This energy transfer process gives rise to circularly polarized luminescence from the excited state of Mn2+ (4T1 → 6A1), exhibiting a photoluminescence quantum yield up to 24% and a dissymmetry factor of 11%. The exciton fine structures of undoped and Mn2+-doped (R-MPA)2PbBr4 were further studied through magnetic circular dichroism (MCD) spectroscopy. Our analysis shows that chiral organic cations lead to an exciton fine structure splitting energy as large as 5.0 μeV, and the splitting is further increased upon Mn2+ doping. Our results reveal the strong impacts of molecular chirality and magnetic dopants on the exciton structures of halide perovskites. In the third project, we used magnetic circular dichroism to probe the exciton spin splitting in a series of chiral 2D perovskites. Our results show that the anisotropy factor of circular dichroism is indeed proportional to the exciton spin splitting energy, with larger splitting energy yielding larger anisotropy factors. Further structural analysis showed that the splitting energy is closely correlated with both the in-plane and out-of-plane distortion structural parameters of the inorganic lattice. Our work provides an important mechanistic understanding of chiroptical activity and establishes the structure–property relationship for 2D chiral perovskites</p
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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