1,720,985 research outputs found
Adsorption Dynamics of Methanol on Si Surfaces Investigated by Photostimulated Desorption
No full textInitial stage of NO adsorption on Si(100)-(2 x 1) studied by synchrotron radiation photoemission and photodesorption
No full textThe NO adsorption on the Si(100)-(2 x 1) surface was investigated by synchrotron radiation photoemission and photodesorption in the energy ranges including the valence band and the Si 2p, N 1s and O 1s core levels. The study was performed both ass function of NO exposure and as a function of temperature in the range 20-300 K. The photoemission experiments show clear evidence of a dissociative adsorption process both at room temperature as well as at temperatures as low as 20 K. Furthermore, the silicon surface states are involved in the adsorption process. The core level spectroscopy shows a complex adsorption pattern of the atomic species, which might involve a sub-surface migration of nitrogen atoms. The photodesorption yields only O+ in the Si 2p and O Is energy ranges. No nitrogen ion desorption is detected. In the Si 2p energy range the O+ photodesorption pattern follows the enhanced secondary electron yield when crossing the ionization threshold. In the O Is energy range the O+ photodesorption pattern is interpreted in terms of a partial sub-surface migration of oxygen atoms. (C) 2000 Elsevier Science B.V. All rights reserved
Low-temperature adsorption states of benzene on Si(111)7x7 studied by synchrotron-radiation photoemission
No full textThe benzene adsorption on Si(111)7 x 7 was investigated by synchrotron-radiation valence-band photoemission in the temperature range 30-300 K. We found that when benzene is adsorbed on Si(111)7 x 7 at low temperature there is a one-to-one correspondence between the adsorbed and the gas-phase features. Furhermore, the interaction of benzene with the surface states is very weak, hinting at a physisorption process. Upon temperature increase, the adsorption features change gradually, but significantly. In particular, we observe a splitting of the features related to the degenerate orbitals, indicating that the benzene bond to the silicon surfaces is turning into chemisorption. This is the first evidence by photoemission spectroscopy that such a transition occurs, to our knowledge. Furthermore, the spectrum we obtain upon transition from the physisorbed to the chemisorbed state corresponds to the one obtained by dosing benzene at room temperature, thus showing that the chemisorption state does not depend on the way it is achieved. Upon exposure to a benzene multilayer we observe a direct transition from multilayer to chemisorbed state without intermediate transition to a physisorbed state, thus indicating that the multilayer desorption and the physisorption-to-chemisorption transition occur simultaneously. The adsorption of a few benzene overlayers on Si(111)7 x 7 at low temperature allowed us to monitor simultaneously both the first adlayer (hence the physisorption-to-chemisorption transition) and the overlayer features (hence the multilayer desorption), confirming that the physisorption-to-chemisorption transition and multilayer desorption are competing processes, and indicating a way to study substrate-adsorbate systems
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
Different role of filled and empty surface states in a polyfunctional molecule adsorption: Geranyl acetone on Si(111)7x7
No full textNew perspectives in molecular electronics are opening up through controlled surface molecular synthesis. The first step of such a synthesis implies the adsorption of a polyfunctional molecule, which might use one functional group for the surface adsorption, and the other one(s) for further reactions. Here we present an adsorption study of Si(111)7x7 of geranyl-acetone (C13H22O, E-5,9 undecadien-one) characterized by a ketone and two unconjugated double bonds. The study has been performed by temperature and coverage dependent valence band photoemission and room temperature scanning tunneling microscopy. The use of these combined techniques allows us to infer that the interaction between the geranyl acetone and the silicon surface occurs selectively through the rest atom and the carbonyl group, most likely through the oxygen atom. The geranyl acetone does not undergo any fragmentation upon adsorption Si(111)7x7, as has been observed for smaller molecules on the same surface {acetaldehyde [Y. Bu, J. Breslin, M. C. Lin, J. Phys. Chem. B 101, 1872 (1997)] for instance}. The interaction of the chain with the surface is weak and is characterized in the STM images as a darkening of one adatom in positive bias, around the reacted rest atom. (C) 2002 American Institute of Physics
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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