1,721,034 research outputs found
Solid-state dewetting of thin Au films studied with real-time, in situ spectroscopic ellipsometry
No full textWe report the design and testing of a small, high vacuum chamber that allows real-time, in situ spectroscopic ellipsometry (SE) measurements; the chamber was designed to be easily inserted within the arms of a commercial ellipsometer. As a test application, we investigated the temperature-induced solid-state dewetting of thin (20 to 8 nm) Au layers on Si wafers. In situ SE measurements acquired in real time during the heating of the samples reveal features that can be related to the birth of a localized surface plasmon resonance (LSPR), and demonstrate the presence of a temperature threshold for the solid-state dewetting
Monitoring the solid-state dewetting of densely packed arrays of Au nanoparticles
No full textWe report a real time, in-situ spectroscopic ellipsometry study of the temperature-induced solid-state dewetting of Au nanowires into nanoparticles. Very large spectral variations are observed at different temperatures. Analysis of the key features in the acquired spectra reveals two different regimes: up to 300 °C the variation in the optical response is dominated by solid-state dewetting, while above that temperature, smaller variations not compatible with such mechanism are visible. Therefore our ellipsometry measurements allow us to determine in real time at which temperature the solid-state dewetting ceases and the morphology of our sample becomes stable. We point out that this observation is possible thanks to the higher sensitiviy of ellipsometry with respect to reflectance/transmittance measurements
Thermoplasmonics of Ag Nanoparticles in a Variable-Temperature Bath
No full textSilver represents, by and large, the best plasmonic metal available, due to its very low optical losses in a broad photon-energy range encompassing all the visible optical spectrum. Its performances are, more often than not, severely hampered by the presence of a few-nanometer thick surface-tarnish layer; thermal annealing under high-vacuum (HV) conditions may however lead to its decomposition, thereby allowing to attain the clean-metal response. Here, we report an experimental investigation of the temperature dependence of the plasmonic response of Ag nanoparticles, either clean or tarnished, by means of in situ optical spectroscopies under HV conditions. For tarnished nanoparticles, we observed the temperature dynamics of thermal decomposition of the contamination layer in real time and compared it with the corresponding behavior of spatially extended, flat surfaces. For clean Ag nanoparticles we witness instead a remarkable temperature invariance of the localized-plasmon response, indicating Ag as a potential candidate for temperature-invariant thermoplasmonics applications
Temperature-dependent permittivity of silver and implications for thermoplasmonics
No full textSilver is an extremely appealing metal for plasmonics due to its very low optical losses in the visible and near-ultraviolet range and its relatively low reactivity. Within the emerging field of thermoplasmonics, where light-metal interactions are exploited to generate heat on the nanometric scale, knowledge of temperature-dependent complex permittivities of plasmonic materials is indispensable. We extracted the temperature-dependent complex permittivity of silver Ag by spectroscopic ellipsometry under high-vacuum conditions. For rising T, we observed an increase of the free-electron contribution to the imaginary part of the permittivity Im[Ag] and a temperature-dependent absorption band splitting off the interband absorption edge in the 320-360-nm range. Around 340 nm the relative increase of Im[Ag] at 600 K with respect to its room-temperature value is around 500%. In order to understand the implications of this behavior on silver thermoplasmonics, we computed the temperature-dependent extinction efficiency of oblate Ag ellipsoids with localized plasmon resonance within the 320-360-nm range. We predict that dramatic damping of the plasmon resonance occurs for increasing temperature, possibly leading to intriguing self-limiting effects in Ag thermoplasmonics
Plasmonics of Au nanoparticles in a hot thermodynamic bath
No full textElectromagnetically-heated metal nanoparticles can be exploited as efficient heat sources at the nanoscale. The assessment of their temperature is, however, often performed indirectly by modelling their temperature-dependent dielectric response. Direct measurements of the optical properties of metallic nanoparticles in equilibrium with a thermodynamic bath provide a calibration of their thermo-optical response, to be exploited for refining current thermoplasmonic models or whenever direct temperature assessments are practically unfeasible. We investigated the plasmonic response of supported Au nanoparticles in a thermodynamic bath from room temperature to 350 °C. A model explicitly including the temperature-dependent dielectric function of the metal and finite-size corrections to the nanoparticles' permittivity correctly reproduced experimental data for temperatures up to 75 °C. The model accuracy gradually faded for higher temperatures. Introducing a temperature-dependent correction that effectively mimics a surface-scattering-like source of damping in the permittivity of the nanoparticles restored good agreement with the data. A finite-size thermodynamic effect such as surface premelting may be invoked to explain this effect
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
Detecting ultrathin ice on materials for optical coatings at cryogenic temperatures
No full textThe performance of optical cavities in gravitational wave detectors (GWD) is negatively affected by the growth of ice layers when operating at cryo temperatures. Loss of performance begins when the ice overlayer is only a few-nm thick. Careful planning is then required to minimize, monitor and take into account the presence of ultrathin ice on cryo-cooled optical surfaces. Here we employed spectroscopic ellipsometry (SE) to study icing on the surfaces of SiO2 and Ti:Ta2O5 thin films, two materials used in the high-reflective mirrors of current GWD. SE measurements were performed at 75 K. The data presented suggest that SE is a most convenient tool to monitor in operando the ice formation on the surfaces of GWD mirrors. Furthermore, ultrathin ice layers can affect the evaluation of the optical properties of materials at low temperatures, a valuable task for those next-generation GWD that will operate at cryogenic temperatures. The characterization of an ultrathin ice overlayer ( < 10 nm) allowed to determine for the first time the low-temperature optical properties of Ti:Ta2O5. The same approach could be applied to determine the low-temperature optical properties of other dielectric films, thus helping to screen new materials for cryo-operated GWD mirrors
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