1,720,963 research outputs found
Development of nanocrystalline graphite for MEMS and membranes
No full textThin carbon films such as graphite and graphene are promising materials for micro- and nanoelectromechanical systems (MEMS and NEMS) applications, including resonators and switches, and also to be used as membranes for molecular sieving. The potential of these materials to be used in such applications is due to their electrical and mechanical properties, and also because they may be used as ultra-thin films. However, the most widely-used methods to synthesise these films have a tendency to cause poor performance in MEMS and NEMS. The most common technique, chemical vapour deposition (CVD) onto a catalyst, is followed by a physical transfer of the film to a separate substrate. This causes wrinkling and a variation in strain across the film, which leads to variable performance of MEMS and NEMS. Therefore, plasma-enhanced CVD (PECVD), which can be used to deposit nanocrystalline graphitic films directly onto large-area substrates, such as 6-inch silicon wafers, is a promising route to overcome this issue.Doubly-clamped beams and square micromechanical membranes were fabricated using nanographite films of 300 to 400 nm thickness, on silicon substrates. The compressive built-in stress of the film, measured as 436 MPa, caused these microstructures to buckle out-of-plane when they were released. The buckling behaviour of both structures was used as a characterisation tool to measure the Young’s modulus of nanographite, which is a key mechanical parameter of materials, and was measured as 23 GPa.To demonstrate the use of nanographite in a MEMS application, cantilever and doubly-clamped beam resonators of thickness around 300 nm were fabricated. Despite the built-in compressive stress of the film, the doubly-clamped beams were fabricated without buckling, and were under an effective tensile stress. This was achieved through the fabrication procedure, by using a 25 to 30 μm isotropic etch undercut of the 200 μm-wide anchors. The stress gradient in the film caused deflection of the anchors which ‘pulled’ the beams tight through the application of tensile stress. The devices were actuated electrostatically and the vibration response was measured using laser Doppler vibrometry. Cantilevers were measured with fundamental natural frequencies between 5 and 25 kHz, and for doubly-clamped beams natural frequencies were measured between 245 and 640 kHz. Quality factors under ambient pressure were around 5 to 10 for cantilevers and 20 to 30 for doubly-clamped beams, and around 1800 under 30 mTorr vacuum for a doubly-clamped beam.An ultrahigh vacuum system with mass spectrometer was constructed to measure the permeance of gases through nanographite thin films. The permeance of He, H2, Ne, CO2 and O2 through 350 nm thick nanographite membranes was measured. The permeance of He, H2 and Ne at 150 °C was 5.1, 4.0 and 0.08 × 10-10 mol / (m2 ·s · Pa), respectively, but the permeance of CO2 and O2 was below the limit of detection of the mass spectrometer. An estimation of the maximum permeance of CO2 and O2 respectively were 1.12 × 10-12 and 4.76 ×10-15 mol / (m2 ·s · Pa). The low permeance of Ne, CO2 and O2 relative to H2 and He showed that nanographite is a promising membrane material for molecular sieving
Effects of air exposure on the interfacial capacitance of laser-induced graphene (LIG) with and without silver (Ag) nanoparticle loading
No full textResearch on laser-induced graphene (LIG) and LIG with silver nanoparticles loading (Ag-LIG) are increasing by the day as more of its potential are uncovered each day. With the LIG fabrication looking to increase further in the future, it will be useful to confirm and verify any changes in the quality of LIG when it is exposed to the ambient air. In normal laboratory conditions, researchers store samples in petri dishes or any other covered storage, but inevitably the air within the storage will still be in contact with the samples. In this study, we left LIG and Ag-LIG samples in a lidded petri dish after its fabrication and measured the interfacial capacitance of each sample using a standard three-electrode electrochemical setup with a potential range from 0 V to 0.4 V on different days. Results show that the interfacial capacitance of both LIG and Ag-LIG drops as it is left in the storage container longer after its fabrication, with Ag-LIG showing a greater decrease after 10 days compared to LIG. This indicates that the silver nanoparticles played an important part during the oxidation process, making Ag-LIG more sensitive to its environment during prolonged unuse. The findings from this study shows the potential usage of LIG and Ag-LIG as a low-cost single-use indicator for air exposure
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
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
- …
