1,721,002 research outputs found
Fabrication and characterisation of CVD-graphene nanoribbon single electron transistors
No full textGraphene was the first 2 dimensional material discovered and rapidly received a lot of attention because of its astounding properties. It is still the highest conductivity material recorded and very robust despite its single atomic layer thickness. However a key issue with graphene has been that it is a semimetal and not a semiconductor, so it lacks a band gap. Originally a large amount of focus was on researching methods to overcome this issue for logic devices. At first the patterning into nanoribbons was seen as a method to achieve this, but the fabrication of a nanoribbon came at a cost of graphene’s high mobility electrons. From conducting this research an interesting property of graphene emerged. It was capable of acting intrinsically as a single electron transistor, enabling a different type of more than Moore device to be fabricated that can be used in future nanoelectronic applications.The aim of this project has been to investigate the transport properties of polycrystalline graphene grown using chemical vapour deposition. The use of polycrystalline graphene enables the fabrication of wafer scale devices that can be stacked on a large variety of surfaces. So far though there has been a lack of investigation into the scaling effects of polycrystalline graphene nanoribbons and the single electron tunnelling properties associated with them. This work presents the first detailed investigation into their properties and shows that polycrystalline graphene can be used for producing high quality single electron transistors. Nanoribbons are fabricated down to sub 20 nm widths with high aspect ratio transitions from wide to narrow segments. The single electron transistor has demonstrated a single quantum dot impacted by the effect of energy level spacing
Sensing performance of nanocrystalline graphite based humidity sensors
Full text linkEnvironmental sensors play a crucial role in a wide range of applications. Amongst them, humidity sensors that are stable and operational in harsh environments are incredibly important for process control and monitoring. Nanocrystalline graphite (NCG) is a type of carbon-based thin film material. Previous work has shown that NCG has excellent mechanical properties and is able to withstand high radiation doses. The granular structure of the NCG film makes it a good candidate for humidity sensing as the film consists of conductive graphitic grains with a high density of sp2 bonds and amorphous grain boundaries with high resistivity, adsorption of water molecule onto the film forms conductive pathways between grains through the Grotthuss mechanism which lowers the resistance of the film by a measurable amount. Here we report for the first time, a working humidity sensor with linear response, fabricated using NCG as the sensing material for harsh, real-world environments, which include exposure to weak acids via rainfall, UV radiation, mechanical wear, and high humidity environments. The calculated sensitivity of the best-fabricated sensor is S = 0.0334%, with a maximum resistance change of -4.4 kOhms, over the range of 15% RH to 85% RH. The response time of the sensor is 20ms with the current measurement setup. The baseline resistance value of the sensor at 15% RH is 210 kOhms. The sensor has the potential to be used as a humidity sensor for harsh environments due to the chemical, thermal and mechanical stability of the NCG film
Estimating the surface adhesion force using pull-in/-out hysteresis in comb-drive devices
No full textSurface adhesion forces play a critical role in the operation of NEM relays, but characterization data for micro/nanoscale contact areas of relevant materials are scarce. A novel technique to estimate the adhesion force between two contacting surfaces is presented. This method uses the hysteresis in the pull-in/-out voltages measured experimentally in electrostatically actuated comb-drive and circular NEM devices with two contacting electrodes. In these geometries the electrostatic actuation force is independent of the device displacement and the surface adhesion forces can be analytically calculated from the force balance describing the pull-out event. Finite-element ANSYS simulations of the electromechanical behavior of the devices support the analytical approach. Adhesion forces of 0.081 μN and 0.167 μN were calculated for Au-Au and Ti-Ti contacts with areas of 750 nm × 300 nm and 100 nm × 300 nm, respectively.</p
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
Awl spring MEMS switches with nanocrystalline graphite sidewall coating using spacer etch method
No full textLong cycling of MEMS switches, especially in a high temperature environment, can degrade the contact resulting in decreased switching reliability. Different contact coatings including metals, amorphous carbon and nanocrystalline graphite (NCG) have been proposed but carbon-based contact appear to greatly increase cycling reliability due to their low stiction and friction coefficient properties. However, establishing a good contact coating on the beam sidewall of an in-plane MEMS switch is still challenging, while out-of-plane MEMS fabrication is complicated as it involves multiple lithography steps and suffers residual stresses in deposited layers. Therefore, we propose a one-step lithography process to define the MEMS switch structure and then use a spacer etch method to create a reliable NCG sidewall coating on the drain contact region. We use plasma enhanced chemical vapour deposition (PECVD) method to deposit undoped NCG coatings on a double-clamp in-plane awl meander spring MEMS switch. The MEMS switch is subjected to cold- and hot-cycling electrical measurements to evaluate which of the NCG coatings is suitable for long switching operation
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
- …
