1,721,812 research outputs found
Realistic absorption coefficient of ultrathin films
No full textBoth a theoretical algorithm and an experimental procedure are discussed of a new route to determine the absorption/scattering properties of thin films deposited on transparent substrates. Notably, the non-measurable contribution of the film–substrate interface is inherently accounted for. While the experimental procedure exploits only measurable spectra combined according to a very simple algorithm, the theoretical derivation does not require numerical handling of the acquired spectra or any assumption on the film homogeneity and substrate thickness. The film absorption response is estimated by subtracting the measured absorption spectrum of the bare substrate from that of the film on the substrate structure but in a non-straightforward way. In fact, an assumption about the absorption profile of the overall structure is introduced and a corrective factor accounting for the relative film-to-substrate thickness. The method is tested on films of a well known material (ITO) as a function of the
film structural quality and influence of the film–substrate interface, both deliberately changed by thickness tuning and doping. Results are found fully consistent with information obtained by standard optical analysis and band gap values reported in the literature. Additionally, comparison with a conventional method demonstrates that our route is generally more accurate even if particularly suited for very thin films
Photoelectron-Beam Generation Up To Short Threshold
No full textWe report on the behaviour of electron beams extracted from metal cathodes illuminated by a powerful XeCl-laser beam. The target materials used were Zn, Y and Ge. During the electron extraction a plasma was created on the target surface. At high laser energies and high accelerating voltages the plasma introduces an impedance into the cathode-anode region. Owing to the plasma formation short-circuits occur in the accelerating region thus limiting the maximum output current. Under our experimental conditions, a laser energy of 27 mJ and 3 mm of distance cathode-anode, a maximum output corrent density of about 4.9 A/cm2 was obtained with the Zn cathode. The yttrium target may provide a higher current density but so far it could not be demonstrated due to plasma formation which short-circuits the anode-cathode region. The experimental results obtained with Ge targets are interesting for obtaining short electron pulses
Two different contact lens care systems effect on surface roughness in hydrogel and silicone hydrogel materials
No full textElectron Beams Induced By Excimer Lasers On Metal Targets
No full textThis work reports on the experimental results concerning electron beam emittance and current photo-extracted from aluminium, zinc and copper targets utilising two excimer lasers of different wavelengths, 308 nm (XeCl) and 222 nm (KrCl). The maximum laser energies utilised were limited by the high plasma density on the cathode that short-circuited the diode gap. The output current was higher with the KrCl laser than with the XeCl laser for the three metals used. The maximum extracted current, 1.03 A, was obtained with Cu targets at 20 kV of accelerating voltage, while at the same acceleration voltage a computer simulation of a space-charge limited electron beam resulted in a total current of only 200 mA and a normalised emittance of 22 pi mm mrad. The output current for large anode-cathode distance was higher than that predicted by the Child-Langmuir law while for small distances the current was lower than that theoretically calculated. This behaviour was attributed to plasma formation on the cathode during the laser action
Realistic absorption coefficient of each individual film in a multilayer architecture
No full textA spectrophotometric strategy, termed multilayer-method (ML-method), is presented and discussed to realistically calculate the absorption coefficient of each individual layer embedded in multilayer architectures without reverse engineering, numerical refinements and assumptions about the layer homogeneity and thickness. The strategy extends in a non-straightforward way a consolidated route, already published by the authors and here termed basic-method, able to accurately characterize an absorbing film covering transparent substrates. The ML-method inherently accounts for non-measurable contribution of the interfaces (including multiple reflections), describes the specific film structure as determined by the multilayer architecture and used deposition approach and parameters, exploits simple mathematics, and has wide range of applicability (high-to-weak absorption regions, thick-to-ultrathin films). Reliability tests are performed on films and multilayers based on a well-known material (indium tin oxide) by deliberately changing the film structural quality through doping, thickness-tuning and underlying supporting-film. Results are found consistent with information obtained by standard (optical and structural) analysis, the basic-method and band gap values reported in the literature. The discussed example-applications demonstrate the ability of the ML-method to overcome the drawbacks commonly limiting an accurate description of multilayer architectures
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
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