1,720,978 research outputs found
High resolution pixel definition in hybrid microcavities
No full textIn this work, we demonstrate the realization of a multicolor organic microcavity built in a single step process by locally tuning the optical length of the cavity by means of a suitable pattern. A lithographic 3D hard pattern has been realized on the surface of the top mirror and then pressed over the bottom one, which was coated with a PMMA-rubrene blend. Because of the different height of the pattern, the optical length of the cavity is spatially modulated, while the physical length remains constant on the whole device. This allows to locally tune the single mode resonance with a high spatial resolution. (c) 2007 Elsevier B.V. All rights reserved
Fabrication of disordered photonic crystal structures for organic random lasing devices
Full text linkIn this work we show the fabrication of disordered structures for organic random lasing devices by means of the combined use of two
high resolution techniques, namely electron beam lithography (EBL) and nano imprint lithography (NIL). We have developed a model
for random lasing disordered structures by introducing a well defined degree of disorder in a regular photonic crystal (PC) pattern.
Before the fabrication of the device, a preliminary modelling of the ordered 2D-PC has been realized by a finite difference time domain
(FDTD) based simulation software. Subsequently, random point defects were introduced in the ordered pattern in order to study the
influence of disorder on the reflection spectra and to establish the presence of localized modes. The engineered random pattern was transferred
through EBL and reactive ion etching (RIE) onto a Si substrate, thus obtaining an hard master used in the following imprint process
of polyfluorene (PFO). Preliminary optical characterization collected from one edge of the structure show the occurrence of localized
modes which have been attributed to random scattering in the patterned organic layer
Fabrication of high efficiency compact 90° bend waveguide by using a dielectric 2D-PC structure
No full textIn this paper we propose the design and the fabrication of 90° bend ridge waveguide (WG) assisted by a two-dimensional photonic crystal (2D-PC). 2D-PCs act as efficient minors along the boundaries of the bend ridge thus reducing the in-plane losses. The ridge waveguide consists of a 3 μm x 0.75 μm titanium dioxide core on a silica bottom cladding. The 2D-PC structure surrounding the bend waveguide is composed of a triangular array of circular dielectric pillars having a height of 0.75 μm. The titanium dioxide waveguiding core layer is covered with PMMA in order to create a quasi-symmetric structure. A photonic band gap centered around 1.3 μm is obtained by a PC radius r = 0.33a and lattice period a = 0.450 μm. The design of the whole structure is subsequently optimized by using a 3D Finite Difference Time Domain based computer code. The ridge waveguide assisted by a 2D-PC has been fabricated by using electron beam lithography and reactive ion etching. For the pattern transfer we have used ∼ 50 nm thin layer Cr metal etch mask obtained by means of a lift-off technique based on the use of bi-layer resist (PMMA/MMA). The presence of the 2D-PC around the bend waveguide leads to a sharp increase of the transmission efficiency around 1.3 μm for curvature radius of 2.5 μm. The bend transmission results to be in the range between 0.76 and 0.85 when the thickness of the ridge WG and of the 2D-PC pillars is between 0.75 and 1.3 μm. This value is more than twice with respect to the bend waveguide without 2D-PC
High efficiency and high modal gain InAs/InGaAs/GaAs quantum dot lasers emitting at 1300 nm
No full textHigh performance 1300 nm lasers based on self-organized InAs/InGaAs quantum dots (QDs) are reported. By optimizing the QD growth parameters and decreasing the waveguide thickness, a high modal gain and a low transparency current density of 32 cm-1 and 35 A cm-2, respectively, were obtained from a device containing five stacked QD layers. The internal quantum efficiency is as high as 90%
Fabrication of colloidal quantum dot microcavities by imprint lithography
No full textColloidally synthesized CdSe/ZnS core/shell semiconductor nanocrystals (NCs) show highly efficient, narrow-width and size-tunable luminescence. Moreover, they can be incorporated in polymer matrices and deposited on solid substrates by means of spin-coating techniques. When embedded between two mirrors a NCs/polymer blends microcavity is realised, thus allowing to tailor the photoluminescence spectrum of these emitters. By virtue of the quantized photonic and electronic density of states, colloidal quantum dots embedded in a single mode vertical microcavity are good candidates for the fabrication of high-efficiency emitting devices with high spectral purity and directionality. In this paper, we have applied an organic-inorganic hybrid technology for the fabrication by imprint lithography (IL) of vertical microcavities that embed colloidal quantum dots. The technique exploits a λ-thick microstructured dielectric top-mirror pressed onto the bottom one, previously coated with the active layer, to sandwich the cavity and precisely control its thickness. Room-temperature photoluminescence measurements show a Q-factor as high as 146 for our devices
High-Purcell-factor dipolelike modes at visible wavelengths in H1 photonic crystal cavity
No full textThe optimization of H1 photonic crystal cavities for applications in the visible spectral range is reported, with the goal to obtain a versatile photonic platform to explore strongly and weakly coupled systems. The resonators have been realized in silicon nitride and weakly coupled to both organic (fluorophores) and inorganic (colloidal nanocrystals) nanoparticles emitting in the visible spectral range. The theoretical Purcell factor of the two dipolelike modes in the defect has been increased up to ∼90, and the experimental quality factor was measured to be ∼750
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
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