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Light Emission from Silicon Nanocrystals - Size Does Matter !
Robert G. Elliman,Andrew R. Wilkinson,Barry Luther-Davies,Marc G. Spooner,Marek Samoc,Max J. Lederer,Nathanael Smith,Tessica D.M. Weijers 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
A brief overview of two recent Si nanocrystal studies undertaken at the Australian National University is presented: recent work on hydrogen passivation of non-radiative defects and attempts to measure optical gain in waveguide structures. In the rst study, a generalized treatment of hydrogen passivation and desorption is employed to model the in uence of hydrogen on silicon nanocrystal luminescence. Values for reaction-rate parameters are determined from the model and found to be in excellent agreement with values previously determined for paramagnetic Si danglingbond defects (Pb-type centers) found at planar Si/SiO2 interfaces. In the second study, an attempt is made to measure optical gain in silicon nanocrystals by monitoring the intensity of a probe beam propagating in a waveguide structure containing silicon nanocrystals during photo-excitation of the nanocrystals. The probe beam is shown to be attenuated by the excitation demonstrating the dominance of absorptive processes. No gain was observed.
Choi, E. Y.,Mazur, L.,Mager, L.,Gwon, M.,Pitrat, D.,Mulatier, J. C.,Monnereau, C.,Fort, A.,Attias, A. J.,Dorkenoo, K.,Kwon, J. E.,Xiao, Y.,Matczyszyn, K.,Samoc, M.,Kim, D.-W.,Nakao, A.,Heinrich, B.,Ha The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.32
<P>We investigate the photophysical and amplified spontaneous emission properties of a series of monodisperse solution-processable oligofluorenes functionalized with hexyl chains at the C9 position of each fluorene unit. Thin films of these oligofluorenes are then used in organic field-effect transistors and their charge transport properties are examined. We have particularly focused our attention on the influence of oligofluorene length on the absorption and steady-state fluorescence spectra, on the HOMO/LUMO energy levels, on the photoluminescence lifetime and quantum yield as well as on the amplified spontaneous emission properties and the charge carrier mobilities. Differential scanning calorimetry and X-ray diffraction measurements demonstrate that, among all oligofluorene derivatives used in this study, only the structure and morphology of the pentafluorene film is significantly modified by a thermal treatment above the glass transition temperature, resulting in a 9 nm blue-shift of the fluorescence spectrum without significant changes in the photoluminescence quantum yield and in the amplified spontaneous emission threshold. In parallel, hole field-effect mobility is significantly increased from 8.6 × 10<SUP>−7</SUP> to 3.8 × 10<SUP>−5</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> upon thermal treatment, due to an increase of crystallinity. This study provides useful insights into the morphological control of oligofluorene thin films and how it affects their photophysical and charge transport properties. Moreover, we provide evidence that, because of the low threshold, the tunability of the amplified spontaneous emission and the photostability of the films, these oligofluorenes are promising candidates for organic solid-state laser applications.</P> <P>Graphic Abstract</P><P>We investigate the charge transport, photophysical and amplified spontaneous emission properties of a series of monodisperse solution-processable oligofluorenes functionalized with hexyl chains at the C9 position of each fluorene unit. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp01134a'> </P>
Charge carrier mobility study of a mesogenic thienothiophene derivative in bulk and thin films
Mazur, L.,Castiglione, A.,Ocytko, K.,Kameche, F.,Macabies, R.,Ainsebaa, A.,Kreher, D.,Heinrich, B.,Donnio, B.,Sanaur, S.,Lacaze, E.,Fave, J.L.,Matczyszyn, K.,Samoc, M.,Wu, J.W.,Attias, A.J.,Ribierre, Elsevier Science 2014 Organic electronics Vol.15 No.4
A novel mesogenic 2,5-bis-(5-octylthiophene)-thieno[3,2b]thiophene (TT) derivative has been synthesized. The fused-ring thiophene, end-capped with two octylthiophenes, exhibits ordered lamellar mesophases which were characterized by polarizing optical microscopy, differential scanning calorimetry and small-angle X-ray diffraction at various temperatures. The charge transport properties were investigated by time-of-flight technique as a function of temperature. On cooling from isotropic phase, a maximum hole mobility value of 0.07cm<SUP>2</SUP>V<SUP>-1</SUP>s<SUP>-1</SUP> was measured in the highly ordered mesophase of the bulk films. Field-effect transistor experiments on both solution and vacuum deposited thin films have also been performed. The solution-processed films exhibit charge carrier mobilities several orders of magnitude lower than values extracted from bulk time-of-flight curves and from vacuum deposited thin film transistors. This work provides evidence that the melt-processing route is an efficient alternative to commonly used solution-processing for fabrication of charge transporting layers from liquid crystalline semiconductors, with performances comparable to evaporation techniques.