1,720,986 research outputs found
White light-emitting LED using electrospun Alq3/P3BT composite microfibers
No full textWe prepared a white light-emitting LED by electrospinning small organic molecules (Alq3) and polymer (P3BT) composite microfibers directly onto a blue LED. The formation of the composite microfiber was optically characterized using the photoluminescence and Raman spectroscopy at the single strand level. We found that the 23:1 weight ratio of Alq3 and P3BT produced optimized white emission when combined with the intrinsic blue emission from the LED due to the fluorescence resonance energy transfer from the Alq3 to the P3BT. The environmentally friendly Alq3/P3BT organic composite microfibers efficiently demonstrated the photo conversion of blue LED into pure white LED. © 2014 Elsevier B.V.1561sciescopu
Heterogeneous modulation of exciton emission in triangular WS2 monolayers by chemical treatment
No full textChemical treatments were recently shown to be very effective in enhancing the exciton emission of monolayer transition metal dichalcogenides (1L-TMDs) by suppressing the exciton quenching caused by structural defects. However, the effects of these chemical treatments varied greatly depending on the synthesis method and the type of 1L-TMD; therefore, the exact origin of the emission enhancement is still elusive. Here we report the spatially heterogeneous effects of bis(trifluoromethane) sulfonimide (TFSI) and benzyl viologen (BV) treatment on the optical properties of triangular 1L-WS2 grown by chemical vapor deposition (CVD). Nanoscale photoluminescence (PL) and Raman spectral maps showed that TFSI had a minimal effect on the inner region of the triangular WS2 grain, whereas the PL of the edge region was enhanced up to 25 times; further, BV reduced the PL, also more strikingly in the edge region. Systematic variation of the spectral weights among neutral excitons, trions, and bi-excitons indicated that p-doping and n-doping with TFSI and BV, respectively, occurred in both the inner and edge regions; however, the PL enhancement was attributed mainly to the reduction of structural defects caused by TFSI treatment. Our observation of the spatially heterogeneous effects of chemical treatment suggests that the inner and edge regions of CVD-grown 1L-WS2 are populated with different types of structural defects and helps in clarifying the mechanism by which chemical treatment enhances the optical properties of 1L-TMDs. This journal is ©The Royal Society of Chemistry 20176
Gold nanoparticle hybridized rubrene nanofibers made by electrospinning: enhancement of optical and structural properties
No full textWe prepared gold nanoparticle (Au NP) hybridized organic rubrene nanofibers (NFs) using a convenient
electrospinning method. Au NPs of size 2–3 nm were incorporated throughout the light emitting
rubrene NFs, which was confirmed by high resolution transmission electron microscopy. Au NP
hybridized rubrene NFs showed a distinct nanoporous surface, compared to the smooth surface of
rubrene NFs. Nanoscale confocal spectroscopy was performed on a single NF level and the results
showed that the photoluminescence (PL) of the hybrid NFs made with 15 wt% Au NP mixture solution
was 2.5 times higher than the PL of the rubrene NFs. And the optical extinction (scattering and
absorption) of hybrid NFs increased monotonically with increasing Au NP concentrations. These
enhanced optical properties of hybrid NFs were attributed to localized surface plasmon resonance of the
embedded Au NPs. Structural modification from the monoclinic phase to the orthorhombic phase of the
rubrene structure was obtained by XRD analysis indicating a better ordering along the rubrene ab plane
of the hybrid NFs.1441sciescopu
Gate-Tunable Hole and Electron Carrier Transport in Atomically Thin Dual-Channel WSe2/MoS2 Heterostructure for Ambipolar Field-Effect Transistors
No full textAn ambipolar dual-channel field-effect transistor (FET) with a WSe2/MoS2 heterostructure formed by separately controlled individual channel layers is demonstrated. The FET shows a switchable ambipolar behavior with independent carrier transport of electrons and holes in the individual layers of MoS2 and WSe2, respectively. Moreover, the photo-response is studied at the heterointerface of the WSe2/MoS2 dual-channel FET
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim8911sciescopu
Simple method of DNA stretching on glass substrate for fluorescence imaging and spectroscopy
Full text linkWe demonstrate a simple method of stretching DNA to its full length, suitable for optical imaging and atomic force microscopy (AFM). Two competing forces on the DNA molecules, which are the electrostatic attraction between positively charged dye molecules (YOYO-1) intercalated into DNA and the negatively charged surface of glass substrate, and the centrifugal force of the rotating substrate, are mainly responsible for the effective stretching and the dispersion of single strands of DNA. The density of stretched DNA molecules could be controlled by the concentration of the dye-stained DNA solution. Stretching of single DNA molecules was confirmed by AFM imaging and the photoluminescence spectra of single DNA molecule stained with YOYO-1 were obtained, suggesting that our method is useful for spectroscopic analysis of DNA at the single molecule level. © 2014 Society of Photo-Optical Instrumentation Engineers.1771sciescopu
Confocal absorption spectral imaging of MoS2: Optical transitions depending on the atomic thickness of intrinsic and chemically doped MoS2
No full textWe performed a nanoscale confocal absorption spectral imaging to obtain the full absorption spectra
(over the range 1.5–3.2 eV) within regions having different numbers of layers and studied the variation of
optical transition depending on the atomic thickness of the MoS2 film. Three distinct absorption bands
corresponding to A and B excitons and a high-energy background (BG) peak at 2.84 eV displayed a
gradual redshift as the MoS2 film thickness increased from the monolayer, to the bilayer, to the bulk MoS2
and this shift was attributed to the reduction of the gap energy in the Brillouin zone at the K-point as the
atomic thickness increased. We also performed n-type chemical doping of MoS2 films using reduced
benzyl viologen (BV) and the confocal absorption spectra modified by the doping showed a strong
dependence on the atomic thickness: A and B exciton peaks were greatly quenched in the monolayer
MoS2 while much less effect was shown in larger thickness and the BG peak either showed very small
quenching for 1 L MoS2 or remained constant for larger thicknesses. Our results indicate that confocal
absorption spectral imaging can provide comprehensive information on optical transitions of microscopic
size intrinsic and doped two-dimensional layered materials.11411411sciescopu
Formation of nanosized monolayer MoS2 by oxygen-assisted thinning of multilayer MoS2
No full textWe report the controllable nanosized local thinning of multi-layer (2 L and 3 L)-thickness MoS2 films down to the monolayer (1 L) thickness using the simple method of annealing in a dry oxygen atmosphere. The annealing temperature was optimized in the range of 240 °C to 270 °C for 1.5 h, and 1 L thick nanosized pits were developed on the uniform film of the 2 L and 3 L MoS2 grown using the chemical vapor deposition method. We characterized the formation of the 1 L nanosized pits using nanoscale confocal photoluminescence (PL) and Raman spectroscopy. We observed that the PL intensity increased and the Raman frequency shifted, representative of the characteristics of 1 L MoS2 films. A subsequent hydrogen treatment process was useful for removing the oxygen-induced doping effect resulting from the annealing. © 2016 Author(s)6711sciescopu
Photoluminescence wavelength variation of monolayer MoS2 by oxygen plasma treatment
No full textWe performed nanoscale confocal photoluminescence (PL), Raman, and absorption spectral imaging measurements
to investigate the optical and structural properties of molybdenum disulfide (MoS2) monolayers synthesized
by chemical vapor deposition method and subjected to oxygen plasma treatment for 10 to 120 s under high
vacuum(1.3 × 10−3 Pa). Oxygen plasma treatment induced red shifts of ~20 nmin the PL emission peaks corresponding
to A and B excitons. Similarly, the peak positions corresponding to A and B excitons of the absorption
spectra were red-shifted following oxygen plasma treatment. Based on the confocal PL, absorption, and Raman
microscopy results, we suggest that the red-shifting of the A and B exciton peaks originated from shallow defect
states generated by oxygen plasma treatment.1991sciescopu
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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