1,721,037 research outputs found
Room temperature adsorption of Na on Si(111)-7×7 as studied by resonant optical second harmonic generation
No full textResonantly enhanced optical second harmonic generation at a pump laser energy of 1.17 eV was applied to investigate the Na-adsorption process on the 7 x 7 reconstructed Si(1 1 1) surface at room temperature. The change of second harmonic (SH) intensity as a result of Na deposition at normal incident pump radiation varies significantly from that measured at 45 degrees angle of incidence. The observed difference can be explained in terms of electronic transitions from the rest-atom state to the adatom state of the 7 x 7 reconstructed Sill 1 1) surface as well as of the features of Na growth on the silicon surface. By measuring the SH polarization dependence for different stages of Na deposition, a change of the interface symmetry in both directions, namely, parallel and perpendicular to the (1 1 1) plane, was clearly observed at the very beginning of the adsorption process. (C) 2001 Elsevier Science B.V. All rights reserved
Resonant effects in optical second-harmonic generation from alkali covered
No full textPolarized second-harmonic generation (SHG) coverage dependencies
for alkali (\chem{Na, Li}) adsorption on \chem{Si(111)}
both at room and at low temperatures are obtained for fundamental
wavelengths of 497\un{nm}, 570\un{nm} and 1067\un{nm}, showing
characteristic and reproducible non-monotonic changes of SHG
efficiency. At submonolayer coverage the SHG intensities are
qualitatively different for visible vs. near-resonant IR
radiation. In the coverage regime , low-symmetry
\chem{Na}-\chem{Si} bonds, resulting from a \chem{Na}-induced surface
reconstruction, are formed, which are resonant with 1067\un{nm}
radiation. By comparing parallelly and perpendicularly polarized
coverage dependencies, we deduce that the resonant contribution in
the parallel configuration is due to the
-component
Organic nanofibers as new media for lasing, waveguiding and photonic sensing
No full textWe report waveguide amplification of spontaneous emission and coherent random laser action in individual self-assembled organic nanofibers grown by high-vacuum deposition. The interpretation of the experimental results is given on the basis of simple models, including transfer matrix calculations in one-dimensionally disordered structures. We present also the numerical results for light scattering from a nanofiber which can be used as a basis for further experiments
Pulsed laser desorption of alkali atoms from PDMS thin films
No full textThe dynamics of short pulsed laser-induced desorption of alkali atoms from poly-dimethylsiloxane (PDMS) coated glass prism surfaces is investigated. Kinetic energies of desorbing sodium atoms of several hundred meV are found, increasing with increasing laser fluence. Evanescent wave measurements suggest that the desorbed atoms stem from a subsurface layer of the PDMS film, resulting in diffusional characteristics for the total yield of the desorption process. © 2004 Elsevier B.V. All rights reserved
Degradation pathways in standard and inverted DBP-C 70 based organic solar cells
Get PDFAchieving long-term stability in organic solar cells is a remaining bottleneck for the commercialization of this otherwise highly appealing technology. In this work, we study the performance and stability differences in standard and inverted DBP/C70 based organic solar cells. Differences in the charge-transfer state properties of inverted and standard configuration DBP/C70 solar cells are revealed by sensitive external quantum efficiency measurements, leading to differences in the open-circuit voltages of the devices. The degradation of standard and inverted solar cell configurations at ISOS aging test conditions (ISOS-D-3 and ISOS-T-3) was investigated and compared. The results indicate that the performance drop in the small molecule bilayer solar cells is less related to changes at the D-A interface, suggesting also a pronounced morphological stability, and instead, in the case of inverted cells, dominated by degradation at the electron transport layer (ETL) bathocuproine (BCP). Photoluminescence measurements, electron-only-device characteristics, and stability measurements show improved exciton blocking, electron transport properties and a higher stability for BCP/Ag ETL stacks, giving rise to inverted devices with enhanced performance and device stability
Dynamics of laser-induced Cesium atom desorption from porous glass
No full textThe dynamics of short pulsed infrared laser-induced desorption of Cesium atoms from porous silica samples has been investigated. We find most probable kinetic energies of 69 ± 6 meV for desorption laser fluences between 60 and 190 mJ/cm2, significantly higher compared to those obtained for Cs desorption from plain glass, 40 ± 2 meV, but lower compared to those observed for Na and Rb desorption from polymeric surfaces, 200 meV. This is explained qualitatively by scattering of the desorbing atoms with the silica nanochannels, thus suggesting different pulsed laser photodesorption processes for atoms embedded in hard porous dielectrics as compared to polymeric thin films. © 2006 Elsevier B.V. All rights reserved
UV laser-induced grating formation in PDMS thin films
No full textExcimer laser (193 nm and 157 nm) induced ablation and structure formation in poly-dimethylsiloxane (PDMS) thin films is demonstrated. Ellipsometric measurements provide values of the optical constants of the films as well as their thicknesses, which are below 1 mum. At fluences above 160 mJ/cm(2) two pulses of UV light induce gratings with at minimum 1-mum periods and crossed gratings with 4-mum periods. The structure heights are between 10 nm and 20 nm with ridge widths of several hundred nanometres. The ablation occurs after a single incubation pulse with a threshold that increases logarithmically with the ablation wavelength increasing from 157 nm to 1064 nm. At 193 nm the ablation rate for 2 J/cm(2) is 127 nm/pulse
Organic crystalline nanofibers; Manipulation, integration and electrical characterization
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