33,220 research outputs found
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
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
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
Bibliographie Hilarion G. Petzold 1958 – 2009 mit Anhang als Einführung
No full textDieses Archiv enthält die Gesamtbibliographie der Werke des Autors nebst einiger Texte „Über H. G. Petzold“ im Schlussteil der Bibliographie sowie einen Anhang mit einer Einführung in die Architektur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author and some texts about H. G. Petzold, moreover an epilogue with an introduction to the architecture of the works in its epistemological structure and composition and as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2009-petzold-h-g-gesamtbibliographie-h-g-petzold-1958-2009-updating-november2009/peerReviewedpublishedVersio
Wissenschaftliche Bibliographie Hilarion G. Petzold 1958 – 2014 mit Anhang von 2007 als Einführung
No full textDieses Archiv enthält die Gesamtbiliograpie der Werke des Autors bis Dez. 2013 nebst einiger Texte „Über H. G. Petzold“ und einen Anhang mit einer Einführung in die Struktur des Werkes in seinem wissenslogischen Aufbau als Ausarbeitung seines „Tree of Science Modells“ (2007).This archive contains the complete bibliography of the author up to Dec. 2013 and some texts about H. G. Petzold, moreover an appendix with an introduction to the structure of the work in its epistemological structure and composition as an elaborations of Petzold’s „Tree of Science Modell (2007).https://www.fpi-publikation.de/polyloge/01-2014-petzold-h-g-2014-wissenschaftliche-gesamtbibliographie-1958-2014/peerReviewedpublishedVersio
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
Graphene Properties by Functionalization with Organic Molecules
No full textWe review first the unique band structure of graphene and explain how the linear dispersion near the Fermi level determines the so called Dirac cones and relativistic effects. Then we will deal with simple organic moieties on graphene and discuss the modification of the electronic structure of the pristine graphene by donor and acceptor chemisorbed radicals and physisorbed molecules. The peculiar magnetism induced by functionalization with chemisorbed molecules is accounted for. For excited organic molecules we will outline the charge transfer process to graphene. Electron core-level excitations to the valence shell will be considered as in the measurements of transfer times by resonant spectroscopies. The lifetimes for charge transfer are considered and possible applications outlined. Femtomagnetism in graphene with core-excited adsorbates is presented together with its implications for magnetic ordering. The electric conduction in single molecular switches with graphene electrodes is analyzed. Finally, the properties of functionalized graphene as sensor are summarized
Nanooptics using organic nanofibers
No full textThe possibility to separate nanofibers from each other by distances that are larger than the wavelength of the emitted light allows one to investigate in detail the influence of morphological changes in the nanometer-range on the optical properties. As an example we show in Fig. 9.1 spectra obtained from a single para-hexaphenylene (p6P) nanofiber (circles) and from an ensemble of p6P nanofibers (solid line). The spectrum from the single nanofiber has been obtained by illuminating the nanofiber inside a microscope with UV light and sampling the emitted light also inside the microscope with an optical fiber, connected to a miniature spectrometer. The well-separated spectral lines are due to a vibronic progression of the exciton emission (perpendicular lines on top of the graph). In the case of the single nanofiber spectrum the highest energy (0,0) band is not visible due to a cut-off filter in the microscope. Nevertheless, comparison with the spectra from the needle ensembles reveals that the light emission becomes more focussed to a narrow color range (namely 420±5 nm) if an individual nanoaggregate is considered. More extended spectroscopic measurements along a nanofiber show that the spectral width of this residual line depends on the morphology of the aggregate and that it becomes narrower if the nanofiber width decreases, e.g., at the tip of the nanofiber [1]
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