3,664 research outputs found
Influence of nitrogen and temperature on the plasma deposition of fluorinated amorphous carbon films
No full textIn this work, the effects of nitrogen addition on the properties of a-C:H:F films produced by rf plasma enhanced chemical vapor deposition at different temperatures are reported. The structural and optical properties were investigated by x-ray photoelectron spectroscopy, Raman spectroscopy, ultraviolet-visible transmittance and ellipsometry measurements. The dependence of both fluorine and nitrogen incorporation in the carbon matrix on the deposition temperature was analyzed. The main effect of progressive nitrogen incorporation is a decrease of transmittance and optical band gap of the samples grown at room temperature and at 400 degreesC. Raman spectra evidence that for films deposited at 400 degreesC a sudden loss of sp(3) carbon bonding occurs. In particular, at fixed plasma composition, the decrease of the optical band gap is interpreted as a clustering of the existing sp(2) carbon sites. Ellipsometry characterization indicates that nitrogen incorporation for the samples deposited at room temperature induces an increase of the refractive index while films deposited at 400 degreesC are characterized by a reduction of the refractive index; this has been correlated to changes in the graphitic cluster size of the network. In particular, the increase in the deposition temperature produces an increase in the size of the graphitic clusters. (C) 2002 American Vacuum Society. RI Kenny, Jose/F-9372-201
Color-center waveguides in low-energy electron-bombarded lithium fluoride
No full textWe employ a differential version of m-line spectroscopy through grating coupling in order to measure the refractive index of low-energy electron irradiated lithium fluoride crystal channel waveguides for broadband emission. Using photoresist films and a holographic setup for grating fabrication, we perform an accurate characterization of bidimensional structures and a direct quantitative comparison between treated and blank materials
Structural changes of fluorinated amorphous carbon films by nitrogen incorporation
No full textIn this work, the effects of nitrogen addition on the properties of a-C:H:F films produced by radio-frequency plasma enhanced chemical vapor deposition at different temperatures are reported. The structural and optical properties were investigated by X-ray photoelectron spectroscopy, Raman spectroscopy, UV-VIS transmittance and ellipsometry measurements. The main effect of progressive nitrogen incorporation is a decrease of transmittance of the optical band gap of the samples grown at room temperature and at 400degreesC. Raman spectra evidence that for films deposited at 400degreesC a sudden loss of sp(3) carbon bonding occurs. In particular, at fixed plasma composition the decrease of the optical band gap is interpreted as a clustering of the existing sp(2) carbon sites. Ellipsometry characterization indicates that films deposited at 400degreesC are characterized by a reduction of the refractive index. In particular, the increase in the deposition temperature produces an increase in the size of the graphitic clusters. (C) 2002 Elsevier Science Ltd. All rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-201
Emission and excitation spectra of silicon-related luminescent centers in CVD-grown diamond films
No full textLuminescence properties of silicon-related centers in CVD-grown diamond films and their spatial distribution along the growth direction have been investigated. It is found that the lineshape and peak position of the emission band depend both on excitation energy and light focalization depth, suggesting the coexistence of two optical centers related to isolated vacancies and to silicon-vacancy complexes. A simple model of the electronic structure of this defect is proposed. (C) 1997 Elsevier Science S.A
Diamond photoluminescence spectra: dependence on excitation energy and microstructure
No full textPhotoluminescence data are presented for diamond films grown by different techniques (hot-filament CVD, microwave PECVD, DC arc-jet) and excited in the range 450-650nm by different laser sources. In large-grain textured samples, sharp vibronic structures, related to nitrogen and silicon impurity centers, are clearly observed, whereas in small-grain, randomly oriented films spectra are dominated by broad luminescence bands, whose maxima move with excitation energy. In the former case a careful deconvolution of emission spectra allows us to obtain vibronic parameters of the centers and their fine structure details, while excitation spectra give the energy location of higher electronic excited states. On the other hand, the line-shape and the excitation-dependent shift of broad luminescence bands are related to a continuous distribution of gap states, able to trap photogenerated electron-hole pairs. (C) 1998 Elsevier Science S.A
High-resolution X-ray imaging by polycapillary optics and lithium fluoride detectors combination
No full text""Abstract – Novel results on high-resolution X-ray imaging by a table-top laboratory system based on lithium fluoride (LiF) imaging radiation detectors and a X-ray tube combined with polycapillary optics are reported for the first time. In this paper, imaging experiments of reference objects, as well as thick geological samples, show some of the potentialities of this approach for the development of a compact laboratory X-ray microscopy apparatus. The high spatial resolution and dynamic range of versatile LiF imaging detectors, based on optical reading of photoluminescence from X-ray–induced color centers in LiF crystals and films, allow us to use very simple contact imaging techniques. Promising applications can be foreseen in the fields of bio-medical imaging diagnostics, characterization of X-ray sources and optical elements, material science and photonics."
Spontaneous emission properties of color centers based optical microcavities
No full textOptical microcavities based on lithium fluoride films treated by low-energy electrons to create visible-emitting F-2 color centers have been fabricated, and their radiative properties characterized for the first time. By tuning the photon cavity mode to the maximum of the luminescence band for the F-2 centers (similar to 670 nm), spectral narrowing, peak-intensity enhancement of the emission band as well as a highly directional radiation pattern have been observed comparatively for experiments performed on a half-cavity and a full microcavity, Spontaneous emission decay times have been measured, and a shortening of lifetime by the cavity has been observed. (C) 2001 Elsevier Science B.V. All rights reserved
Structural and optical properties of low energy electrons irradiated KCl:LiF multilayer films
No full textThe optical behaviour of point defects created by low energy electron beams is studied in multilayer KCI:LiF films, grown by thermal evaporation onto amorphous substrates at constant temperatures ranging from 30 to 350 degrees C. The surface morphology of the samples was observed by the atomic force microscopy (AFM) technique, Large concentration of F and F-aggregate centres has been produced by 3-7 keV electron irradiation both in KCI and LiF layers which constitute the film. By pumping our films with appropriate Ar+ laser lines, we measured, for the first time, the luminescence in the near infrared region due to F-2 and F-3 centres in KCl and the typical emission of F-2 and F-3(+) centres in LiF in the visible region
ZERO-PHONON LINES IN THE R2 ABSORPTION OF F3 CENTERS IN KF
No full textThe zero-phonon line and the structured multiphonon sideband of the R2 absorption in KF have been investigated in the temperature range 2-100 K. The values of the Huang-Rhys factor (approximately 2) and of the Debye temperature (241 K) were determined for R2 transition. Transverse acoustical phonons propagating along directions are most likely involved in the coupling of the F3 centres with the KF host lattice
Defect generation in low-energy ion-assisted thermal deposited lithium fluoride films
No full textWe present first results concerning stable formation of primary electronic defects and lithium nanometer sized clusters in LiF thin films grown by ion-assisted thermal deposition. The optical and morphological properties of the as grown LiF films, dependent on the deposition conditions, such as ion-beam energy and ion species (Xe, Ar), are reported. The experimental results show a larger efficiency of low-energy Xe ions in inducing the formation of lithium nano-clusters. To analyse the role of the deposition conditions, a preliminary interpretation of the lithium nano-cluster formation mechanism based on the spherical and/or cylindrical spike thermal model is given. (C) 2003 Elsevier B.V. All rights reserved
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