F. Flora

ENEA, Roma, Latium, Italy

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Publications (208)200.66 Total impact

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    ABSTRACT: a b s t r a c t Plasma wakefield acceleration is the most promising acceleration technique known nowadays, able to provide very high accelerating fields (10–100 GV m À 1), enabling acceleration of electrons to GeV energy in few centimetres. However, the quality of the electron bunches accelerated with this technique is still not comparable with that of conventional accelerators; radiofrequency-based accelerators, in fact, are limited in the accelerating field (10–100 MV m À 1) requiring therefore kilometric distances to reach the GeV energies, but can provide very bright electron bunches. Combining high brightness electron bunches from conventional accelerators and high accelerating fields reachable with plasmas could be a good compromise allowing to further accelerate high brightness electron bunches coming from LINAC while preserving electron beam quality. Following the idea of plasma wave resonant excitation driven by a train of short bunches, we have started to study the requirements in terms of plasma for SPARC-LAB [1,2]. In particular, here we focus on the ionization process; we show a simplified model to study the evolution of plasma induced by discharge, very useful to design the discharge circuit able to fully ionize the gas and bring the plasma at the needed temperature and density. & 2013 Published by Elsevier B.V.
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    ABSTRACT: Schwarzschild objectives are widely used in the extreme ultraviolet (EUV)/soft X-ray spectral region both as reduction and magnification optics, e.g. for small-field projection lithography and microscopy, respectively. When using a Schwarzschild objective as a micro-exposure tool (MET) at high spatial resolution (half-pitch≤0.1 μm), in addition to the tight requirements on the design and surface figure for the single optics, also an accurate alignment between the two mirrors is needed to reach the planned spatial imaging detail. Ideally, at-wavelength alignment should be done in order to overcome limitations due to diffractive effects. While this can be easily performed on synchrotron beam lines, it becomes time expensive (and components consuming) on low-power laboratory plasma sources. In this work we propose and test a new technique to align a EUV Schwarzschild objective by means of ultraviolet light. The aligned objective allowed the attainment of lithographic patterning with edge response of 90 nm, as part of the laboratory-scale MET for EUV projection lithography realized at the ENEA Frascati Research Centre.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2013; 720:168–172. · 1.14 Impact Factor
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    ABSTRACT: While developing a laboratory-scale micro-exposure tool for extreme ultraviolet (EUV) projection lithography which uses a laser-produced plasma emitting EUV pulsed radiation, we faced the problem of suppressing the various debris (ions, neutrals, particulate, clusters, droplets) emitted by the plasma target. The suppression of debris is a crucial task in the frame of EUV projection lithography, mainly because debris seriously limit both lifetime and performance of the expensive optics and filters put close to the plasma source. In this paper we present the experimental measurements of main debris characteristics (velocity, size, charge, momentum, spectral energy, spatial distribution). Then, we present the operating results of a patented debris mitigation systems (DMS) specifically designed to suppress debris with the measured characteristics. We achieved reduction factors ∼800 for atoms and nm-size clusters, and ∼1600 for particles larger than 500 nm. These results are at the forefront in this field. The excellent performance of our DMS was a breakthrough to achieve a 90-nm patterning on commercial resists by our micro-exposure tool EUV projection lithography.
    Applied Surface Science 05/2013; 272:13–18. · 2.54 Impact Factor
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    ABSTRACT: An analytical method, based on an approximated solution of Keplero’s equations, is here proposed. This method allows, in a simple and fast way, to calculate the sun position at any time and everywhere in the world at an angular accuracy of 1 minute. The algorithm can easily be implemented in economic microprocessors so that any sun tracking device for concentrating solar installations could be guided toward the sun at high accuracy without the need of optical components. Two methods for a correct trackers installation are finally described.
    ENEA Technical Report. 12/2012; 2012(24).
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    ABSTRACT: We present a recently patented apparatus which consists of an extreme ultraviolet radiation source writing invisible patterns on thin tags of alkali halides. The tags patterned using this method are almost impossible to counterfeit, and offer a much better protection against fakes than available anti-counterfeiting techniques. We will discuss if this novel technology is ready for industrial production of anti-counterfeiting tags.
    Proc SPIE 01/2012;
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    Knowledge, Diagnostics and Preservation of Cultural Heritage, Edited by P. Clemente, P. Di Lazzaro, R. Giorgi, 01/2012: chapter Is this artwork original or is it a copy? The answer by a new anti-counterfeiting tag: pages 162-168; ENEA.
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    ABSTRACT: We present the realization and characterization of photoluminescent nanometric periodic patterns of color centers (CCs) in lithium fluoride (LiF) produced by an interferometric method based on a coherent soft X-ray laser beam. Among broad-band light-emitting materials, LiF, in the form of crystals and thin films, is a radiation-sensitive material well known in dosimetry and as a laser-active medium in optically pumped photonic devices. Primary and aggregate electronic defects can be produced in LiF by low-penetrating electromagnetic radiation, like soft X-ray. The high brightness and spatial coherence of a capillary discharge laser, with the emission wavelength of 46.9 nm, allowed writing periodic lines of stable CCs at a nanometric scale emitting visible light under optical pumping. Interferometric encoding of luminescent nano-structures in LiF proved to be a powerful tool for producing low-dimensionality optical devices for photonic applications.
    Journal of Non-Crystalline Solids 08/2010; 356:1968-1971. · 1.72 Impact Factor
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    ABSTRACT: The Los Alamos suite of atomic codes is used to model several high-resolution spectral measurements from recent laser-produced plasma experiments involving barium fluoride targets. The spectral range of observation is from 7.8 to 9.5 Å and the observed lines correspond to 3–5, 3–6, 3–7 and 3–8 transitions of principal quantum number, for Ga-like through Co-like barium ions. The observed spectra are complicated because of many overlapping lines from the various ion stages in a small wavelength region. A MUTA model that includes many configurations is compared to a detailed level-to-level collisional-radiative model that includes fewer configurations. Spectra are calculated to show the sensitivity to plasma temperature, density and size. The contributions to the spectra for the individual ion stages are also presented. The model calculations are in reasonable agreement with experiment.
    Journal of Physics B Atomic Molecular and Optical Physics 08/2010; 43(17):175701. · 2.03 Impact Factor
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    ABSTRACT: Among insulating materials containing point defects, lithium fluoride (LiF) is a radiation-sensitive alkali halide well known in dosimetry and as active medium in light-emitting devices and lasers. Electronic point defects can be produced in LiF crystals and films by different kinds of radiation. Some of these electronic defects, known as colour centres, are optically active, with broad absorption and emission bands in the visible spectral range. Novel thin-film imaging detectors for extreme ultraviolet and soft X-rays, based on photoluminescence from aggregated colour centres in LiF, have been proposed and are currently under development, successfully extending their operation also in the hard X-ray region, up to 10 keV. Among the main peculiarities of LiF-based detectors, there are intrinsic high spatial resolution, in principle limited only by the point defect size, large field of view and wide dynamic range. These imaging detectors feature great versatility, as they can be grown in the form of thin films on different substrates by well-assessed physical deposition techniques. We present the promising results obtained using different X-ray laser–plasma sources in the field of nanotechnology, biology and in material science in view of future perspectives of research and development.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2010; · 1.14 Impact Factor
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    ABSTRACT: The use of LiF thin films and single crystals was proposed and tested as X-ray imaging detector based on optically stimulated luminescence from visible-emitting color centers. The main peculiarities of this detector – i.e. high spatial resolution on a large field of view, wide dynamic range, versatility and simplicity of use – make it very promising as X-ray imaging plate for applications in photonic devices, biology and material science, as well as in the characterization of intense X-ray sources. In order to investigate the response and the sensitivity of this detector to soft X-rays, a suitable characterization of colored thin layers is performed by means of optical spectrophotometry and photoluminescence spectroscopy for samples colored under different irradiation conditions.
    Journal of Luminescence 12/2009; 129(12):1964-1967. · 2.14 Impact Factor
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    ABSTRACT: This study is related to the application of the X-ray dual-energy microradiography technique together with the atomic absorption spectroscopy (AAS) for the detection of lead on Zea mays stem, ear, root, and leaf samples. To highlight the places with lead intake, the planar radiographs taken with monochromatic X-ray radiation in absorption regime with photon energy below and above the absorption edge of a given chemical element, respectively, are analyzed and processed. To recognize the biological structures involved in the intake, the dual-energy images with the lead signal have been compared with the optical images of the same Z. mays stem. The ear, stem, root, and leaf samples have also been analyzed with the AAS technique to measure the exact amount of the hyperaccumulated lead. The AAS measurement revealed that the highest intake occurred in the roots while the lowest in the maize ears and in the leaf. It seems there is a particular mechanism that protects the seeds and the leaves in the intake process.
    Microscopy Research and Technique 12/2009; 73(6):638-49. · 1.59 Impact Factor
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    ABSTRACT: Debris mitigation is still a critical issue for the development of extreme ultraviolet projection lithography (EUVL). Here, we describe the analysis of the efficiency of the debris-mitigation system (DMS) presently in use in the laser–plasma–source micro-exposure tool (MET) operating at the Frascati ENEA Research Center. Basic to such an analysis is a code specifically developed for processing the images of debris-flux-exposed glass slides. The code stands out as a tool for further plasma debris-related analyses.
    Applied Physics B 08/2009; 96(2):479-490. · 1.78 Impact Factor
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    ABSTRACT: We present a low-cost microexposure tool for projection lithography at 14.4 nm we have designed and operated at the ENEA Research Centre, Frascati. It is a laboratory-scale system based on a Schwarzschild-type projection optics which uses a laser-plasma soft X-ray source, equipped with a patented debris mitigation system in order to preserve the collector optics. As a preliminary result, we achieved a 90-nm optical resolution patterning on commercial resist. A sharp improvement in resolution size is expected when operating this tool by a large-output energy excimer laser in order to obtain a single-shot patterning.
    IEEE Transactions on Plasma Science 05/2009; · 0.87 Impact Factor
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    ABSTRACT: Spectra have been recorded from a Xe discharge capillary source in the extreme ultraviolet (EUV) region of the spectrum, between 10 and 18 nm. Features due to 4d–4f and 4d–5p transitions in a range of ions have been observed, with the 4d–4f emission from ions Xe8+–Xe12+ clearly identified in the spectrum. The power emitted into a range of bands in the EUV has been measured and the effects on the spectrum of adding SnO2 and In2O3 powders to the Xe discharge have been quantified. The influence of indium ions on the spectrum, in particular, is to increase the emission in the region of 14.3 nm by as much as 30% over the pure xenon spectrum.
    Plasma Sources Science and Technology 02/2009; 18(2):025014. · 2.52 Impact Factor
  • Synchrotron Radiation and Nanostructures: Papers in Honour of Paolo Perfetti - The Workshop; 01/2009
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    ABSTRACT: We report the high-resolution patterning achieved by the laboratory-scale micro-exposure tool for extreme ultraviolet projection lithography realized at the ENEA Frascati Research Center in the frame of a National Project. Such a result obtained using a laser-produced-plasma source, a couple of twin ellipsoidal collectors and a low-cost Schwarzschild-type projection optics shows that it is possible to attain a nanometer-scale spatial resolution using relatively inexpensive projection optics.
    EPL (Europhysics Letters) 12/2008; 84(5):58003. · 2.26 Impact Factor
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    ABSTRACT: A lithium fluoride (LiF) crystal has been utilized as a new soft X-ray detector to image different biological samples at a high spatial resolution. This new type of image detector for X-ray microscopy has many interesting properties: high resolution (nanometer scale), permanent storage of images, the ability to clear the image and reuse the LiF crystal, and high contrast with greater dynamic range. Cells of the unicellular green algae Chlamydomonas dysosmos and Chlorella sorokiniana, and pollen grains of Olea europea have been used as biological materials for imaging. The biological samples were imaged on LiF crystals by using the soft X-ray contact microscopy and contact micro-radiography techniques. The laser plasma soft X-ray source was generated using a Nd:YAG/Glass laser focused on a solid target. The X-ray energy range for image acquisition was in the water-window spectral range for single shot contact microscopy of very thin biological samples (single cells) and around 1 keV for multishots microradiography. The main aim of this article is to highlight the possibility of using a LiF crystal as a detector for the biological imaging using soft X-ray radiation and to demonstrate its ability to visualize the microstructure within living cells.
    Microscopy Research and Technique 10/2008; 71(12):839-48. · 1.59 Impact Factor
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    ABSTRACT: Within a National Project on nanotechnologies, at the ENEA Research Centre in Frascati a micro-exposure tool for projection lithography at 14.4 nm has been developed. The laser-plasma soft X-ray source is equipped with a patented debris mitigation system developed in the frame of a European Integrated Project, in order to preserve the collecting optics. A 90-nm-resolution patterning has been achieved on resist by this laboratory-scale tool based on a Schwarzschildtype projection optics.
    Proc SPIE 10/2008;
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    ABSTRACT: In this article, a method to reveal the presence of Mg content inside the different parts of leaves of Hedera helix is presented. In fact a sample of a Hedera helix's leaf, commonly characterized by a green and a white side, is analyzed under X-ray radiation. The presence of two zones with different colors in the Hedera helix's leaf has not been explained. In this connection, there are presently three hypotheses to explain the characteristic double-color appearance of the leaf. The first hypothesis suggests a different cytoplasmic inheritance of chloroplasts at the cell division, the second a different allelic composition, homozygote and heterozygote, between the two zones, and finally the third the action of a virus which changes the color properties in the Hedera's leaves. The resulting effect is a different content of "something" between the green and the white side. We utilized X-ray radiation, obtained from a plasma source with a Mg target, to image Hedera helix leaves and we found that the green side of the leaf is highlighted. We may suppose that the reason why the X-rays from a Mg plasma source, allow us to pick up the green side is probably due to the greater presence of the amount of Mg (from chlorophyll or other complexes and/or salts) in the two sides, green and white, of the leaf.
    Microscopy Research and Technique 07/2008; 71(6):459-68. · 1.59 Impact Factor
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    ABSTRACT: An extremely promising complete nanofabrication process of metallic patterns, to achieve periodic structure resolution well below 100 nm, has been successfully demonstrated. The process includes the EUV patterning encoding on the photoresist and its transfer from the polymer onto a Si substrate using a 46.9 nm table top soft x-ray laser and an interference lithography scheme. After optimizing the PMMA-poly(methyl methacrylate)-preparation thickness and development, by controlling the metal deposition and subsequent liftoff process on the exposed PMMA/SiO(2)/Si(1 0 0) samples, we have fabricated large arrays of 200 nm spaced nickel strips on Si surfaces.
    Plasma Sources Science and Technology 05/2008; 17(2). · 2.52 Impact Factor

Publication Stats

733 Citations
200.66 Total Impact Points


  • 1990–2013
    • ENEA
      • • Applied Physics Division
      • • Frascati Research Centre
      Roma, Latium, Italy
  • 2005
    • Vanderbilt University
      • Department of Physics and Astronomy
      Nashville, MI, United States
  • 2004
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
  • 2002
    • Brno University of Technology
      • Institute of Physical Engineering
      Brno, South Moravian Region, Czech Republic
  • 1997
    • École Polytechnique
      Paliseau, Île-de-France, France