A. Creti

INO - Istituto Nazionale di Ottica, Florens, Tuscany, Italy

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Publications (25)48.97 Total impact

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    ABSTRACT: In this work two quantum dot (QD) solar cell structures have been proposed and compared as potential solutions for the realization of the Intermediate Band Solar Cell concept: the well known dot/barrier material system InAs / GaAs and an engineered InAlGaAs/AlGaAs combination. The Al-based structures have been obtained by a suitably developed growth procedure with the aim of increasing island density and engineering the absorption spectrum and the energy band profile in the near infrared region. Along with tunability of the confined electron energy levels, the proposed Al-based structures exhibit transport features, such as reduced edge recombination losses and lower reverse saturation current density with respect to the InAs/GaAs QD system, which can be useful for enhancing device performances.
    Photonics Technology, 2014 Fotonica AEIT Italian Conference on, Naples; 05/2014
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    ABSTRACT: In this paper we report on optical absorption measurements performed on several metal oxide nanoparticles (ZnO, CeO2, Fe2O3) as a function of temperature in the range 25500 °C, in order to study the optical properties, and to investigate how several heating cycles could affect nanoparticle structural stability and absorption characteristics. These are quite important issues to be investigated in order to assess the possibility to use such metal-oxide nanoparticles as gas-based high temperature nanofluid in concentrated solar power (CSP).
    09/2013; 773:80-86. DOI:10.4028/www.scientific.net/AMR.773.80

  • XVII International Sol-Gel Conference, Madrid; 01/2013
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    ABSTRACT: The optical response by NO2 gas adsorption at different concentrations has been investigated, at room temperature, in ZnO nanostructured films grown by controlled vapor phase deposition. The variation (quenching) in the photoluminescence signal from excitonic and defects bands, due to the interactions between the oxidizing gas molecules and the sample surface, has been detected and dynamic responses and calibration curves as a function of gas concentration have been obtained and analyzed for each band. We showed that the sensing response results larger in excitonic band than in defect one and that the emission signal rises from two different quenchable and unquenchable states. A simple model was proposed in order to explain the quenching processes on the emission intensity and to correlate them to the morphological features of the samples. Finally, the reversibility of the quenching effects has also been tested at high gas concentration.
    Journal of Applied Physics 04/2012; 111(7):73520. DOI:10.1063/1.3700251 · 2.18 Impact Factor

  • Encyclopedia of Laser Research (3 Volume Set), 03/2012: chapter 30: pages 883-922; Nova Science Publishers., ISBN: 978-1-61324-545-3
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    ABSTRACT: We have investigated the optical properties of colloidal seed-grown CdSe (seed)/CdTe (arms) nanotetrapods both experimentally and computationally. The tetrapods exhibit a type-II transition arising from electrons localized in the CdSe seed region and holes delocalized in the CdTe arms, along with a residual type-I recombination in long-arm tetrapods. Experiments and theory helped to identify the origin of both types of transitions and their size dependence. In particular, time-resolved experiments performed at 10 K evidenced a size-dependent, long living type-II radiative emission arising from the peculiar electron–hole wave function localization. Temperature-dependent photoluminescence (PL) studies indicate that, at high temperature (>150 K), the main process limiting the PL quantum efficiency of the type-I PL is thermal escape of the charge carriers through efficient exciton-optical phonon coupling. The type-II PL instead is limited both by thermal escape and by the promotion of electrons from the conduction band of the seed region to that of the arms, occurring at T > 200 K.
    The Journal of Physical Chemistry C 08/2011; 115(37-37). DOI:10.1021/jp2048162 · 4.77 Impact Factor
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    ABSTRACT: Various kinds of zinc oxide (ZnO) nanostructures, such as columns, pencils, hexagonal pyramids, hexagonal hierarchical structures, as well as smooth and rough films, were grown by pulsed laser deposition using KrF and ArF excimer lasers, without use of any catalyst. ZnO films were deposited at substrate temperatures from 500 to 700°C and oxygen background pressures of 1, 5, 50, and 100 Pa. Quite different morphologies of the deposited films were observed using scanning electron microscopy when different laser wavelengths (248 or 193 nm) were used to ablate the bulk ZnO target. Photoluminescence studies were performed at different temperatures (down to 7 K). The gas sensing properties of the different nanostructures were tested against low concentrations of NO2. The variation in the photoluminescence emission of the films when exposed to NO2 was used as transduction mechanism to reveal the presence of the gas. The nanostructured films with higher surface-to-volume ratio and higher total surface available for gas adsorption presented higher responses, detecting NO2 concentrations down to 3 ppm at room temperature.
    Laser Physics 03/2011; 21(3):588-597. DOI:10.1134/S1054660X11050045 · 1.03 Impact Factor
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    ABSTRACT: This chapter aims to present a brief review about a very interesting application of laser beams in the field of materials science: the growth of zinc oxide (ZnO) nanostructured films by Pulsed Laser Deposition (PLD), and in particular by means of excimer laser ablation. After an introduction giving an overview on properties and applications of ZnO and its nanostructures and on some growth techniques used to obtain these materials, this survey will present several results, obtained by different research groups in the world, about nanostructured ZnO grown by excimer laser ablation. Then this study will be focused on the results obtained by our research group in this field so far. By properly changing some deposition parameters (substrate temperature, oxygen pressure and ablation laser wavelength) we obtained nanostructured films with hexagonal pyramids, columns, hexagonal hierarchical structures and pencils, as well as smooth or rough films. In particular the different ablation laser wavelengths (248 nm of KrF and 193 nm of ArF) are shown to have a deep influence on both morphology and crystal quality of the grown samples. Scanning electron microscopy (SEM), x-ray diffraction (XRD) and photoluminescence (PL) measurements were used to inspect the film properties. Finally, some results about our optical gas sensing tests conducted on the grown samples are presented.
    Laser Beams: Theory, Properties and Applications, 01/2011: chapter 4: pages 205-244; Nova Science Publishers., ISBN: 978-1-60876-266-8
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    ABSTRACT: Matrix-assisted pulsed laser evaporation (MAPLE) was used to deposit layers of poly(9,9-dioctylfluorene) (PFO) to study the relation between the solvent properties (laser light absorption, boiling temperature and solubility parameters) and the morphology of the deposited films. To this end, the polymer was diluted (0.5 wt%) in tetrahydrofuran—THF, toluene and toluene/hexane mixtures. The thickness of the films was equal to 70±20 nm. The morphology and uniformity of the films was investigated by Atomic Force Microscopy and by the photoluminescence emission properties of the polymer films, respectively. It is shown that, although the solubility parameters of the solvents are important in controlling the film roughness and morphology, the optical absorption properties and boiling temperature play a very important role, too. In fact, for matrices characterized by the same total solubility parameter, lower roughness values are obtained for films prepared using solvents with lower penetration depth of the laser radiation and higher boiling temperatures.
    Applied Physics A 12/2010; 101(4):759-764. DOI:10.1007/s00339-010-5990-8 · 1.70 Impact Factor
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    ABSTRACT: In this work, the evolution of the Au assisted-growth of ZnO nanorods deposited by vapour phase deposition both on sapphire and on indium–tin–oxide on glass (ITO-glass) substrates has been studied. Our investigation demonstrates that the growth proceeds first as a 3D growth, giving rise to a buffer layer, few microns thick, formed by ZnO grains with different orientation. Then a 1D transition occurs with the nucleation of a dense array of vertically aligned nanorods. A different degree of crystalline order and nanorods alignment was found between the samples grown on ITO-glass and sapphire substrates, which was ascribed to the different morphology that the Au seed layer acquires on the two different substrates. A semi-quantitative analysis of the ZnO crystalline orientation was carried out by X-ray diffraction (XRD) measurements performed at fixed incidence configuration and supported by high resolution scanning electron microscopy (HR-SEM) investigations on focused ion beam (FIB) prepared cross-sections.
    Materials Science and Engineering B 09/2010; 172(3):225-230. DOI:10.1016/j.mseb.2010.05.021 · 2.17 Impact Factor
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    ABSTRACT: We report on nitrogen dioxide (NO2) sensing measurements by means of zinc oxide films presenting different morphologies. The variation in the photoluminescence emission of the films is employed as transduction mechanism to detect the presence of NO2 gas molecules at room temperature. The significant role of film morphology on the sensing properties is presented and possible limits in the use of ZnO nanostructures for NO2 detection at high gas concentration (>20 ppm) and low gas flow (50 ml/min), where a worsening of the sensor response is observed, are discussed. These features are ascribed to a likely incomplete reversibility of the NO2 adsorption process and examined in connection with the mechanisms of interaction between NO2 molecules and ZnO.
    Sensors and Actuators B Chemical 03/2010; 145(1):167. DOI:10.1016/j.snb.2009.11.064 · 4.10 Impact Factor
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    ABSTRACT: We investigated the excitation density dependence of the photoluminescence spectra of hybrid poly(9,9-dioctylfluorene)-CdSe/ZnS nanocrystals (PF8-NCs) thin films. We demonstrate that this experiment allows the determination of the efficiency of all the CdSe/ZnS NCs excitation processes and that the presence of amplified spontaneous emission (ASE) from the PF8 leads to a strong dependence of the NC excitation processes from the laser excitation density. Below the PF8 ASE threshold only about 6% of the excitons in the NCs are due to pump laser absorption, while about 94% of the NC excitation is due to the interaction with the PF8, and it is due for about 58% to PF8-->NC Forster resonant energy transfer (FRET) and for about 37% to reabsorption by the NCs of the PF8 luminescence. The presence of PF8 ASE significantly modifies this scenario by strongly decreasing the FRET importance and strongly increasing the reabsorption one. The interplay between reduced FRET and increased reabsorption overall decreases the NC excitation due to PF8 indicating that ASE from the donors should be avoided if efficient NCs excitation under strong pumping is wished.
    The Journal of Physical Chemistry A 02/2010; 114(5):2086-90. DOI:10.1021/jp906860c · 2.69 Impact Factor

  • Advances in Nanotechnology - Volume 4, 01/2010: chapter 1: pages 1-42; Nova Science Publishers., ISBN: 978-1-61668-618-5
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    ABSTRACT: Zinc oxide (ZnO), particularly in its nanostructured forms, is one of the materials extensively studied in the last years due to the great number of its possible applications. Several growth techniques can be used to realize this kind of material and, among them, the Pulsed Laser Deposition (PLD) technique has been demonstrated to be a very versatile method to easily control the properties of the grown material.In this regard, this book aims to presents a review about the growth of zinc oxide (ZnO) nanostructured films by Pulsed Laser Deposition (PLD), and in particular by means of excimer laser ablation.
    01/2010; Nova Science Publishers., ISBN: 978-1-61668-034-3
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    ABSTRACT: Zinc oxide films with different morphologies have been grown by pulsed laser deposition, varying substrate temperature and oxygen pressure. At low oxygen pressure and low substrate temperature continuous films with different roughness have been obtained, while at high substrate temperature a film with sparse hexagonal pyramids has been observed. Increasing the oxygen pressure the film became rougher and at 100 Pa a rod-array has been deposited. The columns of this rod-array grew along the wurtzite c-axis perpendicularly to the substrate surface as proved by X-ray diffraction measurements. Near to the sample borders the columns were slightly tilted towards the center of the sample. The possible growth mechanisms giving rise to the different morphologies have been discussed. Low-temperature photoluminescence measurements allowed to get information about the film quality, showing the variations of the excitonic peak and two defect bands (green and violet-blue) with the different deposition parameters.
    Applied Surface Science 09/2009; 255(24):9680-9683. DOI:10.1016/j.apsusc.2009.04.051 · 2.71 Impact Factor
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    ABSTRACT: The optical response at room temperature of ZnO nanostructures, grown by controlled vapour phase deposition, to low concentrations of NO<sub>2</sub> gas mixed in dry-air has been investigated. In particular the quenching in the emission signal, due to the interactions between oxidizing gas molecules and sample surface, has been monitored in excitonic and defect band, as a function of NO<sub>2</sub> gas concentration. The dynamic responses and the resulting calibration curves, obtained for each emission band, have been compared. Furthermore responses of nanorods with different size and nanostructures with different exotic shape have been discussed in order to clarify the role of the morphology and/or dimensions and structural quality. In particular we have correlated the growth conditions and the resulting structural and optical properties of the samples, highlighting their role in the optical sensing response.
    Sensors, 2008 IEEE; 11/2008
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    ABSTRACT: We report on the observation of coherent confined acoustic phonons in CdSe core nanorods. We show that photobleaching and photoabsorption dynamics of nanocrystals, obtained with femtosecond pump-probe transient spectroscopy with a resonant pumping energy, exhibit evidence of oscillatory modulation, due to the modulation of the bandgap, despite the weak excitation regime (< mu J). In particular we found that the modulation frequency corresponds to the coherent radial breathing modes of the rods, suggesting that only the transverse ( radial) mode of coherent phonons is observed. No evidence of modulation is observed in the corresponding rod sample overcoated with a thin shell of CdS/ZnS, suggesting that the shell produces a strongly damped mechanism.
    Journal of Optics A Pure and Applied Optics 06/2008; 10(6-6). DOI:10.1088/1464-4258/10/6/064004 · 1.92 Impact Factor
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    A. Creti · G. Leo · A. Persano · A. Cola · L. Manna · M. Lomascolo ·
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    ABSTRACT: In this work, we present the morphological, optical and electrical transport properties of CdSe colloidal nanorods as building blocks in electro-optical conversion devices, as a function of the thin-film deposition technique and of substrate functionalization. In particular, we show the role of the ligand molecules and of the defect states in phototransport and optical properties. (C) 2007 Elsevier B.V. All rights reserved.
    Physica E Low-dimensional Systems and Nanostructures 04/2008; 40(6-6):2063-2065. DOI:10.1016/j.physe.2007.09.101 · 2.00 Impact Factor
  • Arianna Cretì · Mauro Lomascolo · Gabriella Leo · Liberato Manna · Marco Anni ·
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    ABSTRACT: We quantitatively investigated, by time-resolved photoluminescence (PL) spectroscopy, the shell thickness dependence of exciton trapping and its effects on the PL quantum yield (QY) in colloidal CdSe/CdS/ZnS core/shell quantum rods. The defects passivation, due to a thin shell (0.6 monolayer), leads to a 2 times reduction of the trapping from both emitting and high-energy excited states, thus explaining the observed 4.3 times increase of the PL QY. Moreover, the QY decrease in the thick shell (1.3 monolayers) sample is fully explained in terms of increased trapping from the emitting states, which is ascribed to new defects caused by the strain relaxation at the core-shell interface. (C) 2007 Elsevier B.V. All rights reserved.
    Journal of Luminescence 03/2008; 128(3-3):361-365. DOI:10.1016/j.jlumin.2007.09.001 · 2.72 Impact Factor
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    ABSTRACT: The authors investigated, by femtosecond pump-probe measurements, the effects on Auger and trapping processes of excitation resonant (R) to the 1S absorption in CdSe nanorods. They demonstrate that R pumping allows one to avoid exciton trapping in high energy defect states and that the presence of empty defect states leads to an enhancement of the Auger relaxation, with respect to the pumping at energies high above the band gap. Moreover, they show that, despite the Auger enhancement, R pumping increases the stimulated emission lifetime demonstrating that it is not limited by Auger scattering, as widely believed, but by photoabsorption processes, involving defect states.
    Applied Physics Letters 09/2007; 91(9-91):093106 - 093106-3. DOI:10.1063/1.2776847 · 3.30 Impact Factor

Publication Stats

441 Citations
48.97 Total Impact Points


  • 2008-2012
    • INO - Istituto Nazionale di Ottica
      Florens, Tuscany, Italy
  • 2011
    • Istituto Italiano di Tecnologia
      Genova, Liguria, Italy
  • 2006
    • Politecnico di Milano
      • Department of Physics
      Milano, Lombardy, Italy
  • 2003
    • Università del Salento
      • Department of Engineering for Innovation
      Lecce, Apulia, Italy