Z. Zaaboub

University of Monastir, Tunis-Ville, Tūnis, Tunisia

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Publications (11)19.73 Total impact

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    ABSTRACT: A novel strategy to synthesize CdS nanocrystal modified with thiophenol (PHSH). CdS–PHSH NCs are used as an acceptor in a MEH-PPV. Pl and PLRT measurement provided evidence for charge transfer at the interface. Thiophenol passivated CdS in conjunction with MEH-PPV is a promising composite for hybrid solar cell. a b s t r a c t The role of organic capping ligand of semiconductor nanoparticles in dictating the interfacial charge transfer processes in hybrid semiconductor nanoparticles/polymer-based photovoltaic devices is in-vestigated. Morphology, optical and structural study of the CdS nanoparticles and the hybrid material were accomplished using X-ray diffraction (XRD), absorption (UV–vis), atomic force microscopy (AFM), transmission electron microscopy (TEM), photoluminescence (PL) and time resolved photoluminescence spectroscopy (PLRT). A broad band absorption in UV–visible region and considerable fluorescence quenching of MEH-PPV in the composites are noted indicating a photo-induced charge transfer and dissociation of excitons. Time-resolved photoluminescence measurements indicating decreased lifetime further confirm this process. The solar cells open-circuit voltage and short-circuit current were improved using thiophenol modified CdS nanoparticles as electron acceptor in comparison to MEH-PPV only device demonstrating a promising approach to enhance charge transport in the hybrid nanoparticles–polymer composite photovoltaic cells (PV). &
    Physica E Low-dimensional Systems and Nanostructures 01/2015; 69. DOI:10.1016/j.physe.2015.01.031 · 1.86 Impact Factor
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    ABSTRACT: Cadmium sulfide (CdS) nanoparticles were synthesized by a novel wet chemical route with various organic thiol stabilizers. Systematic experimental studies, including X-ray diffraction (XRD), ultraviolet–visible (UV–vis) spectroscopy, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), photoluminescence (PL) spectroscopy, and time-resolved photoluminescence (TRPL), have evidenced that the stability, crystallinity, and optical properties of the CdS nanoparticles are affected by the organic groups which generate significant effects in surface reconstruction. Particle size was evaluated from UV–vis spectroscopy using the effective mass approximation (EMA) method and from XRD patterns based on Scherrer׳s formula. The S–H vibrations are not detectable in the infrared (IR) spectra of any of the bound ligands, which are expected for thiols covalently bound to the surface of nanoparticles. PL studies reveal that the emission from the nanostructures is not much influenced by the surface states, indicating a good passivation of the particle׳s surface. The time-resolved measurements reveal a biexponential decay behavior. The fast decay component is attributed to the recombination of core states, while the slow decay component of PL is associated with the charge-carrier recombination process with the involvement of surface states.
    Journal of Physics and Chemistry of Solids 08/2014; 75(8):936–944. DOI:10.1016/j.jpcs.2014.03.007 · 1.59 Impact Factor
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    ABSTRACT: In this work, low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) experiments have been carried out to investigate the optical and electronic properties of InAs/GaAs quantum dots (QDs) subjected to room-temperature proton implantation at various doses (5 × 1010–1014 ions cm−2) and subsequent thermal annealing. The energy shift of the main QD emission band is found to increase with increasing implantation dose. Our measurements show clear evidence of an inhomogeneous In/Ga intermixing at low proton implantation doses (�5 × 1011 ions cm−2), giving rise to the coexistence of intermixed and non-intermixed QDs. For higher implantation doses, a decrease of both the PL linewidth and the intersublevel spacing energy have been found to occur, suggesting that the dot-size, dot-composition and dot-strain distributions evolve towards more uniform ones.
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    ABSTRACT: In this work, we present the temperature-dependence and time-resolved photoluminescence (PL) of CdS nanoparticles capped independently with three different ligands thiophenol, thioglycerol, and L-cysteine over a broad temperature range from 10 to 300 K. The respective nanoparticles sizes in the three systems studied in this work are 1.5, 4, and 2 nm as determined from X-ray diffraction (XRD). From the analysis of AFM images, it was found that the lateral particle sizes of capped CdS nanoparticles are greater than those deduced from XRD or optical absorption measurements. The aim of this study is the investi-gation of the impact of the organic ligands on the radiative recombination dynamics in organically capped CdS nanoparticles. From the PL study and based on the temperature-dependence and time-resolved emission spectroscopy, we conclude that the emission of CdS QDs film originates from recombination of the delocalized carriers in the internal core states with a small contribution of the localized carriers at the interface. The PL decay reveals a biexponential behavior for the entire three samples at all temperatures. One of the two exponen-tial components decays rapidly with a time s 1 in the range 0.5–0.8 ns, whereas the other decays much more slowly, with a time s 2 in the range 1–3 ns. The weak activation energy (32–37 meV) deduced from the temperature dependence of the PL intensity suggests the involvement of shallow traps. The analysis of the experimental results reveals a rela-tively narrow size distribution, an efficient surface passivation, and a satisfactory thermal stability of CdS nanocrystals.
    Journal of Nanoparticle Research 01/2014; 16(2242). DOI:10.1007/s11051-013-2242-9 · 2.28 Impact Factor
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    ABSTRACT: The electronic and the structural properties of n-GaAs layers grown on rough surface of silicon substrate by molecular beam epitaxy (MBE) has been investigated by photoluminescence (PL), time resolved photoluminescence (TRPL) and high resolution X-ray diffraction (HRXRD). The relationship between electronic and structural properties of the n-GaAs layer was checked, showing that the defect density is a strong cause for trapping the minority carriers. The impact of introducing intermediate rough silicon layer between silicon substrate and n-GaAs layer on the electronic properties was observed, showing that the structure grown on rough Si involves higher lifetime than those developed on flat silicon substrate. Such structure could be used for economic solar cells fabrication.
    Current Applied Physics 09/2012; 12(5):1256–1258. DOI:10.1016/j.cap.2012.03.005 · 2.03 Impact Factor
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    ABSTRACT: Low temperature photoluminescence (PL) measurements are carried out to investigate the influence of the high extent of intermixing induced by proton implantation and subsequent annealing on the optical and electronic properties of the InAs/GaAs quantum dots (QDs). Several QDs structures were proton implanted at various doses (5×10<sup>11</sup>–1×10<sup>15</sup> ions   cm <sup>-2</sup>) with an acceleration energy of 18 keV and then annealed at 700 ° C for 30 s. A saturation of the emission energy blueshift is found to occur for implantation doses higher than 5×10<sup>13</sup> ions   cm <sup>-2</sup> accompanied with a continual decrease in the intersublevel spacing energy suggesting that the intermixing process persists beyond the emission energy blueshift saturation. An additional emission peak was found to appear in PL spectra for proton doses higher than 1×10<sup>14</sup> ions   cm <sup>-2</sup> and attributed to the coalescence of closely spaced QDs. Strain assisted predominant lateral intermixing is proposed as the main factor responsible for the observed behavior.
    Journal of Applied Physics 07/2010; 107(12-107):124306 - 124306-4. DOI:10.1063/1.3436594 · 2.19 Impact Factor
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    ABSTRACT: Low-temperature photoluminescence (PL) experiments have been carried out to investigate In/Ga intermixing in InAs/GaAs self-assembled quantum dots (QDs) by studying the changes in the optical properties of the system by rapid thermal annealing (RTA) and by room temperature proton implantation at various doses followed by RTA. The study of the RTA effect on the investigated structure shows that thermal stability can be ensured for an annealing temperature below 675°C. For higher annealing temperatures, the thermal intermixing is found to change both the optical transition energy and the inter-sublevel spacing of the QD energy levels. By using proton implantation at various doses and subsequent annealing at 675°C for 30s, a tunable energy shift up to 130meV has been obtained. The band gap tuning limit for this system has been achieved for an implantation dose of 5×1013cm−2. Regardless of the intermixing technique employed, a pronounced PL peak broadening is found to occur at low annealing temperatures and/or proton implantation doses.
    Materials Science in Semiconductor Processing 02/2009; 12(1):71-74. DOI:10.1016/j.mssp.2009.07.005 · 1.76 Impact Factor
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    ABSTRACT: In this work, low-temperature photoluminescence (PL) and photoluminescence excitation (PLE) experiments have been carried out to investigate the optical and electronic properties of InAs/GaAs quantum dots (QDs) subjected to room-temperature proton implantation at various doses (5 × 10(10)-10(14) ions cm(-2)) and subsequent thermal annealing. The energy shift of the main QD emission band is found to increase with increasing implantation dose. Our measurements show clear evidence of an inhomogeneous In/Ga intermixing at low proton implantation doses (≤5 × 10(11) ions cm(-2)), giving rise to the coexistence of intermixed and non-intermixed QDs. For higher implantation doses, a decrease of both the PL linewidth and the intersublevel spacing energy have been found to occur, suggesting that the dot-size, dot-composition and dot-strain distributions evolve towards more uniform ones.
    Nanotechnology 07/2008; 19(28):285715. DOI:10.1088/0957-4484/19/28/285715 · 3.67 Impact Factor
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    Z. Zaâboub, B. Ilahi, L. Sfaxi, H. Maaref
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    ABSTRACT: The effect of post-growth rapid thermal annealing on the photoluminescence properties of long wavelength low density InAs/GaAs (001) quantum dots (QDs) with well defined electronic shells has been investigated. For an annealing temperature of 650 °C for 30 s, the emission wavelength and the intersublevel spacing energies remain unchanged while the integrated PL intensity increases. For higher annealing temperature, blue shift of the emission energy together with a decrease in the intersublevel spacing energies are shown to occur due to the thermal activated In–Ga interdiffusion. While, this behaviour is commonly explained as a consequence of the enrichment in Ga of the QDs, the appearance of an additional exited state for annealing temperatures higher than 650 °C suggests a variation of the intermixed QDs's volume/diameter ratio toward QDs's enlargement.
    Materials Science and Engineering C 07/2008; 28(5):1002-1005. DOI:10.1016/j.msec.2007.10.069 · 2.74 Impact Factor
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    ABSTRACT: This work reports on InAs/GaAs quantum dots (QDs) intermixing, induced by phosphorous ion implantation and subsequent rapid thermal annealing. The implantation process was carried out at room temperature at various doses (5×1010–1014 ions/cm2), where the ions were accelerated at 50 keV. To promote the atomic intermixing, implanted samples are subjected to rapid thermal annealing at 675 °C for 30 s. Low temperature photoluminescence (PL) measurements are carried out to investigate the influence of the interdiffusion process on the optical and electronic properties of the QDs. PL emission energy; linewidth and integrated intensity are found to exhibit a drastic dependence on the ion implantation doses. The band gap tuning limit has been achieved for an implantation dose of 5×1013 ions/cm2. However, our measurement reveals that the accumulated defects for implantation doses higher than 1012 ions/cm2 drive the system towards the degradation of the QDs structure's quality.
    Physics Letters A 06/2008; 372(26):4714-4717. DOI:10.1016/j.physleta.2008.05.008 · 1.63 Impact Factor