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Phosphorus Based Ceramics for Positive Electrode Synthesis and Characterization  [PDF]
Diouma Kobor, Abdou Kadri Diallo, Modou Tine
Journal of Modern Physics (JMP) , 2014, DOI: 10.4236/jmp.2014.515147
Abstract: Historically, the LiCoO2 is the most used as active material for battery positive electrode because of its great potential (3.7 - 4.2 V), its interesting specific capacity (150 mA·h·g-1) and its excellent life cycle [1]. However, its toxicity, the cobalt cost and its structural instability oriented research towards new materials more stable that can replace it. In another context, hybrid, electrical vehicles and communication (computers and mobile phones...) have increased the scientific and technological research for new materials capable of storing and return energy through a system called accumulator. And research has identified the phosphate olivine structure as the most prolific ceramic material for positive electrode. LiFePO4 is a promising cathode material for Lithium-ion batteries. It provides high thermal stability and is synthesized using low cost materials. Unfortunately LiFePO4 suffers from a low electrical conductivity, which is harmful to its electrochemical performance. Decreasing the particle size, coating the particles with carbon or doping with metal atoms can increase the conductivity of the material. In this paper, we present the synthesis, physico-chemical and electrical characterization of lithium and iron doped Al-phosphorrus-based ceramic. The NPK Fertiliser was used as Al and phosphorus precursors. The powder XRD spectrum shows a possible presence of LiFePO4 and Fe2(PO)3 in theheterostrcture. An important quantity of Al is found by EDX spectra which supposed that the most important based atom is Aluminum and not Phosphorus. This can explain the increase of the conductivity value 102 times more important than those found in the literature for LiFePO4.
Mn Effect on Nonlinear and Structural Properties of <110> Oriented PZN-4.5PT Single Crystals  [PDF]
Diouma Kobor, Modou Tine, Abdelowahed Hajjaji, Laurent Lebrun, Daniel Guyomar
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.35056
Abstract: Ferroelectric single crystals Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) are promising full materials for non resonant or large bandwidth transducers due to the large values of their piezoelectric properties (d ij , k ij ) and their low mechanical quality factor (Q ij ). Many studies on <001> oriented PZN-4.5PT single crystals were carried out but it is very difficult to find research findings on <110> oriented Mn doped PZN-PT. Thus, investigations were made using XRD, Raman and EPR characterization for <110> oriented PZN-4.5PT grown through the Flux method. Mn doping effect on structural, dielectric, mechanical and piezoelectric properties with two values of Mn percentage (1 and 2 mol%) are also reported in this paper. Through the XRD study, the lattice parameters of doped PZN-PT crystals are slightly increased compared to the undoped one but the Mn didn’t change its structure. The room temperature dielectric permittivity along <110> direction is about 1572 and 1626 (respectively 1% and 2% Mn doped crystals) which are much lower than that of the undoped PZN-4.5PT (2553). The remnant polarization and coercive field of <110> oriented doped crystal measured at 1 KHz are respectively 30 μC/cm2 and 4.30 kV/cm (PZN-4.5PT), 32 μC/cm2 and 6.10 kV/cm (PZN-4.5PT + 1% Mn) and 28 μC/cm2 and 7.30 kV/cm (for the 2% Mn doped crystal). The mechanical quality factor Qm changed from 139 to 441 respectively for the pure and 1% Mn doped single crystals at room temperature while it decreases slightly to 336 for the 2 mol% Mn doped.
Determination of the Vibro-Rotational Constants, the Dipole Moment’s Function and the Intensities of the HTO’s ν1 (ν3 by Usual Convention) Band  [PDF]
Modou Tine, Diouma Kobor, Ibrahima Sakho, Laurent Coudert
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.312243
Abstract: In the first part of this paper, an analysis of the high-resolution spectrum of the HTO molecule ν1(ν3) band, from 3630 to3950 cm1, was undertaken. The rotational transition of this band was assigned using combination differences. Their wavenumbers were analyzed with a least squares fit program in order to obtain spectroscopic constants. A perturbed state has been evidenced. In the second part, with a view towards building a spectroscopic data base, a calculation of the dipolar momentum function was undertaken.
Electrical Instability in Pentacene Transistors with Mylar and PMMA/Mylar Gate Dielectrics Transferred by Lamination Process  [PDF]
Abdou Karim Diallo, Abdoul Kadri Diallo, Diouma Kobor, Marcel Pasquinelli
Journal of Applied Mathematics and Physics (JAMP) , 2016, DOI: 10.4236/jamp.2016.47125
Abstract: This study deals with electrical instability under bias stress in pentacene-based transistors with gate dielectrics deposited by a lamination process. Mylar film is laminated onto a polyethylene terephthalate (PET) substrate, on which aluminum (Al) gate is deposited, followed by evaporation of organic semiconductor and gold (Au) source/drain contacts in bottom gate top contact configuration (Device 1). In order to compare the influence of the semiconductor/dielectric interface, a second organic transistor (Device 2) which is different from the Device 1 by the deposition of an intermediate layer of polymethyl methacrylate (PMMA) onto the laminated Mylar dielectric and before evaporating pentacene layer is fabricated. The critical device parameters such as threshold voltage (VT), subthreshold slope (S), mobility (μ), onset voltage (Von) and Ion/Ioff ratio have been studied. The results showed that the recorded hysteresis depend on the pentacene morphology. Moreover, after bias stress application, the electrical parameters are highly modified for both devices according to the regimes in which the transistors are operating. In ON state regime, Device 1 showed a pronounced threshold voltage shift associated to charge trapping, while keeping the μ, Ioff current and S minimally affected. Regardless of whether Device 2 exhibited better electrical performances and stability in ON state, we observed a bias stress-induced increase of depletion current and subthreshold slope in subthreshold region, a sign of defect creation. Both devices showed onset voltage shift in opposite direction.
Dielectric and Mechanical Nonlinear Behavior of Mn Doped PMN-35PT Ceramics  [PDF]
Diouma Kobor, Abdelowahed Hajjaji, Jose E. Garcia, Rafel Perez, Alfons Albareda, Laurent Lebrun, Daniel Guyomar
Journal of Modern Physics (JMP) , 2010, DOI: 10.4236/jmp.2010.14032
Abstract: This paper presents an investigation on dielectric and mechanical nonlinear properties in Mn-doped PMN-35PT ceramics. The structural study of the ceramics verifies that the 1% mol Mn doped PMN-35PT is a pure perovskite phase with a tetragonal symmetry. SEM micrograph shows the same microstructural mor- phology of an undoped ceramic. From the EPR spectra, it has been concluded that the major part of Mn is present in Mn2+ rather than in Mn4+ form. The addition of Mn2+ ions acts on the dielectric, piezoelectric and mechanical properties by decreasing the relative dielectric permittivity (3800 to 2074), the dielectric losses (0.60 to 0.53), the piezoelectric coefficient d33 (650 to 403 pC/N), and increasing the mechanical quality fac- tor Qm (78 to 317). It was found that in Mn2+ doped ceramics the dielectric response can not be described by Rayleigh law. This result can be understood taking into account that reversible motion of the domain wall is a relevant contribution to response of this material.
Fabrication and Characterization of PZN-4.5PT Inorganic Perovskites Nanoparticles Thin Films Deposited on P-Type Silicon Substrate  [PDF]
Rémi Ndioukane, Moussa Touré, Diouma Kobor, Laurence Motte, Marcel Pasquinelli, Jeanne Solard
Journal of Modern Physics (JMP) , 2018, DOI: 10.4236/jmp.2018.92018
Abstract: This work involves an investigation of nanostructures, microelectronic properties and domain engineering of nanoparticles thin layers of Pb(Zn1/ 3Nb2/3)O3-PbTiO3 (PZN-PT) ferroelectric single crystals deposited on nanostructured silicon substrate. In this study, devices made from PZN-4.5PT nanoparticles thin films successfully deposited on silicon substrate have been studied and discussed. SEM images show the formation of local black circles and hexagonal shapes probably due to the nucleation of a new Si-gel component or phase induced by annealing. Micro Xray Fluorescence mapping shows that the high values of Si and B atoms (7 and 4 normalized unit respectively) can be explained by the fact that the substrate is p-type silicon. The most interesting result of optical measurements is the very good absorption for all the thin films in UV, Visible and NIR regions with values from 70% to 90% in UV, from 75% to 93% in Visible and NIR. Tauc plots present particularities (rarely encountered behavior) with different segments or absorption changes showing the presence of multiple band gaps coming from the heterogeneity of the thin films (nanowires, gel and nanoparticles). Their values are 1.9 and 2.8 eV for DKRN-Gel, 2.1 and 3.1 eV for DKRN-UD and 2.1 and 3.2 eV for DKRN-D) corresponding respectively to the band gap of nanowires and that of the gel while the last ones correspond to the undoped and doped nanoparticles (3.1 and 3.2 eV respectively).
Optimization of 6,13Bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) Organic Field Effect Transistor: Annealing Temperature and Solvent Effects  [PDF]
Diallo Abdoul Kadri, Diallo Abdou Karim, Mané Seck, Kobor Diouma, Pasquinelli Marcel
Materials Sciences and Applications (MSA) , 2018, DOI: 10.4236/msa.2018.911065
Abstract: In this contribution, we report on the effect of solvents with different boiling points and annealing temperature on the performance of TIPS-pentacene transistors. Several solvents have been used for TIPS-pentacene thin film processing: toluene, chlorobenzene and tetrahy-drofuran. To study the influence of solvent and temperature; the electrical parameters of TIPS-pentacene field effect transistor were measured. The highest values of mobilities were 7.1 × 10-3 cm2·V-1·s-1, 4.5 × 10-3?cm2·V-1·s-1 and 1.43 × 10-3 cm2·V-1·s-1 respectively for TIPS-pentacene field effect transistor using chlorobenzene, toluene and tetrahydrofuran and annealed respectively at 120°C, 150°C and 120°C. We have correlated these electrical performances with AFM images in order to point out the role of morphological properties. It is found that the grain size, and roughness highly affect the electrical parameters.
Dielectric and Ferroelectric Properties of PZN-4.5PT Nanoparticles Thin Films on Nanostructured Silicon Substrate for Ferrophotovoltaic and Energy Storage Application  [PDF]
Rémi Ndioukane, Moussa Touré, Diouma Kobor, Laurence Motte, Jeanne Solard, Laurent Lebrun
Journal of Modern Physics (JMP) , 2019, DOI: 10.4236/jmp.2019.106043
Abstract: The integration of ferroelectric materials as thin films has attracted considerable attention these last years thanks to their outstanding performances that allow considering new features for the realization of photovoltaic devices. Our study focuses on investigating structural, dielectric and ferroelectric properties of undoped and Mn doped PZN-4.5PT nanoparticles thin films on Silicon substrate. We fabricate very stable PZN-4.5PT nanoparticles thin films deposited on nanostructured silicon substrate with giant relative dielectric permittivity of 2.76 × 104 and 17.7 × 104 for respectively the undoped and Mn doped thin films. These values are very large compared to those found in single crystals and might be explained by the influence of the gel in which nanoparticles were dispersed. The SEM images show the crystallization of new hexagonal phases on the film surface probably coming from interaction between Si and the gel. The hysteresis loops permitted to determine the spontaneous polarization (Ps), remnant polarization (Pr) and coercive field Ec which are equal to 11.73 μC/cm2, 10.20 μC/cm2 and 20 V/cm, respectively for the undoped nanoparticles thin film and 22.22 μC/cm2, 19.32 μC/cm2 and 20 V/cm respectively for the Mn doped one. These values are high and correspond to the best ones found in literature compared to typical ferroelectric thin films.
DaVIE: Database for the Visualization and Integration of Epigenetic data.
Anthony P. Fejes,Michael S. Kobor
Frontiers in Genetics , 2014, DOI: 10.3389/fgene.2014.00325
Abstract: One of the challenges in the analysis of large data sets, particularly in a population-based setting, is the ability to perform comparisons across projects. This has to be done in such a way that the integrity of each individual project is maintained, while ensuring that the data are comparable across projects. These issues are beginning to be observed in human DNA methylation studies, as the Illumina 450k platform and next generation sequencing-based assays grow in popularity and decrease in price. This increase in productivity is enabling new insights into epigenetics, but also requires the development of pipelines and software capable of handling the large volumes of data. The specific problems inherent in creating a platform for the storage, comparison, integration and visualization of DNA methylation data include data storage, algorithm efficiency and ability to interpret the results to derive biological meaning from them. Databases provide a ready-made solution to these issues, but as yet no tools exist that that leverage these advantages while providing an intuitive user interface for interpreting results in a genomic context. We have addressed this void by integrating a database to store DNA methylation data with a web interface to query and visualize the database and a set of libraries for more complex analysis. The resulting platform is called DaVIE: Database for the Visualization and I of Epigenetics data. DaVIE can use data culled from a variety of sources, and the web interface includes the ability to group samples by sub-type, compare multiple projects and visualize genomic features in relation to sites of interest. We have used DaVIE to identify patterns of DNA methylation in specific project and across different projects, identify outlier samples, and cross-check differentially methylated CpG sites identified in specific projects across large numbers of samples.
Comparative characterization of rhombohedral and tetragonal PZN-PT single crystals
D. Kobor,M. Tine,A. Hajjaji,L. Lebrun
AIP Advances , 2011, DOI: 10.1063/1.3599587
Abstract: Ferroelectric single crystals Pb(Zn1/3Nb2/3)O3–PbTiO3 (PZN–PT) are promising full materials for nonresonant or large bandwidth transducers due to the large values of their piezoelectric properties (dij, kij) and their mechanical quality factor (Qij). However the properties of these materials depend greatly on the content of titanium which influences very significantly the symmetry of the crystal. In this paper we try to understand the influence of the percentage of Titanium in these crystals by studying the two compositions that are in very different phases at room temperature (rhombohedral and tetragonal symmetries). Crystals of pure PZN–4.5PT and PZN-12PT were grown by a Flux technique. The typical single crystals obtained are brown yellow. The room temperature dielectric permittivity along the <001> direction is about 900 for the PZN-12PT, which is smaller than that of the PZN–4.5PT (5840). The Curie point Tc of the tetragonal crystal is about 220 °C (which is higher than that of the rhombohedral one (166 °C)), while the ferroelectric phase transition temperature is 130 °C for the PZN-4.5PT single crystal. The remnant polarization and coercive field of <001> oriented crystals measured at 1 kHz are around 40 μC/cm2 and 3.30 kV/cm, respectively for the PZN-4.5PT, 27μC/cm2 and 11.1 kV/cm for the PZN-12PT single crystal. The d33 versus uniaxial stress shows that this coefficient is more stable for the single crystal with low Ti than for that with high rate of Ti. The study of temperature stability on these crystals shows a possible presence of an unidentified phase in the low and negative range temperature for the PZN-4.5PT.
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