EPR studies were performed on MgSiF6.6H2O single crystals using Mn2+ paramagnetic probes substituted for Mg2+ ions. The spin-Hamiltonian parameters (SHPs) are determined accurately for the different phases: the monoclinic phase below... more
EPR studies were performed on MgSiF6.6H2O single crystals using Mn2+ paramagnetic probes substituted for Mg2+ ions. The spin-Hamiltonian parameters (SHPs) are determined accurately for the different phases: the monoclinic phase below Tc=301 K, the rhombohedral phase above T0=370 K and the intermediate phase between Tc and T0. The sets of SHPs are interpreted in the light of structural changes between these phases. The EPR line features in the intermediate phase are analysed in the framework of a static and an order-disorder model. We interpret the EPR spectrum behaviours around T0-20 K as the occurrence of a crossover between static and dynamic disorder in the material.
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Successful strategies on combining the versatility of mechanochemical synthesis with rf-sputtering technique were developed for the controllable deposition of non-toxic and stable monoclinic BiVO4 thin films, which has a relatively narrow... more
Successful strategies on combining the versatility of mechanochemical synthesis with rf-sputtering technique were developed for the controllable deposition of non-toxic and stable monoclinic BiVO4 thin films, which has a relatively narrow band gap (z2.4 eV) that allows a direct photoactivation under visible light. The coupled deposition approach enables the stabilization of single phase, high-quality monoclinic BiVO4 thin films, deposited using sintered target made with nano-powders produced from mechanochemical process. Investigations of structural, vibrational, morphological and optical properties were carried out using HT-XRD, XRD, Raman, AFM, FE-SEM and UV-Visible absorption techniques. Monoclinic scheelite phase of BiVO4 was studied with different morphologies and textures of thin film surfaces including the occurrence of organized nano-islands (20-50 nm) under defined deposition pa- rameters. The sputtered BiVO4 films display an electronic band gap of 2.5 eV, which is suitable for harvesting visible light radiation. Photocatalytic (PC) experiments were performed with selected textured BiVO4 thin films for the degradation of rhodamine 6G (Rh6G) dyes under visible light irradi- ation. Different PC efficiencies were obtained and the results were interpreted based on the thin film morphologies and surface characteristics.
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Thin films based on silicon carbide and alumina were synthesized by means of rf-sputtering using a co-deposition process. Several nanostructures were created which consist of thin films (∼200nm thick) with homogeneous distribution of SiC... more
Thin films based on silicon carbide and alumina were synthesized by means of rf-sputtering using a co-deposition process. Several nanostructures were created which consist of thin films (∼200nm thick) with homogeneous distribution of SiC nanocrystals (∼5nm mean diameter) in the host alumina matrices. Characterization methods including X-ray photoelectrons spectroscopy (XPS), UV–vis absorption and photoluminescence (PL) were used to identify the
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We study the narrow soliton regime near Tc=195 K in Rb2ZnCl4 with the help of the paramagnetic probe Mn2+ (S=(5/2, I=(5/2), which fits the Zn2+ crystal site nicely. Clearing the hyperfine interaction out of the EPR spectrum enables us to... more
We study the narrow soliton regime near Tc=195 K in Rb2ZnCl4 with the help of the paramagnetic probe Mn2+ (S=(5/2, I=(5/2), which fits the Zn2+ crystal site nicely. Clearing the hyperfine interaction out of the EPR spectrum enables us to account for the spin-crystal-field interaction in terms of an amplitude modulation and of a soliton density. For a slow cooling
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ABSTRACT Transparent aluminium-doped ZnO (AZO)-conducting oxide films were deposited on a glass substrate, using an ultrasonic spray pyrolysis (USP) system at 475°C. We investigated the effects of the Al/Zn atomic ratios on the structural... more
ABSTRACT Transparent aluminium-doped ZnO (AZO)-conducting oxide films were deposited on a glass substrate, using an ultrasonic spray pyrolysis (USP) system at 475°C. We investigated the effects of the Al/Zn atomic ratios on the structural properties of the AZO films. All the deposited AZO thin films presented hexagonal wurtzite structure. As Al doping increased in the film, the preferential orientation switched from [002] to [101], and crystallite sizes varied from 31.90 nm to 34.5 nm. Field emission scanning electron microscopy showed a change in the surface morphology of the AZO films with respect to the Al/Zn ratio, and secondary ion mass spectroscopy showed that the amount of Al incorporated into the films was proportional to the concentration of the starting solution. A fast Fourier transform of the AZO film measurements confirmed the presence of (100), (102), and (200) reflections, corresponding to a wurtzite structure of the AZO thin films. The plane corresponding to AZO was simulated, and matched the experimental pattern obtained from high-resolution transmission electron microscopy. An un-doped ZnO layer was deposited onto the AZO film using USP at 400°C, and a bilayer of AZO/ZnO was annealed in vacuum for 20 min at 350°C. The resistivity of these bilayer films was lower than that of a single-layered AZO film, and it further decreased by vacuum annealing.
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ABSTRACT Molybdenum doped BiVO4 powders were prepared by sol-gel method. X-ray diffraction (XRD) patterns and micro-Raman vibrational bands confirm the monoclinic scheelite phase. Doping of molybdenum in BiVO4 matrix was confirmed from... more
ABSTRACT Molybdenum doped BiVO4 powders were prepared by sol-gel method. X-ray diffraction (XRD) patterns and micro-Raman vibrational bands confirm the monoclinic scheelite phase. Doping of molybdenum in BiVO4 matrix was confirmed from XRD by higher angle 2 shift of the characteristic peak (-121) and from Raman showing lower frequency shift of dominant peak from 831 to 822 cm-1 which corresponds to V-O symmetric stretching mode. EPR investigations confirmed the substitution of Mo in the crystalline sites of monoclinic BiVO4. SEM analysis showed spherical shaped particles around 100-200 nm with weak agglomerated particles. Homogeneous presence of molybdenum in BiVO4 matrix was confirmed from STEM analysis. Diffuse reflectance spectra showed higher absorption in the range of 550-850 nm and optical band gap energies were calculated by using Kubelka-Munk formula, i.e, 2.46 eV for 2 wt.% Mo-BiVO4 and 2.48 eV for undoped BiVO4. This confirms that, Mo-BiVO4 particles have almost same energy band gap but induce higher absorption in visible light region as compared to undoped material.
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Visible photoluminescence (PL) broad bands are observed in the Raman spectra of SiC nanoparticles (np-SiC) with diameters ranging from 10 to 25 nm. The phenomenon is studied versus the particle size, chemical composition, annealing, and... more
Visible photoluminescence (PL) broad bands are observed in the Raman spectra of SiC nanoparticles (np-SiC) with diameters ranging from 10 to 25 nm. The phenomenon is studied versus the particle size, chemical composition, annealing, and oxidation treatments. In the case of quasistoichiometric np-SiC, excitation by 514-nm radiation gives rise to broad red PL emissions mainly enhanced by the amorphous fraction
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... 94 (1998) 123 [20] J. Sanetra, D. Bogdal, S. Niziol, P. Armatys, J. Pielichowski, Synth. ... 34 (1999) 745 [22] M. Melancholin, Methods of the crystallography measurements, Moscow, Nauka, 1983 [23] RJ Pressley (Ed.), Handbook of... more
... 94 (1998) 123 [20] J. Sanetra, D. Bogdal, S. Niziol, P. Armatys, J. Pielichowski, Synth. ... 34 (1999) 745 [22] M. Melancholin, Methods of the crystallography measurements, Moscow, Nauka, 1983 [23] RJ Pressley (Ed.), Handbook of Lasers with selected Data on Optical Technology ...
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ABSTRACT This paper proposes the cluster approach methodology to simulate electronic properties of semiconducting isolated nanocrystalline materials as well as functionalized by organic dye molecules. The proposed cluster approach... more
ABSTRACT This paper proposes the cluster approach methodology to simulate electronic properties of semiconducting isolated nanocrystalline materials as well as functionalized by organic dye molecules. The proposed cluster approach considers the nanoobject construction with the crystal structure in the internal part while the surface is modified according to the environmental interaction. In this aim, the (TiO2)n clusters with n = 2–140, indoline dye molecule D102, and their hybrid composites were investigated. The electronic properties of (TiO2)n were computed thanks to different DFT potentials, considering the nanobject sizes evaluation, their environmental surface modification and saturation, and the interface effects occurring between the cluster and sensitizer. The studies prove that the electronic features of (TiO2)n nanoparticles with surface being altered by the external environment may be coherently computed using DFT methodology with LC-BLYP potential by modifying the long-range separation parameter μ. The values of μ depend on the composition of the investigated system, whereas the surface saturation of the studied clusters possessing suitable size did not have any critical impact on their electronic properties. It is shown that the developed methodology is also relevant to characterize the charge transfer involved in the hybrid forms associating dye molecules and (TiO2)n clusters. The mentioned process is crucial in the efficiency of photovoltaic devices based on the hybrid systems.
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ABSTRACT Stoichiometric and nitrogen doped SiC nanopowders have been investigated by multi-approaches EPR methods. The paramagnetic intrinsic defects formed in the nanoparticles were studied by cw EPR, field swept electron spin echo,... more
ABSTRACT Stoichiometric and nitrogen doped SiC nanopowders have been investigated by multi-approaches EPR methods. The paramagnetic intrinsic defects formed in the nanoparticles were studied by cw EPR, field swept electron spin echo, pulsed electron nuclear double resonance and hyperfine sublevel correlation spectroscopy. We observe weak 29Si and 13C superhyperfine couplings with silicon and carbon atoms in the second coordination sphere and beyond indicating a high delocalization of the electronic wave function of the unpaired electron. Additional coupling with protons from presumably clustered hydrogen atoms have been detected. Although nitrogen has been found to be present in the nanomaterials no related shallow donor state was formed.
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The and energy structure of large-sized SiC nanocomposites (above 10 nm) was calculated. We used self-consistent norm-conserving pseudopotential method and molecular dynamics simulations of the nanocrystallite interface geometry.... more
The and energy structure of large-sized SiC nanocomposites (above 10 nm) was calculated. We used self-consistent norm-conserving pseudopotential method and molecular dynamics simulations of the nanocrystallite interface geometry. Essential changes of the band energy parameters versus the nanocrystallite sizes have been observed. Molecular dynamics structural simulations allowed to find a relation between the degree of hexagonality H (relative presence of
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ABSTRACT The paper concerns numerical analysis of superparamagnetic clusters by means of Langevin paramagnetism theory and simulated annealing (SA) procedure supplemented with some additional constraints. In order to determine a proper... more
ABSTRACT The paper concerns numerical analysis of superparamagnetic clusters by means of Langevin paramagnetism theory and simulated annealing (SA) procedure supplemented with some additional constraints. In order to determine a proper calculation algorithm and its parameters the three methods, i.e., simple SA, SA with maximum entropy, and SA with local maximum entropy were tested. Within the analyzed SA procedures (carried out for the computer generated semi-empirical curves) the best results were obtained by making use of the local entropy constraint. It was also shown that this algorithm can be successfully applied to determination of superparamagnetic cluster distribution. The tested SA procedure was applied to analysis of measured magnetic isotherms for Al–RE–Ni amorphous alloys and thin SiC–Mn layers deposited on a Si substrate.
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... Pezeril, M. and J. C. Fayet. (1982). J. Phys. Lettres, 43, L267. Ribeiro, J. L., JC Fayet, J. Emery, M. Pezeril, J. Albers, A. Klopperpieper, Almeida, MP Chaves. (1988). Walisch, R., J. M. Perez-Mato and J. Petersson. (1989). Phys.... more
... Pezeril, M. and J. C. Fayet. (1982). J. Phys. Lettres, 43, L267. Ribeiro, J. L., JC Fayet, J. Emery, M. Pezeril, J. Albers, A. Klopperpieper, Almeida, MP Chaves. (1988). Walisch, R., J. M. Perez-Mato and J. Petersson. (1989). Phys. Rev. B, 40, 10740. J. Physique, 49, 813.
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ABSTRACT Titanium oxide based mesoporous structures and gels are synthesized and investigated by means of advanced X-ray techniques and EPR spectroscopy. In these systems, annealing treatments were performed up to 500 °C in order to... more
ABSTRACT Titanium oxide based mesoporous structures and gels are synthesized and investigated by means of advanced X-ray techniques and EPR spectroscopy. In these systems, annealing treatments were performed up to 500 °C in order to improve the crystalline structure of the titanium dioxide with a stable polytype and to incorporate the nitrogen ions inside the crystal sites. EPR experiments were performed to analyze the involved paramagnetic centres and their evolution with respect to the synthesis conditions and the performed treatments.For the gel based titanium oxide, three characteristic molar ratios in the ternary phase diagram (TiOCl2, H2O, DMF) have been chosen for representative gels with good optical transparency. Photo-induced phenomena were investigated by using UV-irradiation of the gels which leads to charge transfer on the titanium ions. The kinetics of the photoinduced reactions are investigated by EPR which contributes also to analyze and to assign the local environments around titanium as function of the material composition, the carried out thermal treatment and UV-irradiation. The kinetic features and their correlation with the microstructure of the gels are discussed as well as the properties of the electronic active centres.
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The dielectric properties of non-stoichiometric silicon carbide nanoparticles (np-SiC), with a silicon-rich composition in the atomic ratio C/Si = 0.85, are investigated in a wide frequency and temperature range. Two samples, namely S1400... more
The dielectric properties of non-stoichiometric silicon carbide nanoparticles (np-SiC), with a silicon-rich composition in the atomic ratio C/Si = 0.85, are investigated in a wide frequency and temperature range. Two samples, namely S1400 and S1700, obtained from the same synthesis batch but submitted to annealing at, respectively, 1400 and 1700 °C, are representative of this class of material. In particular,
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Electron paramagnetic resonance (EPR) investigations are carried out on mesoporous silica (SBA15) functionalized by Ni-cyclam complexes (1,4,8,11-tetraazacyclotetradecane groups chelating nickel ions). The magnetic behaviour of... more
Electron paramagnetic resonance (EPR) investigations are carried out on mesoporous silica (SBA15) functionalized by Ni-cyclam complexes (1,4,8,11-tetraazacyclotetradecane groups chelating nickel ions). The magnetic behaviour of nickel-cyclam groups, their mutual interactions and dispersions in the mesoporous silica are compared with respect to the doping rates and the synthesis procedures. The spin-spin interactions and the relaxation processes were clarified from the thermal evolution in the temperature range (4 K, 300 K) of the paramagnetic spin susceptibilities and EPR line widths. Thus, the relaxation mechanisms seem marked by the Jahn-Teller effect on the nickel ions mediated by exchange interactions between nearest spins. Isolated Ni-cyclam molecules are involved in some samples while others show the formation of clusters where phonon-assisted one-dimensional (1D) ferromagnetic ordering occurs below 45 K. The performed experiments point out the efficiency of the EPR technique to probe the degree of functionalization of mesoporous silica by Ni-cyclam molecules and to give valuable feedback to improve the synthesis routes.
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Electron paramagnetic resonance (EPR) experiments were performed on mesoporous silica powders in which (1,4,8,11-tetraazacyclotetradecane) cyclam groups were incorporated. These functionalised groups allow an easy binding with copper and... more
Electron paramagnetic resonance (EPR) experiments were performed on mesoporous silica powders in which (1,4,8,11-tetraazacyclotetradecane) cyclam groups were incorporated. These functionalised groups allow an easy binding with copper and nickel ions. Comparative studies are carried out on samples functionalised by cyclam groups located either inside the pores or in the walls of the mesoporous structures. Copper and nickel EPR parameters, including
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The dispersion behaviour of laser-synthesized silicon carbide nanoparticles (npSiC) in water is investigated by photon correlation spectroscopy (PCS). With regard to previous studies and due to an application in the processing of optical... more
The dispersion behaviour of laser-synthesized silicon carbide nanoparticles (npSiC) in water is investigated by photon correlation spectroscopy (PCS). With regard to previous studies and due to an application in the processing of optical materials, this paper concerns low npSiC contents (from 0.05 to 10 wt.%). The role played by the particle surface state is be pointed out through the consideration
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Abstract Incorporation of indium (dopant) into CdS crystals have been successfully achieved by a mechanical alloying process. Powders are prepared with various In/Cd ratio from 1 to 10 at% and milled at 300 revolution per minute (rpm) for... more
Abstract Incorporation of indium (dopant) into CdS crystals have been successfully achieved by a mechanical alloying process. Powders are prepared with various In/Cd ratio from 1 to 10 at% and milled at 300 revolution per minute (rpm) for 60 min. X-ray diffraction (XRD) ...
Research Interests: Engineering, Materials Science, High Resolution Transmission Electron Microscopy, Mechanical Alloying, Zinc, and 10 moreGrain size, CHEMICAL SCIENCES, Second Order, X ray diffraction, Dielectric Constant, Fourier transform, Surface Energy, Field Emission Scanning Electron Microscopy, Raman Spectra, and Longitudinal Optical
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Structural and vibrational properties are investigated in SiC nanopowders synthesized by a CO2 laser pyrolysis of (SiH4, C2H2) gaseous mixture and thermally treated up to 1800 °C. The structural modifications of the SiC crystallites and... more
Structural and vibrational properties are investigated in SiC nanopowders synthesized by a CO2 laser pyrolysis of (SiH4, C2H2) gaseous mixture and thermally treated up to 1800 °C. The structural modifications of the SiC crystallites and the arrangement of the carbon in excess are monitored at different annealing stages. A critical behaviour is revealed in the powder annealed at T_a =
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The physical properties of nanosized SiC particles are investigated as a function of the C/Si ratios. The synthesis by the laser pyrolysis process monitors the particle stoichiometry by the initial fluxes of the reactants (SiH4 and C2H2)... more
The physical properties of nanosized SiC particles are investigated as a function of the C/Si ratios. The synthesis by the laser pyrolysis process monitors the particle stoichiometry by the initial fluxes of the reactants (SiH4 and C2H2) and leads to Si- or C-rich batches. Spectroscopic methods such as EPR and Raman are used to probe the paramagnetic active electronic centres
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We show how to record and analyze solid-state NMR spectra of organic paramagnetic complexes with moderate hyperfine interactions using the Cu-cyclam complex as an example. Assignment of the (13)C signals was performed with the help of... more
We show how to record and analyze solid-state NMR spectra of organic paramagnetic complexes with moderate hyperfine interactions using the Cu-cyclam complex as an example. Assignment of the (13)C signals was performed with the help of density functional theory (DFT) calculations. An initial assignment of the (1)H signals was done by means of (1)H-(13)C correlation spectra. The possibility of recording a dipolar HSQC spectrum with the advantage of direct (1)H acquisition is discussed. Owing to the paramagnetic shifting the resolution of such paramagnetic (1)H spectra is generally better than for diamagnetic solid samples, and we exploit this advantage by recording (1)H-(1)H correlation spectra with a simple and short pulse sequence. This experiment, along with a Karplus relation, allowed for the completion of the (1)H signal assignment. On the basis of these data, we measured the distances of the carbon atoms to the copper center in Cu-cyclam by means of (13)CR2 relaxation experiments combined with the electronic relaxation determined by EPR.
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N,N′-Bis(4-aminophenyl)1,4-quinonenediimine doped with silicotungsten polyacid were investigated by Raman, IR and UV–Vis absorption methods and the results analyzed based on numerical approaches. In this aim, density functional theory... more
N,N′-Bis(4-aminophenyl)1,4-quinonenediimine doped with silicotungsten polyacid were investigated by Raman, IR and UV–Vis absorption methods and the results analyzed based on numerical approaches. In this aim, density functional theory (DFT) calculations were performed to optimize the geometry and to clarify the electronic and optical features of the investigated molecules. Three main systems were considered and consist in a conjugated organic group
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An electro-optical activity has been recently reported for hybrid nanocomposite thin films where inorganic silicon carbide nanocrystals (ncSiC) are incorporated into polymer matrices. The role of the interface SiC polymer is suggested as... more
An electro-optical activity has been recently reported for hybrid nanocomposite thin films where inorganic silicon carbide nanocrystals (ncSiC) are incorporated into polymer matrices. The role of the interface SiC polymer is suggested as the origin of the observed second order nonlinear optical susceptibility in the hybrid materials based on poly-(methylmethacrylate) (PMMA) or poly-( N -vinylcarbazole) matrices. In this work, we
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