The influence of the particle size distribution of a petroleum coke sample compared to its sulfur content was investigated. For this matrix, an optimization procedure of the Suspension Assisted Analysis (SAA) by Total-reflection X-Ray Fluorescence (TXRF) quantitative method was developed. SAA-TXRF sulfur recoveries were evaluated for three particle size distributions of the same coke sample. The sulfur recovery increased when the particle size distribution was smaller. The observed behaviour was correlated and validated with CHNS elemental analysis and microwave-assisted digestion TXRF measurements. The results indicate that the sulfur signal is strongly influenced by the particle size distribution and the deposition morphology of the petroleum coke material. This effect could be explained by the presence of a strong absorption effect for the sulfur signal in combination with the distortion of the X-ray Standing Waves (XSW) field observed between the analyte, S, and the elements Ti and Co, which were used as an internal standard. The variation in sulfur observed was up to 45.5% lower than the higher recovery obtained by CHNS. This investigation suggests that for an adequate application of the SAA-TXRF method in petroleum coke or similar matrices, careful optimization of the final particle dispersion of the ground coke is crucial and necessary. In this case, the use of a high- power ultrasound probe was the key.

This article presents a new methodology developed to quantify the amount of crumb rubber used in asphalt bitumen by Total-reflection X-Ray Fluorescence (TXRF) spectrometry. For the evaluation of the crumb rubber content in rubberized binders, the samples were completely digested by microwave-assisted acid digestion in a mixture of HNO3:HF acids. TXRF spectrometry has proven to be a powerful analytical technique capable to detect up to 12 elements in these matrixes with detection limits of only a few ppb's (μg/L). From those elements, Zn was elected as indicator of recycled crumb rubber and used for its quantitative correlation. The results obtained show that the proposed methodology is capable of quantifying the content of recycled crumb rubber in asphalt bitumen in a robust, accurate and reproducible way.

The influence of the organic content, sample preparation process and the morphology of the depositions of two types of Coke beverage, traditional and light Coke, have been investigated by mean of Total-reflection X-ray Fluorescence (TXRF) spectrometry. Strong distortions of the nominal concentration values, up to 128% for P, have been detected in the analysis of traditional Coke by different preparation methods. These differences have been correlated with the edge X-ray energies of the elements analyzed being more pronounced for the lighter elements. The influence of the organic content (mainly sugar) was evaluated comparing traditional and light Coke analytical TXRF results. Three sample preparation methods have been evaluated as follows: direct TXRF analysis of the sample only adding internal standard, TXRF analysis after open vessel acid digestion and TXRF analysis after high pressure and temperature microwave-assisted acid digestion. Strong correlations were detected between quantitative results, methods of preparation and energies of the X-ray absorption edges of quantified elements. In this way, a decay behavior for the concentration differences between preparation methods and the energies of the X-ray absorption edges of each element were observed. The observed behaviors were modeled with exponential decay functions obtaining R2 correlation coefficients from 0.989 to 0.992. The strong absorption effect observed, and even possible matrix effect, can be explained by the inherent high organic content of the evaluated samples and also by the morphology and average thickness of the TXRF depositions observed. As main conclusion of this work, the analysis of light elements in samples with high organic content by TXRF, i.e. medical, biological, food or any other organic matrixes should be taken carefully. In any case, the direct analysis is not recommended and a previous microwave-assisted acid digestion, or similar, is mandatory, for the correct elemental quantification by TXRF.

The main goal of this work was to investigate, in a systematic way, the influence of the controlled modulation of the particle size distribution of a representative solid sample with respect to the more relevant analytical parameters of the Direct Solid Analysis (DSA) by Total-reflection X-Ray Fluorescence (TXRF) quantitative method. In particular, accuracy, uncertainty, linearity and detection limits were correlated with the main parameters of their size distributions for the following elements; Al, Si, P, S, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Rb, Sr, Ba and Pb. In all cases strong correlations were finded. The main conclusion of this work can be resumed as follows; the modulation of particles shape to lower average sizes next to a minimization of the width of particle size distributions, produce a strong increment of accuracy, minimization of uncertainties and limit of detections for DSA-TXRF methodology. These achievements allow the future use of the DSA-TXRF analytical methodology for development of ISO norms and standardized protocols for the direct analysis of solids by mean of TXRF.

This work presents the study carried out to evaluate quantitatively the germanium content in organometallic materials by mean of Total-reflection X-Ray Fluorescence (TXRF). Samples were prepared by using different acid mixtures; aqua regia, HNO3 and H2O:HF:HNO3 (1:1:1) and different digestion processes; open vessel and microwave-assisted digestion. Germanium recoveries, as poor as 0.05%, were obtained after the measure of the initial acid digestions by mean of TXRF and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). In this way, direct solid sample preparation methodology combined with TXRF technique (DSA-TXRF) was applied and compared with the results obtained by mean of acid digestion. DSA-TXRF procedure proved to be adequate avoiding Ge loses by volatilization, or precipitation, and reaching an average analytical recovery of 95.4%. The acid mixture H2O:HF:HNO3 (1:1:1) by using open vessel digestion was also adequate for Ge quantification by TXRF and ICP-MS obtaining average analytical recoveries of 98.8% and 99.2% respectively and therefore validating the DSA-TXRF developed procedure.

This work presents the first application of total-reflection X-ray fluorescence (TXRF) spectrometry, a new and powerful alternative analytical method, to evaluation of the bioaccumulation kinetics of gold nanorods (GNRs) in various tissues upon intravenous administration in mice. The analytical parameters for developed methodology by TXRF were evaluated by means of the parallel analysis of bovine liver certified reference material samples (BCR-185R) doped with 10 μg/g gold. The average values (n = 5) achieved for gold measurements in lyophilized tissue weight were as follows: recovery 99.7%, expanded uncertainty (k = 2) 7%, repeatability 1.7%, detection limit 112 ng/g, and quantification limit 370 ng/g. The GNR bioaccumulation kinetics was analyzed in several vital mammalian organs such as liver, spleen, brain, and lung at different times. Additionally, urine samples were analyzed to study the kinetics of elimination of the GNRs by this excretion route. The main achievement was clearly differentiating two kinds of behaviors. GNRs were quickly bioaccumulated by highly vascular filtration organs such as liver and spleen, while GNRs do not show a bioaccumulation rates in brain and lung for the period of time investigated. In parallel, urine also shows a lack of GNR accumulation. TXRF has proven to be a powerful, versatile, and precise analytical technique for the evaluation of GNRs content in biological systems and, in a more general way, for any kind of metallic nanoparticles.

A study of Cu 2 ZnSnS 4 thin films grown by flash evaporation and subsequently annealed in Ar atmosphere has been carried out. Prior to thin film deposition, Cu 2 ZnSnS 4 bulk compounds with stoichiometric and Zn-rich compositions were synthesized as evaporation sources. The characteristics of the bulk compounds and thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and elastic back scattering. Cu 2 ZnSnS 4 deposited films contain lower concentrations of Zn than the bulk compounds used as evaporation sources, which is related to a preferential Zn re-evaporation during the deposition process. The desired kesterite composition for solar cell applications was achieved by using a Zn-rich compound as the evaporation source plus a thermal treatment at 620 °C in Ar atmosphere.

Molybdenum-coated polyimide films are excellent candidates to be used as flexible back contact layers in photovoltaic applications. In this work novel polymeric films consisting of filled polyimides containing mineral fillers (SiO2, sepiolite, Li and Na salts) have been prepared and used as substrates for the preparation of sputtered Mo thin films. A non-filled, i.e., as-prepared polyimide film, was additionally coated with Mo for comparison. The morphology and microstructure of the Mo films and their influence on the optical and electrical properties are studied as a function of the filler nature. A Mo film grown onto a non-filled polyimide film showed a low electrical resistivity (20μΩcm) and a high maximum optical reflectance of 93% (at λ=2250nm). Mo films grown onto polyimides filled with fumed SiO2 and NaCl showed, by comparison, an improved reflectance of 99% and resistivities of 13 and 180μΩcm, respectively.

The dielectric function of MnIn2S4 single crystals grown by the directional crystallization method was measured over the energy range 0.7–4.7eV at room temperature using variable angle spectroscopic ellipsometry. The spectral dependence of the real and imaginary parts of the complex dielectric function as well as of the refractive index, extinction and absorption coefficients and the normal-incidence reflectivity for MnIn2S4 in the photon energy range studied was determined.

A comparative study of chalcopyrite-related Cu2In7Se11.5 and CuIn5Se8 crystals by spectroscopic ellipsometry is presented. Their complex dielectric function ɛ(ω)=ɛ1(ω)+iɛ2(ω) has been determined in the 0.8–4.7eV photon energy range. The spectral dependence of ɛ1(ω) and ɛ2(ω) as well as the complex refractive index, the absorption coefficient and the normal-incidence reflectivity for tetragonal Cu2In7Se11.5 and trigonal CuIn5Se8 crystals have been modelled using the Adachi's model for interband transitions. The results are in a good agreement with the experimental data over the entire range of photon energies. The model parameters, including the energies corresponding to the lowest direct gap (E0) and higher critical points (E1A, E1B), have been determined using the simulated annealing algorithm. The results show that the tetragonal CuIn3Se5, the tetragonal Cu2In7Se11.5 and the trigonal CuIn5Se8 crystals belong to different phases of the Cu4In2nSe2+3n system, n=6, n=7 and n=10, respectively.

Distinguishing the scattering contributions of isoelectronic atomic species by means of conventional x-ray- and/or electron diffraction techniques is a difficult task. Such a problem occurs when determining the crystal structure of compounds containing different types of atoms with equal number of electrons. We propose a new structural model of Cu(InxGa1−x)3Se5 which is valid for the entire compositional range of the CuIn3Se5–CuGa3Se5 solid solution. Our model is based on neutron and anomalous x-ray diffraction experiments. These complementary techniques allow the separation of scattering contributions of the isoelectronic species Cu+ and Ga3+, contributing nearly identically in monoenergetic x-ray diffraction experiments. We have found that CuIII3Se5 (III=In,Ga) in its room temperature near-equilibrium modification exhibits a modified stannite structure (space group I4¯2m). Different occupation factors of the species involved, Cu+, In3+, Ga3+, and vacancies have been found at three different cationic positions of the structure (Wyckoff sites 2a, 2b, and 4d) depending on the composition of the compound. Significantly, Cu+ does not occupy the 2b site for the In-free compound, but does for the In-containing case. Structural parameters, including lattice constants, tetragonal distortions, and occupation factors are given for samples covering the entire range of the CuIn3Se5–CuGa3Se5 solid solution. At the light of the result, the denotation of Cu-poor 1:3:5 compounds as chalcopyrite-related materials is only valid in reference to their composition.

X-ray powder diffraction data for CuGa0.15In0.85Se2 and CuGa0.50In0.50Se2 are reported. Indexing of the X-ray diffraction powder pattern and the Rietveld refinement confirmed that these compounds crystallize in the tetragonal crystal system, with space group I-42d (No. 122) and lattice parameters of a=5.7528(2) Å and c=11.5225(3) Å for CuGa0.15In0.85Se2 and a=5.6847(1) Å and c=11.2817(1) Å for CuGa0.50In0.50Se2. The CuGaxIn1−xSe2 system presents the chalcopyrite type crystal structure (CuFeS2) and corresponds to two stacked zinc-blende unit cells. The metal atoms Cu, In, and Ga are regularly ordered in the unit cell. Every Se atom is tetrahedrally bonded to two Cu and two In and Ga atoms.

The dielectric functions of Cu2ZnGeS4 bulk crystals grown by the Bridgman method were measured over the energy range 1.4 to 4.7 eV at room temperature using variable angle spectroscopic ellipsometry. The observed structures in the dielectric functions were adjusted using the Adachi’s model and attributed to interband transitions E0, E1A, and E1B at Γ:(000), N(A):2π/a(0.5 0.5 0.5), and T(Z):2π/a(0 0 0.5) points of the first Brillouin zone, respectively. The model parameters (threshold energy, strength, and broadening) have been determined using the simulated annealing algorithm. The decrease in the first gap, E0, has been attributed to a higher Ge–S hybridization. The spectral dependence of the complex refractive index, the absorption coefficient, and the normal-incidence reflectivity were also derived.

X-ray powder diffraction data for CuGa0.15In0.85Se2 and CuGa0.50In0.50Se2 are reported. Indexing of the X-ray diffraction powder pattern and the Rietveld refinement confirmed that these compounds crystallize in the tetragonal crystal system, with space group I-42d (No. 122) and lattice parameters of a=5.7528(2) Å and c=11.5225(3) Å for CuGa0.15In0.85Se2 and a=5.6847(1) Å and c=11.2817(1) Å for CuGa0.50In0.50Se2. The CuGaxIn1−xSe2 system presents the chalcopyrite type crystal structure (CuFeS2) and corresponds to two stacked zinc-blende unit cells. The metal atoms Cu, In, and Ga are regularly ordered in the unit cell. Every Se atom is tetrahedrally bonded to two Cu and two In and Ga atoms.

Variable angle spectroscopic ellipsometry has been applied to characterize the optical constants of bulk Cu(In0.7Ga0.3)5Se8 and Cu(In0.4Ga0.6)5Se8 crystals grown by the Bridgman method. The spectra were measured at room temperature over the energy range 0.8–4.4eV. Adachi’s model was used to calculate the dielectric functions as well as the spectral dependence of complex refractive index, absorption coefficient, and normal-incidence reflectivity. The calculated data are in good agreement with the experimental ones over the entire range of photon energies. The parameters such as strength, threshold energy, and broadening, corresponding to the E0, E1A, and E1B interband transitions, have been determined using the simulated annealing algorithm.

Institute of Applied Physics, Academy of Sciences of Moldova, 5, Academiei str., MD-2028, Chisinau, Republic of Moldova Department of Energy, CIEMAT, 22, Avda Complutense, 28040, Madrid, Spain Department of Theory of Signal and Communications, ETSIT, URJC, Campus Fuenlabrada, 28943, Madrid, Spain Department of Applied Physics, Universidad Autónoma de Madrid (UAM), Cantoblanco, 28049, Madrid, Spain E-mail: galinagurieva@gmail.com (Received 12 January 2010)

Optical measurements of Cu(In1-xGax)(5)Se-8 were performed at room temperature in the photon energy range from 0.8 to 4.7 eV. Spectral dependence of the complex dielectric functions was derived. The structures observed in the measured spectra have been analyzed by fitting the second derivative of the experimental spectrum to analytical line shapes and have been attributed to the interband transitions E-0, and E-1A. The energies corresponding to the electronic transitions as well as the parameters as strength and broadening were determined. Besides, the values of E-0 and E-1A are found to increase linearly with increasing Ga content.

The optical properties of bulk Cu-(In1-xGax)-Se alloys grown by the Bridgman method are presented. The optical measurements were performed at room temperature in the photon energy range from 0.8 to 4.7eV using a variable-angle spectroscopic ellipsometer. The spectral dependences of the complex dielectric function, the refractive index, the absorption coefficient and the normal-incidence reflectivity were derived. The observed structures attributed to the interband transitions E0, E1A, and E1B were modelled using a modification of the Adachi’s model. The model parameters were determined using the simulated annealing (SA) algorithm. The values of E0 and E1A were found to increase linearly with Ga content.