Cristy Leonor Azanza Ricardo

Stoichiometry effect on Cu2ZnSnS4 thin films morphological and optical properties

Thin films of Cu 2ZnSnS4 (CZTS) were prepared by sulfurization of multilayered precursors of ZnS, Cu, and Sn, changing the relative amounts to obtain CZTS layers with different compositions. X-Ray Diffraction (XRD), Energy Dispersive X-Ray spectroscopy, and SEM were used for structural, compositional, and morphological analyses, respectively. XRD quantitative phase analysis provides the amount of spurious phases and information on Sn-site occupancy. The optical properties were investigated by spectrophotometric measurements and Photothermal Deflection Spectroscopy. These films show a clear dependence of the optical and microstructural properties on the tin content. As the tin content increases we found: (i) an increase in both crystalline domain and grain size, (ii) an abrupt increase of the energy gap of about 150 meV, from 1.48 to 1.63 eV, and (iii) a decrease of sub-gap absorption up to two orders of magnitude. The results are interpreted assuming the formation of additional defects as the tin content is reduced.

Correlation between microstructure and bioequivalence in Anti-HIV Drug Efavirenz

Polymorphism and particle size distribution can impact the dissolution behaviour and, as a consequence, bioavailability and bioequivalence of poorly soluble drugs, such as Efavirenz (EFV). Nevertheless, these characteristics do not explain some failures occurring in in vitro assays and in in vivo studies. EFV belongs to Class II and the High Activity Antiretroviral Therapy (HAART) is considered the best choice in the treatment of adults and children. EFV is a drug that needs bioequivalence studies for generic compounds. In this work, six raw materials were analyzed and two of them were utilized with human volunteers (in vivo assays or bioequivalence). All the routine pharmaceutical controls of raw materials were approved; however, the reasons for the failure of the bioequivalence assay could not be explained with current knowledge. The aim of this work was to study microstructure, a solid-state property of current interest in the pharmaceutical area, in order to find an explanation for the dissolution and bioequivalence behaviour. The microstructure of EFV raw materials was studied by Whole Powder Pattern Modelling (WPPM) of X-ray powder diffraction data. Results for different EFV batches showed the biorelevance of the crystalline domain size, and a clear correlation with in vitro (dissolution tests) and in vivo assays (bioequivalence).

Measurement of stress factors and residual stress of a film by in situ X-ray diffraction during four-point bending

A method is proposed for the simultaneous measurement of the stress factors and residual stress state of a film by in-situ X-ray diffraction during four-point bending. The externally applied load acts as an additional degree of freedom in the stress–strain relation, which allows the problem to be solved for both residual stress and elastic moduli without assuming any grain interaction model. The procedure was tested on a galvanic nickel deposit and the predictions of existing grain interaction models were compared with the experimental results.

Thin Film Stress and Texture Analysis at the MCX Synchrotron Radiation Beamline at ELETTRA

The main instrumental characteristics of MCX, the new beamline at the Italian synchrotron Elettra in Trieste, are presented. Design and geometrical set-up are well suited to the X-ray diffraction stress and texture analysis of thin films and surfaces, and are such to guarantee a full control of the main instrumental errors. Besides exploiting the typical features of synchrotron radiation, like high brilliance, tuneable beam energy and optimal beam geometry, MCX can also host tools for in-situ studies, like X-ray diffraction during four point bending. A few examples of current applications are shown.

Residual Stress Depth-Profiling in Shot-Peened Al Alloy Components Subjected to Fatigue Testing

The residual stress profile in a shot-peened Al alloy component was studied by a recently proposed method based on the known procedure of progressive thinning and X-ray Diffraction measurements. The effect the cyclic stress on the fatigue life was studied in detail, showing the correlation between nominal load and residual stress relaxation. Besides showing the expected decrease of compressive stress with the load and number of cycles, the present work highlights the importance of changes in the through-the-thickness residual stress distribution.

Chloride-based route for monodisperse Cu2ZnSnS4 nanoparticles preparation

A new approach based on hot injection method is proposed to gram-scale Cu2ZnSnS4 nanoparticles production minimizing the use of organic solvents. Nanocrystal synthesis was performed starting from metal chlorides and pure sulphur powder and using Oleylamine as capping agent. As a result, core-shell nanoparticles with a narrow size distribution were obtained.

Analysis of Residual Stress-Texture Relationships in Thin Films

A new software was developed for the X-ray stress analysis of textured materials, especially useful in the case of thin films and coating. Literature data for a sputtered Cu thin film were used as a test case. Good agreement with the published results was found considering a grain interaction mechanism based on the combination of four models (Ruess/Voigt/Vook-Witt/inverse Vook-Witt). A similar value for the in-plane residual stress was obtained by the Eshelby-Kröner model, by optimizing the grain aspect-ratio. Main features and numerical/graphic output are briefly discussed.

Sub-Surface Residual Stress Gradients: Advances in Laboratory XRD Methods

A new algorithm is proposed to determine the through-thickness residual stress gradient by X-ray Diffraction measurements on progressively thinned components. The procedure is based on a chemical or electrochemical attack of the component surface, which is then measured at each thinning stage. The simple algorithm provided for by a specific norm has been revised to take into account the X-ray absorption effects and the conditions of mechanical equilibrium of the component. The new procedure is illustrated for a typical case of study concerning a shot-peened metal component.

Influence of Shot-Peening Parameters on the Sub-Surface Residual Stress Profiles in Al-7075 Alloy Components

Aluminum alloy (Al-7075-T6) samples were analyzed to determine the in-depth residual stress profile induced by a shot-peening treatment. The influence of coverage degree and Almen intensity on the surface residual stress and on the sub-surface residual stress gradient was investigated. Residual stress profiles were obtained using three different techniques: (i) standard laboratory X-ray diffraction (XRD) residual stress analysis with progressive chemical layer-removal; (ii) XRD residual stress analysis with synchrotron radiation using different X-ray energies, thus changing the penetration depths, and (iii) Blind Hole Drilling (BHD). A comprehensive comparison of the results given by the used techniques is shown.