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Cu(In,Ga) Se 2 (CIGS) and Cu 2 ZnSnS 4 (CZTS) are potential absorber materials for solar cell applications. We report an investigation of these materials using muon spin spectroscopy. In these experiments, positive muons produced at accelerator facilities (here the ISIS Facility, Rutherford Appleton Laboratory, U.K.) are implanted into the material and come to rest at interstitial sites in the host lattice. The muon is a sensitive local probe to study materials properties on an atomistic level. An advantage of the method is that interface properties can be studied by placing the probe particles at different depths in the sample. Muonium, the positive muon with an electron, can be considered as a light isotope of hydrogen (mass ratio 1/9) with almost identical electronic properties to hydrogen. Thus, muon spectroscopy provides also information about hydrogen in the host material. The aim of the present experiment is to obtain information about the muonium/hydrogen states formed in CIGS and CZTS solar cell materials. A major goal of the experiment is to obtain information about the physical embedding process of the implanted particle into the host lattice. The present study combines experimental measurements with total energy calculations in the framework of density functional theory. We obtain the final configurations of muonium in CZTS, that we discuss in parallel to those in CIGS. This allows us to deepen our understanding of the influence of the hydrogen impurity on the properties of these materials. We also discuss the final steps in the process of muon implantation in these materials. [ABSTRACT FROM AUTHOR]

Despite the fact that yttria-stabilized zirconia has been studied experimentally by optical and electron energy-loss spectroscopies, a first-principles theoretical interpretation of the dielectric response and electronic excitations is still lacking. The present study reports calculations of the complex dielectric function, reflectivity spectrum and electron energy-loss function of two ordered yttria–zirconia compounds: Zr6Y2O15 and Zr3Y4O12. The adopted methodology is based on linear-response theory with a semilocal density functional and the random-phase approximation including local-field effects. Comparisons with existing experimental data show an acceptable agreement showcasing how the different yttria content affects dielectric properties and spectra lineshapes. Strong discrepancies with experimental data are mainly confined to the low-energy part of the optical spectra and concern both the peak positions and the lineshape intensities. The onset of the optical absorption is considerably underestimated from the calculations owing to the well-known deficiency of semilocal density functionals to describe the quasiparticle band gaps. The energy-loss spectra, instead, are reproduced extremely well provided that local-field effects are included in the response functions. These effects are particularly important for the description of the semicore Zr–4p and Y–4p excitations, which dominate for higher energies (>30 eV) in the valence region. [ABSTRACT FROM AUTHOR]

The local binding and migration behavior of the proton defect in cubic yttria-stabilized zirconia (YSZ) is studied by first-principles calculations and muon-spin spectroscopy (μSR) measurements. The calculations are based on density-functional theory (DFT) supplemented with a hybrid-functional approach with the proton defect embedded in quasi-random supercells of 10.3 mol% yttria content, where the yttrium–zirconium substitutional defects are charge compensated by oxygen vacancies. Representative migration pathways for the proton comprising both transfer and bond reorientation modes are analysed and linked to the underlying microstructure of the YSZ lattice. The μSR data show the evolution of the diamagnetic fraction corresponding to the muon-isotope analogue with an activation energy of diffusion equal to 0.17 eV. Comparisons between the calculations and the experiment allow an assessment of the character of the short-range migration of the proton particle in cubic YSZ. [ABSTRACT FROM AUTHOR]

First-principles calculations were performed jointly with muon-spin (μSR) spectroscopy experiments in order to examine the electrical activity of hydrogen in mixed-cation chalcopyrite Cu(In 1 − x ,Ga x )Se 2 (CIGS) alloys and other related compounds commonly used as absorbers in solar-cell technology. The study targeted the range of Ga concentrations most relevant in typical solar cells. By means of a hybrid-functional approach the charge-transition levels of hydrogen were determined and the evolution of the defect pinning level, E(+/–), was monitored as a function of the Ga content. The use of E(+/–) as a metric of the charge-neutrality level allowed the alignment of band structures, thus providing the band offsets between the CuInSe 2 compound and the CIGS alloys. The μSR measurements in both thin-film and bulk CIGS materials confirmed that the positively charged state is the thermodynamically stable configuration of hydrogen for p-type conditions. The interpretation of the μSR data further addressed the existence of a metastable quasi-atomic neutral configuration that was resolved from the calculations and led to a formation model for muon implantation. [ABSTRACT FROM AUTHOR]

Abstract Introduction Recent studies have reported a risk reduction in the progression of benign breast disease to breast carcinoma through COX-2 pathways. Case presentation We present a case of severe epithelial hyperplasia in a 47-year-old woman with increased breast density submitted to scintimammography by the proliferation-imaging tracer Technetium-99m-labelled pentavalent dimercaptosuccinic acid, before and after an oral ibuprofen treatment for 4 weeks. The radiotracer uptake after ibuprofen intake was significantly reduced, both visually and by semi-quantitative analysis, based on a calculation of lesion-to-background ratios. Conclusion In proliferating breast lesions, scintigraphically displayed reduction in Technetium-99m-labelled pentavalent dimercaptosuccinic acid uptake may indicate inhibition by ibuprofen in the pathway of malignant epithelial cell transformation.