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  • 1
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    Surface X-ray Diffraction Study of a Bi-Layer Junction Based on Cu and Cd Sulfides for Photovoltaic Applications (2020)
    Molecular Diversity Preservation International
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    Publication Date: 2020-05-14
    Description: The development of new-generation photovoltaic devices through more sustainable production techniques and materials is driven by the need to contain the threats to the biosphere while guaranteeing the safety of the supply, accounting for the limited availability of fossil fuels. This study investigates the crystal structure of thin films of chalcogenides, particularly a junction with a p-type (Cu2S) and an n-type (CdS) layer deposited one on top of the other on a Ag(111) substrate, starting from an aqueous solution and by means of electrochemical atomic layer deposition (E-ALD) (the system is denoted by (Cu2S)60/(CdS)60/Ag(111)). The experiment highlights the profound epitaxial relationship existing between the films and the bulk, consequent to the homogenization of the metrics of the CdS and the Cu2S structures to values commensurate to the surface periodicity of the substrate. Cadmium sulfide develops an elementary cell with crystallographic axes parallel to those of the Ag(111) and parameters |a|, |b| and |c| not found in any of the known mineral phases. The comparison with the wurtzite-type structure of greenockite shows a compensation mechanism related to the strain imposed by the film growth on the crystallographic Ag(111) surface. The positions in the reciprocal space of the Cu2S reflection is compatible with a pseudo-hexagonal pattern rotated by 30° with respect to the Ag, as already noticed in relation to a Cu2S/Ag(111) E-ALD deposit (Giaccherini et al., 2017). The Cu2S c axis results parallel to the direction [111] of the Ag substrate and its structure is characterized by the strong occurrence of the 3.963 Å periodicity, which corresponds to the interatomic distance S-S in the triangular CuS3 groups, the basis of all the mineral Cu2-xS group structures. These data suggest a pseudo-hexagonal chalcocite-like structure with a planarization of S layers (Giaccherini et al., 2017) as a result of the strong epitaxial relationship existing with the CdS below. This study confirms E-ALD as an energy efficient method for the growth of semiconducting heterostructures with tailored properties.
    Electronic ISSN: 2673-4605
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Molecular Diversity Preservation International
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  • 2
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    Interplay between abiotic and microbial biofilm-mediated processes for travertine formation: Insights from a thermal spring (Piscine Carletti, Viterbo, Italy) (2023)
    Wiley
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    Publication Date: 2023-03-16
    Description: Active hydrothermal travertine systems are ideal environments to investigate how abiotic and biotic processes affect mineralization mechanisms and mineral fabric formation. In this study, a biogeochemical characterization of waters, dissolved gases, and microbial mats was performed together with a mineralogical investigation on travertine encrustations occurring at the outflow channel of a thermal spring. The comprehensive model, compiled by means of TOUGHREACT computational tool from measured parameters, revealed that mineral phases were differently influenced by either abiotic conditions or microbially driven processes. Microbial mats are shaped by light availability and temperature gradient of waters flowing along the channel. Mineralogical features were homogeneous throughout the system, with euhedral calcite crystals, related to inorganic precipitation induced by CO2 degassing, and calcite shrubs associated with organomineralization processes, thus indicating an indirect microbial participation to the mineral deposition (microbially influenced calcite). The microbial activity played a role in driving calcite redissolution processes, resulting in circular pits on calcite crystal surfaces possibly related to the metabolic activity of sulfur-oxidizing bacteria found at a high relative abundance within the biofilm community. Sulfur oxidation might also explain the occurrence of gypsum crystals embedded in microbial mats, since gypsum precipitation could be induced by a local increase in sulfate concentration mediated by S-oxidizing bacteria, regardless of the overall undersaturated environmental conditions. Moreover, the absence of gypsum dissolution suggested the capability of microbial biofilm in modulating the mobility of chemical species by providing a protective envelope on gypsum crystals.
    Description: Published
    Description: 837-856
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: biofilms; gypsum; hot spring; microbial mat; travertine
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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