Suchergebnisse

The experiment at HASYLAB/DESY was performed within the project I-20180036 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Filipe Correia is grateful to the Fundação para a Ciência e Tecnologia (FCT, Portugal) for the Ph.D. Grant SFRH/BD/111720/2015 . Joana Ribeiro is grateful to the Project WinPSC - POCI-01-0247-FEDER-017796, for the research grant, co-funded by the European Regional Development Fund (ERDF) , through the Operational Programme for Competitiveness and Internationalisation (COMPETE 2020), under the PORTUGAL 2020 Partnership Agreement. The authors acknowledge the funding from the following institution Fundação para a Ciência e Tecnologia (FCT, Portugal) /PIDDAC through the Strategic Funds project reference UID/FIS/04650/2013. The Spanish Ministry of Economy, Industry, and Competitiveness through the "Severo Ochoa" Program for Centers of Excellence in R&D (SEV-2015-0496), projects No. MAT2017-90024-P (TANGENTS)-EI/FEDER and MAT2015-70850-P (HIBRI2), and the Generalitat de Catalunya through grant 2017-SGR-00488 . M. K. acknowledges the Ph.D. programme in Materials Science from Universitat Autonoma de Barcelona in which she is enrolled. ; Transparent n-type niobium-doped titanium dioxide thin films (TiO2:1.5 at.%Nb) with pronounced thermoelectric properties were produced from a composite Ti:Nb target by reactive magnetron sputtering. The thin films were comprehensively characterized by X-ray diffraction, X-ray photoelectron spectroscopy, optical spectroscopy, electrical conductivity, and thermoelectric measurement techniques. The local structure of the thin films was investigated in detail by X-ray absorption spectroscopy at the Ti and Nb K-edges. A set of radial distribution functions were extracted from the simultaneous analysis of EXAFS data at two absorption edges using the reverse Monte Carlo method. It was found that Nb dopant atoms modify the local environment of the films, but their average structure remains close to that of the anatase phase. This conclusion is also supported by the ab initio simulations of XANES. A very high absolute Seebeck coefficient (S = 155 μV/K) for n-type TiO2 was achieved with Nb doping, yielding a maximum power factor and thermoelectric figure of merit of 0.5 mW m−1 K−2 and 0.18 at a temperature of 300 K, respectively, for a 150 nm thick film. From frequency-domain thermoreflectance experiments, a thermal conductivity value of 1.3 W m−1 K−1 was obtained for the optimized TiO2:Nb film. ; Fundo Regional para a Ciência e Tecnologia POCI-01-0247-FEDER-017796; Generalitat de Catalunya 2017-SGR-00488; MAT2015-70850-P,HIBRI2; SEV-2015-0496,MAT2017-90024-P; UID/FIS/04650/2013; European Regional Development Fund; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

The experiment at HASYLAB/DESY was performed within the project I-20180036 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. Filipe Correia is grateful to the Fundação para a Ciência e Tecnologia (FCT, Portugal) for the Ph.D. Grant SFRH/BD/111720/2015. Joana Ribeiro is grateful to the Project WinPSC - POCI-01-0247-FEDER-017796, for the research grant from the Agência Nacional de Inovação, co-funded by the European Regional Development Fund (ERDF), through the Operational Programme for Competitiveness and Internationalisation (COMPETE 2020), under the PORTUGAL 2020 Partnership Agreement. The authors acknowledge the funding from the Fundação para a Ciência e Tecnologia (FCT, Portugal) / PIDDAC through the Strategic Funds project reference UIDB/04650/2020-2023. Part of this work was developed within the scope of the project i3N, UIDB/50025/2020, financed by national funds through the FCT/MEC. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020- WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2. The authors would like to thank the valuable help from Dr. Alec LaGrow and Dr. Dr. Alex Bondarchukat the International Iberian Nanotechnology Laboratory (INL), in Braga, Portugal, for the STEM/HRTEM experiments ; Transparent undoped ZnO and additionally doped with Ga and Bi thin films were produced by magnetron sputtering. The thin films were comprehensively characterized by X-ray absorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission and scanning transmission electron (TEM, STEM) microscopy and Raman spectroscopy. All undoped and doped films crystallise in a ZnO phase with the hexagonal wurtzite crystal structure. The local structure of the thin films was investigated by temperature-dependent X-ray absorption spectroscopy at the Zn and Ga K-edges, as well as at the Bi L3-edge. It was found that the doping of Ga3+ and Bi3+ ions in the ZnO wurtzite structure produces distinct effects on the thin film microstructure. The substitution of Zn2+ ions by smaller Ga3+ ions introduces a static disorder to the thin film structure, which is evidenced by an increase in the mean-square relative displacements σ2(Zn‒O) and σ2(Zn‒Zn). At the same time, large Bi3+ ions do not substitute zinc ions, but are likely located in the disordered environment at the ZnO grain boundaries. This conclusion was directly supported by energy-dispersive X-ray spectroscopy combined with TEM and STEM observations as well as by resonant and non-resonant μ-Raman experiments at room temperature, where the ZnO and ZnO:Bi spectra are similar, suggesting a lack of structural disorder in the wurtzite cell. On the other hand, the Raman disorder-activated phonon is pronounced for Ga-doping of the ZnO lattice, confirming the compositional disorder. Both XRD and XPS ruled out Ga2O3 phase in Ga-doped ZnO; conversely, Bi2O3 and a small amount of Bi‒metal phases are clearly discerned by XPS experiments, further suggesting that Bi is not incorporated in the ZnO wurtzite cell, but segregated to grain boundaries.--//--This is the preprint version of the following article: Filipe C. Correia, Joana M. Ribeiro, Alexei Kuzmin, Inga Pudza, Aleksandr Kalinko, Edmund Welter, Adelio Mendes, Joana Rodrigues, Nabiha Ben Sedrine, Teresa Monteiro, Maria Rosário Correia, Carlos J. Tavares; The role of Ga and Bi doping on the local structure of transparent zinc oxide thin films, Journal of Alloys and Compounds: Volume 870, 25 July 2021, 159489, which has been published in final form at https://www.sciencedirect.com/science/article/abs/pii/S0925838821008987?via%3Dihub#! This article may be used for non-commercial purposes in accordance with Elsevier Terms and Conditions for Sharing and Self-Archiving. This work is licensed under a CC BY-NC-ND license. ; Project I-20180036 EC; CALIPSOplus under the Grant Agreement 730872; Ph.D. Grant SFRH/BD/111720/2015; Project WinPSC - POCI-01-0247-FEDER-017796 from the Agência Nacional de Inovação, co-funded by the European Regional Development Fund (ERDF); Fundação para a Ciência e Tecnologia (FCT, Portugal) / PIDDAC; i3N, UIDB/50025/2020, financed by national funds through the FCT/MEC; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2.