| 1. |
- Abad, Manuel David, et al.
(author)
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Identification of Ternary Phases in TiBC/a-C Nanocomposite Thin Films : Influence on the Electrical and Optical Properties
- 2011
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In: Plasma Processes and Polymers. - : Wiley. - 1612-8850 .- 1612-8869. ; 8:7, s. 579-588
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Journal article (peer-reviewed)abstract
- The local structure of TiBC and amorphous carbon (a-C) nanocomposite films (TiBC/a-C) was correlated with their optical and electrical properties. TiBC/a-C films with increasing C content were deposited by magnetron co-sputtering from TiC:TiB(2) (60: 40) and graphite targets. Chemical composition is determined by electron energy-loss spectroscopy. Grazing incidence X-ray diffraction reveals that the microstructure of the films is amorphous with small nanocrystallites emerging by increasing the C content that could be attributed to the formation of ternary (TiB(x)C(y)) or mixed binary (TiB(2) and TiC) phases. Further information was then obtained by studying the chemical bonding by measuring the near-edge fine structure (NES) by electron energy-loss (B K-, C K-, and Ti L-edges) and X-ray absorption (B K-and Ti L-edges) spectroscopies. The NES analysis indicates the formation of a nanocrystalline ternary TiB(x)C(y) compound concomitant with the segregation of an a-C phase as the carbon content is increased. The optical properties were studied by spectroscopic ellipsometry and the electrical resistivity was measured by the Van der Pauw method between 20 and 300 K. The films continuously lose their metallic character in terms of optical constants and resistivity with increasing carbon content. Theoretical fitting of the electrical properties using the grain-boundary scattering model supported the formation of a nanocomposite structure based on a ternary TiB(x)C(y) phase embedded in a matrix of a-C. The electron transport properties are mainly limited by the high density of point defects, grain size, and transmission probability.
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| 2. |
- Fallberg, Anna, et al.
(author)
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A NEXAFS and XPS study of oxygen doped Cu3N
- 2024
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In: Journal of Physics D. - : IOP Publishing Ltd. - 0022-3727 .- 1361-6463.
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Journal article (peer-reviewed)abstract
- Thin films of pure and oxygen doped Cu3N, deposited by Chemical Vapour Deposition, have been studied with the NEXAFS technique both in the FLY and TEY mode and compared with XPS results. Cu, CuO and Cu2O have been used as reference samples in the investigation for detection of surface oxidation and contaminants. The aim has been to investigate how and if the chemical environment changes around Cu, N and O upon incorporation of oxygen in the Cu3N lattice. The recorded NEXAFS spectra are discussed in terms of valence electrons, crystal structure and local bonding environment. It was found that basically two oxygen absorption sites are possible in the crystal structure, (½, ½, 0) and (¼, ¼, ¼), and that the oxygen distribution between the two sites is probably given by the oxygen concentration.
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| 3. |
- Horwat, David, et al.
(author)
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On the deactivation of the dopant and electronic structure in reactively sputtered transparent Al-doped ZnO thin films
- 2010
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In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 43:13, s. 132003-
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Journal article (peer-reviewed)abstract
- We report on the possible origin of electrical heterogeneities in 4 at% Al-doped ZnO (AZO) reactively sputtered films. It is found through the Zn L-3 and Al K edge x-ray absorption near-edge structure that a fraction of the Al dopant is deactivated by its positioning in octahedral conformation with oxygen. This fraction as well as the conductivity, optical bandgap and c-axis parameter of ZnO wurtzite are all found to depend on the sample position during deposition. The present results suggest the formation of a metastable Al2O3 (ZnO) m homologous phase that degrades the electrical conductivity.
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| 4. |
- Moreno, Maiara, 1993-
(author)
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Wear behavior of Ti1-xAlxN-based coatings during turning
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Ti1-xAlxN coatings are extensively used on cutting tools used for metal cutting. In this thesis, the wear behavior of TiN, TiAlN with different Al-content, and TiAlWN and TiAlMoN coatings is investigated after turning, using electron microscopy and X-ray absorption spectroscopy techniques. An in operando study using high-energy X-ray diffraction during turning is also carried out, to understand the strain and phase evolution of TiAlN coatings during machining. The main wear mechanisms when cutting stainless steel 316L with cutting speeds from 60 m/min up to 220 m/min are investigated. The results show a difference in wear behavior with cutting speed. At low cutting speeds, adhesive wear is the main mechanism that generates coating failure, causing fracture of the coating. The higher Al-content coatings (x ≥ 0.53) perform better compared to lower Al-content coatings, likely due to a better fracture resistance. At higher cutting speeds, 220 m/min, crater wear due to abrasive wear and chemical reactions between coating and workpiece material occurs. In this case, the high temperatures achieved during turning results in formation of hexagonal (h)-AlN in Ti0.38Al0.62N coatings, which lowers their wear resistance. For TiAlMoN and TiAlWN, an improved wear behavior is observed compared to pure TiAlN, because it retards spinodal decomposition and the subsequent formation of h-AlN. Investigations of the sliding area using TEM, EDS and XANES spectra from the Ti 1s-edge reveals that there are differences in level of spinodal decomposition, thus differences in temperature, in different regions of the tool. During in operando orthogonal turning of alloy steel, spinodal decomposition was observed to take place after only 10 s of turning for the highest Al-content coatings. Decomposition occurs where the temperature of the rake face is the highest. In summary, the results achieved lead to a better understanding of the interactions between tool and workpiece material and the different wear mechanisms which may expand the application envelope for these coatings.
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| 5. |
- Mosquera, Adolfo, et al.
(author)
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Thermal decomposition and fractal properties of sputter-deposited platinum oxide thin films
- 2012
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In: Journal of Materials Research. - : Springer Science and Business Media LLC. - 0884-2914 .- 2044-5326. ; 27:5, s. 829-836
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Journal article (peer-reviewed)abstract
- Porous platinum thin films were prepared by thermal decomposition at temperatures from 25 to 675 degrees C of platinum oxide films deposited by a pulsed reactive sputtering technique. The samples' chemistry and structure were investigated by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and x-ray absorption near edge structure (XANES), showing that the decomposition of the oxide begins as low as 400 degrees C and follows a sigmoidal trend with increasing annealing temperature. In the XRD spectra, only an amorphous-like signature was observed for temperatures below 575 degrees C, while Pt 4f XPS showed that the deposited oxide was a mixture of PtO2 and PtO. Pt-L-3 edge XANES and Pt 4f XPS spectra showed that the Pt concentration and electronic structure are predominant for temperatures equal to or above 575 degrees C. The morphologies of the films were investigated by the area-perimeter method from atomic force microscopy and scanning electron microscopy (SEM) images, indicating that the surfaces exhibit a combination of Euclidian and fractal characteristics. Moreover, the thermal evolution of these characteristics indicates the agglomeration of the grains in the film as observed by SEM.
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