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Register a new userCharacterization of TiAlSiON Coatings Deposited by Plasma Enhanced Magnetron Sputtering: XRD, XPS, and DFT Studies
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The results of characterization of TiAlSiON hard coatings deposited on ferric-chromium AISI 430 stainless steel by plasma enhanced magnetron sputtering are presented. The coating with maximum hardness (of 45 GPa) was obtained at the following optimal values of elemental concentrations: Si ~5 at.%, Al ~15 at.%, and Ti ~27 at.%. The elastic modulus of the coating was 590 GPa. The reading of gaseous mixture (Ar-N2) pressure was 1*10-3 Torr and the reading of partial pressure of oxygen (O2) was 1*10-5 Torr. The X-ray diffraction (XRD) measurements showed the presence of Ti(Al)N. High-energy resolved XPS spectra of core levels revealed the formation of Ti-N, Ti-O-N, Si-N and Al-O-N bonds. Comparison of XPS valence band spectra with specially performed density functional theory calculations for two ordered and few disordered TiN1-xOx (0 =< x <= 1) demonstrates that a Ti(Al)OxNy phase is formed on the surface of AISI430 steel upon the plasma enhanced magnetron sputtering, which provides this material with a good combination of high hardness and improved oxidation resistance.
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In the prospect of understanding the photoluminescence mechanisms of AlN films doped with erbium and targeting photonic applications we have synthesized non doped and Er-doped AlN films with different crystallized nanostructures by using PVD magnetron sputtering. Their crystalline morphology and their visible photoluminescence properties were precisely measured.Due to the weak cross-section absorption of rare earths like erbium, it is necessary to obtain an efficient energy transfer mechanism between the host matrix and the rare earth to obtain high luminescence efficiency. Our strategy is then to elaborate some nanostructures that could introduce additional intermediate electronic levels within the gap thanks to the presence of structural defects (point defects, grain boundaries{ldots}) and could lead to energy transfer from the AlN matrix to the rare earth.Doped and non-doped AlN films were prepared by radio frequency magnetron sputtering by using different experimental conditions that will be detailed. It will notably be shown how a negative polarization of samples during deposition allows obtaining crystalline morphologies ranging from the classical columnar structure to a highly disordered polycrystalline structure with grains of several nanometers (nearly amorphous). The nanostructures of the films could be categorized in three types: 1) type 1 was nanocolumnar (width of column ~ 15 nm), 2) type 2 was made of short columns (width of column ~ 10 nm) and 3) the last type was made of equiaxed nanocrystallites (size of grains ~3-4 nm).High-resolution photoluminescence spectroscopy was performed to characterize their optical behaviour. The samples were excited by the laser wavelengths at 458, 488 or 514 nm. A broad photoluminescence band was observed centred around 520 nm in columnar samples. In the same energy range, the highly resolved spectra also showed several sharp emission peaks. This fine structure could be attributed to erbium transitions. This fine structure tended to disappear going from type 1 to type 3 samples. Indeed, the relative intensity of the peaks decreased and their full width at half maximum increased. This change could be related to the density of defects that increased when the size of the grains decreased. The photoluminescence properties of the films in the visible range will be discussed in relation with their structure.
In this work, we studied phase formation, structural and magnetic properties of iron-nitride (Fe-N) thin films deposited using high power impulse magnetron sputtering (HiPIMS) and direct current magnetron sputtering (dc-MS). The nitrogen partial pressure during deposition was systematically varied both in HiPIMS and dc-MS. Resulting Fe-N films were characterized for their microstructure, magnetic properties and nitrogen concentration. We found that HiPIMS deposited Fe-N films show a globular nanocrystalline microstructure and improved soft magnetic properties. In addition, it was found that the nitrogen reactivity impedes in HiPIMS as compared to dc-MS. Obtained results can be understood in terms of distinct plasma properties of HiPIMS.
Inverse Heusler alloy Mn2CoAl thin films, known as a spin-gapless semiconductor (SGS), grown by three different methods: ultra-high vacuum magnetron spattering, Ar-ion beam assisted sputtering, and molecular beam epitaxy, are investigated by comparing their electric transport properties, microstructures and atomic-level structures. Of the samples, the Mn2CoAl thin film grown by MBE consists of Mn- and Co-rich phases, the structures of which are determined to be the L21B-type and disordered L21-type, respectively, according to anomalous XRD analysis. None of them forms the XA-type structure expected for SGS Heusler alloy, although they all show SGS characteristics. We suggest, to validate SGS characteristics, it is necessary to extract not only magnetic and electric transport properties but also information about microstructures and atomic-scale structures of the films including defects such as atomic swap.
Two different types of boron-doped graphene/copper interfaces synthesized using two different flow rates of Ar through the bubbler containing the boron source were studied. X-ray photoelectron spectra (XPS) and optically stimulated electron emission (OSEE) measurements have demonstrated that boron-doped graphene coating provides a high corrosion resistivity of Cu-substrate with the light traces of the oxidation of carbon cover. The density functional theory calculations suggest that for the case of substitutional (graphitic) boron-defect only the oxidation near boron impurity is energetically favorable and creation of the vacancies that can induce the oxidation of copper substrate is energetically unfavorable. In the case of non-graphitic boron defects oxidation of the area, a nearby impurity is metastable that not only prevent oxidation but makes boron-doped graphene. Modeling of oxygen reduction reaction demonstrates high catalytic performance of these materials.
Er-doped aluminum nitride films, containing different Er concentrations, were obtained at room temperature by reactive radio frequency magnetron sputtering. The prepared samples show a nano-columnar microstructure and the size of the columns is dependent on the magnetron power. The Er-related photoluminescence (PL) was studied in relation with the temperature, the Er content and the microstructure. Steady-state PL, PL excitation spectroscopy and time-resolved PL were performed. Both visible and near infrared PL were obtained at room temperature for the as-deposited samples. It is demonstrated that the PL intensity reaches a maximum for an Er concentration equal to 1 at. % and that the PL efficiency is an increasing function of the magnetron power. Decay time measurements show the important role of defect related non radiative recombination, assumed to be correlated to the presence of grain boundaries. Moreover PL excitation results demonstrate that an indirect excitation of Er 3+ ions occurs for excitation wavelengths lower than 600 nm. It is also suggested that Er ions occupy at least two different sites in the AlN host matrix.
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