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Tensile and Compressive Stress in a film sputtered onto a substrate. It is clear that a tensile stress in film, will correspond to a compressive stress in substrate surface and vice-versa a compressive stress in the film will correspond to a tensile stress in substrate surface.
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Thick films have bulk like properties. In this paper it is explored the possibility to sputter 70 micron thick films in order to get rid of the Q-slope in Niobium sputtered Copper Cavities. An innovative method based on the multi-layer deposition of zero-stress single layers is reported. The deposition of zero-stress thick films into 6 GHz Copper s...
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... As mentioned earlier, getting bulk like performance on Nb films is an important step. Activities have been conducted at UKRI, INFN and USI [6,8,12,17,[26][27][28]. ...
Now that bulk Nb technology has reached it full maturity , improving SRF technology demands that new materials need to be developed. For reasons explained in the talk, all next generation SRF materials will be in the form of thin films. The IFAST project has the ambition to coordinate European activities on that topic, not only throughout its own program (that will be presented here), but also by keeping in touch with all actors worldwide, with the hope of developing a more efficient collaborative actions in a limited funding context. In this paper, we will present the challenges presented by the development of new thin films materials, each developed for tailored applications and the main research direction proposed by the thin film community.
... Finally, if the substrate of the cavity is made of OFE copper, a superconducting thin film of few micrometers is deposited on the inner surface of the SRF cavity. A thick film approach has also been proposed by Palmieri et al. [35] in an attempt to obtain performances similar to bulk niobium cavities [36]. One or multiple tuning steps are also added in the sequence to ensure that the fundamental frequency of the formed cavity is equal to the designed one. ...
... 35 shows the hole formed with EP in the tensile specimen deformed at a strain rate of ~1 000 s -1 . Two regions, namely A and B, were characterized at high magnifications of up to 200kx. ...
... 35 andFigure 5.36 show BF and DF STEM images of two areas (A1 and A2) in region A. The dislocation density is higher in A1, but, more importantly, both areas show short dislocation segments, no cell walls, and no preferred dislocation alignment directions.This differs from the low strain rate specimens with the same orientation (2-158) and with shear bands. Recall that a reduction of strength anisotropy at a strain rate of ~1 000 s -1 was measured(Figure 4.2) and explained by the activation of multiple slip systems at high strain rate to accommodate the imposed deformation. ...
Manufacturing of superconducting radiofrequency (SRF) cavities with high performances is paramount to increase the collision energy in new particle accelerators. The use of high-speed sheet forming techniques, such as electro-hydraulic forming, can be beneficial, but requires a detailed understanding of the mechanical properties of the materials being deformed and the consequence on their microstructure. This thesis focuses on the characterization of high-purity niobium single crystals, polycrystalline niobium sheets, and polycrystalline OFE copper sheets. The results from this study are separated in two parts. In Part I, the characterization of niobium single crystals focused on the mechanical properties in tension and compression at strain rates of 10-4 to 103 s-1 and on the microstructure (analyzed using SEM, EBSD, TEM, and nanoindentation) of the deformed specimens. The effect of crystal orientation, strain rate, and loading direction on the mechanical properties, the crystal rotation, and the dislocation substructures are presented. In Part II, the forming limit diagram (FLD) of polycrystalline niobium sheets and OFE copper sheets were measured at a quasi-static strain rate. The FLDs of those materials should provide important data for manufacturers using conventional techniques, such as deep-drawing and spinning. The second part also presents the mechanical properties of electron beam (EB) welded polycrystalline niobium sheets and OFE copper sheets deformed in tension and compression at strain rates of 10-3 to 103 s-1.
Superconductive Nb films deposited on copper cavities has been widely studied, but simulation studies on the growth of Nb films have rarely been reported in the literature.
In this study, effects of Nb atom incidence energy, incidence angle and deposition temperature on Nb film growth were investigated by molecular dynamics simulations.
It was found that for the growth of Nb films, a moderate increased the incidence energy of Nb atoms can attenuate the shadow effect, and both too high and too low incident energy are not conducive to the production of high quality Nb films, and the substrate temperature mainly affects the quality of the crystal structure of Nb films.
In a word, Nb atoms with higher incidence energy (i.e. 10 eV) deposited vertically on Cu substrates at 473.15 K are more favorable for the growth of Nb films with lower surface roughness, higher crystallinity and fewer defects, providing an important reference for the preparation of high quality superconductive Nb films on SRF cavities.
Within the framework of the study, fine-grained nanocrystalline aluminum nitride films were obtained using the PEALD method at the temperature of 250 °С and the number of deposition cycles from 80 to 500 on single-crystal silicon substrates. Low-temperature synthesis processes were carried out in the self-limited growth regime of the PEALD method at the constant growth rate of ∼0.115 nm/cycle. The obtained samples were studied by ellipsometry, FTIR-spectroscopy, X-ray diffraction analysis, Auger spectroscopy, Scanning electron and Atomic force microscopy. It was found that the samples in the IR-absorption spectra and ω/2θ-scans had bands and reflections characteristic for wurtzite AlN with hexagonal structure. It was shown that an increase in the coating thickness led to an increase in the crystallinity and optical density of the film material, the crystallites size, and values of the root-mean-square (RMS) roughness. In this case, significant changes in the crystal lattice parameter and relaxation of internal mechanical stresses within the obtained values of the AlN layers thicknesses were not observed.
