Indeed, in these conditions the mean free path is about assumed to be equal to the substrate orientation angle and the 74 mm and with a target-to-substrate distance of mm, the critical zone is only noticed as a particular characteristic.
Due to the average number of collisions is 1. The negative discharge voltage of the E-mail address: aurelien. The angle used in this paper is calculated from the a is the angle between the substrate and target's normal. Posi- resultant vector of the particles impinging the substrate. Thus it is tions of the substrate on the holder are chosen in order to minimize representative of the in-plane and the out of the plane distribution self-shadowing.
Each holder has a width of 2 cm and the distance and also of the position and orientation of each substrate compared between two holders is 1 cm. The deposition time was 16, 19 and to the center of the target. These durations were chosen in order to obtain 1 mm thick 3. Thickness thickness variations [28]. From these observations, the thickness and the varying with the substrate inclination angle are illustrated in Fig. One should and Ti coating is about 2. This amount is linked to the substrate in the plane of both target and substrate normal cut projected surface parallel to the target plane , which evolution plane of Fig.
Aluminum is the closest, where chromium is slightly higher. For these variations, a law, coss E t2 1 a , proposed by Woo et al. The substrate curvatures, i. The values level off, and this effect is more pronounced for titanium subtraction of the initial curvature image to the coated one allows than for chromium and aluminum. In our case, the target could not be considered as a perfect punctual source as supposed in the cosine law. Consequently, the particular transport conditions, i. A good linear correlation between the experimental and calcu- lated results is found for all materials.
Some dispersion is observed between the thickness and the calculated number of particles and the particular behavior of each material. The target and the substrate-holder are centered. Titanium coatings are 1. The diameter of the columns changes from to nm. For titanium, columns facing 0. The same types of morphologies have previously been reported [41e44]. The evolution of this angle for each coating is compared with two theoretical models.
The second model is a purely geometrical particles. Related to the thickness, an apparent critical angle could be [37]. Mostly, the experimental measurements present thickness evolution follows approximately the cosine law or its large deviations in comparison to the theoretical laws [41,42,47e51]. For higher angles, the evolution presents a strong and Following these works, the real relationship between a and b is unusual deviation.
These deviations are explained by simulation complex and seems to depend on the ballistic i. Indeed, in this study for the three metallic deposited materials, 3. Coatings morphology this deviation is also obvious for the column tilt angle versus the substrate inclination angle Fig.
Two zones can be observed: Fig. In the second zone, distributed on the surface. Indeed, the evo- chromium. Nevertheless using the calculated incident angle, nounced critical angle, nor strong deviation Fig.
The incidence material, this evolution can be predicted with an acceptable accu- angle is a very local parameter that depends on several macroscopic racy by the theoretical laws.
The residual variation should come parameters see previous section and the substrate inclination from the other contribution to the columns growth: temperature angle is just one of these macroscopic parameters. Only in some and material properties. Hence, because the temperature is kept constant in this study, The stress state depends on adatoms' mobility and thus on the the following section investigates the intrinsic stresses of the energy of the impinging particles.
In this study, there is only one layers. It means that the ejection energy distribution is the same for each sample and only the 3. Indeed, one could have used the calculated inci- the average particles energy increases with the substrate inclina- dence angle or the experimental column tilt angle, but it produces tion angle. Experimentally, and relatively to each metal behavior, only a shift of the stress values without adding more information.
For chromium and titanium, the So for convenience and because it describes well the different tensile stress increases to higher values, while for aluminum, the samples, the substrate inclination angle is still used, even if this compressive stress decreases and tends to become tensile.
As stress is induced partially by the stress state. The suddenly. Experimentally, it corresponds to a sudden decrease of average energy of the impinging particles metallic neutral is ob- the tensile stress more marked for titanium and a change from tained and the difference DEaverage in comparison to the result for a compressive to tensile stress for aluminum.
The stress levels for sample under normal orientation and inclination of the substrates. Consequently, the fraction of low energetic particles MPa 50 MPa [54]. In the same time, the shadowing of to lower values. For chromium, this behavior is low energetic particles with high scattering. In particular the density at grain boundary has a main role.
In the observations made on aluminum and titanium. The decrease of the stress shadowing during the growth. Express 16 Besnard, N. Martin, C. Millot, J. Gavoille, R. One can suggest that inside a polycrystalline column, the Conf. Messier, V. Venugopal, P. A 18 e The stress level is not directly controlled by the growth, J. Indeed, the transport [7] Y.
Thin Film Substrates. Crytstal Materials. Evaporation Sources Boats Thermal Filaments. The power supply is a high voltage RF source often fixed at However, it is most commonly used for depositing dielectric sputtering target materials. In the first cycle, the target material is negatively charged. Niederberger, M. Song, R. Small 13 9 , Abd El-Fattah, H. Key Eng. Article Google Scholar. Feng, X. CrystEngComm 22 18 , — Lizandara-Pueyo, C.
CrystEngComm 16 8 , — Sadri, B. Ivanov, V. CrystEngComm 13 17 , — Hu, M. CrystEngComm 11 11 , — Jin, B. CrystEngComm 22 24 , — Banner, D. Cookman, J. Liao, H. Science , — Aluminum would have the additional advantage of lower material cost than copper, and relative ease of machining and forming. However, the vast experience of making RF cavities from copper at CERN, Fermi Lab and other places would not be fully applicable, and other issues should be expected.
Much of the exploration reported here focused on making niobium films on aluminum substrates having an aluminum oxide surface. In order to process actual cavities, a set of two, movable cylindrical magnetrons was used.
Their size was selected such as to deposit films on 1. The two magnetrons were mounted on movable arms, as shown in Fig. Figure 3: As figure 1 but with krypton as sputter gas. For more details see Ref. The current curves in figures 2 and 3 show a characteristic first peak that is associated with gas Figure 4: Deposition chamber dedicated to the coating of rarefaction [26], a reduction of gas density due to the flux 1.
For conditions below the arms, indicated by the arrows, which allows them to runaway threshold i. Using cathodic arc plasmas, such where the bias is one of the main parameters for film optimization of pulsed bias was shown to enable optimization. If there was only one magnetron, as conformal coating and filling of sub-micrometer features indicated in Figure 5, one would conveniently use the [19, 30].
The polarity of the targets is sputtering of niobium, i. Thus Hz. As a result, the cavity does not participate in the no argon or krypton or any other gas is needed this discharge process and can be biased at will, using another, would eliminate the issues related to noble gas inclusion. Corresponding contaminants. The main result is reproduced in Fig. When the cavity is used as the anode of the discharge, the sheath voltage is not independently available as a process parameter.
Adhesion on copper is moderate: while not peeling off on its own, the film could be removed by scratching and by the common Scotch Tape test. The copper: one can see that the film replicates all features of inset shows the transition to superconductivity with the substrate including grain boundaries and defects.
To emulate deposition on aluminum cavities, polished grid aluminum sheet as well as silicon wafers sputtered-coated with aluminum were used. It was assumed that the coated silicon gives a smoother surface and thus most measurements were done on these samples. The aluminum films of about nm were deposited using standard dc magnetron sputtering with the substrate at room temperature.
The niobium films were deposited on top after briefly exposing the aluminum surface to an oxygen plasma from a 40 W, V oxygen glow discharge. Figure 9 shows a measurement of the critical temperature using measuring currents in the range to A. From figure 9 one can derive the RRR value for this sample, which is 4. There are several reasons why it is low. First, the niobium is sitting on top of an aluminum film, and therefore the measurement includes the contribution of aluminum and the RRR does not represent the true value for niobium.
Second, the deposition was done in the high vacuum Figure Aluminum layer deposited at room temperature general-use chamber, which implies that impurities are by dc-sputtering: the surprisingly large surface roughness gettered by the film. Third, and this is a point realized in is an issue for the quality of the successively deposited hindsight, room temperature aluminum tends to grow in a niobium film. This did not change the crystallinity very much, whereas is illustrated in figures 10 and Besides larger crystals, temperature leads to larger grains and hence narrower x- one can also see a shift of the niobium peak toward ray diffraction peaks Fig.
The important role of the substrate is further high power mode, which is strikingly obvious just by emphasized when using an amorphous substrate such as observing the different colors of the discharge: it is either glass.
The resulting film of niobium is finely grained gas dominated Fig. No with a characteristic gain pattern as shown in Fig. Deposition on an insulating substrates was motivated to eliminate a conducting underlayer which distort RRR measurements, however, clearly, the film structure greatly depends on the texture of the substrate.
Figure SEM of a niobium film on glass reveals the fine-grained crystalline surface morphology. Figure Niobium film of Fig. Scratches of the substrate are replicated in the film, stressing the importance of proper substrate pretreatment.
Figure Dual HIPIMS magnetron operating at the relatively low average power of W, with V applied to the target: the light emission is mainly from excited argon.
Figure X-ray diffraction patterns for niobium films grown on aluminum films that were deposited by dc magnetron sputtering on silicon at room temperature. As with the previous setup, the HIPIMS current of A: the light is mainly emitted from discharge can ran away to high current levels, and by niobium. The camera sensor exposure is reduced choosing the applied voltage one can maintain a low or compared to Fig.
Cifariello, E. Di Gennaro, Physica C: Superconductivity The opportunities with the new system are clear: one [10] X. Zhao, A. Valente-Feliciano, C. Xu, R. Geng, needs to perform systematic studies on film quality using L. Phillips, C. Reece, K. Seo, R. Crooks, M.
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