MgyNi1−y(Hx) thin films deposited by magnetron co-sputtering

Abstract

Abstract:In this work we have synthesised thin films of Mg y Ni 1-y (H x ) metal and metal hydride with y between 0 and 1. The films are deposited by magnetron co-sputtering of metallic targets of Mg and Ni. Metallic Mg y Ni 1-y films were deposited with pure Ar plasma while Mg y Ni 1-y H x hydride films were deposited reactively with 30% H 2 in the Ar plasma. The depositions were done with a fixed substrate carrier, producing films with a spatial gradient in the Mg and Ni composition. The combinatorial method of co-sputtering gives an insight into the phase diagram of Mg y Ni 1-y and Mg y Ni 1-y H x , and allows us to investigate structural, optical and electrical properties of the resulting alloys. Our results show that reactive sputtering gives direct deposition of metal hydride films, with high purity in the case of Mg~2NiH~4. We have observed limited oxidation after several months of exposure to ambient conditions. Mg y Ni 1-y and Mg y Ni 1-y H x films might be applied for optical control in smart windows, optical sensors and as a semiconducting material for photovoltaic solar cells.

Annealing-induced structural rearrangement and optical band gap change in Mg–Ni–H thin films

“…1(d) could be attributed to the (110) peak of the monoclinic LT phase, suggesting the existence of that phase prior to the first step of annealing. This is in agreement with what reported previously by Mongstad et al [16] who observed signs of a monoclinic structure in a TEM study of reactively sputtered thin films, which were found to be amorphous by XRD. The presence of the (110) peak of LT phase confirms that not all of the crystallites have taken the cubic HT phase as preferred.…”

The dielectric functions and optical band gaps of thin films of amorphous and cubic crystalline Mg~2NiH~4

“…Although the films are found to be amorphous for XRD with Cu Kα radiation, our earlier work has showed that crystallites of monoclinic Mg 2 NiH 4 are observable with transmission electron microscopy (TEM) [20]. The crystal size found with TEM was 5-10 nm [20].…”

“…This is not very surprising since a very thin intermediate oxide layer would be difficult to detect on a glass substrate due to the low refractive index contrast. [20]. We have do not presented the data for samples with y < 1.9 and y > 2.4 because the optical absorption for these films was high below the band gap, and thus suggesting high presence of metallic particles.…”

“…The most common structural form of thin-film Mg 2 NiH 4 is the amorphous, which is the typical result after hydrogenation of Pd-capped metallic Mg 2 Ni films at room temperature [5] or films deposited in-situ by reactive deposition [12,20], both processes at room temperature. In this work we have used reactive co-sputtering to form the hydride films.…”

Sputtering onto liquids: a critical review

“…Here again, extra care should be taken regarding the elemental composition of the deposited materials as it might depend on the position where the elemental analysis is made on the substrate, especially if a spatially resolved analysis is carried out by a technique such as scanning (transmission) electron microscopy combined with energy-dispersive X-ray spectroscopy (S(T)EM-EDS). Typical examples of the formation of compositional gradients on coated surfaces can be found, for example, in [ 54 – 55 ]. Further control on film chemistry is obtained through reactive (magnetron) sputtering.…”