Growth and orientation relationships of Ni and Cu films annealed on slightly miscut (11¯02) r-sapphire substrates

Abstract

Nano-crystalline Ni and Cu films deposited on the r-plane of sapphire (α-Al 2 O 3) develop a 〈1 1 1〉 fiber-texture upon annealing, in which grains grow up to 300 to 500 times larger than the film thickness. Most of the largest grains, which have grown at the expense of others, display one of four preferred orientation relationships (ORs) to the substrate. The four preferred ORs are OR1r = Me(1 1 1)[1 1 0]//α-Al 2 O 3 (1 1 0 2)[1 1 2 0], OR2r = Me(1 1 1)[1 1 0]//α-Al 2 O 3 (1 1 0 2)[1 1 0 1] (Me = Ni or Cu), and their twins, which are rotated 60°about the 〈1 1 1〉 axis perpendicular to the substrate. For these ORs, one of the densest 〈1 1 0〉 atomic rows that lies within the Me {1 1 1} interfacial plane, aligns with the direction of the step edges that form at the intersection of the r-plane with one of its neighboring facets on the equilibrium shape of sapphire (i.e. the c-(0 0 0 1), p-{1 1 2 3} or s{1 0 1 1}-planes). One of the ORs is most preferred when the steps at the interface are such that a {1 0 0}-type ledge of the Me {1 1 1} interfacial plane faces the ledge of the sapphire step. This observation provides a useful insight into the origin of the preferred ORs, and confirms the important role of surface steps in texture development. The evolution of Ni films of different thicknesses, ranging from 100 to 560 nm, was analyzed. Grain boundary grooving inhibits grain boundary motion and favors hole formation and dewetting in the thinnest films (100 nm). The crystals left behind after dewetting display ORs which may differ from the preferred ones. Large grains with the preferred ORs can grow at the expense of others when the film thickness is greater than 300 nm.

Microstructure evolution and thermal stability of equiatomic CoCrFeNi films on (0001) α-Al2O3

“…In this study, we found the same trend as in previous studies on the orientation relationships of fcc grains on c-sapphire: grains prefer to grow in OR1/t at low temperature but are likely to adopt OR2/t at high temperature. However, OR2/t grains may not appear if they cannot expand from pre-existing small OR2/t grains [52]. In this work, CoCrFeNi films heated up to 0.8 T m either grow to 10 µm large grains in OR1/t or ~1000 µm large OR2/t grains within a ±10° in-plane deviation.…”

“…Anneals were performed at 973 K, 1273 K or 1423 K for 1 h, each one on a different as-deposited sample. The heating rate was 25 K/min while the cooling rate was imposed by switching the furnace power off as described in detail in [52]. It takes about two hours for the temperature decreases down to 723 K where the diffusion of the alloy components becomes very slow.…”

“…The ORs of the grains of the metallic film with the c-sapphire are obtained by comparing the {110} pole figures of the fcc-alloy to the stereogram of the sapphire substrate, centered on the (0001) pole, and displaying the {1100} {1120} and {1102} poles. Both crystallographic data on the film and the sapphire are acquired during the same run on each film-sapphire sample as explained in [52].…”

“…Larger grains exceeding 50 times the film thickness, have been found in ultrathin (< 100 nm) films of Si on SiO 2 [90]. Recently, much bigger grains have been prepared in fcc films (Ni and Cu) thicker than 300 nm, deposited on a (1102) sapphire substrate [52]. On this substrate, the Ni grain size could reach 300 times the film thickness when annealed at 0.82 T m (1423 K) for 1 h, and the Cu grain size could extend to 500 times the film thickness when annealed at 0.92 T m (1253 K) for 78 h. In the present work, CoCrFeNi grains well beyond these sizes have been found when their orientation relationship to the c-sapphire substrate is OR2/t and the film thickness and annealing temperature combination is such that grain growth is not impeded by grooving; after 1 hour at 0.8 T m (1423 K), the CoCrFeNi grains are more than 1000 times the film thickness.…”

Influence of step structure on preferred orientation relationships of Ag deposited on Ni(111)

“…There is an advantage to the presence of these steps, because, by breaking the high symmetry of the substrate surface, they favor one of the grain orientation variants, and the growth of single crystal thin films [3]. Therefore, controlling the nature of the substrate stepstructure, and identifying the types of substrate miscut orientations, and step directions, that will produce single-crystalline films, may lead to improvement of the film stability by limiting the presence of GBs.…”