Importance of interfacial step alignment in hetero-epitaxy and orientation relationships: the case of Ag equilibrated on Ni substrates. Part 2 experiments

The orientation relationships (ORs) that develop when Ag films are equilibrated on more than 200 different Ni substrate orientations distributed over the standard stereographic triangle have been determined by electron backscatter diffraction. Four different types of OR have been observed, including cube-on-cube, twin-related, oct-cube (that develops only on Ni(100)), as well as a family of more complex ORs (referred to as ‘‘special’’) that arise during the gradual transition from the oct-cube to the twin OR. The importance of the alignment of step edges on the Ag side of the interface with those of the Ni substrate, in the development of ORs, has been validated by comparison with the results obtained on the large range of substrate orientations investigated in this study. This step alignment occurs in the early stages of film formation, but is also consistent with equilibrium ORs as it tends to produce minimum energy interfaces. This feature of heteroepitaxy and of the resulting ORs has not previously been emphasized. Introduction The purpose of this paper is to determine the origins of the orientation relationships (ORs) obtained by equilibrating a deposit of one face-centered cubic (FCC) metal on a substrate of a different FCC metal. The literature contains reports of experimental and modeling studies of several such FCC A-on-B systems, including Ag on Ni [1–16], Ni on Ag [17], Au on Cu [11], Pb on Cu [18], and Pb on Ni [19]. Thus far, experimental investigations have focused on B-substrates with low-index surfaces oriented along (111) and (100) crystallographic planes. Detailed studies of B-substrates with a (110) surface orientation have also been reported for Ag on Ni [5, 6, 11, 12]. Both experiments and computer simulations have been performed and compared on these three low-index substrate orientations. It is important to mention that previous experiments have been performed by two different approaches, either by ‘‘heteroepitaxial’’ growth or by the particle rotation method [20]. Literature reports indicate that on these low-index substrate orientations, the most important parameter for determining the resulting OR is the difference in atomic size between the A and B species. When the A species is equilibrated on B(111), it adopts an OR in which A{111}// B(111), with either a cube-on-cube or a twin-related OR [6]. In contrast, on B(100), either a cube-on-cube OR with A(100)//B(100), or a so-called oct-cube OR with A(111)// B(100), has been reported [6, 13]. Furthermore, the results of some simulations have indicated that the oct-cube OR is more likely when the atomic size of the A-component is much larger than that of the B-component [17]. For Ag on a Ni (110) substrate, Allameh et al. [11] report a cube-oncube OR. We have chosen to investigate the Ag–Ni system because of the negligible mutual solubility of these & Dominique Chatain [email protected] Paul Wynblatt [email protected] Anthony D. Rollett [email protected] Gregory S. Rohrer [email protected] 1 Aix-Marseille Université, CNRS, CINaM, UMR 7325, 13288 Marseille, France 2 Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA 123 J Mater Sci (2015) 50:5276–5285 DOI 10.1007/s10853-015-9075-0