The plasticity index of the ”soft-film/softsubstrate” coated systems

Abstract

The advanced devices from the last years contain thin films deposited on substrates of materials with different properties, thus forming coated systems (CS) of film/substrate type. Scientists, as well as engineering staff are increasingly interested in knowing the mechanical properties of CS used in micro- and nanoelectromechanical systems [1]. In this paper, we investigate CS of the type „soft-film/soft-substrate” – Cu/LiF with different thickness of films: nanometric (t1=85 nm), submicronic (t2=470 nm) and micrometric (t3=1000 nm), obtained by the magnetron sputtering method. The mechanical properties of the CS mentioned above were investigated by using the nanoindentation (NI) tester equipped with a trihedral diamond Berkovich pyramid as an indenter [2]. Along the hardness (H) and Young's module (E), the mechanical properties of CS are also characterized by the H/E ratio called "plasticity index" [3]. We show that for the studied materials, the values of H and H/E change with the Pmax load increase. We show these dependences in Fig. 1. a) b) Fig. 1. Dependencies reflecting the variations of the hardness (H) a) and plasticity index H/E b) of the load Pmax value in the range (5±900) mN at NI tester for all CS Cu/LiF and monolithic crystals. The respective curves are characterized by: 1 – the polycrystal Cu, 2 – the single crystals LiF, 3 – Cu/LiF, t1=85 nm, 4 – Cu/LiF, t2=470 nm, 5 – Cu/LiF, t3=1000 nm. From Fig. 1a) one can see that the H(P) CS dependences have the form similar to the hardness H(P) of the LiF substrate, however, they have higher values compared to the polycrystalline Cu. The values of the plasticity index, H/E, of the CS (Fig. 1b) demonstrate the higher values compared with materials used for the creation of these structures that indicates their higher resistance to plastic deformation.