Mismatch design of AuxNi1-x(111)/α-Al2O3(0001) interfaces and their correlative investigation by X-ray diffraction and electron microscopy

In this contribution, the influence of lattice mismatch on the structure and chemistry of the Au x Ni 1-x /α-Al 2 O 3 interface is investigated. For this, Au/Ni bilayers are deposited on α-Al 2 O 3 (0001) surfaces, annealed at elevated temperatures and quenched to room temperature to produce micron-sized Au x Ni 1-x alloy particles by solid-state dewetting. The lattice mismatch is controlled by the Au concentration x, which is adjusted by the relative thickness of the Au and Ni layers. Electron backscatter diffraction revealed the formation of particles with a mismatch-dependent epitaxial orientation relation (OR). Particles with a positive lattice mismatch show a clear dominance of OR1 with Au x Ni 1-x ( 111 ) [ 1 1 ¯ 0 ] ||α-Al 2 O 3 ( 0001 ) [ 10 1 ¯ 0 ] , while for particles with a negative mismatch a strong increase of OR2 with Au x Ni 1-x ( 111 ) [ 112 ] ||α-Al 2 O 3 ( 0001 ) [ 10 1 ¯ 0 ] is recorded. The occurrence of a near coincident site lattice is identified as a possible stabilizer for OR2. Correlative in-plane (IP) XRD and TEM in plan-view and cross-section geometry revealed (i) a semi-coherent interface for a positive mismatch of 0.68 %, indicated by a prominent diffuse background in IP XRD and moiré fringes in TEM plan-view images, (ii) a nearly coherent interface for reduced mismatch of 0.21 %, marked by a decrease in diffuse background and an interface structure similar to that of lattice-matched Pd/α-Al 2 O 3 ( 0001 ) and (iii) an incoherent interface with OR2 for negative mismatch. Comparison of experimental and simulated micrographs confirmed an Al 2 termination of the Al 2 O 3 ( 0001 ) substrate for all samples. Additionally, chemical analysis revealed Au segregation at the interface, which is discussed in terms of mechanical stress effects and electrochemical interactions across the AuNi-Sapphire interface.