THE INTERACTION OF THIN NIO LAYERS WITH SINGLE-CRYSTALLINE ALPHA-AL2O3(11(2)OVER-BAR0) SUBSTRATES

In order to investigate the interfacial reaction between NiO and alpha -Al2O3 to NiAl2O4 at monolayer level, thin Ni layers (4-29 x 10(15) at oms/cm(2) Ni) were vapour-deposited onto Al2O3(11 (2) over bar 0) subs trates and subsequently annealed in O-2 at temperatures ranging from 4 00 to 1100 degrees C. The samples were subsequently analyzed by high e nergy ion channeling, X-ray photoelectron spectroscopy and atomic forc e microscopy. From ion channeling analysis it is deduced that formatio n of bulk NiAl2O4 does not occur at temperatures up to 950 degrees C. Due to sintering of NiO quite large nickel oxide particles (maximum he ight about 50 nm) were observed by AFM after annealing at 900 degrees C in O-2. Considerably smaller particles were observed after annealing at 1000 degrees C, and almost no particles were found on the sample k ept at 1100 degrees C. These findings are consistent with the XPS resu lts. At 1000 degrees C and higher temperatures, the rate of the solid state reaction to NiAl2O4 is apparently comparable to or higher than t he rate of NiO-island formation. Furthermore, several indications for the formation of some Ni-Al-O precursor compound at the interface belo w the onset temperature of the reaction to NiAl2O4 are discussed.