On the stability of (001) Au/Ni artificially modulated structures grown byMBE

We report on the structural stability upon annealing of (0 0 1) Au/Ni artif icially modulated structures (AMS) grown by molecular beam epitaxy (MBE). T he structural evolution of samples with a nominal periodicity of 2, 6 and 7 monolayers (ML) and Ni atomic fractions of 0.4 and 0.5 has been investigat ed by in situ X-ray Diffraction and compared with what occurs for AuNi soli d solutions of the same compositions, for which a modulated structure with a periodicity between 3 and 4 ML along the growth direction has been report ed previously. The effect of the epitaxial strain imposed by the buffer lay er on which the AMS is deposited has also been studied. It is shown that, w hatever the nominal period is, the AMS evolve towards a modulated structure having a similar to3 ML period, provided that the epitaxial strain is high enough. These experimental results are explained in terms of an epitaxial- strain-stabilized ordering, as supported by numerical simulations. (C) 2001 Published by Elsevier Science B.V.