X-ray diffraction study of order in epitaxial thin AuNi films on a Au(100)substrate during temperature change

There is a lack of miscibility for the bulk AuNi system. But because of the coherent Molecular Beam Epitaxy stresses, ultra-thin solid solution Au1-cN ic layers have been grown on Au(001) substrate, with c=0.2 to 0.5. Then, th e temperature evolution of these materials has been studied by in-situ temp erature C-rays diffraction, in a range between 200 and 240 degrees C. The e xperimental device is described, and details are given about surstsructures coming out due to composition modulations. The measured wavelength of thes e modulations are comparable with those observed in bulk material, but it i s the first time than several wavelengths are simultaneously observed for c > 0.4. Therefore a lateral structure with more or less large domains is de duced, than HRTEM has confirmed. Inside each domain, periodic alternation o f Ni rich and Au rich planes is observed, but the average composition over each period is close to the bulk layer one. The calculated periods are link ed to the local composition.