SURFACE-DENSITY OSCILLATIONS IN DISORDERED BINARY-ALLOYS - X-RAY REFLECTIVITY STUDY OF CU3AU(001)

We present X-ray reflectivity studies of the Cu3Au(001) surface using Synchrotron radiation and show that the intensity distribution along t he specular rod exhibits the same features as in the case of liquid me tals which has been discussed in recent literature. The results are di scussed within the framework of the distorted wave Born approximation which allows a straightforward easy-to-apply scheme to analyze such re flectivity data in the entire q-range including the total external ref lection regime. The data analysis gives a direct evidence for an oscil lating average density profile which is analogous to the so-called sur face layering at liquid surfaces. The experimental values for the ther mal roughness indicate that surface roughness is suppressed in the ord ered phase and allowed to softly grow with temperature above the bulk order-disorder phase transition. The presented experimental and theore tical study of X-ray reflectivity from binary alloys demonstrates the potential of this technique for the study of surface roughening, surfa ce layering and surface segregation phenomena at solid and liquid surf aces.