X-RAY REFLECTIVITY OF THE CU(11O) SURFACE

The specular reflectivity from the (110) surface of a Cu single crystal has been measured for temperatures between 300 and 1100 K. At lower temperatures, the reflectivity is well described by a model which yields a contraction of the spacing between the first and the second surface layers by 8% relative to the bulk layer separation. The fits also show large surface-normal vibrational amplitudes within the first few atomic layers. The line shape of the scattering transverse to the specular direction has two components below 1000 K, and evolves with increasing temperature. However, our data do not preclude the existence of a surface-roughening transition.