X-ray study of the roughening transition of the Ni(113) surface

We present X-ray diffraction data as a function of temperature for Ni(113) that show dramatic changes in one of the crystal truncation rods. The variation of the observed intensity is in good agreement with previous work on Cu(113), but we can now resolve changes of lineshape as well. We develop a theory of diffraction of rough surfaces and use it to show conclusively that the surface has finite height fluctuations below the transition that become divergent above. The exact functional form of the divergence cannot be evaluated uniquely, however.