An experimental verification of the theory of surface roughening from a quantitative STM study

The roughening transition on the vicinal Ag(115) surface is investigated by variable-temperature STM. We make use of pattern recognition on the STM images to quantify the height fluctuations. Although the height correlation function is expected to remain finite below the roughening temperature T_R and to diverge logarithmically above T_R, the measured height correlation function diverges linearly at all addressed temperatures. This unexpected behaviour is shown to be due to the effect of small errors in local surface orientation. We can remove this effect from the height correlation function by an automatic procedure, which selects regions in each image with the proper surface orientation. On the basis of a quantitative analysis of the height correlation function measured on these parts, we conclude that the vicinal Ag(115) surface undergoes a Kosterlitz-Thouless type roughening transition at a temperature of T_R =465±25 K.