Size-dependent reactivity of aluminum cluster cations toward water molecules

Using the autocorrelation of speckles in the deep Fresnel region is a novel approach to measuring surface parameters of a rough surface. In this letter, we construct a scanning system using a fibre-optic probe for detecting the speckle field with excellent resolution. By relating the autocorrelation function of the speckle intensity and the surface height with the Kirchhoff approximation theory, we realise the measurement of the surface parameters. Three parameters, i.e. the roughness w, the lateral correlation length ξ and roughness exponent α are extracted. We measure two sample surfaces in the experiment, and the results are consistent with those measured by atomic force microscope (AFM).