Quantitative analysis of the order of Bi ion induced dot patterns on Ge

We demonstrate that the temperature-dependent focused ion beam irradiation of (100) Ge surfaces with 20 keV Bi+ ions leads to variably ordered hexagonal dot patterns. We show that the average information gain about the spatial order can be significantly increased by image preprocessing transforming the power spectral density into the pair correlation function. Order parameters are derived from the pair correlation function for the comparison of highly ordered patterns.