A Scanning Tunneling Microscopy Investigation of Adsorption and Clustering of Potassium on the Si(111)7×7 Surface

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Abstract
The adsorption process of potassium on the Si(111)7×7 surface is studied by scanning tunneling microscopy (STM). At low coverages, an STM image reveals that potassium (K) atoms adsorb preferentially on the faulted-halves of the 7×7 unit cells rather ionically so that they do not appear in the filled-state image but present bright images in the empty-state mode. The coverage at which both the faulted and the unfaulted regions are uniformly occupied by K is estimated to be about 6/49. At coverages higher than this, the K atoms tend to form neutral clusters, preferentially in the faulted-regions. The electronic structure around the clusters is modified markedly, which suggests a local charge redistribution.