A scanning tunneling microscopy investigation of adsorption and clustering of potassium on the Si(111)7x7 surface

The adsorption process of potassium on the Si(111)7x7 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 7x7 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.