Reflectance Difference Spectroscopy: Experiment and Theory for the Model System Si(001):As and Application to Si(001)

Reflectance difference spectroscopy (RDS), scanning tunneling microscopy, and calculations of the RDS spectra have been performed for the bare Si(001) surface and Si(001):As, thereby relating identified structures with RDS features. For the As-terminated surface, which exhibits a $2\times 1$ symmetric As-As dimer structure, we demonstrate excellent agreement between measured and calculated spectra. For clean Si(001), which shows a more complex structure arising from dimer asymmetry, we provide identification of RDS spectral features arising from transitions between dangling-bond surface states.