Deciphering the Structure of Etched Si(100) Surfaces

A simple aqueous etchant has recently been shown to create near-atomically flat Si(100) surfaces. We use a combination of STM, vibrational spectroscopy, and density functional theory to propose a new model for the etched silicon surface structure. This model contradicts long-standing interpretations of the spectrum of H-terminated Si(100). Broadness in the absorbance bands previously attributed to roughened surfaces is actually caused by variations in the interadsorbate stress. Also, etchant pH is shown to have a surprisingly large effect on morphology. The low pHs used in many industrial processes are shown to cause pronounced roughening and nanoscale hillock formation. The interpretation of these relatively simple H/Si(100) spectra sheds light on the chemical mechanisms that lead to much more complicated Si(100) morphologies.