Silicon surface optimization prior to film growth is central to the fields of chemical vapor deposition and molecular beam epitaxy. We have examined a method for low-temperature in situ cleaning of the Si (100) surfaces utilizing a submonolayer coverage of germanium. Synchrotron excited x-ray photoemission data indicate that Ge atoms arriving at a Si (100) surface can break silicon-oxygen bonds, thereby producing new chemical species which sublimate at 625°C. In the absence of Ge, the observed silicon oxide species were stable at temperatures well in excess of 750°C. These results are used to investigate the mechanisms by which adsorbed Ge can be used to produce oxide-free Si (100) surfaces at 625°C.