  Using combined low temperature scanning tunneling microscopy (STM) and atomic
force microscopy (AFM), we demonstrate hydrogen passivation of individual,
selected dangling bonds (DBs) on a hydrogen-passivated Si(100)-2$\times$1
surface (H-Si) by atom manipulation. This method allows erasing of DBs and thus
provides an error-correction scheme for hydrogen lithography. Si-terminated
tips (Si tips) for hydrogen desorption and H-terminated tips (H tips) for
hydrogen passivation are both created by deliberate contact to the H-Si surface
and are assigned by their characteristic contrast in AFM. DB passivation is
achieved by transferring the H atom that is at the apex of an H tip to the DB,
reestablishing a locally defect-free H-Si surface.
