L. Vitali et al., SUBSTITUTIONAL GEOMETRY AND STRAIN EFFECTS IN OVERLAYERS OF PHOSPHORUS ON SI(111), Physical review. B, Condensed matter, 57(24), 1998, pp. 15376-15384
The structure and bonding topology of phosphorus adatoms on Si(lll) su
rfaces have been investigated by scanning tunneling microscopy (STM) a
nd scanning tunneling spectroscopy, in conjunction with low-energy ele
ctron diffraction and Auger electron spectroscopy. At room temperature
P adatoms substitute for the Si adatoms of the Si(111)7X7 surface at
low coverages as revealed by the chemical contrast between P and Si ad
atoms in the filled-state STM images. A statistical evaluation of the
STM images within the framework of a simple reaction model suggests th
at the corner adatoms of the faulted half of the (7X7) unit cell act a
s primary reaction centers for the P-2 molecules from the gas phase, i
n agreement with theoretical expectation. At elevated temperature (500
-650 degrees C) a (6 root 3x6 root 3)R30 degrees structure is the prev
ailing P-induced surface reconstruction. Atomically resolved STM image
s show that this structure is a domain-wall structure containing hexag
onal domains that tesselate the entire surface. The 6% contracted (1X1
) phosphorus domains are separated by straight, 4% expanded light doma
in walls of irregular lengths. The structure displays a complex in-pha
se-antiphase-stacking fault relationship between adjacent domains, whi
ch has been modeled successfully with a P adlayer in a substitutional
bonding geometry on an unreconstructed Si(lll) surface. The large tens
ile surface stress introduced by the P-SI bonding is responsible for t
he domain-wall formation and precludes the formation of a global (1X1)
-P structure on Si(lll) surfaces.