Exchanges between group-III (B, Al, Ga, In) and Si atoms on Si(111)-root 3x root 3 surfaces

High-temperature scanning tunneling microscopy (HT-STM) observation of exchanges between group-III and Si atoms on Si(111)-root 3X root 3 surfaces is reported. The exchange rates are obtained from the HT-STM images as a function of the temperature. The activation energies of the exchange are 1.4, 1.7, and 1.4 eV for Al, Ga, and In adatoms, respectively. The prefactors are within the range 10(10)-10(13) s(-1). These prefactors are close to that for the exchange between Pb and Si adatoms on a Si(111)-root 3X root 3 surface and much larger than that for the exchange between Pb and Ge adatoms on a Ge(111)-c(2X8) surface. The adatom exchange mechanisms on Si(111)-root 3X root 3 and Ge(111)-c(2 X 8) are different. We also investigated exchanges between B and Si atoms in the second layer of the Si(111)-root 3X root 3 surface. The obtained activation energy and prefactor are 3.5 eV and 1X10(18) s(-1) and the activation energy is close to that of B diffusion in bulk Si.