Km. Schirm et al., O2 K/GE(100)2X1 AND O2/CS/GE(100)2X1 - PUZZLING BEHAVIOR OF K AND CS IN THE OXIDATION OF GERMANIUM/, Applied surface science, 68(3), 1993, pp. 433-438
The effect of alkali-metal overlayers (Y, Cs) on the room-temperature
oxidation of the Ge(100)2 x 1 surface in the presence of molecular oxy
gen was investigated by core-level and valence-band photoemission spec
troscopy using synchrotron radiation. In strong contrast to the behavi
or observed for many other elemental or compound semiconductor surface
s, the presence of a K or Cs layer does not enhance the oxidation rate
as expected but rather poisoned it since the K (Cs) covered Ge(100)2
x 1 surface exhibits significantly smaller amount of oxides for the sa
me oxygen exposures. This behavior indicates that K does not act as a
catalyst as observed in the cases of many other semiconductor surfaces
, but as an oxygen acceptor, in agreement with a classical model of el
ectron affinity.