  Methods for the creation of thin amorphous silicon dioxide (aSiO2) layers on
crystalline silicon substrates with very high densities of silicon dangling
bonds (so called E' centers) have been explored and volume densities of [E']>
5x10^18 cm-3 throughout a 60nm thick film have been demonstrated by exposure of
a thermal oxide layer to a low pressure Argon radio frequency plasma. While the
generated high E' center densities can be annealed completely at 300C, they are
comparatively stable at room temperature with a half life of about one month.
Spin relaxation time measurements of these states between T = 5K and T = 70K
show that the phase relaxation time T2 does not strongly depend on temperature
and compared to SiO2 films of lower E' density, is significantly shortened. The
longitudinal relaxation time T1 ~195(5)us at room temperature is in agreement
with low-density SiO2. In contrast, T1 ~625(51)us at T = 5K is much shorter
than in films of lower E' density. These results are discussed in the context
of E' centers being used as probe spins for spin-selection rules based single
spin-readout.
