PAC investigation of 77Br→77Se on silicon surfaces

The perturbed γγ-angular correlation (PAC) method has been applied to investigate the sites occupied by isolated 77Br-atoms on silicon surfaces. The nuclear quadrupole interaction was used to determine the electric field gradients (efg) acting at the 5/2- state in 77Se, populated in the 77Br decay. For the Si(100)2 x 1 surface two different field gradients have been observed with the parameters νQ1=583(5) MHz, η1=0.0(1) and νQ2=543(5) MHz, η2=0.40(3). Typical values for the Si(111)7 x 7 surface from preliminary data are νQ=548(9) MHz, η=0.54(6). These electric field gradients are identified with adsorption sites of the selenium at dangling bonds of the silicon surfaces. (orig.)