PAC investigation of77Br→77Se on silicon surfaces

The perturbedγγ-angular correlation (PAC) method has been applied to investigate the sites occupied by isolated77Br-atoms on silicon surfaces. The nuclear quadrupole interaction was used to determine the electric field gradients (efg) acting at the 5/2− state in77Se, populated in the77Br decay. For the Si(100)2×1 surface two different field gradients have been observed with the parametersνQ1 = 583(5) MHz,η1 = 0.0(1) andνQ2=543(5) MHz,η2 = 0.40(3). Typical values for the Si(111)7×7 surface from preliminary data areνQ=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.