Chemical information in positron annihilation spectra

Positron annihilation spectra of arsenic- and gold-implanted silicon are compared with spectra from bulk samples of arsenic and gold. Spectra with strongly reduced background intensities were recorded using a two detector coincidence system with a variable-energy positron beam. It is shown that features in the high-momentum region of the spectra (∼514–520 keV) can be identified with particular elements and that this identification is independent of structure, i.e., whether the element forms the bulk or is an implanted impurity. Proportionality between the intensity of characteristic spectral features and the fraction of annihilating positrons is also demonstrated, using the native oxide on a silicon wafer as a test case.