Reproducing the Backscattering Spectrum of an Amorphous Target from a Single Crystal

We show experimentally to an accuracy of about 1%, using silicon wafers of 〈100〉, 〈110〉 and 〈111〉 orientation, that the backscattering spectrum of an actual amorphous silicon film is correctly reproduced by rotating a single-crystalline sample around its main crystalline axis tilted by 5–15° away from the direction of the incident 4He beam. Data were taken primarily with a 2.0 MeV beam, but results were also obtained at energies of 0.7, 1.25 and 3.0 MeV. The spectra of a poly-crystalline and a rotating Si〈111〉 sample also overlap very closely.