Unusual orientation relationship for a copper film on Si(111)

The texture of a copper film deposited on bare Si(111) is studied. Deposition is done using the partially ionized beam technique where no potential is applied to the substrate. Pole figure analysis shows a very sharp texture where Cu{531} is parallel to Si(111). In the plane of the film, two variants of copper orientation are present with orientation relationships Si〈112̄〉//Cu〈13̄4〉and Si〈112̄〉//2.5° from Cu〈35̄0〉. The rotation between variants of 56.5° is less than the Cu(111) twin orientation. Possible reasons for the mismatch are discussed.