Structural changes of single-crystalline Cu(111)/Nb(110) layers on sapphire (<11(2)over bar 0>) substrates irradiated with 260 keV Ar-40(+) ions at 56 K and room temperature have been studied by means of the Rutherford backscattering spectrometry (RBS)-channeling technique with 2.7 MeV He-4(+) ions. Ar+ ion irradiation of the Cu/Nb layer induces crystal imperfections mainly in the Cu layer while good crystal quality is kept in the Nb layer. The imperfections in the Cu layer were introduced after a fluence of 1.0 x 10(16) ions/cm(2), while no channeling effect was observed after a fluence of 5.0 x 10(16) ions/cm(2). This phenomenon can be explained by dislocation multiplication followed by the polygonization. The atomistic sputtering effect also occurs in the Cu layer. It was found by scanning electron microscopy (SEM) observation that the Cu layer was easily changed into an irregular structure with holes, as a result of sputtering.