MeV 4He++ channeling studies of epitaxially grown Pt films on Al2O3(0 0 0 1)

Crystallinity and structural properties of the epitaxially grown Pt films on Al2O3(0 0 0 1) substrate by RF magnetron sputtering at a substrate temperature of 600 deg. C were studied by using backscattering spectrometry (BS)/channeling and transmission electron microscopy (TEM) measurements. The Pt layer on Al2O3(0 0 0 1) substrate grew epitaxially to the direction of (1 1 1) with sixfold symmetry. Twin rotated by 180 deg. around Pt(1 1 1) axis was observed from the analysis of BS/channeling and TEM. In spite of the formation of twin in Pt film, the channeling minimum yield is as low as 4%. The result can be supported by the facts that (i) (1 1 1) direction of two kinds of Pt domain is parallel to each other and consistent with the direction of incident 4He ions. (ii) Pt layer is only 180 deg. rotationally twinned at the twin boundary paralleled to the interface between Pt(1 1 1) and Al2O3(0 0 0 1) with same <1 1 1> axial channel. Therefore, incident 4He ions do not experience dechanneling at the boundary of two domains. When the thickness of Pt film was less than 20 nm, a steep increase of the channeling minimum yield of Pt film was observed. It is suggested that when Pt film will be used as a buffer or seed layer for ferroelectric Pb(Zr,Ti)O3(PZT) and GMR metals, the optimum thickness of Pt film kept with a good crystalline quality should be larger than 20 nm