  The amorphous-to-crystalline transition in Al(1.0%wtSi)/Zr and Al(Pure)/Zr
multilayers grown by direct-current magnetron sputtering system has been
characterized over a range of Al layer thicknesses (1.0-5.0 nm) by using a
series of complementary measurements including grazing incidence X-ray
reflectometry, atomic force microscopy, X-ray diffraction and high-resolution
transmission electron microscopy. The Al layer thickness transition exhibits
the Si doped in Al could not only disfavor the crystallization of Al, but also
influence the changing trends of surface roughness and diffraction peak
position of phase Al<111>. An interesting feature of the presence of Si in Al
layer is that Si could influence the transition process in Al(1%wtSi) layer, in
which the critical thickness (1.6 nm) of Al(Pure) layer in Al(Pure)/Zr shifts
to 1.8 nm of Al(1.0%wtSi) layer in Al(1.0%wtSi)/Zr multilayer. We also found
that the Zr-on-Al interlayer is wider than the Al-on-Zr interlayer in both
systems, and the Al layers do not have specific crystal orientation in the
directions vertical to the layer from SAED patterns below the thickness (3.0
nm) of Al layers. Above the thickness (3.0 nm) of Al layers, the Al layers are
highly oriented in Al<111>, so that the transformation from asymmetrical to
symmetrical interlayers can be observed. Based on the analysis of all
measurements, we build up a model with four steps, which could explain the Al
layer thickness transition process in terms of a critical thickness for the
nucleation of Al(Pure) and Al(1%wtSi) crystallites.
