The transition from amorphous to crystalline in Al/Zr multilayers

TL;DR

This study investigates the amorphous-to-crystalline transition in Al/Zr multilayers, revealing how Si doping influences critical thickness, surface roughness, and layer orientation, using multiple characterization techniques.

Contribution

It provides a detailed analysis of how Si doping affects the transition process and critical thickness in Al/Zr multilayers, introducing a four-step model for the transition.

Findings

Si doping shifts the critical thickness from 1.6 nm to 1.8 nm.

Al layers become highly oriented in Al<111> above 3.0 nm thickness.

Zr-on-Al interlayer is wider than Al-on-Zr in both systems.

Abstract

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.