Structural evolution of Ti/Cu multilayers as a function of period thickness

TL;DR

This study investigates how the period thickness in Ti/Cu multilayers influences their structural properties, revealing a transition from interfacial mixing at small periods to crystallization and texture development at larger periods.

Contribution

It provides detailed insights into the structural evolution of Ti/Cu multilayers across a range of period thicknesses using advanced microscopy and diffraction techniques.

Findings

At 4 nm, multilayers show reduced periodic contrast due to interfacial mixing.

At 10 nm, multilayers are preserved but affected by roughness and waviness.

Larger periods exhibit increased crystallization and texture development.

Abstract

Ti/Cu multilayers with periods ranging from 4 to 52.5 nm were synthesized by magnetron sputtering to examine how the period thickness affects morphology, crystallization, texture development, and preservation of periodicity. The structural evolution was analyzed using complementary transmission electron microscopy techniques with X-ray diffraction and reflectometry. The results show that the period thickness governs the balance between interfacial transition-region formation, crystallization, and growth-induced morphological instabilities. At the smallest period of 4 nm, the structure has strongly reduced periodic contrast, which may be attributed to extended interfacial regions, partial Cu-Ti intermixing, and suppression of well-defined layer formation. At 10 nm, the multilayer structure is preserved but remains affected by accumulated roughness and layer waviness; local modification of the Cu lattice is suggested to be significant relative to the bilayer period, likely due to mixed Cu-Ti interfacial regions and/or coherent strain. With increasing period, the multilayers become more regular, and the layers show progressive crystallization and texture development during growth. Cu crystallizes predominantly in the fcc structure with a strong Cu(111) contribution, whereas Ti exhibits a more complex structural evolution, from an amorphous or weakly crystallized state near the substrate toward a more ordered and textured state closer to the surface.