Thermal stability study of Weyl semimetal WTe₂/Ti heterostructures by Raman scattering

Abstract

Weyl semimetal Td-phase WTe₂, a novel topological matter, possesses a strong spin-orbit coupling and non-trivial topological band structure, and thus becomes a very promising superior spin current source material. By constructing the WTe₂/Ti heterostructures, the issue that the ferromagnetic layer with perpendicular magnetic anisotropy cannot be directly prepared on WTe₂ layer can be well addressed, and meet the requirements for high-performance spin-orbit torque devices. To be compatible with the semiconductor technology, the device integration usually involves a high temperature process. Therefore, the thermal stability of WTe₂/Ti is critical for practical device fabrication and performance. However, the thermal stability of WTe₂/Ti interface has not been very clear yet. In this work, the micro-Raman scattering technique is used to systematically study the WTe₂/Ti interface annealed at different temperatures. It is found that the thermal stability of the interface between WTe₂ and Ti is related to the thickness of WTe₂ flake; appropriate increase of the WTe₂ thickness can lead to the improvement of thermal stability in WTe₂/Ti heterostructures. In addition, high temperature annealing can cause a significant interfacial reaction. After annealed at 473 K for 30 min, the interface between WTe₂ (12 nm) and Ti changes dramatically, leading to the formation of Ti-Te interface layer. This observation is highly consistent with the observations by high-resolution transmission electron microscopy and the elemental analysis results as well. This study will provide useful information for further exploring the influence of the WTe₂/Ti interface on the spin-orbit torque effect, and greatly invigorate the research area of energy efficient spintronic devices based on WTe₂ and other novel topological materials.