Experimental and Theoretical Studies of the Surface Oxidation Process of Rare-Earth Tritellurides

Abstract

Recent studies have established Van der Waals (vdW) layered and 2D rare-earth tritellurides (RTe ₃) as superconductors and near room-temperature charge density wave (CDW) materials. Their environmental stability raises nat-ural concern owing to aging/stability effects observed in other tellurium-based layered crystals. Here, the results establish the stability and environmental aging characteristics of these RTe ₃ systems involving a variety of metals such as La, Nd, Sm, Gd, Dy, and Ho. The atomic force microscopy (AFM) and scan-ning electron microscopy (SEM) results show that all the RTe3 sheets oxidize to form thin TeOx layers that are primarily confined to the surface, edges, and grain boundaries. Time-resolved in situ Raman spectroscopy measurements are used to understand the kinetics of the oxidization process for different lanthanide metal cations and establish their relative stability/resilience to oxi-dization. Overall results indicate that the vdW layers show higher air stability as the 4f electron number decreases going from Ho to La, resulting in the most stable LaTe ₃ compared to the least stable HoTe ₃. Comprehensive quantum mechanical simulations reveal that environmental degradation originates from a strong oxidizing reaction with O ₂ molecules, while humidity (H2O) plays a negligible role unless Te vacancies are present. Moreover, the simulations explain the effects of 4f electrons on the work function and Te vacancies forma-tion, which directly impact the aging characteristics of RTe ₃ layers. Interest-ingly, optical and electrical measurements show that the CDW response is still observed in aged RTe ₃ layers owing to the presence of underlying pristine/nonoxidized RTe₃ layers, except CDW transition temperatures increase due to the thickness effect. Overall results offer the first in-depth environmental aging studies on these materials, which can be applied to engineer and design their chemical stability, surface properties, and overall CDW characteristics