Widely Tuneable Composition and Crystallinity of Graded Na1+xTaO3±Î´ Thin Films Fabricated by Chemical Beam Vapor Deposition.

Combinatorial approach has been widely recognized as a powerful strategy to develop new-higher performance materials and shed the light on the stoichiometry-dependent properties of known systems. Herein, we take advantage of the unique features of chemical beam vapor deposition to fabricate compositionally graded Na1+xTaO3±Î´ thin films with −0.6 < x < 0.5. Such a varied composition was enabled by the ability of the employed technique to deliver and combine an extensive range of precursors flows over the same deposition area. The film growth occurred in a complex process, where precursor absolute flows, flow ratios, and substrate temperature played a role. The deviation of the measured Na/Ta ratios from those predicted by flow simulations suggests that a chemical-reaction limited regime underlies the growth mechanism and highlights the importance of the Ta precursor in assisting the decomposition of the Na one. The crystallinity was observed to be strongly dependent on its stoichiometry. High under-stoichiometries (e.g., Na0.5TaO3−δ) compared to NaTaO3 were detrimental for the formation of a perovskite framework, owing to the excessive amount of sodium vacancies and oxygen vacancies. Conversely, a well-crystallized orthorhombic perovskite structure peculiar of NaTaO3 was observed from mildly under-stoichiometric (e.g., Na0.9TaO3−δ) to highly over-stoichiometric (e.g., Na1.5TaO3+δ) compositions.

Two-Step Approach for Conformal Chemical Vapor-Phase Deposition of Ultra-Thin Conductive Silver Films.

Conductive ultra-thin silver films are commonly fabricated by physical vapor deposition methods such as evaporation or sputtering. The line-of-sight geometry of these techniques impedes the conformal growth on substrates with complex morphology. In order to overcome this issue, volume deposition technologies such as chemical vapor deposition or atomic layer deposition are usually preferred. However, the silver films fabricated using these methods are generally non-electrically conductive for thicknesses below 20-50 nm due to island formation. Here, we demonstrate a novel approach for producing ultra-thin conductive silver layers on complex substrates. Relying on chemical vapor-phase deposition and plasma post-treatment, this two-step technique allows the synthesis of highly conductive and uniform silver films with a critical thickness lower than 15 nm and a sheet resistance of 1.6 Ω/□ for a 40 nm-thin film, corresponding to a resistivity of 6.4 µΩ·cm. The high infrared reflectance further demonstrates the optical quality of the films, despite a still large root-mean-square roughness of 8.9 nm. We successfully demonstrate the highly conformal deposition in lateral structures with an aspect ratio of up to 100. This two-step deposition method could be extended to other metals and open new opportunities for depositing electrically conductive films in complex 3D structures.