Influence of the deposition parameters on the characteristics of Cu xMo 6S 8 thin films in situ grown by pulsed laser deposition

Abstract

Cu x Mo 6S 8 thin films have been grown in situ by pulsed laser deposition (PLD) on R-cut Al 2O 3 single-crystal substrates. Under selected deposition conditions, they are oriented and present epitaxial relationships with the in-plane substrate directions. The influence of deposition parameters on composition or epitaxial quality has been studied in detail. In most samples, an excess of metallic molybdenum has been detected by X-ray diffraction and quantified by Rutherford backscattering spectrometry (RBS). The deposition under argon (8.10 −2 mbar) at 870°C with a target–substrate distance of 38 mm and an average laser fluence of 5 J cm −2, has entailed a significant reduction of this secondary phase. Moreover, using a small-sized, home made vacuum chamber, single-phased Cu x Mo 6S 8 films have been in situ grown for the first time. The epitaxial relations have been investigated by X-ray diffraction in various modes (namely θ-2θ, θ-scans and ϕ-scans) and by scanning electron microscopy. Under secondary vacuum, (100) Rh oriented thin films are obtained above 820°C and a progressive improvement of the epitaxial growth has been observed up to 890°C. The superconducting critical temperature T c, measured by the a.c. susceptibility method, appears insensitive to the microstructural modifications. Such deposition conditions have been applied to other substrates like Al 2O 3C, (100) MgO or (100) Y: ZrO 2 and have led to new complex epitaxial growth relations.