THE EFFECT OF X-RAY PENETRATION DEPTH ON STRUCTURAL CHARACTERIZATION OF MULTIPHASE BI-SR-CA-CU-O THIN-FILMS BY X-RAY-DIFFRACTION TECHNIQUES

X-ray diffraction has been used extensively to assess the crystalline phase composition of superconducting ceramics. In instances where randomly oriented powders are available, X-ray diffraction provides a means of identifying not only the phases present but also the volume fraction of each phase. In instances where ultrathin films ( < 0.2-mu-m) are analyzed X-ray diffraction provides a means of identifying phases present, preferred texture of the phases, and calculating an index that indicates a relative volume fraction of each phase. In the case of thin films ( > 0.2-mu-m) the ability to measure phase composition by X-ray diffraction is hampered by the fact that due to the limited effective X-ray penetration depth the X-ray beam may not sample all depths of the film equally. This phenomenon could result in a lessening of the contribution to the final diffraction pattern by phases concentrated near the substrate-film interface. This paper describes the characterization of Bi-Sr-Ca-Cu-O superconducting films by X-ray diffraction. Reactive beam ion etching experiments made it possible to observe the change in the relative volume fraction of three superconducting phases as a function of etch depth.