High-resolution X-ray rocking curves are often used to determine precisely the composition and thickness of epitaxial alloy films. Rigaku's SmartLab® diffractometer, which offers variable resolution optics, is ideal for such purposes. The modular design of the SmartLab optics allows users to easily insert different optical elements of their choice, such as Ge(220)x2, Ge(220)x4, Ge(400)x2, or Ge(440)x4 monochromators for the incident beam and a Ge(220)x2 analyzer for the diffracted beam. These optic modules can be automatically detected by the controlling computer and are aligned automatically. An automatic variable receiving slit is also available for the diffracted beam.
In the figure below, the rocking curve of an AlxGa1-xAs ternary alloy film grown on a GaAs (001) substrate by molecular beam epitaxy (MBE) measured on a SmartLab diffractometer with a standard 2 kW sealed tube generator and a Ge (220)x2 monochromator is shown. The entire scan took about 2 min. In addition to the GaAs substrate peak and the AlxGa1-xAs film peak, thickness fringes due to the interference effect of the X-rays reflected at the substrate and the film surfaces are clearly recorded. From the separation of the film and the substrate peaks (0.104°), the composition of the film is determined to be x=0.95. From the separation of the thickness fringes (0.006°), the film thickness is determined to be 8772.8 Å.