This lecture covers X-ray reflectivity (XRR) and small-angle X-ray scattering (SAXS) techniques for analyzing crystalline and amorphous films. XRR measures interference of reflected waves to determine layer thickness, material density, and surface roughness. SAXS probes particle size, shape, and nanostructures. The instructor explains the principles, measurement setups, and applications of XRR and SAXS in characterizing materials at the nanoscale.