Fig. 2.

Ultrasound M-mode image, where the x-axis is the time elapsed during a given test and the y-axis is the time delay between ultrasound emission and echo detection by the transducer (a: Ag₂₀Ge₄₀ and c: Ge₂₀Ge₄₀); variation in time of flight for the E₀, E₁, and E₂ echoes during a test, obtained from the analysis of the M-mode image and the corresponding rf signals (b: Ag₂₀Ge₄₀ and d: Ge₂₀Ge₄₀).