Atomic force microscope cantilever as focused GHz ultrasound transducer
R. H. Guis (TU Delft - Mechanical Engineering)
M. U. Arabul (ASML)
Z. Zhou (ASML)
G. J. Verbiest (TU Delft - Mechanical Engineering)
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Abstract
We demonstrate that an atomic force microscope (AFM) tip acts as a nano-acoustic horn, focusing GHz ultrasound into its apex through gradual impedance matching. Using photo-acoustic pump–probe measurements, we show tip echoes exceeding geometric expectations by up to 150× between 20–50 GHz. Mode conversion near the apex reduces longitudinal signal strength, but optimizing tip geometry can suppress this effect and enhance transmission efficiency. These results establish AFM cantilevers as effective GHz ultrasound transducers, enabling nanometer-scale acoustic focusing and paving the way for high-resolution subsurface acoustic atomic force microscopy.
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