抄録
We present a novel nondestructive inspection technique for nanowires using picosecond ultrasound spectroscopy. Resonance frequencies of nanostructures are highly affected by their elastic modulus and the boundary conditions. Defects in a nanowire should lower the elastic modulus and then resonance frequencies decrease. If detachment appears, the elastic waves which had been generated from nanowires and propagate toward the substrate, will disappear. Therefore, the damage accumulation in nanowires and adhesion strength with the substrate can be evaluated by measuring mechanical resonance frequencies of nanowires. In this study, we measure resonance frequencies of Cu nanowires fabricated on Si and glass substrates using the electronbeam lithography. We succeeded in observing the through-thickness resonance and Rayleigh-wave resonance related with the nanowires. During the electromigration, the through-thickness resonance frequencies significantly decrease, remaining the Rayleigh-wave resonance frequencies unchanged, indicating defect accumulation inside the nanowire without detachment.
