New Research


A New Direction in Nano-Mechanics

-Resonance Measurement for Nanomaterias-

Professor Masahiko Hirao, Associate Professor Hirotsugu Ogi, Assistant Professor Nobutomo Nakamura

   We have succeeded in measuring resonance frequencies in nanomaterials, including ultrathin films and nanowires, where representative dimensions are in 10 nanometers. This method uses the pump-probe technique, where the pump light pulse causes vibrations in the nanomaterials, which are detected by the delayed probe light pulse.
   The elasticity is one of fundamental properties of materials. This means the mechanical resistance to the deformation caused by the applied external force. Diamond exhibits the highest elasticity. The elastic constants, representing numerically the elasticity, are then studied in materials science and needed in practical applications for designing structures.
   Tensile, bending and torsional tests were performed to evaluate the elastic constants. However, these conventional static methods cannot be applied to nanomaterials because of difficulties of applying the intended force and measuring small deformations.
   We then developed a noncontacting method using pulse lights. Pump light pulse irradiates the specimen surface to cause coherent phonons, which are detected by the delayed probe light pulses. With this method, we have discovered unusual elastic properties of ultrathin films, which cannot be explained with the conventional theory.

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