Yuki Imakita

Optical manipulation of nonlinear vibration of graphene mechanical resonator

We demonstrate manipulation of nonlinear vibration of graphene mechanical resonator (G-MR) optically by photothermal effects of laser. Different photothermal effects are induced by combining of scattering light and different standing waves of light, which have different effects on nonlinear vibration. Experimental results indicate that nonlinearity is suppressed or promoted for each photothermal effects without almost changing its amplitude. These changes cannot be explained by conventional nonlinear vibration that the nonlinearity increases with increasing amplitude. To reveal the principle of the modulation, we proposed novel vibration model including photothermal effects in nonlinear vibration. Numerical calculation from the model well fits experimental results and revealed the principle. We believe that these technics of controlling nonlinear vibration open the further applications of G-MR.

Phonon engineering of graphene by local strain

Due to its extremely high thermal conductivity, graphene is one of the potential candidates for thermal management materials. Because the main heat carrier is phonon, thermal conductivity of graphene can be modulated by inducing the local strain in graphene networks. Here we propose a device structure with which the in-plane thermal conductivity can be measured while inducing the strain into graphene. From atomic force microscopy under 7.3×103 Pa, the deflection at the center of the graphene membrane was 35 nm, indicating that the surface area increases by 0.14% from the original surface area under atmospheric pressure. Nanoindentation measurement shows 56% increase in the pretention of the graphene membrane under 7.3×103 Pa. Thus, the device structure can be used to measure the thermal conductivity while inducing strain by the pressure difference across the membrane.