【研究成果】2016年-

研究成果94

Near-field optical mapping of single gold nano particles using photoinduced polymer movement of azo-polymers
Hidekazu Ishitobi, Taka-aki Kobayashi, Atsushi Ono, Yasushi Inouye
Optics Communications Volume 387, 15 March 2017, Pages 24–29

We studied polymer movement that was induced in azo-polymer films by optical near-fields generated near single gold nano particles (GNPs) to visualize near-field distribution with a spatial resolution beyond the diffraction limit of light. A linearly polarized (Ex) laser beam was irradiated into GNPs to excite local surface plasmon resonance that enhanced the near-field around the GNPs. The findings indicated that different GNP diameters (that is, 50 nm and 80 nm) resulted in different deformation patterns on the films. The results were compared with theoretical calculations of near-field distributions, and the observations revealed that the deformation patterns were dependent on the ratio between Ex and Ey wherein each possessed a different field distribution.

AFM images of the surface deformations after induction by a plasmonically enhanced near-field in the vicinity of an 80 nm GNP covered by a 50 nm azopolymer on a glass substrate. The irradiation intensity and the exposure time corresponded to 100 mW/cm2 and 750 s, respectively. The polarization of the incident light was parallel to the X-axis.
[Left fig.] Calculated in-plane field intensity distributions around an 80 nm GNP covered by a 50 nm azo-polymer on a glass substrate. The figure shows each components of electric field intensities of (a)|Ex|2, and (b)|Ey|2. Specifically, X and Y are parallel to the film surface, and Z corresponds to the optical axis. The polarization of the incident light is along the X-axis. The incident light intensity (|E0|2) normalized the field intensity. The distributions were calculated in the X-Y plane that was parallel to the film surface and across the GNP center (10 nm below the interface between the polymer and air). It was assumed that the polymers in which |Ey|2 had high intensity (as denoted by the white circles) were moved by the anisotropic fluidic force from high light intensity regions to low light intensity regions along the Y direction. The polymers were then accumulated to the positions marked by the red circles. It is reasonable to consider that this type of a small difference in the ratio determined final deformation patterns because the same mass (polymer) was pulled by different directional forces (Fx vs. Fy).