| 研究実績の概要 |
In our research, we utilized graphene nanoridge structures, which is a natural structure on graphene. Since it is a part of graphene itself, and also has no defect,4,21 it overcomes the problem of foreign object introduction. In this report, we will present how we use nanoridges structures as a graphene plasmon launcher and direction controller.Interestingly, at the conditions of stationary mode, the ratio between plasmon wavelength (top axis, can be calculated from excitation wavelength and permittivity of graphene) and ridge curve length is almost an integer fraction (1/2, 1/3, 1/4, etc.). At the conditions, there is also 180° phase flip of the launched SPP wave.
To understand this phenomenon, we formulate an analytic model. By modelling the nanoridge as a plasmon generation zone with length L and each point in this zone generate SPP wave. The electric field of launched SPP from the ridge would be the interference result of SPP launched from every point on the ridge.
This analytic model explains the simulation result that the amplitude goes to zero when L/λspp is an integer, resulting in the stationary mode. When the term sin(πL/λspp) is negative, the overall term can still be interpreted as positive value but with 180° flip;. This explain the phase flip in the simulation.
The single ridge system is a symmetric structure, therefore the launched plasmon to both side is also symmetric. To attain directional launching, we put 100-nm and 150-nm nanoridges alongside each other.
|
| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
Graphene is modeled as being 0.5 nm thick. The nanoridge is modeled using circular curve and attached to flat graphene with small inverse circular curve so that there is no sharp corner. The permittivity is calculated following references (random phase approximation).40,41 Fermi energy, temperature and relaxation energy of graphene are set to typical value of single layer graphene at 0.5 eV, 300 K, and 0.1 meV, respectively. Mid-IR illumination of 2.50-8.00 μm is focused (using paraxial approximation of gaussian beam) on the nanoridge. The polarization of the illumination is across the ridge. For most calculation, only 2 dimension (XY) is considered.
|
