Study Of Electromagnetic Enhancement Of Metallic Nanoparticle Array Structure

To manipulate light in nanoscale regions is an important goal for near-field optical research and nanoscale photonic devices. The optical properties of noble metal nanoparticle-based structures have drawn particular interest in nanoscience for localized surface plasmons of metallic nanostructures couples with electromagnetic fields. The plasmon resonance of nanoparticle arrays can be tuned by their size, shape, composition and surrounding medium. In this paper, the optical properties of spherical nanoparticles and array structure are studied using the finite difference time domain (FDTD) method.The FDTD code is programmed according to extended Drude model. The computing result is compared with the Mie theory of scattering and other researchers' simulation. Then, the optical properties of a goldden spherical nanoparticle dimer as illuminated by a linearly polarized plane wave are investigated by this simulation program. As the distance between two nanoparticles decreases, the field intensity in the gap increases significantly. And then, the optical responses of silver spherical nanoparticle dimer arrays are studied in the range of visible-nearinfrared wavelength. The surface plasom resonance wavelength is nearly proportional to the radius of nanoparticles. Hence the plasmon resonance behavior of this structure is predictable. The resonant peak wavelength is approximately 8-10 times of the radius of nanoparticles in the arrays.The simulation presents that the five-dimer array can excite different plasmon modes as illuminated by different wavelength of the incident light. For surface plasmon resonant cases, the energy of incident light is confined effectively in the gap of penultimate dimer. To further explore the mechanism of the surface plasmon resonance, the generated plasmon current density is calculated. The vector directions are determined by the real part of the electric field and the amplitude is the module of the electric field. The current density exhibits explicit dipole and quadruple characteristic. It's noticeable that a circular electricfield generated on the surface of two closely spaced dimers should be assigned as the quadruple excitation. Under the influence of quadruple electricfield, the energy of the reflected plasmons at the end of array structure is almost diverted into the penultimate gap. The polarization charges of penultimate dimer change into the dipolelike charge distribution, which can be deduced from the similar curve of nearfield intensities with various incident light wavelength in the gap of fourth dimer and observed plasmon current on the surface of penultimate dimer. Therefore, the energy of incident light is almost concentrated in the gap of penultimate dimer. An extraordinary enhanced local field is obtained and the energy of incident light is confined effectively. Furthermore, we can choose the suitable radius of nanoparticles to obtain the resonant peak at optional position in the visible-nearinfrared wavelength. The novel plasmonic device that can highly confine electromagnetic field is a kind of promising candidate for nanoscale integrated optics and sensors.