Polariton condensation and surface enhanced Raman in spherical ZnO microcrystals

Preparation and characterization of polariton Bose–Einstein condensates in micro-cavities of high quality are at the frontier of contemporary solid state physics. Here, we report on three-dimensional polariton condensation and confinement in pseudo-spherical ZnO microcrystals. The boundary of micro-spherical ZnO resembles a stable cavity that enables sufficient coupling of radiation with material response. Exciting under tight focusing at the low frequency side of the bandgap, we detect efficiency and spectral nonlinear dependencies, as well as signatures of spatial delocalization of the excited states which are characteristics of dynamics in polariton droplets. Expansion of the photon component of the condensate boosts the leaky field beyond the boundary of the ZnO microcrystals. Using this, we observe surface polariton field enhanced Raman responses at the interface of ZnO microspheres. The results demonstrate how readily available spherical semiconductor microstructures facilitate engineering of polariton based electronic states and sensing elements for diagnostics at interfaces.

Magnetic-plasmonic Ni@Au core-shell nanoparticle arrays and their SERS properties

In this paper, large-area magnetic-plasmonic Ni@Au core–shell nanoparticle arrays (NPAs) with tunable compositions were successfully fabricated by direct laser interference ablation (DLIA) incorporated with thermal dewetting method. The magnetic properties of the Ni@Au core–shell NPAs were analyzed and the saturation magnetization (Ms) of the Ni80@Au20 nanoparticles was found higher than that of nickel-only nanoparticles with the same diameter. The surface enhanced Raman scattering (SERS) property of the Ni@Au core–shell NPAs was then examined using the Rhodamine 6G (R6G) as a Raman reporter molecule and a SERS enhancement factor of 2.5×106 was achieved on the Ni50@Au50 NPA substrate, which was of 9 times higher than that for Au nanoparticles with the same size distribution. It was due to the enhanced local surface plasmon resonance (LSPR) between the ferromagnetic Ni cores and the surface polariton of Au shells of each nanoparticle. The fabrication of the Ni@Au core–shell NPAs with different compositions offers a new avenue to tailor the optical and magnetic properties of the nanostructured films for chemical and diagnostic applications.

Polaritons in Nanocomposites of Metal Nanoparticles – Dielectric

The article studies the main characteristics of surface polaritons in composite nanomaterials. The authors consider composite media such as noble metal nanoparticles randomly distributed in a transparent dielectric matrix and build dispersion curves of polaritons in such nanocomposites. The paper shows calculating optical parameters of the surface polariton for several values of the radius of metal nanoparticles and the nanocomposite filling parameter. The authors also present the calculations of the complex refractive index for polaritons in composites with nanoparticles of different metals. In addition, the authors find the dependences of the real and imaginary parts of the complex refractive index of the nanocomposite on the normalized frequency for membranes with different thicknesses and calculate real and imaginary parts of dielectric constant for waves in several metals. Besides, the article provides an overview of important stages in the study of surface electromagnetic waves. It shows that the variation of the structure materials, size and concentration of nanoparticles opens wide possibilities for controlling the optical properties of composite mediums and their practical application. The considered nanocomposites are artificially created media whose material parameters can be controlled. The first method consists in changing the relative volume of the nanoparticles filling of the dielectric matrix. The second method consists in changing the dielectric constant of the nanocomposite matrix. The authors emphasize that the dielectric constant of the nanocomposite in this case acquires resonant properties in contrast to the permeability of the nanoparticles themselves.