Nanoslit Arrays Research Articles

High-sensitivity surface plasmon resonance spectroscopy based on a metal nanoslit array

We have chemically modified metal nanoslit array surfaces with alkanethiol self-assembled monolayers and have characterized the resulting spectral shift of optical transmission. Adsorption of a self-assembled monolayer (1.5nm thick) on a silver nanoslit array (slit width of 30–50nm and grating period of 360nm) is found to cause an 11nm redshift of the main transmission peak. Strong confinement of optical fields in the narrow slit region allows sensitive transduction of surface modification into a shift of surface plasmon resonance wavelength.

Ultrafast dynamics of surface plasmon polaritons in plasmonic metamaterials

Using near-field scanning optical microscopy and ultrafast laser spectroscopy, we study the linear optical properties of subwavelength nanoslit and nanohole arrays in metal films, which are prototype structures for novel plasmonic metamaterials. Near-field microscopy provides direct evidence for surface plasmon polariton (SPP) excitation and allows for spatial imaging of the corresponding SPP modes. By employing spectral interferometry with ultrashort 11-fs light pulses, we directly reconstruct the temporal structure of the electric field of these pulses as they are transmitted through the metallic nanostructures. The analysis of these data allows for a quantitative extraction of the plasmonic band structure and the radiative damping of the corresponding SPP modes. Clear evidence for plasmonic band gap formation is given. Our results reveal that the coherent coupling between different SPP modes can result in a pronounced suppression of radiative SPP damping, increasing the SPP lifetime from 30 fs to more than 200 fs. These findings are relevant for optimizing and manipulating the optical properties of novel nano-plasmonic devices.

Blueshift of surface plasmon resonance spectra in anneal-treated silver nanoslit arrays

Silver nanoslit arrays were anneal treated in vacuum, and the effects on the surface morphology of silver and the surface plasmon resonance characteristics were investigated. Optical transmission through nanoslit arrays shows a distinctive change in the spectral profiles after annealing: A clear blueshift of the transmission peaks and dips (20nm shift for an anneal temperature of 150°C). Scanning electron microscopy reveals a morphological change of silver: Increased grain sizes, and smooth and round surface profiles after the anneal treatment. The observed blueshift of transmission spectra correlates well with the geometrical and dimensional changes of silver islands defined between slits, which are found to alter the surface plasmon resonance conditions involving various mechanisms in different regimes.

Dynamic evolution of surface plasmon resonances in metallic nanoslit arrays

We have investigated surface plasmon interactions in a metallic nanoslit array structure that shows characteristic transmission spectra with well-defined transmission minima and maxima in the visible-to-infrared range. The time evolution of the surface plasmon resonances occurring in various different regimes of the spectra was analyzed by performing finite-difference time-domain analysis of the plasmon field, energy flow, and polarization charge distributions in the nanoslit array structure. At the transmission dip that corresponds to the surface plasmon resonance at metal/dielectric(substrate) interface, the polarization charges are found to distribute such that they form in-plane standing-wave oscillations along the dielectric side of the metal surface. At the transmission peak, surface plasmon waves oscillate along the periphery of each metal island with a quadrupolar distribution of polarization charges. At the longer wavelength regime, the polarization charges at each island show a dipolar distribution along the array direction. Optical transmission in this regime is found to critically depend on slit width, which affects the near-field coupling between metal islands.

Refractive transmission of light and beam shapingwith metallic nano-optic lenses

We have performed finite-difference time-domain (FDTD) analysis of optical transmission through a nanoslit array structure formed on a metal layer with tapered film thickness. The analysis result shows refractive transmission of light through the nanoslit array, opening up the possibility of creating metallic lenses that resemble glass lenses in their shape. Metallic lenses with curved surfaces are designed such that each nanoslit element transmits light with phase retardation controlled by the metal thickness in the aperture region. The FDTD analysis result demonstrates a focusing or collimating function of convex-shaped metal lenses.