Multipitched plasmonic nanoparticle grating for broadband light enhancement in white light emitting organic diodes

We apply regular arrays of plasmonic nanodisks to enhance light emission from an organic white light emitting diode WOLED . To achieve broadband enhancement, we apply, first, aluminum as a nanodisk material with moderate loss throughout the whole visible spectral range. Second, broadband light coupling is mediated by surface lattice resonances from a multipitch array built from two superimposed gratings with different grating constants formed by elliptic and circular nanodisks. To demonstrate the viability of this concept, the grating structure was embedded in the hole transport layer of a solution processed phosphorescent WOLED exhibiting a current efficiency of 2.1 cd A at 1000 cd m2. The surface lattice resonances in the grating raise the current efficiency of the device by 23 to 2.6 cd A at 1000 cd m2, while the device emission changes from a neutral white to a warm white appearance with CIE1931 x,y coordinates of 0.361, 0.352 and 0.404, 0.351 , respectively. The WOLED was characterized in detail optically by extinction and angle resolved photoluminescence and as well by electroluminescence measurements for its opto electronic characteristics. The experimental results agree well with finite difference time domain simulations that aim at a better understanding of the underlying physical mechanisms. In summary, our work presents a novel versatile approach for achieving broadband enhancement of light emission in WOLEDs over a wide spectral rang

Surface Plasmon mediated near-field imaging and optical addressing in nanoscience

We present an overview of recent progress in plasmonics. We focus our study on the observation and excitation of surface plasmon polaritons (SPPs) with optical near-field microscopy. We discuss in particular recent applications of photon scanning tunnelling microscope (PSTM) for imaging of SPP propagating in metal and dielectric wave guides. We show how near-field scanning optical microscopy (NSOM) can be used to optically and actively address remotely nano-objects such as quantum dots. Additionally we compare results obtained with near-field microscopy to those obtained with other optical far-field methods of analysis such as leakage radiation microscopy (LRM)

Nanoscale waveguiding methods

While 32 nm lithography technology is on the horizon for integrated circuit (IC) fabrication, matching the pace for miniaturization with optics has been hampered by the diffraction limit. However, development of nanoscale components and guiding methods is burgeoning through advances in fabrication techniques and materials processing. As waveguiding presents the fundamental issue and cornerstone for ultra-high density photonic ICs, we examine the current state of methods in the field. Namely, plasmonic, metal slot and negative dielectric based waveguides as well as a few sub-micrometer techniques such as nanoribbons, high-index contrast and photonic crystals waveguides are investigated in terms of construction, transmission, and limitations. Furthermore, we discuss in detail quantum dot (QD) arrays as a gain-enabled and flexible means to transmit energy through straight paths and sharp bends. Modeling, fabrication and test results are provided and show that the QD waveguide may be effective as an alternate means to transfer light on sub-diffraction dimensions

Compact-2D FDTD for Waveguides Including Materials with Negative Dielectric Permittivity, Magnetic Permeability and Refractive Index

An efficient compact-2D finite-difference time-domain method is presented for the numerical analysis of guided modes in waveguides that may include negative dielectric permittivity, negative magnetic permeability and negative refractive index materials. Both complex variable and real variable methods are given. The method is demonstrated for the analysis of channel-plasmon-polariton guided modes in triangular groves on a metal surface. The presented method can be used for a range of waveguide problems that were previously unsolvable analytically, due to complex geometries, or numerically, due to computational requirements of conventional three-dimensional finite-difference time-domain methods. A 3-dimensional finite-difference time-domain algorithm that also allows analysis in the presence of bound or free electric and equivalent magnetic charges is presented and an example negative refraction demonstrates the method

Spectroscopy and nonlinear microscopy of Au nanoparticle arrays: Experiment and theory

Regular arrays of rectangular gold nanoparticles on glass substrates are characterized by using linear extinction spectroscopy (in the wavelength range of 450-950 nm) and nonlinear scanning optical microscopy, in which two-photon photoluminescence (TPL) excited with a strongly focused laser beam (in the wavelength range of 720-800 nm) is detected. The dimensions of the nanoparticles (‚àº150vó150vó50 nm3) are chosen to realize the localized-surface-plasmon (LSP) resonance at the wavelength of ‚àº750 nm, which is clearly seen on the obtained extinction spectra as well as with the recorded TPL images. Extinction spectra are modeled using a finite-difference time-domain approach with the dielectric function of gold approximated by a Drude-Lorentz formula, showing rather good agreement between the experimental and theoretical spectra simulated for the nominal geometrical parameters of gold nanoparticles. The developed modeling tool is further used to evaluate the field intensity enhancement at the particles, which is then compared to the intensity enhancement estimated from the TPL images. We find good agreement between the intensity enhancement levels and indications that the LSP resonance wavelengths seen in the extinction spectra might differ from those deduced from the intensity enhancement spectra. The implications of the results obtained are discussed