This PDF contains the front matter associated with SPIE Proceedings Volume 6642, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Nanoparticle assemblies hold great promise as new materials in catalysis, nanoelectronic and nanophotonic applications. Many of their properties, which depend on the relative arrangement of the individual nanoparticles within the assembly, are not sufficiently well-understood because of a lack of methods to systematically assemble them into well-defined discrete model systems. In here we discuss a method for the ready access to a large number of discrete nanoparticle assemblies using a small number of single-stranded and cyclic DNA templates that are also dynamic. A triangular template and a square template are used to generate gold nanoparticle assemblies with geometrical control by the simple tagging of each particle to be organized with a DNA sequence that serves to dictate its final position within the construct. The same triangular template is used to access all the possible triangular combinations that two gold nanoparticles of different sizes may be organized in (i.e. three larger, two larger / one smaller, one larger/ two smaller, all smaller). The same square template is used to generate nanoparticle assemblies in which four gold nanoparticles are organized into square, trapezoidal and rectangular arrangements. Post-assembly addressability is demonstrated by a write/erase experiment in which three gold nanoparticles of a single size are assembled into a triangular arrangement, a specific particle is erased using an external eraser strand, and the empty position is re-written with a smaller sized particle. Our approach could be generalized to easily generate large sets of nanoparticle groupings with control over the position, size, type and addressability of each nanoparticle within the construct.

Rapid advance of nanostructuring technologies offers new possibilities for flexible and low-cost fabrication of plasmonic components and devices. In this contribution, we study applications of laser-based nonlinear lithography for the fabrication of dielectric surface-plasmon-polariton (SPP)-structures. These structures can be used for localization, guiding, and manipulation of SPPs on a subwavelength scale. Effective excitation of SPPs on dielectric structures and focusing of the generated SPPs are studied. The characterization of the SPP structures is performed by plasmon leakage radiation microscopy. Laser-based nonlinear lithography, e.g. two-photon polymerization technique, allows the fabrication of dielectric waveguides, splitters, and couplers directly on metal surfaces. The fabricated dielectric structures on metal films are demonstrated to be very efficient for the excitation of SPPs. Using these structures, excitation, focusing, and guiding will be demonstrated.

Nearfield scanning optical microscopy (NSOM) offers a practical means of optical imaging at a resolution well beyond the diffraction limit of the light. However, its applications are limited due to the strong attenuation of the light transmitted through the sub-wavelength aperture. In this paper, we report the development of particle enhanced plasmonic nearfield scanning optical microscope (PEP-NSOM) with a high optical coupling efficiency and a high spatial resolution. Two plasmonic components, a gold nanoparticle and a plasmonic lens, are integrated on a PEP-NSOM probe. By exciting both propagating surface plasmons and localized surface plasmons, PEP-NSOM probes are capable of focusing light onto the nanoparticle assembled on the aperture of the plasmonic lens, which can further squeeze the light to a few tens of nanometers. Nearfield intensity at the focus points of PEP-NSOM probes is 590 times higher than that of incident light according to numerical simulations. The E-field profile is also shown to be confined laterally <50nm at the imaging plane, which promises good nearfield images with high spatial resolution and low signal-noise ratio. Investigation indicates the local intensity enhancement can be further increased to be 4830 when using a gold nanodimer on the PEP-NSOM probe, which suggests the PEP-NSOM to be an open system of utilizing plasmonic nanostructures for nano-imaging. By providing a strong nano-scale light source, PEP-NSOM can be used as a high speed nano-scale imaging tool for single molecule detection and many other applications requiring high temporal/spatial resolution.

This report presents an overview of our recent near-field investigation of both local and surface plasmon resonance (SPR) with a scattering-type scanning near-field optical microscope (s-SNOM) which has sub-10 nanometer resolution. With the ability to perform near-field optical experiments at multiple excitation wavelengths simultaneously, this instrument has recorded near-field intensity and phase images of a wide range of subwavelength plasmonic structures: single nanohole and nanoslit, circular and elliptical hole arrays, etc. The near-field results obtained with different excitation wavelengths were confirmed by numerical calculation and were made direct correspondence with far-field observations by comprehensive models. The multi-wavelength s-SNOM proves to be an essential tool to unravel many interesting plasmonic phenomena in nanometer scale. This work investigates the nature of subwavelength plasmon optics which potentially will play an important role in the development of many innovative highly efficient optoelectronic devices (light-emitting devices and solar cells) and highly sensitive sensors based on SPR and surfaceenhanced Raman scattering.

We report in this paper the near-field microscopic studies on localized plasmon resonances in gold nanoparticles and their assemblies (nanorods, triangular nanoplates, and assembled nanospheres). We have utilized near-field measurements of linear transmission/scattering, as well as nonlinear two-photon excitation, to enable spectroscopic imaging of local electric field or local density of electromagnetic states. We show that the wavefunction of the plasmon excitation in the nanoparticle is visualized by the near-field methods. For single nanorod, many plasmon resonances were observed in the near-field transmission spectrum. At each resonant peak wavelength, the near-field image of the nanorod gave a characteristic spatially oscillating feature along the long axis of the nanorod. The feature is attributable to the square modulus of the resonant plasmon-mode wavefunction. In the assembled nanoparticles, strong electric-field enhancement localized in the interstitial sites ("hot spot"), which was theoretically predicted previously, was clearly imaged by the near-field two-photon excitation method. Major contribution of the hot spots to surface enhanced Raman scattering is also shown for the samples weakly doped with Raman-active dye molecules, by the near-field excited Raman spectra and images.

A surface plasmon polariton (SPP) phase imaging microscope with a subwavelength grating structure is developed for high-resolution in-plane image measurement, which can be used on biological samples. Conventionally, most of SPP image systems use prism couplers to induce surface plasmons (SPs), but this approach has some drawbacks such as non-normal incident light producing optical aberration in imaging and making the metrology instrument more complicate. It can be improved by utilizing a normal incident light to excite the SPs through subwavelength grating structure, which replaces the prism so that it can observe in-plane sample on the sensing surface and simplify the instrument. Instead of measuring the intensity of the reflectivity, the phase measurement with higher sensitivity is proposed. In this study, the proposed SPP microscope integrates a common-path phase-shift interferometry (PSI) technique to obtain the two-dimensional spatial phase variation caused by biomolecular interactions on the sensing surface without requiring additional labeling. The common-path PSI technique provides long-term stability, even when it is subjected to external disturbances, to match the requirements of biomolecular interaction analysis. The microscope is presented as a high stability, high sensitivity, and in-plane SPP phase image.

Vibrational spectroscopy, including Raman spectroscopy can be used for identifying molecular species, which is not possible by a scanning probe microscopy or an electron microscopy. Moreover, vibrational spectra contain structural information, such as intermolecular interactions, molecular orientations, and symmetry distortions of each species. Therefore, Raman spectroscopy is a powerful tool for studying the chemical composition of matter. By employing Tip-enhanced Raman spectroscopy (TERS), we can perform Raman spectroscopy with nano-scale spatial resolution. Our approach relies on the enhanced filed near a laser irradiated metal tip which works as the Raman excitation source. We have investigated nano-composite materials by TERS. Near-field Raman spectra revealed the nano-scale properties of molecules encapsulated in single-wall carbon nanotubes (SWNT). The enhanced field act on encapsulated molecules through the wall of SWNT to extract chemical information inside. &bgr;-carotene which has strong Raman intensities under visible light illuminations is used as an encapsulated molecule. The advantage of Raman spectroscopy is that the information of both SWNT and &bgr;-carotene can be obtained at the same time. So, it is possible to discuss the interaction between SWNT and the encapsulated molecules. Near-field Raman spectra measured at several different positions on SWNT bundle show that &bgr;-carotenes inside the tube are not uniformly distributed. We also find that the filling rates and the peak positions of the radial breathing mode of SWNT are linearly correlated.

This study utilizes a nanoplasmon-enhanced Raman scattering based on the attenuated-total-reflection (ATR) method to investigate the secondary structures of long oligonucleotides and their influence on the DNA hybridization. It is found that the ring-breathing modes of adenine, thymine, guanine, and cytosine in Raman fingerprint associated with three 60mer oligonucleotides with prominent secondary structures are lower than those observed for the two oligonucleotides with no obvious secondary structures. It is also determined that increasing the DNA hybridization temperature from 35 ^oC to 45 ^oC reduces secondary structure effects. The kinetics of biomolecular interaction analysis can be performed by using surface plasmons resonance biosensor, but the structural information of the oligonucleotides can not observed directly. The ATR-Raman spectrum can provide the structural information of the oligonucleotide monolayer on the sensing surface with the help of a silver patterned nanostructure film based on the finite-difference time-domain simulation and the e-beam lithography fabrication adapted as an ATR-Raman active substrate.

Surface plasmon resonance (SPR) biosensors based on attenuated total reflection (ATR) have been widely used in biochemistry and genetic engineering, because it is a sensitive and label-free method. The dimension of the sensing probe is millimeters or more, so that the required amount of a sample solution is more than 100 μL even if a micro chamber is used. For multifunctional biosensing applications, therefore, a small biosensing platform is needed. We employed localized surface plasmons (LSPs) in gold nanostructures, instead of the conventional ATR-based SPR, to realize such small sensing probes. A few works on biosensing developed in our research group will be shown in this paper. One is a fabrication method of gold nanoparticles by annealing of thin gold film less than 10 nm thick. The optimized condition for producing nanoparticles for biosensing applications is discussed. The other is a sensitive optical fiber biosensor based on LSPs in gold nanoparticles. This optical fiber biosensor has advantages: easy handling and remote sensing. These merits come from the fact that the sensor probe is formed at the endface of a standard multimode optical fiber whose core diameter is 50 μm. Instead of such a small probe area, it has similar sensitivity to that of the ATR-based SPR sensors. This optical fiber biosensor enables us to perform biosensing with a sample solution of less than 100 nL. Finally we show biosensing based on nonlinear optics. Second-harmonic generation is one of the secondorder nonlinear optical phenomena and is a surface sensitive phenomenon. Here we show that it provides us a highly sensitive way for biosensing.

Recent advances in near-field optics and sub-wavelength-precision fabrication technology allow the design of optical devices and systems at densities beyond those conventionally limited by the diffraction of light. Such higher integration density, however, is only one of the benefits of optical near-fields over conventional optics and electronics. In this paper, we exploit additional notable features in optical near-field interactions, which are physical hierarchy in optical nearfields and the properties associated with energy dissipation processes. We present their theoretical backgrounds and their applications. We deal with security aspects of optical near-field interactions by noticing environmental factors. We also demonstrate hierarchical systems based on dipole-dipole interactions and angular spectrum representation of optical near-fields as well as associating them with energy dissipation processes, which lead to another functionality such as traceability of information.

The extinction spectra of hole arrays in a silver film are investigated with discrete dipole approximation method. The influences of distances between holes to the extinction spectra are explored; the effects of shapes and sizes of holes on the extinction spectra are also probed. For holes of the same areas, simulations show that the holes with square and rectangular shapes exhibit more efficient couplings compared with the circular ones. The increased aspect ratios (length/width) of rectangular holes perpendicular to the polarization direction strengthen their couplings. The influences of hole distances to the extinction spectra are examined. In the simulations, the lattice areas of hole arrays are first kept to be a constant (400×400 nm²), and then allowed to be changed with one fixed edge length of the rectangular lattice arrays. The calculations indicate that the extinction resonance wavelengths are more sensitive to the hole spacings along the polarization direction. The distance variations perpendicular to the polarization direction only alter the strengths of the coupling between holes and show little impact to the resonance wavelengths.

In this paper, we introduce an analytic effective medium theory of plasmonic metamaterials founded on electrostatic eigenfunctions of plasmon states. The emphasis is on the sub-wavelength particles and metamaterials with unit cell much smaller than the optical wavelength. The theory covers plasmonic structures with arbitrary degree of symmetry: from completely asymmetric (including chiral) structures to fully isotropic ones. We also review several previously reported theoretical techniques used for calculating the effective parameters of plasmonic metamaterials in connection with our new theory. Several examples of negative permittivity and negative permeability plasmonic metamaterials are used to illustrate the theory.

Superlens imaging based on negative refractive index behavior of surface plasmon polaritons is described. The design of a magnifying superlens is based on two-dimensional plasmonic metamaterials consisting of alternating layers of positive and negative refractive index.

The behaviors of multiple resonances (or surface plasmon modes) produced by electrically small (the dimension of the sphere is much smaller than the wavelength) metallic nanospheres and coated nanospheres (whose outer radius is much smaller than the wavelength) are addressed in this paper. The plasmon resonances for electrically small nanospheres happen when the real part of the relative plasmon permittivity is near Re[ε_r(ω_n)] = -(n+1)/n, where n = 1, 2, ... The peak values of the scattered field are shown versus the angle of incidence for different n and electrical parameter q (q = k₀a where k₀ denotes the wavenumber in free space and a stands for the radius of the sphere). New formulas for extinction and scattering cross sections for both cases have been derived and given. For coated structures, the situation is a bit more complicated. The scattered field near resonances can be enhanced significantly with small dissipation of the relative permittivity. Within the instrumental error, the spectral range, within which the material Ag has low dissipation so that we can get the greatest scattering energy, is considered for the coated sphere. Two cases, i.e., silver core and coating, are investigated. The relative parameters such as the refractive indices of the core m₁ and the coating m₂, and the volume ratio f (f = a³/b³ where a and b denote the inner and outer radii of the coated sphere) have been derived at resonances. The near field energy intensity distributions around the coated sphere are also shown. The peak value of the scattered energy intensity is given for the lossless cases. This optical property may have potential applications in surface cleaning, etching, nanopatterning and so on.

Nano-optoelectronics devices are those realizing functions of signal transfer/processing in nanometer scale based on optical near-field excitation transfer between nanometer-sized electronic systems. Important issues involved in fabricating and operating nano-optoelectronics devices are to understand and control space-time correlation and hierarchy feature involved in optical near-field interactions as well as dissipation processes as the basis of unidirectional excitation transfer in non-equilibrium open system. In this work, we study the function and fundamental processes of nano-optoelectronics devices from these view points.

A long range surface plasmon polaritons Bragg grating is investigated by a complex mode matching method. A high order finite difference method is employed to find the complex eigenmodes. Benefited from the cascading and doubling algorithm, the computation effort is significantly saved for Bragg gratings with large number of periods. Numerical results are verified by previous reported experiments.

We apply an efficient eigen-decomposition method to analyze the plasmonic modes in metal nanoparticle structures. The proposed method has the advantage of simultaneously showing the dispersion relation and the mode quality, and at the same time, it also separates the material properties from the geometrical properties so that its efficiency, therefore, does not depend on the complexity of the material polarizability. We use the method to analyze the guided plasmonic modes of single metal nanoparticle chain and a pair of chains. Closed form solutions for all modes, including in-plane and out-of- plane modes, are given. We discuss the evolution of the dispersion relation as the complexity of the structure increases.

In this work, we report the substantial compensation of loss of propagating SPPs at the interface between silver film and optically pumped polymer with dye. The large magnitude of the effect, nearly threefold change of the reflectivity, enables a variety of applications of "active" nanoplasmonics. In order to quantify the observed phenomenon, we have extended the theoretical formalism relating the reflectivity in ATR experiment and the SPP propagation length to the case of active dielectric media.

Single silver nanorod (the size is much less than the optical wavelength) is an excellent surface plasmon generator. Under the interaction with a polarized optical wave, the s1ilver nanorod behaves like a funnel of the electromagnetic field, the gathered electromagnetic fields (surface plasmons) surround the nanorod. Due to the effect of the localization, the surface plasmons are highly enhanced in comparison with the incident wave. Consider a hexagonal nanocrystal which is constructed by identical silver nanorods, and the nanorods are embedded in a silica block. As a polarized optical wave illuminates on the crystal, a nanoimage is formed by the coupling of surface plasmons below the crystal. Interestingly, the nanoimage is dependent on the direction of the polarization, that is, the nanoimages are varied with the rotation of the polarization. On the other point of view, the nanocrystal is like a nano-kaleidoscope. The intensity of the nanoimage is higher than the incident wave, if the patterns of the nanoimages can be controlled, the applications of the nanoimages will never to be overlooked.

We developed an optical fiber biosensor based on localized surface plasmon resonance in gold nanoparticles. The sensor system enables us to analyze biological molecules in ultra small amount of analytes. In spite of a simple optical setup, the limit of detection of avidin was about 0.09 μg/mL, which was similar to the value previously reported in a standard absorption experiment. Since the sensor probe is made at the endface of the optical fiber, it has following advantages: (1) it is easy to handle, and (2) it is possible to detect a small amounts of samples (<1μL) such as DNA and proteins. Because of the feature (2), it is possible to carry out DNA and protein detection with a sample solution of 100 nL.

In the optical lithography technique, the higher aspect ratio is critical as well as small spot size. To achieve higher aspect ratio with the same nano scale spot size, in this report, we control the confocal parameters of Ag superlens by changing the position of lens. In our FDTD (Finite Difference Time Domain) calculation, Drude dispersion is employed to represent the frequency-dependent permittivity of the Ag superlens while the refractive index of Ag matches with the host material, air and PMMA, at the wavelength of 338nm and 360nm. By changing the wavelength from 330nm to 340nm, in addition, we investigated the tunable superlensing effects and the amplification of evanescent wave with Ag slab related to surface plasmon polariton. Consequently, we observed the variation of the confocal parameters of Ag superlens depending on the position and the tunable wavelength in our results.