<b>Analytical and approximation approaches to solve the hybrid plasmonic–plasmonic only transition of the TM</b>_{<strong>0</strong>}<b> mode in a dielectric-semiconductor-insulator-metal four layer structure</b>

An analytical solution to the fundamental TM0 mode on the model system of a dielectric-semiconductor-insulator-metal four layered planar structure is obtained. A transition from the ‘hybrid plasmonic’ mode to ‘plasmonic only’ mode is ratified by the change from sinusoidal to exponential wave functions in the semiconductor layer as the propagation constant of the TM0 mode exceeds that of the light in bulk form of the semiconductor. A variational method based on the mode hybridization picture is proposed to approximate the dispersion relation of the fundamental TM0 mode. It is demonstrated that the variational method can well produce the dispersion relation of the TM0 mode in the ‘hybrid plasmonic’ region but deviate significantly in ‘plasmonic only’ region if the trial wave function based on mode hybridization is used, which suggests that the mode hybridization idea should only be applied to the ‘hybrid plasmonic’ region.</p

Low loss photonic nanocavity via dark magnetic dipole resonant mode near metal

The dielectric-semiconductor-dielectric-metal 4 layered structure is a well-established configuration to support TM hybrid plasmonic modes, which have demonstrated significant advantages over pure photonic modes in structures without metal to achieve low loss resonant cavities at sub-diffraction limited volumes. The photonic modes with TE characteristics supported by the same 4 layered structure, on the other hand, are less studied. Here we show that a low loss photonic mode with TE01 characteristics exists in the dielectric-semiconductor-dielectric-metal 4 layered structure if a truncated cylindrical disk is chosen as the semiconductor core. This mode exhibits the lowest cavity loss among all resonant modes, including both pure photonic and hybrid plasmonic modes, at cavity radius <150 nm and within the wavelength range 620 nm to 685 nm, with a footprint ~0.83 (λ/2neff)2, physical size ~0.47 (λ/2neff)3 and a mode volume down to 0.3 (λ/2neff)3. The low cavity loss of this TE01 mode is attributed to its substantially reduced radiation loss to the far field by the creation of image charges through the metal response. Because of the low mode penetration in the metal, this photonic mode show equally low cavity loss near industry relevant metals such as Cu. Our study demonstrates an alternative to hybrid plamonic modes and metallo-dielectric modes to achieve low loss cavities with extremely small footprints

A framework for far-field infrared absorption microscopy beyond the diffraction limit

A framework is proposed for infrared (IR) absorption microscopy in the far-field with a spatial resolution below the diffraction limit. The sub-diffraction resolution is achieved by pumping a transient contrast in the population of a selected vibrational mode with IR pulses that exhibit alternating central minima and maxima, and by probing the corresponding absorbance at the same wavelength with adequately delayed Gaussian pulses. Simulations have been carried out on the basis of empirical parameters emulating patterned thin films of octadecyltrichlorosilane and a resolution of 250 nm was found when probing the CH2 stretches at 3.5 mu m with pump energies less than ten times the vibrational saturation threshold. (C) 2012 Optical Society of Americ

A Universal study on the effect thermal imidization has on the physico-chemical, mechanical, thermal and electrical properties of polyimide for integrated electronics applications

Polyimides (PI) are a class of dielectric polymer used in a wide range of electronics and electrical engineering applications from low-voltage microelectronics to high voltage isolation. They are well appreciated because of their excellent thermal, electrical, and mechanical properties, each of which need to be optimized uniquely depending on the end application. For example, for high-voltage applications, the final polymer breakdown field and dielectric properties must be optimized, both of which are dependent on the curing process and the final physico-chemical properties of PI. The majority of studies to date have focused on a limited set of properties of the polymer and have analyzed the effect of curing from a physicochemical-, mechanical- or electrical?centric viewpoint. This paper seeks to overcome this, unifying all of these characterizations in the same study to accurately describe the universal effect of the cure temperature on the properties of PI and at an industrial processing scale. This paper reports the widest-ranging study of its kind on the effect that cure temperature has on the physico-chemical, mechanical, thermal and electrical properties of polyimide, specifically poly (pyromellitic dianhydride-co-4, 40 -oxydianiline) (PMDA/ODA). The optimization of the cure temperature is accurately studied not only regarding the degree of imidization (DOI), but also considering the entire physical properties. Particularly, the analysis elucidates the key role of the charge–transfer complex (CTC) on these properties. The results show that while the thermal and mechanical properties improve with both DOI and CTC formation, the electrical properties, particularly at high field conditions, show an antagonistic behavior enhancing with increasing DOI while degrading at higher temperatures as the CTC formation increases. The electrical characterization at low field presents an enhancement of the final PI properties likely due to the DOI. On the contrary, at high electric field, the conductivity results show an improvement at an intermediate temperature emphasizing an ideal compromise between a high DOI and PI chain packing when the thermal imidization process is performed over this equilibrium. This balance enables maximum performance to be obtained for the PI film with optimized electrical properties and, overall, optimal thermal and mechanical properties are achieved. </p

Ultrathin oxide controlled photocurrent generation through a metal–insulator– semiconductor heterojunction

Recent advances in nanoscale lasers, amplifiers, and nonlinear optical converters have demonstrated the unprecedented potential of metal–insulator–semiconductor (MIS) structures as a versatile platform to realize integrated photonics at the nanoscale. While the electric field enhancement and confinement have been discussed intensively in MIS based plasmonic structures, little is known about the carrier redistribution across the heterojunction and photocurrent transport through the oxide. Herein, we investigate the photo-generated charge transport through a single CdSe microbelt-Al2O3-Ag heterojunction with oxide thickness varying from 3 nm to 5 nm. Combining photocurrent measurements with finite element simulations on electron (hole) redistribution across the heterojunction, we are able to explain the loss compensation observed in hybrid plasmonic waveguides at substantially reduced pump intensity based on MIS geometry compared to its photonic counterpart. We also demonstrate that the MIS configuration offers a low-dark-current photodetection scheme, which can be further exploited for photodetection applications.</p

APTES duality and nanopore seed regulation in homogeneous and nanoscale-controlled reduction of Ag shell on SiO2 microparticle for quantifiable single particle SERS

Noble-metal nanoparticles size and packing density are critical for sensitive surface-enhanced Raman scattering (SERS) and controlled preparation of such films required to achieve reproducibility. Provided that they are made reliable, Ag shell on SiO2 microscopic particles (Ag/SiO2) are promising candidates for lab-on-a-bead analytical measurements of low analyte concentration in liquid specimen. Here, we selected nanoporous silica microparticles as a substrate for reduction of AgNO3 with 3-aminopropyltriethoxysilane (APTES). In a single preparation step, homogeneous and continuous films of Ag nanoparticles are formed on SiO2 surfaces with equimolar concentration of APTES and silver nitrate in ethanol. It is discussed that amine and silane moieties in APTES contribute first to an efficient reduction on the silica and second to capping the Ag nanoparticles. The high density and homogeneity of nanoparticle nucleation is further regulated by the nanoporosity of the silica. The Ag/SiO2 microparticles were tested for SERS using self-assembled 4-aminothiophenol monolayers, and an enhancement factor of ca. 2 × 106 is measured. Importantly, the SERS relative standard deviation is 36% when a single microparticle is considered and drops to 11% when sets of 10 microparticles are considered. As prepared, the microparticles are highly suitable for state-of-the-art quantitative lab-on-a-bead interrogation of specimens

Comparative analysis of metals and alternative infrared plasmonic materials

In the past decade or two, the field of nanophotonics has seen rapid development, empowered by introducing the concepts of plasmonics and metamaterials. The enabling feature behind this progress has been the use of noble metals that exhibit negative dielectric permittivities over a wide spectral range of visible and infrared wavelengths that allowed for manipulating the light on the subwavelength scale. Consequently, numerous interesting phenomena that otherwise do not exist in nature have been demonstrated in laboratories, but their transitions to practical applications have been painfully slow due to the large ohmic losses that are inherent in all metals. Doped semiconductors with lower losses have been proposed as new plasmonic materials to replace noble metals. Because the electron densities that are introduced with the artificial doping are always a few order of magnitude lower than what naturally available in metals, their plasma frequencies are shifted considerably toward longer wavelengths to the infrared (IR). This work compares these two categories of plasmonic media in structures that support either localized or propagating surface plasmon polaritons (SPPs) in mid-IR We have found that in both cases new plasmonic materials underperform noble metals in terms of enhancing optical field in localized SPPs and reducing SPP propagation loss in plasmonic waveguides. The cause of this subpar performance is the inherently low electron density that yields a significantly reduced plasma frequency compared to noble metals. This fundamental property associated with all new plasmonic materials dictates that, while new materials do hold a number of advantages, including tunability and ability to withstand high temperatures, noble metals, even with their ohmic losses, are not likely to be replaced in the foreseeable future

Surface plasmon propagation enhancement via bowtie antenna incorporation in au-mica block waveguides

The optimum geometry for waveguide propagation was determined by comparing bowtie and semicircle antenna cuts to a standard plain waveguide with a 635 nm laser. The results of both experimental data and COMSOL simulations proved that the bowtie antenna increased waveguide output in comparison to the plain waveguide with the semicircle pattern showing no enhancement. It was also determined that the propagation was highest when the polarization direction of the laser was perpendicular to the direction of the waveguide for all patterns, while polarization along the propagation direction led to little or no output in all antenna and plain waveguide cases. The waveguide output of the bowtie antenna and plain structures was then measured using a tunable laser for wavelengths from 570 nm to 958 nm under both parallel and perpendicular polarization conditions. The results indicated that the bowtie antenna performed better over the entire range with an average increase factor of 2.12 ±0.40 over the plain waveguide pattern when perpendicularly polarized to the waveguide direction, and 1.10±0.48 when parallel. The measured values indicate that the structure could have applications in broadband devices

High resolution imaging with differential infrared absorption micro-spectroscopy

Although confocal infrared (IR) absorption micro-spectroscopy is well established for far-field chemical imaging, its scope remains restricted since diffraction limits the spatial resolution to values a little above half the radiation wavelength. Yet, the successful implementations of below-the-diffraction limit far-field fluorescence microscopies using saturated irradiation patterns for example for stimulated-emission depletion and saturated structured-illumination suggest the possibility of using a similar optical patterning strategy for infrared absorption mapping at high resolution. Simulations are used to show that the simple mapping of the difference in transmitted/reflected IR energy between a saturated vortex-shaped beam and a Gaussian reference with a confocal microscope affords the generation of high-resolution vibrational absorption images. On the basis of experimentally relevant parameters, the simulations of the differential absorption scheme reveal a spatial resolution better than a tenth of the wavelength for incident energies about a decade above the saturation threshold. The saturated structured illumination concepts are thus expected to be compatible with the establishment of point-like point-spread functions for measuring the absorbance of samples with a scanning confocal microscope recording the differential transmission/reflection. (C) 2013 Optical Society of Americ

Surface-ligand-modified CdSe/CdS nanorods for high-performance light-emitting diodes

Colloidal nanocrystals (NCs) play an important role in the field of optoelectronic devices such as photovoltaic cells, photodetectors, and light-emitting diodes (LEDs). The properties of NC films are strongly affected by ligands attached to them, which constitute a barrier for charge transport between adjacent NCs. Therefore, the method of surface modification by ligand exchange has been used to improve the electrical conductivity of NC films. However, surface modification to NCs in LEDs can also affect emission characteristics. Among NCs, nanorods have unique properties, such as suppression of nonradiative Auger recombination and linearly polarized light emission. In this work, CdSe/CdS nanorods (NRs) were prepared by the hot injection method. To increase the charge transport into CdSe/CdS NRs, we adopted ligand modification to CdSe/CdS NRs. Using this technique, we could shorten the injection barrier length between CdSe/CdS NRs and adjacent layers. It leads to a more balanced charge injection of electron/hole and a greatly increased current efficiency of CdSe/CdS NR-LEDs. In the NR-LEDs, the ligand exchange boosted the electroluminance, reaching a sixfold increase from 848 cd/m2 of native surfactants to 5600 cd/m2 of the exchanged n-octanoic acid ligands at 12 V. The improvement of CdSe/CdS NR-LED performance is closely correlated to the efficient control of charge balance via ligand modification strategy, which is expected to be indispensable to the future NR-LED-based optoelectronic system</p