Showing papers in "Journal of Nanophotonics in 2013"
TL;DR: In this article, the authors proposed a nanowire (NW)-based nanolasers utilizing AlGaInN materials system, which are an emerging and promising area of research.
Abstract: One-dimensional compound semiconductor nanolasers, especially nanowire (NW)-based nanolasers utilizing III-nitride (AlGaInN) materials system, are an emerging and promising area of research. Significant achievements have been made in developing III-nitride NW lasers with emission wavelengths from the deep ultraviolet (UV) to the near-infrared spectral range. The types of lasers under investigation include Fabry-Perot, photonic crystal, plasmonic, ring resonator, microstadium, random, polariton, and two-dimensional distributed feedback lasers. The lasing thresholds vary by several orders of magnitude, which are a direct consequence of differing NW dimensions, quality of the NWs, characteristics of NW cavities, and coupling with the substrate. For electrically injected, such as ultralow-threshold and continuous-wave III-nitride NW lasers that can operate at room temperature, the following obstacles remain: carrier loss mechanisms including defect-related nonradiative surface recombination, electron overflow, and poor hole transport; low radiative recombination efficiency and high surface recombination; poor thermal management; and highly resistive ohmic contacts on the p -layer. These obstacles must be overcome to fully realize the potential of these lasers.
111 citations
TL;DR: In this article, a multilayer graphene-dielectric composite material, comprising graphene sheets separated by subwavelength-thick dielectric spacer, was investigated, and found it to exhibit hyperbolic isoffrequency wavevector dispersion at far-and mid-infrared frequencies, allowing propagation of waves that would be otherwise evanescent in an isotropic Dielectric.
Abstract: We investigated a multilayer graphene-dielectric composite material, comprising graphene sheets separated by subwavelength-thick dielectric spacer, and found it to exhibit hyperbolic isofrequency wavevector dispersion at far- and mid-infrared frequencies, allowing propagation of waves that would be otherwise evanescent in an isotropic dielectric. Electrostatic biasing was considered for tunable and controllable transition from hyperbolic to elliptic dispersion. We explored the validity and limitation of the effective medium approxi- mation (EMA) for modeling wave propagation and cutoff of the propagating spatial spectrum due to the Brillouin zone edge. We reported that EMA is capable of predicting the transition of the isofrequency dispersion diagram under certain conditions. The graphene-based composite material allows propagation of backward waves under the hyperbolic dispersion regime and of forward waves under the elliptic regime. Transition from hyperbolic to elliptic dispersion regimes is governed by the transverse epsilon-near-zero (TENZ) condition, which implies a flatter and wider propagating spectrum with higher attenuation, when compared to the hyper- bolic regime. We also investigated the wide-angle tunable transparency of the multilayer at that condition in contrast to other materials exhibiting ENZ phenomena. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.7.073089)
92 citations
TL;DR: In this article, it was shown that a free material particle absorbs light having spin or twist, it is itself made to spin, in other words, the light exerts a rotational form of radiation pressure.
Abstract: A thin light beam, such as that emitted by a laser, may possess a hidden rotational structure, invisible to the naked eye. This structure is rooted in the electromagnetic wave nature of light and it takes two distinct forms, which may be dubbed spin and twist . Spin is associated with the rotation of the electric and magnetic fields oscillating within the optical wave—i.e., the circular polarization of light. Twist instead occurs in light waves having a helical-shaped (or twisted) wavefront and an optical vortex located at the beam axis. When a free material particle absorbs light having spin or twist, it is itself made to spin—in other words, the light exerts a rotational form of radiation pressure, showing that this kind of light carries angular momentum . More specifically, the angular momentum of light having circular polarization is named as spin angular momentum (SAM), while that associated with a spiral wavefront is called orbital angular momentum (OAM). The OAM of light has recently been attracting much attention for its possible technological applications in the areas of particle manipulation, optical sensing, and classical and quantum optical communication.
59 citations
TL;DR: In this paper, the results of a broadband dielectric investigation of multiwalled CNT (MWCNT)/epoxy resin composites in wide temperature range from room temperature to 450 K were analyzed for percolation.
Abstract: Many attempts have been made to fully explore flexibility, resistance to corrosion, and processing advantage of epoxy resin filled with carbon nanotubes (CNTs) as conductive filler, although sometimes with a certain degradation of polymers’ intrinsic properties. It is important to move the percolation threshold into the region of smaller CNTs’ concentration. The results of a broadband dielectric investigation of multiwalled CNT (MWCNT)/epoxy resin composites in wide temperature range from room temperature to 450 K were analyzed for percolation. Far below the percolation threshold (0.25 wt. % MWCNT) the dielectric properties of the composite are mostly determined by alpha relaxation in pure polymer matrix and the freezing temperature decreases due to the extra free volume at the polymer–filler interface. Close to the percolation threshold, the composite shows the negative temperature coefficient effect in the temperature region, where the pure polymer matrix becomes conductive. The activation energy of DC conductivity increases with the MWCNT concentration far below the percolation threshold and decreases close to it (1.5 wt. % MWCNT). The dielectric analysis of the MWCNT/epoxy resin reveals a significant influence of the polymer matrix on the temperature dependence of composite dielectric properties.
33 citations
TL;DR: In this paper, a quasi-solid-state dye-sensitized solar cell (DSSC) based on graphene-modified mesoscopic carbon-counter electrode is developed, which has a power conversion efficiency (PCE) of 5.09% with the fill factor of 0.63 at 100mW cm −2 AM1.5 illumination.
Abstract: A monolithic quasi-solid-state dye-sensitized solar cell (DSSC) based on graphene-modified mesoscopic carbon-counter electrode is developed. A TiO 2 -working electrode layer, ZrO 2 spacer layer, and carbon counter electrode layer were constructed on a single conducting glass substrate by screen printing. The quasi-solid-state polymer gel electrolyte employed a polymer composite as the gelator, and effectively infiltrated the porous layers. Fabricated with normal carbon-counter electrode (NC-CE) containing graphite and carbon black, the DSSC had a power conversion efficiency (PCE) of 5.09% with the fill factor of 0.63 at 100 mW cm −2 AM1.5 illumination. When the NC-CE was modified with graphene sheets, the PCE and fill factor were enhanced to 6.27% and 0.71, respectively. This improvement indicates excellent conductivity and high electrocatalytic activity of the graphene sheets, which have been considered as a promising platinum-free electrode material for DSSCs.
31 citations
TL;DR: Oblique angle deposition (OAD) has been widely used in the development of well-controlled three-dimensional nanomorphologies such as zigzags and helixes as discussed by the authors, however, most companies seem hesitant to introduce OAD techniques into the factory, owing to the prejudice that OAD thin films are neither durable nor reproducible.
Abstract: Even prior to the recent advent of advanced top-down processes, shadowing growth by oblique angle deposition (OAD) has long been providing self-assembled nanostructures over much larger areas for much lower costs. In the past two decades, significant progress has been made in the development of well-controlled three-dimensional nanomorphologies such as zigzags and helixes. Much effort has been put into theoretical and numerical understanding of the growth mechanism to improve morphology. Many researchers in academia have been investigating useful properties of nanocolumnar thin films in their laboratories. However, most companies seem hesitant to introduce OAD techniques into the factory, owing to the prejudice that the OAD thin films are neither durable nor reproducible. The progress in OAD technology for practical applications is reviewed and discussed.
30 citations
TL;DR: In this article, three different antireflecting structures (ARS) were compared to each other analytically for their reflectivities, using finite difference time domain calculations, in the visible and near-infrared wavelength zone and over a wider angle of incidence.
Abstract: Three different antireflecting structures (ARS), namely, single-diameter nanorods, dual-diameter nanorods, and biomimetic nanotips (resembling moth-eye’s submicrostructures) were compared to each other analytically for their reflectivities, using finite difference time domain calculations. Simulation results establish the biomimetic nanotips as better ARS than the others, in the visible and near-infrared wavelength zone and over a wider angle of incidence. The reflectance values in the nanotips are significantly lower compared to both types of nanorods and also the planar silicon below the Brewster angle (∼75 deg ). The low antireflection translated to enhanced optical absorption in these subwavelength structures. A general antireflection design rule emerged from the simulation results.
30 citations
TL;DR: Martinez-Duart et al. as mentioned in this paper discuss photovoltaics firmly moving to the terawatt scale, and discuss the potential of the Photovoltaic system.
Abstract: Martinez-Duart, J.M., Hernandez-Moro, J., "Commentary: Photovoltaics firmly moving to the terawatt scale", Journal of Nanophotonics, Society of Photo Optical Instrumentation Engineers, 7(1), 078599, (2013). Copyright The Authors 2014 Society of Photo Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited
22 citations
TL;DR: In this article, the role of the electric and magnetic polarization in the Raman selection rules is discussed and a comparison of the retarded and unretarded approaches can be found in Section 2.7.
Abstract: Raman scattering is a nondestructive technique that is able to supply information on the crystal and electronic structures, strain, temperature, phonon-phonon, and electron-phonon interaction. In the particular case of semiconductor nanowires, Raman scattering provides addi- tional information related to surfaces. Although correct, a theoretical approach to analyze the surface optical modes loses critical information when retardation is neglected. A comparison of the retarded and unretarded approaches clarifies the role of the electric and magnetic polarization in the Raman selection rules. Since most III-V compounds growing in the zincblende phase change their crystal structure to wurtzite when growing as nanowires, the polariton description will be particularized for these two important crystal phases. Confined phonons exist in cylin- drical nanowires and couple with longitudinal and transverse modes due to the presence of the nanowire's surface. This coupling vanishes in the case of rotational symmetry. The boundary conditions of the electromagnetic fields on small-size nanowires (antenna effect) have a dramatic effect on the polarization properties of a Raman spectrum. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.7.071598)
22 citations
TL;DR: In this article, the elastic constants of 100 to 500 nm thick nanoporous low-k dielectric materials of significant interest for reducing capacitive delays in nanoelectronic interconnect circuits were determined.
Abstract: Brillouin light scattering (BLS) and picosecond laser ultrasonics (PLU) are two noncontact optical techniques that have garnered significant interest for thin film elastic constant measurements. PLU and BLS measurements were utilized to determine the elastic constants of 100 to 500 nm thick nanoporous low-k dielectric materials of significant interest for reducing capacitive delays in nanoelectronic interconnect circuits. PLU measurements with and without a metal acousto-optic transducer are described in detail and compared to previously reported BLS measurements. The values of Young’s modulus determined by both BLS and PLU were found to be in excellent agreement and consistent with nanoindentation measurements on thicker 2 micrometer films. While successful BLS measurements were achieved for films as thin as 100 nm, PLU measurements were limited to >∼200 nm thick films due to experimental constraints on observing acoustic pulses in thinner films. However, these results clearly demonstrate the capability of both BLS and PLU to determine the elastic constants of low-k dielectric materials at the desired thickness targets for future nanoelectronic interconnect technologies.
20 citations
TL;DR: In this article, a multiphysics approach was adopted to analyze thermal, electrical, and electromagnetic effects in a dipole antenna functioning as a resonant distributed bolometer and the results showed that bolometric performance depends on the choice of materials, the geometry of the resonant structure, the thickness of an insulating layer, and the characteristics of a bias circuit.
Abstract: The electric currents induced by infrared radiation incident on optical antennas and resonant structures increase their temperature through Joule heating as well as change their elec- tric resistance through the bolometric effect. As the thermo-electric mechanism exists throughout a distributed bolometer, a multiphysics approach was adopted to analyze thermal, electrical, and electromagnetic effects in a dipole antenna functioning as a resonant distributed bolometer. The finite element method was used for electromagnetic and thermal considerations. The results showed that bolometric performance depends on the choice of materials, the geometry of the resonant structure, the thickness of an insulating layer, and the characteristics of a bias circuit. Materials with large skin depth and small thermal conductivity are desirable. The thickness of the SiO2 insulating layer should not exceed 1.2 μm, and a current source for the bias circuit enhances performance. An optimized device designed with the previously stated design rules provides a response increase of two orders of magnitude compared to previously reported devices using the same dipole geometry. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JNP.7.073093)
TL;DR: In this article, a collagen thin film consisting of randomly oriented and oriented collagen fibrils/fibers is fabricated by hydrodynamic flow and spin coating, and then they are characterized by atomic force microscopy (AFM).
Abstract: Collagen thin films consisting of randomly oriented and oriented collagen fibrils/fibers are fabricated by hydrodynamic flow and spin coating, and then they are characterized by atomic force microscopy (AFM). Fibroblasts are cultured on these films in order to correlate their morphology and alignment, which are assessed with fluorescence and AFM imaging with different film characteristics. The results showed that the formed films could be used as substrates for culturing cells. Furthermore, cells reacted to film nanocharacteristics and especially to the orientation of fibrils/fibers. The investigation of the influence that the substrate nanotopography has on cells will help to elucidate the mechanisms of cell–biomaterial interactions, and will enable the design of intelligent coatings for implants and tissue engineering purposes.
TL;DR: In this article, an optically characterized hydrogenated amorphous silicon photonic resonators for label-free lab-on-chip biosensors were used for the precise detection of chemicals and biomolecules.
Abstract: The precise detection of chemicals and biomolecules is of great interest in the areas of biotechnology and medical diagnostics. Thus, there is a need for highly sensitive, small area, and low-cost sensors. We fabricated and optically characterized hydrogenated amorphous silicon photonic resonators for label-free lab-on-chip biosensors. The sensing was performed with small-footprint microdisk and microring resonators that detect a refractive-index change via the evanescent electric field. Homogeneous sensing with NaCl and surface-sensing experiments with immobilized bovine serum albumin (BSA) were carried out. A sensitivity as high as 460 nm∕RIU was measured for NaCl dissolved in deionized water for the disk, whereas about 50 nm∕RIU was determined for the ring resonator. The intrinsic limits of detection were calculated to be 3.3 × 10 −4 and 3.2 × 10 −3 at 1550-nm wavelength. We measured the bind- ing of BSA to functionalized ring resonators and found that molecular masses can be detected down to the clinically relevant femtogram regime. The detection and quantification of related analytes with hydrogenated amorphous silicon photonic sensors can be used in medical health- care diagnostics like point-of-care-testing and biotechnological screening. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or repro- duction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JNP.7.073793)
TL;DR: A silicon light-emitting device is designed and realized in standard 3-μm complemen- tary metal oxide semiconductor (CMOS) integrated circuitry as discussed by the authors, which can be integrated with its signal processing CMOS and BiCMOS circuits on the same chip, thus enabling the fabrication of much needed all-silicon monolithic optoelectronic systems operated by a single supply.
Abstract: A silicon light-emitting device is designed and realized in standard 3-μm complemen- tary metal oxide semiconductor (CMOS) integrated circuitry. Accordingly, it can be integrated with its signal processing CMOS and BiCMOS circuits on the same chip, thus enabling the fabrication of much needed all-silicon monolithic optoelectronic systems operated by a single supply. The device emitted light in a broad, bell-shaped spectrum from 500 to 850 nm with characteristic peaks at 650 and 750 nm. Initial investigations indicate that the quantum efficiency is of the order of 10 −8 and the electric-to-optical power conversion efficiency is of the order of 10 −9 . This silicon light-emitting device has obvious applications in the electro-optical inter- connect. © 2013 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.7
TL;DR: Surface-enhanced Raman spectroscopy biotags that carry peptides as cell recognition moieties that can provide cell identification in flow are found, insensitive to normal causes of uncertainty in optical measurements such as variations in focal plane, cell concentration, autofluorescence, and turbidity.
Abstract: Surface-enhanced Raman spectroscopy (SERS) biotags (SBTs) that carry peptides as cell recognition moieties were made from polymer-encapsulated silver nanoparticle dimers, infused with unique Raman reporter molecules. We previously demonstrated their potential use for identification of malignant cells, a central goal in cancer research, through a multiplexed, ratiometric method that can confidently distinguish between cancerous and noncancerous epithelial prostate cells in vitro based on receptor overexpression. Progress has been made toward the application of this quantitative methodology for the identification of cancer cells in a microfluidic flow-focusing device. Beads are used as cell mimics to evaluate the devices. Cells (and beads) are simultaneously incubated with two sets of SBTs while in suspension, then injected into the device for laser interrogation under flow. Each cell event is characterized by a composite Raman spectrum, deconvoluted into its single components to ultimately determine their relative contribution. We have found that using SBTs ratiometrically can provide cell identification in flow, insensitive to normal causes of uncertainty in optical measurements such as variations in focal plane, cell concentration, autofluorescence, and turbidity.
TL;DR: A new nanotechnological transporter, gH625, is based on a viral peptide sequence derived from the herpes simplex virus type 1 glycoprotein H (gH) that has proved to be a useful delivery vehicle, due to its intrinsic properties of inducing membrane perturbation.
Abstract: The internalization of bioactive molecules is one of the most critical problems to overcome in theranostics In order to improve pharmacokinetic and pharmacodynamic proper- ties, synthetic transporters are widely investigated A new nanotechnological transporter, gH625, is based on a viral peptide sequence derived from the herpes simplex virus type 1 glycoprotein H (gH) that has proved to be a useful delivery vehicle, due to its intrinsic properties of inducing membrane perturbation The peptide functionalization with several kinds of nanoparticles like quantum dots, dendrimers, and liposomes could be of particular interest in biomedical applica- tions to improve drug release within cells, to increase site-specific action, and eventually to reduce related cytotoxicity © The Authors Published by SPIE under a Creative Commons Attribution 30 Unported License Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI (DOI: 101117/1JNP7071599)
TL;DR: The new book by G. A. Mansoori et al. on diamondoid molecules may be one of the first steps toward a paradigm shift in the pharmaceutical and biotech industry, with a thorough presentation of current and future applications of diamondoids.
Abstract: The pharmaceutical and biotech industries face difficult problems. Namely, enormous amounts of capital are spent on research and development, but a very small number of tested compounds become truly marketable. Moreover, many of the compounds currently on the market are, in essence, evolutionary designed. Thus, although it is equipped with the most advanced technology and backed up with a comprehensive theoretical framework, the current biotech industry lags in productivity when compared to the old-style, animal-model-based research. Some researchers have expressed their belief in a need for a paradigm shift. But what might that paradigm shift be? It may be a new way to screen and test molecules, but it could also be an introduction of a completely new set of molecular building blocks. The new book by G. A. Mansoori et al. on diamondoid molecules may be one of the first steps toward that shift. Diamondoid Molecules is a thorough presentation of current and future applications of diamondoids. It is composed of seven chapters and a comprehensive glossary. Every chapter is excellently illustrated with plenty of clearly designed figures and graphs and well-organized tables.
TL;DR: In this paper, counter-propagating plasmons have been used to control optical fields and SERS intensity at a plasmonic nanowire-nanoparticle (NW-NP) junction.
Abstract: Surface-enhanced Raman scattering (SERS) has emerged as a powerful tool to probe molecules at nanoscale. By utilizing plasmon polaritons on metallic nanowires, remote-excitation SERS can be achieved. Enhancement and modulation of remote-SERS intensity are vital for nano-optical spectroscopy. Counter-propagating plasmons have been excited in a plasmonic nanowire-nanoparticle (NW-NP) system and further utilized to perform remote-excitation SERS. By using the polarization of counter-propagating fields, remote-SERS intensity from NW-NP hot-spot junction was enhanced and modulated. Such capabilities of counter-propagating plasmons to control optical fields and SERS intensity at NW-NP junction can have implications in nanowire photonics and nano-optical spectroscopy.
TL;DR: In this article, a chronology of spectrometer development shows that a simple numerical point-of-view affords important insights, such as optical path volumes of about 1 mm3 and spectral resolutions of 10 to 23 nm.
Abstract: Miniaturized optical instruments have become very important in industry as smart
phones and tablet PCs increase in popularity. A chronology of spectrometer development shows that a simple numerical point of view affords important insights. A tiny spectrometer, which is smaller than a few millimeters size, cannot easily rely on the conventional Fraunhofer diffraction due to its optical criterion limit. As an alternate solution to build smaller spectrometers, a Fresnel spectrometer chip with a gradient line grating is attractive. The fabricated Fresnel spectrometers have optical path volumes of about 1 mm3 and spectral resolutions of 10 to 23 nm.
TL;DR: In this paper, a chiral sculptured thin film (STF) was fabricated with/without substrate rocking, and their transmittance spectrums for incident linearly and circularly polarized plane waves were measured.
Abstract: Chiral sculptured thin films (STFs) produced by substrate rotation during physical vapor deposition exhibit the circular Bragg phenomenon, whereby normally incident left- and right-circularly polarized plane waves are discriminated in a spectral regime called the circular Bragg regime. Theory had predicted that substrate rocking, in synchrony with substrate rotation, during deposition could suppress the propensity to exhibit the circular Bragg phenomenon. Therefore chiral STFs of a dielectric material were fabricated with/without substrate rocking, and their transmittance spectrums for incident linearly and circularly polarized plane waves were measured. With sufficient rocking amplitude, the discrimination between incident left- and right-circularly polarized light nearly vanished, whereas a Bragg phenomenon for all normally incident plane waves was observed. Thus, chiral STF technology can be used to produce both ordinary and circular-polarization Bragg filters.
TL;DR: Paper-supported solvent-responsive elastomeric opal films based on hard-soft core-interlayer-shell spheres featuring remarkably distinct iridescent reflection colors were investigated in this paper.
Abstract: Paper-supported solvent-responsive elastomeric opal films based on hard-soft core-interlayer-shell spheres featuring remarkably distinct iridescent reflection colors were investigated. By using extrusion and compression molding, elastomeric opal films could be obtained, which were incorporated into a porous paper sheet to build robust composites. Swelling of the opal paper composites caused by various solvents was accompanied with a tremendous photonic band gap shift of the reflection colors. The combination of the extraordinary optical properties of the elastomeric opal films used with the remarkable features of highly porous paper can be the basis for a whole family of polymer-based soft sensors featuring a fascinating optical, fast and reversible response.
TL;DR: In this article, a well-ordered Ag nanodot array on indium-tin-oxide (ITO) glass is adopted as a sensor platform based on surface-enhanced Raman scattering (SERS).
Abstract: Well-ordered Ag nanodot array on indium-tin-oxide (ITO) glass is adopted as a sensor platform based on surface-enhanced Raman scattering (SERS). SERS has attracted extensive attention in the development of sensitive chemical or biological sensors due to its property of the amplification of electromagnetic fields on a metal nanostructure. The key issue for the applications of SERS is to secure the fabrication technique of a noble metal nanostructured surface. For an SERS-active surface with stability and reproducibility, a Ag nanodot array is fabricated on the ITO glass using a nanoporous alumina mask with uniform through holes. The signal intensity of SERS from methylene blue (MB) adsorbed on the Ag nanodot array showed much stronger scattering than the one from the Ag film of 50-nm thick. The SERS intensity on the Ag nanodot array is consistently enhanced by increased concentration of MB. These results confirm that the Ag nanodot array on ITO glass can be utilized as a stable platform for the sensitive detection of chemical materials based on SERS. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or repro- duction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JNP.7.073798)
TL;DR: In this article, an exact analytical solution for the field distribution is obtained for the sinusoidal spatial variation of complex effective permit-tivity and permeability along a fixed direction, under the assumption that the wave impedance remains spatially uniform across the structure.
Abstract: Gradient refractive index metamaterials are of interest for various applications of transformation optics. Wave propagation through gradient index metamaterials using an exact analytical approach is investigated. Composite materials containing constituents with negative real and positive real indexes of refraction are considered. An exact analytical solution for the field distribution is obtained for the sinusoidal spatial variation of complex effective permit- tivity and permeability along a fixed direction, under the assumption that the wave impedance remains spatially uniform across the structure. Loss factors in the constituent materials can be different from each other corresponding to the realistic situations. Temporal dispersion can be arbitrary subject to the physical limitations imposed by the Kramers-Kronig relations. A numerical model based on the Z-transform is developed to verify the analytical results. The approach can be applied to arbitrary periodic refractive index profiles using the Fourier series method. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JNP.7.073086)
TL;DR: In this paper, a method to design quarter-wave dielectric multilayers, which exhibit reflection properties approximating a given reflection spectrum, was proposed, which can be used as a design procedure for N-band antireflection coatings.
Abstract: We devise a method to design quarter-wave dielectric multilayers, which exhibit reflection properties approximating a given reflection spectrum. The method can be used as a design procedure for N-band antireflection coatings. Dual- and three-band antireflection coatings are designed using this method.
TL;DR: A grating theory-based modeling approach for STFs as fully three-dimensional (3-D) periodic structures is developed and guidelines for robust design of STF-based devices are developed.
Abstract: Sculptured thin films (STFs) are nano-engineered materials that have controllable porosity, structural chirality, and periodicity in one, two, or three dimensions. They have been exploited in developing optical elements such as thin-film filters, polarizers, sensors, and waveguides for integrated optics. A grating theory-based modeling approach for STFs as fully three-dimensional (3-D) periodic structures is developed. Input for this model consists of a structural parameter set that is easily accessible experimentally. This parameter set is common to evaluating STFs from a fabrication as well as modeling perspective and thus furnishes a basis for developing appropriate process monitoring and control methods necessary for successful commercial production. Using the proposed model, a quantitative understanding of the limits of applicability of traditional modeling methods for STFs and guidelines for robust design of STF-based devices are developed. This knowledge gained is applied to explore STFs in two illustrative examples: (1) as a notch filter and (2) as a 3-D photonic crystal.
Abstract: A structurally right-handed chiral sculptured thin film (STF) with a central 90 deg-twist defect was made by thermal evaporation of chalcogenide glass and the use of a serial bi-deposition process to exhibit a narrowband hole in the spectrum of the right-circularly polarized light reflected when right-circularly polarized light is normally incident on the chiral STF. In an attempt to build a tunable filter, the chiral STF was then infiltrated with a highly birefringent nematic liquid crystal (LC), which caused a linear reflectance peak to redshift by ∼350 nm . But the circular Bragg phenomenon exhibited by the uninfiltrated chiral STF was greatly diminished owing to the similarity in the constitutive properties of the LC and the chalcogenide glass. No temperature dependence of the shifted peak was observed, which provided clear evidence that the LC molecules are not ordered inside the chiral STF but are randomly aligned instead.
TL;DR: In this article, the carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film was found to depend on the incidence polarization of the photoexciting beam.
Abstract: The carrier concentration injected from a silicon substrate to a copper phthalocyanine thin film was found to depend on the incidence polarization of the photoexciting beam. The modulation efficiency of terahertz transmission due to transverse-magnetic (TM)-polarized excitation is distinctly higher than that due to transverse-electric (TE)-polarized excitation. Underlying this difference is the enhancement of carrier injection when the TM-polarized light is more transmitted through the surface of organic thin films than the TE-polarization light.
TL;DR: In this paper, the dependence of magnitude of the electric near-field on the separation between metal nanoparticles for surface-enhanced Raman spectroscopy (SERS) substrates was experimentally verified.
Abstract: The dependence of magnitude of the electric near-field on the separation between metal nanoparticles for surface-enhanced Raman spectroscopy (SERS) substrates was experimentally verified. Diameters of gold-coated nanopores in a ceramic alumina substrate were varied to study the charge buildup near interparticle junctions and its effect on the enhancement factor due to SERS. The substrates were characterized by sensing a Rhodamine dye and calculating the associated Raman enhancement factors. Decreasing Au interparticle distance increases the electric near-field and shifts the plasmon resonance peak accordingly.
TL;DR: In this paper, the electron-lattice coupling properties of PbS quantum dots with different quantum confinement regimes (weak, moderate, and strong with radii 14, 11, and 7 nm, respectively) were investigated.
Abstract: Nanostructures of lead sulfide (E g ∼0.67 to 1.7 eV) corresponding to different quantum confinement regimes (weak, moderate, and strong with radii 14, 11, and 7 nm, respectively) have been synthesized through facile aqueous colloidal method and have been capped using poly vinyl alcohol. There is a marked difference in electron-lattice coupling properties as revealed through Fourier transform infrared data with strong quantum confined PbS quantum dots (QDs) exhibiting pronounced electron-lattice coupling characteristics. Opto-impedance characteristics of these samples suggest the enhanced mobility of charges, in particular under the supra gap excitation for strong quantum confined QDs.
TL;DR: Byun et al. as mentioned in this paper proposed an optical method of measuring the number of layers in a graphene sample and compared with the conventional surfaceplasmon resonance (SPR)detections.
Abstract: Kyung Hee University, Department of Biomedical Engineering, Yongin 446-701,Republic of Koreakmbyun@khu.ac.krAbstract. An optical method of measuring the number of layers in a graphene sample is formu-latedandcomparedwiththeconventionalsurfaceplasmonresonance(SPR)detectionscheme,thelatter being appropriateonly for averyfew graphenelayers.Numericalresultsbased ontransfer-matrixmethodsupportthatanalternativemethod,whereintheSPRsubstrateincludesadielectricoverlayer,isfeasibleoverawiderangeofgraphenelayernumbers.Whilethemultilayergraphenemay lead to a broad and shallow SPR curve owing to the nonzero imaginary part in its relativepermittivity, the dielectric overlayer makes the resonant surface plasmons less affected by gra-phene, resulting in a strong and deep absorption band at resonance. Linear regression analysisshows that the measurable graphene layer number can be as high as 50.