This PDF file contains the editorial “Book Review: The Nature of Light: What is a Photon?” for JNP Vol. 2 Issue 01

This PDF file contains the editorial “Book Review: What is What in the Nanoworld: A Handbook on Nanoscience and Nanotechnology” for JNP Vol. 2 Issue 01

The US Air Force Research Laboratory, Materials and Manufacturing Directorate (AFRL/RX) is heading up an international team of government, industrial and university researchers investigating biologically based (natural) materials and devices for electronic and photonic applications. This opens up an exciting new field for bioengineering demonstrating that biotechnology can benefit many areas, in addition to genomic sequencing and clinical diagnosis and treatment alone.

Plasmons are collective oscillations of electron gas: loosely speaking they happen when all the electrons move together in the same fashion. They can exist in the bulk of metals but also at their surfaces. In that case, they are called Surface Plasmons. As a matter of fact, surface plasmons have been known for years: scientific studies involving plasmons date back to the beginning of the twentieth century [1]. Due to the oscillations of the electrons, to these oscillations is associated an electromagnetic field. Conversely, an incoming electromagnetic field exerts a coulomb force on electrons that are forced to oscillate. This oscillation results in turn into a scattered field. This interaction can be confined on a surface and lead to a propagating field along this surface: it is then called a Surface Plasmon Polariton (SPP). Surface plasmons polaritons are really what is of interest for telecommunications and information technology [2].

Thermoelectric and solar-energy technologies are the focus of significant research, and can make a major contribution to the need to find alternative methods of power generation, heating and cooling. Solar-energy, or photovoltaic technology, is established as an alternative energy source, and in common with wind, biomass, wave and geothermal, is considered a renewable energy source. Thermoelectric technology is often overlooked, but can be used in applications where other technologies could not be used, or in combination with other renewable technologies. Contemporary problems surrounding climate change will act as a stimulus for the development of thermoelectrics, and the technology is successful in cooling, refrigeration and space-craft power, with potential for growth in power generation applications.

Many nanostructures exhibit electrically stimulated change of resistance and have been proposed as the basis for non-volatile random access memories (NVRAM), but progress toward implementation has been delayed by difficulties in understanding and controlling the resistive switching phenomena [1]. To design a device that can be reliably used for information processing, one needs (i) a mathematically consistent theory for modeling the circuit component, and (ii) knowledge of the underlying operating principles so that one might improve a device by fine tuning parameters such as doping and geometrical profile. Recent breakthrough occurred at Hewlett-Packard Laboratories has been receiving increasing attention in both fundamental researches and commercial applications. In May 2008, HP scientists announced the discovery of the missing circuit element memristor, acronym for memory resistor. The memristor concept gives a simple explanation for many puzzling voltage-current characteristics in nanoscale electronics [2]. Researchers also clarified coupled electron-ion dynamics responsible for memristive switch [3]. With the reported advance, HP is promising prototypes of ultradense memory chips in 2009.

No Abstract Available.

No Abstract.

The advancement of enabling photonic components developed for fiber-optic communication systems began nearly forty years ago while advantages of using light-wave communication in computing systems have been discussed for several decades. Following the history of microelectronics, the size of required photonic components for future communication systems will certainly need to be scaled down dramatically along a route of exploring higher system performance. The concept of photonic bandgap crystals has been around more than two decades. A line-defect within a two-dimensional photonic bandgap crystal provides efficient spatial confinement of light, which is a building block of a variety of routing and processing schemes of light. In contrast, silicon in the form of complementary metal semiconductor oxide (CMOS) platform has been a core in microelectronics. Silicon nanophotonics that allow CMOS platforms to handle light, thus, would offer a wide range of photonic functions that are required for CMOS platforms to further progress. While the photonic bandgap crystal and silicon nanophotonics are still subject to the diffraction limit of light, photonic devices that use surface plasmon polaritons and / or energy transfer mechanisms relying upon optical near-field interactions would pave the road toward ultimate photonic integration beyond the diffraction limit of light.

Room temperature visible and near-infrared photoluminescence from black silicon has been observed. The black silicon is manufactured by shining femtosecond laser pulses on silicon wafers in air, which were later annealed in vacuum. The photoluminescence is quenched above 120 K due to thermalization and competing nonradiative recombination of the carriers. The photoluminescence intensity at 10K depends sublinearly on the excitation laser intensity confirming band tail recombination at the defect sites.

Highly lattice mismatched InP/Si nanowire heterostructures were synthesized using metal organic chemical vapor deposition (MOCVD) process at 450 °C. The InP nanowire diameter as high as 500 nm is much thicker than the critical diameter (~24 nm for InP/Si) predicted by a recent theoretical work on the coherent growth of nanowire heterostructures. We investigated possible factors that lead to the unusually large diameters in a highly lattice mismatched material system. Dislocations formed at the interfacial plane of the heterostructure due to high lattice mismatch were found to contribute to the growth of nanowires with very large diameters. An extra pair of dislocation lines at the interfacial plane was found to support an increase in nanowire diameter by ~12 nm.

Planar lightwave circuits (PLCs) based on Si nanowires exhibit several serious problems due to the small cross sections of the nanowires. These problems include large scattering loss, large coupling loss to a single-mode fiber, and high dependency on polarization. Several solutions to these problems have emerged. Recent progress on Si-nanowire-based passive PLC devices encompasses arrayed waveguide grating (de)multiplexers, microring resonators, and multimode interference couplers.

Optical filters based on resonant gratings have spectral characteristics that are lithographically defined. Nanoimprint lithography is a relatively new method for producing large area gratings with sub-micron features. Computational modeling using rigorous coupled-wave analysis allows gratings to be designed to yield sharp reflectance maxima and minima. Combining these gratings with microfluidic channels and micromechanical actuators produced using micro electromechanical systems (MEMS) technology forms the basis for producing tunable filters and other wavelength selective elements. These devices achieve tunable optical characteristics by varying the index of refraction on the surface of the grating. Coating the grating surface with water creates a 33% change in the resonant wavelength whereas bringing a grating into contact with a quartz surface shifts the resonant wavelength from 558 nm to 879 nm, a fractional change of 58%. The reflectivity at a single wavelength can be varied by approximately a factor of three. Future applications of these devices may include tunable filters or optical modulators.

We studied the interaction of different pathways by which extraordinary transmission through nanoscale aperture arrays arises and obtained a complete physical picture that incorporates both propagating plasmonic and surface plasmon modes. The transmission behavior is qualitatively different depending on the number of transmission pathways present in the regime of operation. If only one pathway is present, it can give rise to high transmission. When multiple pathways are present simultaneously, their interplay must be studied in order to understand the rich and complex transmission behavior. The frequency range of these pathways can be controlled by varying the structures and, in particular, by coating the surface of the arrays or by filling the apertures with dielectrics that differ from the surrounding medium.

Spontaneous emission characteristics are not an inherent property of an emitter, but may be modified by a nanostructured environment surrounding the emitter. The use of one-, two-, and three-dimensional photonic crystals allows for significant and practical control of the spontaneous emission properties in optoelectronic communications devices. Particularly, one-dimensional photonic crystal structures, which are also known as microcavities, already are used in commercial devices. Two- and three dimensional photonic crystals permit a more comprehensive control of the spontaneous emission properties. By employing photonic crystals the device efficiency is enhanced, the angular radiation pattern can be engineered, and faster devices are achieved by decreasing the radiative lifetime. Photonic-crystal defect structures allow further engineering of the emission properties. Important applications for spontaneous emission control are light-emitting diodes, lasers, and single-photon sources.

This PDF file contains the editorial “Guest Editorial: Nanophotonics for Communications” for JNP Vol. 2 Issue 01

In the long-wavelength regime, the effective properties of particulate composites, including nanocomposites, may be estimated using one of various homogenization formalisms, such as the Bruggeman and Maxwell Garnett formalisms, and the approach of the strong-property-fluctuation theory (SPFT). In the conventional implementations of these formalisms, the constituent particles are treated as point-like scattering centres. However, extended formalisms have been established--which involve integral formulations--that take account of the spatial extent of the constituent particles. In particular, the extended second-order SPFT takes account of both the size of the constituent particles and their statistical distributions. We derived explicit representations of the extended second-order SPFT appropriate to isotropic chiral and uniaxial dielectric homogenized composite mediums. These results may also be employed in extended versions of the Bruggeman and Maxwell Garnett formalisms.

We conducted a theoretical investigation of second harmonic generation and other nonlinear features that result from the magnetic Lorentz force, when a single aperture is cut on a thick, opaque palladium substrate. We studied the dependences of linear pump transmission and second harmonic generation near resonance conditions, and explored the different physical mechanisms and their dependences, for example, geometrical features. We found that it is possible to exploit field localization and surface plasmon generation to enhance second harmonic generation in the regime of extraordinary transmittance of the pump field. Both transmitted and backward second harmonic generation conversion efficiencies were investigated. The results reveal that it may be possible to access several potential new applications. In particular, we demonstrated that the exploitation of a combination of nonlinear effects and enhanced transmission makes possible a palladium-based device suitable for H₂-leak-detection.

Analysis of adiabatic and non-adiabatic nano-focusing in tapered metal nano-rods leads to the determination of optimal taper angles and rod lengths as functions of material parameters (for gold, silver, and aluminum) at frequencies from the optical and near infra-red ranges. The considered nano-focusing structures appear to be highly tolerant to such structural and fabrication imperfections as variations of length of the rod and taper angle around their optimal values. However, the major parameter that tends to sig-nificantly affect the nano-focusing capabilities of the rods is the radius of the tip, and this is the parameter that should be carefully reproduced in the experiments. Comparison of the numerical results with the adiabatic theory of nano-focusing for different metals and different wavelengths demonstrates the validity of the adiabatic theory in a much wider range of taper angles (up to tens of degrees) than it was previously expected. Major predicted local field enhancements of up to ~ 2,500 times in the considered structures within nano-scale regions as small as a few nanometers will make tapered metal rods highly promising for single molecule detection and development of a new generation of sensors, measurement and nano-manipulation techniques.

Novel photonic devices, based on time-dependent dielectrics, to shift the optical frequency, may be conceived from two complementary principles, Doppler shift and time refraction, and possibly realized as as single cavities or as Coupled Resonator Optical Waveguides (CROWs). Simulations with the finite-difference time-domain method bore out these possibilities and also provided design rules. Preliminary experiments, limited to a pulsed excitation (without any frequency shift) of whispering gallery modes in a LiNbO₃ whispering gallery disk resonator in a full fiber-optics setup, the first experiments of an optical whispering-gallery resonator functioning in the steady-pulsed regime, led to a consistent Q-factor measurement between CW and pulsed ringdown characterization. The repetition rate was tuned to an integer submultiple 1/N of the free spectral range of the resonator. The output rate of the resonator was equal to the input rate multiplied by N, thereby showing functionality as a frequency multiplier. The impact of nonlinearity and of dispersion was minimized by the low power level and the limited bandwidth of pulses.

Solid immersion lens (SIL) microscopy combines the advantages of conventional microscopy with those of near-field techniques, and is being increasingly adopted across a diverse range of technologies and applications. A comprehensive overview of the state-of-the-art in this rapidly expanding subject is therefore increasingly relevant. Important benefits are enabled by SIL-focusing, including an improved lateral and axial spatial profiling resolution when a SIL is used in laser-scanning microscopy or excitation, and an improved collection efficiency when a SIL is used in a light-collection mode, for example in fluorescence micro-spectroscopy. These advantages arise from the increase in numerical aperture (NA) that is provided by a SIL. Other SIL-enhanced improvements, for example spherical-aberration-free sub-surface imaging, are a fundamental consequence of the aplanatic imaging condition that results from the spherical geometry of the SIL. Beginning with an introduction to the theory of SIL imaging, the unique properties of SILs are exposed to provide advantages in applications involving the interrogation of photonic and electronic nanostructures. Such applications range from the sub-surface examination of the complex three-dimensional microstructures fabricated in silicon integrated circuits, to quantum photoluminescence and transmission measurements in semiconductor quantum dot nanostructures.

It has been experimentally shown that absorption loss in metal, which causes damping of localized surface plasmons (SPs) and propagating surface plasmon polaritons (SPPs), can be compensated by optical gain in dye-doped dielectric media adjacent to a metallic surface. In particular, (i) six-fold increase of Rayleigh scattering caused by an enhancement of SP resonance in aggregated metallic nanoparticles, (ii) significant elongation of the propagation length of SPPs by gain, and (iii) stimulated emission of SPPs has been demonstrated. The obtained results pave the road to many applications of nanoplasmonics and metamaterials.

Optical trapping is an established field for movement of micron-size objects and cells. However, trapping of metal nanoparticles, nanowires, nanorods and molecules has received little attention. Nanoparticles are more challenging to optically trap and they offer ample new phenomena to explore, for example the plasmon resonance. Resonance and size effects have an impact upon trapping forces that causes nanoparticle trapping to differ from micromanipulation of larger micron-sized objects. There are numerous theoretical approaches to calculate optical forces exerted on trapped nanoparticles. Their combination and comparison gives the reader deeper understanding of the physical processes in an optical trap. A close look into the key experiments to date demonstrates the feasibility of trapping and provides a grasp of the enormous possibilities that remain to be explored. When constructing a single-beam optical trap, particular emphasis has to be placed on the choice of imaging for the trapping and confinement of nanoparticles.

This PDF file contains the editorial “Guest Editorial: Nanophotonics in Europe” for JNP Vol. 2 Issue 01

Vacuum UV spectroscopic ellipsometry (VUV SE) was developed with a multichannel detection system. This system can cover up to 8.5 eV with brief nitrogen purge through optical path. We applied this technique to the characterization of zirconium oxide (ZrO₂) films for which the conventional spectroscopic ellipsometer fails due to the poor sensitivity. ZrO₂ is one of the high-k dielectrics which can be used for the storage capacitor in dynamic random access memory devices. However, due to the large leakage current of ZrO₂, thin layer of aluminum oxide (Al₂O₃) is sandwiched between two ZrO₂ layers forming 'ZrO₂(top)/Al2O₃/ZrO₂(bottom)'. This structure also prevents the reaction between Al2O3 and electrodes during deposition. As overall thickness of this structure is less than 10 nm, the thickness and the properties of each layer need to be controlled precisely in order to fabricate a well-defined capacitor. However, the optical properties of ZrO₂ films are highly dependent on the preparation process and conditions. Thus, many considerations are required for the analysis of VUV SE data. Through the complicated analysis, we find that the optical properties of the bottom ZrO₂ film are dependent on its own thickness as well as the deposition temperature for the subsequent Al₂O₃ layer. Moreover, those of the top ZrO₂ layer showed the dependence on the crystalline structure of the bottom ZrO₂ along with the thickness of interfacial Al₂O₃ layer.

A sculptured nematic thin film (SNTF) is an assembly of parallel nanowires that are shaped in a fixed plane orthogonal to the substrate on which the film is deposited. The absorbance, reflectance, and transmittance of a linearly polarized, obliquely incident plane wave were calculated for a planar metal/SNTF interface in the Kretschmann configuration, the wave vector of the plane wave lying wholly in the morphologically significant plane of the SNTF. The permittivity profile of the chosen SNTF was supposed to have been sculptured during physical vapor deposition by varying the vapor incidence angle sinusoidally about a mean value. Calculations revealed that (i) multiple surface-plasmon-polariton (SPP) trains of the same color can be independently guided by the metal/SNTF interface, (ii) not all SPP trains have to be co-propagating, and (iii) not all SPP trains have to be of the same linear polarization state. As different SPP trains move with different speeds, guided by the interface, exciting prospects emerge for error-free sensing and plasmonics-based communication.

Nanocrystalline TiN/SiN composite (nanocomposite) thin films were reactively co-sputtered from pure Ti and Si targets over the mid-frequency range of 50-250 kHz using two asymmetric bipolar pulsed direct current power supplies. The resulting films were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, and nanoindentation in addition to measurement of the plasma properties during deposition. Due to lengthy fabrication and characterization, only nine samples exist in this data set for films deposited at 10 mTorr in pure nitrogen. Using the Vickers hardness of the films as the response, a principal components analysis of 13 predictors comprised of characterization and plasma parameters was conducted to find which parameters are most responsible in determining the hardness. Principal component analysis was then applied to the data to capture the variable relationships graphically and to reduce the number of predictors to a set of components. A correlation matrix established that the percent (111) and (200) crystallographic orientation and the momentum-per-atom best explained the variation in hardness. The momentum-per-atom has shown promise as a universal variable, independent of sputter deposition system, and is a statistically sound predictor of hardness in Ti-Si-N thin films.

Optical imaging using unspecific contrast agents as well as targeted and disease-specific agents play a vital role in preclinical research. Moreover, optical imaging is on the verge of establishing itself as a clinically relevant imaging modality. Also in-vitro diagnostical procedures rely to a large degree on optical labels to report disease-specific events. Materials that fulfill the basic requirements of this market are being used today, with cyanine dyes and semiconductor quantum dots being excellent examples. Other materials are being tested in laboratories throughout the world. Design rules suitable to develop new optical labels for in-vivo near-infrared optical imaging procedures have been formulated by us, and we have developed synthesis routes that lead to nano particles with small diameter, narrow size distribution, high quantum yield, and with stable surfaces required for bioconjugation to disease-specific ligands.

A flexible and versatile method combining sputtering and electrospinning techniques was used to shape different palladium morphological structures with nanoscale features. The samples were prepared by dc-magnetron sputtering onto thermally degradable polymer templates. The sputtering parameters were chosen to deposit the metal under low adatom-mobility conditions. After deposition, the template was removed by heat treatment, thereby forming different palladium morphologies with shapes resembling ribbons and half tubes, amongst others. X-ray diffraction studies demonstrated that they are composed of crystalline palladium or palladium oxide, depending on the heat treatment. The cylindrical walls are composed of 30 nm or smaller crystallites, as measured from transmission electron microscopy images. A mathematical simulation demonstrate that the morphological structures obtained are a consequence of the sputtering line-of-sight deposition process. This fabrication process can be varied to modify three types of structures at the nanoscale level: the external shape, the columnar shape of the walls, and the nano-crystallinity. The external shape can be modified by controlling the deposition time and the fiber template diameter. The columnar shape of the walls and the nano-crystallinity can be modified by changes in the sputtering process parameters. The nanoscale morphologies created have potential uses in sensing and photonic applications.

A titanium dioxide (TiO2) chiral sculptured thin film (STF) fabricated using a serial bi-deposition (SBD) method based on electron beam evaporation has been studied using spectroscopic Mueller matrix ellipsometry (MME). Complete Mueller matrices for the SBD TiO2 chiral STF have been measured using a dual-rotating compensator spectroscopic ellipsometer over the spectral range from 250 to 825 nm in transmission mode, both at normal incidence (θ_i = 0°) and over a range of oblique angles (5° ≤ θ_i ≤60°). A multilayer structurally-graded optical model has been applied to deduce spectra in the three principal indices of refraction that characterize the locally biaxial structure, using as input the complex amplitude transmission ratios deduced from the Mueller matrix measured at normal incidence. A Bragg resonance feature has been observed, and this feature blue-shifts with increasing angle of incidence. Predictions of the transmittance for circularly polarized light normally incident upon the SBD TiO₂ chiral STF can be obtained simply by multiplying the unnormalized Mueller matrix by the appropriate Stokes vector, and the results are in excellent agreement with direct measurements.

Biological carbonate mineralization induced by both microorganisms and higher phyla organisms is very important in many different natural processes. The organisms precipitate calcium carbonate to form very sophisticated biomaterials that they used for many different functions. Organisms control calcium carbonate precipitation using specific organic macromolecules which are released at specific times and regulate crystal growth. Calcium carbonate crystals are formed and arranged in several representative biomaterials (e.g., avian eggshell, mollusk nacre and bacterially induced precipitates). Through these examples, we get an insight on how organisms are not only able to precipitate calcium carbonate but also comprehensively on how organisms control this process, during the nucleation, polymorphism selection and crystal growth stages, resulting in materials which highly reproducible characteristics at different scales from the nano- to the millimeter scale. The ordered arrangement of crystals in these materials is in part controlled by the organic matrix and in part determined by self-organization processes.

Structured wide bandgap semiconductor thin films have been developed as a technique for growing thin films with low threading dislocation densities. A growth technique called Pendeo-Epitaxy (PE) has been applied to the deposition of GaN and AlGaN thin films. Low densities of dislocations on GaN stripes on AlN/6H-SiC(0001) and AlN/3C-SiC(111)/Si(111) substrates have been achieved. The dislocation density was reduced by at least five orders of magnitude. The characterization of the resulting materials is being reported in this paper. By using a mask on the [100]-direction oriented GaN stripes, the vertical propagation of threading dislocations during PE regrowth is blocked. Tilting in the laterally moving growth fronts, and associated crystallographic misregistry in the areas of coalescence over the stripes, and the generation of dislocations propagating from the resulting boundaries has been observed. A potential solution to this problem has been developed and is based on the elimination of the mask, as determined via X-ray diffraction and scanning and transmission electron microscopies.

Thin-film morphology---its origin at the atomic level and its evolution---has a long and rich history dating to the very first papers on thin-film deposition in the mid-1800s. I have traced this literature for films prepared under low adatom-mobility conditions and collected my thoughts on the efforts and the current status toward morphology quantification. An atomistic model of evolutionary thin film morphology, based upon atomic clustering at the nm-level, atomic self-shadowing, and competition for columnar growth, forms the backbone for these quantitative approaches. The connection between the science of morphology modeling and the technology of practical thin-film development emerged through research on sculptured thin films

No Abstract available.

The many interesting and unique physical properties of nanocrystalline-Si/amorphous-SiO₂ superlattices stem from their vertical periodicity and nearly defect-free, atomically flat, and chemically abrupt nanocrystalline-Si/SiO₂ interfaces. By combining a less than 5% variation in the initial as-grown amorphous-Si layer thickness with control over the Si nanocrystal shape and crystallographic orientation produced via an appropriate annealing process, systems of nearly identical Si nanocrystals having remarkably different shapes (spheres, ovoids, bricks, etc.) have been produced. Such details governing the fabrication of nanocrystalline-Si/amorphous-SiO₂ superlattices have dramatic effects on their structural and optical-Raman scattering and photoluminescence-properties. The reliable fabrication of Si-based nanostructures with control over the nanocrystal size, shape, and crystallographic orientation is an important first step in their applications in Si photonics.

The science of energy harvesting has recently undergone radical change, with the advent of new materials exploiting mechanisms fundamentally different from those of traditional solar cells. Utilizing principles that are in many cases acquired from breakthroughs in molecular photobiology, the introduction of a range of new synthetic polymers, multichromophore arrays and nanoparticle-based materials heralds a marked resurgence of interest, a shift of focus and heightened expectations in the science of light-harvesting. The interplay between structure and mechanism significantly impinges upon issues extending from fundamental theory to the principles of energy-harvesting materials design. Understanding and exploiting the principles allows materials to be engineered that can harness absorbed energy with heightened efficiency. Two of the key areas of application are dendrimers and rare-earth doped solids.

Wave propagation and diffraction in a membrane photonic crystal with finite height were studied in the case where the free-space wavelength is large with respect to the period of the structure. The photonic crystals studied are made of materials with anisotropic permittivity and permeability. Use of the concept of two-scale convergence allowed the photonic crystals to be homogenized.

The design and fabrication of gold nanostructures through nanosphere lithography utilizing dispersed nanospheres, on glass substrate for the applications of localized surface plasmon resonance, were investigated in detail. The fabrication of the nanostructures was realized through the gold film deposition onto nanospheres dispersed on a substrate and the subsequent directional gold etching. Depending on the deposition and etching conditions of the gold, a variety of gold nanostructures can be fabricated. So far through this method, only 2D nanocrescents had been reported. However, either 2D or 3D non-conformal nanostructures are formed in this way, and the profiles of the obtainable nanostructures were simulated under various conditions. For nanostructures fabricated on glass, the simulated profiles coincided well with the fabricated ones. These results prove that our profile simulation program can realize the design of 2D and 3D nanostructures obtainable by dispersed nanospheres, and reduce the effort and cost for achieving desired nanostructures by experiments in the trial-and-error stage.

Experimental specific-heat measurements in single-walled carbon-nanotube (SWNT) ropes show marked increase when He-4 is allowed to be adsorbed, the increase in the values varying from 2 to 2.5 times in the temperature range 2-20 K. Beyond 20 K, the effect of adsorption on the specific heat of SWNT ropes is negligible. The phonon frequency distribution function (FDF) of the dynamical modes was extracted by employing the unfolding technique from the observed experimental temperature variation of the specific heat and a trial phonon FDF. The agreement between the observed experimental values of specific heat and the values obtained using the above method is quite good, the error being less than 10% in the temperature range 2-20 K and within 6% for 20 ≤ T ≤ 300 K at most of the temperature values. The change in the values of the specific heat can be attributed to the fact that the phonon FDF of He-4 adsorbed SWNT ropes shows marked difference from that when there is no adsorption for energies less than 200 K. The sensitivity of specific heat to adsorption at low temperatures by SWNT ropes is highlighted, particularly, by the appearance of large number of dynamical modes at 15 K. This can be experimentally checked using Rayleigh recoilless fraction of Mossbauer γ-ray photons from the carbon nanotube ropes sample.

We fabricated polymer optical fiber (POF) amplifiers operating between 440 and 480 nm, using POFs doped with a series of fluorene oligomers, including tri-, penta-(9,9-dioctylfluorene) and hepta-(9,9-dihexylfluorene). The gain properties of pure oligofluorene films demonstrate gain coefficients on the order of 250 dB/cm and amplified spontaneous emission thresholds between 1 and 8 μJ c^m-2, significantly lower than other fluorene gain media. The optical and morphological characteristics of PMMA thin films doped with the oligomers demonstrate that the oligomers are largely isolated within the PMMA. The optical and gain properties of POFs produced using an adapted preform-drawing technique and doped with the oligofluorenes provide gain values on the order of 0.07 dB for 2 mm of doped POF. The oligofluorenes are largely isolated within the POFs, paving the way for all optical gain-switching.

A comparative study of enhancement of omnidirectional high-reflection wavelength range in one-dimensional ternary structured photonic crystals (PCs) was carried out. The PCs investigated are of the dielectric-birefringent type and the dielectric-metallic type. These were compared with a 1D all-dielectric ternary PC investigated earlier by us. The dielectric-birefringent PC gives a larger range enhancement as compared to the all-dielectric one, together with a reduction in the number of periods of the structure. Maximum range enhancement is obtained in the metallodielectric ternary PC, with a further reduction in size, as only six layers need to be deposited in this case. This implies easier fabrication methods and lower costs.

Anisotropic metal-based nanomaterials have been proposed as potential contrast agents due to their strong surface plasmon resonance. We evaluated the contrast properties of gold, silver, and gold-silver hybrid nanorods for molecular imaging applications in three-dimensional biological samples. We used diffuse reflectance spectroscopy to predict the contrast properties of different types of nanorods embedded in biological model systems of increasing complexity. The predicted contrast properties were then validated using wide-field and high-resolution imaging. Results demonstrated that silver nanorods yield images with higher positive-contrast than gold nanorods; however, it is more difficult to synthesize silver nanorods which are homogeneous in shape and size. Gold-silver hybrid nanorods combine the homogeneous synthesis of gold nanorods with the higher scattering properties of silver nanorods. The spectroscopic and imaging results demonstrated that the image contrast properties that can be achieved with anisotropic nanomaterials depend strongly on the material composition, mode of imaging, presence of targeting molecules, and the biological environment. We also found that gold, silver, and gold-silver hybrid nanorods are stable and biocompatible sources of positive and absorptive contrast for use in reflectance molecular imaging and are promising for future clinical translation.

Ultra-compact polymer modulators were proposed and simulated, based on the hybrid integration of functional polymer materials with Si based photonic-crystal ring resonators (PCRRs). The simulations were carried out on device characteristics with an effective ring radius of 2.3 μm and tunable polymer index from 1.785 to 1.805. Investigating the loss, the cavity quality factor Q, and the free spectral range of such PCRRs, we found a 0.02 dB intrinsic loss that is independent of diameter, unlike the loss that varies inversely with diameter in microstrip resonators. Close to 100% drop efficiency at the drop channel of 1557.5 nm was obtained by design with a high spectral selectivity of Q greater than 1319 in the single-ring PCRR-based add-drop filters with ring radius of 1.2 μm.

A new type of structure which is composed of a Gaussian profile-shaped metallic nanograting, was put forth from the nanofabrication point of view. Dependence of the structural parameters on the sensitivity was analyzed by means of a multiple multipole program (MMP) method. One of the important applications of the nanograting is in biosensing: immunoassay. Our numerical simulation results showed that the sensitivity to refractive index of 490 nm/RIU and the reflection spectra at site of full-width at halfmaximum (FWHM) ~9 nm can be obtained through the optimized structure. The figure of merit (FOM) of the sensor can exceed 55. The resonant wavelength increases linearly with increasing of the refractive index of bio-samples. These reflection properties make the nanograting more suitable to be used in the localized surface plasma resonance (LSPR)-based biosensors for immunoassay.

The utilization of the enhanced local field near trapped metallic nanoparticles due to surface-plasmon resonance (SPR) for the optical trapping of dielectric fluorescent nano-objects is of considerable interest for single-molecule manipulation. Theoretical calculations as well as experimental measurements show that even with moderate SPR based field enhancement factors, gradient force based trapping of fluorescent molecules would be rather difficult. While trapping of the fluorescent molecule at resonance wavelength showed decreased stiffness, at wavelengths far away from resonance, increase in stiffness was found which was attributed to interplay of SPR-enhanced absorption and gradient forces.

Permanent gratings were written, without the aid of external fields, in planar nematic liquid crystal cells doped with only Methyl Red (MR) as well as cells doped with both Methyl Red and single-wall carbon nanotubes (CNTs). Grating formation based on trans-cis photoisomerism of MR followed by surface adsorption of the cis-isomer was attempted. The diffraction efficiency was easily enhanced and modulated by application of ac fields covering wide ranges of frequency and voltage; thus, allowing for tuning the diffracted signals. Cells doped with MR and CNTs had a maximum relative diffraction efficiency of 67% while cells doped only with MR exhibited a maximum of 28%. The maximum diffraction efficiency appears to be associated with the Fréedericksz threshold voltage. The permanent gratings are robust and have remained stable for over two years.

We prepared of electrodes that consist of TiO₂ with addition of tin-doped indium oxide (ITO) or fluorine-doped tin oxide (FTO) nanoparticles and the application of such electrodes on dye-sensitized solar cell. As compared to TiO₂ alone, the addition of ITO and FTO nanoparticles resulted in an efficiency improvement of ~20% up to ~54% for the TiO₂-ITO and TiO₂-FTO systems, respectively. This improvement was partly attributed to a slightly enhanced dye-adsorption behavior and a change in the TiO₂ surface chemistry due to the presence of ITO or FTO nanoparticles.

Analytical expressions for the plasmon resonance frequencies of prolate and oblate spheroids and their dependence on ellipticity are derived, and approximate bounds on these frequencies established. These formulas may be useful in tuning the plasmon resonance within certain limits. With increasing aspect ratio, the prolate spheroid resonance is red shifted relative to a sphere with no lower limit under the assumptions of a Drude dispersion model. On the other hand, the oblate resonances are blue shifted as the spheroid becomes increasingly flat, but up to a limit.

We demonstrated a high-quality single-photon emitter based on excitation energy transfer between two different-sized CuCl quantum dots (QDs). It is operated under triple blockade mechanisms. The mechanisms are tuning the incident light to the smaller QD and using an electric dipole forbidden excitation energy level in the larger QD, using the optical near-field interaction to transfer energy from the smaller QD to the electric dipole forbidden level of the larger QD, and using a single exciton emission level in the larger QD. These mechanisms are supported by the large binding energy of the exciton molecule. A 99.3% plausibility of single-photon emission was confirmed with 99.98% accuracy based on a photon correlation experiment with 80-MHz repetition frequency using an optical fiber probe.

The applicability of Lewin's homogenization formula is restricted to composite materials wherein: (a) the inclusions are small relative to wavelength in the host material and the inclusion material; (b) the real parts of the permittivities (and/or the permeabilities) of the host and inclusion materials have the same sign, for weakly nondissipative materials; and(c) the volume fraction of the inclusion material is less than approximately 0.3.

The ability of a weakly anisotropic thin film to modulate the polarization state of light was considered. We found that, in a configuration for enhanced polarization conversion, most polarization states can be generated by tuning the direction of incident linear polarization and the aspect of the anisotropic thin film. The modulation for omniform polarization state can be extended to a broad wavelength range by adding an isotropic thin film in the system.

This PDF file contains the editorial “Editorial: Preparing for a Nanotechnological Future” for JNP Vol. 2 Issue 01

This PDF file contains the editorial “Editorial: Commentaries” for JNP Vol. 2 Issue 01