This PDF file contains the errata for “JNP Vol. 3 Issue 01 Paper JNP ERR-2009-1” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book Review: Basics of Nanotechnology” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book Review: Periodic Materials and Interference Lithography for Photonics, Phononics and Mechanics” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book Review: Nanosciences--The Invisible Revolution” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book Review: Nanostructures in Electronics and Photonics” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book Review: Gold Chemistry: Applications and Future Directions in the Life Sciences” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book Review: Optical Properties and Spectroscopy of Nanomaterials” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book review: Excitonic and Vibrational Dynamics in Nanotechnology: Quantum Dots vs. Nanotubes” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Book Review: Nano: The Essentials / Understanding Nanoscience and Nanotechnology” for JNP Vol. 3 Issue 01

This PDF contains the commentary "Femtosecond-laser nanolithography for photonic applications."

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This PDF contains the commentary "Commentary: Focusing light: still full of surprises."

This PDF contains the commentary "Nanobiophotonics: example of scientific convergence."

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The potentials of a nanophotonic platform, including compactness, low power consumption, integrability with other functionalities, and high sensitivity make them a suitable candidate for sensing applications. Strong light-matter interaction in such a platform enables a variety of sensing mechanisms, including refractive index change, fluorescence emission, and Raman scattering. Recent advances in nanophotonic devices include the demonstration of silicon and silicon-nitride microdisk resonators with high intrinsic Q values (0.5-2×10⁶) for strong field enhancement and the realization of compact photonic crystal spectrometers (high spectral resolution at 100-μm length scales) for on-chip spectral analysis. These two basic building blocks, when combined with integrated fluidic channels for sample delivery, provide an efficient platform to implement different sensing mechanisms and architectures.

Increasing the sensitivity of surface plasmon resonance (SPR) sensors is important to enable controlling small concentrations of materials in liquid solutions or for gas sensing. Upon using a 10-15 nm top layer of dielectric film with a high value of the real part 'of the dielectric function, on top of an SPR sensor in the Kretschmann configuration, the sensitivity is improved by few times. The imaginary part "of the top nano layer permittivity needs to be small enough in order to reduce the losses and get sharper dips. The stability of the sensor is also improved because the nano layer is protecting the silver from interacting with the environment. In the near infrared range, the sensitivity is enhanced contrary to the standard SPR mode without top nanolayer. The calculated evanescent field is enhanced near the top layer - analyte interface, thus the enhancement is partially due to this fact and partially due to an increase of the interaction length as a waveguiding effect.

The optical properties of the sandwich of Ag nanorod array (NRA)/structured dielectric layer/Ag mirror have been investigated theoretically and experimentally, where the structured dielectric layer has stacked sublayers of an anisotropic nanocolumnar layer and a uniform layer. The functions of the nanocolumnar and the uniform sublayers are to control shape of the Ag nanorods and to tune optical path length inside the sandwich, respectively. Calculations based on a simple model by treating the NRAs as uniform effective media indicate that the antireflection condition is realized by changing the thickness of the dielectric layer and that the Ag nanorods absorb most of the incident light. The designed structures have been successfully fabricated by taking advantages of the dynamic oblique-angle deposition technique. Under the experimental antireflection condition, Raman scattering measured on the Ag NRA in the near infrared region exhibits significant enhancement. This indicates that the local electric field close to the Ag nanorods can be controlled by the interference of light in the nanostructured sandwiches.

The potentiality to exert optical control, over the migration of electronic excitation energy between particles with suitably disposed electronic levels, affords a basis for all optical switching. Implemented in a configuration with nanoparticles arrayed in thin films, the process can offer an ultrafast parallel-processing capability. The mechanism is a near-field transfer of energy from donor nanoparticles in one layer (written into an electronically excited state by the absorption of light) to counterpart acceptors; the transfer effect proves amenable to activation by non-resonant laser radiation. The possibility of optical control arises under conditions where the donor-acceptor energy transfer is rigorously forbidden in the absence of laser light, either on the grounds of symmetry or energetics. Under such conditions, optical switching can be produced by the throughput of a single off resonant beam or, with more control options, by two coincident beams. In model electrodynamical calculations the transfer fidelity, signifying the accuracy of mapping an input to its designated output, can be identified and cast in terms of key optical and geometric characteristics. The results show that, at reasonable levels of laser intensity, cross talk drops to insignificant levels. Potential applications extend beyond simple switching into all-optical elements for logic gates and optical buffers.

Porous silicon-based photonic crystals of finite thickness were designed aiming at their subsequent use in the field of optical chemical- and bio-sensing. These structures consist in nanometric porous silicon rods arranged as to form a triangular lattice embedded into a silicon slab. These structures have two-dimensional periodicity and index-guiding is used to confine light in the third dimension. This way, the fabrication of photonic crystals in thin dielectric slab systems is enabled. The photonic band structure for the odd and even modes was calculated as a function of the thickness of the slab, finding a significant dependence on this parameter. The existence of a photonic bandgap for even modes was verified and its size was maximized. A change in the index of refraction of porous silicon caused by infiltration with chemical or biochemical species changes the band structure.

The response to applied electric fields of vanadium dioxide thin films above and below the phase transition depends on the size of grains if below ~200nm across, and on aluminum doping above a critical concentration. T_c drops as doping level increases, but does not depend on grain size. The observed phase transition undergoes a remarkable qualitative shift as the applied field goes from optical to low frequencies. The expected insulator to metal transition is found at optical frequencies, but at low frequencies an insulator-to-insulator transition occurs. Optical switching at both T < T_c and T > T_c is nearly independent of doping level and grain size. In contrast dc properties in both phases are sensitive to both factors. The band gaps from optical and dc data differ, and densities of states change with doping level. Such behaviour can arise if there is a transient phase change. The way doping and grain size can support such a phase is discussed. Only individual nanograins need to switch phases coherently to explain data, not the whole sample. Resistance as a function of composition across the transition was derived using effective medium compositional analysis of optical data in the hysteresis zone. The percolation thresholds are not at the usual T_c values.

Many applications require the ability to image a scene in several different narrow spectral bands simultaneously. Conventional multi-layer dielectric filters require control of film thickness to change the resonant wavelength. This makes it difficult to fabricate a mosaic of multiple narrow spectral band transmission filters monolithically. We adjusted the spectral transmission of a multi-layer dielectric filter by drilling a periodic array of subwavelength holes through the stack. Multi-band photonic crystal filters were modeled and optimized for a specific case of filtering six optical bands on a single substrate. Numerical simulations showed that there exists a particular air hole periodicity which maximizes the minimum hole diameter. Specifically for a stack of SiO₂ and Si3N₄ with the set of filtered wavelengths (nm): 560, 576, 600, 630, 650, and 660, the optimal hole periodicity was 282 nm. This resulted in a minimum hole diameter of 90 nm and a maximum diameter of 226 nm. Realistic fabrication tolerances were considered such as dielectric layer thickness and refractive index fluctuations, as well as vertical air hole taper. Our results provide a reproducible methodology for similar multi-band monolithic filters in either the optical or infrared regimes.

Wave propagation in thin nanostructured films in the low frequency regime were studied. By means of a two-scale analysis, the medium can be homogenized, i.e. described by effective electromagnetic parameters. The effective permeability and permittivity were obtained from a set of partial differential equations. A numerical approach based on the Fourier Modal Method was devised in order to solve these equations.

This PDF file contains the editorial “Guest Editorial: Nanostructured Thin Films” for JNP Vol. 3 Issue 01

Carrier-density-dependent internal optical loss sets an upper limit for operating temperatures and considerably reduces the characteristic temperature of a quantum dot (QD) laser. Such a loss also constrains the shallowest potential well depth and the smallest tolerable size of a QD at which the lasing can be attained. In a laser with a single layer of QDs, this loss can strongly limit the output power and cause a rollover of the light-current curve; it also imposes limitations on the conventional method of determining the internal quantum efficiency. Excited-state-mediated capture of carriers from the waveguide into the QD ground-state places a fundamental limitation on ground-state lasing - the output power saturates at high injection currents. The saturation power is controlled by the transition time between the excited- and ground-state in a QD. The longest, cut-off transition time exists, beyond which no ground-state lasing is possible. The maximum number of longitudinal modes that can oscillate in a QD laser increases with increasing surface density of QDs and remains limited (first increases and then decreases) with increasing scatter in the QD-size. In addition to the maximum tolerable scatter, there also exists the minimum scatter in the QD-size for each higher-order mode to start lasing.

Significant developments have occurred in the area of III-V compound semiconductor nanostructures. The scope of developments includes quantum dots and nanowires epitaxially grown on Si substrates, as well as their applications in light emitting diodes and lasers. Such nanoscale heterostructures exhibit remarkable structural, electrical, and optical properties. The highly effective lateral stress relaxation, due to the presence of facet edges and free surfaces, enables the achievement of nearly defect-free III-V nanoscale heterostructures directly on Si, in spite of the large lattice mismatches and the surface incompatibility. With the incorporation of multiple quantum dot layers as highly effective three-dimensional dislocation filters, self-organized quantum dot lasers monolithically grown on Si exhibit, for the first time, relatively low threshold current (J_th = 900 A/cm²) and very high temperature stability (T₀ = 244 K). III-V semiconductor nanowire light emitting diodes on Si, with emission wavelengths from UV to near-infrared, have also been demonstrated.

Due to its unique optoelectronic properties, the quantum dot (QD) has become a promising material for realizing photonic components and devices with high quantum efficiencies. Quantum dots in colloidal form can have their surfaces modified with various molecules, which enables new fabrication process utilizing molecular self-assembly and can result in new QD photonic device structures in nano-scale. In this review paper, we describe QD waveguides for sub-diffraction-limit waveguiding, nano-scale QD photodetectors for sensing with high spatial resolution and sensitivity, as well as integration of these two nanophotonic components. The paper will provide an overview on the operating principles, fabrications and characterizations of the devices. The QD waveguide achieved a transmission loss of 3 dB/4 micron, which is lower than the experimental results from other sub-diffraction limit waveguides that have been reported. It also demonstrated a comparable waveguiding effect through a waveguide with a sharp bend. The QD photodetector showed a sensitivity of 60 pW over a device with a nano-gap of 25 nm for detection. The compatibility between the fabrication processes for these two components with colloidal QDs allows integration of them through self-assembly fabrications.

As an alternate Quantum Dot (QD) fabrication method to self-assembled SK mode QDs, diblock copolymer nano-patterned QDs were investigated. By employing selective growth of QDs on diblock copolymer nano-patterned masks, independence from the problematic wetting layer and controllability on QD size and distribution associated with SK growth mode QDs were realized. The diblock copolymer nano-patterned masks were fabricated using a diblock copolymer template and a dielectric mask, and InxGa1-xAs QDs were selectively grown on patterned GaAs and InP substrates by Metalorganic Chemical Vapor Deposition (MOCVD). The optical properties from diblock copolymer patterned QDs on III-V substrates were investigated at low temperature.

Developments in the self-assembly by droplet epitaxy in our research group have enabled us to fabricate various GaAs quantum nanostructures of high optical quality such as quantum dots, single quantum rings, and concentric double quantum rings. We clarified their electronic states and relaxation processes by micro photoluminescence experiments. We achieved lasing of lattice-matched GaAs quantum dots and their excitonic Rabi oscillation by resonant excitation. We succeeded in the control of their photon emission rate by photonic crystal micro cavities.

Intersubband Quantum-Box (IQB) lasers; that is, devices consisting of 2-D arrays of ministacks (i.e., 2-4 stages) intersubband QB emitters are proposed, as an alternative to 30-stage quantum-cascade (QC) devices, as sources for efficient room-temperature (RT) emission in the mid-infrared (4-6 μm) wavelength range. Preliminary results include: 1) the design of devices for operation with 50% wallplug efficiency at RT;2) realization of a novel type of QC device: the deep-well (DW)QC laser, that has demonstrated at λ=4.7μm low temperature sensitivity of the threshold current, a clear indication of suppressed carrier leakage; 3) the formation of 2-D arrays at nanopoles by employing nanopatterning and dry etching; 4) the formation of 40nm-diameter, one-stage IQB structures on 100nm centers by preferential regrowth via metal-organic vapor phase epitaxy (MOVPE).

Quantum-dot infrared photodetectors (QDIPs) are positioned to become an important technology in the field of infrared (IR) detection, particularly for high-temperature, low-cost, high-yield detector arrays required for military applications. High-operating temperature (≥150 K) photodetectors reduce the cost of IR imaging systems by enabling cryogenic dewars and Stirling cooling systems to be replaced by thermo-electric coolers. QDIPs are well-suited for detecting mid-IR light at elevated temperatures, an application that could prove to be the next commercial market for quantum dots. While quantum dot epitaxial growth and intraband absorption of IR radiation are well established, quantum dot non-uniformity remains as a significant challenge. Nonetheless, state-of-the-art mid-IR detection at 150 K has been demonstrated using 70-layer InAs/GaAs QDIPs, and QDIP focal plane arrays are approaching performance comparable to HgCdTe at 77 K. By addressing critical challenges inherent to epitaxial QD material systems (e.g., controlling dopant incorporation), exploring alternative QD systems (e.g., colloidal QDs), and using bandgap engineering to reduce dark current and enhance multi-spectral detection (e.g. resonant tunneling QDIPs), the performance and applicability of QDIPs will continue to improve.

Integrated photonic devices were realized using colloidal quantum dot composites such as flexible microcavity laser, microdisk emitters and integrated active-passive waveguides. The microcavity laser structure was realized using spin coating and consisted of an all-polymer distributed Bragg reflector with a poly-vinyl carbazole cavity layer embedded with InGaP/ZnS colloidal quantum dots. These microcavities can be peeled off the substrate yielding a flexible structure that can conform to any shape and whose emission spectra can be mechanically tuned. Planar photonic devices consisting of vertically coupled microring resonators, microdisk emitters, active-passive integrated waveguide structures and coupled active microdisk resonators were realized using soft lithography, photo-lithography, and electron beam lithography, respectively. The gain medium in all these devices was a composite consisting of quantum dots embedded in SU8 matrix. Finally, the effect of the host matrix on the optical properties of the quantum dots using results of steady-state and time-resolved luminescence measurements was determined. In addition to their specific functionalities, these novel device demonstrations and their development present a low-cost alternative to the traditional photonic device fabrication techniques.

This PDF file contains the editorial “Guest Editorial: Quantum Dots” for JNP Vol. 3 Issue 01

We present a new design of a miniaturized modulator on a silicon chip. The modulation principle is based upon the plasma dispersion effect in which free electrons affect the real and the imaginary part of the refractive index. The novelty of the modulation configuration is related to its periodically patterned electrodes due to which the applied voltage generates axially periodic change in index of refraction. This results with the generation of an effective Bragg filter. Such filter allows having shorter device with the same extinction ratio or having a device with the same length but with improved modulation contrast.

Hexagonal symmetry InGaAsP membrane type cavities with embedded InAs quantum dots as active emitters were investigated by room temperature photoluminescence experiments at wavelengths near 1.50 μm. Cavities consisting of simple defects of just removing one or seven air holes were studied as well as modified cavities with additional holes decreased in size and shifted in position. The latter include the H0 cavity, in which only two adjacent holes were modified, but none removed. Low-Q cavity modes were observed for the simple cavities while high-Q modes were observed after modification of the surrounding holes. The resonant frequencies were varied over a large range of lithographic parameters both by changing the lattice spacing or the size of the modified holes. More than 15 nm reversible dynamic optical tuning of the resonance modes was observed by changing the applied laser power up to 5 mW. For thermo-optic tuning, this corresponds to a heating of up to 200 °C.

We considered figures of merit for chemical and biological sensors based on plasmonic structures and utilizing adsorption/desorption mechanism. The operation of these devices in general is limited by noise determining the minimum detectable refractive-index change. We dedicated our work to the intrinsic noise mechanisms connected with the plasmonic process itself. In contrast, most of the available literature is almost exclusively dedicated to the external noise sources (illumination source and photodetector). Reviewing the refractive-index fluctuations caused by thermal, adsorption-desorption and 1/f noise, we observed a striking analogy between the qualitative behavior of noise in (nano)plasmonic devices and that in semiconductor infrared detectors. The power spectral densities for noise in both of these have an almost identical shape; the adsorption-desorption noise corresponds to generation-recombination processes in detectors, while the other two mechanisms exist in the both types of the devices. Thus the large and mature existing apparatus for infrared detector noise analysis may be applied to the plasmonic sensors. Based on the observed analogy, we formulated the noise-equivalent refractive-index and the specific detectivity as the figures of merit to analyze the ultimate performance of plasmon sensors. The approach is valid for conventional surface plasmon resonance sensors, but also for nanoplasmonic and metamaterial-based devices.

Quantitative phase imaging needs of a holographic setup in order to retrieve the sample phase distribution. Often this new phase information is obtained at the cost of reducing the useful range in other parameters of the imaging system such as field of view or resolution. We devised an experimental setup that allows complex amplitude evaluation and phase image quantification of three-dimensional (3-D) samples in wide-field digital holographic microscopy. The basis is a common-path interferometric configuration that can be implemented in two configurations depending on the position and the basic period of the grating: static grating and windowed Fourier filtering method or with phase-shifting moving grating. Both configurations allow complex amplitude recovery and, thus, quantitative phase imaging of the sample under test. Moreover, by combining the basic setup with tilted illumination and time multiplexing, it is possible to generate a synthetic aperture enlargement that improves the final image resolution. Experimental results validated our concepts.

We evaluated the morphology of ultra-thin a-Se photodeposited nano-structures obtained by direct deposition of a-Se on glass substrates. Photodeposition (PD) from solutions has been used for realizing various thin film patterns, of sub-microscopic thicknesses i.e., 5-500 (nm) to produce various spatially distributed components for optical applications. During PD nanometer particles appear on the irradiated zones of any transparent substrates, such as glass used in this investigation. In this work, CW Photodeposition from a-Se colloid solutions onto glass substrates a Xenon UV-Visible lamp has been employed. A new technique based on capturing the evanescent light leaking image, named Differential Evanescent Light Intensity (DELI), is used to get the information about the photodeposited a-Se nanostructures profiles in the deposited zone on glass substrates serving as waveguides. The deposited particles observed on the substrates have diameters typically in the range of 100-300 nm as obtained by other microscopy methods. The morphology of the nano-structures observed by DELI during this work conditions consist of a random array of individual particles adsorbed onto the surface. The deposited material morphological profile was observed for fluences in excess of F > F_th ~ 25 J/cm² for the particular experimental conditions of this work for a-Se. The highest merits found for the DELI technique are the fast and ease of measurements, comparable z-resolution to SEM and capability of large areas profiling and mean thickness measurements. We obtained that deposition fluences of about F ≈ 300 J/cm² were enough to produce layers up to about 340 nm thickness, similar to values needed for CW Ar⁺ ion laser PD deposition at λ = 498 nm reported in previous investigations.

We measured light scattered from gold nanoparticles with darkfield microscopy in order to perform single molecule detection based on tethered particle motion (TPM). This combination results in a signal to noise ratio of about 40 dB, which allowed us to use 80 nm diameter gold particles as reporters instead of the typically used polystyrene particles whose sizes are up to 1 μm. The particle size is crucial in TPM experiments as it can induce a volume-exclusion effect, which results in a stretching force acting on the DNA tether. This affects both the biophysical and statistical properties of the anchored DNA and hence the interpretation of the experimental data. We demonstrated that the gold nanoparticles and darkfield microscopy can be used to characterize the confined Brownian motion of dsDNA-tethered gold particles with a spatial precision of 3 nm. Physical parameters such as the spring constant of the tethered DNA fragment and the persistence length can be derived from the two dimensional (2D) (x, y) projected image data. We have applied this method to various MgCl₂ and glycerol concentrations as a proof of principle.

This PDF file contains the editorial “Guest Editorial: Mediterranean Nanophotonics” for JNP Vol. 3 Issue 01

The radiation resistance of organic electro-optic and optoelectronic materials for space applications is receiving increased attention. An earlier investigation reported that guest-host poled polymer EO modulator devices composed of a phenyltetraene bridge-type chromophore in amorphous polycarbonate (CLD/APC) did not exhibit a decrease in EO response (i.e., an increase in modulation-switching voltage- _Vπ) following irradiation by low dose [10-160 krad(Si)] ⁶⁰Co gamma-rays. To provide further evidences to the observed radiation stability, the post-irradiation responses of ⁶⁰Co gamma-rays on CLD1/APC thin films are examined by various chemical and spectroscopic methods including: a solubility test, thin-layer chromatography, proton nuclear magnetic resonance spectroscopy, UV-vis absorption, and infra-red absorption. The results indicate that CLD1 and APC did not decompose under gamma-ray irradiation at dose levels ranging from 66-274 krad(Si) and from 61-154 krad(Si), respectively which support the previously reported data.

Dust contamination is a serious problem for equipment and vehicles for space mission applications. Dust contamination gathers on photonic sensors inhibiting motion and data gathering. In addition, devices that require transparency to light for maximum efficiency such as solar photovoltaic power systems, video cameras and optical or infrared detectors will suffer from the dust accumulation. For example, on the lunar surface, regolith (lunar dust) contamination is a serious problem for equipment and vehicles since the lunar soil has fine texture compared to terrestrial dust particle size distributions. The electrostatic charging of the lunar surface is caused by its interaction with the local plasma environment and solar UV and X-rays induced photoemission of electrons. The lunar thermal environment poses unique challenges to coatings since it is characterized by large temperature variations, long hot and cold soak times, and reduced heat rejection capability due to the presence of the lunar regolith. Fundamental forces (van der Waals) allow certain contamination to adhere to critical photonic surfaces and can be mitigated using various passive coatings phenomenology (hydrophilic to hydrophobic).

Quantum dot enhanced solar cells have been evaluated both theoretically and experimentally. A detailed balance simulation of InAs quantum dot (QD) enhanced solar cells has been performed. A 14% (absolute) efficiency improvement has been predicted if the middle junction of a state-of-the-art space multi-junction III-V solar cell can be bandgap engineered using QDs. Experimental results for a GaAs middle junction enhanced with InAs QDs have shown an 8% increase in short circuit current compared to a baseline device. The current enhancement per layer of QD was extracted from device spectral response (0.017 mA per QD layer). This value was used to estimate the efficiency of multi-junction solar cells with up to 200 layers of QDs added to the middle current-limiting junction. In addition, the radiation tolerance of QD cells, key to operation of these cells in space environments, shows improved characteristics. Open circuit voltage (VOC) in QD devices was more resilient to both alpha and proton displacement damage, resulting in a 10X reduction in the rate of VOC degradation.

A novel optical power limiter (OPL) has been designed and fabricated by synergistically combining the different optical power limiting mechanisms of various chromophores that include nanoparticulates such as fullerenes. The multi-mechanistic material, thus obtained, has been put together in a hyperbranched-polymer-based matrix system. Solid films and filters have been successfully fabricated using a solventless curing process, resulting in OPL filters of very high optical quality. These OPL filters have been subjected to gamma radiation and the effects on the OPL properties have been evaluated. The fabricated filters show potential for protecting optical sensors from laser-pulse damage in the space environment. Temperature- and space-radiation-induced effects in optical and electronic materials are well known and can cause disruption in OPL functions or, in the worst case, even failure of a sensor.

This PDF file contains the editorial “Guest Editorial: Nanophotonics for Space Applications” for JNP Vol. 3 Issue 01

Reflectance anisotropy spectra of porphyrin thin films (30 monolayers) show a permanent change in their line shape when porphyrins are exposed to some specific analytes (e.g., amines). From this experimental evidence, we concluded that a molecular package adjustment occurred in the film upon interaction with the volatile compound, most likely in the outermost layers. This result is of paramount importance for the consequent application of these films in optical gas-sensors. Consequently, this system could be used as a prototype for optical gas-sensing of aggressive analytes or, more ambitiously, to investigate the porphyrin-analyte interaction.

Spectral characteristics including photoluminescence (PL) spectra and its excitation spectra for different AlN materials (AlN ceramics, macro size powder and nanostructured forms such as nanopowder, nanorods and nanotips) were investigated at room temperature. Besides the well known UV-blue (around 400 nm) and red (600 nm) luminescence, the 480 nm band was also observed as an asymmetric long-wavelength shoulder of the UV-blue PL band. This band can be related to the luminescence of some kind of surface defects, probably also including the oxygen-related defects. The mechanisms of recombination luminescence and excitation of the UV-blue luminescence caused by the oxygen-related defects were investigated. It was found that the same PL band is characteristic for different AlN materials mentioned above; however, in the nanostructured materials (nanorods, nanotips and nanopowder) the intensity of UV-blue PL is remarkable lower than in the bulk material (ceramics). In the case of nanostructured AlN materials, excitation of the oxygen-related defect is mainly realized through the energy transfer from the host material (electron/hole or exciton processes) to the defects and this mechanism prevails over the mechanism of direct defect excitation.

We investigated the Raman, nuclear magnetic resonance (NMR), and transport characteristics of ¹³C-enriched single-walled carbon nanotubes (¹³CNTs). Systematic Raman spectroscopy measurements show that the ¹³C content of ¹³CNT can be controlled by the ¹³C source. Full width at half maximum of Raman spectra show a broad peak around 50% of ¹³C while G/D ratio remains almost constant. ¹³C NMR measurements indicate that the spin-lattice relaxation consists of two mechanisms and spin-spin relaxation time is of order of sub-millisecond. In transport measurement, we demonstrate that ¹³CNT shows quantum-dot features at low temperatures.

Advances in micro and nanofluidics have influenced technological developments in several areas, including materials, chemistry, electronics and bio-medicine. The phenomena observed at micro and nanoscale are characterised by their inherent multiscale nature. Accurate numerical modelling of these phenomena is the cornerstone for enhancing the applicability of micro and nanofluidics in the industrial environment. We investigated different strategies for applying macroscopic boundary conditions to microscopic simulations. Continuous rescaling of atomic velocities and velocity distribution functions, such as Maxwell-Boltzmann or Chapman-Enskog, were investigated. Simulations were performed for problems involving liquids and gases under different velocity and temperature conditions. The results revealed that the selection of the most suitable method is not a trivial issue and depends on the nature of the problem, availability of computational resource and accuracy requirement.

We study the two-particle dynamics in one-dimensional (1D) electron systems described by the Tomonaga-Luttinger model. By using bosonization methods we compute analytically two different kinds of two-particle response functions. In the first case the creation of the two particles does not involve any other degree of freedom in the system, and the subsequent propagation is described by a standard two-body Green's function. This is relevant to address, e.g, the behavior of recently observed local pairs in 1D optical lattices. In the second case the creation of the two particles occurs coherently with the decay of a third localized particle. Such a condition is crucial to study the Auger transitions in 1D systems like carbon nanotubes, where two holes are left in the valence band after the decay of a core-hole.

This paper shows, through a new geometrical approach, how to build some special deltahedra, which might represent nano-architectures of molecular structures, in nature commonly known as fullerenes, as well as new intriguing macro-architectures for designing innovative structures. We have realized models of these nano and macro architectures including a roof-like structure for a tennis court and educational games.

Metal endohedral fullerenes are large clusters mainly composed by carbon atoms characterized by unique properties. Fullerenes, the third form of solid carbon exhibit peculiar properties whose understanding is relevant for both fundamental studies and technological applications. A systematic investigation of both vibrational and structural properties of M@C82* (M=Y, La and Gd) compounds was performed by means of temperature dependent Fourier Transorf InfraRed (FTIR) and X-ray Absorption Near Edge Structure (XANES) spectroscopy. Among the nine possible isomers of the C₈₂ series: C_2v and C_s isomers were synthesized and characterized. Looking at both synchronous and asynchronous correlations of two dimensional (2D)-correlation plots of combined x-ray and InfraRed (IR) data we may support the identification of C_2v and C_s isomers. Different energy regions in x-ray and IR spectra have been selected and analyzed in order to distinguish isomers and understand the unique properties of metal-doped fullerene clusters.

We investigated the emission of terahertz radiation from a doubly interdigitated grating gates high electron mobility transistor. The experiment was performed using Fourier spectrometer system coupled with high sensitive 4 K Silicon bolometer under the vacuum. The observed emission was explained as due to the excitation of the plasma waves by means of hot 2D plasmons. We also investigated the optical stimulation of the plasma waves by subjecting the device to a CW 1.5 μm laser beam. Dependence of the emission on the gate bias (i.e. on electron density) was observed and interpreted as due to the self oscillation of the plasma waves.

Self-assembled monolayers are surfaces consisting of a single layer of molecules on a substrate: widespread examples of chemical and biological nature are alkylsiloxane, fatty acids, and alkanethiolate which can be deposited by different techniques on a large variety of substrates ranging from metals to oxides. We have found that a self-assembled biofilm of proteins can passivate porous silicon (PSi) based optical structures without affecting the transducing properties. Moreover, the protein coated PSi layer can also be used as a functionalized surface for proteomic applications.

I devised a method of electron beam lithography for patterning thin-film silicon- nitride membranes with nanoscale metal arrays of known dimensions. Employing SEM image-based metrology and ellipsometry to determine all three spatial dimensions of the metal nanostructures in the array, the calculated mass of each individual one can be used as a standard for elemental X-ray microanalysis. Thereafter, the net X-ray counts from the patterned nanostructures on a thin silicon-nitride substrate and nanoparticle unknowns can be compared directly for a "standards-based" quantitative analysis. The minimum mass detectable by this technique is ~10^-15 gm, supporting the determination of the absolute mass of nanoparticles with diameters as small as 20 to 30 nm. I then used a JEOL 6500F SEM equipped with a Bruker Quantax XFlash 4030 silicon drift detector (SDD) to assess the absolute masses of nickel nanoparticles contained in agglomerates of single-walled carbon nanotubes.

We investigated on the growth, by molecular beam epitaxy, of InAs quantum dots on nanoscale areas of the GaAs(001) surface defined by an e-beam lithographed SiO₂ mask. The selective self-assembling of the InAs dots inside the holes of the mask was obtained by a suitable choice of the growth parameters and of the pattern size. Photoluminescence from the spatially confined dots showed a blue-shifted emission but a radiative decay comparable to that of dots nucleated on the extended GaAs surface.

This PDF file contains the editorial “Guest Editorial: Selected Papers from the INFN-LNF Conference on Nanoscience and Nanotechnology” for JNP Vol. 3 Issue 01

Recent developments in the field of silicon nanostructures, particularly those properties and phenomena that are related to the photoluminescence (PL) from silicon nanostructures, have attracted much attention lately. A major source of controversy and disagreement among researchers is the underlying mechanism behind the PL. Two classes of models, i.e., the quantum confinement model that assigns the PL to quantum size effects in the nanocrystalline silicon core of the nanostructures and the surface chemistry model that assign the PL to surface phenomena at the interface between the crystalline core and the host matrix that wrap the nanostructures, are the most notable ones. In recent years, alternative structures to porous silicon, which allow synthesizing high quality silicon nanostructures with better control of their dimensionality, shape and size distribution, have emerged. In particular, fabrication techniques of silicon nanocrystals embedded in silicon-dioxide (SiO₂) matrices have reached a level where consistent investigation of surface and quantum size phenomena can be performed. Recent experimental results and theories suggest that none of the above models alone can explain the entire spectrum of optical phenomena in silicon nanostructures. Instead, a refined model that takes into account the mutual role of quantum confinement and surface chemistry in shaping the optical properties of these nanostructures should be considered.

Optical super resolution is one of the most applicable as well as scientifically exciting field of optics dealing with imaging and aiming to improve the spatial resolvable capabilities of any imaging system (digital or ophthalmic) without modifying the optical parameters of the imaging lenses or the geometry of the detection array. Recent developments in nanotechnological fabrication capabilities open new doors of possibilities in fulfilling modified and improved super resolving configurations. Fundamental concepts for obtaining super resolved imaging are related with time, angular, wavelength, polarization and gray levels multiplexing. The state of the art in the field of optical super resolution is reviewed while showing its relation with nanophotonics.

Rising demands of energy in emerging economies, coupled with the green house gas emissions related problems around the globe have provided a unique opportunity of exploiting the advantages offered by photovoltaic (PV) systems for green energy electricity generation. Similar to cell phones, power generated by PV systems can reach over two billion people worldwide who have no access to clean energy. Only silicon based PV devices meet the low-cost manufacturing criterion of clean energy conversion (abundance of raw material and no environmental health and safety issues). The use of larger size glass substrates and manufacturing techniques similar to the ones used by the liquid crystal display industry and the large scale manufacturing of amorphous silicon thin films based modules (~ GW per year manufacturing at a single location) can lead to installed PV system cost of $3/Wp. This will open a huge market for grid connected PV systems and related markets. With further research and development, this approach can provide $2/Wp installed PV system costs in the next few years. At this cost level, PV electricity generation is competitive with any other technology, and PV power generation can be a dominant electricity generation technology in the 21st century.

The diverse optical properties of colloidal semiconductor nanocrystals, including the linear and non-linear aspects of systems ranging from bulk-like to quantum confined, have been a topic of intense investigation for more than twenty years. However, many of the fundamental issues in these materials remain unresolved. Understanding these issues is key to their future use since the direct interrelation between their synthetically controllable size and shape and their physical properties make these systems ideal candidates for the development of designed materials.

New enhanced linear optical effects were found for crystalline solutions of fullerenes in toluene. They are referred to as enhanced Raman scattering and enhanced luminescence of both solvent and fullerenes and are attributed to clustering the solute molecules themselves and solute and solvent molecules together. The effects are due to the excitation of localized charge-transfer excitons of the fullerene nanoclusters which makes the latter act as amplifiers of local electric fields.

The absorbance, reflectance, and transmittance of a linearly polarized, obliquely incident plane wave were calculated for the planar interface of a metal and a sculptured nematic thin film (SNTF) in the Kretschmann configuration, the wave vector of that plane wave being arbitrarily oriented with respect to 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. Regardless of the orientation of the wave vector, multiple surface-plasmon-polariton (SPP) trains or waves of the same color but different phase speeds and guided by the metal/SNTF interface can be excited.

Based on coupled quantum electrodynamics the light propagation in active silicon nanocrystals was reported in this paper. The classical electron oscillator model was employed to bridge the link between the rate equations of the four-level atomic system of the active medium and the electromagnetic interaction. With the assistance of auxiliary differential equations we numerically solved the system by using the Finite-difference Time-domain (FDTD) method. Both stimulated and spontaneous emissions were taken into account in the active medium system. Light amplification characteristics due to stimulated emission were investigated under various pumping rates. To enhance the spontaneous emission, microcavities based on one-dimensional photonic crystals were designed to maximize the nonlinear interaction between the active medium and electromagnetic waves. Preliminary experimental investigation of the cavity-enhanced luminescence was performed to demonstrate the validation of the proposed simulation scheme.

A hybrid Au-Ag subwavelength metallic zone plate-like structure was put forth for the purpose of preventing oxidation and sulfuration of Ag film, as well as realizing superfocusing. The Au film acts as both a protector and modulator in the structure. Focusing performance is analyzed by means of three-dimensional finite-difference and time-domain (FDTD) algorithm-based computational numerical calculation. It can be tuned by varying thicknesses of both Au and Ag thin films. Our calculation results show that thickness difference between the Au and Ag thin films plays an important role for transmission spectra. Ratio of Au to Ag film thicknesses, h_Au/h_Ag is proportional to the relevant peak transmission intensity. In case of h_Au≈h_Ag=50 nm, both transmission intensity and focusing performance are improved. In addition, the ratio h_Au/h_Ag strongly influences position of peak wavelengths λAu and λAg generated from beaming through the metallic structures.

A simple single mode matching (SMM) method is proposed to analyze the optical throughput for subwavelength metal tapers. Both a 2D gold-clad taper gap and a 3D gold taper rod are analyzed with the SMM method. Including metal losses, these structures are calculated to have optimal squeezing taper angles of 14° with 71% efficiency and 32° with 44% efficiency, which is in good quantitative agreement with previous finite-difference time-domain simulations. The SMM method uses only analytic calculations and 2-by-2 matrix multiplication. Therefore, compared to past approaches, the SMM method is an efficient method to optimize the subwavelength metallic taper structures, while including losses, and it can be extended to more complex tapers and gratings in an obvious way. It also has the potential for fully analytic calculations.

The absorbances of two samples of a bilayer comprising a metal film and a periodically nonhomogeneous sculptured nematic thin film (SNTF) were measured in the Kretschmann configuration, the incident plane waves being linearly polarized with their wave vectors lying wholly in the morphologically significant plane of the SNTF. Comparison of experimental data with theoretical predictions confirmed the possibility of independently launching multiple surface-plasmon-polariton waves of the same color (frequency) but different phase speeds and polarization states. Exciting prospects are in store for plasmonics-based sensing, imaging, and communication.

The original Bruggeman and Maxwell Garnett formulas for the average dielectric function of a composite medium satisfy a scaling law: if the dielectric functions of both components are scaled by the same factor, the average dielectric function scales by this factor. These formulas are independent of the size of polarizable elements. Extended formulas explicitly account for size, but at least one formula fails to satisfy the scaling law, a likely failing of all such formulas.

We devised an approach for realizing add-drop filters. This approach uses strip waveguides to couple light into photonic crystal based resonators. We used silicon on insulator substrate with a 240 nm thick Si layer. Theoretical analysis, simulation and experiments were conducted. We compared the new device to a ring-based add-drop filter and found that for rings with radii smaller than 1.414 μm, our device has significant advantages.

We optically characterized colloidal gold nanoparticles using polarized light scattering which is utilized to investigate both optical anisotropy and aspect ratio of the particle and to observe particle's rotational dynamics. By monitoring time-trace of the polarized scattering from a particle, we could observe rotational dynamics as fluctuations in the measured anisotropy. With typical particle dimension of 97 nm, the maximum anisotropy was measured experimentally to be 0.1 to 0.5, and with comparison to our analytical model, this range is equivalent to an aspect ratio range of 1 to 1.3, which reveals that the colloidals are predominately spherical as predicted by transmission electron microscope (TEM) images analysis. Our method has the advantage to be simple, easy to implement, and can yield access to different projections of the particle due to its rotation. Polarized light scattering can be an ultrasensitive measure for biosensing applications.

The lowest oscillating waveguide mode can exist in guiding layer of a double-negative material that is symmetrically encapsulated in a double-positive material, even when the guiding layer's thickness is many times smaller than the operating free-space wavelength.

This PDF file contains the editorial “Editorial: Is the editor my peer?” for JNP Vol. 3 Issue 01

This PDF file contains the editorial “Editorial: False erudition” for JNP Vol. 3 Issue 01