Resonant leaky modes can be induced on dielectric, semiconductor, and metallic periodic layers patterned in one or two dimensions. In this paper, we summarize their physical basis and present their applicability in photonic devices and systems. The fundamental amplitude and phase response of this device class is presented by computed examples for TE and TM polarizations for lightly and heavily spatially modulated gratings. A summary of potential applications is provided followed by discussion of representative examples. In particular, we present a resonant polarizer enabled by a single periodic silicon layer operating across 200-nm bandwidth at normal incidence. Guided-mode resonance (GMR) biosensor technology is presented in which the dual-polarization capability of the fundamental resonance effect is applied to determine two unknowns in a biodetection experiment. In principle, using polarization and modal diversity, simultaneously collected data sets can be used to determine several relevant parameters in each channel of the sensor system; these results exemplify this unique capability of GMR sensor technology. Applying the GMR phase, we show an example of a half-wave retarder design operating across a 50-nm bandwidth at λ~1550 nm. Experimental results using a metal/dielectric design show that surface-plasmon resonance and leaky-mode resonance can coexist in the same device; the experimental results fit well with theoretical simulations.

Scattering of light is considered a nuisance in microscopy. It limits the penetration depth and strongly deteriorates the achievable resolution. However, by gaining active spatial control over the optical wave front it is possible to manipulate the propagation of scattered light far in the multiple scattering regime. These wave front shaping techniques have given rise to new high-resolution microscopy methods based on strong light scattering. This is based on the realization that scattering by stationary particles performs a linear transformation on the incident light modes. By inverting this linear transformation, one can focus light through an opaque material and even inside it. An extremely high resolution focus can be obtained using scatterers embedded in a high-index medium, where the diffraction limit for focusing is reduced by a factor n. We have constructed a scattering lens made of the high-index material gallium phosphide (GaP) which is transparent over most of the visible spectrum and has the highest index of all nonabsorbing materials in the visible range. This yields a focal spot resolution of less than 100 nm, and it seems theoretically possible to create a focus of order 70 nm. The system resolution of a microscope based on this lens could be substantially higher.n

To deal with molecular information at a molecular level based on external signaling, a photonic DNA processor is a primal processing core of a nanoscale information system that works in molecular environment, for example, in situ. Use of photonic signals enables remote and spatio-temporal control of the processor. As an implementation example, we report a photonically-controlled DNA nanomachine which identifies and processes molecular information and implements physical processing as reporting the result using fluorescence signal. The nanomachine has two hairpin DNAs incorporating azobenzene and forms a tweezers-like structure. The hairpin structures are opened by ultraviolet-light irradiation, and a single-strand region is exposed to activate functionality in recognizing a target molecule. In contrast, visible-light irradiation makes the hairpin DNA close to inactivate the sensing function, and it releases the captured molecule. During activated term, the nanomachine changes its tweezers-like structure depending on existence or absence of the target molecule: the nanomachine transmutes into the closed state from the open state (initial state) by binding to the target molecule. Depending on the state, the nanomachine generates a fluorescence signal owing to fluorescence resonance energy transfer. In experiments, we demonstrated that the fluorescence intensities changed depending on existence and absence of the target molecule under photonic activation and inactivation. The result indicates that the nanomachine obtained information on the target molecule, changed the state, and reported the information to the outside world. In addition, we confirmed experimentally the functionality in measuring the concentration of the target molecule.image

Threshold current is a key parameter in the design and proper operation of quantum well lasers. In this publication, threshold current analysis and calculations are done on four PbSe/Pb0.934Sr0.066 Se quantum well laser structures: SQW, SCH-SQW, MQW, and MMQW. The current work is a continuation to previous publications where energy levels, modal gain, optical confinement, and total losses were published for these four structures assuming the energy bands are non-parabolic. The threshold current as a function of total losses, cavity length, and cavity end mirror reflectivity was obtained for these structures. It is shown that the threshold current decreases with a decrease in the cavity length and then increases at a critical cavity length. The effects of non-parabolicity on the threshold current values are more obvious for short cavities and decreases with an increase in cavity. Whether the SQW or the MQW is the better structure depends on the loss level. At low loss, the SQW laser is always better because of its lower current density where only one QW has to be inverted. At high loss, the MQW is always better because the phenomena of gain saturation can be avoided by increasing the number of QW's although the injected current to achieve this maximum gain also increases. Owing to this gain saturation effect, there exists an optimum number of QW's for minimizing the threshold current for a given total loss. At this typical value, the effects of non-parabolicity on the threshold current values can be neglected without loss of accuracy. However, there is a 20% shift in the output lasing energy that cannot be neglected.

Microfluidic structures in poly(dimethylsiloxane) (PDMS) are usually fabricated by optically patterning a resist and subsequently transferring this pattern to PDMS. Such microsystems suffer from reduced resolution, which in turn inhibit the manipulation of sub-micron scale entities such as bacteria, as well as their optical properties (e.g. long period gratings and radiation losses). In this paper we discuss how electron beam lithography (EBL) can be employed in prototyping SU8 moulds and nanostructures for poly(dimethylsiloxane) (PDMS) based microfluidics and optofluidics. In comparison to conventional optical methods, direct patterning of SU8 with an electron beam enabled both sub- and few micron scale structures with reduced complexity and duration. We will also discuss how to synthesize optofluidic circuits with this method and discuss our preliminary results on how such sub-micron scale structures can be employed in the optofluidic analysis of bacteria.

We describe nanotechnologies that improve the conversion efficiency of solar energy into electricity, and enhance the round-trip efficiency of energy storage systems. We describe nanostructures that enhance light concentration, light trapping, photon absorption, charge generation, carrier multiplication, hot electron extraction, charge transport, and current collection in photovoltaic systems, as well as nanomaterials that enhance the efficiency of electrochemical processes, boost gravimetric and volumetric energy densities, reduce the rate of self-discharge, increase the peak power rating, and extend the cycle life of secondary batteries.

Solar cells currently used are silicon based because they have higher efficiency than cells from other materials, but the manufacturing cost is high. Though, cheaper cells can be fabricated using organic materials because it solution processable, the efficiency is very low. Hybrid solar cells have improved the efficiency of organic solar cells. Hybrid solar cells with ZnO nanorods as the inorganic and P3HT (poly 3-hexylthiophene) and PCBM ((6, 6)-phenyl C61 butyric acid methyl ester) as the active layer reported in literature is usually prepared by spin coating. The major drawback of using spin coating technique is that large area fabrication is not possible and material wastage makes this technique uneconomical. Large scale production is feasible if these cells can be prepared by spray coating. Here we will discuss the fabrication and characterization of hybrid solar cells by spray coating technique.

The paper presents the creation of well aligned, vertically oriented, single crystal, high aspect ratio zinc oxide nanorods (ZnO NRs) for the purpose of gas detection in a chip based sensor. It is hypothesized that the best sensor functionality will be observed when the ZnO NRs are uniform and well controlled in their growth. The resulting process will maximize aspect ratio and attempt to find an optimal NR density for surface gas absorption.

Detectors currently used for UV detection are Si based and photomultiplier tubes, but these are bulky and less sensitive. ZnO based detector is an alternative to silicon and photomultiplier tubes due to its high sensitivity to UV light and can be fabricated cheaply and compactly. Here we attempt to increase the sensitivity of ZnO based detector by using electrode design that resembles a Wheatstone bridge and the detector has metal-semiconductor-metal structure. This new improved design enhances the collection of carriers and also miniaturization of the detector. The nanorods for the detector were grown by solution growth technique and the response of the detector on the length of the interdigitated fingers and spacing between the interdigitated fingers were also studied.49518

Polyaniline hydrochloride was prepared by the oxidation of aniline hydrochloride with ammonium peroxodisulfate in dilute hydrochloric acid. The polyaniline films were produced during the polymerization on the microscope glass surfaces immersed in the reaction mixture. The thin film was created and its thickness has been about 100 nm. We have measured the spectral transmittance together with temperature changes. The polyaniline thin film is conductive and we observed changes in optical transmittance spectra and reflective spectra with electric current. Optical spectra have been measured in range from 380 nm to 1010 nm. The electric conductivity has been changed with silicate substrate. This substrate influenced the free electrons distribution and therefore the optical properties of polyaniline. Due to electric current going through the nanofilm its sensitivity to temperature has been increased. We also observed two specific spectral windows. The first one was characterized by its insensitivity to temperature; the second one has been temperature sensitive. The central wavelength of insensitive window is about 500nm. This property can be the base for novel sensors structures. We used Ocean Optics USB spectrometer for evaluation of spectral changes. Wideband white light halogen source from the same manufacturer has been applied as a light source. Small polarizing dependence of reflected light has been observed too.

Organic crystalline nanofibers made from phenylene-based molecules exhibit a wide range of extraordinary optical properties such as intense, anisotropic and polarized luminescence that can be stimulated either optically or electrically, waveguiding and random lasing. For lighting and display purposes, the high quantum yield and the easy tunability of the color by changing the molecular building blocks are especially important. The application of such nanostructures as electrically driven light-emitters requires integration with suitable metal electrodes for efficient carrier injection. Here, we demonstrate the implementation of a method for achieving such nanostructure integration. The method relies on growing the nanostructures directly between metal electrodes on a substrate that has been specially designed to guide the nanostructures growth. We present results in terms of morphological characterization and demonstrate how appropriate biasing with an AC gate voltage enables electroluminescence from these in-situ grown organic nanostructures.

We present a method for homogeneous deposition of sol-gel sensor materials, which enable fabrication of sensor spots for optical pH and oxygen measurements inside plastic containers. A periodic pattern of posts is imprinted into a polycarbonate substrate and, using the principle of hemi-wicking, a deposited droplet spreads, guided by the posts, to automatically fill the imprinted structure, not being sensitive to alignment as long as it is deposited inside the patterned area. Hemi-wicking is an effective method to immobilize a low viscosity liquid material in well-defined spots on a surface, when conventional methods such as screen- or stamp-printing do not work. On length scales of the order of the microstructure period, surface tension will govern the shape of the liquid-air interface, and the liquid will climb up the pillars to keep a fixed contact angle with the sidewalls. The surface to volume ratio is therefore constant all over the surface of the liquid spread by hemi-wicking, when considering length scales larger than the microstructure period. Material redistribution caused by solvent evaporation, i.e., the "coffee ring effect", can therefore be avoided because the evaporation rate does not vary on length scales larger than the periodic pattern.

InAs nanowire-tunnel eld eect transistors (NW-TFETs) are being considered for future, beyond-Si electronics. They oer the possibility of beating the ideal thermal limit to the inverse subthreshold slope of 60 mV/dec and thus promise reduced power operation. However, whether the tunneling can provide sucient on-current for high-speed operation is an open question. In this work, for a p-i-n device, we investigate the source doping level necessary to achieve a target on-current (1 A) while maintaining a high I_ON=I_OFF ratio (110⁶) for a range of NW diameters (2 -8 nm). With a xed drain bias voltage and a maximum gate overdrive, we compare the performance in terms of the inverse subthreshold slope (SS) and I_ON=I_OFF ratio as a function of NW- diameter and source doping. As expected, increasing the source doping level increases the current as a result of the reduced screening length and increased electric eld at source which narrows the tunnel barrier. However, since the degeneracy is also increasing, it moves the eective energy window for tunneling away from the barrier where it is the narrowest. This, in turn, tends to decrease the current for a given voltage which, along with the consideration of inverse SS and I_ON=I_OFF ratio leads to an optimum choice of source doping.

The electronic structure and optical properties of Ge-core/Si-shell nanocrystal or quantum dot (QD) are investigated using the atomistic tight binding method as implemented in NEMO3D. The thermionic lifetime that governs the hole leakage mechanism in the Ge/Si QD based laser, as a function of the Ge core size and strain, is also calculated by capturing the bound and extended eigenstates, well below the band edges. We also analyzed the eect of core size and strain on optical properties such as transition energies and transition rates between electron and hole states. Finally, a quantitative and qualitative analysis of the leakage current due to the hole leakage through the Ge-core/Si-shell QD laser, at dierent temperatures and Ge core sizes, is presented.

Our work is devoted to the development of YAG:Ce³⁺ nanoparticle based films for white LEDs. Very stable suspensions of YAG:Ce nanoparticles are synthesized by a glycothermal method at relatively low temperature (300°C). A protected annealing in a silica matrix allows further treatment of these nanoparticles at high temperature without any aggregation and growth and with a significant improvement of their quantum yield and photostability. The obtained colloidal nanoparticles are finally incorporated into different matrices to be used as converter layer for white LEDs. First, the incorporation in epoxy caps confirms that the annealed particles are much more efficient than the as-made ones and leads to white light generation. YAG:Ce nanoparticles are also dispersed into a sol-gel matrix of TiO₂. Thanks to the relative matching of refractive indexes between TiO₂ and YAG, and to the sub-wavelength particles size, YAG/TiO₂films are not scattering, contrary to the same film containing the commonly used micron size phosphor. Nevertheless, they are not absorbent enough. Thus, YAG:Ce suspensions are then spray-coated to obtain thicker and non diluted films. These films are a bit scattering but this can be solved by filling their porosity with a high refractive index matrix. A yellow component is detected when deposited onto a blue LED, meaning that they absorb much more than the YAG:Ce/TiO₂ system. When used as light converters for white LEDs, these spray-coated films could offer the opportunity to diminish the backscattered light absorption losses.

The paper presents the results of 6H-SiC nanocrystals (NCs) characterization using atomic force microscope (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence spectroscopy techniques. XRD study shows the investigated porous 6H-SiC layers contain inclusions of 4H-SiC and 15R-SiC polytypes. Photoluminescence study of porous SiC layers with different thicknesses and SiC NC sizes (50-250 nm) reveals the intensity stimulation of exciton related PL bands in different SiC polytypes. The intensity enhancement for exciton-related PL bands is attributed to the exciton recombination rate increasing due to the realization of exciton-polariton effects in big size SiC NCs of different polytypes (6H-PSiC with inclusions of 15R- and 4H-PSiC).

We study the formation of complex pattern geometries and beam shapes in diffraction-based extreme ultraviolet interference lithography. In particular, we demonstrate numerically as well as experimentally the potential of interfering multiple beams with well-controlled relative phase relations for the fabrication of high resolution periodic and quasiperiodic nanostructures.

A method which combines colloidal lithography with the principle of a pinhole camera is presented for the fabrication of well-ordered arrays of complex structures. By using atomic beams, it is possible to overcome the diffraction limit of light for apertures with nanometer dimensions. There are no geometrical or chromatic aberrations, since no refracting elements exist. Limitations due to the finite size of the nanopinholes, which lead to a certain blurring of the replica, are discussed.

We have fabricated nanotextured Si substrates that exhibit controllable optical reflection intensities and colors. Si Nanopore, which has photon-trapping nanostructure but has abrupt changes in the index of refraction displaying a darkened specular reflection. Aluminum is evaporated on the surface of N-type Si by e-beam evaporation. Nanopore structure is formed by a two-step AAO formation in oxalyic acid. Diameter size from 30 to 80 nm is achieved, depending on the condition of anodization and etch. Deep reactive ionic etch (DRIE) is done, with AAO as the mask layer. The nanopore AAO template allows etching depth of up to 1600 nm. By tuning the nanoscale silicon structure, the optical reflection peak wavelength and intensity are changed, making the surface to have different reflectivity and apparent colors. Parameters that affect the fabrication are evaluated. Optical properties of various pore depths are discussed. The relation between the surface optical properties with the spatial features of the photon trapping nanostructures is examined. The tunable photon trapping silicon structures have potential applications in enhancing the performance of semiconductor photoelectric devices.ope>

In this work we present a cost-effective fabrication method for metal ring-shaped nanostructure arrays based on nanosphere lithography. Periodic arrays of nanorings and nanocrescents were fabricated using a simple method that includes self-assembled monolayer formation, plasma treatment and deposition of metal. Lower cost and higher throughput were achieved due to the replacement of ion beam milling with reactive ion etching usually used in other methods. The dimensions of ring-like structures could be controlled by the size of the polystyrene spheres, the amount of deposited metal and the argon plasma etching time. These nanostructures can be made of essentially any metal and used as elements in optoelectronic nanodevices.

The conventional approach to calculate the transmission and reflection spectra of a photonic crystal (PC) waveguide device by the finite-difference time-domain method is both time and memory demanding. Here we propose a more efficient approach to obtain these spectra. First, the PC-based absorbing boundary condition is employed. Second, the reflected pulse is obtained by subtracting from a reference waveform. For a T-junction in square lattice PC, a computational cell of 40 x 36 lattice constants can be used instead of 180 x 140 lattice constants. The simulation time is reduced to only one tenth of that using the conventional approach.

In this work, we design a 60-degree waveguide bend with a wide high-transmission bandwidth (~ 9.8% of the center frequency, or 150 nm at the wavelength of 1550 nm) in a triangular photonic crystal slab. Within the high-transmission bandwidth, power reflection at the bend is found to be lower than 2% of the input power. Based on this 60-degree bend, a sharp 120-degree bend with a compact device area is proposed. Similar transmission efficiency is also found for this 120-degree bend.tis@ep

We present results of imaging properties of the lens-crystal system for hard x-ray radiation. The system is based on a beryllium parabolic refractive lens placed in front of the sample, and an asymmetric silicon single crystal placed behind the sample. The beryllium refractive lens has such advantages as small absorption and high efficiency which allow high spatial resolution. We demonstrate a phenomenon of image formation using the Bragg reflection of focused x-ray beam from asymmetric single crystal. For recording the magnified x-ray phase contrast image the asymmetric single crystal Si (220) with asymmetry factor b = 1/6 was used at the x-ray energy 15 keV. The experiment was performed at the beam line BM-5 of the European Synchrotron Radiation Facility (ESRF). The peculiarities of image transformation are investigated both experimentally and theoretically when the focus of refractive lens is moved across and along the optical axis. The computer program was elaborated for a simulation of image formation in the system based on the refractive lens and the crystal with asymmetric Bragg diffraction. The algorithm is based on the FFT procedure for making a transition from a real space to a plane wave space.n/mswo

Crystalline Si photovoltaic modules still have high production cost due to significant consumption of the Si wafer. Reducing the large amount of Si material consumption is thus a critical issue. Here we develop a two-step metal-assisted etching technique for forming vertically-aligned Si nanohole thin films from bulk Si wafers. The formation of Si nanohole thin films includes a series of solution processes: deposition of Ag nanoparticles in an AgNO₃/ HF aqueous solution, formation of Si nanohole arrays at the first-step metal-assisted etching, and side etching of the roots of the nanohole structure at the second-step metal-assisted etching. All the processes can proceed at around room temperature. A Si nanohole thin film with an average hole-size of 100 nm and a thickness of 5ìm-20ìm was hence formed at the top of the wafer. Afterwards, the Si nanohole thin film was transferred onto alien substrates. The Si nanohole thin film has the crystal quality similar to the bulk Si wafer. The above bulk Si substrate can be reused. With similar processes, other Si nanohole thin films can be formed from the above recycled Si wafer. The hole size and thickness are similar. The Si wafers recycled will significantly reduce the material consumption of Si. Thus, such technique is promising for lowering the cost of Si solar cells.m.

Up to now, rechargeable batteries are mostly used for energy storage purposes. However, their electrochemical working principle limits the field of application. Capacitors with very high energy densities are an alternative approach for energy storage. They can be very quickly charged/discharged and have long lifetimes. We develop novel capacitors on the basis of 0-3 composites, where nanoparticles of perovskites are embedded in a matrix material. Specific organic and inorganic surfactants are used for coating of the nanoparticles. This coating enhances their uniform distribution in the matrix. The new materials combine the electrical advantages of ceramics and glasses/polymers (high permittivities and breakdown voltages) and can easily be processed as thin films.

Graphene is one of the strongest, lightest and most conductive materials that have ever been discovered. Graphene is stronger and stiffer than diamond, yet can be stretched by a quarter of its length. Graphene properties are attractive for scientists and electrical engineers for great deal of reasons. For example, it can provide us with circuits that are smaller and faster than what we have in silicon or we can have many other useful devices like super small computers. In this work, we have discussed a method in which we can control the charge transfer in graphene by using an electric field existed by a kind of variable external bias perpendicular to the graphene surface. This vertical electric field makes a rectangular barrier. The electrons go through the barrier in different angles. By solving the Dirac equation in different areas, the components of the Dirac spinor can be achieved. Finally, by applying the boundary conditions, we have evaluated the electronic transmission coefficient and probability. Our results show the complete transmission at the normal incident angle without being affected by the barrier height or length. While as the incident angle increases from zero, we can observe different values for the transmission probability including special angles at which we have resonances. Besides, the transmission probability has an oscillatory behavior as a function of barrier length which is related to quantum behaviors of the system. In addition, our calculations show that by manipulating the adjustable electric barriers on graphene, it is possible to control angle-dependent electronic transmission. In other words, we can control the electron transmission by manual tuning the external gate voltage from zero to unit. This formalism can be used in designing graphene base nano electeronic divices including field effect transistors.