This PDF file contains the front matter associated with SPIE Proceedings Volume 8094, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Nanomaterials have the potential to revolutionize photovoltaics with the promise of new physics, novel architectures and low cost synthesis. Silicon quantum dots, relative to their II-VI counterparts, are understudied due to the difficulty of solution synthesis and chemical passivation. However, silicon is still an attractive solar cell material, providing an optimal band gap, low toxicity, and a very solid body of physical understanding of bulk silicon to draw from. We have synthesized silicon quantum dots with plasma enhanced chemical vapor deposition, and have developed a method for chemical passivation of these silicon quantum dots that can be used on particles created in a variety of ways. This versatile method utilizes oxidation via wet chemical etch and subsequent siloxane bond formation. The attachment of a silane to the SiOx shell leads to stability of the silicon core for over a month in air, and individual particles can be seen with TEM; thus a stable, colloidal suspension is formed. The future for this technique, including increasing quantum yield of the particles by changing the nature of the oxide, will be discussed.

A device to control strength of interactions between adjacent nanostructures, namely Precise Interaction Control System for Nanostructures (PICSN) is developed. The PICSN is operated by combinations of DC motor and capacitancepositioning sensor. In this system, nanostructures are deposited on a flexible substrate and the strength of interactions can be controlled by changing a distance between adjacent nanostructures, stretching or shrinking the flexible substrate. Using the PICSN, we investigate photoluminescence of Au nanoclusters (NCs), which include at least Au5, Au8 and Au13 NCs, deposited on poly(dimethylsiloxane) substrate. We observed a blue shift of PL peak position with increasing interdot distance. Considering the relationship between absorption and emission energies of Au NCs, the blue shift is thought to be a result of fluorescent resonant energy transfer from smaller sized Au NCs to larger ones.

This paper presents briefly the history of the study of Si quantum dot (QDs) structures and the advances of different applications of Si quantum dots (QDs) in quantum electronics, such as: Si QD light emitting diodes, Si QD solar cells and memory structures, Si QD based one electron devices and double QD structures for spintronics [1].

We demonstrate 16 times increase in light absorption nano-structured metal compared to the flat surface by fabricating a subwavelength grating on gold surface. This light-trapping phenomenon can be used in many areas from solar energy conversion to photovoltaics. Here, we describe application to field enhancement in photocathodes where we show theoretically a performance increase of three orders of magnitude over conventional systems. We also describe the fabrication of these devices and present initial optical results.

The morphological stability of organic nanowires over time and under thermal load is of major importance for their use in any device. In this study the growth and stability of organic nanowires from a naphthyl end-capped thiophene grown by organic molecular beam deposition is investigated via atomic force microscopy (AFM). Aging experiments under ambient conditions already show substantial morphological changes. Nanoscopic organic clusters, which initially coexist with the nanowires, vanish within hours. Thermal annealing of nanowire samples leads to even more pronounced morphology changes, such as a strong decrease in nanowire number density, a strong increase in nanowire height, and the formation of new types of crystallites. This happens even before sublimation of organic material starts. These experiments also shine new light on the formation process of the nanowires.

We report here a method to enhance light extraction from the top face of a TiO₂ waveguide doped with a molecular emitter. Sol-gel TiO₂ surface is patterned by a 2D photonic crystal with a 400-nm period and a 40-nm depth, as verified by Scanning Electron Microscopy and Atomic Force Microscopy. We evidence that light emitted in the TiO₂ layer is efficiently extracted by the surface patterning and quantify the extraction enhancement by measuring the emission spectra as a function of the emission angle. We measured an enhancement factor of 3 within 50° off normal.

We report structural and vibrational properties of Mg doped ZnO nanoparticles. Structural studies are performed by X-ray diffraction technique, confirms that the prepared particles are in hexagonal wurtzite structure and the lattice parameters changes considerably due to doping. Vibrational properties done with Fourier Transform Infrared red spectroscopy (FTIR) show a band centered at 427cm^-1 corresponds to E₁(TO) mode. It is also observed that the intensity decreases with the increase of Mg concentration, apart from that the surface phonon modes are appeared at 460 and 521cm^-1. Compare to the undoped sample all the normal modes show red shift.

Evolution and natural selection have generated complexity and efficiency in all living families. Morpho sulkowskyi - a butterfly from Neotropic ecozone (South America) and belonging to the Nymphalidae family - concentrates on its wings distinct but complementary features contributing to its exceptional visual attraction: i) the wings are predominantly white but ii) present a bright blue metallic flash due to an iridescence process; iii) the presence of fluorescent molecules producing a violet-blue coloration when irradiated by ultraviolet light and finally iv) the particular ultrastructure of the scales presenting a three-dimensions natural photonic crystal. Due to the confinement of the fluorescent sources in a photonic crystal, the emission is preferentially directed in space and its efficiency is enhanced for particular detection angles. Furthermore, a clear correlation is observed between the reflection and the fluorescent processes that control the surface optical response. So, collecting and analyzing data over every emerging direction is shown to be crucial. To quantify these observations and characterize these optical effects, three types of measurements were carried out. First of all, the morphology of the butterfly was examined by means of scanning electron microscopes. In addition, the angular distribution of the reflected light was measured with a high performance viewing angle instrument, providing BRDF data (Bidirectional Reflectance Distribution Function). Finally, an automatic method coupling an ultraviolet source to a gonio-spectrophotometer allows fluorescent emission characterization. This set-up, developed on purpose, is composed of various excitation and analysis modules and provides angular emission maps. Tentative explanation for the measured correlation are presented.

We have observed a dynamic self-organization of laser scattering from the biosynthesized nanofluids with silver and gold nanoparticles. Various procedures for nanofluid synthesis suitable for different applications are under constant investigation. In our present research the green biosynthesis process has been used for noble nanoparticles production. The aqueous solution of Magnolia Grandiflora leaves has been used as a reductant for silver and gold nanofluids.. We have applied the UV-visible spectroscopy method to control reaction process, fluorescent spectroscopy and nonlinear interferometric imaging experiments for characterization of nanofluids. From the number of laser-induced photothermal interferometric fringes it is possible to estimate the nonlinear refractive index coefficient changes. The kinetics observed in the pump-probe experiments with blue and red CW laser allowed us to estimate a timescale (~1s) of photothermal lens formation and dissipation. Moreover, we have observed the very exciting and unusual phenomena of self-organization of the laser scattering reflected from the fluid's surface. The diverse regular diffraction patterns (hexagons, rolls, squares etc), resembling diffraction of X-rays on crystal structures, were self-organized in biosynthesized solutions of nanoparticles. From the angular size of the observed hexagonal diffraction patterns it was possible to estimate the diameter of diffracting nanoclusters as 18 microns for silver and gold nanofluids and 9 microns for the Magnolia broth. The kinetics of the hexagonal scattering shows a quasiperiodic pattern, with a period of about 12 seconds with the slow build-up and sharp disappearance of scattering.

In this research we studied the resonant reflection of circularly polarized light from a chiral stack of twisted ultra-thin birefringent layers such as found in the exocuticle of the beetle Proagoderus brucei. This beetle is interesting as it belongs to a very small group of species exhibiting different colors on different parts of its body. Measurements were compared with a computer model of the structure. In this way observations could be explained, some unknown parameters could be quantified and the properties of similar artificial structures with possible practical applications can be predicted.

The birdwings butterfly Troides magellanus possesses interesting properties for light and thermal radiation management. The black wings of the male exhibit strong (98%) absorption of visible light as well as two strong absorption peaks in the infrared (3 μm and 6 μm) both due to chitin. These peaks are located in the spectral region where the black body emits at 313K. The study of absorption enhancement in this butterfly could be helpful to design highly absorbent biomimetic materials. Observations of the wings using a scanning electron microscope (SEM) reveal that the scales covering the wings are deeply nanostructured. A periodic three-dimensional (3D) model of the scale nanoarchitecture is elaborated and used for numerical transfer-matrix simulations of the absorption spectrum. The complex refractive index of the wing material is approximated by a multi-oscillator Lorentz model, leading to a broad absorption in the visible range as well as two peaks in the infrared. The absorption peak intensities turn out to be dependent on the complexity of the nanostructures. This result clearly demonstrates a structural effect on the absorption. Finally, a comparison with a planar layer of identical refractive index and material volume lead us to conclude that the absorption is enhanced by nanostructures.

We have synthesized highly luminescent Cu-In-S(CIS) nanocrystals (NCs) by heating the mixture of metal carboxylates and alkylthiol under inert atmosphere. We modified the surface of CIS NCs with zinc carboxylate and subsequent injection of alkylthiol. As a result of the surface modification, highly luminescent CIS@ZnS core/shell nanocrystals were synthesized. The luminescence quantum yield (QY) of best CIS@ZnS NCs was above 50%, which is 10 times higher than the initial QY of CIS NCs before surface modification (QY=3%). Detailed study on the luminescence mechanism implies that etching of the surface of NCs by dissociated carboxylate group (CH3COO-) and formation of epitaxial shell by Zn with sulfur from alkylthiol efficiently removed the surface defects which are known to be major non-radiative recombination sites in semiconductor nanocrystals. In this study, we developed a novel surface modification route for monodispersed highly luminescent Cu-In-S NCs with less toxic and highly stable precursors. Investigation with the timeand the temperature-dependent photoluminescence showed that the trap related emission was minimized by surface modification and the donor-acceptor pair recombination was enhanced by controlling copper stoichiometry.xb

We provide the first experimental evidence of sharp resonant extinction in free-standing arrays of non-resonant dielectric nanorods. Nearly perfect optical extinction is shown for transparent material. High-resolution optical measurements (absolute transmission and reflection) of one dimensional gratings with very low fill factors have been obtained. The results can be fully explained by coherent multiple scattering in arrays of non-resonant subwavelength nanorods and are in good agreement with an analytical model.

Silicon nitride alloys emit photoluminescence all over the visible range. Recent studies ascribed this luminescence to quantum-size effects within silicon nanocrystals that were either shown or assumed to form inside the silicon nitride matrix; luminescence of the matrix itself was ignored. Observing the same luminescence without the presence of silicon nanocrystals, our work identifies the silicon nitride matrix itself to be responsible for the photoluminescence. In contrast to the silicon nanocrystal approach, the applied band tail luminescence model explains all aspects of the luminescence. We conclude that silicon nitride is an inappropriate matrix for investigating photoluminescence from silicon nanocrystals.

We report optical properties and X- ray peak broadening analysis of the Na doped ZnO nanostructures. To prepare Na doped ZnO, simple room temperature wet chemical method is adopted. X ray diffraction pattern shows prepared particles are in hexagonal wurtzite structure. The individual contributions of small crystallite sizes and lattice strain to the peak broadening in undoped and Na doped ZnO nanoparticles are studied using Williamson-Hall (W-H) analysis. Morphological properties are investigated through Scanning Electron Microscopic (SEM). Optical absorption measurements show an exciton absorption peak centred at 360 nm and as the doping concentration increases, exciton peak maximum shifts towards the higher wavelength. Photoluminescence measurements are carried out by exciting at 335 nm: reveal an exciton peak emission and oxygen vacancy band emissions. From Fourier Transform Infrared Spectroscopy (FTIR), the band at 433 cm^-1 is attributed to Zn-O bond

Nanostructures of the tin oxide, indium oxide and tin-doped indium oxide have been fabricated on silicon by chemical vapor deposition from a mixture of metal oxide nanoparticles and single-wall carbon nanotubes (SWCNT). Different ratios of the metal oxide to SWCNT have been used. It was found that the morphology of the nanostructures depends on the substrate temperature. The morphology, growth direction and optical properties have been studied by scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy.

In this paper, we report 150 MeV Ag³⁺ ions irradiation effect on ZnO nanoparticles prepared by sol-gel method. The fluence kept as 10₁₂ and 10₁₃ ions/cm³ using 15 UD Pelletron accelerator. The pristine as well as irradiated ZnO nanostructures were characterized by XRD, photoluminescence and FTIR to study the radiation induced effects on the local structure and optical properties. Irradiation with the fluence changes the colour of the sample from white to yellow. XRD measurement shows prepared particles are in hexagonal wurtzite structure and irradiation induces significant change in the lattice parameters. Photoluminescence measurements are done at the excitation wavelength of 335 nm, a broad spectrum consists near band edge emission and defect related visible emission band. FTIR spectra show a band at 514 cm^-1 is due to the stretching vibrations of Zn-O bond.

In this work, it is presented the synthesis of ZrO₂:Yb³⁺, Er³⁺ nanocrystals by precipitation method with a hydrothermal process and annealing at 1000 °C. Samples were prepared with 2 mol% of Yb³⁺ and 1mol% of Er³⁺, and sensitized with different concentration of Gd³⁺ and S²⁺. The ceramic powders were characterized with different techniques to determine their chemical composition, crystalline structure, crystallite size, morphology and upconversion emission. All samples present the tetragonal crystalline phase with crystallite size lower than 70 nm with cubic shape. Experimental results suggest the presence of SO₄ on the surface of nanocrystals reducing the OH's and then improving the signal emitted. The nanocrystals presented strong upconversion emission enhanced by the presence of both sensitizer Gd³⁺ and S²⁺. A synergistic effect was observed with the combination of both sensitizers, improving the upconverted visible emission. The red emission peak centered at 655 nm dominates the signal emitted but the red/green intensity ratio can be changed by controlling the dopant composition.

We have studied using frequency and temperature dependent admittance some electronic properties of InAs QDs embedded in a GaAs structure. The presence of QDs in our structure is evidenced in the C-V characteristics at all temperatures and frequencies by a plateau-like structure that is related to charging and discharging of QDs. Concurrently, the conductance shows a manifest peak in a certain bias range for temperatures below 150K. The conductance dependence on both temperature and applied bias reveal two different mechanisms of carrier escape from the QDs. Moreover, the conductance data at a given frequency was used to estimate rates and activation energies in association with the electron escape mechanisms from the QDs.