A simple, versatile, and scalable procedure for synthesizing high-quality colloidal ZnO quantum dots from homogeneous polar aprotic solutions has been developed. TEM and x-ray diffraction data show that the nanocrystals synthesized by this procedure are highly crystalline, pseudo-spherical, and have a narrow size distribution. This procedure allows large quantities of homogeneous ZnO quantum dots to be prepared with relative ease, and is also conducive to the introduction of dopants.

Silicon nanocrystals have been prepared in thermally oxidized hydrogenated amorphous silicon (a-Si:H) and annealed silicon-rich oxynitride (SRON) films with [O/Si]=0.17 [N/Si]=0.07, in the temperature range 400-800°C and 850-1150°C respectively. Glancing Angle X-ray Diffraction (GAXRD) measurements show the presence of silicon nanocrystals embedded in silicon oxide films. Warren-Averbach Analysis of GAXRD data indicates the presence of ~9 nm silicon crystallites in a-Si:H films oxidized at 800°C. Room temperature photo-luminescence (PL) was observed from silicon nanocrystals embedded in oxidized a-Si:H films. Modeling the PL data indicates the presence of 6 nm silicon nanocrystals. This discrepancy is attributed to the columnar growth of silicon nanocrystals in thermally oxidized a-Si:H films. Silicon nanocrystals were not formed by thermal oxidation of SRON films under similar reaction conditions. However, silicon nanocrystals could be fabricated by annealing SRON films for 4 h in vacuum over the temperature range 850-1150°C. Silicon crystallite sizes remained constant (~4 nm) for films annealed below 1050°C and increased to 9 nm for films annealed at 1150°C. The presence of nitrogen played an important role in the silicon nanocrystal precipitation in SRON films. While the nanocrystal formation in a-Si:H films was due to oxidation and crystallization progressing simultaneously in the films, nanocrystal formation in SRON films appears to be due to the high temperature precipitation of excess silicon in the film.

This paper describes a simple and convenient procedure for fabricating polycrystalline titania nanofibers with controllable diameter and porous structures. By combining sol-gel technique and electrospinning, nanofibers made of poly(vinyl pyrrolidone) (PVP) and amorphous TiO₂ were firstly obtained by electrospinning an ethanol solution containing both PVP and titanium tetraisopropoxide under appropriate high voltages. These nanofibers could be subsequently converted to anatase without changing their morphology via calcination in air at 500°C. The average diameter of these ceramic nanofibers could be controlled in the range from 20 to 200 nm by varying a number of parameters such as the voltage, the feeding rate of the precursor solution, the ratio between PVP and titanium tetraisopropoxide, and their concentrations in the alcohol solution. Titanium tetraisopropoxide could be transferred to titania nanofibers with ~100% yield by using this technique.

Electrochromic materials are of interest for a wide variety of applications, such as displays and smart windows. Many electrochromic oxide materials are synthesized through sol-gel processing. We have demonstrated a general technique for the synthesis of oxide nanorods using sol electrophoretic deposition with an appropriate template. This technique can be applied for the synthesis of nanorods of electrochromic materials, such as TiO₂, V₂O₅ and Nb₂O₅, with diameters of ~100 nm and a length of ~10 μm. By attaching these nanorods to a conducting substrate (such as ITO coated glass), it is possible to characterize the electrochromic behavior of these materials via UV-Vis absorbance spectroscopy. A similar technique has been used to make nanorods of the transparent conducting oxide indium tin oxide (ITO), which is often used as a working electrode in electrochromic devices. Such ITO nanorods have diameters of ~75-140 nm and lengths up to 60 μm.

Template-based growth of single crystal V₂O₅ nanorods by either electrochemical or electrophoretic deposition was studied. Specifically, standard electrochemical deposition from VOSO₄ solution, electrochemically induced deposition by local pH change of VO₂⁺ solution, and electrophoretic deposition of nanoclusters in V₂O₅ sol were investigated. From each route, uniformly sized V₂O₅ nanorods about 10 μm in length were grown over large area with nearly unidirectional alignment, but with various extent of lateral shrinkage when fired at 500°C. These grown V₂O₅ nanorods all have the same single-crystal structure, regardless of deposition method and initial solutions or sol used.

A solution-phase approach has been developed for the large-scale synthesis of metal nanostructures with well-defined shapes in the presence of a polymeric surfactant, i.e., poly(vinyl pyrrolidone) (PVP). As a demonstration, nanowires and nanocubes of silver have been synthesized through a modified polyol process that involved the reduction of silver nitrate with ethylene glycol heated at 160°C. Both reactant concentrations and the molar ratio between PVP and silver nitrate played critical roles in determining the shape and dimension of the final products. Relatively high concentrations of silver nitrate were favorable for the formation of silver nanocubes, while nanowires or nanorods became the dominated products if the concentration of silver nitrate was below 0.1 mM. The edge lengths of nanocubes and the lateral dimensions of nanowires synthesized with this method could be varied in the ranges of 50-180 nm and 30-60 nm, respectively. Nanocubes were single crystals mainly bounded by {100} facets. Each nanowire/nanorod, however, was characterized with a pentagonal cross-section, five straight side edges, and five flat side surfaces. It is believed that these silver nanostructures with well-defined shapes should find uses in a number of areas such as electronics, photonics, and catalysis.

Nanomaterials are advantageous for photoelectrochemical solar cell devices for high efficient conversion of light to electrical power due to its large surface area at which photoelectrochemical processes take place. One of the current solar cell systems utilizes dye-functionalized mesoporous titania films that consist of an interconnected network of nanometer-sized crystals. This type of structure imparts a large surface area for efficient dye adsorption and, thus, efficient electron-hole formation. This structure formed with connected nanoparticles possesses mesoscopic pores with an irregular and non-uniform pore structure. Such a structure imparts two problems: the transport of electrons through such a random structure, particularly through the necks between two particles, may become a limiting step, and the irregular mesoporous structure may not be ideal for dye assembly. In addition, a liquid electrolyte has to be used to accommodate such irregular mesoporous structures. In this paper, we propose to explore and present some preliminary results of ordered dye-functionalized titania nanostructures for potential enhancement of electron percolation pathways and light conversion. Such dye-sensitized, uniformly-sized, and unidirectionally-aligned titania nanorods and indium-tin-oxide nanorods coated with a titania layer have been synthesized and characterized for discussion.

Thin films of europium-doped yttrium oxide (Y₂O₃:Eu), a well-known luminescent material, were grown using electron beam evaporation, in combination with the Glancing Angle Deposition (GLAD) technique. GLAD makes use of controlled substrate motion during physical vapour deposition (PVD), resulting in a high degree of control over the nanostructure of the film. Until recently GLAD had not been used with luminescent materials. Films were deposited using pre-doped Y₂O₃:Eu source material, with either 4.0% (wt) Eu doping or 5.6% (wt) Eu doping. The nanostructure of these films was characterized through scanning electron microscopy, while the light emission properties of these films was characterized by photoluminescence measurements. In order to optimize the light emission properties of the films the partial pressure of oxygen during the deposition of the films was varied. Films were deposited on both silicon and sapphire substrates, in order to compare how different substrates affect the growth and light emission of the films.

This work exploits the localized surface plasmon resonance (LSPR) spectroscopy of noble metal nanoparticles to achieve sensitive and selective detection of biological analytes. Noble metal nanoparticles exhibit an LSPR that is strongly dependent on their size, shape, material, and the local dielectric environment. The LSPR is also responsible for the intense signals observed in surface-enhanced Raman scattering (SERS). Ag nanoparticles fabricated using the nanosphere lithography (NSL) technique exploits this LSPR sensitivity as a signal transduction method in biosensing applications. The current work implements LSPR biosensing for the anti dinitrophenyl (antiDNP) immunoassay system. Upon forming the 2,4 dinitrobenzoic acid/antiDNP complex, this system shows a large LSPR shift of 44 nm when exposed to antiDNP concentration of 1.5 x 10^-6 M. In addition, due to the unique molecular characteristics of the functional groups on the biosensor, it can also be characterized using SERS. First, the nanoparticles are functionalized with a mixed self-assembled monolayer (SAM) comprised of 2:1 octanethiol and 11-amino undecanethiol. The SAM is exposed to 2,4-dinitrobenzoic acid with the 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) coupling reagent. Finally, the 2,4-dinitrophenyl terminated SAM is exposed to various concentration of antiDNP. LSPR shifts indicate the occurrence of a binding event. SER spectra confirm binding of 2,4 dinitrobenzoic acid with amine-terminated SAM. This LSPR/SERS biosensing method can be generalized to a myriad of biologically relevant systems.

Photonic crystal templating of optically active hydrogel sensors is a topic of growing interest in materials chemistry. When interactions between a mesostructured hydrogel and the analyte molecules cause a reversible dimensional change of the hydrogel, the corresponding change in optical diffraction can be detected either spectroscopically or visually. Using poly(styrene) photonic crystals as templates, we synthesized inverse opal hydrogels through photopolymerization of 2-hydroxyethylmethacrylate and various functional monomers, and demonstrated the ability to sense pH and glucose at different ionic strengths and other experimental conditions. The diffraction of the pH sensitive hydrogel shifted from 544 nm to 850 nm when the pH was increased from 4 to 7, while the diffraction of the glucose sensitive hydrogel changed from 599 nm to 719 nm when the glucose concentration was raised from 0 mM to 100 mM. Diffraction response kinetics on the order of ~30 minutes were observed, which may be attributed to diffusion of analyte molecules through thin (12 - 24 μm) hydrogel samples. These mechanically robust inverse opal hydrogel sensors may form a starting point for chemical and biological sensing using diffractive three-dimensional mesostructures.

The demand for increasing optical data storage densities is ever present and there are currently many methods being researched, which address this problem. In order to achieve these densities many techniques, based upon near-field optical recording, will most certainly super-cede the far-field recording technique, in which the classical diffraction limit constrains recording density. A near-field recording technique based upon a Solid Immersion Lens (SIL) has proved to be a probable solution to this. In order to increase the resolution, the wavelength can be reduced or the numerical aperture (NA) increased. The downside of this is the reduction in the depth of focus, which places more demands on the optical system. The increase in resolution for SIL, compared to a conventional head is by a factor of 1/n as first introduced by Mansfield and Kino, where n is the refractive index of the SIL lens. SIL has continued to be of interest in the data storage community and has the potential to compete with other technologies to achieve the high data storage capacities desired in the current and future market. The system to be developed is to be based on an existing Scanning Laser Microscope, which will be adapted to incorporate a PZT positioning structure to control the SIL to sample gap height, and also the SIL's attitude. This is required in order for the collimated beam to focus through the SIL to a spot on the sample and achieve the required resolution. After the structure is complete, SIL's (firstly, hemisperical SILs ) of varying sizes will be used to form the investigation into the SIL structure, material, size and the affect this has on the system build and the materials being imaged. A variety of SIL configurations will be used to study this. The results obtained will be verified using a magnetic force microscope.

Recent progress in developing high-performance organic polymers for electro-optics and photonics is reviewed. A highly fluorinated hyperbranched aromatic polymer with the degree of branching around 0.51 was prepared by a mild one-step polyesterification of an AB₂ type monomer. Further post-functionalization with and thermally cross-linking by aromatic trifluorovinyl ethers (TFVE) afforded thermally stable, low loss optical polymer with improved solvent resistance. By more precisely controlling the molecular nano-architecture, we have developed a series of highly fluorinated crosslinkable dendrimers. These materials possess most of the desirable properties needed for the fabrication of optical waveguides, such as high solubility in common organic solvents (up to 50 wt%), very low optical loss, and excellent thermal stability. To overcome the “nonlinearity-stability tradeoff,” a facile and reversibly crosslinkable NLO polymer system is developed that combines both advantages of high poling efficiency and good alignment thermal stability. By smartly controlling the poling and crosslinking processes through the reversible Diels-Alder (DA) reactions, it allows highly polarizable chromophores to be efficiently poled at the stage of low viscosity linear thermoplastic polymer. The resulting nonlinear optical polymer exhibits a combination of a very large r₃₃ value (76 pm/V at 1.3 μm) and good temporal stability at 70°C.

Energy transfer studies were performed with polyphenylene-type polymers as the donating species and a series of organic dyes as the acceptors. The polymers were synthesized via Suzuki coupling of 2,5-didecyloxyphenyl-1,3-bisboronic acid with a corresponding dihaloarene. Coupling with 1,4-dibromobenzene produced a para-only polymer, while 3,5-dibromoethylbenzoate produced a polymer with alternating para- and meta-linkages. Several Coumarins served as singlet acceptors, while some porphyrins were used as triplet acceptors. Photophysical data and energy transfer parameters are presented.

Incorporation of two dyes into polystyrene beads was achieved through a core-shell emulsion free polymerization. The beads consisted of a central core, a dye containing emissive layer, and an overcoat layer. The overcoat layer thickness determined the final size of the nanospheres. The nanospheres were monodisperse and spherical. The nanospheres were used to asemble two photonic crystals. One in which the stop band overlapped with the dye emission of the donor dye, and one which had no overlap. The crystals formed were characterized by photoluminescence and reflectance studies. The crystal's emission was suppressed where the stop band overlapped the emission. This suppression shows the expected angular dependence and contributes to changes in the efficiency of energy transfer from Coumarin 334 to Nile Red. Suppression of emission and energy transfer impart an angular dependence of the color of emission to the crystal. This results in a material that is tunable with angle of both its reflectivity and its emission.

Novel complexes based on a europium(III) core surrounded by three β-diketonate ligands were synthesized. The diketonates were synthesized by condensations of ethyl-2-pyrazinecarboxylate with various aromatic ketones. The metal centered emissions of the europium complexes as well as the ligand centered emission of the gadolinium complexes were studied. The complexes based on gadolinium were studied to establish the singlet and triplet energy levels of the ligands. These europium complexes were used to harvest energy from conjugated polymers. PPP-type polymers with bipyridine moieties and terpyridine pendant groups were studied initially. The europium complex attached to the bipyridine and terpyridine moieties facilitated energy transfer from polymer to europium. A novel class of polymers with a β-diketonate pendant group was synthesized and studied. Each of the polymers were synthesized via Suzuki coupling of 1,4-phenylbisboronic acid with a dibromoarenecarboxylate. Ethyl 3,5-dibromobenzoate was used in the polymerization to synthesize alternating copolymers of phenyl groups. These polymers were then reacted with 2-acetylthiophene to obtain polymers with β-diketonate pendant groups. The photophysics of these polymers and their lanthanide complexes were determined.

In this paper, a nano-dots one-dimensional (1-D) photonic bandgap (PBG) filter design based on SOI waveguide is presented. The air dots in the polymer rod with various radii are compared in this paper. The simulation technique of the light propagates in our designed 1-D PBG waveguides is using the beam propagation method (BPM). The 1-D SOI PBG geometry we investigated consists of a three-layered dielectric structure. We assume various wavelengths at 1.3 μm and 1.5 μm windows are launched to the 1-D PBG SOI filter waveguide to see the simulation results. The air nano-dot wavelength selection effect is demonstrated. The output spectrum adjustment with nano-dots in 1-D PBG filter is dependent on the size of these PBG rods.

Effects of In_xGa_1-xAs strain relaxation layers on the optical and structural properties of InAs quantum dots (QDs) were studied systemically. 300 K-photoluminescence (PL) shows that PL peak energy of the QDs is blue-shifted in GaAs/InAs QDs/5 nm-thick In_0.1Ga_0.9As structure compared to GaAs/InAs QDs/GaAs structure. This is attributed to the intermixing of materials between the QDs and the InGaAs layer below the QDs, whereas capping of a 5 nm-thick In_0.1Ga_0.9As layer leads to red shift due to strain relaxation effect. As thickness of In_xGa_1-xAs capping layer (TI) increases, 300 K-PL peaks experience red shift below TI < ~7 nm. Unlikely, TI above 7 nm results in blue shift. Considering average height of the QDs is ~ 7 nm, this is attributed to intermixing of material between the QDs and InGaAs capping layers. The blue shift in x = 0.2 over TI > ~7 nm is relatively smaller compared to that in x = 0.1. It is noteworthy that strain difference between the InAs QDs and the In_xGa_1-xAs is smaller in x = 0.2 rather than in x = 0.1. Finally, InAs QDs are sandwiched by asymmetric thickness (7.5 nm-thick capping InGaAs, 0, 1.2, and 2.5 nm-thick bottom InGaAs) of In_0.2Ga_0.8As layers. 300 K-PL spectrum shows that 1.2 nm-thick bottom InGaAs leads to the longest wavelength (1306 nm) among this sample set. This is attributed to reduced barrier height and ignorable accumulated strain effect in thin bottom InGaAs layers. In this report, we justify merit of dots in an asymmetric well structure over conventional dots in a symmetric well structure and strain relaxation structure for the control of PL peak energy.

Carbon nanotubes (CNT) have been grown in a honeycomb configuration on silicon substrates using nanosphere self-assembly and plasma enhanced chemical vapor deposition. The optical properties of the arrays were also studied. Diffraction efficiency was found to be a function of the wavelength, angle of incidence and state of polarization of incident light. The unique optical properties of the arrays combined with the excellent mechanical and electrical properties of carbon nanotubes indicates that these materials may find many uses in the field of optoelectronics. In addition to their optical properties, periodic CNT arrays have a host of other unique electromagnetic and mechanical properties that may be exploited for numerous applications. Polarization measurements indicate that the intensity of both the diffracted light and diffusely scattered light is dependent on wavelength and angle of incidence. These arrays not only reflect and diffract light, but can also have a photonic band gap in, or around, the visible frequency range. The precise frequency location and size of this gap can be controlled by the structural and material parameters of the arrays.

Monolayer-stabilized nanoparticles of LaF₃ and LaPO₄ doped with the luminescent trivalent lanthanide ions Eu³⁺, Nd³⁺, Er³⁺, Pr³⁺, Ho³⁺, and Yb³⁺ have been prepared. These ions emit in the visible and in the near-infrared part of the electromagnetic spectrum. The ions Nd³⁺, Er³⁺ Pr³⁺, and Ho³⁺ are the main focus in this research because they show emissions in telecommunication windows. The Eu³⁺ ion is an excellent probe for the structural environment of the luminescent ion. It is shown that these lanthanide ions are incorporated in the inorganic host of the particles and that the particles are dispersable in organic solvents. The luminescent lifetimes of the ions are increased orders of magnitude compared to organic complexes, with values ranging from several microseconds for Pr³⁺ and Ho³⁺, up to about 200 μs for Nd³⁺, and 1 ms for Er³⁺. This increase in the luminescence lifetime is indicative of an effective shielding of the lanthanide ions from non-radiative decay of the excited state by the high-energy vibrations of the solvents and the coordinated organic ligands. A model is proposed to describe the non-exponential behavior of the lumienscence decay by quenching from outside the particle.

Silicon nanoparticles in the range from 2 nm to 5 nm was prepared from Zintl salt, soldium silicide (NaSi) by sonochemical method. This synthesis permits the reaction completed as fast as in a few hours and the easy alkyl-modification of nanocrystals surface at room temperature and ambient pressure. The average size of nanoparticles measured by the dynamic light scattering analysis was 2.7 nm. The high-resolution transmission electron micrograph cofirmed the material identity of nanoparticles as crystalline silicon. FT-IR spectra are consistent with the surface states of nanocrystals that is chlorine- or butyl-capped. The emission peak center moved to longer wavelength (up to 430 nm) with the reaction time, under a 325 nm excitation. The luminescence of silicon colloids looks bright bluish-white under excitation using a commercial low-intensity UV lamp.

Optically transparent superhydrophobic silica-based coatings were obtained by means of sol-gel processing and self-assembling. Superhydrophobicity was achieved through a combination of enhanced surface roughness by incorporating nanoclusters and modification of surface chemistry by self-assembly. The self-assembly monolayer (SAM) was prepared using the chemical coupling reaction between chlorosilyl groups and hydroxylated coating surface. The optical transparence of such hydrophobic coatings was found to be higher than 95%, which is attributed to the fact that the roughness scale is too small to scatter the visible light. The water contact angle was of approximately 150°.