The fourth generation of optics uses modulation of optical axis orientation in anisotropic materials for achieving a wide variety of optical functions. 4G optical components blend the thinness of zero-order waveplates with the high efficiency one gets with Bragg volume holographic gratings and in a broad band of wavelengths typical of conventional glass lenses, prisms, etc. (the first generation of optics). We will discuss the technology for applications in communications and astronomy. Particularly, we will present challenges and opportunities for fabrication of vector vortex waveplates and cross-waveplates for coronagraphy, and waveplate lenses - Pancharatnam-Berry phase lenses - for optical communications and imaging.

Nonlinear transmission is found to be significantly enhanced by introducing heavy metal atoms on the periphery of macrocycle porphyrin complexes via rhenium selenide clusters that are coordinated to four pyridyl groups. Experiments on 5, 10, 15, 20-tetra(4-pyridyl) porphyrin (H2TPyP), CuTPyP, [Re6(μ3-Se)8(PEt3)5]4(H2TPyP)(SbF6)8 (abbreviated as P5H2TPyP), and [Re6(μ3-Se)8(PEt3)5]4Cu(TPyP)(SbF6)8 (abbreviated as CuP5TPyP) using 10 ns laser pulses at 523 nm show that, in contrast to CuTPyP and P5H2TPyP, which are saturable absorbers at a low fluence of 1-100 mJ/cm2 and become nonlinear absorbers with a threshold larger than 1000 mJ/cm2 at high fluence, CuP5TPyP exhibits an excellent nonlinear transmission performance with a threshold as low as 20 mJ/cm2. A bulky rhenium selenide cluster was coordinated to pyridyl groups in tetrapyridyl porphyrin. The modified copper (II) porphyrin complex CuP5TPyP has strong nonlinear absorption at 523 nm and synergistic interaction between CuTPyP and P5H2TPyP is one of possible mechanisms.

Sodium chloride (NaCl) was found to be very helpful in producing single crystal zinc oxide (ZnO) nanowires in gram quantities. The growth involves heating the mixture of zinc powder and NaCl to 600-700 degrees C in flowing gases of oxygen and argon. A conversion efficiency of 70-80% (Zn to ZnO) was achieved when NaCl was used, and 5-10% without NaCl. The NaCl was completely removed by soaking and rinsing the mixture in water a few times. Photoluminescence spectra using excitation of 325 nm showed a very strong emission only in the visible frequency range, indicating that the surface states dominate the emission.

In this paper, we describe nano-assembly of amphiphilic polyelectrolytes within aluminosilicate nanoplates by layer-by-layer deposition and demonstrate how the resulting films are capable of functioning as hydrophobic barrier. The polyelectrolytes with a rigid backbone and long alkyl substitutes organized within the inorganic nanosheets, to form a double layer of interdigitated alkyl substitutes. The resulting 100nm-thick hydrophobic barriers efficiently blocked transport of moisture and hence enhanced the water vapor barrier properties of a relatively thick substrate (Nafion membrane, ca. 50μm) up to 22 times.

Carbon nanotubes were grown on silicon and quartz substrates in a honeycomb configuration using self-assembly nanosphere lithography and plasma enhanced chemical vapor deposition methods. Photonic nanoarrays were fabricated with varying spacing and carbon nanotube height. Both periodic and nonperiodic arrays were produced and evaluated. Optical properties of the arrays were studied and related to array geometry. Three dimensional diffraction maps were created that reveal the manner in which the nanoarrays interact with visible 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.

ZnO nanowires were grown in gram quantities on graphite flakes (as collector) using the vapour transport and condensation approach. The yield, defined as the weight ratio of ZnO nanowires to the original graphite flakes, has been studied thoroughly by tuning the various growth parameters such as pressure and temperature inside the tube furnace, the amount of graphite powder in the original source, the source to collector ratio, etc. A yield as high as 200% has been achieved, equivalent to a 40% conversion of the ZnO powder in the original source. A study comparing the photoluminescence spectra of the ZnO nanowires grown on both graphite flakes and substrates with commercially available ZnO powder has been carried out.

Abstract Electrostatically layered aluminosilicate nanocomposites have been prepared by the sequential deposition of poly(allylamine hydrochloride)/poly(acrylic acid)/poly(allylamine hydrochloride)/saponite (PAH/PAA/PAH/saponite)10 on poly(ethylene terephtalate) (PET) film. Exfoliated saponite nanoplatelets were obtained by extensive shaking, sonication, and centrifugation of a water suspension. To minimize permeability and improve the mechanical integrity, cross‐linking of composite films was carried out at different temperatures. The formation of amide linkage induced through heating was observed by Fourier Transform Infrared (FT‐IR) and x‐ray photoelectron spectroscopy (XPS). The cross‐linking of nanocomposites (PAH/PAA/PAH/saponite)10 showed 60% decrease in permeability of oxygen when compared with the pristine PET substrate film. In contrast, water permeability of the nanocomposite membrane was not affected by heating temperature and deposition cycles.

Wurtzite ZnO nanowall structures have been synthesized on a (110) Al2O3 substrate by a thermal evaporation and condensation method. The nanowalls are connected to each other and have a thickness of about 20–100 nm. An excellent epitaxial relationship with the substrate has been observed by X-ray diffraction. Edge-dislocation dipoles were observed by transmission electron microscopy. Photoluminescence measurements show strong UV emission at 390 nm for the white-gray nanowalls grown at high temperature, and very weak UV emission for the reddish nanowalls grown at low temperature.

We demonstrate here that large area periodic arrays of well-aligned carbon nanotubes can be fabricated inexpensively on Ni dots made by the process of self-assembly nanosphere lithography. These periodic arrays appear colorful due to their efficient reflection and diffraction of visible light. In addition, due to their honeycomb lattice structure, these arrays can act as photonic band gap crystals in the visible frequency range. In this report, we present the initial exploration of the optical properties of such arrays. Here we show that these potential 2D photonic band gap crystal arrays might find very important applications in optoelectronics.

A variety of novel ZnO nanostructures such as nanowires, nanowalls, hierarchical nanostructures with 6-, 4-, and 2-fold symmetries, nanobridges, nanonails have been successfully grown by a vapor transport and condensation technique. Doping both In and Sri into ZnO hierarchical nanostructures can be created. The 2-fold eutectic ZnO structures can also be created without any doping in the source. It was found that the hierarchical nanostructures can be divided into two categories: homoepitaxial and heteroepitaxial where heteroepitaxy creates the multifold nanostructures. The novel ZnO nanowalls and aligned nanowires on a-plane of sapphire substrate have also been synthesized and the photoluminescence is studied. The ZnO nanowires also demonstrated very good field emission properties, comparable to carbon nanotubes. These nanostructures may find applications in a variety of fields such as field emission, photovoltaics, transparent EMI shielding, supercapacitors, fuel cells, high strength and multifunctional nanocomposites, etc. that require not only high surface area but also structural integrity.

Carbon nanotubes (CN-T) 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 the 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.

Large-quantity (grams) one-dimensional ZnO nanowires of different sizes have been synthesized by a simple thermal evaporation of ZnO powder in a tube furnace at a temperature controlled to 1000–1200 °C and pressure to 1–2 Torr air. A mixture of ZnO and graphite powder was used as the source. Fine graphite flakes were used to promote the growth. The graphite flakes are the key for large-quantity yield and were easily removed by oxidation in flowing O2 at about 700 °C for 1–3 h. The scanning- and transmission-electron-microscopic studies show that the diameter and length of the nanowires vary from 20 to 100 nm and 0.5 to 10 μm, respectively. Room temperature photoluminescence studies found that the luminescent intensity depends on the processing conditions. A reduced band edge ultraviolet (380 nm) and deep-band green (520 nm) emission have been observed for these nanowires. Most importantly, the method can be extended to any other oxide nanowires that will be the building block of future nanoscale devices.