利用LB技术制备发红光聚苯乙烯超薄膜

利用Langmuir-Blodgett(LB)技术,以二次水为亚相,在亚相表面直接铺展掺杂有稀土配合物Eu(TTA)3phen的苯乙烯分子,然后在一定表面压下进行现场聚合,制得了发红光的聚苯乙烯超薄膜,并用红外光谱、紫外-可见光谱、透射电子显微镜、荧光显微镜、光谱型椭圆偏振仪等对薄膜进行了表征。     

Polarized light reflection from strained sinusoidal surfaces

We propose optical polarization imaging as a minimally invasive technique for measuring the mechanical properties of plastics and soft tissues through their change in reflectance properties with applied strain or force. We suggest that changes in surface roughness are responsible for the linear reflectivity changes with applied stretch or strain. Several aspects of this model are tested, including the dependence on the angle of incidence, the change in scattering and absorption coefficients with strain, and the lateral spatial resolution. The application of the technique to multilayer structures such as skin and competing optical effects such as laser speckle are discussed.     

Spectroscopic studies of large sheets of graphene oxide and reduced graphene oxide monolayers prepared by Langmuir-Blodgett technique

Graphene oxide (GO) sheets prepared by chemical exfoliation were spread at the air-water interface and transferred to silicon substrates by Langmuir-Blodgett technique as closely spaced monolayers of 20-40 μm size. Hydrazine exposure followed by annealing in vacuum and argon ambient results in the formation of reduced graphene oxide (RGO) monolayers, without significantly affecting the overall morphology of the sheets. The monolayer character of both GO and RGO sheets was ascertained by atomic force microscopy. X-ray photoelectron spectroscopy supported by Fourier transform infrared spectroscopy revealed that the reduction process results in a significant decrease in oxygen functionalities, accompanied by a substantial decrease in the ratio of non-graphitic to graphitic (sp² bonded) carbon in the monolayers from 1.2 to 0.35. Raman spectra of GO and RGO monolayers have shown that during the reduction process, the G-band shifts by 8-12 cm^− 1 and the ratio of the intensities of D-band to G-band, I(D)/I(G) decreases from 1.3 ± 0.3 to 0.8 ± 0.2, which is in tune with the smaller non-graphitic carbon content of RGO monolayers. The significant decrease in I(D)/I(G) has been explained by assuming that substantial order is present in precursor GO monolayers as well as RGO monolayers obtained by solid state reduction.     

Field emission properties of composite nano-Au/DLC films prepared by CVD technique

Nanocrystalline gold incorporated diamond-like carbon (nano-Au/DLC) films were deposited by capacitively coupled plasma (CCP) r.f. chemical vapour deposition (CVD) technique. Gold content in the DLC matrix was controlled by the amount of argon in the argon + methane mixture in the plasma. Field emission properties of these films were studied critically. Bonding environment (sp²/sp³ ratio) in these films was obtained from Raman measurements. Modification of the surface with the incorporation of gold nanocrystallites and associated modulation of sp²/sp³ ratio in the films culminated in improved field emission properties. Fowler-Nordheim model was used to ascertain the work function (?) which varied between 19 and 64 meV. The field factor (β) varied between 172 and 1050.     

Polarized light scattering by aerosols in the marine atmospheric boundary layer

The intensity and polarization of light scattered from marine aerosols affect visibility and contrast in the marine atmospheric boundary layer (MABL). The polarization properties of scattered light in the MABL vary with size, refractive index, number distributions, and environmental conditions. Laboratory measurements were used to determine the characteristics and variability of the polarization of light scattered by aerosols similar to those in the MABL. Scattering from laboratory-generated sea-salt-containing (SSC) [NaCl, (NH(4))(2) SO(4), and seawater] components of marine aerosols was measured with a scanning polarization-modulated nephelometer. Mie theory with Gaussian and log normal size distributions of spheres was used to calculate the polarized light scattering from various aerosol composition models and from experimentally determined distributions of aerosols in the marine boundary layer. The modeling was verified by comparison with scattering from distilled water aerosols. The study suggests that polarimetric techniques can be used to enhance techniques for improving visibility and remote imaging for various aerosol types, Sun angles, and viewing conditions.     

Infrared light emission from porous silicon

Very intense broad sub-bandgap infrared (IR) light emission around 1,550 nm was observed on porous silicon by photoluminescence (PL) measurements. The integrated intensity of the IR signal is two orders of magnitude higher than that of the band–band emission in Cz silicon. PL measurements with the sample immersed in different media, e.g., in HF and H₂O₂, confirmed that the broad IR band originates from the Si/SiO _x interface. Electroluminescence spectroscopy was carried out on a porous silicon p–n junction sample contacted with indium-tin oxide. The IR band was detected at room temperature at both forward and reverse bias. The results indicate that radiative recombination through interface states is very efficient at room temperature.     

Optical properties of Langmuir-Blodgett films investigated by a photoacoustic technique

A photoacoustic (PA) technique based on a four-layer prism configuration has been developed for nondestructive determination of the optical properties of Langmuir-Blodgett (LB) films, in which the PA signal amplitudes are measured as functions of the incident angle of light. With this technique the experimental PA angular spectra of manganese stearate and cadmium stearate LB films were obtained. Based on the electromagnetic theory and taking into account the anisotropic properties of LB films, as well as use of the numerical optimization method, we have simultaneously determined the optical constants and thicknesses of films based on experimental PA angular spectra.     

Field emission from vertical graphene sheets formed by screen-printing technique

Vertical graphene field emission cathodes were fabricated using screen-printing and the following selective photoetching techniques. Excellent field emission properties of the screen-printed vertical graphene film were obtained with low turn on field, high maximum current density, and large field enhancement factor. The organic layer anchoring the vertical graphene sheets acted as negative feedback layer, which contributed to the high uniformity and stability of the field emission device. The results pave the low-cost way for applications of graphenes in large-scale field emission devices.     

Enhanced light extraction from GaN-based LEDs with a bottom-up assembled photonic crystal

Photonic crystal (PhC) structure is an efficient tool for light extraction from light-emitting diodes (LEDs). The fabrication of a large area PhC structure on the light output surface of LEDs often involves sophisticated equipments such as nanoimprint lithography machine. In this study a monolayer of polystyrene (PS) microspheres was employed as a template to fabricate a noninvasive photonic crystal of indium tin oxide (ITO) on the surface of GaN-based LED. PS spheres can help to form periodic arrangement of bowl-like holes, a photonic crystal with gradually changed fill factors. Importantly, the electroluminescence intensity of LED with a photonic crystal was significantly enhanced by 1.5 times compared to that of the conventional one under various forward injection currents.     

Modeling of fluorescence emission from cyanine-dye-impregnated Langmuir-Blodgett films deposited on the surface of an optical fiber

Fluorescence emission was collected from cyanine-dye-impregnated Langmuir-Blodgett (LB) films of cadmium arachidate deposited on the surface of a quartz multimode optical fiber. A Y-type fiber optic coupler system was used to allow remote, distal-end spectral excitation and collection as the fiber tip was repeatedly dipped into the LB trough. Built-up LB films of up to 400 LB layers were examined. Fluorescence emission intensities were modeled as a function of the number of layers, or LB film thickness, using a simplified theory based on planar thin film optics. The fit of theory to experiment was qualitatively satisfying, indicating that LB films of reasonable optical quality can be deposited on the surface of cylindrical optical fibers.     

Polarized light scattering by dielectric and metallic spheres on silicon wafers

The polarization and intensity of light scattered by monodisperse polystyrene latex and copper spheres, with diameters ranging from 92 to 218 nm, deposited on silicon substrates were measured with 442-, 532-, and 633-nm light. The results are compared with a theory for scattering by a sphere on a surface, originally developed by others [PhysicaA 137,209 (1986)], and extended to include coatings on the sphere and the substrate. The results show that accurate calculation of the scattering of light by a metal sphere requires that the near-field interaction between the sphere and its image be included in acomplete manner. The normal-incidence approximation does not suffice for this interaction, and the existence of any thin oxide layer on the substrate must be included in the calculation.     

Release of furosemide from sustained release microcapsules prepared by phase separation technique

Furosemide Eudragit RL-100 sustained release microcapsules were prepared using phase separation technique. The results of the release studies, in sorensen phosphate buffer at PH 7.4, indicated good sustained release of the prepared microcapsules. Increasing drug to polymer ratio resulted in a decrease in the release, while increased release obtained by increasing the PH of the dissolution medium. Dosing of healthy human volunteers with sustained release microcapsules resulted in a reduced and sustained urine volume compared to the profuse diuresis obtained with the conventional furosemide capsules.     

AlCu alloy films prepared by the thermal diffusion technique

100-nm thick films of Al_1 ? xCu_x alloys were prepared on glass substrates by thermal diffusion technique. The Cu atomic concentration was varied from 10% to 90%. Alloys were prepared at different temperatures into a vacuum oven with Argon atmosphere. Two thermal processes were used: i) heating the film at 400 °C in a single step, and ii) heating the films in sequential steps at 100, 200, 300 and 400 °C. Morphology, electrical resistivity, and crystalline orientation of the alloys were studied. The electrical resistivity and surface roughness of the alloys were found to depend strongly on the atomic composition and the diffusion temperature. However, we did not find differences between samples prepared under the two thermal processes. Alloys prepared with x = 0.6 and x = 0.1–0.3 as Cu at concentration exhibited values on electrical resistivity and surface roughness lower than pure Al. Different phases of the Al_1 ? xCu_x films were observed as a function of Cu concentration showing a good agreement with the AlCu phase diagram.     

Growth of fullerene nanoparticles prepared by the gas-evaporation technique

C60 and C70 fullerene nanoparticles prepared by evaporating their powders in inert gas were investigated by electron microscopy and X-ray diffraction. Crystal structures of the particles were face centred cubic (fcc) which is a stable phase at high temperature, with lattice parameters of a=1.42 nm for C60 and a=1.499 nm for C70. Nanoparticles with definite crystal habits were sometimes observed among those with irregular ones. For the C70 nanoparticles, the higher the source temperature was, the better-defined the crystal habits were.     

乳液法制备有机硅弹性体泡沫

通过乳液聚合方法制备了有机硅弹性体泡沫,制备的油包水型乳液的液滴直径小于20μm.讨论了乳液中水和交联剂的用量对泡沫材料密度、孔隙率、孔尺寸的影响.研究表明,硅树脂对硅氧烷交联体有良好的增强作用;采用高氢值、低用量的含氢硅油作为交联剂,弹性体泡沫材料泡孔尺寸减小,密度增高;弹性体泡沫密度随乳液水含量的增加而降低.     

Polarized light scattering by microroughness and small defects in dielectric layers

The polarization of light scattered by the surface of a material contains information that can be used to identify the sources of that scatter. Theories for light scattering from interfacial roughness of a dielectric layer and from defects in that dielectric layer are reviewed. Methods for calculating the Mueller matrix or the Stokes vector for scatter from multiple sources and for decomposing a Stokes vector into contributions from two nondepolarizing scattering sources are derived. The theories are evaluated for a specific sample and geometry. Results show that some incident polarizations are more effective than others at discriminating among scattering sources, with s-polarized light being least effective. The polarization of light scattered from interfacial roughness depends upon the relative roughness of the two interfaces and the degree of correlation between the two interfaces. The scattering from defects in the film depends on the depth of the defect and differs from that from any one of the cases of interfacial roughness. The scattering from defects randomly distributed in the film and for small dielectric permittivity variations in the film is also calculated. Experimental results are presented for a 52-nm SiO2 film thermally grown on microrough silicon.     

Optimized light emission from layered porous silicon structures

We discuss in detail the physics of light emission from porous silicon microcavities formed by periodically modulating the porosity to produce multilayered structures. Changing the porosity alters not only the refractive index and absorption but also the luminescence, resulting in a complex interplay of effects that has not yet been addressed in the literature as far as we know. A transfer matrix model is developed that accounts for the dispersion of the refractive index, absorption, and photoluminescence. A multilayer porous silicon mirror is found to emit light almost as well as a conventional distributed feedback microcavity system with a mid-stop-band resonant state.     

Green light stimulates terahertz emission from mesocrystal microspheres

The discovery of efficient sources of terahertz radiation has been exploited in imaging applications, and developing a nanoscale terahertz source could lead to additional applications. High-frequency mechanical vibrations of charged nanostructures can lead to radiative emission, and vibrations at frequencies of hundreds of kilohertz have been observed from a ZnO nanobelt under the influence of an alternating electric field. Here, we observe mechanical resonance and radiative emission at ～ 0.36 THz from core-shell ZnO mesocrystal microspheres excited by a continuous green-wavelength laser. We find that ～ 0.016% of the incident power is converted into terahertz radiation, which corresponds to a quantum efficiency of ～ 33%, making the ZnO microspheres competitive with existing terahertz-emitting materials. The mechanical resonance and radiation stem from the coherent photo-induced vibration of the hexagonal ZnO nanoplates that make up the microsphere shells. The ZnO microspheres are formed by means of a nonclassical, self-organized crystallization process, and represent a straightforward route to terahertz radiation at the nanoscale.     

Unidirectional broadband light emission from supported plasmonic nanowires

Metal nanowires are thought to become key elements in future nanophotonics applications. Here we show that single crystal silver nanowires supported on a dielectric interface behave similar to broadband unidirectional antennas for visible light. The degree of directionality can be controlled through the nanowire radius and its dielectric environment and the effect can be interpreted in terms of so-called leakage radiation from surface plasmons propagating in a single direction along a wire. We measure a forward-to-backward emission ratio exceeding 15 dB and an angular spread of 4° for wires with radii of the order 150 nm on glass in air. These findings could pave the way for development of metal nanowires as subwavelength directors of light in solar, sensor, and spectroscopy applications.