基于双层微透镜阵列的移动视差式立体显示屏

受限于微透镜的数值孔径和像差问题,目前移动视差式立体显示屏存在多视场空间、视场区之间存在视场跳变、主视场空间角度小、显示效果模糊等问题.本文基于离散采样思想,分析了移动视差型三维显示系统的工作机理,结合加工工艺,设计了复合曲面反射层的双层微透镜阵列屏.仿真结果表明:所设计显示屏的视场观看空间角可提升到60°,相对于传统的三维显示屏,双层微结构显示屏可有效提高视场角和显示性能.     

One-step synthesis and stabilization of gold nanoparticles and multilayer film assembly

Au nanoparticles (NPs) were synthesized in the one-pot procedure in water at room temperature with the wheel-shaped V^V-V^IV mixed-valence tungstovanadate [P₈W₄₈O₁₈₄{V₄^VV₂^IVO₁₂(H₂O)₂}₂]³²⁻ (V12) acting as both reducing and stabilizing agents. The V12 stabilized Au NPs (Au@V12 NPs) were characterized by SEM, TEM, DLS, UV-vis spectroscopy, XPS, and XRD analyses and the negatively charged surface of the Au@V12 NPs was proved by the zeta potential analysis. Based on the layer-by-layer assembly (LbL), the Au@V12 NPs-containing multilayer films have been fabricated on ITO-coated glass slide and quartz substrates with poly(ethyleneimine) (PEI). The regular growth of the multilayer films was monitored by UV-vis spectroscopy and cyclic voltammetry, the composition was characterized by XPS. The Au@V12 NPs based composite films showed electrocatalytic activities towards the reduction of dioxygen and the oxidation of methanol. This approach is expected to open the way towards procedures aimed at the one-step fabrication of Au NPs and polyoxometalates (POMs) into the multilayer films.     

Algebraic foundations of split hypercomplex nonlinear adaptive filtering

A split hypercomplex learning algorithm for the training of nonlinear finite impulse response adaptive filters for the processing of hypercomplex signals of any dimension is proposed. The derivation strictly takes into account the laws of hypercomplex algebra and hypercomplex calculus, some of which have been neglected in existing learning approaches (e.g., for quaternions). Already in the case of quaternions, we can predict improvements in performance of hypercomplex processes. The convergence of the proposed algorithms is rigorously analyzed. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of AlxGa1−xAs/GaAs heterostructures for single quantum wells grown by a solid arsenic MOCVD system

This work presents the results of the growth and characterization of Al_xGa_1−xAs/GaAs multilayer structures obtained in a metallic-arsenic-based-MOCVD system. The main goal is to explore the ability of the growth system to grow high quality multilayer structures like quantum wells. The use of metallic arsenic could introduce important differences in the growth process due to the absence of the hydride group V precursor (AsH₃), which manifests in the electrical and optical characteristics of both GaAs and Al_xGa_1−xAs layers. The characterization of these epilayers and structures was performed using low-temperature photoluminescence, Hall effect measurements, X-ray diffraction, Raman spectroscopy, secondary ion mass spectroscopy (SIMS) and Atomic Force Microscopy (AFM).     

Microstructure, hydrogenation and optical behavior of Mg-Ni multilayer films deposited by magnetron sputtering

Mg-Ni multilayer films with sequential Mg and Ni layers were prepared by direct current magnetron sputtering. The substrate temperature influences the microstructure of the films greatly. The film deposited at 298 K exhibits multilayered structure, while the film shows nanocrystalline/amorphous composite structure at the deposition temperature of 473 K. The optical properties between hydrogenation/dehydrogenation states of the films were performed using spectrophotometer in visible light region. The film deposited at 473 K can switch from mirror-like metallic state towards brownish yellow transparent state under 0.6 MPa H₂ at 298 K, and the optical transmittance modulation reaches up to 20% both at a wavelength of 770 nm and IR region, while the film deposited at 298 K exhibits low optical change, and the optical switching behavior can hardly be found. The extra free energy stored in the boundary of the nanocrystallines benefits the formation of magnesium-based hydride, resulting in the enhancement of the optical switching properties of the Mg-Ni film deposited at 473 K.     

Transparent conductive and near-infrared reflective Cu-based Al-doped ZnO multilayer films grown by magnetron sputtering at room temperature

Cu-based Al-doped ZnO multilayer films were deposited on glass substrates by DC magnetron sputtering at room temperature. Three kinds of multilayer structures (AZO/Cu, AZO/Cu/AZO, and Cu/AZO) were designed for comparison, and the effects of the Cu layer thickness on photoelectrical properties of the multilayer films were investigated. The results revealed that the transparent-conductive property and near-infrared reflectance of the films are closely correlated with the Cu layer thickness, and among the three structures, AZO/Cu bi-layer films exhibited preferable photoelectrical properties. The AZO/Cu bi-layer film with a Cu layer thickness of 7 nm displayed the highest figure of merit of 4.82 × 10⁻³ Ω⁻¹, with a low sheet resistance of 21.7 Ω/sq and an acceptable visible transmittance of 80%. The near infrared reflectance above 50% can be simultaneously obtained. The good performance of the coatings indicates that they are promising for coated glasses, thin film solar cells and heat-reflectors.     

Multilayer laser printing for Organic Thin Film Transistors

Functional laser printed Organic Thin Film Transistors (OTFTs) have been achieved from multilayer substrates composed with semiconductor and electrodes. The p-type copper phthalocyanine (CuPc) was used to form the active layer. Different kinds of metallic materials were used for source and drain electrodes. Multilayer donor substrates were prepared by the successive depositions of materials by either thermal evaporation under vacuum or laser printing. The materials were transferred together in a single step onto a receiver substrate by laser pulses in the picosecond regime. The latter substrate formed the gate and the dielectric of the transistor. The results are compared with the step-by-step laser printing process, where electrodes and organic layer were successively printed from two different donor substrates. The multilayer laser printing reveals an improvement of the performances of the OTFT devices.     

Pulsed laser deposition of polymer-metal nanocomposites

Different polymer-metal nanocomposites, metal clusters on a polymer surface and for the first time also polymer/metal multilayers, were pulsed laser deposited at a wavelength of 248 nm. Poly(methyl methacrylate) (PMMA) and Bisphenol A dimeth-acrylate (BisDMA), which strongly differ in their hardness of 3 and 180 N/mm², respectively, were taken as polymer components. Metals Ag and Cu were chosen because of their different reactivity to polymers. When depositing Ag on PMMA, spherical clusters are formed due to high diffusion and total coalescence. For Cu, much smaller grains with partially elongated shapes occur because of lower diffusivity and incomplete coalescence. Compared to the results on the soft PMMA, the clusters formed on the harder BisDMA are much larger due to higher diffusivity on this underlayer. In PMMA/Cu multilayers, wavy layered structures and buckling is observed due to relaxation of compressive stress in the Cu layers. Smooth Cu layers with higher thicknesses can only be obtained, when the hardness of the polymer is sufficiently high, as in the case of BisDMA/Cu multilayers.     

Reduced exchange coupling and hysteresis loops in two-phased magnetic nanosystem

The reduced exchange coupling has been incorporated in our micromagnetic calculations for the hysteresis loops of Nd₂Fe₁₄B/α-Fe and Sm₄₀Fe₆₀/Ni₈₀Fe₂₀ multilayers. Analysis shows that nucleation and pinning fields are sensitive to the value of the interface coupling constant Jⁱ when the soft layer thickness L^s is small. Hysteresis loops have been obtained for a trilayer system with a soft α-Fe sandwiched between two Nd₂Fe₁₄B layers for different values of L^s and Jⁱ. As Jⁱ decreases, nucleation field decreases while the pinning field increases. In the meantime, the squareness of the loops is deteriorated, which results in smaller energy product. For thick soft layer the coercivity mechanism transforms from pinning to nucleation as the interface coupling decreases, and vice versa. The above calculations have been extended to a Sm₄₀Fe₆₀/Ni₈₀Fe₂₀ bilayer and compared with available experimental data. The theoretical loop is consistent with the experimental one when the value of Jⁱ is taken as 10% of the bulk one, demonstrating that the interface coupling in the experiment is far away from perfect coupling.     

Interfacial thermal resistance in multilayer graphene structures

The cross-plane thermal conductivities of multilayer graphene are investigated using nonequilibrium molecular dynamics simulation. It is found that the interfacial thermal resistance in multilayer graphene structures is strongly layer number dependent. It decreases with increasing layer number and reaches a limit as layer number is large enough. The interfacial thermal resistance for graphite and multilayer graphene has an anomalous relationship with temperature compared with that in superlattice structures. It increases with the temperatures above room temperature, which is attributed to phonon tunneling effects. Phonon tunneling probability is reduced due to the decreased phonon wavelength while temperature rises, which in turn causes the increased interfacial thermal resistance.