Visible-light photochromism of phosphomolybdic acid and polyvinyl alcohol by inorganic-organic nanocomposite multilayer films

A novel visible-light photochromic inorganic-organic multilayer was constructed based on phosphomolybdic acid (PMoA) and polyvinyl alcohol (PVA) which was prepared using the layer-by-layer (LbL) assembly technique to form the multilayer film. The structures of the multilayer films were characterized via Fourier transform infrared spectra (FT-IR) and atomic force microscopy (AFM). The grown process, internal interaction, the surface topography and photochromic properties could be obviously studied through ultraviolet–visible (UV–vis) spectra and X-ray photoelectron spectra (XPS). The advantage of the structure and performance of the multilayer films prepared by layer-by-layer method could be found. It was suggested that the nearly linear growth process in peak-top absorbance in multilayer assembly. The PVA polymer substrate could disperse PMoA particles and changed the surface morphology. The polymer skeleton and PMoA particles were with strong interfacial interactions. The PMoA/PVA LbL film had wonderful visible light response. The oxygen acted a significant part during the bleaching process. According to XPS resoults, 51% of Mo⁶⁺ in the PMoA turned into Mo⁵⁺, obvious photoinduce oxidation and reduction reactions happened from PVA and PMoA through the proton transfer mechanism.     

Layer-by-layer assembly and tribological property of multilayer ultrathin films constructed by modified graphene sheets and polyethyleneimine

A series of graphene sheets (GS)-based multilayer films was constructed in virtue of layer-by-layer electrostatic self-assembly technique based on the negatively charged poly(sodium 4-styrenesulfonate) (PSS) mediated GS (PSS-GS) and the positively charged polyethyleneimine (PEI). High-resolution transmission electron microscope, atomic force microscope and micro-Raman spectrum characterizations demonstrated that the PSS-GS has been synthesized and could be assembled on the single-crystal silicon substrate. Ellipsometric thickness measurement and ultraviolet-visible absorption spectroscope confirmed the successive assemblies of GS. Finally, the macrotribological behaviors of different multilayer films were evaluated on a ball-on-plate macrotribometer and the results indicated that the prepared three- and five-layer films had high load affording ability and long anti-wear life, which could be highly dependent upon the high coverage and excellent self-lubricant properties that the GS owns intrinsically.     

基于多层膜结构的亚波长光栅研究

利用表面等离子体共振效应理论及金属-介质复合膜的特殊纳米光学效应对平面多层膜超分辨光刻技术进行了研究. 在曝光光源为365 nm的情况下,实现周期230 nm,线宽100 nm的超分辨光刻成像. 讨论了均匀金属-介质多层膜的结构参数选择,并通过数值仿真得到有效的光强度和对比度, 然后用等离子体纳米光刻进行试验验证,通过最优化选择,最终得到了亚波长结构多层膜的大区域范围超分辨成像.     

Geometry and composition of thin multilayer films based on lead and cadmium selenides

The formation of Cd _x Pb_{1 ? x} Se substitutional solid solutions at the interfaces of (CdSe-PbSe) _n multilayer films (n = 2–6) is revealed by X-ray diffraction and scanning electron microscopy. The films are fabricated by the hydrochemical layer-by-layer deposition of individual metal selenides. For a six-layer structure (CdSe-PbSe)₃, the sequence of layers is determined using gray levels on images by constructing profilograms.     

Theoretical model for thin ferroelectric films and the multilayer structures based on them

A modified Weiss mean-field theory is used to study the dependence of the properties of a thin ferroelectric film on its thickness. The possibility of introducing gradient terms into the thermodynamic potential is analyzed using the calculus of variations. An integral equation is introduced to generalize the well-known Langevin equation to the case of the boundaries of a ferroelectric. An analysis of this equation leads to the existence of a transition layer at the interface between ferroelectrics or a ferroelectric and a dielectric. The permittivity of this layer is shown to depend on the electric field direction even if the ferroelectrics in contact are homogeneous. The results obtained in terms of the Weiss model are compared with the results of the models based on the correlation effect and the presence of a dielectric layer at the boundary of a ferroelectric and with experimental data.     

Morphology and characterization of ITO-Ag-ITO films on fibers by layer-by-layer method

Indium tin oxide embedded with silver particles (ITO-Ag-ITO) multilayer films are deposited on the surface of fibers as reflective coatings through layer-by-layer method. Surface of fibers was modified by sodium dodecylbenzene sulfonate which is used as an excellent surfactant to increase the charge negativity of fibers. Silver layer was in situ obtained due to the reduction of SnCl₂. Based on the electrostatic adsorption mechanism, scanning electron microscope (SEM) and electron dispersive spectroscopy (EDS) results show that multilayer films are well deposited onto fibers smoothly and densely. Transmission tests show that multilayer coated fibers have better near infrared (NIR) and Fourier transform infrared (FT-IR) reflectivity due to the embedded silver layer and the reflectivity is increased during high-temperature densification process.     

Enhanced water vapor barrier properties for biopolymer films by polyelectrolyte multilayer and atomic layer deposited Al2O3 double-coating

Commercial polylactide (PLA) films are coated with a thin (20 nm) non-toxic polyelectrolyte multilayer (PEM) film made from sodium alginate and chitosan and additionally with a 25-nm thick atomic layer deposited (ALD) Al₂O₃ layer. The double-coating of PEM + Al₂O₃ is found to significantly enhance the water vapor barrier properties of the PLA film. The improvement is essentially larger compared with the case the PLA film being just coated with an ALD-grown Al₂O₃ layer. The enhanced water vapor barrier characteristics of the PEM + Al₂O₃ double-coated PLA films are attributed to the increased hydrophobicity of the surface of these films.     

Organosilane self-assembled multilayer formation based on activation of methyl-terminated surface with reactive oxygen species generated by vacuum ultra-violet excitation of atmospheric oxygen molecules

A xenon excimer lamp which irradiates vacuum ultra-violet (VUV) light at 172 nm in wavelength was applied to the photochemical surface conversion of n-octadecyltrimethoxysilane self-assembled monolayer (ODS-SAM) in the presence of atmospheric oxygen and subsequent multilayer fabrication. The terminal functional groups of ODS-SAM, -CH₃ groups, were converted into polar functional groups, like -COOH, by the reaction with atomic oxygen species generated photochemically through VUV excitation of atmospheric oxygen molecules. The structure of the resulting organosilane multilayer with different numbers of superimposed monolayers (from 1 to 11), prepared on a smooth and hydrophilic silicon substrate by the layer-by-layer (LbL) approach, was examined in terms of molecular organization as well as the intra- or interlayer binding modes in such novel films. Ellipsometry and grazing angle X-ray reflectivity measurements revealed that multilayer films of up to 11 discrete monolayers were successfully obtained, indicating that the self-assembly is a viable technique for the construction of relatively thick (16 nm and above) multilayer films.     

Three-dimensional reversible laser micromachining with subnanojoule femtosecond pulses based on two-photon photochromism

Three-dimensional reversible laser micromachining of polymer materials based on two-photon photochromism is demonstrated. Unamplified 60-fs, 0.5-nJ pulses of 790-nm Ti:sapphire laser radiation are used to induce a refractive-index change in a polymethyl methacrylate (PMMA) sample doped with spiropyran molecules through a two-photon absorption process. Waveguides are written in the bulk of spiropyran-doped PMMA samples by scanning these samples with respect to a tightly focused Ti:sapphire laser beam. Laser-induced fluorescence is used for on-line monitoring of the laser-micromachining process. The structures written in photochromic samples can be erased and reconfigured due to the reversibility of the photochromic effect. Received: 23 April 2003 / Published online: 6 June 2003 RID="*" ID="*"Corresponding author. Fax: +7-095/939-51-74, E-mail: zheltikov@top.phys.msu.su     

A theoretical interpretation of the abnormal D0→F4 intensity based on the Eu local coordination in the Na9[EuW10O36]·14H2O polyoxometalate

The Na₉[EuW₁₀O₃₆]·14H₂O polyoxometalate studied here has shown a peculiar 4f-4f emission spectrum that has two main differences in comparison to data reported previously in the literature: a ⁵D₀→⁷F₀ line with much smaller intensity and an abnormally high intensity of the ⁵D₀→⁷F₄ transition. These results have been theoretically interpreted in terms of the Ω_λ intensity parameters and their dependence on the nature and local symmetry of the chemical environment around the Eu³⁺ ion, leading to the conclusion that the chemical environment is highly polarizable with a local symmetry corresponding to a slightly distorted D_4d coordination geometry. Further evidences corroborating this interpretation were obtained by progressively dissolving the polyoxometalate in water, inducing a progressive accommodation of the coordination polyhedron towards lower symmetries.     

Humidity sensor based on localized surface plasmon resonance of multilayer thin films of gold nanoparticles linked with myoglobin

Layer-by-layer self-assembled multilayer thin films of gold nanoparticles (GNPs) linked with myoglobin (Mb) show substantial sensitivity to humidity at room temperature according to measurements of localized surface plasmon resonance (LSPR) absorption that relies on the interparticle interaction present in the film. The sensor response is reversible, with response and recovery times as low as 5 s. The sensing mechanism is as follows: as the ambient humidity changes, Mb molecules change their size, making the GNP-to-GNP spacing and thereby the interparticle interaction change; the change in the interparticle interaction causes a change in the LSPR absorption of the multilayer thin film. We found that the LSPR band of the multilayer thin film was almost insensitive to both the surrounding refractive index and the adlayer thickness, rendering the multilayer-film-based humidity sensor highly immune to ambient disturbances.     

Measuring sticking and stripping in muon-catalyzed dt fusion with multilayer thin films

We propose a direct measurement of muon sticking to alpha particles in muon-catalyzed dt fusion at a high density. Exploiting the features of a multilayer thin-film target developed at TRIUMF, the sticking is determined directly by detection of charged fusion products. Experimental separation of initial sticking and stripping may become possible for the first time. Monte Carlo simulations, as well as preliminary results of test measurements are described.     

高电阻率多层纳米颗粒膜软磁特性及微波磁导率

研究了应用于微波频段的多层纳米颗粒膜的电阻率、软磁特性和微波磁导率.采用多次顺序沉积Co₄₀Fe₄₀B₂₀和SiO₂薄层制备了薄膜.在100kA/m均匀面内磁场经过250℃真空退火2h,制备的Co₄₀Fe₄₀B₂₀/SiO₂多层膜具有难轴矫顽力为210A/m、饱和磁化强度为838.75kA/m、电阻率为2.06×10^{3关键词： 纳米颗粒膜 电阻率 软磁特性 微波磁导率}     

Effect of temperature of annealing on optical, structural and electrochromic properties of sol-gel dip coated molybdenum oxide films

The sol-gel dip-coating method is used for the preparation of MoO₃ thin films. The 6 layered MoO₃ films were prepared and annealed at various temperatures in the range of 200-350 °C. The band gap value for MoO₃ films were calculated from optical absorption measurements and it is in the range of 3.55-3.73 eV. XRD spectrum reveals (0 2 0) is the major diffraction plane for the films prepared above 250 °C, which reveals the formation of MoO₃ in α-orthorhombic phase. The films prepared at 200 °C and 250 °C exhibits amorphous nature. The FTIR spectrum confirms the presence of Mo-O-Mo and MoO bonds. Nanorods were observed in the SEM images in the case of MoO₃ films prepared above 250 °C. The films prepared at 250 °C exhibit maximum anodic diffusion coefficient of 9.61 × 10⁻¹¹ cm²/s. The same film exhibits the change in optical transmission of 58.4% at 630 nm with the optical density of 0.80.     

Thickness effects on the optical properties of layer-by-layer poly(p-phenylene vinylene) thin films and their use in energy-modulated structures

Poly(p-phenylene vinylene) (PPV) thin films were produced by layer-by-layer (LbL) method, using soluble PPV-precursor and dodecylbenzenesulfonate salt (DBS). The amount of deposited layers strongly influences the optical properties of the thermally converted PPV film. The absorbance and luminescence spectra of ultra-thin films (consisting of only two or three PPV layers) are shifted to smaller wavelengths with respect to spectra of thicker films. This is related to the smaller average conjugation length of polymer chains, resulting in a higher HOMO-LUMO gap energy of the material. However, if a thick film is produced by repeating the deposition process and thermal conversion of ultra-thin layers, the optical spectra are still displaced to higher energies in comparison with those of thicker films produced by the conventional continuous deposition of layers. This result enabled the production of multilayered polymeric films with modulated energy profile, taking the number of deposited layers as the only variable in the manufacturing process of the structure. The aim is to guide the excitation to specific regions of the material through the Förster-type energy transfer processes. Such systems can be used at interfaces electrode/polymer and/or electrode/polymeric active layers in order to improve the performance of organic optoelectronic devices.     

ITO/Au/ITO multilayer thin films on transparent polycarbonate with enhanced EMI shielding properties

ITO/Au/ITO multilayer thin films were deposited onto polycarbonate substrate via magnetron sputtering technique without intentional heating. The deposition times of both ITO and Au layers were studied to optimize the overall transparency and conductivity. As-prepared thin films were characterized using X-ray diffraction analysis, secondary ion mass spectroscopy, scanning and transmission electron microscopy, atomic force microscopy and physical property measurement system. The optical measurement results revealed that the transmittance of the films were enhanced by increasing the gold deposition time up to 15 s. Beyond this point, further increasing the duration caused a decrease in optical transmittance. Upon optimization of the Au deposition time, the deposition duration of ITO layers was also studied to increase electromagnetic interference (EMI) shielding effectiveness (SE). Maximum EMI SE in this work was measured as 26.8 dB, yielding 99.8% power attenuation, which was verified by simulation results.     

微型平面复合薄膜电爆炸开关的设计和研究

开关技术是影响爆炸箔起爆系统可靠作用、微型化、低能化、集成化的关键技术。电爆炸平面开关是利用强脉冲电流使触发极金属桥箔发生电爆炸,产生高温高压等离子体,使爆炸桥区两侧的电极导通。基于微加工技术,采用Al/CuO复合薄膜材料作为触发电极,设计制造了微型平面复合薄膜电爆炸开关。采用扫描电子显微镜、差示扫描量热法和光谱谱线测温研究了触发极Al/CuO复合薄膜的形貌、反应性和电爆炸等离子体温度,通过放电电流测试研究了开关性能。结果表明,在主回路电压2000 V时,开关输出电流峰值约为1938 A,上升时间390 ns,性能优于仅以铜薄膜为触发电极的电爆炸平面开关。     

Improving the performance of acoustic invisibility with multilayer structure based on scattering analysis

In this paper, acoustic scattering from the system comprised of a cloaked object and the multilayer cloak with only one single pair of isotropic media is analyzed with a recursive numerical method. The designed acoustic parameters of the isotropic cloak media are assumed to be single-negative, and the resulting cloak can reduce acoustic scattering from an acoustic sensor while allowing it to receive external information. Several factors that may influence the performance of the cloak, including the number of layers and the acoustic dissipation of the medium are fully analyzed. Furthermore, the possibility of achieving acoustic invisibility with positive acoustic parameters is proposed by searching the optimum value in the parameter space and minimizing the scattering cross-section.