Langmuir–Blodgett multilayers of imidazoles

Langmuir–Blodgett (LB) multilayers have been formed from a wide variety of compounds but the basic studies from which others have developed have involved a long hydrocarbon chain terminated at one end by a hydrophilic group. The quaternary ammonium ion has a greater attraction for water than do the other groups which have been used and is so hydrophilic as to preclude the formation of LB layers of straight chain molecules terminated by this group. Certainly all such molecules up to and including octadecyl trimethyl ammonium bromide form micelles in preference to monolayers at the air/water interface though metastable monolayers of this compound have been reported. Quaternized imidazoles have, like quaternary ammonium ions, a positive charge but seem more likely to form LB films. We have thus explored the properties of several of these compounds with a view to producing one which has the desired properties. In order to combat the highly hydrophilic nature of the imidazole group it is necessary to employ a highly hydrophobic ‘tail group’. Thus our most successful compound contains two octadecyl alkyl chains. We have studied the behaviour of this compound at the air/water interface and have found that the nature of the subphase has a very marked influence on the shape of the isotherms. With nitric acid added to the subphase to bring about a pH of 3.5 it is possible to obtain good Y deposition with deposition ratios equal to one in both the upward and downward directions. However we have not been able to achieve LB deposition using any other acid. On heating, the compound in question it changes from a crystalline structure to a smectic structure at 55°C.     

纳米多层膜制备概述

纳米多层膜具有很多特殊性能，得到了广泛的应用。阐述了多种纳米多层膜的制备方法，主要包括电化学沉积法、物理和化学气相沉积法、溶胶-凝胶法、组装技术以及其它制备技术。大量研究和试验表明，不同的制备方法得到的多层膜具有其特殊的性能。     

Effect of subphase divalent ions on optical second harmonic properties of hemicyanine Langmuir-Blodgett films interleaved with compatible spacer

The surface pressure-area (π-A) isotherms of 1.10-bistearyl-4.6.13.15-tetraene-8-nitrogen-crown-6 (NC) monolayers at the air-water interface, the UV-visible absorption spectra and optical nonlinear properties of Y-type hemicyanine/NC interleaving Langmuir-Blodgett (LB) multilayers containing divalent ions in the subphase (such as Cd²⁺, Ba²⁺ and Co²⁺) were investigated in the paper. It was found that the π-A isotherms of the NC monolayer, the peak position of absorption spectra and the optical second harmonic intensity in the alternating LB multilayers strongly depend on the divalent ions in the subphase. The 2ω resonance effect of molecular hyperpolarizability β was responsible for the change of the observed second order polarizability χ⁽²⁾ of LB multilayers.     

一种低温共烧压电陶瓷的制备

压电陶瓷多层膜的低温共烧特性及压电性能密切依赖于其成分。采用调节压电材料成分,以0.90Pb(Zr0.48Ti0.52)O3-0.05Pb(Mn1/3Sb2/3)O3-0.05Pb(Zn1/3Nb2/3)O3四元体系为研究对象,同时添加烧结助剂CuO来实现多层膜的低温烧结。对多层膜的流延、排胶、烧结、极化等工艺进行探索以优化工艺参数,最终获得850℃烧结温度下的高致密度多层压电陶瓷。压电性能的测试表明三层结构的压电多层膜陶瓷表观d33达873pC/N,远高于同成分单层陶瓷306 pC/N的d33值。采用多普勒激光测振仪进行扫频实验,测定了多层陶瓷纵向振动速度的频谱,确定了基于该多层膜压电振子的最优谐振频率。     

Preparation of Langmuir-Blodgett “built-up” multilayer films of a lightly substituted model aromatic, anthracene

It is generally considered almost impossible to make Langmuir-Blodgett “built-up” multilayer films of conjugated (aromatic) molecules unless their aromaticity is very heavily diluted with aliphatic substituents or molecules; this severely limits the scientific and technological applications of such films. For example, even to handle anthracene-derivative monolayers on water (without any attempt to transfer them to a substrate) has in the past required the anthracene to be substituted with an aliphatic side chain containing at least twelve carbon atoms; this prevents instability of the water-borne monolayer. As a result, the interesting and useful electrical and optical properties which conjugated multilayers would be expected to possess (because of the extended molecular π electron systems) are heavily diluted by aliphatic properties. We now report the successful deposition of high quality multilayers of lightly substituted anthracene derivatives, with aliphatic side chains as short as four CH₂ units. Improved techniques may well permit even shorter side chains to be used. We describe the deposition methods in detail and give experimental evidence that high quality films from one monolayer thick (about 1.5 nm) to 500 monolayers were indeed obtained; the interesting electrical and optical properties of these films, and their unique structure, will be discussed in detail at a later date. If these preparation techniques can be extended to other conjugated systems, as seems likely, the range of highly organized structures which can be constructed by the Langmuir-Blodgett method has been greatly increased, and the prospects for its technological use (in applications ranging from electronic devices to high temperature superconductors) have been improved.     

Effect of interface structure correlation on magnetoresistance of Fe/Cr multilayers

Effect of interfacial roughness on giant magnetoresistance (GMR) in Fe/Cr multilayers has been studied. A set of samples is prepared by simultaneously depositing on a set of float-glass (FG) substrates with varying rms surface roughness. This causes the correlated part of the rms roughness to vary from sample to sample. Another set of specimen is irradiated with 200 MeV Ag ions in order to induce uncorrelated roughness at the interfaces. In both the cases morphological and other microstructural features of different multilayers remained similar, thus allowing one to separate the effect of interface roughness from that of morphological changes. GMR measurements on these multilayers show that increasing interfacial roughness causes GMR to decrease nonlinearly. It is found that the effect of uncorrelated part of the roughness is much stronger than that of the correlated part.     

Advances in self-assembled ultrathin polyoxomolybdates multilayers

The research on the assembly and function of organized molecular films has gained more and more interest. Electrostatic interactions can be employed to assemble polyoxomolybdates in surface confined multilayers. Ultrathin multilayer films of polyoxomolybdates and organic molecules by the self-assembly method have been reviewed. At the same time, self-assemblies in aqueous solution are also reported, such as wheel-shaped clusters (Mo154), hollow spherical “blackberry”-like vesicles (Mo₇₂Fe₃₀) and Keggin structures. Polyoxomolybdate multilayers are promising candidates for diverse applications including electrocatalytic, photo- and electrochromic systems. The development in this particular field of materials science may be highlighted in the future.     

Optical and mechanical characteristics of zinc sulphide-thorium fluoride mixed composition thin films for use in the near infrared region (1–10µm)

Mixed composition thin films of zinc sulphide-thorium fluoride have been deposited on glass and silicon substrates by thermal evaporation of mixtures of these materials in different proportions, from a single resistively heated source. The films are characterized for their optical properties (refractive index and extinction coefficient), mechanical properties (intrinsic stress), surface morphology and chemical composition. It is found that these films have tailorable refractive indices and low losses, and that films with certain compositions have low intrinsic stress and smooth surface morphology, making them suitable for incorporation in thin film multilayers for use in the near infrared region up to at least 10μm.     

Aperiodic multilayers with enhanced reflectivity for extreme ultraviolet lithography

We have developed novel aperiodic multilayers, covered by capping layers resistant to environmental attack, that offer superior performance for extreme ultraviolet lithography. We have designed these coatings using an optimization procedure based on an algorithm able to acquire domain knowledge inside the space of possible solutions. An integrated intensity increase of up to 2.18 times that obtained using standard periodic multilayers has been estimated. The aperiodic structures have minimal absorption in the topmost layers, which makes them especially insensitive to both the choice of capping layer material and any subsequent capping layer degradation due to oxidation or contamination. This property allows for the use of the most resilient capping layer materials available, thereby leading to a significantly improved lifetime. We have produced prototype capped aperiodic coatings and have measured their performance.     

Investigations for InAs/GaAs multilayered quantum-dot structure treated by high energy proton irradiation

This paper focuses on the high energy proton irradiation effect of InAs/GaAs multilayers quantum-dot (QD) wafer and photodetector. With high energy proton path simulation, the releases of proton energy and trap distribution in QD multilayers are predicted well. Treated by 1 and 3 MeV protons, all protons almost penetrate the multilayers of QD structures and stop deeply in GaAs substrate. InAs QD multilayer structures/Infrared photodetector have been irradiated by protons with different energies (1 and 3 MeV) and doses (1 × 10⁹∼ 1 × 10¹³ protons/cm²). The photoluminescence (PL) and photoresponsivity (PR) spectrum of samples were measured and discussed with as grown and post irradiation.     

Electron beam deposition system for X-ray multilayer mirrors

We have developed a multi source electron beam evaporation system toprepare high quality X-ray multilayer mirrors. The system has three electron guns mounted in an ultra high vacuum chamber. The deposition system is evacuated by a turbo molecular pump and two sputter ion pumps. A movable masking system is mounted to deposit several kinds of multilayers. First results on niobium-carbon X-ray multilayers are presented.     

A coupled numerical analysis of shield temperatures, heat losses and residual gas pressures in an evacuated super-insulation using thermal and fluid networks: Part II: Unsteady-state conditions (cool-down period)

This paper analyses the cool-down period of a 300 L super-insulated cryogenic storage tank for liquid nitrogen. Storage tank and evacuated shields are the same as described in part I of this paper where stationary states were investigated. The aim of the present paper is to introduce thermal resistance networks as a tool to quantitatively understand and control also unsteady-states like cool-down of super-insulations. Numerical simulations using thermal resistance networks have been performed to determine time dependence of local shield temperatures and heat loss components. Coupling between radiation and solid conduction is investigated under these conditions. Using the numerical results, we have checked an experimental method suggested in the literature to separate heat losses through the insulation from losses through thermal bridges by measurement of unsteady-state evaporation rates. The results of the simulations confirm that it takes the outer shields much longer to reach stationary temperature; cool-down does not proceed uniformly in the super-insulation. Coupling between different heat transfer modes again is obvious. Thermal emissivity is important also during the early phase of cool-down. Using the obtained numerical results, the experimental method to separate heat loss components could only roughly been confirmed for thick metallic foils.     

Design and performance of capping layers for extreme-ultraviolet multilayer mirrors

Multilayer lifetime has emerged as one of the major issues for the commercialization of extreme-ultraviolet lithography (EUVL). We describe the performance of an oxidation-resistant capping layer of Ru atop multilayers that results in a reflectivity above 69% at 13.2 nm, which is suitable for EUVL projection optics and has been tested with accelerated electron-beam and extreme-ultraviolet (EUV) light in a water-vapor environment. Based on accelerated exposure results, we calculated multilayer lifetimes for all reflective mirrors in a typical commercial EUVL tool and concluded that Ru-capped multilayers have approximately 40x longer lifetimes than Si-capped multilayers, which translates to 3 months to many years, depending on the mirror dose.     

Spray-Assisted Polyelectrolyte Multilayer Buildup: from Step-by-Step to Single-Step Polyelectrolyte Film Constructions

The alternate deposition of polyanions and polycations on a solid substrate leads to the formation of nanometer to micrometer films called Polyelectrolyte Multilayers. This step-by-step construction of organic films constitutes a method of choice to functionalize surfaces with applications ranging from optical to bioactive coatings. The method was originally developed by dipping the substrate in the different polyelectrolyte solutions. Recent advances show that spraying the polyelectrolyte solutions onto the substrate represents an appealing alternative to dipping because it is much faster and easier to adapt at an industrial level. Multilayer deposition by spraying is thus greatly gaining in interest. Here we review the current literature on this deposition method. After a brief history of polyelectrolyte multilayers to place the spraying method in its context, we review the fundamental issues that have been addresses so far. We then give an overview the different fields where the method has been applied.     

Theoretical explanation of Ag/Cu and Cu/Ni nanoscale multilayers softening

Relationship between metallic multilayers hardness and monolayer thickness has been investigated and explained for electroplated Ag/Cu and Cu/Ni multilayers using a modified Thomas-Fermi-Dirac electron theory. Experiments reveal that the peak hardness of Ag/Cu multilayers occurs at the monolayer thickness of about 25 nm, while the peak hardness of Cu/Ni multilayers occurs at about 50 nm. Critical monolayer thickness corresponding to the peak hardness is approximated by the grain size limit of stable dislocations in Ag crystals for the Ag/Cu multilayers and in Cu crystals for Cu/Ni multilayers. Grains size limits are calculated based on a modified Thomas-Fermi-Dirac electron theory. Developed relationship between the critical monolayer thickness and the grains size limit helps understand nanoscale metallic multilayers softening.     

Morphology of multilayers assembled by electrostatic attraction of oppositely charged model polyelectrolytes

Alternating multilayers assembled stepwise with two prototype polyelectrolytes, i.e. poly(allylamine) hydrochloride (PAA) and poly(vinyl sulfate) potassium salt (PVS), have been examined by means of reflection–absorption infrared (RAIR) spectroscopy and atomic force microscopy (AFM). The growth step revealed by the RAIR spectroscopy was in good agreement with the ellipsometric data. The RAIR spectral data revealed that both macromolecules were randomly oriented in the (PVS/PAA) composite system without any preferential alignment. The atomic force microscopy measurements showed that the morphology of the (PVS/PAA) multilayers prepared in the absence of NaCl were quite homogeneous in agreement with a recent report. However, the morphology of the multilayers prepared in the presence of NaCl was observed to be significantly heterogeneous; the morphology was gradually roughened upon an increase in the number of bilayers. The highly coiled, compact macromolecules present in a NaCl solution seemed preferentially to anchor on the oppositely charged, aggregated surface sites without spreading over the interfacial region. Nonetheless, the morphology of the surface of the (PVS/PAA) system was hardly subjected to change once a stable film had been assembled, regardless of the presence of NaCl.     

静电自组装膜研究进展

由静电自组装技术来制备功能型薄膜是发展迅速的新研究领域。本文着重阐述了静电自组装聚电解质-聚电解质复合膜、静电自组装聚电解质-无机纳米粒子复合膜、静电自组装聚合物-半导体纳米粒子复合膜、静电自组装其他多层膜体系制备方法和特点,展望了静电自组装在渗透分离膜、基因传输、传感器系统、光伏设备等领域的应用前景。     

A new type of organic-inorganic multilayer: fabrication and photoelectric properties

Fabrication and photoelectric characteristics of a new type of organic-inorganic alternating multilayer are reported. The multilayers exhibit a strong photovoltaic response in spite of their weak absorbance. Electric field induced surface photovoltage spectroscopy (EFISPS) indicates obvious unilateral selectivity for the application of an external voltage on multilayers     

纳米多孔薄膜孔结构的非破坏性表征

对纳米多孔低介电常数薄膜孔洞率、孔径、孔径分布和孔洞连通性等孔结构的表征有助于理解薄膜的结构和提高其性能。近年来开展了利用与特殊X射线反射联用的小角中子散射、小角X 射线散射、椭偏测孔仪、正电子湮没谱和表面声波谱等非破坏性方法表征多孔低介电常数薄膜孔结构的研究。介绍了这些方法的基本原理,综述了利用这些方法研究低介电常数介质薄膜及其集成工艺的进展,总结了这些方法表征多孔薄膜孔结构的特征。     

Grenzflächen‐optimierte Mo/Si Multischichten als Reflektoren für den EUV Spektralbereich. Interface‐optimized Mo/Si multilayers as reflectors for the EUV spectral range

EUV lithography is the most promising technique for the fabrication of semiconductor structures below 50 nm. This requires the use of reflecting multilayers as optical elements. These multilayers must have reflectances as high as possible since it determines the efficiency of the technique and therefore the throughput of a future chip fab. In this work we present investigations on the interface quality of Mo/Si multilayers which are prepared by magnetron sputter deposition. Starting from the two‐component Mo/Si system, that has mainly been optimized with respect to interface roughness, we show that interface interdiffusion can also be reduced by the introduction of tiny barrier layers. In pure Mo/Si multilayers particularly a low Ar sputter gas pressure is important to get smooth layers, whereas the interdiffusion can be reduced by the deposition of C and B₄C barrier layers on the individual interfaces. As result of our work, we have prepared Mo/Si multilayers with outstanding high reflectances: R_EUV = 70.1 % (λ = 13.3 nm, α = 1.5°), R_EUV = 71.4 % (λ = 12.5 nm, α = 22.5°).