Super fast switching and low operating of liquid crystals sandwiched between ion beam-spurted ITO thin layers

Ion beam (IB)-spurted indium tin oxide (ITO) thin layers are used to align liquid crystals (LC) with a lower driving voltage. During IB spurting process, the microcrystals transforming to large crystals of ITO is intimated by the change of In (3d), Sn (3d) and O (1s) core level in XPS spectra and the surface topology modifications in SEM and AFM images, and IB-spurted ITO thin layers are comparably transparent and conductive compared with ITO thin layers. The increased interactions between LC and IB-spurted ITO thin layers together with the roughed surface topology of ITO thin layers are the main causes for LC alignment. The fast response and distribution of electrical dipoles to external voltage in LC causes LC’s extremely low threshold voltage drive; in addition, LC directly aligned on ITO thin layers free from alignment layers shield effect further decreases LC’s threshold voltage. 1.8-keV IB-spurted ITO thin layers are more appropriate to align LC with the threshold voltage of 0.4853 V and the rising time of 0.237 ms.     

Infrared reflection-absorption spectroscope using thin film structures

Infrared reflection-absorption spectroscopy (IRRAS) has been used extensively in the study of adsorbates and thin layers on metal surfaces, but little work has been performed on non-metals due to the low sensitivity which results when these materials are used. In this work, thin film structures consisting of a thin layer of a semiconductor (silicon) on a metal (copper) surface are used to increase the sensitivity of the technique for examining layers of poly(methylmethacrylate).     

薄层缓蚀剂液膜对907A钢防蚀效果的电化学测量技术

本文研究饱和海水湿气环境中对 90 7A钢施加缓蚀剂的防蚀作用 ,利用恒电量技术等电化学方法对同材质的三电极大气腐蚀监测探头 (ACM )进行腐蚀测量 .结果表明 :利用电化学方法监测薄层缓蚀剂液膜的防蚀效果可以更清楚地获知缓蚀剂成膜的过程 ,并对薄层缓蚀剂液膜防蚀效果作出快速评价     

Monolayers at solid–solid interfaces probed with infrared spectroscopy

The sensitivities of infrared spectra of thin adsorbate layers measured in either transmission, internal reflection or external reflection can be greatly increased if a light incidence medium with a high refractive index such as an IR-transparent solid material is used. This increase in sensitivity is due to the strong enhancement of the perpendicular electric field in a thin layer of low refractive index sandwiched between two high refractive index materials. Based on model calculations of a hypothetical sample layer, the influence and optimization of experimental parameters such as incidence angle, sample layer thickness and optical contact between layers are investigated. Under optimized conditions, this enhancement can exceed a factor of 100 when compared to conventional surface IR techniques. In addition, the spectra of sandwiched sample layers are governed by a uniform surface selection rule, such that only the perpendicular vibrational components are enhanced, and they permit a straightforward, substrate-independent analysis of surface orientations. Experimental examples of monolayer spectra of long-chain hydrocarbon compounds adsorbed onto gold and silicon substrates and contacted with a germanium crystal used as the incidence medium demonstrate the simple experimental realization and unprecedented sensitivity of this sandwich technique, and they offer novel insights into the chemistry and structure of monolayers confined and compressed between two solid surfaces. Figure IR reflection spectrum of a monolayer of a fatty acid methyl ester sandwiched between silicon and germanium.     

Hydrophobic-hydrophilic interactions of water with alkanethiolate chains from first-principles calculations.

The interaction of water with alkanethiolate chains is studied from first principles. A detailed analysis is performed by optimizing the structure of small water clusters, one-dimensional water chains, and ordered and disordered thin water layers adsorbed on hydroxyl(OH)- and methyl(CH3)-terminated alkanethiol monolayers. The hydrophilic/hydrophobic character of these two different substrates is investigated by means of an energetic analysis combined with hydrogen-bond counting. On the hydrophilic OH-terminated alkanethiol surface, zigzag, one-dimensional water chains and disordered thin water layers are the energetically favored structures. The ab initio results can be used to determine the optimal value of the empirical parameters characterizing a suitable force field to be used in classic molecular dynamics simulations.     

Transient grating studies of femtosecond processes in ultra-thin layers of PTCDA

Elementary processes like energy transfer, charge transport, and exciton diffusion in thin films occur on time scales of femtoseconds. Time-resolved photo-electron spectroscopy, a technique limited to ultra-high vacuum environment and the proper choice of a substrate, has been used to study ultrafast processes in sub-nanometer thin films so far. Herein we show that a transient (population) grating created by the interference of laser pulses can be used to study ultrafast processes in such films under ambient conditions. Our investigations of exciton dynamics in 1.4±0.2 nm and 0.4±0.2 nm thin films, formed by nanocrystals of 3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) on glass and mica, show that the dynamics differ with the crystal size, possibly due to the confinement induced changes in the electronic structure. The technique is sensitive enough to investigate the dynamics in systems, where only 20 % of the surface is covered by nano-crystals. We expect such an optical technique that is sensitive enough to study dynamics in few to sub-nanometer thin layers under ambient conditions to become important in investigating ultrafast dynamics on surfaces, interfaces, functionalized materials, organic semiconductors, and quantum phenomena in ordered structures of reduced dimensions, such as quantum dots and graphene sheets.     

Characterization of phospholipid bilayer formation on a thin film of porous SiO2 by reflective interferometric Fourier transform spectroscopy (RIFTS)

Classical methods for characterizing supported artificial phospholipid bilayers include imaging techniques such as atomic force microscopy and fluorescence microscopy. The use in the past decade of surface-sensitive methods such as surface plasmon resonance and ellipsometry, and acoustic sensors such as the quartz crystal microbalance, coupled to the imaging methods, have expanded our understanding of the formation mechanisms of phospholipid bilayers. In the present work, reflective interferometric Fourier transform spectrocopy (RIFTS) is employed to monitor the formation of a planar phospholipid bilayer on an oxidized mesoporous Si (pSiO(2)) thin film. The pSiO(2) substrates are prepared as thin films (3 μm thick) with pore dimensions of a few nanometers in diameter by the electrochemical etching of crystalline silicon, and they are passivated with a thin thermal oxide layer. A thin film of mica is used as a control. Interferometric optical measurements are used to quantify the behavior of the phospholipids at the internal (pores) and external surfaces of the substrates. The optical measurements indicate that vesicles initially adsorb to the pSiO(2) surface as a monolayer, followed by vesicle fusion and conversion to a surface-adsorbed lipid bilayer. The timescale of the process is consistent with prior measurements of vesicle fusion onto mica surfaces. Reflectance spectra calculated using a simple double-layer Fabry-Perot interference model verify the experimental results. The method provides a simple, real-time, nondestructive approach to characterizing the growth and evolution of lipid vesicle layers on the surface of an optical thin film.     

A tribute to Professor Revaz R. Dogonadze: The man and his works

In materials with high optical absorption, such as in metals, the interaction of light and medium is sufficiently strong for the observation of light scattering (LS) from various surface excitations. Here the surface enhanced Raman scattering has definitely in the past attracted the most attention. In the case of the magnetic surface excitations it is only the Damon Eshbach (DE) type of surface mode which has up to now been detected by this method. Earlier investigations of this mode were performed by means of microwave experiments. In this article the present state of the LS investigations is described. The physical background of various theoretical and experimental aspects will be discussed. The benefits of the new method are essentially threefold. Firstly it can be used for the determination of magnetic parameters from the observation of LS from the standing spinwave modes in thin films. Secondly, it allows a direct observation of thermal amplitudes. Of particular interest here are very thin films, where the DE mode amplitudes display a tremendous increase. Thirdly, LS is also particularly well suited to investigate the magnetic modes of multilayer systems. Recent theoretical investigations show that for such systems the coupling of the DE modes of the single layers is of great importance.     

Atom probe tomography characterization of thin copper layers on aluminum deposited by galvanic displacement

″Ultrathin″ metallization layers on the order of nanometers in thickness are increasingly used in semiconductor interconnects and other nanostructures. Aqueous deposition methods are attractive methods to produce such layers due to their low cost, but formation of ultrathin layers has proven challenging, particularly on oxide-coated substrates. This work focused on the formation of thin copper layers on aluminum, by galvanic displacement from alkaline aqueous solutions. Analysis by atom probe tomography (APT) showed that continuous copper films of approximately 1 nm thickness were formed, apparently the first demonstration of deposition of ultrathin metal layers on oxidized substrates from aqueous solutions. The APT reconstructions indicate that deposited copper replaced a portion of the surface oxide film on aluminum. The results are consistent with mechanisms in which surface hydride species on aluminum mediate deposition, either by directly reducing cupric ions or by inducing electronic conduction in the oxide, thus enabling cupric ion reduction by Al metal.     

Development of dextran-derivative arrays to identify physicochemical properties involved in biofouling from serum

To control protein adsorption on surfaces, low-fouling polymer coatings such as poly(ethylene oxide) (PEG or PEO) and polysaccharides are used. Their ability to resist protein adsorption is related to the layer structure, hence the immobilization mode. A polymer array technology was developed to study the structural diversity of carboxymethyl dextran (CMD) layers, whose immobilization conditions were varied. CMD arrays were analyzed by X-ray photoelectron spectroscopy (XPS) and by atomic force microscopy (AFM) colloidal probe force measurements. Serum protein adsorption was studied directly on the CMD arrays using surface plasmon resonance (SPR) microscopy. Physicochemical characterization revealed that pinning density regulates surface coverage and the amount of adsorbed molecules, and that salt concentration influences the surface structure of the charged polymer, forming extended or short layers. Protein adsorption experiments from serum showed that repulsive CMD layers are dense, with extended flexible chains. The present study underlines the usefulness of polymer arrays to study structural diversity of thin graft layers and to relate their physicochemical properties to their resistance to nonspecific protein adsorption.     

Methods of measuring rheological properties of interfacial layers (Experimental methods of 2D rheology)

Current methods of studying the rheological properties of interfacial layers at the interfaces of fluids are reviewed. This area of research includes two-dimensional 2D rheology. Regardless of the similarities between the parameters of rheological properties of two-dimensional and bulk (three-dimensional) systems, when measuring surface properties, it is necessary to reformulate the main experimental methods to allow for the different dimensions of surface and bulk characteristics of material. Parameters of shear and dilational (measured upon expansion-compression) properties of interfacial layers are distinguished, and the latter are considered to be independent parameters of a system. The most attention was given to the rotational methods of measuring shear viscosity and the components of the complex 2D elastic modulus, as well as to measuring surface tension upon harmonic changes of the bubble (droplet) surface area, which allows characteristics of the dilational behavior of thin liquid films to be determined. Both groups of methods are widely used in laboratory practice and realized in the form of a number of original and commercial instruments. Dilational measurements of interfacial layers can also be performed with oscillations of a movable barrier on a Langmuir trough. In addition, methods based on the propagation of capillary waves across the surface of a liquid, as well as rarer methods of capillary flow in thin channels forced by either a surface tension gradient or the motion of the interface, are considered.     

聚苯胺Langmuir－Blodgett膜的电聚合制备及电化学性质

在加有苯胺的亚相上,铺展硬脂酸分子,在气液界面上可形成苯胺－硬脂酸Ｌａｎｇｍｕｉｒ膜．随膜压增大至５．０×１０￣（－６）Ｎ时,苯胺与硬脂酸间的氢键会发生重排,形成另外一种构型的Ｌａｎｇｍｕｉｒ膜,分子所占面积减小,膜增加一个苯环的厚度．将膜转移到ＳｎＯ＿２导电玻璃基底上,制成硬脂酸－苯胺Ｌａｎｇｍｕｉｒ－Ｂｌｏｇｄｅｔｔ膜,经电化学氧化,苯胺可聚合成薄膜。膜夹在两层硬脂酸分子间,它的电化学行为不仅受到离子膜中传输过程的影响,同时受到硬脂酸极性亲水端（－ＣＯＯ￣－）的作用．     

Chemical derivatization techniques in the determination of functional groups by X-ray photoelectron spectroscopy

The fundamentals of chemical derivatization techniques as applied to the quantitative analysis of ultrathin surface layers of various organic compounds via functional groups were considered. Using X-ray photoelectron spectroscopy as an example of the most informative and almost nondestructive technique for characterization of thin layers, the general requirements imposed on the selective chemical reactions and possible artifacts were discussed. The validity of the technique was illustrated by the examples of analyses of surface layers of organic polymers with known concentrations of surface functional groups, plasma-modified polymers, and carbon fibers. It was noted that selective chemical reactions are successfully used in other techniques for studying material surfaces. The surface analysis of organic materials via functional groups can be performed with a simultaneous increase in the sensitivity of the corresponding spectral technique.     

表面印迹交替层状组装薄膜

在简要概述非常规交替层状组装这一进展后,重点总结了如何利用非常规交替层状组装以实现表面印迹膜的制备.模板分子与聚电解质在溶液中组装形成超分子复合物,然后以此超分子复合物为构筑基元,与感光性高分子,如重氮树脂,通过常规交替层状组装形成聚合物多层膜.利用聚合物多层膜之间的光化学反应形成稳定的多层膜,然后去除模板分子得到分子...     

Responsive organometallic polymer grafts: electrochemical switching of surface properties and current mediation behavior

Quantitative adherence and friction measurements between atomic force microscopy (AFM) tips and reversibly oxidized and reduced poly(ferrocenyl dimethylsilane) (PFDMS) molecular layers grafted to Au are reported. Poly(ferrocenylsilanes) (PFSs) such as PFDMS owe their redox responsiveness to the presence of ferrocene units, bridged by substituted silicon units, in the main chain. Polymers were obtained by anionic polymerization, which allowed us to copolymerize sulfur containing end groups that facilitated grafting to Au surfaces. Electrochemical atomic force microscopy (ECAFM) was used to study adherence and friction as a function of the oxidation state of the polymer. Measurements of interfacial friction as a function of applied load on the nanoscale using Si(3)N(4) AFM tips revealed a reversible increase of the friction coefficient and adherence strength of the PFDMS layers with increasing oxidation state in NaClO(4) electrolytes. The variation of the electrolyte salts (NaClO(4) or NaNO(3)) allowed an assessment of surface counterion adsorption effects. Issues related to the interpretation of observed friction and adherence changes such as electrolyte anion-ferrocenium ion pair effects, and electrostatic forces due to tip surface charges are discussed. Unidirectional current flow was detected in cyclic voltammograms of the PFDMS layers in NaClO(4). This electrode rectification behavior could in principle be utilized for applications in thin film devices based on PFS films.     

The use of radionuclides for the study of crystal structure of solids

It is well known that by the coordinated action of atoms arranged in rows and planes in the crystal lattice, the motion of charged particles such as protons, alpha particles and heavier ions can be influenced so that their range in the single crystals is considerably enhanced in low-index directions. A technique has been developed based on such enhanced penetration (channeling) of radioactive atoms (²²⁰Rn) emitted by recoil with a 100 keV energy from a²²⁴Ra point source to record channeling patterns which show the crystal structure. The radioactive recoil atoms impinging from this source on the surface of a single crystal penetrate deeper in places where their direction of impact is identical with low index crystal directions and planes. These places can be visualized by autoradiography when having first stripped a thin layer from the surface corresponding to the random range of the atoms. This technique is generally applicable in close packed crystals and gives information about the crystal structure of very thin surface layers.     

Graphene‐Supported Ultrafine Metal Nanoparticles Encapsulated by Mesoporous Silica: Robust Catalysts for Oxidation and Reduction Reactions

Graphene nanosheet‐supported ultrafine metal nanoparticles encapsulated by thin mesoporous SiO₂ layers were prepared and used as robust catalysts with high catalytic activity and excellent high‐temperature stability. The catalysts can be recycled and reused in many gas‐ and solution‐phase reactions, and their high catalytic activity can be fully recovered by high‐temperature regeneration, should they be deactivated by feedstock poisoning. In addition to the large surface area provided by the graphene support, the enhanced catalytic performance is also attributed to the mesoporous SiO₂ layers, which not only stabilize the ultrafine metal nanoparticles, but also prevent the aggregation of the graphene nanosheets. The synthetic strategy can be extended to other metals, such as Pd and Ru, for preparing robust catalysts for various reactions.     

Comparative TOF-SIMS and MALDI TOF-MS analysis on different chromatographic planar substrates

A comparison is made between two high resolution, surface-based, mass spectrometric methods: time-of-flight secondary ion mass spectrometry (TOF-SIMS) and matrix-assisted laser desorption/ionisation mass spectrometry (MALDI TOF-MS) in indication of abietic and gibberellic acids molecular profiles on different chromatographic thin layers. The analytes were applied to silica gel chromatographic thin layers with SIMS on-line interfacing channel, monolithic silica gel ultra-thin layers, and thin layers specifically designed for direct Raman spectroscopic analysis. Two MALDI matrices were used in this research: ferulic acid and 2,5-dihydroxybenzoic acid. The silica gel SIMS-interfacing channel strongly supported formation of numerous different MALDI MS fragments with abietic and gibberellic acids, and ferulic acid matrix. The most intense fragments belonged to [M-OH](+) and [M](+) ions from ferulic acid. Intense conjugates were detected with gibberellic acid. The MALDI MS spectrum from the monolithic silica gel surface showed very low analyte signal intensity and it was not possible to obtain MALDI spectra from a Raman spectroscopy treated chromatographic layer. The MALDI TOF MS gibberellic acid fragmentation profile was shielded by the matrix used and was accompanied by poor analyte identification. The most useful TOF-SIMS analytical signal response was obtained from analytes separated on monolithic silica gel and a SIMS-interfacing modified silica gel surface. New horizons with nanostructured surfaces call for high resolution MS methods (which cannot readily be miniaturised like many optical and electrochemical methods) to be integrated in chip and nanoscale detection systems.     

Comparative characterisation by atomic force microscopy and ellipsometry of soft and solid thin films

Ellipsometry and atomic force microscopy (AFM) were used to study the film thickness and the surface roughness of both ‘soft’ and solid thin films. ‘Soft’ polymer thin films of polystyrene and poly(styrene–ethylene/butylene–styrene) block copolymer were prepared by spin‐coating onto planar silicon wafers. Ellipsometric parameters were fitted by the Cauchy approach using a two‐layer model with planar boundaries between the layers. The smooth surfaces of the prepared polymer films were confirmed by AFM. There is good agreement between AFM and ellipsometry in the 80–130 nm thickness range. Semiconductor surfaces (Si) obtained by anisotropic chemical etching were investigated as an example of a randomly rough surface. To define roughness parameters by ellipsometry, the top rough layers were treated as thin films according to the Bruggeman effective medium approximation (BEMA). Surface roughness values measured by AFM and ellipsometry show the same tendency of increasing roughness with increased etching time, although AFM results depend on the used window size. The combined use of both methods appears to offer the most comprehensive route to quantitative surface roughness characterisation of solid films. Copyright © 2007 John Wiley & Sons, Ltd.     

Diffusion in ultrathin liquid films

Inhomogeneous molecular diffusion in layered structures of thin liquid films deposited on solid surfaces is observed via wide field single molecule microscopy. The fluorescence dyes Rhodamine 6G and Oregon Green 514 are used to probe the diffusion in tetrakis(2-ethylhexoxy)-silane and polydimethylsiloxane. A broad distribution of diffusion constants is observed which can be attributed to diffusion within distinct layers of the liquid. Comparison with computer simulations shows that diffusion is normal but depends strongly on the distance of the molecules from the solid surface. Diffusion within layers is faster than between the layers and additional temperature activation is necessary to speed up interlayer diffusion.