Investigation of the performance of an SPR-based optical fiber sensor using finite-difference time domain

Finite-difference time domain (FDTD) method was used to investigate the performance of surface plasmon resonance (SPR)-based optical fiber sensors. The results show that the performance of the fiber sensor can be optimized by choosing a proper combination of metal layer thickness of 40–60 nm and residual cladding thickness of 400–500 nm. Furthermore, the roughness effect of the gold surface layering the fiber sensor is significant in rough surfaces when sigma rms is greater than 5 nm or correlation length is lower than 100 nm.     

Kinetic six-vertex model as model of bcc crystal growth

The growth of bcc crystals is studied using van Beijeren's mapping onto the six-vertex model. The growth-evaporation processes are described in terms of vertices. The time evolution is given by a master equation for the probability of the six-vertex configurations. The model, studied in the finite-size case by both Monte Carlo and analytic methods, applies to the (001) surface and its vicinal surfaces. Different growth modes (including nucleation) are found, depending on the strength of disequilibrium and on temperature, and the transition between them is investigated.On leave of absence from the Institute of Physics, Czechoslovak Academy of Science, Prague, Czechoslovakia.     

The adsorption of carbon monoxide on TiO2(110) supported palladium

Palladium overlayers deposited on TiO₂(110) by metal vapour deposition have been investigated using LEED, XPS and FT-RAIRS of adsorbed CO. Low coverages of palladium (<3 ML) deposited at 300 K adsorb CO exclusively in a bridged configuration with a band (B₁ at 1990 cm⁻¹) characteristic of CO adsorption on Pd(110) and Pd(100) surfaces. When annealed to 500 K, XPS and LEED indicate the nucleation of Pd particles on which CO adsorbs predominantly as a strongly bound linear species which we associate with edge sites on the Pd particles (L* band at 2085 cm⁻¹). Both bridged and linear CO bands are exhibited as increases in reflectivity at the resonant frequency, indicating the retention of small particle size during the annealing process. Palladium overlayers of intermediate coverages (10–20 ML) deposited at 300 K undergo some nucleation during growth, and adsorbed CO exhibits both absorption and transmission bands in the B₁ (1990 cm⁻¹) and B₂ (1940 cm⁻¹) regions. The latter is associated with the formation of Pd(111) facets. Highly dispersed Pd particles are produced on annealing at 500 K. This is evidenced by the dominance of transmission bands for adsorbed CO and a significant concentration of edge sites, which accommodate the strongly bound linear species at 300 K. Adsorption of CO at low temperature also allows the identification of the constituent faces of Pd and the conversion of Pd(110)/(100) facets to Pd(111) facets during the annealing process. High coverages of palladium (100 ML) produce only absorption bands in FT-RAIRS of adsorbed CO associated with the Pd facets, but annealing these surfaces also shows a conversion to Pd(111) facets. LEED indicates that at coverages above 10 ML, the palladium particles exhibit (111) facets parallel to the substrate and aligned with the TiO₂(110) unit cell, and that this ordering in the particles is enhanced by annealing.     

Looking at the micro-topography of polished and blasted Ti-based biomaterials using atomic force microscopy and contact angle goniometry

Surface topography of polished and blasted samples of a Ti6Al4V biomaterial has been studied using an atomic force microscope. Surface RMS roughness and surface area have been measured at different scales, from 1 to 50 μm, while at distances below 10 μm the surface RMS roughness in both kinds of samples is not very different, this difference becomes significant at larger scanning sizes. This means that the surface roughness scale that could have a main role in cell adhesion varies depending on the size, shape and flexibility of participating cells. This consideration suggests that in cell–material interaction studies, surface roughness should not be considered as an absolute and independent property of the material, but should be measured at scales in the order of the cell sizes, at least if a microscopic interpretation of the influence of roughness on the adhesion is intended. The microscopic information is contrasted with that coming from a macroscopic approach obtained by contact angle measurements for polar and non-polar liquids whose surface tension is comprised in a broad range. Despite the very large differences of contact angles among liquids for each surface condition, a similar increase for the blasted surface with respect to the polished has been found. Interpretation of these results are in accordance with the microscopic analysis done through the use of a functional roughness parameter, namely the valley fluid retention index, evaluated from the AFM images, which has been shown not to correlate with the RMS roughness, one of the most commonly used roughness parameter.     

Bonding mechanisms of laser‐fabricated titanium/polyimide and titanium coated glass/polyimide microjoints

In this study, two bimaterial joining systems, namely, titanium coated glass/polyimide (TiGPI) and titanium/polyimide (TiPI) are considered. The joints were prepared by employing transmission type laser‐joining procedure. Both the TiGPI and TiPI bimaterial systems were subjected to tensile loading using a microtester, and failure loads per unit bond length were documented. The average failure strengths of the TiPI and TiGPI samples were found to be 5.1 and 7.3 N/mm, respectively. It is thus clear from the failure data that the TiGPI joints are stronger (1.4 times) than the TiPI joints although same chemical bonds between titanium and polyimide (PI) exist for both the systems. It is thus believed that material surface morphology has contributed to such variation in the microjoint strengths. Later, atomic force microscopy (AFM) of titanium surfaces of both titanium coated glass and titanium foil was performed, and was observed that they had root mean squared (RMS) surface roughnesses of 220 and 55 nm, respectively. The surface roughness provides improved surface contact area, number of chemical bonds, and mechanical interlocking that may have resulted in higher bond strength for the TiGPI system. Copyright © 2007 John Wiley & Sons, Ltd.     

Radiative Striations and Surface Roughness of Alkoxide-Derived Spin Coating Films

Spin coating silica films were prepared from acid-catalyzed tetraethoxysilane (TEOS) solutions, and the magnitude of radiative striations formed on the surface of the resulting films was quantitatively evaluated by measuring surface roughness using a contact probe profilometer. Wave-like transverse profiles were obtained on the films prepared. Surface roughness parameters, Ra (arithmetical mean deviation), Rz (ten point height of irregularities) and S (mean spacing of local peaks), were determined. When the gel films were heated at higher temperatures (500°C), the film thickness decreased up to 22%, while none of Ra, Rz or S varied with heat-treatment temperature, indicating that the surface of the films is already densified at room temperature. Higher substrate rotation speeds caused decrease in Ra, Rz and S, revealing that the striations decreased both in amplitude and wavelength. Application of viscous sols aged for longer periods of time resulted in increased amplitude (Rz) of striations without change in wavelength (S).     

Quantum size effects in the low temperature layer-by-layer growth of Pb on Ge(0 0 1)

The electronic properties of thin metallic films deviate from the corresponding bulk ones when the film thickness is comparable with the wavelength of the electrons at the Fermi level. This phenomenon, referred to as quantum size effect (QSE), is also expected to affect the film morphology and structure leading to the “electronic growth” of metals on semiconductors. Such effect may be observed when metals are grown on substrates held at low temperature and are manifested through the occurrence of “magical” thickness islands or critical thickness for layer-by-layer growth. In particular, layer-by-layer growth of Pb(1 1 1) films has been reported for deposition on Ge(0 0 1) below 130 K. An extremely flat morphology is preserved throughout deposition from four up to a dozen of monolayers. These flat films are shown to be metastable and to reorganize into large clusters uncovering the first Pb layer pseudomorphic to the underlying Ge(0 0 1) substrate already at room temperature. Indications of QSE induced structural variations of the growing films have been reported for Pb growth on both Si(1 1 1) and Ge(0 0 1). In the latter case, the apparent height of the Pb(1 1 1) monatomic step was shown to change in an oscillatory fashion by He atom scattering (HAS) during layer-by-layer growth at low temperature. The extent of the structural QSE has been obtained by a comparison of the HAS data with X-ray diffraction (XRD) and reflectivity experiments. Whereas step height variations as large as 20% have been measured by HAS reflectivity, the displacement of the atomic planes from their bulk position, as measured by XRD, has been found to mainly affect the topmost Pb layer, but with a lower extent, i.e. the QSE observed by HAS are mainly due to a perpendicular displacement of the topmost layer charge density. The effect of the variable surface relaxation on the surface vibration has been studied from the acoustic dispersion of the low energy phonons, as measured by inelastic HAS.     

Application of Jäntti’s method for the explanation of adsorption onto rough surfaces

Jäntti introduced a method to calculate the final value of the adsorbed mass already in a very early stage of adsorption measurements. His method was restricted to gravimetric measurements and to adsorptions, which satisfy the simplest molecular model. One of the advantages of his method was that when more complicated molecular models were necessary, the curve resulting from Jäntti`s calculations showed discrepancies from the curve predicted for the simple situation. We used such deviations to evaluate the parameters of the models necessary for the explanation of the measurements. One of the examples we discussed concerned the influence of the occurrence of two parallel and simultaneous adsorptions. In the present paper we discuss the application of these results to adsorption onto a surface where roughness could be expected to play a part. If we consider a rough surface as the sum of two extra surfaces we can apply Jäntti’s method by using our former results of parallel adsorption. We characterise roughness by two parameters which we evaluated with Jäntti’s method. We emphasise that the existence of roughness is not demonstrated by Jäntti’s method, but that the method is useful for the evaluation of parameters introduced by other arguments or from other sources.     

Surface‐Roughness Evolution During the Cementation of Silver Ions on Solid Copper in Aqueous Sulfuric Acid Solution

The evolution of the surface roughness during cementation of Ag⁺ conducted either in O₂‐free or O₂‐saturated aqueous H₂SO₄/CuSO₄ was investigated at two different initial concentrations of Ag⁺. The kinetics data of the process determined previously in the rotating cylinder were linked directly with scanning‐electron‐microscope (SEM) images and surface‐height‐distribution diagrams calculated for various cementation times. It was found that, at the beginning of the process, the surface roughness decreases due to formation of a flat Ag layer on the top of the surface, independent of the presence or absence of O₂ in the system. With increasing reaction time, an increase in the surface roughness was observed. The rate enhancement of the process is mainly responsible for the increase of the surface roughness in the O₂‐saturated solutions, especially at the higher initial Ag⁺ concentration (100 mg/dm³). The rate enhancement observed at a latter stage of the process, connected with the increase of the effective surface area of the cathodic sites, was separated from the rate enhancement induced by the competitive chemical process occurring in O₂‐free solution. The difference in the mechanisms of the processes conducted under aerobic and anaerobic conditions was reflected in the surface‐heigth distributions calculated from the SEM images.     

大口径铜反射镜的加工

叙述铜反射镜的加工过程,提出“两面同时加工,自然释放应力”的加工方法。