Analysis of the composition of the passive film on iron under pitting conditions in 0.05 M NaOH/NaCl using Raman microscopy in situ with anodic polarisation and MCR‐ALS

The composition of the surface film formed on pure iron was investigated in a solution of 0.05 M NaOH and 0.05 M NaCl. Raman spectra of the film were recorded in situ during anodic polarisation over the passive region after addition of the NaCl to the electrolyte, under conditions of preresonance enhancement using excitation at 636.4 nm. Multivariate curve resolution with alternating least squares analysis was applied to the spectra to measure the relative amounts of different iron oxide and oxyhydroxides in the film at different potentials. The water content was also determined in this way from Raman spectra recorded using excitation at 514.5 nm. It was found that the composition of the film and the amount of incorporated water were influenced by the applied anodic potential. The results show that stable pitting can occur when the composition changes from the primary constituents β‐FeOOH and Green Complex (a hydrated, amorphous magnetite) with smaller amounts of γ‐Fe₂O₃ and γ‐FeOOH, to δ‐FeOOH and Green Complex, simultaneously with a reduction in water content. These changes result in conditions that favour the rate of localised breakdown of the film by Cl⁻ ions over the rate of repassivation by water in the passive film. Copyright © 2011 John Wiley & Sons, Ltd.     

Parallel-quadrature phase-shifting digital holographic microscopy using polarization beam splitter

We present a digital holography microscopy technique based on a parallel-quadrature phase-shifting method. Two π/2 phase-shifted holograms are recorded simultaneously using polarization phase-shifting principle, slightly off-axis recording geometry, and two identical CCD sensors. The parallel phase-shifting is realized by combining circularly polarized object beam with a 45° degree polarized reference beam through a polarizing beam splitter. DC term is eliminated by subtracting the two holograms from each other and the object information is reconstructed after selecting the frequency spectrum of the real image. Both amplitude and phase object reconstruction results are presented. Simultaneous recording eliminates phase errors caused by mechanical vibrations and air turbulences. The slightly off-axis recording geometry with phase-shifting allows a much larger dimension of the spatial filter for reconstruction of the object information. This leads to better reconstruction capability than traditional off-axis holography.     

Material characterization of a nanocrystal based photovoltaic device

Nanocomposites have shown promise as the active layer for photovoltaic energy conversion. One example is the CdSe nanocrystal \polymer composite demonstrated by Hyunh and Greenham [#!Ref1!#,#!Ref2!#]. In this paper we investigate the baseline properties of the materials used in such a device. We present surface chemical information for CdSe nanocrystals and chemical analysis for poly-(3-hexylthiophene) (P3HT) polymer. Received 30 November 2000     

ICF分解实验中的平面调制靶

 介绍采用多次电镀Ni图形转移工艺将激光干涉法获得的耦合在光刻胶表面的起伏图形进行复制以获得Ni基图形转移模板, 并进一步将表面起伏图形复制到聚苯乙烯薄膜的表面, 以获得具有表面起伏图形的平面调制靶。为提高图形转移的精度、研究电镀图形转移工艺和聚苯乙烯薄膜图形复制工艺对表面起伏图形转移精度的影响, 以扫描电子显微镜对整个图形转移流程进行监控, 比较光刻胶表面图形, 一次、二次电镀转移图形和转移到聚苯乙烯上图形的形貌。     

Charge–orbital ordering above room temperature in the 2D Pr1−xCa1+xMnO4 manganites

The investigation of the n=1 member of the Ruddlesden Popper family, Pr_1−xCa_1+xMnO₄, using electron microscopy, transport and magnetic measurements shows that these 2D manganites exhibit long-range charge–orbital ordering over a wide composition range (0.50x0.80). These oxides show a remarkably high T_CO temperature depending on the x value, up to 330 K, the highest that has been observed to date in 2D manganites. They are characterized by the appearance of a smooth structural transition from P- to C-type inside the charge-ordered state. The high-resolution electron microscopy images of Pr_0.5Ca_1.5MnO₄ registered at room temperature evidence a system of double stripes similar to those observed for Bi_0.5Sr_0.5MnO₃, suggesting that double stripes of one sort of manganese alternate with double or quadruple stripes of a second sort of manganese.     

STM-theory: Image potential, chemistry and surface relaxation

A critical review of the different methods used nowadays for calculating tunneling currents and STM-images is presented with a special emphasis on the role played by the interface image potential and the interaction between the tip and the sample at short distances. After presenting the most commonly used approaches to this problem, we discuss in full detail how the image potential modifies critically the interface tip–sample barrier and how neglecting this effect underestimates the tunneling currents by several orders of magnitude. Although interface non-local image potential effects are difficult to introduce in a plane-wave Density Functional approach, we show how a Green’s function Density Functional formalism based on a local-orbital basis set allows us to introduce those image effects with a good accuracy. The effect of the interaction between the tip and the sample is illustrated for an Al-tip approaching an Al surface; and the role of the electronegative atoms adsorbed on the tip is discussed considering the O/Pd(1 1 1) interface and the effect of having an O-atom adsorbed on the tip apex. Finally, by analyzing the Si(1 1 2)–Ga interface we also show how the Green’s function Density Functional approach based on a local orbital basis can also be reliably used to analyze surface steochiometries.     

Surface composition of alloys

The practical importance of alloy surfaces in catalysis, corrosion andother aspects of materials performance is widely recognized. What is needed now is sufficient knowledge of the relationship between externally controllable factors — alloy composition, temperature, environment — and surface properties — composition, structure, chemical activity — to control materials performance in these applications. Our purpose here is to review progress in determining and predicting the relationship between one surface property, composition, and certain externally controllable variables: overall composition, temperature, environment and physical form.We find that theoretical treatments of metal alloy surface composition now include essentially all significant physical effects and can predict values for most parameters of interest. Though improvements are still possible, the accuracy of predictions is more often limited by uncertainties or absence of the basic data for the calculations (e.g., thermochemical values) than by the models themselves.Alloy surface composition can now be measured well. The first monolayercomposition of large alloy slabs can be determined quantitatively over a wide temperature range in ultra-high vacuum. Difficulties with specimens of practical interest still challenge experimentalists. Among these are supported catalysts, surfaces under chemisorbed layers and composition of layers below the first. Significant progress is being made and we expect the next few years will see success.     

Visualisation of polysaccharide fouling on microporous membrane using different characterisation techniques

Although many studies assessed fouling behaviour in microporous membrane processes like membrane bioreactors (MBRs), in situ or direct observation of the fouling layer has not yet been possible. The observation of the fouling layer resulting from the filtration of model solutions allowed better understanding of MBR fouling intensity and mechanisms. In this study, alginate has been used as a model for polysaccharide (one of the main foulants in MBRs). Three visualisation techniques, confocal laser scanning microscopy (CLSM), environmental scanning electron microscopy (ESEM), and direct observation (DO) have been tested to observe the alginate fouling. The work presented in this paper revealed the advantages and limitations of each technique used for this specific application. Although no coating is required for this technique, ESEM allowed distinct non-destructive observation of clean membrane. However, the lack of structure in the alginate fouling layer limited the use of this technique for fouled membranes. While CLSM requires the use of expensive fluorescent markers, DO appeared as the most promising technique for direct and in situ observation of MBR fouling. DO of alginate/bentonite and alginate/bacteria solutions revealed the creation of a well-structured dual fouling system (bentonite-concentrated layer of 50 μm embedded and covered by a concentration polarisation of alginate greater than 240 μm) on the surface of hollow fibre membrane.     

Hadamard transform fluorescence image microscopy using one-dimensional movable mask

With a 511-slit one-dimensional (1D) Hadamard mask and a highly sensitive linear charge-coupled device (CCD), spatial multiplexing is performed and a programmable Hadamard transform (HT) microscopic fluorescence imaging system was developed. The system can generate 511×512 pixel format images for small samples. Sensitivity, signal to noise ratio, imaging speed and spatial resolution of this system were discussed. The results show that the system can be applied for single-cell imaging sensitively in a short time. Spatial resolution up to 0.24 μm/pixel, which is close to the resolution limit of the conventional optical microscope, has been obtained under oil lens. The weak native fluorescence imaging for pollen cells can be realized within 1 min. The system has been applied for multi-parameter evaluation of tumor malignancy based on nuclear DNA ploidy measurements for one breast tumor specimen. The result indicates that the system has good application prospect in cell biology and medicine.