Quantitative surface analysis by Auger and x-ray photoelectron spectroscopy

Recent developments in quantitative surface analysis by Auger (AES) and x-ray photoelectron (XPS) spectroscopies are reviewed and problems relating to a more accurate quantitative interpretation of AES/XPS experimental data are discussed. Special attention is paid to consideration of elementary physical processes involved and influence of multiple scattering effects on signal line intensities. In particular, the major features of core-shell ionization by electron impact, Auger transitions and photoionization are considered qualitatively and rigorous approaches used to calculate the respective transition probabilities are analysed. It is shown that, in amorphous and polycrystalline targets, incoherent scattering of primary and signal Auger and photoelectrons can be described by solving analytically a kinetic equation with appropriate boundary conditions. The analytical results for the angular and energy distribution, the mean escape depth, and the escape probability as a function of depth of origin of signal electrons as well as that for the backscattering factor in AES are in good agreement with the corresponding Mote Carlo simulation data. Methods for inelastic background subtraction, surface composition determination and depth-profile reconstructions by angle-resolved AES/XPS are discussed. Examples of novel techniques based on x-ray induced photoemission are considered.     

Phase Transitions,Thermal Desorption of Gases,and Electroconduction in BaCeO<Subscript>3</Subscript>, a Base for High-Temperature Protonic Conductors

Investigations of phase transitions in barium cerate are carried out by methods of dilatometry and differential scanning calorimetry. Thermal desorption of gases and temperature dependences of electroconduction in dry and humid air are studied. Barium cerate exhibits complex polymorphism, undergoing a number of structural conversions at 300– 1300 K. The peaks in the spectra of thermal desorption of CO₂ and H₂O correlate with variations in the crystal lattice. Structural changes in BaCeO₃ affect activation energies for the carrier transport and the shares of partial conductivities.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 620–626.Original Russian Text Copyright © 2005 by Kuz’min, Gorelov, Vaganov, Korzun, Kazantsev, Aksenova, Khromushin.     

KINETICS OF NON-ISOTHERMAL CRYSTALLIZATION OF POLY (ETHYLENE TEREPHTHALATE) MODIFIED BY POLY (ETHYLENE GLYCOL)

The non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET) modified by poly (ethlene glycol) (PEG) were determined by DSC. The dual linear regression method was used to evaluate the relationship between the reciprocal of t 1/2 ( the half life of crystallization) and the appropriate temperature variable. The parameters such as the activation energy (Ed) for transport, the equilibrium melting temperature (T_m~0),the nucleation parameter (ψ),themaximum crystallization temperature (T_(e, max)), and the kinetic crystallizability (G) for the copolyesters were obtained. The influence of the PEG content in PET chains on the parameters characterizing crystallization kinetics and crystallization thermodynamics was discussed.     

胶束增敏导数—可变角同步荧光法同时测定两种羟基联苯

本文建立了２，２’－二羟基联苯（ＤＨＰ）和４－羟基联苯（ＨＰ）的胶束增敏导数－可变角同步荧光同时分析方法，可变角同步扫描所得到的ＤＨＰ和ＨＰ的谱峰位置均对应于常规光谱中的最佳激发－发射位置，经二阶求导后，消除分析谱带干扰，所得的二阶导数－可变角同步光谱即可用于两物质的同时测定，方法快速灵敏，ＤＨＰ测定范围为０．０５～０．５ｍｇ／Ｌ，ＨＰ测定范围为０．０７～２ｍｇ／Ｌ。     

Ageing of Conductive Polyaniline/Poly(Ethylene-co-Vinylacetate) Composites Studied by Thermal Methods

The long-term environmental ageing of conductive composite films containing ethylene-co-vinyl-acetate (EVA) copolymer and a complex of polyaniline (PANI) and dodecylbenzenesulfonic acid (DBSA) was studied by using differential scanning calorimetry (DSC). We assume that both phase separation and crosslinking of PANI main chains occur in the systems. On the other hand, the competition between PANI–DBSA complex self-organization and crystallization of EVA matrix result in structural changes and formation of continuous conductive network, responsible for significantly increased (ca five orders of magnitude) electrical conductivity of the aged films. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lysophosphatidic acid induces astrocyte proliferation in hippocampus slices partially through activating extracellular signal-regulated kinases

The goal of the present study is to test the hypothesis that LPA induces proliferation of astrocytes in hippocampus in vivo via phosphorylation of ERK 1/2. We first characterized the expression of GFAP, a special marker fiber protein of astrocytes, in brain slices after direct injection of LPA into hippocampus by immunohistochemistry, and found that LPA induced a remarkable proliferation of astrocytes. Then double-lablled immunofluorescence was used to detect GFAP and phosphorylation ERK 1/2 (p-ERK 1/2), LPA induced an immediate (10 min) and transient (<30 min) phosphorylation of ERK 1/2, and sequence sustained activation of ERK 1/2 was observed, which last for at least 3 weeks after injection of LPA. Reactions are inhibited by U0126, a specific pharmacological mitogen-activated protein kinase (MEK) inhibitor. Laser confocal scanning was used to study spatial relationship of p-ERK and astrocytes. Amazingly, the early (<7 days) phosphorylation of ERK 1/2 is not expressed in astrocytes but in area where neurons and/or in other cell type(s) occupied, expression of p-ERK 1/2 in astrocytes is not detected until 14 days after LPA injection and lasts for at least 3 weeks. Taken together, these data suggest that LPA play an important role in proliferation of astrocytes through phosphorylation of ERK 1/2 in hippocampus. It provides further proof for the functions of LPA in CNS injury, and may contribute to clinical therapy for relative diseases.     

Characterisation and analysis of micro-contaminants in industrial polymers

Analysis of very small particles can present problems. This paper describes the application of temperature programmed solid insertion probe mass spectrometry (TP-SIP-MS), scanning electron microscopy and SEM X-ray microanalysis to the identification of foreign particles present in an industrial product. The relative advantages and limitations of the techniques are discussed. It is shown that TP-SIP-MS is a powerful tool for such work and complements the use of more conventional microanalytical methods.     

Studying Cu2–xSe phase transformation through DSC examination

The thermal effect accompanying the transition of Cu_2–xSe into a superionic conduction state was studied by non-isothermal measurements, at different heating and cooling rates (β=1, 2.5, 5, 10 and 20°C min^–1). During heating the peak temperature (T_p) remains almost stable for all values of β, (136.8±0.4°C for Cu₂Se and 133.0±0.3°C for Cu_1.99Se). A gradual shift of the initiation of the transformation towards lower temperatures is observed, as the heating rate increases. During cooling there is a significant shift in the position of the peak maximum (T_p) towards lower temperatures with the increase of the cooling rate. A small hysteresis is observed, which increases with the increase of the cooling rate, β. The mean value of transformation enthalpy was found to be 30.3±0.8 J g^–1 for Cu₂Se and 28.9±0.9 J g^–1 for Cu_1.99Se. The transformation can be described kinetically by the model f(ǯ)=(1–ǯ)^n(1+kcatX), with activation energy E=175 kJ mol^–1, exponent value n equal to 0.2, logA=20 and log(k_cat)= 0.5.     

CURING KINETICS AND PROPERTIES OF ACRYLIC RESIN CURED WITH AZIRIDINE CROSSLINKER

A kind of aziridine crosslinkers was synthesized and used to crosslink acrylate copolymers. The crosslinkingproperties and curing kinetics of the resin were studied. It was found that with the increase of the content of crosslinker in theemulsion, the mechanical properties and solvent resistance of the resin will be apparently improved, but its glass transitiontemperature (T_g) is very low. The lowest amount of crosslinker used in the acrylic resin emulsion is 0.25%. Curing kineticsstudied by DSC show that this curing reaction occurs readily because the apparent activation energy of the reaction is low(65.1 kJ/mol). These results demonstrate that the aziridine crosslinker is indeed a low temperature crosslinking agent and canbe used at room temperature.