EFTEM and EELS Analysis of a Pt/NiO Interface

 Energy-filtering transmission electron microscopy (EFTEM) is more and more becoming an important nanoanalytical technique in both materials science and biology. The main advantage of the method lies in the possibility to obtain two-dimensional chemical information from large specimen areas as well as from features on a nanometer scale. Due to its excellent lateral resolution it is perfectly suited for the investigation of nanometer sized features (e.g. interfaces). In this paper we will show how EFTEM can be used to characterize the interface between a Pt layer and a NiO crystal as part of a coulometric titration cell. In addition to elemental distribution maps electron energy-loss spectra (EELS) across the interface (EELS linescans) have been acquired to obtain quantitative compositional profiles. By employing these methods the following interfacial layers could be identified, all of which containing Pt, Ni and O in different proportions: 13 nm Pt-rich, 32 nm Ni-rich and 29 nm Pt-rich. The origin of these is discussed in terms of displacement reactions.     

Application of EELS to the microanalysis of materials

Electron energy loss spectroscopy (EELS) is used in analytical electron microscopy (AEM) because it can provide results on the chemical composition and structure of a small volume of material. The practical application of EELS was demonstrated by the investigation of a refractory hard metal of the type WC-TiC-Co and by the investigation of a BaTiO₃ ceramic material. To demonstrate the present status of quantitative analysis by EELS, the spectra of Be₂SiO₄, TiB₂ and BaTiO₃ were quantified and the results indicate that quantitative analysis is feasible for major concentrations of light elements and also of heavier elements even in the presence of severe edge overlap.     

Structural and Chemical Analysis of Materials with High Spatial Resolution

 An understanding of the correlation between microstructures and properties of materials require the characterization of the material on many different length scales. Often the properties depend primarily on the atomistics of defects, such as dislocations and interfaces. The different techniques of transmission electron microscopy allow the characterization of the structure and of the chemical composition of materials with high spatial resolution to the atomic level: high resolution transmission electron microscopy allows the determination of the position of the columns of atoms (ions) with high accuracy. The accuracy which can be achieved in these measurements depends not only on the instrumentation but also on the quality of the transmitted specimen and on the scattering power of the atoms (ions) present in the analyzed column. The chemical composition can be revealed from investigations by analytical microscopy which includes energy dispersive X-ray spectroscopy, mainly quantitatively applied for heavy elements, and electron energy-loss spectroscopy. Furthermore, the energy-loss near-edge structure of EELS data results in information on the local band structure of unoccupied states of the excited atoms and, therefore, on bonding. A quantitative evaluation of convergent beam electron diffraction results in information on the electron charge density distribution of the bulk (defect-free) material. The different techniques are described and applied to different problems in materials science. It will be shown that nearly atomic resolution can be achieved in high resolution electron microscopy and in analytical electron microscopy. Recent developments in electron microscopy instrumentation will result in atomic resolution in the foreseeable future.     

Vibrational Spectroscopy and Analytical Electron Microscopy Studies of Fe–V–O and In–V–O Thin Films

Summary.  Orthovanadate (M ³⁺VO₄; M = Fe, In) and vanadate (Fe₂V₄O₁₃) thin films were prepared using sol-gel synthesis and dip coating deposition. Using analytical electron microscopy (AEM), the chemical composition and the degree of crystallization of the phases present in the thin Fe–V–O films were investigated. TEM samples were prepared in both orientations: parallel (plan view) and perpendicular (cross section) to the substrate. In the first stages of crystallization, when the particle sizes were in the nanometer range, the classical identification of phases using electron diffraction was not possible. Instead of measuring d values, experimentally selected area electron diffraction (SAED) patterns were compared to calculated (simulated) patterns in order to determine the phase composition. The problems of evaluating the ratio of amorphous and crystalline phases in thin films are reported. Results of TEM and XRD as well as IR and Raman spectroscopy showed that the films made at lower temperatures (300°C) consisted of nanograins embedded in the dominating amorphous phase. Characteristic vibrational spectra allowed to distinguish between the different crystalline phases, since the IR and Raman bands showed broadening due to the decreasing particle size of the films thermally treated at lower temperatures. Vibrational analysis also showed that the electrochemical cycling of crystalline films led to spectra that were in close agreement with the spectra of the nanocrystalline films prepared at lower temperatures. The formation of a nanocrystalline structure is therefore a prerequisite for obtaining a higher charging/discharging stability of Fe–V–O and In–V–O films. Received October 4, 2001. Accepted (revised) November 23, 2001     

Thin-Film Zinc/Manganese Dioxide Electrodes

Summary.  Thin-film electrodes allow the manufacturing of flat batteries of variable design. Their electric performance is better than that of customary cells because of a larger contact area between anode and cathode and better utilization of the electrochemically active materials. Bipolar thin-film electrodes for the rechargeable alkaline zinc/manganese dioxide system were assembled using graphite-filled plastics (high-density polyethylene and polyisobutylene). In a different approach, extremely thin electrodes were obtained using 25 μm thick foils made of non-conductive micro-porous polypropylene. The electroactive materials were electrolytically deposited into the pores of the previously metallized foil, providing the required conductive connection through the plastic matrix by themselves. Cycle behavior, cumulated capacities, and energies of batteries with up to two bipolar units were measured. At this early stage of development, batteries based on graphite-filled polymer foils showed better results with regard to storage capacity per unit area and to cycle life. Prototypes based on micro-porous polypropylene suffered from the relatively small fraction of pore volume available for the deposition of active material (about 38%) and from current collector corrosion. Received May 30, 2000. Accepted December 18, 2000     

Fourier Transform Infrared Spectroscopy Applied to the Characterisation of 17th–20th Century Calcographic and Xylographic Inks

 The aim of this paper is to optimize the analytical method for the characterisation of 17th–20th century calcographic and xylographic inks. It is very important to use not only non destructive techniques, but also analytical instruments that require a minimal amount of material so as to analyze unique or valuable samples, and simultaneously to obtain as much information as possible about their composition. This study compares different ways of sample preparation for further analysis by Fourier transform infrared spectroscopy. It has been possible to analyze the most important absorptions that appear in the spectra and therefore to associate them with the compounds contained in inks. Some of the compounds identified are: hydroxyapatite (calcium phosphate), Prussian blue (ferric ferrocyanide), linseed oil, carbonates, nitrates and sulfates. Received January 10, 1999. Revision March 17, 1999.     

Examination of the Spatial Distribution of Dyes and Polymers in Thin Films by Two-Photon Microscopy

Summary.  Two-photon absorption induced fluorescence microscopy was used as a tool for the examination of the spatial distribution of a thin dye film. The two-photon absorption induced fluorescence signal is essentially the same as that produced by excitation with a single photon of equivalent energy. When femtosecond pulses are focused into a sample there is an intrinsic spatial selectivity of the two-photon emission signal, since it is dependent upon the square of the light intensity. This has tremendous implications in fluorescence microscopy. Since two-photon absorption is confined in a small region at the focal waist of an objective lens, photodamage and photobleaching of the sample are significantly reduced. In addition, the two-photon signal has inherent z-axis spatial resolution, which facilitates the construction of 3-D images. In the present work an application of this technique to a thin film of a dye is presented. The method can generally be applied to thin films made from photonic polymers. Received June 23, 2000. Accepted (revised) July 31, 2000     

DPASV Method for Determination of Trace Concentrations of Manganese in Non-Buffered Chloride Solutions by Addition of Cyanide as a Masking Agent

 A highly sensitive, selective, and rapid differential pulse anodic stripping voltammetric method at HMDE is described for the determination of trace concentrations of Mn²⁺. The determination of Mn²⁺ in non-buffered chloride solution is seriously disturbed by the presence of Ni²⁺, Co²⁺, Cr³⁺, Zn²⁺ and Cu²⁺ due to intermetallic compound formation. The procedure is based on the addition of low amounts of cyanide as a masking agent. The interference of < 20 μgL⁻¹ of Ni²⁺, Co²⁺ and Cr³⁺ and < 75 μgL⁻¹ of Cu²⁺ and Zn²⁺ can thus be avoided, as the formed cyanide complexes prevent intermetallic compound formation during the short accumulation period. Thus, the addition of cyanide greatly improves the DPASV determination of manganese in non-buffered medium. A comparison between the determination of Mn²⁺ in the presence of a mixed cyanide/non-buffered chloride and in the ammoniacal buffer solution shows that the peak current of manganese in the presence of cyanide is four times higher with the same peak potential. The proposed method is shown to be applicable for the Mn²⁺ determination in both ground and tap water. A good agreement is obtained between the results by DPASV and AAS. Received May 14, 1999. Revision May 25, 2000.     

Characterization of Nanocomposite Coatings in the System Ti–B–N by Analytical Electron Microscopy and X-Ray Photoelectron Spectroscopy

Summary.  Superhard nanocomposite coatings of different composition in the quasi-binary system TiN–TiB₂ were deposited onto stainless steel sheets by means of unbalanced DC magnetron co-sputtering using segmented TiN/TiB₂ targets. The chemistry and microstructure of a TiB_0.6N_0.7 coating was investigated using X-ray and electron diffraction, photoelectron spectroscopy, energy-filtering transmission electron microscopy, and electron energy-loss spectrometry. High resolution elemental mapping of the elements Ti, B, N, and O with energy-filtering TEM reveals a homogeneous distribution on the nanometer scale. X-Ray and electron diffraction exhibit only TiN crystallites of nanometer size, but no information on the boron-rich phase. The near-edge fine structures of the BK and NK ionization edges in the EELS spectra of the Ti–B–N coatings were used to derive information on the phases by comparing the edges with those of reference compounds. It was found that the TiN nanocrystals occur together with TiO _x particles; the grains are embedded in a strongly disordered or quasi-amorphous matrix consisting mainly of TiB₂ particles and, near the steel substrate, also boron oxide (B₂O₃). Received October 4, 2001. Accepted (revised) January 10, 2002     

Effect of Manganese Dioxide Dispersion on the Absorbing Properties of Manganese Dioxide (MnO2)‐Epoxy Composites

Manganese dioxide (MnO₂) particle was synthesized and introduced into epoxy resin to be microwave absorber. The spectroscopic characterization of the formation processes of MnO₂ was studied by using X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Microwave absorbing properties with different volume fractions of MnO₂ were investigated by measuring complex permittivity, complex permeability and reflection loss in the 2–18 and 18–40 GHz microwave frequency range using the free space method. The absorbing performance of MnO₂‐epoxy composites at same sample thickness and at various sample thickness were also studied. It was found that the best absorbing property and an absorption frequency range shifting could be obtained at the frequency range of 2–18 and 18–40 GHz.     

Study of the Interface Microstructures of CVD Diamond Films by TEM

 The characteristics of the interface microstructures between a CVD diamond film and the silicon substrate have been studied by transmission electron microscopy and electron energy loss spectroscopy. The investigations are performed on plan-view TEM specimens which were intentionally thinned only from the film surface side allowing the overall microstructural features of the interface to be studied. A prominent interfacial layer with amorphous-like features has been directly observed for CVD diamond films that shows a highly twinned defective diamond surface morphology. Similar interfacial layers have also been observed on films with a <100> growth texture but having the {100} crystal faces randomly oriented on the silicon substrate. These interfacial layers have been unambiguously identified as diamond phase carbon by both electron diffraction and electron energy loss spectroscopy. For the CVD diamond films that exhibit heteroepitaxial growth features, with the {100} crystal faces aligned crystallographically on the silicon substrate, such an interfacial layer was not observed. This is consistent with the expectation that the epitaxial growth of CVD diamond films requires diamond crystals to directly nucleate and grow on the substrate surface or on an epitaxial interface layer that has a small lattice misfit to both the substrate and the thin film material.     

Growth of Anodic Films on Compound Semiconductor Electrodes: InP in Aqueous (NH4)2S

Summary.  Film formation on compound semiconductors under anodic conditions is discussed. The surface properties of InP electrodes were examined following anodization in an (NH₄)₂S electrolyte. The observation of a current peak in the cyclic voltammetric curve was attributed to selective etching of the substrate and a film formation process. AFM images of samples anodized in the sulfide solution revealed surface pitting. Thicker films formed at higher potentials exhibited extensive cracking as observed by optical and electron microscopy, and this was explicitly demonstrated to occur ex situ rather than during the electrochemical treatment. The composition of the thick film was identified as In₂S₃ by EDX and XPS. The measured film thickness varies linearly with the charge passed, and comparison between experimental thickness measurements and theoretical estimates for the thickness indicate a porosity of over 70%. Cracking is attributed to shrinkage during drying of the highly porous film and does not necessarily imply stress in the wet film as grown. During the growth of the thick porous film, spontaneous current oscillations have been observed. The frequency of oscillation was found to be proportional to the current density, regardless of whether the measurements were carried out during a potential sweep or at constant potential. Thus, the charge passed per oscillation remained constant. A characteristic value of approximately 0.3 C · cm⁻² was measured under potential sweep conditions, and a similar value was obtained at constant potential. Received October 16, 2001. Accepted (revised) December 21, 2001     

Application of Microbeam Techniques in the Steel Industry

 Steel is a very complex material, and nowadays all types of microbeam techniques are used to characterise it. This paper describes how and why microbeam techniques are used in the steel industry, with special emphasis on micro-analysis of precipitates and surface analysis.     

Preparation and Spectroscopic Characterization of Two Manganese(II)semiquinone Complexes

Summary. The complexes [CTA][Mn(II)(SQ)₃] were isolated in the solid state and purified. SQ is the o-semiquinone of L-dopa or dopamine and CTA is the cetyltrimethylammonium cation. These complexes were characterized by Raman, infrared, EPR and thermogravimetry (TG) techniques. The EPR spectra of the solids presented an intense signal characteristic of the o-semiquinone radical anion with g=2.0062 and g=2.0063 for L-dopa and dopamine, respectively. Six characteristic lines around the organic radical signal confirm the presence of the Mn²⁺ ion. The most intense Raman bands were observed at for dopamine and at 1356 cm^–1 for L-dopa and assigned to a C–O stretching with major C₁–C₂ character. The absence of an intense Raman band at ca. , characterizes the ligands as an o-semiquinone radical anion. Broad bands in the region can be assigned to deformations associated with the five-member ring chelate including the manganese ion, the oxygens, and the C₁–C₂ bonds. The more intense IR bands for the dopamine and the L-dopa-derived ligands at are assigned to CO. Mass loss mechanisms for the two complexes, based on the TG results, were proposed and confirm the formula proposed.     

PbTiO3/SrTiO3(010)异质界面上的周期性失配位错及电子富集

It is important to determine the effects of misfit dislocations and other defects on the domain structure, ferroelectricity, conductivity, and other physical properties of ferroelectric thin films to understand their ferroelectric and piezoelectric behaviors. Much attention has been given to ferroelectric PbTiO₃/SrTiO₃ or PbZr_0.2Ti_0.8O₃/SrTiO₃ heterointerfaces, at which improper ferroelectricity, a spin-polarized two-dimensional electron gas, and other physical phenomena have been found. However, those heterointerfaces were all (001) planes, and there has been no experimental studies on the growth of (010) PbTiO₃/SrTiO₃ heterointerface due to the 6.4% misfit between two materials. In this study, we selected an atomically flat (010) PbTiO₃/SrTiO₃ heterointerface grown using a two-step hydrothermal method as the research subject, and this is the first experimental report on that interface. Interfacial dislocations can play a significant role in causing dramatic changes in the Curie temperature and polarization distribution near the dislocation cores, especially when the size of a ferroelectric thin film is scaled down to the nanoscale. The results of previous studies on the effects of interfacial dislocations on the physical properties of ferroelectric thin films have been contradictory. Thus, this issue needs to be explored more deeply in the future. This study used aberration corrected scanning transmission electron microscopy (STEM) to study the atomic structure of a (010) PbTiO₃/SrTiO₃ heterointerface and found periodic misfit dislocations with a Burgers vector of a[001]. The extra planes at the dislocation cores could relieve the misfit strain between the two materials in the [001] direction and thus allowed the growth of such an atomically sharp heterointerface. Moreover, monochromated electron energy-loss spectroscopy with an atomic scale spatial resolution and high energy resolution was used to explore the charge distribution near the periodic misfit dislocation cores. The fine structure of the Ti L edge was quantitatively analyzed by linearly fitting the experimental spectra recorded at various locations near and at the misfit dislocation cores with the Ti³⁺ and Ti⁴⁺ reference spectra. Therefore, the accurate valence change of Ti could be determined, which corresponded to the charge distribution. The probable existence of an aggregation of electrons was found near the a[001] dislocation cores, and the density of the electrons calculated from the valence change was 0.26 electrons per unit cell. Based on an analysis of the fine structure of the oxygen K edge, it could be argued that the electrons aggregating at the dislocation cores came from the oxygen vacancies in the interior regions of the PbTiO₃. This aggregation of electrons will probably increase the electron conductivity along the dislocation line. The physics of two-dimensional charge distributions at oxide interfaces have been intensively studied, however, little attention had been given to the one-dimensional charge distribution. Therefore, the results of this study can stimulate research interest in exploring the influence of the interfacial dislocations on the physics of ferroelectric heterointerfaces.     

An Unusual Photoreaction of 3,4-Di-O-benzyl-hypericin

Summary.  Upon irradiation of 3,4-di-O-benzyl-hypericin and proton sponge (bis-1,8-N,N-dimethylamino-naphthalene) in benzene solution, a stable radical ion pair formed which exhibited an intense absorption band around 800 nm. This was advanced by UV/Vis, NMR, and ESR spectroscopy. In presence of oxygen, irradiation of this photoproduct led to an activated oxygen species which then attacked the proton sponge. Received July 17, 2000. Accepted July 20, 2000     

Microstructure and Defect Characterization of Nanostructured Ni<Subscript>3</Subscript>Al

Summary.  Nanostructured Ni₃Al was produced by the inert gas condensation and in situ compaction technique and characterized by means of high-resolution transmission electron microscopy (HRTEM), X-ray diffraction, and density measurements. The defect structure was investigated using positron annihilation lifetime spectroscopy (PALS). It is shown that in some samples besides the cubic also the martensitic phase can be present. The defect structure can be divided into three major components: vacancy-like defects in the grain boundaries and nano-voids with a size of 1 nm as seen with PALS, and large pores with sizes up to 8 nm as seen with HRTEM. Furthermore, it is shown that an increasing compaction temperature leads to significantly smaller nano-voids. Received October 5, 2001. Accepted (revised) November 12, 2001     

Mechanism of the Nickel-Catalyzed Electrosynthesis of Ketones by Heterocoupling of Acyl and Benzyl Halides

Summary.  The mechanism of the nickel-catalyzed electrosynthesis of ketones by heterocoupling of phenacyl chloride and benzyl bromide has been investigated by fast scan rate cyclic voltammetry with [Ni(bpy)²⁺ ₃](BF₄ ⁻)₂ as the catalytic precursor (bpy = 2,2{−}{ bipyridine}). The key step is an oxidative addition of Ni⁰(bpy) (electrogenerated by reduction of the Ni(II) precursor) to PhCH₂Br whose rate constant is found to be 10 times higher than that of PhCH₂COCl. The complex PhCH₂Ni^IIBr(bpy) formed in the oxidative addition is reduced at the potential of the Ni^II/Ni⁰ reduction by a two-electron process which affords an anionic complex PhCH₂Ni⁰(bpy)⁻ able to react with PhCH₂COCl to generate eventually the homocoupling product PhCH₂COCH₂Ph. The formation of the homocoupling product PhCH₂COCOCH₂Ph is prevented because of the too slow oxidative addition of Ni⁰(bpy) to PhCH₂COCl compared to PhCH₂Br. The formation of the homocoupling product PhCH₂CH₂Ph is also prevented because PhCH₂Ni⁰(bpy)⁻ does not react with PhCH₂Br. This explains why the electrosynthesis of the ketone can be performed selectively in a one-pot procedure, starting from an equal mixture of PhCH₂COCl and PhCH₂Br and a nickel catalyst ligated by the bpy ligand. Received June 27, 2000. Accepted July 11, 2000     

A HREM and Analytical STEM Study of Precipitates in an AZ91 Magnesium Alloy

 The paper focuses on the microstructural characterisation of secondary phases in an AZ91 magnesium alloy. The orientation relationship and atomic structure of semi-coherent Mg/Mg₁₇Al₁₂ interfaces are studied by means of selected area diffraction, EDS and high resolution TEM. Besides the common Mg₁₇Al₁₂ semi-coherent platelets of high density and coarser incoherent Mg₁₇Al₁₂ particles, other, less frequent precipitates were found, rich in Al and Mn. The quasicrystalline nature of these precipitates was detected by means of electron diffraction.     

Electron Backscattering from Real and In-Situ Treated Surfaces

 Significant differences in backscattered electron (BSE) yields exist between the surfaces cleaned by methods used in electron microscopy and spectroscopy. These differences have been observed for Au, Cu and Al specimens, and are interpreted on the basis of simulated BSE yields. Composition and thickness of the surface contamination layers, responsible for the differences, are estimated. The results (7 nm of carbon on Au or 3 nm of oxide on Al) remain within expectation and indicate that the BSE yield measurements and BSE images should be interpreted cautiously. Peculiar results are obtained for Cu, perhaps due to a different cleaning procedure. A new concept of an information depth for the BSE signal is introduced as a depth within which the total BSE yield can be modelled as composed of the yields of layers proportional to their thickness weighted by the escape depths. This concept proved satisfactory for thin surface layers and brought the information depth values 2 to 4 times smaller than first estimated, i.e. half the penetration depth.