SeSAME, a Monte Carlo simulation program which can handle totally arbitrarily shaped twodimensional geometries, has been extended for the modeling of whole x-ray spectra in absolute units. The so called single scattering model has been used for the simulations presented here. Elastic scattering processes are modeled using a partial wave approach according to a relativistic expression derived by Mott. For the calculation of the electron energy loss the stopping power formula from Joy and Luo has been applied.

Two different double differential cross sections for continuous x-ray production have been implemented into SeSAME. The first one is an analytical model derived by Kirkpatrick and Wiedmann and is based on a non-relativistic theory developed by Sommerfield and Elwert. The second one uses tabulated values for the shape function for atomic-field Bremsstrahlung and scaled Bremsstrahlung cross sections differential only in photon energy according to Kissel at al.

Typical modern histories of the discovery of the chemical elements report that element 43 was discovered in Italy in 1937 by Perrier and Segre. According to these accounts, the discovery was made by chemical separation in a sample of deuteron-bombarded molybdenum, supplied by E. Lawrence, and thus represent the first discovery of an element produced artificially and is the reason for the name “technetium” (Tc) chosen by the investigators. Some accounts might note in passing that the existence of element 43 was predicted in the early part of the 20th century on the basis of the periodic table, and that the element was reported as discovered in natural samples by x-ray emission spectroscopy in 1925 and called “masurium” (Ma). These reports, however, invariably call this discovery erroneous and sometimes refer to the investigators (typically left unnamed) as “deluded”.

The original reported discovery of “masurium” was made in an exhaustive investigation of some thousand mineral separates of Nb-Mo-U-rich phases involving early elegant use of wavelengthdispersive x-ray microanalysis.

The analytical expressions used in ZAF and ϕ(ρz) calculations give single values for the composition of each element for a single set of intensity measurements from samples and standards. Confidence intervals in composition are established by looking at the variability of repeated measurements. They are usually attributed to x-ray counting statistics or experimental reproducibility factors such as sample repositioning. Uncertainty in the equations themselves or the parameters that go into them are rarely considered. The derivations of ZAF and ϕ(ρz) equations are primarily based on the case where flat single-phase regions, relative to the x-ray excitation volume, are examined using normal electron beam incidence. Use of these equations has been extended to non-normal electron beam incidence as well as the quantitative analysis of layered structures, but usually with less theoretical justification. Finally, special experimental cases including porous structures, rough surfaces, vertical interfaces and small particles are very difficult or impossible to model by the single application of a set of analytical equations to convert measured x-ray intensities to elemental composition.

For quantitative thin-film microanalysis using X-ray energy dispersive spectrometry (XEDS) in analytical electron microscopy (AEM) the Cliff-Lorimer ratio technique is widely applied. One of the critical steps in the ratio technique is to determine the aiff-Lorimer k factor relating the characteristic X-ray intensities to the compositions. The k factor can be determined experimentally with the relative error of ˜ ± 1%. So, the most accurate quantification can be performed using the experimental k factors. To determine the k factors experimentally, standard thin-filrns with known composition are required. Unfortunately, this is not always possible because such the standards may not be available. Even if all standards are available, many k factors should be determined in multi-component system. This is time consuming. These limitations in k-factor determination make thin-film quantification harder. This paper presents a new quantitative procedure for thin specimens to overcome these limitations.

For a number of years we have used in our laboratory a simple extension to light elements of the classical ClifF-Lorimer approach using stoichiometric compound standards containing pairs of heavier elements to determine independently the EDS detector sensitivity contribution to quantitative analysis in the AEM. It is now also extended to direct light element LVEDS analysis in the SEM at low voltage (<5kV). This approach may be more practical, accessible and easily reproducible for routine use than the elegant custom thin film fabrications reported by Egerton, but the latter method has other substantial advantages, including well defined thicknesses, in the most sophisticated applications. As the types of advanced materials have expanded to include ceramics and polymers the requirements for analysis have also changed. In many cases the light elements are now the majority species in advanced materials and the corrections based on older standards are huge; and therefore inevitably rather limited in accuracy.

The II-VI semiconductor mercury cadmium telluride, composed of 80 mole percent HgTe and 20 mole percent CdTe, has been grown on Earth and aboard two NASA Space Shuttle flights in order to study the solidification of a solid solution semiconductor having a wide separation between liquidus and solidus. Segregation during solidification, high volatility of mercury, and strain fields associated with large temperature gradients make the growth of homogeneous, high-quality, bulk crystals extremely difficult. The traditional growth methods yield crystals with axial and radial compositional variations and secondary precipitates of tellurium, probably caused by gravityinduced, thermosolutally-driven flows just ahead of the growth interface. The purpose of growing these crystals in microgravity is to reduce gravity-induced convection. This should be advantageous for minimizing the density of crystal defects while also minimizing compositional variation transverse to the crystal growth direction.

The ground based experiments consisted of growing crystals in several different configurations of heat pipe furnaces and NASA’s Advanced Automated Directional Solidification Furnace (AADSF).

The electrical properties of SrTiO3 (strontium titanate) ceramics are strongly influenced or even dictated by grain boundary segregation of charged point defects, such as dopant atoms, impurities, vacancies, or self-interstitials. The atomistic structure of the grain boundaries, their energy, and the segregation of point defects mutually depend on each other. Grain boundary segregation of charged point defects induces the formation of space charge layers in the adjoining crystals. In order to investigate the relation between grain boundary structure and composition, grain boundaries in Fedoped SrTiO3 bicrystals and in SrTiO3 ceramics were studied by HRTEM and by AEM with subnanometer resolution.

Quantitative HRTEM served to investigate the atomistic structure of Σ=3, (111) grain boundaries in Fe-doped SrTiO3 bicrystals with a doping level of Fe/Ti= 0.04at% (Fig. 1). Analysis of the translation state revealed that the Σ=3, (111) grain boundary has an excess volume: normal to the boundary plane, the spacing between the two crystals exceeds what one would expect from a coincidence site lattice model by (0.06 ±0.01 )nm.

The small probe size and high spatial resolution of TEM offer unique capabilities for studying interfaces of materials. Compared with neutron and x-ray diffraction, TEM is often considered nonquantitative. In HREM, especially, atomic images can alter significantly with imaging parameters that are often difficult to determine experimentally. The weakness of the HREM can be circumvented by a multiprobe approach, i.e., the combined use of a wide range of TEM techniques, such as B-F/D-F imaging, nano-probe EDS and EELS, electron diffraction, and strain-field characterization. Quantitative analysis, based on the calculations and experimental TEM data, is often necessary to correctly derive the crystal-, chemical-, and electronic-structure of an interface.

We review our multiprobe approach in studying interfaces in complex systems of superconductors, starting with the simplest interface, twin boundary, in YBa2Cu3O7-δ. Although HREM suggested that there are two types of twin boundaries, with and without a ˜d110 lattice translation at the boundaries, the structural characteristics of the interfaces were determined by analyses of the interfacial δ-α fringe and the associated diffuse scattering, while EELS revealed their association with the local oxygen/hole concentration.

The interaction of a liquid with a solid substrate has been the subject of intense research since the early 1800s. The subject is relevant and very important even today from a basic science as well as technological standpoint. Liquid-phase-sintered oxide ceramics often contain a siliceous glassy layer in the grain boundaries which affect the properties of the ceramic. The wetting of the grain boundaries by the liquid has a strong dependence on the crystallography. While some boundaries are preferably wet, other special boundaries appear to be completely ‘dry’. The presence of the liquid film also affects the faceting behavior of the boundary plane. While several studies have been carried out on these intergranular glass films, many of the basic issues still remain unclear. The development of modern microscopy techniques facilitate the characterization of structure and chemistry at a high spatial resolution. This paper deals with the microstructural examination of two of the important issues involved with these intergranular films, i.e., faceting of grain boundaries in the presence of a glassy phase and the behavior of interfaces between two glassy phases of different compositions.

A large number of bulk and thin-film electroceramic systems contain electrically active interfaces which dictate the various useful electronic properties of these devices. The electrical activity of these interfaces stems from a complex interplay among various interfacial attribute but often involves formation of some form of electrostatic potential at the interfaces which is modified under applied bias of current and/or voltage.

Figure la schematically shows charge distribution at a model grain boundary (GB), while Figure 1(b) shows its corresponding potential distribution. As shown in Figure 1(c), the energy band structure bends opposite to this built-in potential, causing a downward shift at the grain boundary . The difficulty with evaluating the Schottky barrier model, which is often invoked to explain GB electrical activity, is that the charge density distribution and therefore the band bending is expected to dynamically alter as bias is applied across the grain boundary. This variation adds another level of complexity to theoretical descriptions of the barrier behavior

Some properties of transition metal oxides are related to the presence of elements with mixed valences. In electron energy-loss spectroscopy (EELS), the L or M ionization edges of transition-metal, rare-earth and actinide elements usually display sharp threshold peaks known as white-lines. EELS experiments have shown that a change in cation valence state introduces a significant change in the White-line intensity ratio [1]. With the use of valence state information provided by the white lines, an experimental approach is demonstrated here to map the valence state distributions of Mn and Co using an energy-filtered transmission electron microscope (TEM). A spatial resolution of ˜ 2 nm has been achieved. This technique should be particularly useful in studying valence states of cations in magnetic oxides.

To map the distribution of ionization states, an energy window of ˜ 10 eV in width is required to isolate the L3 from L2 white lines (Figure 1).

Bismuth titanate (Bi4Ti3O12) belongs to a family of layered perovskites (Aurivillius phases) that are important for nonvolatile ferroelectric memory applications. Recently epitaxial (001) Bi4Ti3O12 thin films have been grown on (001) SrTiO3 by reactive molecular beam epitaxy (MBE) in an adsorptioncontrolled growth regime. Bi4Ti3O12 has a monoclinic layered perovskite structure at room temperature which consists of alternating Bi2O2 and Bi4Ti3O10 perovskite layers (see the upper part of Fig. 1(b)). Due to the significant difference in crystal structure between film and substrate, the surface termination of the SrTiO3 substrate and the way in which growth is initiated might be expected to have a significant influence on the interfacial structure. In this work, we present high-resolution transmission electron microscope (HRTEM) studies of the Bi4Ti3O12 / SrTiO3 interfacial structure for Bi4Ti3O12 films grown on SrTiO3 substrates terminated with either the TiO2- or SrO-layers.

Bi4Ti3O12 thin films were grown on SrO- or TiO2-layer terminated homoepitaxial SrTiO3 buffer layers grown on SrTiO3 (001) substrates by reactive MBE.

The ability to obtain chemical information with (near) atomic resolution has recently become possible by a combined approach of Z-contrast imaging with electron energy-loss spectroscopy (EELS) in scanning transmission electron microscopes. This method is particularly interesting for the characterization of structure-property relationships in novel multicomponent oxides, which possess added functionality due to their high nonstoichiometry.

In this paper we demonstrate the capabilities of this method in analyzing the microstructural mechanisms of accommodation of non-stoichiometry, using two example systems: (Ba,Sr)TiO3thin films for DRAM applications, grown by MOCVD with different amounts of excess titanium, and an oxygen-deficient perovskite ceramic, SrCoOx. The experiments were performed in a JEOL JEM 201 OF field emission transmission electron microscope, operating at 200 kV, equipped with an annular dark-field detector, scanning unit and a post-column imaging filter (Gatan GIF 200). This microscope has been demonstrated to achieve probe sizes of under 1.5 Å .

The observation of atomic-scale structures of grain boundaries (GBs) via axial illumination HREM has been largely restricted to tilt GBs, due to the requirement that the electron beam be parallel to a low-index zone axis on both sides of the interface. This condition can be fulfilled for all tilt GBs with misorientation about a low-index direction. The information obtained through HREM studies in many materials has brought important insights concerning the atomic-scale structure of such boundaries. However, it is well known that tilt GBs occupy only an infinitesimally small fraction of the 5-dimensional phase space which describes the macroscopic geometry of all GBs. Therefore, although tilt GBs are very important due to their low energy, it would be usefulto also study twist GBs and general GBs that contain twist and tilt components.

We have prepared thin-film Au samples by an epitaxy technique in which (01l) and (001) grains are grown side by side.

The electrical activity of grain boundaries in perovskites, of which SrTiO3 is a model system, is the basis for their use as capacitors, varistors and positive-temperature coefficient resistors. In related materials this same electrical activity is often detrimental. The outstanding example of a negative effect is the reduction in critical current by several orders of magnitude across grain boundaries in YBa2CU3O7-δ as the boundary misorientation is increased from 0°-45°. Grain boundaries are also likely to profoundly affect properties such as domain wall motion in ferroelectric and magnetic perovskites. The origin of the electrical activity is ubiquitously attributed to the existence of grain boundary donors, usually assumed to be impurities, which set up a double Schottky barrier as they are screened by dopants in the adjacent bulk crystal. We show here, that although electrical barriers can doubtless be modified by dopants, the grain boundary structure itself is the intrinsic origin of the socalled grain boundary donors.

Ferroelectric thin films have received much attention because of their nonvolatile ferroelectric random access memory (NVFRAM) applications. Recently SrBi2Ta2O9 (SBT), a bismuth-layered ferroelectric compound, has been recognized as a leading candidate for the NVFRAM applications because of its negligible fatigue, low leakage currents and ability to maintain bulk characteristics when fabricated in very thin films. While most work up to date has been focused on its thin film forms for nonvolatile memory applications, its intrinsic properties, basic structure and the effects of defects on the properties are not well understood, mainly due to the lack of sizable single crystals and the details of defects. In this paper we report the first direct determination of a novel planar defect structure in SrBi2Ta2O9, using high-resolution Z-contrast imaging.

The n+1TinO3n+1 Ruddlesden-Popper homologous series are promising candidates in the search for low loss tunable dielectric materials. SrTiO3 (n=∞) has the perovskite structure with alternating TiO2 and SrO layers. However, those members of the n+1TinO3n+1 series with n≠∞ have tetragonal symmetry and space group 14/mmm. These phases are formed by inserting a rock-salt SrO layer every n SrTiO3 perovskites, resulting in a successive perovskite blocks being mutually sheared by [1/2,1/2,0] (Fig. 1).

Previously, the n = 1 - 3 members of this series have been made in polycrystalline form using solid state synthesis methods. Attempts to synthesize intermediate members (4≤n<∞) have been unsuccessful and resulted in mixed phase samples. Fortunately, significant advancement in epitaxial growth techniques makes it possible to control the synthesis of a wide variety of homologous oxide crystal systems. In the present work, thin films of the Srn+1TinO3n+1, RP series with n = 1 - 5 have been synthesized using reactive molecular beam epitaxy (MBE).

A vanadium-bearing variant of 316 stainless steel that was rapid solidification processed (RSP) by gas atomization and hot extrusion of the powder (10:1 extrusion ratio at 900°C) has been studied previously by conventional atom probe field ion microscopy (APFIM). The mechanical properties of this steel were markedly improved by RSP and aging (600°C for 1000 hours). High nitrogen (0.45 at% (0.2 wt%)) and oxygen (0.16 at% (0.05 wt%)) contents were intentionally introduced by melting under 80% nitrogen/20% oxygen gas and atomizing in nitrogen gas. A nominal boron concentration of 0.04 at% (0.01 wt%)) is present as a tramp element. As a result, a large number density (˜ 2 × 1021 m-3) of 25 nm plate-like vanadium-rich nitrides precipitate during aging of the alloy and these precipitates contribute a major portion of the strengthening. Previous efforts to locate the oxygen in the structure using APFIM were inconclusive largely due to poor counting statistics.

The technique of atom probe tomography (APT) enables the x, y, and z coordinates and the elemental identities of the atoms in a small volume to be determined at the atomic level. Therefore, the APT technique may be used to characterize solute segregation to interfaces and precipitation in terms of concentration gradients and precipitate morphology. This type of information may be used to optimize the design of alloys.

The material that was used to illustrate the capabilities of atom probe tomography is a complex polycrystalline nickel-based superalloy, Alloy 718. The composition of this commercial superalloy is Ni- 3.2 at. % Nb, 0.96% Al, 1.15% Ti, 20.3% Fe, 21.8% Cr, 0.26% Co, 1.8% Mo, 0.16% Mn, 0.21% Si and 0.26% C. The material was characterized after a heat treatment oM h at 1038°C + 8 h at 870°C + 500 h at 600°C. Previous atom probe field ion microscopy characterizations of this material has demonstrated that there is no intragranular precipitation after the anneal at 1038°C.

The transistors planned for commercial use ten years from now in many electronic devices will have gate lengths shorter than 130 atoms, gate oxides thinner than 1.2 nm of SiO2 and clock speeds in excess of 10 GHz. It is now technologically possible to produce such transistors with gate oxides only 5 silicon atoms thick[l]. Since at least two of those 5 atoms are not in a local environment similar to either bulk Si or bulk SiO2, the properties of the interface are responsible for a significant fraction of the “bulk” properties of the gate oxide. However the physical (and especially their electrical) properties of the interfacial atoms are very different from .bulk Si or bulk SiO2. Further, roughness on an atomic scale can alter the leakage current by orders of magnitude.

In our studies of such devices, we found that thermal oxidation tends to produce Si/SiO2 interfaces with 0.1-0.2 nm rms roughness.