The optimization of disc manufacturing conditions is required to increase the storage capacities of magnetic recording media, which is strongly related to both magnetic properties and microstructural features. Analyzing the microstructure requires transmission electron microscopy (TEM), since the small grain sizes of the media prevent other tools from characterizing them. This paper discusses several fascinating characteristics of TEM in understanding and analyzing the properties of the recording media.

Off-axis electron holography and micromagnetic calculations that involve solutions to the Landau-Lifshitz-Gilbert equations are used to study magnetization reversal processes in lithographically patterned submicron-sized Co and Co/Au/Ni magnetic elements.

Advanced Fresnel- & Foucault-Lorentz microscopy were applied to analyze magnetic behavior of the grain boundaries in Nd-Fe-B hard magnets. In-situ TEM magnetizing experiments combined with these imaging methods revealed the process of magnetization reversal in polycrystalline sintered and die-upset Nd-Fe-B under various magnetic fields. Fine details of magnetic flux distribution, derived from the magnetic interferograms created by phase-coherent Foucault imaging, provide a quantitative description of the local variation of magnetic flux. Our study suggests that the grain boundaries play an important multi-functional role in the reversal of magnetization, by acting as (a) pinning centers of domain walls, (b) centers of nucleation of reversal domains, and (c) sinks or sources for migrating magnetostatic charges and/or dipoles. They also ensure a smooth transition for irreversible remagnetization in polycrystalline samples.

We describe studies of refractory metals Mo and Nb, grown heteroepitaxially in the (011) orientation on sapphire (1120), using low energy electron microscopy (LEEM). A wide variety of structural and dynamical phenomena are observed and recorded as video sequences. These are organized here in five categories as follows. First are surface impurity phases identified by LEED. It is an important point, established here for Mo, that almost ideally clean surfaces with mainly single stepped terraces, can be prepared on thin films for use in surface science. Second, surface reconstruction phenomena can also be identified by diffraction. This is illustrated here by a reconstruction of the Nb surface, with two equivalent domains that form a stripe phase, owing to competing long and short range interactions. Detailed studies of nucleation, fluctuations and the equilibrium of these variants are described. The third area is surface topography, illustrated here by almost ideal stepped surfaces of Mo and Nb at high temperatures, and by nanofaceting by step edge coalescence to form {110} facets on Nb at lower temperatures. The phase diagram for nanofaceting is discussed. Fourth are processes at the internal Al2O3-metal interface, as interfacial dislocations, misorientation steps and defects become visible in the LEEM image through the displacement fields they cause. The final category includes bulk process where the observed dynamics of threading screw and edge dislocations and accompanying slip traces reveal their release at high temperatures from Cottrell atmospheres. The kinetics are tracked as surface diffusion smooths dislocation slip traces, and the interactions among dislocations and surface steps are measured.

EBSD in the SEM has been developed into a tool that can provide identification of unknown crystalline phases with a spatial resolution that is better than one micrometer. This technique has been applied to a wide range of materials. Use of the HOLZ rings in the EBSD patterns has enabled the reduced unit cell to be determined from unindexed EBSD patterns. This paper introduces EBSD for phase identification and illustrates the technique with examples from metal joining and particle analysis. Reduced unit cell determination from EBSD patterns is then discussed.

HOLZ lines formed in a CBED pattern provide the most accurate means to measure a local strain tensor with high spatial resolution over mesoscopic length scales. With the advent of energy-filtering in a field-emission TEM, the precision of this measurement increases by filtering out the inelastically scattered electrons. This paper presents an alternate approach to obtaining the same increased precision by image processing of CBED patterns formed in a conventional LaB6 microscope. This technique results in the determination of the full strain tensor within ±0.01%. It is based on developing a Wiener filter for CBED patterns, deconvoluting the point spread function of the CCD camera, using the Hough transform to measure distances between HOLZ line intersections, and subtracting out an experimentally determined projector lens distortion. The present technique has been used to measure the strain tensor for the two types of grain boundaries found in MBE grown Al thin films on Si which have the mazed bicrystal microstructure.

The basic design features of a controlled environment transmission electron microscope and the details of the one at the University of Illinois are described. Examples of how this instrument has been used to determine fundamental mechanisms of hydrogen embrittlement in metals are presented.

The high mobility of anion vacancies in oxygen deficient perovskite type materials makes these ceramics potential candidates for oxygen separation membranes. As a preliminary investigation of the defect chemistry in these oxides, we show here the analysis of SrCoO3−σ using atomic resolution Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope. In particular, after being subjected to oxidation/reduction cycles at high temperatures we find the formation of ordered microdomains with the brownmillerite structure.

The NIST microcalorimeter energy dispersive x-ray spectrometer provides important advances in x-ray spectrometry. The high spectral resolution, approaching 2 eV for photon energies below 2 keV, the wide photon energy coverage, 250 eV to 10 keV, and the energy dispersive operation enable a wide range of materials characterization problems to be addressed. This performance is especially critical to high spatial resolution, low-voltage x-ray microanalysis performed with the field-emission gun scanning electron microscope.

Ultra-high-vacuum segregation studies on in-situ fractured Cu-Sb alloys were performed in terms of nanometer scale scanning Auger/Electron microscopy. S contamination leads to the formation of Cu2S precipitates which, upon removal due to fracture, expose pits with morphology that depends on the precipitate size and shape. Local variations of S and Sb distributions inside the pits were correlated to local surface orientations as Atomic Force Microscopy analysis revealed.

Steels used in steam turbine applications are susceptible to temper embrittlement if operated at temperatures above 400°C. The cause of this embrittlement is the segregation of impurity elements, mainly phosphorus, to the prior austenite grain boundaries. Molybdenum can act as an effective scavenger for phosphorus, but the scavenging effect is lost when the molybdenum is precipitated in carbides during service at these elevated temperatures. Thus, the very slow temper embrittlement is controlled by the rates of alloy carbide formation, rather than by the diffusion of phosphorus. The presence of vanadium apparently retards the embrittlement process even more by interfering with the formation of the molybdenum-rich carbides. Vanadium carbonitrides, are small, only a few nanometers in size, and difficult to see by standard TEM contrast mechanisms. Analysis of segregating elements to the grain boundaries has to be carried out on areas which are devoid of precipitates, especially small V precipitates or other precipitates that could be interpreted as segregation rather than precipitation. One method of detecting precipitates in the matrix is by X-ray mapping areas of interest. This paper describes a new method of X-ray mapping of multi-component steels that have overlapping lines. The method has been found to be effective in removing thickness effects from the maps and discriminating between real and artificial compositional components, which are created by the overlapping lines.

We have optimized the sensitivity of convergent beam electron diffraction (CBED) by orienting the specimen such that the central (000) diffraction disc shows a pattern of defect lines that are most sensitive to tetragonal distortion. We compare the position of these lines in the experimentally obtained patterns with results from computer simulations, which need to be based on dynamical diffraction theory. In both experimental and simulated patterns the positions of the defect lines are determined by applying a Hough transformation. As a result of this optimized approach, we can measure the tetragonal distortion of a low temperature grown GaAs layer as low as 0.04%.

Quantitative evaluation of coherency strains around particles in the alloy Ni-12 at.% Al has been performed by means of high resolution electron microscopy (HREM) and convergent bean electron diffraction (CBED). Evaluation of the elastic strain fields around particles can give insight into the elastic interaction between particles during their coarsening mechanism and especially for the late stages where the elastic energy becomes particularly important. Typically, particles form spatial arrangements after long aging times. In the case of fcc-type structures, they align along the <001> soft elastic directions and form groups of many particles. HREM has been used to acquire images including the particle matrix interface. The selected zone axis is [001]. The quantitative analysis to determine the positions of the intensity maxima and the subsequent evaluation of the lattice parameters, is made by using the software Darip. Two different directions with respect to the particle matrix interface (parallel and perpendicular) are considered for the evaluation. These measurements are compared to determinations made by means of quantitative evaluation based on calibrated CBED patterns taken from similar regions of the samples.

The paper reports an electron microscope study of diffusion controlled deformation mechanisms in two-phase titanium aluminides which apparently cause the degradation of the strength properties at elevated temperatures. Climb velocities were analyzed in terms the critical vacancy supersaturation necessary for the operation of diffusion assisted dislocation sources. Particular emphasis was paid on structural changes occurring during long-term creep, which are apparently associated with dislocation climb.

Plasma spraying of yttria-stabilized zirconia on stainless steel substrates generates rapidly solidified thin film discs called splats. Constraint due to adhesion at their interface generates sufficient stresses during cooling from the splat melting to generate extensive cracking. Stress relief by cracking always accompanied by delamination of the thin films at the edges of cracked segments. It is shown here that images obtained in the SEM through amplification of the specimen current signal generate the right contrast for delineating regions of edge delamination in the cracked segments of a splat. Image analysis using this contrast provides a quantitative measure of the extent of delamination at the interface. Greater delamination in the splats formed on cooler substrates. Correlation also indicates complimentary nature of stress relief by delamination and cracking. A detailed analysis including data from solidification and cooling and cracking statistics will give a measure of the adhesion strength at the interface. This technique is a quick method for measuring delamination of microscopic degree in thin insulating films on conducting substrates.

Melting and solidification of metallic materials have been observed directly using an in-situ heating experiment in an electron microscope. In pure Al melting initiates at the surface, while in a eutectic alloy melting initiates preferentially at eutectic interfaces and grain boundaries. The atomic structure of a solidliquid interface was identified by comparing an experimental image with computed ones.

Atom location by channeling enhanced microanalysis (ALCHEMI) has been used to characterize the site distributions of Nb and Cr alloying additions in the L10-ordered γ phase of ternary titanium aluminides. Two alloys, Ti50Al48Cr2 and Ti50A148Nb2, were processed by furnace cooling from 1300°C (within the α-γ two phase field) as well as by rapid solidification using twin-anvil splat quenching of electromagnetically levitated and undercooled samples. ALCHEMI studies of furnace cooled samples yield results generally consistent with those in the published literature. Nb alloying additions are found to partition exclusively to the ‘Ti’ sublattice, while Cr alloying additions exhibit an ‘Al‘ sublattice preference. However, a higher degree of disorder can be achieved with rapid solidification and high solid state cooling rates (105-106 K/s). Significant distribution of the ternary elements between the ‘Ti’ and ‘Al‘ sublattices has been measured in the splat quenched samples, with up to 12% of the Nb atoms occupying the ‘Al‘ sublattice and the fraction of Cr atoms on the ‘Ti’ sublattice doubling to ∼30%. Rapid solidification of TiAl produces an equiaxed hexagonal α phase solidification structure that transforms in a massive fashion to the tetragonal γ phase. Although the amount of massively transformed γ is dependent upon the solid state cooling rate, ternary alloying additions can more strongly influence the transformation kinetics. The Nb-modified alloy exhibits significant amounts of the massively tranformed γ, similar to the Ti52Al48 binary alloy, whereas little massively transformed γ is observed in the Cr-modified alloy. These results can be correlated with the relative atomic size, lattice distortion, and sublattice site occupancy of Nb and Cr in the L10 unit cell.

High angular resolution electron channeling x-ray spectroscopy (HARECXS) was examined as a practical tool to locate lattice-ions in spinel crystals. The orientation dependent intensity distribution of emitted x-rays obtained by HARECXS is so sensitive to lattice-ion configuration in the illuminated areas that the occupation probabilities on specific positions in the crystal lattice can be determined accurately through comparison with the theoretical rocking curves. HARECXS measurements have revealed partially disordered cation arrangement in MgO·nAl2O3 with n= 1.0 and 2.4. Most A13+ lattice-ions occupy the octahedral (VI) sites with 6-fold coordination, while Mg2+ lattice-ions reside on both the tetrahedral (IV) and the octahedral (VI) sites. The structural vacancies are enriched in the IV-sites. Further evacuation of cations from the IV-sites to the VI-sites is recognized in a disordering process induced by irradiation with 1 MeV Ne+ ions up to 8.9 dpa at 870 K.

Stabilization of zirconia by anion exchange (N for O) is a novel idea. A number of oxy-nitrides with flourite-related (cubic) structure have been reported to form at high temperatures (1100°C). We have used a TEM equipped with environmental cell and Gatan Imaging Filter (GIF) to study the nitridation behavior of zirconia. The in situ observations reveal the formation of a cubic structure at ≈800°C when the Zr(OH) 4×H2O precursor was heated in ≈2 torr of NH3. The presence of N in the lattice is confirmed by electron energyloss spectroscopy.

In this paper a method is described to observe shrinkage microcracks on ‘wet’ specimen cross-sections of cement-based materials with Environmental Scanning Electron Microscopy (ESEM). A sample cooling device which can be used in the ESEM chamber was built to control the relative humidity above a microscope sample. The accuracy of measuring relative humidity is determined to be 5% at a sample temperature of 3°C. A microscope sample preparation method and a pump-down sequence of the ESEM-chamber, both without any drying of the sample, are described. Preliminary results show that in the studied mortar the visibility of shrinkage microcracks on a ‘wet’ specimen cross-section is low due to closure of microcracks by swelling of the cement paste.