Direct current (dc) electrodeposition was used to co-deposit cobalt and antimony in citric-based solutions. Growth behavior of Co–Sb alloy thin films was systematically studied under various deposition conditions. Effects of deposition parameters (i.e., deposition potential, cobalt sulfate concentration, and pH value) on the microstructure, chemical, and phase composition of the deposited materials were also studied and are discussed in detail.

In the production of turbine discs, the final wrought structure is critically dependent on aspects of the ingot grain structure produced by vacuum arc remelting (VAR) prior to cogging and forging. Variations in the as-cast grain structure in the nickel-based superalloy INCONEL 718 were investigated, focusing upon regions where strings of equiaxed grains interrupt a predominately columnar-dendritic structure. These features, termed "tree rings," form concentric circles that can be observed visually on etched transverse sections of the VAR ingot. These structures are of interest because they correlate with perturbations in control of the process and have also been associated with the occurrence of defects. This article describes an experimental study of these tree rings, which both characterizes them and investigates possible mechanisms for their formation. Fluctuations in the macroscopic heat, mass, and momentum transfer, which can increase the grain nucleation at the mushy zone front (similar to a columnar-to-equiaxed transition), were considered to be the most likely of the mechanisms hypothesized. In a second article, a multiscale mathematical model is developed to quantify these concepts and to determine whether they account for the features observed.

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

The reconstruction of individual nanoparticles or of arrays of nanoparticles inside a matrix has recently become a major aim of electron tomography [1][2][3][4]. The generation of iso-threshold displays or video-animations of rotational views is the standard method of communicating results of tomography studies. Beyond visualisation, there is also a significant amount of quantifiable information to be gained from postprocessing of tomograms. Often the tomogram as a 3D voxel value distribution contains too much detail and a compression of information into key quantities, such as volumes, surface areas, shape asymmetry, or surface roughness estimates is desirable. Three examples of such processing is presented: (i) Nanoparticle volume estimation: Homogeneous CeO 2 nanoparticles with constant density and chemistry have been reconstructed by and are binarised here after backprojection so as to separate all voxels into two groups "inside =1, and outside=0" of the particle. The sum of all voxels is then a measure of the volume. Errors arise from noise on the input images, thresholding ambiguities, and (mostly) the missing wedge artefact. A regularly shaped nanoparticle is therefore the ideal test object, as it allows the comparison of the "reconstructed volume" V r with the "geometric volume" V g as calculated from edges and basal planes directly from the micrograph. (ii)Particle volume fraction of a nanocomposite: Dendritic CeO 2 precipitates inside a borosilicate glass [5] appear with a high contrast ratio in ADF-STEM due to Z-contrast. A tomogram of a micrometre-sized glass fragment [6] with a dozen of nanoparticles can therefore be thresholded and binarised twice: at a lower level to reveal the glass fragment total shape, and at a higher level to isolate all CeO 2 particles above a dark background. The total voxel count of the two binary tomograms then quantify glass fragment volume and precipitate volumes, and the ratio estimates the essential particle volume fraction V v . Alternatively stereological analysis [7] of any cross section using a wire mesh superimposed and counting knots inside particles and matrix gives a good estimate [8], while the same technique on a projection (TEM image) instead of a tomogram requires estimates for particle size and shape to correct for the overestimation by one order of magnitude. (iii)Single particle: One dendrite from the same glass composite can be evaluated for its actual volume and its relative volume by dividing by an "envelope" volume [9]. A surface estimate (and surface/volume ratio) can be gained by edge enhancement (Laplace filter) and binarisation. The sum of all non-zero surface voxels then gives the surface area. According to Fig 3, the ratio of the crosssectional area of the dendrite relative to a square envelope is 0.57 (0.43 with a non-square envelope), while the ratio of its edge contour length relative to the contour length of a square envelope is 5.2 indicating a high degree of fractality. Threshold values to be chosen, sampling of the data (resp. resolution...

Tungsten tips are widely used as probes for scanning tunneling microscopy (STM), and are particularly suitable for in-situ manipulation in scanning electron microscopy (SEM) and nanoindentation experiments in transmission electron microscopy (TEM) [1]. Tomography [2] has been made applicable to crystalline objects using either EFTEM [3], Z-contrast [4], or EDX [5], andW tips have been analysed by Z-contrast in [6]. Here, a novel EDX tomography mode is presented for the chemical analysis of W tip cross-sections. Artefacts from this novel technique are also explored.W tip preparation via electrochemical etching leads to various degrees of oxide shell coverage. We explore our homemade tips by direct mounting on a Gatan high tilt tomography holder using a special cylindrical specimen mount [6]. This specimen configuration helps to reach high tilt angles in an ultra-small lens gap, and to prevent X-ray detector shading [5,6]. We used a JEM 2010F FEGTEM (Jeol, Japan) equipped with an ultrathin window Energy Dispersive X-ray (EDX) detector (Oxford Instruments, UK). Figure 1(a) shows an ADF-STEM image (saturated at larger thickness) of a W tip. The EDX spectrum in Figure 1(b) is the central member ofan additional point scan series across the wire and shows the presence of W, O, C and Cu (grid). This point scan series serves for background estimation especially for O and C. The EDX line-scan tilt series was acquired by tilting the specimen from -70 to +50 with a tilt increment of 10 and multiple fast-scanning the beam across the line L until noise is sufficiently low (see Figure 1(c)) at each tilt angle. Figure 2 shows the W-L α , O-K and C-K EDX signals along L at -70 (a), 0 (b) and +50 (c) tilt angles. The EDX line scan series was exported to Interactive Data Language IDL (RSI, USA) and an in-house backprojection code was applied for the reconstruction. Figure 3 (a-c) shows the distribution of tungsten, oxygen and carbon in the cross-section along L, and line contours were added to emphasize compositional variations. The RGB-map in Figure 4 shows the superposition of W and O in the shell, presumably WO 3 , and the C contamination layer, see also EELS results in [6].From Figure 2, it can be seen that the carbon-contamination increased significantly from -70 to +50 . For an ideal tomographic reconstruction, a high tilt range as close as possible to 180 and a tilt increment as small as possible are required. In this experiment, the large tilt increment (10 ) induces star artefacts in Figure 3, but is a compromise between resolution (small increment) and exposure (large increment, signal-to-noise ratio, alignment quality), as an optimisation problem to be presented in detail. The missing-wedge effect [2] appears in Figure 3 as an elongation in the projection direction and anisotropic resolution. From comparing our line scans with and without background subtraction we can conclude on two artefacts: (i) From Figure 3(b), the oxygen distribution is not annular but half annular, which is background-independent and seems to be d...