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Nanostructural features of nickel-base superalloys as revealed by atom probe field ion microscopy (APFIM) and atom probe tomography (APT) are reviewed. The more salient information provided by these techniques is discussed through an almost exhaustive analysis of literature over the last 30 years. Atom probe techniques are shown to be able to measure the composition of tiny γ′ precipitates, a few nanometers in size, and to reveal chemical order within these precipitates. Phase separation kinetics in model NiCrAl alloys was investigated with both 3DAP and Monte-Carlo simulation. Results are shown to be in good agreement. Plane by plane analysis of {001} planes of Ni3Al-type γ′ phase makes it possible to estimate the degree of order as well as the preferential sites of various addition elements (Ti, Cr, Co, W, Ta, Re, Ru, etc.) included in superalloys. Clustering effects of Re in the γ solid solution were also exhibited. Due to its ultrahigh depth resolution, the microchemistry of interfaces and grain boundaries can be characterized on an atomic scale. Grain boundaries in Astroloy or N18 superalloys were found to be enriched in B, Mo, and Cr and Al depleted.
The M emission spectrum of 68Er was reinvestigated using
wavelength dispersive spectrometry, with a TAP diffracting crystal. By
recording the spectra using the second-order reflection, an improved
energy resolution was achieved, which is necessary to resolve the
M5O3 line from the neighboring α
M5N7 transition. In addition to the five
lines/bands tabulated in the classical paper of Bearden, a number of
further lines were observed. These are M1N3,
M3O1, M2N1,
M5O3, M3N1, and
M4N3. For all the lines with an energy below the
M5 absorption structure (M5O3,
M3N1, M4N3, and ζ
M5N3), an increasing relative intensity with
increasing energy of the exciting electrons, E0, was
observed. This dependence has its origin in the fact that these lines are
normally absorbed whereas Mα (M5N7) and Mβ
(M4N6) are additionally affected by anomalous
line-type absorption.
This article describes a simple shield that can be placed on typical
commercial heating holders to reduce the thermal signal during heating to
reasonable levels for in situ energy-dispersive X-ray
spectroscopy analysis. The improved temperature capability provided by the
shield is demonstrated by initial compositional analysis results obtained
across a solid–liquid interface on Al-Si-Cu-Mg alloy powder
particles. Considerations in the design of and improvement for the shield
are discussed.
Morphological and chemical characteristics were determined for
airborne tungsten particles in Fallon, Nevada, a town that is
distinguishable environmentally by elevated airborne tungsten and cobalt.
From samples of airborne dust collected previously at six different places
in Fallon, tungsten-rich dust particles were isolated and analyzed with
automated electron microprobe and wavelength-dispersive spectrometry.
Representative W particles were further analyzed using transmission
electron microscopy. Morphologically, Fallon W particles are angular and
small, with minimum and maximum sizes of ≤1 μm and 5.9 μm in
diameter, respectively. The number and size of tungsten-rich particles
decrease in Fallon with distance from a hard-metal facility located near
the center of town. Chemically, Fallon airborne W particles include
mixtures of tungsten with cobalt plus other metals such as chromium, iron,
and copper. No W-rich particles were identifiable as CaWO4
(scheelite) or MnWO4 (huebnerite). From d-spacings, Fallon
particles are most consistent with identification as tungsten carbide.
Based on these multiple lines of evidence, airborne W particles in Fallon
are anthropogenic in origin, not natural. The hard-metal facility in
Fallon processes finely powdered W and W-Co, and further investigation
using tracer particles is recommended to definitively identify the source
of Fallon's airborne tungsten.
The use of X-ray elemental analysis tools like energy dispersive X-ray
(EDS) is described in the context of the investigation of nuclear
materials. These materials contain radioactive elements, particularly
alpha-decaying actinides that affect the quantitative EDS measurement by
producing interferences in the X-ray spectra. These interferences
originating from X-ray emission are the result of internal conversion by
the daughter atoms from the alpha-decaying actinides. The strong
interferences affect primarily the L X-ray lines from the actinides (in
the typical energy range used for EDS analysis) and would require the use
of the M lines. However, it is typically at the energy of the
actinide's M lines that the interferences are dominant. The artifacts
produced in the X-ray analysis are described and illustrated by some
typical examples of analysis of actinide-bearing material.
The evolution of Guinier-Preston zones in an Al-2.7 at.% Ag alloy was studied using atom probe tomography. The composition and morphology of the GP zones are time dependent, explaining discrepancies in previous work. This result requires the metastable miscibility gap for GP zones to be reevaluated, highlighting the importance of the temporal evolution of the GP zones. Preliminary results on the composition of γ′ and γ plates are also presented.
β-carotene was first identified from the vitreous asteroid bodies
(ABs) excised from one patient with asteroid hyalosis (AH) by confocal
Raman microspectroscopy and was also verified by high performance liquid
chromatography (HPLC). Two patients had been diagnosed with AH and
intervened by surgical vitrectomy due to blurred vision. The morphology
and components of both AB specimens were observed by optical microscopy
and determined by using confocal Raman microspectroscopy and HPLC
analysis, respectively. Surprisingly, two unique peaks at 1528 and 1157
cm−1 were found in the Raman spectrum for the AB specimen
of patient 1 alone, which were in close agreement with that of the Raman
peaks at 1525 and 1158 cm−1 for β-carotene and/or
lutein. However, HPLC analytical data clearly indicated that the retention
time for the extracted sample from the AB specimen of patient 1 was
observed at 13.685 min and just identical to that of β-carotene
(13.759 min) rather than lutein (2.978 min). In addition, the lack of any
peak in the HPLC profile for the AB specimen of patient 2 also confirmed
the absence of Raman peaks at 1525 and 1158 cm−1. Thus
this preliminary study strongly suggests that β-carotene as a unique
component of ABs was specifically detected from the AB specimen of one AH
patient by using confocal Raman microspectroscopy and HPLC analysis.
In using microscopic imaging techniques, unbiased selection of sampling areas is often critical when judgment has to be used to find regions of interest. A conditional random sampling was designed to survey hematite particles on a mica surface using tapping-mode atomic force microscopy, based on three adapted-systematic-sampling methods designed to exclude subjective bias by limiting the freedom of arbitrarily selecting sampling areas. The results of these surveying methods were compared with the average particle surface density modeled by Poisson distribution. It was found that the conditional random sampling could survey particles effectively and improve the data reliability significantly. Ten population-known images from the same mica sheet were used to evaluate these methods, and an average relative error of 12% (maximum 21%) was obtained using the conditional random method with six sampling areas. It was used to investigate the effects of common organic pollutants, benzene, toluene, ethylbenzene, and xylenes on the transport of soil colloids.
The recombinant virulence protein VirE2, capable of forming a complex with single-stranded T-DNA during transfer into plant cells, was isolated, purified, and used for interactions with ssT-DNA. The in vitro interaction of VirE2 and ss-binding protein from Escherichia coli with single-stranded DNA (phage λ) was determined by agarose gel electrophoresis by the formation of high-molecular-weight complexes after preliminary coincubation of purified protein preparations with ssDNA. We show that VirE2 binds to single-stranded DNA and protects it against nuclease S1 degradation much better than does E. coli SSB protein. We for first time observed the VirE2-ssT-DNA complex by using atomic force microscopy. The complex observed by atomic force microscopy after ssT-DNA and VirE2 protein mixing has a length of about 800 nm and a 5–8 nm width in sites with attached VirE2 protein.
Cardiac fibroblasts are the most numerous cells in the heart and are
critical in the formation and normal functioning of the organ. Cardiac
fibroblasts are firmly attached to and surrounded by extracellular matrix
(ECM). Mechanical forces transmitted through interaction with the ECM can
result in changes of overall cellular shape, cytoskeletal organization,
proliferation, and gene expression of cardiac fibroblasts. These responses
may be different in the normally functioning heart, when compared with
various pathological conditions, including inflammation or hypertrophy. It
is apparent that cellular phenotype and physiology, in turn, are affected
by multiple signal transduction pathways modulated directly by the state
of polymerization of the actin cytoskeleton. Morphological changes in
actin organization resulting from response to adverse conditions in
fibroblasts and other cell types are basically descriptive. Some studies
have approached quantifying changes in actin cytoskeletal morphology, but
these have involved complex and difficult procedures. In this study, we
apply image analysis and non-Euclidian geometrical fractal analysis to
quantify and describe changes induced in the actin cytoskeleton of cardiac
fibroblasts responding to mechanical stress. Characterization of these
rapid responses of fibroblasts to mechanical stress may provide insight
into the regulation of fibroblasts behavior and gene expression during
heart development and disease.
The applicability of atom probe to the characterization of photovoltaic devices is presented with special emphasis on high efficiency III–V and low cost ITO/a-Si:H heterojunction cells. Laser pulsed atom probe is shown to enable subnanometer chemical and structural depth profiling of interfaces in III–V heterojunction cells. Hydrogen, oxygen, and phosphorus chemical profiling in 5-nm-thick a-Si heterojunction cells is also illustrated, along with compositional analysis of the ITO/a-Si interface. Detection limits of atom probe tomography useful to semiconductor devices are also discussed. Gaining information about interfacial abruptness, roughness, and dopant profiles will allow for the determination of semiconductor conductivity, junction depletion widths, and ultimately photocurrent collection efficiencies and fill factors.
This article presents a study on the influence of the protocol used for immobilization of bacterial cells onto surfaces by mechanically trapping them into a filter. In this sense, the surface and structure of trapped cells are analyzed. Bacteria can be present solely or with extracellular polymeric substances (EPS). To test the behavior of the EPS layer duing the filtering process, different strains of a well-known EPS-producer bacteria (Staphylococcus epidermidis), which produce an extracellular matrix clearly visible in AFM images, have been used. Results show that this immobilization method can cause severe structural and mechanical deformation to the cell membrane. This altered mechanical state may possibly influence the parameters derived from AFM force curves (which are micro/nano-mechanical tests). Also, our results suggest that the EPS layer might move during the filtering process and could accumulate at the upper part of the cell, thus favoring distorted data of adhesion/pull-off forces as measured by an AFM tip, especially in the case of submicron-sized microbial cells such as bacteria.
Atomic force spectroscopy (AFS) was used to measure interaction forces
between the tip and nanostructured layers of
poly(o-ethoxyaniline) (POEA) in pure water and CuSO4
solutions. When the tip approach and retraction were carried out at low
speeds, POEA chains could be physisorbed onto the
Si3N4 tip via nonspecific interactions. We
conjecture that while detaching, POEA chains were stretched and the
estimated chain lengths were consistent with the expected values from the
measured POEA molecular weight. The effects from POEA doping could be
investigated directly by performing AFS measurements in a liquid cell,
with the POEA film exposed to liquids of distinct pH values. For pH ≥
6.0, the force curves normally displayed an attractive region for POEA,
but at lower pH values—where POEA is protonated—the repulsive
double-layer forces dominated. Measurements in the liquid cell could be
further exploited to investigate how the film morphology and the force
curve are affected when impurities are deliberately introduced in the
liquid. The shape of the force curves and the film morphology depended on
the concentration of heavy metal in the liquid cell. AFS may therefore be
used to study the interaction between film and analyte, with important
implications for the understanding of mechanisms governing the sensing
ability of taste sensors.
Two issues that often impact the cryo-electron microscopy (cryoEM) specimen preparation process are agglomeration of particles near hole edges in holey carbon films and variations in vitreous ice thickness. In many cases, the source of these issues was identified to be the residues and topography often seen in commercially available films. To study and minimize their impact during specimen preparation, an improved holey carbon film has been developed. Rather than using a consumable template based on soft materials that must be removed prior to grid assembly, a method was developed that uses a hard template and a water-soluble release layer to replicate the template pattern into the carbon films. The advantages of this method are the improved purity and flatness of the carbon films, and these attributes are shown to have a dramatic improvement on the distribution of single particles embedded in vitreous ice suspended across the holes. Improving particle distribution is an enabling factor toward increasing the throughput of data collection for cryoEM.
Heart development, especially the critical phase of cardiac looping,
is a complex and intricate process that has not yet been visualized
“live” over long periods of time. We have constructed and
established a new environmental incubator chamber that provides stable
conditions for embryonic development with regard to temperature, humidity,
and oxygen levels. We have integrated a video microscope in the chamber to
visualize the developing heart in real time and present the first
“live” recordings of a chick embryo in shell-less culture
acquired over a period of 2 days. The time-lapse images we show depict a
significant time window that covers the most critical and typical
morphogenetic events during normal cardiac looping. Our system is of
interest to researchers in the field of embryogenesis, as it can be
adapted to a variety of animal models for organogenesis studies including
heart and limb development.