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Elemental distributions in a magnetic multilayer system with the structure Si substrate/Ta/NiFe/Ru/CoFeB/Ru/NiFe were studied using atom probe tomography (APT) along different analysis directions. The distributions of Ru and B atoms, which require a high evaporation field, were strongly influenced by the APT analysis direction. In particular, B in the CoFeB layer appeared near the interface with the lower Ru layer when the analysis was anti-parallel to the film growth direction, while B atoms were observed at the other side of the CoFeB layer when the analysis was parallel to the film growth direction. Moreover, when the analysis was perpendicular to the film growth direction, a homogenous distribution of B atoms was found within the CoFeB layer. Owing to this B behavior, the underlying Ru layer was affected in both of these analysis directions. In APT measurements of such a multilayer system composed of a stack of different evaporation field materials, evaluation of the elemental distribution around interfaces should be performed from more than one analysis direction.
“Color blindness” is a variable trait, including individuals with just slight color vision deficiency to those rare individuals with a complete lack of color perception. Approximately 75% of those with color impairment are green diminished; most of those remaining are red diminished. Red-Green color impairment is sex linked with the vast majority being male. The deficiency results in reds and greens being perceived as shades of yellow; therefore red-green images presented to the public will not illustrate regions of distinction to these individuals. Tools are available to authors wishing to accommodate those with color vision deficiency; most notable are components in FIJI (an extension of ImageJ) and Adobe Photoshop. Using these tools, hues of magenta may be substituted for red in red-green images resulting in striking definition for both the color sighted and color impaired. Web-based tools may be used (importantly) by color challenged individuals to convert red-green images archived in web-accessible journal articles into two-color images, which they may then discern.
Atomic-scale characterization of hydrogen and formation of niobium hydrides, using ultraviolet (wavelength=355 nm) picosecond laser-assisted local-electrode atom-probe tomography, was performed for ultrahigh purity niobium utilizing different laser pulse energies, 10 or 50 pJ/pulse or voltage pulsing. At 50 pJ/pulse, hydrogen atoms migrate onto the 110 and 111 poles as a result of stimulated surface diffusion, whereas they are immobile for <10 pJ/pulse or for voltage pulsing. Accordingly, the highest concentrations of H and NbH were obtained at 50 pJ/pulse. This is attributed to the thermal energy of the laser pulses being transferred to pure niobium specimens. Therefore, we examined the effects of the laser pulse energy being increased systematically from 1 to 20 pJ/pulse and then decreasing it from 20 to 1 pJ/pulse. The concentrations of H, H2, and NbH and the atomic concentration ratios H2/H, NbH/Nb, and Nb3+/Nb2+ were calculated with respect to the systematically changing laser pulse energies. The atomic concentration ratios H2/H and NbH/Nb are greater when decreasing the laser pulse energy than when increasing it, because the higher residual thermal energy after decreasing the laser pulse energy increases the mobility of H atoms by supplying sufficient thermal energy to form H2 or NbH.
Adjuvants are substances that enhance adaptive immune responses when formulated in a vaccine. Alum and MF59 are two vaccine adjuvants licensed for human vaccination. Their mode of action has not been completely elucidated. Here we show the first ultrastructural visualization of Alum and MF59 interaction with immune cells in vitro and in vivo. We observed that Alum is engulfed by cells as inclusions of laminae that are detectable within draining lymph nodes. MF59 is instead engulfed by cells in vitro as low-electron-dense lipid-like inclusions that display a vesicle pattern, as confirmed by confocal microscopy using fluorescently labeled MF59. However, lipid-like inclusions with different high- and low-electron-dense content are detected within cells of draining lymph nodes when injecting MF59. As high-electron-dense lipid-like inclusions are also detected upon injection of Alum, our results suggest that the low-electron-dense inclusions are formed by engulfed MF59, whereas the high-electron-dense inclusions are proper lipid inclusions. Thus, we demonstrated that vaccine adjuvants are engulfed as inclusions by lymph node cells and hypothesize that adjuvant treatment may modify lipid metabolism.
The oxidation of nickel powder under a controlled gas and temperature environment was studied using synchrotron-based full-field transmission X-ray microscopy. The use of this technique allowed for the reaction to be imaged in situ at 55 nm resolution. The setup was designed to fit in the limited working distance of the microscope and to provide the gas and temperature environments analogous to solid oxide fuel cell operating conditions. Chemical conversion from nickel to nickel oxide was confirmed using X-ray absorption near-edge structure. Using an unreacted core model, the reaction rate as a function of temperature and activation energy were calculated. This method can be applied to study many other chemical reactions requiring similar environmental conditions.
Irradiation damage, caused by the use of beams in electron and ion microscopes, leads to undesired physical/chemical material property changes or uncontrollable modification of structures. Particularly, soft matter such as polymers or biological materials is highly susceptible and very much prone to react on electron/ion beam irradiation. Nevertheless, it is possible to turn degradation-dependent physical/chemical changes from negative to positive use when materials are intentionally exposed to beams. Especially, controllable surface modification allows tuning of surface properties for targeted purposes and thus provides the use of ultimate materials and their systems at the micro/nanoscale for creating functional surfaces. In this work, XeF2 and I2 gases were used in the focused ion beam scanning electron microscope instrument in combination with gallium ion etching of high-density polyethylene surfaces with different beam currents and accordingly different gas exposure times resulting at the same ion dose to optimize and develop new polymer surface properties and to create functional polymer surfaces. Alterations in the surface morphologies and surface chemistry due to gas-assisted etching-based nanostructuring with various processing parameters were tracked using high-resolution SEM imaging, complementary energy-dispersive spectroscopic analyses, and atomic force microscopic investigations.
Various practical issues affecting atom probe tomography (APT) analysis of III-nitride semiconductors have been studied as part of an investigation using a c-plane InAlN/GaN heterostructure. Specimen preparation was undertaken using a focused ion beam microscope with a mono-isotopic Ga source. This enabled the unambiguous observation of implantation damage induced by sample preparation. In the reconstructed InAlN layer Ga implantation was demonstrated for the standard “clean-up” voltage (5 kV), but this was significantly reduced by using a lower voltage (e.g., 1 kV). The characteristics of APT data from the desorption maps to the mass spectra and measured chemical compositions were examined within the GaN buffer layer underlying the InAlN layer in both pulsed laser and pulsed voltage modes. The measured Ga content increased monotonically with increasing laser pulse energy and voltage pulse fraction within the examined ranges. The best results were obtained at very low laser energy, with the Ga content close to the expected stoichiometric value for GaN and the associated desorption map showing a clear crystallographic pole structure.
The distribution of boron in tissue samples coming from boron neutron capture therapy protocols can be determined through the analysis of its autoradiography image on a nuclear track detector. A more precise knowledge of boron atom location on the microscopic scale can be attained by the observation of nuclear tracks superimposed on the sample image on the detector. A method to produce an “imprint” of cells cultivated on a polycarbonate detector was developed, based on the photodegradation properties of UV-C radiation on this material. Optimal conditions to generate an appropriate monolayer of Mel-J cells incubated with boronophenylalanine were found. The best images of both cells and nuclear tracks were obtained for a neutron fluence of 1013 cm−2, 6 h UV-C (254 nm) exposure, and 4 min etching time with a KOH solution. The imprint morphology was analyzed by both light and scanning electron microscopy. Similar samples, exposed to UV-A (360 nm) revealed no cellular imprinting. Etch pits were present only inside the cell imprints, indicating a preferential boron uptake (about threefold the incubation concentration). Comparative studies of boron absorption in different cell lines and in vitro evaluation of the effect of diverse boron compounds are feasible with this methodology.
The 50th anniversary of the application of electron probe microanalysis (EPMA) to the Earth Sciences provides an opportunity for an assessment of the state-of-the-art of the technique. Stemming from the introduction of the first automated instruments, the latest developments of EPMA and some typical applications are reviewed with an eye to the future. The most noticeable recent technical achievements such as the field-emission electron gun, the latest generation of energy and wavelength dispersive spectrometers, and the development of analytical methods based on new sets of first principle data obtained by the use of sophisticated computer codes, allow for the extension of the method to the analysis of trace elements, ultra-light elements (down to Li), small particles, and thin films, with a high degree of accuracy and precision and within a considerably reduced volume of interaction. A number of working examples and a thorough list of references provide the reader with a working knowledge of the capabilities and limitations of EPMA today.