Identification of nano-phases: relative merit of local analysis techniques (HRTEM, nanodiffraction, EDS/EELS)

Information for phase identification may be gathered in the electron transmission microscope with spatial resolution down to the nanometre scale. Energy dispersive X-ray and electron energy loss spectrometries are based on inelastic electron/sample interaction. They have the advantage to give a direct knowledge of the chemical nature of the atoms under the electron probe, sometimes also with valence and bonding, but concentrations are mean values over all atoms in the excited volume that may be insufficient when composition is not uniform. Moreover, X-ray absorption, electron scattering and channeling may lead to errors hard to notice and correct. Elastic interaction is observed on diffraction patterns for crystalline phases with the advantage that superimposed patterns in the case of mixtures are easily most often differentiated . It leads to phase identification via crystallographic databases. When the scale of investigation goes down to a few nanometres or tens of nanometres, indexing diffractograms of high-resolution transmission electron microscopy images is attractive, but it is often forgotten that such diffractograms are not actual diffraction patterns of the crystal itself and that lattice spacings may even be shifted by several per-cents in spheroidal nanoparticles

Identification of nano-phases: relative merit of local analysis techniques (HRTEM, nanodiffraction, EDS/EELS)

Information for phase identification may be gathered in the electron transmission microscope with spatial resolution down to the nanometre scale. Energy dispersive X-ray and electron energy loss spectrometries are based on inelastic electronsample interaction. They have the advantage to give a direct knowledge of the chemical nature of the atoms under the electron probe, sometimes also with valence and bonding, but concentrations are mean values over all atoms in the volume excited that may be insufficient when composition is not uniform. Moreover, X-ray absorption, electron scattering and channelling may lead to errors hard to notice and correct. Elastic interaction is observed on diffraction patterns for crystalline phases with the advantage that superimposed patterns in the case of mixtures are easily distinguished in most cases. It leads to phase identification via crystallographic databases. When the scale of investigation goes down to a few nanometres or tens of nanometres, indexing diffractograms of high-resolution transmission electron microscopy images is attractive, but it is often forgotten that such diffractograms are not diffraction patterns of the crystal itself and that lattice spacings may even be shifted by several per-cents in rounded nanoparticles

TEM study of Mg distribution in micrite crystals from the Mishrif reservoir Formation (Middle East, Cenomanian to Early Turonian)

Microporous limestones composed of micrite crystals constitute sizeable hydrocarbon reservoirs throughout the world and especially in the Middle East. However, the crystallization history of micrites is poorly understood. Scanning electronic microscopy (SEM) with X-ray energy dispersive spectroscopy (EDS) studies give morphological and bulk composition information about micrites, but no information exists on the distribution of minor elements inside micrite grains. This study proposes Mg maps obtained with X-ray EDS combined with scanning transmission electron microscopy (STEM) of micrite crystals from the Mishrif reservoir Formation (Middle East, Cenomanian to Early Turonian). Three types of Mg distribution were observed through micrite crystals from five different samples: (1) homogenous Mg concentration, (2) small Mg-enriched areas close to the center of the crystal, and (3) geometric Mg impoverishments near crystal edges and parallel to present crystallographic faces. The homogenous Mg distribution is the most frequent and is found both in microporous and in tight micrites. The second type of distribution showing small Mg-enriched areas inside micrite crystals relatively close to their center comes from a microporous sample located below an emersive surface. These enriched areas may correspond to crystal seeds. The third type of distribution was observed in micrite crystals from another microporous sample situated just below an emersive surface. The Mg-poor zones probably represent overgrowths that precipitated in contact with less Mg-rich meteoric fluid

Pd/SiO2 catalysts: synthesis of Pd nanoparticles with the controlled size in mesoporous silicas

Synthesis of Pd nanoparticles with controlled size (d(Pd) = 1-3.6 nm) was carried out within the pores of the mesoporous HMS and SBA-15 silicas. Pd was ion-exchanged on non-calcined silicas, prepared by solvent extraction of the templates. A high concentration of silanol groups on the mesopore surface allowed attaining Pd loading up to 4.4. wt.%. The Pd/HMS and Pd/SBA-15 were characterised by chemical analysis, XRD, N2 adsorption-desorption and transmission electron microscopy (TEM) methods. The materials possess a high SSA and narrow pore size distribution. Introduction of Pd nanoparticles in HMS resulted in a progressive loss of the regularity in the mesoporous structure. On the contrary, all Pd/SBA-15 composites retained the original well-ordered 2D hexagonal structure of SBA-15. The thick walls of the SBA-15 framework are accounted for the higher stability observed. The TEM investigations confirmed that the Pd nanocrystals were located within the SBA-15 mesoporous framework channels. The particle size did not exceed the mesopore diameter (2-6 nm) at Pd loading of 0.1-4.4wt.%. Pd clusters were found to be resistant against sintering during air-calcination (550 degreesC, 4h). The catalyst 2.1%Pd/SBA-15 used in methane combustion at 520 degreesC demonstrated stable activity during 6h on stream

Highly dispersed gold on activated carbon fibers for low temperature CO oxidation

Gold nanoparticles of 2–5 nm supported on woven fabrics of activated carbon fibers (ACF) were effective during CO oxidation at room temperature. To obtain a high metal dispersion, Au was deposited on ACF from aqueous solution of ethylenediamine complex [Au(en)2]Cl3 via ion exchange with protons of surface functional groups. The temperature-programmed decomposition method showed the presence of two main types of functional groups on the ACF surface: the first type was associated with carboxylic groups easily decomposing to CO2 and the second one corresponded to more stable phenolic groups decomposing to CO. The concentration and the nature of surface functional groups was controlled using HNO3 pretreatment followed by either calcination in He (300–1273 K) or by iron oxide deposition. The phenolic groups are able to attach Au3+ ions, leading to the formation of small Au nanoparticles (9 nm) Au agglomerates after reduction by H2. These catalysts demonstrated lower activity as compared to the ones containing mostly small Au nanoparticles. Complete removal of surface functional groups rendered an inert support that would not interact with the Au precursor. The oxidation state of gold in the Au/ACF catalysts was controlled by X-ray photoelectron spectroscopy before and after the reduction in H2. The high-temperature reduction in H2 (673–773 K) was necessary to activate the catalyst, indicating that metallic gold nanoparticles are active during catalytic CO oxidation

Terminal NK cell maturation is controlled by concerted actions of T-bet and Zeb2 and is essential for melanoma rejection

Natural killer (NK) cell maturation is a tightly controlled process that endows NK cells with functional competence and the capacity to recognize target cells. Here, we found that the transcription factor (TF) Zeb2 was the most highly induced TF during NK cell maturation. Zeb2 is known to control epithelial to mesenchymal transition, but its role in immune cells is mostly undefined. Targeted deletion of Zeb2 resulted in impaired NK cell maturation, survival, and exit from the bone marrow. NK cell function was preserved, but mice lacking Zeb2 in NK cells were more susceptible to B16 melanoma lung metastases. Reciprocally, ectopic expression of Zeb2 resulted in a higher frequency of mature NK cells in all organs. Moreover, the immature phenotype of Zeb2(-/-) NK cells closely resembled that of Tbx21(-/-) NK cells. This was caused by both a dependence of Zeb2 expression on T-bet and a probable cooperation of these factors in gene regulation. Transgenic expression of Zeb2 in Tbx21(-/-) NK cells partially restored a normal maturation, establishing that timely induction of Zeb2 by T-bet is an essential event during NK cell differentiation. Finally, this novel transcriptional cascade could also operate in human as T-bet and Zeb2 are similarly regulated in mouse and human NK cells

Comment on "Structural and Mossbauer studies of evaporated Fe100-x Pd-x thin films" by A. Laggoun, A. Guittoum, S. Bahamida, M. Boudissa and A. Fnidiki

The paper "Structural and Mossbauer studies of evaporates Fe100-x Pd-x thin films" by A. Laggoun et al. contains interpretation errors of XRD patterns and therefore cast some heavy doubt on the actual phases present in the Fe-Pd films