X-ray microanalysis in the environmental scanning electron microscope (ESEM): Small size particles analysis limits

In this work we will present a study of the effects of some parameters such as pressure and data acquisition duration in EDS microanalysis results. The chamber pressure has been increased from 1 Torr (133 Pa) to 15 Torr (1995 Pa). Measurements with times of measurement varying between 180 seconds and 1800 seconds were carried out. Small size particles of iron and silicon are analyzed. The results show that at 1Torr (133 Pa), the primary electron beam can move if the time of measurement is long, which introduces some mistakes in the microananlysis results. Moreover an increase in the chamber pressure induces an amplification of the skirt beam phenomena up to 160 microns. This fact adds some noise coming from the environment around the analyzed particle. We showed that, the displacement of the electron beam during measurement caused a decrease in the iron concentration versus the time of measurment which reachs approximately 15 % when the time of measurement is 1800 seconds.Dans cette étude nous présenterons les effets de certains paramètres tels que la durée d'acquisition et la pression dans la chambre du microscope électronique à balayage environnemental sur les résultats de la microanalyse X. La pression dans la chambre a été augmentée de 1 Torr (133 Pa) à 15 Torr (1995 Pa). Des mesures avec des durées d'acquisition entre 180 secondes et 1800 secondes ont été effectuées. Des particules de fer et de silicium de petites tailles sont analysées. Les résultats ont montré qu'à 1 Torr (133 Pa), le faisceau d'électrons primaire peut fluctuer si la durée d'acquisition est longue, ce qui induit quelques erreurs dans les résultats obtenus. Une augmentation de la pression dans la chambre induit une amplification des phénomènes de diffusion du faisceau d'électrons jusqu'à 160 microns. Ce fait, ajoute un certain bruit venant de l'environnement autour de la particule analysée. Nous avons ensuite montré que le déplacement du faisceau d'électrons pendant la mesure a causé une diminution de la concentration en fer qui atteint 15 % environ pour une durée d'acquisition de 1800 secondes

Electron scattering by gas in the Environmental Scanning Electron Microscope (ESEM): Effects on the image quality and on the X-ray microanalysis

in this work, we studied the electron beam scattering due to the introduction of two gases : water vapour and helium within the specimen chamber of the Environmental Scanning Electron Microscope (ESEM) and the effects of this phenomenon on the image quality and on the microanalysis results. An increase in the pressure involves an amplification of the electron beam scattering phenomenon up to 160 microns when water vapour is used. The best results are obtained with helium. The use of this gas allowed a better focusing of the electron beam on the micronic particle which led to an improvement of the chemical contrast of the images, like the stability of the results of microanalysis X. In addition, with helium we showed an improvement in the signal-to-noise ratio which not only leads to obtain images of good quality but also to improve the limit of detection of the microanalysis system. In spite of the advantages of the use of helium, an important focusing of the electron beam, can induce an increase in the temperature of the surface of the sample by causing its degradation especially for fragile materials or a dehydration of hydrated samples

Study of Mechanisms involved in reactive silica

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Monte Carlo study of the interaction volume changes by the beam skirt in VP-SEM

In this work we present a new contribution for tracking the behavior of electron beam in gas and then in material placed in the chamber of a variable pressure scanning electron microscope using Monte Carlo simulation. Firstly our results for width and depth of interaction volume in high vacuum mode are compared and are consistent with those obtained by several relationships present in literature. Carbon and aluminum are considered as examples in order to establish the reliability of our approach and experimental data available from the literature. Then, we compared the evolution of width in both high (Re_{(HV)}) and low (Re_{(LV)}) vacuum modes with enlargement of skirt (R_{s}). The present work demonstrates that the best resolution conditions for energy, pressure and material, is given by R_{s}=Re_{(HV)}. Finally, the energy that must be used to get the best image resolution for given pressure and material is determined

Étude de la contribution de la diffusion simple et multiple à l'amplitude des atomes voisins du silicium dans SiO2_{2} : application à un granulat soumis à la réaction alcali-silice

Les amplitudes des différentes distributions lointaines de la transformée de Fourier d'un spectre EXAFS contiennent des informations précieuses pour la caractérisation de l'ordre local autour d'un atome donné. Ces informations sont souvent nécessaires pour la proposition de modèles. Or souvent dans cette zone, les distances inter atomiques correspondent à des libres parcours moyens du photoélectron assez importants. La contribution due à la diffusion multiple perturbe le signal propre de la diffusion simple des atomes diffuseurs. Afin de mieux évaluer l'influence de la diffusion multiple dans nos échantillons constitués de granulats à base de SiO$_{2}$ attaqués par la réaction alcali-silice, nous avons calculé les différents parcours de diffusion simple et multiple dans ce composé. Les calculs montrent que lorsque la contribution de la diffusion multiple n'est pas atténuée, l'exploitation des voisins lointains est difficile voir impossible. La modélisation des spectres TF expérimentaux a pu être réalisée uniquement en négligeant la contribution de la diffusion multiple. Ce résultat va nous permettre l'exploitation des voisins lointains en particulier les atomes silicium dans le granulat brut et après dégradation en se basant sur le formalisme de la diffusion simple

Structure of Zinc Oxide Particles Inserted in Nanopores of Microporous Material

The insertion of nanoparticles in the cages of microporous materials raised up a large interest, due to the applications of such systems in the field of catalysis and microelectronics, but the atomic structure of such particles, their location inside the cages and their interaction with the microporous framework is subject to controversies. EXAFS can bring accurate information so far the study of the coordination shells around the central atom can be extended beyond the first one. In zinc exchanged aluminosilicate sodalites, whose cubic structure contains one type of nanopores (6 Å in diameter), it was suggested previously that some zinc oxide particles can be located in the centre of the sodalite cages. The carefull EXAFS analysis at Zn K-edge, including ab-initio calculations using the FEFF code, reveals the presence of Al neighbours belonging to the framework at less than 3 Å from zinc cations as well as an elongation of the Zn-Zn distance with respect to crystalline ZnO. The coordination radii and numbers are consistent with the model of three zinc cations, each of them being located almost in the plane of the 6-oxygen ring of the wall shared by two joined cages

Structural Study of Interlayer Zr Particles in Exchanged and Pillared Beidellite

Zirconia pillared clays (with synthetic beidellite as host material) were prepared by replacing the sodium interlayer cations by zirconium hydroxy polycations, and then heating to stabilize the structure. The pillaring solution was an aqueous solution of zirconyl chloride, but the structure of the polycation which is intercalated remains unknown. From the XRD data. the interlayer spacing was found to be 9 Å in Zr exchanged beidellite and slightly lower (7Å) after calcination. The local environment of zirconium in solid zirconyl chloride and in the pillaring solution was first examined and then in the ion-exchanged and calcined beidellite. The EXAFS results for zirconyl chloride in the solid state and in aqueous solution, showed that the nearest neighbours and the next-nearest-neighbours environments of Zr are identical in solid and in solution. In the Zr-exchanged beidellite, the Zr cations have the same environment as in the pillaring solution. On the opposite. the mean Zr-O and Zr-Zr distances in the calcined sample are shortened with respect to Zr-exchanged beidellite

Chemical and Dielectric Study of PMMA/Montmorionite Nano-Composite Films

International audienceTetrabutylphosphonium intercalated montmorillonite (P-MMT) was dispersed in toluene using sonication technique and a PMMA/toluene solution. The PMMA/P-MMT nano- suspension was then casted as a composite film on a glass plate, using spin coating technique with a rotation of 180 rpm. The composite films were characterized by various analytical techniques such as X-ray diffraction, X-ray fluorescence spectrometry thermo- gravimetric analysis, etc. The montmorillonite interlayer distance, estimated XRD results, was found to be equal to 1.6 nm. The PMMA/3 wt%P-MMT nano-composite film was found to completely decomposed at the temperature Td (PMMA/3 wt%P-MMT) = 370◦C which is slightly higher than that of the neat PMMA, i.e. 365◦C. It was also found that both plots of ε_r and ε__r versus frequency display equivalent behaviour. The optical absorption spectra show a rather large domain of transparency between 300 and 2700 nm, with a rather structured absorption band between 1700 and 2700 nm. Dielectric constant ranges near 1 to 3, depending on the frequency. This is very important for some electronic application, as underlined by former Authors

Etude par EXAFS et fluorescence X de photocatalyseurs zéolithiques renfermant des nanoparticules de ZnO

Nous présentons les premiers résultats obtenus par spectroscopie d'absorption X au seuil K du zinc et d'émission X sur la structure atomique de clusters formés à partir de zinc et d'oxygène, confinés à l'intérieur des cavités de la sodalite. Nous avons commencé par une étude de la structure des références ZnAl2O4 et ZnO. Les résultats obtenus sont en bon accord avec les données cristallographiques. Dans le cas des échantillons de sodalite, le zinc est entouré en premiers voisins par de l'oxygène dans un environnement tétraédrique ; la distance Zn-O est de 1.97 Å. En seconds et troisièmes voisins le zinc est entouré par de l'aluminium et du zinc respectivement à des distances Zn-Al de 2.86 Å et Zn-Zn de 3.38 Å. Une étude de l'influence de la température de calcination a également été faite. Ces résultats ont permis la mise en évidence d'une forte interaction des clusters avec la charpente.The first results on ZnK X-ray emission and Zn K EXAFS studies of ZnO clusters confined inside the cages of sodalite are reported here. The analysis of the first, second and third shells of coordination around Zn in ZnO and ZnAl2O4 references is presented. The results agree fairly well with the crystallographic data. In sodalite samples, the Zn atoms are in tetrahedral coordination with oxygen at 1.97 Å. The second and third neighbours of Zn are Al at 2.86 Å and Zn at 3.38 Å respectively, the former belonging to the sodalite framework. The influence of the calcination temperature on the local order around Zn is also discussed. Interaction between the clusters and the framework is clearly evidenced

Study of structural short order and surface changes of SiO2 compounds

In this work dependence between structure, surface and reactivity of SiO2 is investigated. Different samples are prepared with and without the presence of calcium cations and are characterized by different techniques. The FTIR frequency shifting of the bridging oxygen stretching vibration Si–O–Si and the binding energy shiftingof the Si2p and O1s photoelectron peaks have been observed and discussed. Results show the effect of presence of calcium on the structural change, surface and reactivity of SiO2 aggregate. After reaction, a structural and SiO2 surface changes occur, as the FTIR spectra illustrate depending on the presence of the calcium cations