Electron Energy-loss Spectroscopy EELS Research Articles

Recent weathering promotes C storage inside large phyllosilicate particles in forest soil

Mineral weathering in soils is expected to promote chemical and physical interactions between soil organic matter and mineral phases, which are known to enhance the protection of organic matter from decomposition. The investigation of mineral-organic associations (MOAs) formation during weathering is therefore crucial to understanding carbon storage processes in soils. Until now studies have been mainly conducted by building inferences from soil characteristics, through short-term laboratory experiments in simplified conditions, or over very long-term time scales using soil chronosequences. Weathering can significantly alter the mineral matrix at the annual timescale, but knowledge regarding MOA formation processes occurring in situ, over short time scales and during the first stage of mineral weathering is lacking.To fill this gap, we performed a mesh bag incubation containing large Na-saturated and organic carbon-free vermiculite particles (200–400 µm in size) in acidic soil of a Douglas-fir forest, in the Beaujolais area (France). The vermiculite bags were deposited at the interface between the forest floor and the mineral soil, where intense weathering occurs. After 20 years of soil incubation, the weathered vermiculite particles were collected and characterized at the macroscale (X ray diffraction and physicochemical analyses), at the microscale (scanning electron microscopy-SEM imaging and element mapping) and at the nanoscale (transmission electron microscopy-TEM imaging, element mapping and speciation by electron energy loss spectroscopy-EELS) on a focus ion beam (FIB) section exposing the inside section of vermiculite particles.Cation exchange capacity, exchangeable cations and elemental analysis of the vermiculite particles showed important changes after 20 years of incubation. The initial exchangeable Na pool was completely depleted. The cation exchange capacity strongly decreased from 178.1 cmolc kg−1 to 49.2 cmolc kg−1 due to interlayer hydroxylation of the weathered vermiculite. The weathering budget indicated a 10% vermiculite dissolution and an organic carbon (C) enrichment of 5 mg g−1.Microscope images and elemental mapping of control vermiculite particles (nonincubated) showed a flat, smooth surface morphology with no detected C. In contrast, 20-year weathered vermiculite particles showed irregular outer- and inner-surfaces marked by multiple cracks from chemical dissolution. Some nano- and microscale exfoliation spaces filled with C were observed inside the weathered particles. C in association with Ca occurred in nanoscale exfoliation spaces. C also occurred entrapped in nanocrystalline Mn oxides (hausmannite) or K-rich aluminosilicates, which precipitated in micro-sized exfoliation spaces. These observations indicated that C storage inside the altered vermiculite particles was both mediated by chemical binding and physical entrapment. The functional groups of the organic matter revealed by EELS spectroscopy strongly differed between nano- and microscale exfoliation spaces.This study using the mineral bag incubation method provides evidence of new processes driving C storage inside large phyllosilicate particles during their initial and recent weathering, which could contribute to long-term C stabilization.

SURFACE MODIFICATION OF CHEMICAL VAPOR DEPOSITION (CVD) DIAMOND FILM/SI(111) BY IMPLANTATION WITH Fe + B IONS IN CONJUNCTION WITH THEIR MAGNETIC PROPERTIES

Surface Modification of Chemical Vapor Deposition (CVD) Diamond Film/Si(111) by Implantation with Fe+B ions In Conjunction with their Magnetic Properties. Surfcace modification of CVD manufactured diamond films on Si(111) substrate has been performed by means of Fe+B ion implantation followed by Argon ion gas sputtering with acceleration energy 20 keV and ion dose 1x1015 and 1x1016 ions cm-2. Scanning Transmission Electron Microscope (STEM) imaging shows the formation of amorphous carbon layer on top of the diamond film with thickness ca. 100 nm on the implanted sample and ca. 20 nm on the sample without implantion. The morphology and magnetic property of the films surface were characterized by Atomic and Magnetic Force Microscopy (AFM/MFM). The Electron Energy Loss Spectroscopy EELS analysis has revealed amount of Boron atoms distributed homogenously inside the carbon amorphous layer on both samples which is in close agreement to the result of Raman Spectroscopy showing the changes of the Raman spectrum due to implantation. The magnetic properties of the samples after Fe+B ion implantion were additionally investigated by means of Vibrating Sample Magnetometer (VSM). By increasing ion doses at constant energy 20 keV, the magnetoresistance property decreased from +45% on the sample implanted with dose 1x1015 to +8% on the sample implanted with dose 1x1016 ions cm-2.

Phase evolution of a barium tin 1,2-ethanediolato complex to barium stannate during thermal decomposition

The thermal behaviour of [Ba(C 2H 6O 2) 4][Sn(C 2H 4O 2) 3] used as a BaSnO 3 precursor, and its phase evolution during thermal decomposition are described. The initially formed transient barium tin oxycarbonate phase disintegrates into BaCO 3 and SnO 2, reacting subsequently to BaSnO 3. The existence of the intermediate oxycarbonate phase is evidenced by Fourier transformed infrared (FT-IR), X-ray powder diffraction (XRD) and electron energy loss spectroscopy (EELS (ELNES)) investigations.

Core level electron energy-loss spectra of minerals: pre-edge fine structures at the oxygen K -edge

In a recent paper entitled “Water in minerals detectable by electron energy-loss spectroscopy EELS” by R. Wirth, it has been claimed that OH–- and H2O-bearing minerals exhibit a characteristic peak in the ELNES spectra at about 528 eV prior to the onset of the O K-edge at 532 eV, which could be used for (semi-)quantitative determination of water- or OH-contents on a nanometer scale. It is shown here by parallel electron energy-loss spectroscopy (PEELS) recorded in a transmission electron microscope (TEM) that O K-pre-edge peaks with very high intensities may also exist in water-free compounds and minerals, in particular when they contain transition metals. These spectral features arise from covalent mixing of the metal and oxygen states, which introduces oxygen p character in unoccupied states of mainly metal character. The point is illustrated by the comparison of hematite (α-Fe2O3) and lepidocrocite (γ-FeOOH) O K-edge PEELS spectra which exhibit similar intensities of the pre-edge peak, despite of their grossly different OH– contents. As a consequence, the general validity of the method proposed by Wirth is questioned.

Water in minerals detectable by electron energy-loss spectroscopy EELS

Water in minerals detectable by electron energy-loss spectroscopy EELS

Water in minerals detectable by electron energy-loss spectroscopy EELS

Electron energy-loss spectroscopy EELS of the oxygen K edge of OH– containing minerals and minerals with molecular water reveals a peak at about 528 eV prior to the onset of the O-K edge at 532 eV. This peak is never observed in minerals without water or OH– groups. The intensity of the signal at 528 eV increases with increasing water content of the minerals. The peak at 528 eV is attributed to OH groups or water molecules. From the observations it is concluded that EELS provides a new method to determine the OH– or water content of minerals with a spatial resolution far beyond that of optical spectroscopy.