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Artifacts from manganese reduction in rock samples prepared by focused ion beam (FIB) slicing for X-ray microspectroscopic analysis
Abstract. Manganese (Mn)-rich natural rock coatings, so-called rock varnishes, are discussed controversially regarding their genesis. Biogenic and abiogenic mechanisms, as well as a combination of both, have been proposed to be responsible for the Mn oxidation and deposition process. We conducted scanning transmission X-ray microscopy - near edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS) measurements to examine the abundance and spatial distribution of the different oxidation states of Mn within these nano- to micrometer thick crusts. Such microanalytical measurements of thin and hard rock crusts require sample preparation with minimal contamination risk. Focused ion beam (FIB) slicing, a well-established technique in geosciences, was used in this study to obtain 100–200 nm thin slices of the samples for X-ray transmission spectroscopy. However, even though this preparation is suitable to investigate element distributions and structures in rock samples, we observed that, using standard parameters, modifications of the Mn oxidation states occur in the surfaces of the FIB slices. Based on our results, the preparation technique likely causes the reduction of Mn4+ to Mn2+/3+. We draw attention to this issue, since FIB slicing, SEM imaging, and other preparation and visualization techniques operating in the keV range are well-established in geosciences, but researchers are often unaware of the potential for reduction of Mn and possibly other elements in the samples’ surface layers
Understanding the interaction between energetic ions and freestanding graphene towards practical 2D perforation
We report experimentally and theoretically the behavior of freestanding
graphene subject to bombardment of energetic ions, investigating the ability of
large-scale patterning of freestanding graphene with nanometer sized features
by focused ion beam technology. A precise control over the He+ and Ga+
irradiation offered by focused ion beam techniques enables to investigate the
interaction of the energetic particles and graphene suspended with no support
and allows determining sputter yields of the 2D lattice. We find strong
dependency of the 2D sputter yield on the species and kinetic energy of the
incident ion beams. Freestanding graphene shows material semi-transparency to
He+ at high energies (10-30 keV) allowing the passage of >97% He+ particles
without creating destructive lattice vacancy. Large Ga+ ions (5-30 keV), in
contrast, collide far more often with the graphene lattice to impart
significantly higher sputter yield of ~50%. Binary collision theory applied to
monolayer and few-layer graphene can successfully elucidate this collision
mechanism, in great agreement with experiments. Raman spectroscopy analysis
corroborates the passage of a large fraction of He+ ions across graphene
without much damaging the lattice whereas several colliding ions create single
vacancy defects. Physical understanding of the interaction between energetic
particles and suspended graphene can practically lead to reproducible and
efficient pattern generation of unprecedentedly small features on 2D materials
by design, manifested by our perforation of sub-5-nm pore arrays. This
capability of nanometer scale precision patterning of freestanding 2D lattices
shows practical applicability of the focused ion beam technology to 2D material
processing for device fabrication and integration.Comment: 31 pages of main text (with 4 figures) plus 4 pages of supporting
information (with 2 figures). Original article submitted to a journal for
consideration for publicatio
Multiscale correlative tomography: an investigation of creep cavitation in 316 stainless steel
Creep cavitation in an ex-service nuclear steam header Type 316 stainless steel sample is investigated through a multiscale tomography workflow spanning eight orders of magnitude, combining X-ray computed tomography (CT), plasma focused ion beam (FIB) scanning electron microscope (SEM) imaging and scanning transmission electron microscope (STEM) tomography. Guided by microscale X-ray CT, nanoscale X-ray CT is used to investigate the size and morphology of cavities at a triple point of grain boundaries. In order to understand the factors affecting the extent of cavitation, the orientation and crystallographic misorientation of each boundary is characterised using electron backscatter diffraction (EBSD). Additionally, in order to better understand boundary phase growth, the chemistry of a single boundary and its associated secondary phase precipitates is probed through STEM energy dispersive X-ray (EDX) tomography. The difference in cavitation of the three grain boundaries investigated suggests that the orientation of grain boundaries with respect to the direction of principal stress is important in the promotion of cavity formation
Focused Ion Beam Recovery of Hypervelocity Impact Residue in Experimental Craters on Metallic Foils
The Stardust sample return capsule will return to Earth in January 2006 with primitive debris collected from Comet 81P/Wild-2 during the fly-by encounter in 2004. In addition to the cometary particles embedded in low-density silica aerogel, there will be microcraters preserved in the Al foils (1100 series; 100 micrometers thick) that are wrapped around the sample tray assembly. Soda lime spheres (approximately 49 m in diameter) have been accelerated with a light-gas-gun into flight-grade Al foils at 6.35 km s(sup -1) to simulate the potential capture of cometary debris. The preserved crater penetrations have been analyzed using scanning electron microscopy (SEM) and x-ray energy dispersive spectroscopy (EDX) to locate and characterize remnants of the projectile material remaining within the craters. In addition, ion beam induced secondary electron imaging has proven particularly useful in identifying areas within the craters that contain residue material. Finally, high-precision focused ion beam (FIB) milling has been used to isolate and then extract an individual melt residue droplet from the interior wall of an impact penetration. This enabled further detailed elemental characterization, free from the background contamination of the Al foil substrate. The ability to recover pure melt residues using FIB will significantly extend the interpretations of the residue chemistry preserved in the Al foils returned by Stardust
Fossil biomass preserved as graphitic carbon in a late paleoproterozoic banded iron formation metamorphosed at more than 550°C
Metamorphism is thought to destroy microfossils, partly through devolatilization and graphitization of biogenic organic matter. However, the extent to which there is a loss of molecular, elemental and isotope signatures from biomass during high-temperature metamorphism is not clearly established. We report on graphitic structures inside and coating apatite grains from the c. 1850 Ma Michigamme silicate banded iron formation from Michigan, metamorphosed above 550°C. Traces of N, S, O, H, Ca and Fe are preserved in this graphitic carbon and X-ray spectra show traces of aliphatic groups. Graphitic carbon has an expanded lattice around 3.6 Å, forms microscopic concentrically-layered and radiating polygonal flakes and has homogeneous δ13C values around −22‰, identical to bulk analyses. Graphitic carbon inside apatite is associated with nanometre-size ammoniated phyllosilicate. Precursors of these metamorphic minerals and graphitic carbon originated from ferruginous clayrich sediments with biomass. We conclude that graphite coatings and inclusions in apatite grains indicate fluid remobilization during amphibolite-facies metamorphism of precursor biomass. This new evidence fills in observational gaps of metamorphosed biomass into graphite and supports the existence of biosignatures in the highly metamorphosed iron formation from the Eoarchean Akilia Association, which dates from the beginning of the sedimentary rock record
Site specific characterisation of hydrocracking catalysts using nanoanalytical electron microscopy
During use, carbonaceous material or ‘coke’ can deposit on catalysts resulting in decreased
activity and lifetime. In this thesis, the results of investigations into the structure and
distribution of coke, on hydrocracking catalysts, are reported. The material consists of zeolite
Y, alumina binder as well as tungsten and nickel sulfide.
An extensive investigation regarding the preparation of the catalysts for electron microscopy
was carried out. It was established that microtoming produced specimen damage and hence
regions of porosity, zeolite and alumina binder were difficult to identify. Single beam and
dual beam focused ion beam (FIB) milling produced intact specimens and the spatial
distribution of the catalysts was maintained, although thinner specimens were obtained using
the latter technique. Energy-dispersive X-ray (EDX) mapping identified gallium and
platinum as artefacts in specimens that had been prepared by a single beam FIB system. In
addition, argon ion beam milling was used and this technique produced large regions of thin material.
Energy-filtered transmission electron microscopy (EFTEM) was employed to reveal the
distribution of carbon in the catalyst. Carbon was identified on alumina binder, zeolite grains
and meso-/macro-pores, although the distribution of carbon was generally not uniform as it is
determined by the density and strength of acid sites, geometry of pores and the proximity of
metal sulfide crystallites. All of these factors, especially pores size and shape, vary in the catalysts.
Coke is thought to consist of polyaromatic hydrocarbons (PAHs). Electron energy-loss
spectroscopy (EELS), of selected PAH standards, was performed to obtain the electron
energy-loss near edge structure (ELNES) of carbon. In addition, the ELNES of four PAHs
was modelled using multiple scatter calculations. EELS of the catalysts revealed that PAHs
are present on zeolitic components but ELNES was not identified on the alumina binder. This
is possibly because alumina contains larger pores than zeolite Y; therefore larger molecules
can diffuse into the alumina structure, which increases the chemical variety of the coke
species as the molecules are not sterically impeded
Site-Specific Plan-view (S)TEM Sample Preparation from Thin Films using a Dual-Beam FIB-SEM
Plan-view transmission electron microscopy (TEM) samples are key to
understand the atomic structure and associated properties of materials along
their growth orientation, especially for thin films that are stain-engineered
onto different substrates for property tuning. In this work, we present a
method to prepare high-quality plan-view samples for analytical STEM study from
thin-films using a dual-beam focused ion beam scanning electron microscope
(FIB-SEM) system. The samples were prepared from thin films of perovskite
oxides and metal oxides ranging from 20-80 nm thicknesses, grown on different
substrates using molecular beam epitaxy. A site-specific sample preparation
from the area of interest is described, which includes sample attachment and
thinning techniques to minimize damage to the final TEM samples. While
optimized for the thin film-like geometry, this method can be extended to other
site-specific plan-view samples from bulk materials. Aberration-corrected
scanning (S)TEM was used to access the quality of the thin film in each sample.
This enabled direct visualization of line defects in perovskite BaSnO3 and Ir
particle formation and texturing in IrO2 films
Nanowires fabricated by Focused Ion Beam
This thesis reports research on nanowires fabricated by FIB lithography with experiments to understand their mechanical, electrical and hydrodynamic properties.
Au nanowires fabricated on SiN membranes with width below 50nm exhibit liquid like instabilities and below 20nm the instabilities grow destroying the nanowires due to the Rayleigh- Plateau instability. Stability is better in the case for Si substrates than for the insulators Si0 and SiN.
A series of 4-terminal resistance measurements were carried out on a "platinum" nanowire grown by FIB-induced decomposition of an organometallic precursor. Such nanowires are found to be a two phase percolating system, containing up to 70% by volume carbon. They have unexpected temperature behaviour which is explained using a percolation model with Kirkpatrick conduction in the presence of temperature induced strain.
Au nanowire bridges of very small diameter were probed using AFM to investigate their deformation and fracture strength. Below a diameter 50nm, the mechanical properties are consistent with liquid-like behaviour. After reaching the fracture, the gold molecules from the bridge retract towards the fixed ends; rebinding of the gold causing reforming of the nanowire bridge can occur.
FIB fabrication was also used to form a thermal bimorph MEMS cantilever which was investigated by AFM during actuation
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