High-resolution Chemical Analysis Research Articles

Using Graphene Liquid Cells for High-resolution Chemical Analysis of Nano-particle Reactions

Using Graphene Liquid Cells for High-resolution Chemical Analysis of Nano-particle Reactions

High-resolution chemical analysis by STEM-EELS of nanosized oxide particles in a mechanically-alloyed FeCrAl intermetallic

The chemical composition of nanosized oxides has been analysed in a mechanically-alloyed (MA) iron–chromium–aluminium intermetallic containing yttria additions using an aberration-corrected, high-resolution scanning transmission electron microscope (STEM). The oxide particles are seen to contain yttrium and oxygen only, but very little of the matrix metallic elements, while the matrix in the immediate vicinity shows a very low iron content. Possible reasons for the change of matrix composition outside the particle-matrix interface are discussed.

Dramatic local environmental change during the Early Eocene Climatic Optimum detected using high resolution chemical analyses of Green River Formation stromatolites

The Eocene Green River Formation represents a system of lakes that covered parts of what is now Wyoming, Colorado, and Utah, and captures the Early Eocene Climatic Optimum (EECO, 52–50million years ago or Ma), the warmest period of the Cenozoic Era, and a period associated with very high levels of atmospheric CO2. Lakes, especially closed basin lakes, can respond dramatically to environmental change because of their sensitivity to precipitation and evaporation. In this study, stromatolites from the Rife Bed of the Green River Formation are used as fine-scale records of terrestrial paleoenvironmental change during a global hothouse climate, and to investigate how the environmental dynamics within the lake system affected the growth of stromatolites. The stromatolites are composed of branching microdigitate columns laminated on the 10–100μm scale. Laminae are grouped in cm-scale layers that alternate between calcite fan, micritic, and mixed microstructures. The fan layers are depleted in 18O, Na, and Mg/Ca. The micrite layers, in contrast, are comparatively enriched in 18O, Na, and Mg/Ca. The δ13C and δ18O are strongly positively correlated, suggesting the stromatolites formed in a closed basin lake, consistent with the regional stratigraphy. Additionally, clumped isotope analyses provide the first quantitative values for water temperatures in lake water from the Green River Formation (~35°C for micrite layers and ~28°C for fan layers). Changes in δ18O and sodium ion concentration are likely related to periods of evaporation and recharge, and thus can be used to estimate lake volume change during stromatolite growth. Two models, one using sodium ion concentrations in a conserved system, the other using Rayleigh fractionation and mixing equations to explain changes in oxygen isotopes, converge upon similar results for lake volume changes, revealing multiple episodes of meter-scale lake level rise and fall during the accretion of the ~30cm thick stromatolite. Because of the broad, flat bathymetry of the lake, such lake volume and depth changes would have been accompanied by shoreline shifts on the order of tens of kilometers while the stromatolites were actively growing, challenging the view of a single stromatolite paleoenvironment in the lake. Therefore, the fan microfabric, interpreted here as abiogenic in nature, formed in cooler waters when the lake was deeper, possibly below a thermocline. In contrast, the micrite microfabric, for which there is evidence of biogenicity, formed when the lake was shallow and warm. The alternation between biogenic and abiogenic microfabrics present in the Rife Bed stromatolites is hypothesized to result from dramatic changes in lake level influencing the microbiology and chemistry of the waters in which the stromatolites formed, indicating that stromatolite growth can occur under disparate conditions and therefore does not necessarily represent a single facies.

High-resolution chemical analysis on cycled LiFePO4 battery electrodes using energy-filtered transmission electron microscopy

We demonstrate an ex situ method for analyzing the chemistry of battery electrode particles after electrochemical cycling using the transmission electron microscope (TEM). The arrangement of particles during our analysis is the same as when the particles are being cycled. We start by sectioning LiFePO4 battery electrodes using an ultramicrotome. We then show that mapping of the Fe2+ and Fe3+ oxidation state using energy-filtered TEM (EFTEM) and multivariate statistical analysis techniques can be used to determine the spatial distribution of Li in the particles. This approach is validated by comparison with scanning transmission X-ray microscopy (STXM) analysis of the same samples [Chueh et al. Nanoletters, 13 (3) (2013) 866–72]. EFTEM uses a parallel electron beam and reduces the electron-beam dose (and potential beam-induced damage) to the sample when compared to alternate techniques that use a focused probe (e.g. STEM–EELS). Our analysis confirms that under the charging conditions of the analyzed battery, mixed phase particles are rare and thus Li intercalation is limited by the nucleation of new phases.

How oxidized grain boundaries fail

Macroscopic behaviour of materials is often controlled by microscopic events; this has driven interest in testing and analysing increasingly smaller features. The ability to perform mechanical tests on the micron scale, with modelling and high-resolution chemical and structural analysis on the same scale, now makes it possible to investigate in detail the mechanisms controlling one of the most complex modes of fracture: stress corrosion cracking (SCC). In this paper, through such a multifaceted approach, we show that individual grain boundaries, preferentially oxidized after exposure to simulated pressurized nuclear reactor cooling water, can be mechanically tested and their resistance to fracture quantified. These results have direct consequences in understanding the mechanisms controlling SCC propagation and initiation.

Coherent Ni2(Cr, Mo) precipitates in Ni–21Cr–17Mo superalloy

The microstructure of Ni2(Cr, Mo) precipitates in a Ni–21Cr–17Mo (wt.%) superalloy subjected to a two-step heat treatment has been investigated via high-resolution transmission electron microscopy and electron diffraction, combined with image and diffraction calculations. Various high-density nanoscale Ni2(Cr, Mo) precipitates were distributed homogeneously in the Ni–Cr–Mo matrix, and no other marked secondary phase was observed in the age-hardened alloys. The typical orientation relationship between the precipitates and the Ni–Cr–Mo matrix was determined as (200)matrix//(103) Ni2(Cr,Mo), [001]matrix//[010] Ni2(Cr,Mo). The interfaces between the precipitates and the surrounding matrix were coherent at the atomic scale, resulting in the remarkable improvement on the alloy strength after heat treatment. Moreover, the Ni2(Cr, Mo) particles exhibited a special oval shape, with the long axis perpendicular to the long-range-ordered plane of (Cr, Mo), that is, (220)Ni. A high spatial resolution chemical composition analysis revealed that the Ni2(Cr, Mo) precipitates were enriched in Mo, with an average composition of ∼19wt.% Cr and ∼20wt.% Mo, which probably caused the easy precipitation of the long-range-ordered Ni2(Cr, Mo) phase precipitated in Ni–Cr–Mo alloys with a high Mo content.

UV fs–ns double-pulse laser induced breakdown spectroscopy for high spatial resolution chemical analysis

We study the use of an ultraviolet (UV) femtosecond (fs)–nanosecond (ns) double-pulse scheme to improve the analytical capabilities of Laser Induced Breakdown Spectroscopy (LIBS) in the few-micron (<2 μm) spatial resolution regime. We show that a double-pulse orthogonal configuration can enhance the spectral emission intensity by roughly 360 times as compared to a single-fs laser pulse LIBS of silicon (Si). Although the spectral emission lifetime in single-pulse LIBS is less than 20 ns, the second pulse provides signal enhancement hundreds of nanoseconds later, indicating that a significant number of non-radiative species (neutrals and/or particles) exist in these small length-scale plasmas long after the fs-laser pulse is over. The double-pulse configuration is a practical way to improve the limits of detection of LIBS for micron/submicron spatial resolution.

Identification of chlorinated solvents degradation zones in clay till by high resolution chemical, microbial and compound specific isotope analysis

The degradation of chlorinated ethenes and ethanes in clay till was investigated at a contaminated site (Vadsby, Denmark) by high resolution sampling of intact cores combined with groundwater sampling. Over decades of contamination, bioactive zones with degradation of trichloroethene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA) to 1,2-cis-dichloroethene (cis-DCE) and 1,1-dichloroethane, respectively, had developed in most of the clay till matrix. Dehalobacter dominated over Dehalococcoides (Dhc) in the clay till matrix corresponding with stagnation of sequential dechlorination at cis-DCE. Sporadically distributed bioactive zones with partial degradation to ethene were identified in the clay till matrix (thickness from 0.10 to 0.22 m). In one sub-section profile the presence of Dhc with the vcrA gene supported the occurrence of degradation of cis-DCE and VC, and in another enriched δ(13)C for TCE, cis-DCE and VC documented degradation. Highly enriched δ(13)C for 1,1,1-TCA (25‰) and cis-DCE (-4‰) suggested the occurrence of abiotic degradation in a third sub-section profile. Due to fine scale heterogeneity the identification of active degradation zones in the clay till matrix depended on high resolution subsampling of the clay till cores. The study demonstrates that an integrated approach combining chemical analysis, molecular microbial tools and compound specific isotope analysis (CSIA) was required in order to document biotic and abiotic degradations in the clay till system.

The application of proxy data from high resolution marine archives to palaeoclimate models

Monitoring bioavailable contaminants and determining baseline conditions in aquatic environments has become an important aspect of ecology and ecotoxicology. Since the mid-1970s and the initiation of the Mussel Watch program, this has been successfully accomplished with bivalve mollusks. These (mostly) sessile organisms reliably and proportionately record changes of a range of organic and inorganic pollutants occurring in the water, food or sediment. The great majority of studies have measured the concentration of pollutants in soft tissues and, to a much lesser extent, in whole shells or fractions thereof. Both approaches come with several drawbacks. Neither soft tissues nor whole shells can resolve temporal changes of the pollution history, except through the analysis of multiple specimens collected at different times. Soft tissues and shell fractions provide time-averaged data spanning months or years, and whole shells time-averaged data over the entire lifespan of the animal. Even with regular sampling of multiple specimens over long intervals of time, the resulting chronology may not faithfully resolve short-term changes of water quality. Compounding the problem, whole shell averages tend to be non-arithmetic and non-linear, because shell growth rate varies through seasons and lifetime, and different shell layers often vary ultrastructurally and can thus be chemically different from each other. Mussel Watch could greatly benefit from the potential of bivalve shells in providing high-resolution, temporally aligned archives of environmental variability. So far, only circa a dozen studies have demonstrated that the sclerochronological approach – i.e., combined growth pattern and high-resolution chemical analyses – can provide sub-seasonally to annually resolved time-series documenting the history of pollution over centuries and even millennia. On the other hand, the sclerochronological community has failed to fully appreciate that the formation of the shell and its chemical composition is controlled by the soft parts and that a robust interpretation of the shell record requires a detailed understanding of bivalve physiology, behavior and ecology. This review attempts to bring together the Mussel Watch and sclerochronology communities and lay the foundation of a new subdiscipline of the Mussel Watch: retrospective environmental biomonitoring. For this purpose, we provide an overview of seminal work from both fields and outline potential future research directions.

High-resolution direct chemical analysis of dust in frozen ice cores by cryo-cell laser-ablation ICPMS

High-resolution direct chemical analysis of dust in frozen ice cores by cryo-cell laser-ablation ICPMS

Compositional disorder and transport peculiarities in the amorphous indium oxides

We present results of the disorder-induced metal-insulator transition (MIT) in three-dimensional amorphous indium-oxide films. The amorphous version studied here differs from the one reported by Shahar and Ovadyahu [Phys. Rev. B 46, 10917 (1992)] in that it has a much lower carrier concentration. As a measure of the static disorder we use the dimensionless parameter ${k}_{F}\ensuremath{\ell}$. Thermal annealing is employed as the experimental handle to tune the disorder. On the metallic side of the transition, the low temperature transport exhibits weak-localization and electron-electron correlation effects characteristic of disordered electronic systems. These include a fractional power-law conductivity versus temperature behavior anticipated to occur at the critical regime of the transition. The MIT occurs at a ${k}_{F}\ensuremath{\ell}\ensuremath{\approx}0.3$ for both versions of the amorphous material. However, in contrast with the results obtained on the electron-rich version of this system, no sign of superconductivity is seen down to $\ensuremath{\approx}$0.3 K even for the most metallic sample used in the current study. This demonstrates that using ${k}_{F}\ensuremath{\ell}$ as a disorder parameter for the superconductor-insulator transition (SIT) is an ill defined procedure. A microstructural study of the films, employing high resolution chemical analysis, gives evidence for spatial fluctuations of the stoichiometry. This brings to light that, while the films are amorphous and show excellent uniformity in transport measurements of macroscopic samples, they contain compositional fluctuations that extend over mesoscopic scales. These, in turn, reflect prominent variations of carrier concentrations thus introducing an unusual type of disorder. It is argued that this compositional disorder may be the reason for the apparent violation of the Ioffe-Regel criterion in the two versions of the amorphous indium oxide. However, more dramatic effects due to this disorder are expected when superconductivity sets in, which are in fact consistent with the prominent transport anomalies observed in the electron-rich version of indium oxide. The relevance of compositional disorder (or other agents that are effective in spatially modulating the BCS potential) to other systems near their SIT is discussed.

Scanning photoelectron microscope for nanoscale three-dimensional spatial-resolved electron spectroscopy for chemical analysis

In order to achieve nondestructive observation of the three-dimensional spatially resolved electronic structure of solids, we have developed a scanning photoelectron microscope system with the capability of depth profiling in electron spectroscopy for chemical analysis (ESCA). We call this system 3D nano-ESCA. For focusing the x-ray, a Fresnel zone plate with a diameter of 200 μm and an outermost zone width of 35 nm is used. In order to obtain the angular dependence of the photoelectron spectra for the depth-profile analysis without rotating the sample, we adopted a modified VG Scienta R3000 analyzer with an acceptance angle of 60° as a high-resolution angle-resolved electron spectrometer. The system has been installed at the University-of-Tokyo Materials Science Outstation beamline, BL07LSU, at SPring-8. From the results of the line-scan profiles of the poly-Si/high-k gate patterns, we achieved a total spatial resolution better than 70 nm. The capability of our system for pinpoint depth-profile analysis and high-resolution chemical state analysis is demonstrated.

Ultrafast laser induced breakdown spectroscopy for high spatial resolution chemical analysis

Femtosecond laser induced breakdown spectroscopy (LIBS) was used to identify the spatial resolution limitations and assess the minimal detectable mass restrictions in laser-ablation based chemical analysis. The atomic emission of sodium (Na) and potassium (K) dopants in transparent dielectric Mica matrices was studied, to find that both these elements could be detected from 450 nm diameter ablation craters, full-width-at-half-maximum (FWHM). Under optimal conditions, mass as low as 220 ag was measured, demonstrating the feasibility of using laser-ablation based chemical analysis to achieve high spatial resolution elemental analysis in real-time and at atmospheric pressure conditions.

Characterization of Graphite Crystal Structure and Growth Mechanisms Using FIB and 3D Image Analysis

AbstractConsidering the significant influence of the morphology of graphite inclusions on the properties of cast iron it is important to understand the correlation between manufacturing parameters and resulting microstructure. In particular, understanding the effect of alloying elements and inoculants on the formation and growth mechanisms of the graphite particles provides the basis for exact tailoring of the microstructure and thus exact tailoring of effective properties of cast iron. Experimental observations of the three‐dimensional (3D) structure of graphite particles, high resolution chemical analysis of nuclei and other inclusions, as well as quantitative characterization of possible growth mechanisms have confirmed certain existing theoretical models for nodular and flake graphite and provided a comprehensive description of all intermediate morphologies. Precise analysis of the graphite's crystal structure based on target preparation of transmission electron microscope thin foils opens additional possibilities for estimating of the properties of different graphite types.

EELS and ELNES studies of nano-scale nitride multilayers deposited by unbalanced magnetron sputtering

High spatial resolution chemical analysis and imaging of a CrAlYN/CrN multi-layer coating was performed using sub-nanometer probe electron energy loss spectroscopy in a spherical aberration corrected scanning transmission electron microscope. Analysis indicated the CrN layers to be near stoichiometric with a relative Cr/N ratio of 1.05±0.1 while the CrAlYN layers gave a Cr/N ratio of 0.59±0.02. Analysis of the energy loss near edge structure at the nitrogen K-edge was performed. The experimentally determined fine edge structure in electron energy loss spectra were compared with theoretically determined spectra, calculated using electron density functional theory. For the CrN layers the best match between the direct experimental analysis and the simulated edges corresponds to stoichometric CrN consistent with the quantitative analysis while the best match for the CrAlYN layers was to (Cr0.5Al0.5)N.

High Speed, High Resolution, and Continuous Chemical Analysis of Ice Cores Using a Melter and Ion Chromatography

Measurement of trace chemical impurities in ice cores contributes to the reconstruction of records of the atmospheric environment and of the climate system. Ion chromatography (IC) is an effective analytical technique for ionic species in ice cores but has been used on discretely prepared ice samples, resulting in extensive and slow sample preparation and potential for contamination. A new technique has been developed that utilizes IC as the online detection technique in a melter-based continuous flow system for quantitative determination of major ionic chemical impurities. The system, called CFA-IC for continuous flow analysis with ion chromatography detection, consists of an ice core melter, several ion chromatographs, and an interface that distributes meltwater to the IC instruments. The CFA-IC technique combines the accuracy, precision, and ease of use of IC measurement with the enhanced speed and depth resolution of continuous melting systems and is capable of virtually continuous, high-speed and high-resolution chemical analysis of long ice cores. The new technique and operating procedures have been tested and validated with the analysis of over 100 m of ice cores from Antarctica. The current CFA-IC system provides an all-major-ion analysis speed of up to 8 m a day at a depth resolution of approximately 2 cm.

Glaciochemical reconnaissance of a new ice core from Severnaya Zemlya, Eurasian Arctic

AbstractA deep ice core has been drilled on Akademii Nauk ice cap, Severnaya Zemlya, Eurasian Arctic. High-resolution chemical analysis has been carried out for the upper 53 m of this ice core to study its potential as an atmospheric aerosol archive, despite strong meltwater percolation. These records show that a seasonal atmospheric signal cannot be deduced. However, strong year-to-year variations have allowed the core to be dated, and a mean annual net mass balance of 0.46 m w.e. a-1 was deduced. The chemical signature of an extraordinarily high peak in electrical conductivity at 26 m depth pointed clearly to the eruption of Bezymianny, Kamchatka, in 1956. However, in general, peaks in the electrical conductivity are not necessarily related to deposition of volcanogenic sulphur aerosol. In contrast, maximum sulphate and nitrate concentrations in the ice could be related to maximum SO2 and NOx anthropogenic emissions in the 1970s, probably caused by the nickel- and copper-producing industries in Norilsk and on the Kola peninsula or by industrial combustion processes occurring in the Siberian Arctic. In addition, during recent decades sulphate and nitrate concentrations declined by 80% and 60%, respectively, reflecting a decrease in anthropogenic pollution of the Arctic basin.

High-time-resolution profiles of soluble ions in the last glacial period of a Dome Fuji (Antarctica) deep ice core

AbstractWe measured the depth profiles of soluble ions in the Dome Fuji (Antarctica) ice core to search for possible paleoclimate indications of seasonal climate variations in the last glacial period. A 523 mm long core section between 587.65 and 588.18 m depth was selected for this pilot study, and the high-resolution chemical analysis was done on 2 mm thick samples. Our results indicate that anion– cation trapping in ice affects the profiles of the soluble ions and [Na+] in the core may preserve its seasonal signal. Correlation coefficients and the equivalent balances of the soluble ions suggest the following selective coexistences: (1) [Cl–] = [Na+], (2) [NO3–] = 1/2[Ca2+] + [K+], and (3) [SO42–] = 1/2[Ca2+] + [H+] + [Mg2+]. These coexistences are probably due to (1) a sea-salt source of Na+ and Cl–, (2) reaction of NO3– with dust for Ca2+ and NO3–, and (3) anion–cation trapping in ice for SO42– and Ca2+ (Mg2+), respectively.

Transmission electron microscopy investigation of the microstructure and chemistry of Si/Cu/In/Cu/Si interconnections

Si/Si interconnections, obtained using a Cu metallization and an In interlayer and joined by diffusion soldering are presented. The Si/Cu/In/Cu/Si bonds were accomplished due to isothermal solidification and subsequent interdiffusion of In and Cu in the samples held at 180°C. Application of a transmission electron microscope (TEM) with an attachment for high-resolution chemical analysis allowed characterizing the microstructural and microchemical feature of the intermetallics formed in the joint. Appearance of two phases, namely η(Cu2In) and δ(Cu7In3), was confirmed by electron diffraction patterns and energy-dispersive X-ray (EDX) analysis. The bond quality and the high melting point of the phases (≈630°C) indicate a great potential of this technique for joining of integrated circuits in electronics.

Site-specific cross-sectioning of carbon nanotube-to-metal junctions for high spatial resolution chemical and structural analysis

AbstractIn this study, we have demonstrated successful site-specific cross-sectioning of carbon-nanotube - metal junctions which provided samples suitable for high resolution transmission electron microscopy and electron energy loss spectroscopy. For the cross-sectioning, we have suggested a modified technique based on combination of the Focused Ion Beam (FIB) lift-out and the conventional Ar+ ion milling techniques. Electron-transparent cross-sections of multiwall carbon nanotubes showing no significant surface amorphization or Ga contamination (typical artifacts of conventional FIB lift-out technique) were obtained. High-resolution transmission electron microscopy and electron energy loss spectroscopy of a multi-wall carbon nanotube cross-section have been carried out.