Three-dimensional Chemical Mapping Research Articles

Effect of thermal oxidation on surface chemistry and elemental segregation of Al-Cu-Li alloy

The thermal stability of Al-Cu-Li alloys is critical for the extreme working conditions in the aircraft industry. The initial stages of thermal oxidation of an industrial AA 2050-T8 Al-Cu-Li alloy were investigated by in situ XPS and ToF-SIMS.Annealing the sample at 200 °C leads to a surface enrichment in metallic Li and Ag. When exposed to oxygen at low pressure (PO2 < 10−6 mbar) a mixed Li-Al oxide layer is formed. Photoemission intensities (recorded at 45° and 90° relative to the surface) are consistent with the formation of a continuous oxide layer for oxygen exposure from 0 to 5000 langmuirs (L). Assuming a homogeneous composition of the oxide layer, its thickness was 9 ± 1 Å at 5000 L. The relative content of Li and Al in the oxide layer evolves from an initial value of 50% to stabilize at 70% of Li above 100 L of oxygen exposure. Simultaneously, the content of Li at the alloy substrate surface is reduced from 10% to 0%. Moreover, specific segregation sites are evidenced by ToF-SIMS three-dimensional chemical mapping. For Li, a homogenous surface distribution while for Mg the accumulation at the grain boundaries were observed. The segregation of Ag at the oxide/alloy interface was confirmed by ToF-SIMS ion depth profiles.

Three-Dimensional Chemical Mapping of a Single Protein in the Hydrated State with Atom Probe Tomography.

Unravelling the three-dimensional structures and compositions of biological macromolecules sheds light on their functions and also contributes to the design of future biochemical compounds and processes. Atom probe tomography (APT) is demonstrated in this research as a new and effective approach to explore the structure and chemical composition of a single protein in the hydrated state. By introducing graphene encapsulation, proteins in solution can be immobilized on a metal specimen tip, with an end radius in the range of 50 nm to allow field ionization and evaporation. Using a ferritin particle as an example, analysis of the mass spectrum and reconstructed 3D chemical maps at near-atomic resolution acquired from APT reveals the core consisting of iron and iron oxides, the peptide shell containing amino acids, and the interior interface between the iron core and the peptide shell. The quantitative distribution and proportion of iron isotopes from a single ferritin core have been determined for the first time, as well as identification of the possible sites of amino acids inside the protein shell. The complete experimental protocol is straightforward and lays a foundation for future exploration of various macromolecules in a controlled environment.

Metals and Environment: Chemical Outputs From the Interaction Between Gilded Copper-Based Objects and Burial Soil

Three-dimensional chemical mapping was adopted to investigate an ancient fire-gilded buckle found in Rome. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) were used to detect and locate degradation products aiming to identify the alteration processes. Inorganic and organic compounds present in the outermost part of such a class of cultural heritage objects can be considered the result of long-term interaction with the burial environment. ToF-SIMS depth profiling experiments can provide chemical information at the molecular level and high resolved spatial information (about 1 μm laterally, and 1 nm in depth). In this work, the attention was focused on the identification and localization of the ionic and molecular species involved in the degradation process. Results showed the presence of copper oxides, chlorides, and sulfides as common corrosion products but also the presence of species related to copper and bronze corrosion process such as atacamite and its polymorphs. 3D maps for all the relevant molecular species allowed to visualize at the same time the eruption of copper chlorides throughout the micro/nanochannels present on the gold surface, the recrystallization of compounds of minor elements from the substrate, a pathway followed by silico-aluminates from the surface towards the internal corrosion layers, but mostly the evidence of biological activity of Sulphur Reducing Bacteria (SRB) living in anaerobic conditions.

Enhancing Corrosion Resistance of High-Carbon Steel by Formation of Surface Layers Using Wastes as Input

Series of super-hard ceramic layers have been successfully developed on high carbon steels, with a significant improvement of corrosion resistance and hardness, without changing the original properties, which were derived from mixtures of slag (electric arc furnace), waste glass (bottles), and automotive shredder residue (ASR) plastics (polypropylene) via the single step surface modification technique. Microstructural analysis by laser scanning confocal microscopy (LSCM), crystallography analysis by X-ray diffraction (XRD), micro-level chemical analysis by scanning electron microscopy and energy dispersive spectroscopy (SEM and EDS), and depth profile surface analysis with three-dimensional chemical mapping by time-of-flight secondary ion mass spectrometry (TOF-SIMS), followed by electrochemical corrosion test by the Tafel method and hardness test—Vickers hardness measurement. Three areas have been classified, modified surface, interface, and main substrate areas as the synthesis of ceramic layers into surface of the steels that thermodynamically formed during the heat treatment process. Chemical composition analyses have revealed that generated layers consisting of chromium (Cr)- and magnesium (Mg)-based compound have shown an improved corrosion resistance to 52% and hardness to 70% without modifying the initial volume fraction of constituent phases–martensite and retained austenite. These findings have substantially highlighted to the potential use of waste-integrated inputs as raw materials for production in cost-effective way, concurrently decreasing the demand on new resource for coating, alleviating the disadvantageous impact to the environment from waste disposal in landfills.

Modified linear combination fitting for large-area two-dimensional chemical state mapping

In order to reduce the XAFS/XANES measurement time for the wide area two- or three-dimensional chemical state mapping, modified linear combination fitting method have been developed. When the method is used, we can analyze the chemical states by measuring x-ray absorption coefficient at only several energy points. The detail of the method is precisely described. One of the important feature of the method is that the target spectrum is not required to be preliminarily normalized. Some of the two-dimensional maps obtained using the method have been shown as examples, where it is shown the distribution of the chemical state of the target element in samples have been clearly obtained by using the method.

Mesoscopic Structure Facilitates Rapid CO2 Transport and Reactivity in CO2 Capture Solvents.

Mass transfer coefficients of CO2 are anomalously high in water-lean solvents as compared to aqueous amines. Such phenomena are intrinsic to the molecular and nanoscale structure of concentrated organic CO2 capture solvents. To decipher the connections, we performed in situ liquid time-of-flight secondary ionization mass spectroscopy on a representative water-lean solvent, 1-((1,3-Dimethylimidazolidin-2-ylidene)amino)propan-2-ol (IPADM-2-BOL). Two-dimensional (2D) and three-dimensional (3D) chemical mapping of the solvent revealed that IPADM-2-BOL exhibited a heterogeneous molecular structure with regions of CO2-free solvent coexisting with clusters of zwitterionic carbonate ions. Chemical mapping were consistent with molecular dynamic simulation results, indicating CO2 diffusing through pockets and channels of unreacted solvent. The observed mesoscopic structure promotes and enhances the diffusion and reactivity of CO2, likely prevalent in other water-lean solvents. This finding suggests that if the size, shape and orientation of the domains can be controlled, more efficient CO2 capture solvents could be developed to enhance mass-transfer and uptake kinetics.

Three-dimensional chemical mapping using non-destructive SEM and photogrammetry

The slice and view approach in electron microscopy defines an ensemble of destructive techniques that is widely used for studying in 3D the structure and chemistry of samples with dimensions ranging from µm to mm. Here, a method is presented for measuring with high resolution and quantitatively the morphology and chemical composition of the surface of a sample in 3D. It is non-destructive and therefore, it is complementary to slice and view methods. The scheme is based on the fusion of conventional scanning electron microscopy (SEM) imaging, multi-view photogrammetry and compositional mapping using energy dispersive X-ray spectroscopy (EDXS). We demonstrate its potential by performing an accurate study of adhesion wear of a tungsten carbide tool that is difficult to obtain using conventional characterization techniques.

Optimization of Three-Dimensional (3D) Chemical Imaging by Soft X-Ray Spectro-Tomography Using a Compressed Sensing Algorithm.

Soft X-ray spectro-tomography provides three-dimensional (3D) chemical mapping based on natural X-ray absorption properties. Since radiation damage is intrinsic to X-ray absorption, it is important to find ways to maximize signal within a given dose. For tomography, using the smallest number of tilt series images that gives a faithful reconstruction is one such method. Compressed sensing (CS) methods have relatively recently been applied to tomographic reconstruction algorithms, providing faithful 3D reconstructions with a much smaller number of projection images than when conventional reconstruction methods are used. Here, CS is applied in the context of scanning transmission X-ray microscopy tomography. Reconstructions by weighted back-projection, the simultaneous iterative reconstruction technique, and CS are compared. The effects of varying tilt angle increment and angular range for the tomographic reconstructions are examined. Optimization of the regularization parameter in the CS reconstruction is explored and discussed. The comparisons show that CS can provide improved reconstruction fidelity relative to weighted back-projection and simultaneous iterative reconstruction techniques, with increasingly pronounced advantages as the angular sampling is reduced. In particular, missing wedge artifacts are significantly reduced and there is enhanced recovery of sharp edges. Examples of using CS for low-dose scanning transmission X-ray microscopy spectroscopic tomography are presented.

Metallic nanoshell for three-dimensional chemical mapping of low conductive materials with pulsed-voltage atom probe tomography

Metallic nanoshell for three-dimensional chemical mapping of low conductive materials with pulsed-voltage atom probe tomography

Fast imaging with inelastically scattered electrons by off-axis chromatic confocal electron microscopy.

We introduce off-axis chromatic scanning confocal electron microscopy, a technique for fast mapping of inelastically scattered electrons in a scanning transmission electron microscope without a spectrometer. The off-axis confocal mode enables the inelastically scattered electrons to be chromatically dispersed both parallel and perpendicular to the optic axis. This enables electrons with different energy losses to be separated and detected in the image plane, enabling efficient energy filtering in a confocal mode with an integrating detector. We describe the experimental configuration and demonstrate the method with nanoscale core-loss chemical mapping of silver (M4,5) in an aluminium-silver alloy and atomic scale imaging of the low intensity core-loss La (M4,5@840 eV) signal in LaB6. Scan rates up to 2 orders of magnitude faster than conventional methods were used, enabling a corresponding reduction in radiation dose and increase in the field of view. If coupled with the enhanced depth and lateral resolution of the incoherent confocal configuration, this offers an approach for nanoscale three-dimensional chemical mapping.

Three-Dimensional Chemical Mapping by EFTEM-TomoJ Including Improvement of SNR by PCA and ART Reconstruction of Volume by Noise Suppression

Electron tomography is becoming one of the most used methods for structural analysis at nanometric scale in biological and materials sciences. Combined with chemical mapping, it provides qualitative and semiquantitative information on the distribution of chemical elements on a given sample. Due to the current difficulties in obtaining three-dimensional (3D) maps by energy-filtered transmission electron microscopy (EFTEM), the use of 3D chemical mapping has not been widely adopted by the electron microscopy community. The lack of specialized software further complicates the issue, especially in the case of data with a low signal-to-noise ratio (SNR). Moreover, data interpretation is rendered difficult by the absence of efficient segmentation tools. Thus, specialized software for the computation of 3D maps by EFTEM needs to include optimized methods for image series alignment, algorithms to improve SNR, different background subtraction models, and methods to facilitate map segmentation. Here we present a software package (EFTEM-TomoJ, which can be downloaded from http://u759.curie.fr/fr/download/softwares/EFTEM-TomoJ), specifically dedicated to computation of EFTEM 3D chemical maps including noise filtering by image reconstitution based on multivariate statistical analysis. We also present an algorithm named BgART (for background removing algebraic reconstruction technique) allowing the discrimination between background and signal and improving the reconstructed volume in an iterative way.

Three-Dimensional Chemical Mapping with a Confocal XRF Setup

A new approach for the nondestructive reconstruction of stratified systems with constant elemental composition but with varying chemical compounds has been developed. The procedure is based on depth scans with a confocal X-ray fluorescence setup at certain energies near absorption edges. These so-called marker energies, where XAFS signals of the involved chemical compounds differ significantly, can also be used to uncover the chemical composition and its topology. A prominent field of application is homogeneous material that is degraded due to chemical reactions like oxidation or reduction. A procedure for the semiquantitative reconstruction of stratified material by means of depth scans at marker energies is elaborated and validated and a three-dimensional mapping is presented.

Three-dimensional mapping of nickel oxidation states using full field x-ray absorption near edge structure nanotomography

The reduction-oxidation cycling of the nickel-based oxides in composite solid oxide fuel cells and battery electrodes is directly related to cell performance. A greater understanding of nickel redox mechanisms at the microstructural level can be achieved in part using transmission x-ray microscopy (TXM) to explore material oxidation states. X-ray nanotomography combined with x-ray absorption near edge structure (XANES) spectroscopy has been applied to study samples containing distinct regions of nickel and nickel oxide (NiO) compositions. Digitally processed images obtained using TXM demonstrate the three-dimensional chemical mapping and microstructural distribution capabilities of full-field XANES nanotomography.

Soft X‐ray spectro‐tomography study of cyanobacterial biomineral nucleation

Quantitative three-dimensional (3D) chemical mapping using angle-scan spectro-tomography in a scanning transmission (soft) X-ray microscope (STXM) has been used for the first time to characterize the early stages of CaCO(3) biomineral nucleation on the surface of planktonic freshwater cyanobacterial cells of the strain Synechococcus leopoliensis PCC 7942. The apparatus for STXM angle-scan tomography is described. Aspects of sample preparation, sample mounting and data acquisition and quantitative analysis and interpretation are discussed in detail. Angle-scan tomography and chemically selective 3D imaging at multiple photon energies has been combined with a complete 2D spectromicroscopic characterization of the biochemical and mineralogical composition. This has provided detailed insights into the mechanisms of mineral nucleation, leading to development of a detailed model of CaCO(3) nucleation by the cyanobacterial strain S. leopoliensis PCC 7942. It shows that Ca is absorbed by the extracellular polymeric substances (EPS) of the cyanobacteria and that CaCO(3) with aragonite-like short-range order is precipitated rather homogeneously within the EPS. The precipitation of the thermodynamically more stable calcite polymorph then starts at Ca-rich hot spots within the EPS and close to the cyanobacteria.

3-d chemical imaging using angle-scan nanotomography in a soft X-ray scanning transmission X-ray microscope

Three-dimensional chemical mapping using angle scan nanotomography in a soft X-ray scanning transmission X-ray microscope (STXM) has been used to investigate the spatial distributions of a low density polyacrylate polyelectrolyte ionomer inside submicron sized polystyrene microspheres. Acquisition of tomograms at multiple photon energies provides true, quantifiable 3-d chemical sensitivity. Both pre-O 1s and C 1s results are shown. The study reveals aspects of the 3-d distribution of the polyelectrolyte that were inferred indirectly or had not been known prior to this study. The potential and challenges for extension of the technique to studies of other polymeric and to biological systems is discussed.

Three-dimensional chemical mapping by scanning transmission X-ray spectromicroscopy

Three-dimensional (3-d) chemical mapping using angle-scan tomography in a scanning transmission X-ray microscope is demonstrated. Apparatus, experimental procedures and data processing are presented and the 3-d spatial resolution is evaluated. The technique is illustrated using mapping of a low-density acrylate polyelectrolyte in and outside of polystyrene microspheres dispersed in water in a 4 microm-diameter microcapillary. The 3-d chemical visualization provides information about the microstructure that had not previously been observed.