Energy Dispersive X-ray Spectrum Imaging Research Articles

Dynamics and healing behavior of metallosupramolecular polymers.

Self-healing or healable polymers can recuperate their function after physical damage. This process involves diffusion of macromolecules across severed interfaces until the structure of the interphase matches that of the pristine material. However, monitoring this nanoscale process and relating it to the mechanical recovery remain elusive. We report that studying diffusion across healed interfaces and a correlation of contact time, diffusion depth, and mechanical properties is possible when two metallosupramolecular polymers assembled with different lanthanoid salts are mended. The materials used display similar properties, while the metal ions can be tracked with high spatial resolution by energy-dispersive x-ray spectrum imaging. We find that healing actual defects requires an interphase thickness in excess of 100 nm, 10 times more than previously established for self-adhesion of smooth films of glassy polymers.

Pt Submonolayers on Au Nanoparticles: Coverage-Dependent Atomic Structures and Electrocatalytic Stability on Methanol Oxidation

Deposition of platinum monolayers on Au substrate (denoted as Au@PtML) has been shown an efficient catalyst design strategy for the electrocatalysis of alcohol oxidation due to presumed 100% utilization of Pt atoms and substrate-enhanced catalytic activities. However, the atomic structure and stability of Pt (sub)monolayers on realistic nanoparticulate Au surface still remains elusive. Here, we reveal coverage-dependent atomic structures and electrocatalytic stabilities of Pt submonolayers (sML) on Au nanoparticles for methanol oxidation reaction (MOR) by using high-resolution transmission electron microscopy combined with energy dispersive X-ray spectrum imaging and electrochemical techniques. At lower Pt coverages, the PtsML more resembled monatomic-thick layers, whereas higher Pt coverages above 0.5 ML resulted in 3D subnanometer Pt nanoclusters leading to lower Pt utilization efficiencies. Moreover, the Au@PtsML catalysts with Pt coverage below 0.5 ML showed higher structural and electrocatalytic stab...

An investigation of diffusion-mediated cyclic coarsening and reversal coarsening in an advanced Ni-based superalloy

The anomalous cyclic coarsening behaviour of γ′ precipitates after ageing at 1073 K has been investigated for the low misfit commercial powder metallurgy (PM) Ni-based superalloy RR1000. Using scanning transmission electron microscope (STEM) imaging combined with absorption-corrected energy-dispersive X-ray (EDX) spectroscopy, the elemental segregation as a function of coarsening behaviour has been experimentally observed for secondary γ′ precipitates. Elemental EDX spectrum imaging has revealed nanoscale enrichment of Co and Cr and a depletion of Al and Ti within the γ matrix close to the γ-γʹ interface. Our experimental results, coupled with complementary modelling and synchrotron X-ray diffraction analysis, demonstrate the importance of elastic strain energy resulting from local compositional variations for influencing precipitate morphology. In particular, elemental inhomogeneities, as a result of complex diffusive interactions within both matrix and precipitates, play a crucial role in determining the rate of coarsening. Our findings provide important new evidence for understanding the microstructural evolution observed for advanced superalloys when they are exposed to different heat treatment regimes.

Tin(II) Sulfide (SnS) Nanosheets by Liquid-Phase Exfoliation of Herzenbergite: IV-VI Main Group Two-Dimensional Atomic Crystals.

The liquid-phase exfoliation of tin(II) sulfide to produce SnS nanosheets in N-methyl-2-pyrrolidone is reported. The material is characterized by Raman spectroscopy, atomic force microscopy, lattice-resolution scanning transmission electron microscope imaging, and energy dispersive X-ray spectrum imaging. Quantum chemical calculations on the optoelectronic characteristics of bulk and 10-layer down to monolayer SnS have been performed using a quantum chemical density functional tight-binding approach. The optical properties of the SnS and centrifugally fractionated SnS nanosheet dispersions were compared to that predicted by theory. Through centrifugation, bilayer SnS nanosheets can be produced size-selectively. The scalable solution processing of semiconductor SnS nanosheets is the key to their commercial exploitation and is potentially an important step toward the realization of a future electronics industry based on two-dimensional materials.

Thin Films of Molybdenum Disulfide Doped with Chromium by Aerosol-Assisted Chemical Vapor Deposition (AACVD)

A combined single-source precursor approach has been developed for the deposition of thin films of Cr-doped molybdenum disulfide (MoS2) by aerosol-assisted chemical vapor deposition (AACVD). Tris(diethyldithiocarbamato)chromium(III) can also be used for the deposition of chromium sulfide (CrS). Films have been analyzed by a range of techniques including scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, Raman spectroscopy, and powder X-ray diffraction (pXRD) to elucidate film morphology, composition, and crystallinity. The presence of Cr in the MoS2 films produces a number of striking morphological, crystallographic, and nanomechanical changes to the deposited films. The chromium dopant appears to be uniform throughout the MoS2 from the scanning transmission electron microscopy (STEM) EDX spectrum imaging of nanosheets produced by liquid-phase exfoliation of the thin films in N-methyl-2-pyrollidone.

The effects of transition metal oxide doping on the sintering of cerium gadolinium oxide

The effects of two transition metal oxide dopants, Co and Cr, on the densification properties of Ce0.9Gd0.1O1.95 (CGO) have been examined. While a low concentration of Co oxide was found to reduce the sintering temperature of CGO by over 150°C, the addition of Cr oxide, at concentrations greater than 0.1cat.%, was found to be detrimental to the densification of the material. Energy-dispersive X-ray (EDX) spectrum imaging was used to examine the elemental evolution in both materials. At ∼70% relative density, a continuous transition-metal-oxide-rich film was located around the primary crystallites in both materials. With increasing relative density, the concentration of both dopants was shown to decrease without there being a considerable change in the apparent grain boundary layer thickness. All specimens examined revealed considerable grain boundary Gd enrichment and Ce depletion, with this effect becoming more pronounced with increasing relative density in the Cr-doped CGO. EDX spectrum imaging performed on the high density specimens revealed the presence of discrete second phases in both materials, which were subsequently analysed by electron energy loss spectroscopy. Using the current set of results, mechanisms responsible for the modified densification behaviour in Co-doped and Cr-doped CGO are suggested.

Influence of processing parameters on the growth characteristics and ferroelectric properties of sputtered PZT thin films on stainless steel substrates

Thin PZT films are synthesized on platinized stainless steel substrates by radio frequency magnetron sputtering. Based on the results of X-ray diffractometry, field-emission scanning electron microscopy and analytical scanning/transmission electron microscopy with semi-quantitative elemental mapping using energy dispersive X-ray spectrum imaging and line-scanning, the post-annealing growth of perovskite phase in sputtered PZT films has been scrutinized as a function of film processing conditions. It is observed that working pressure, sputtering gas composition and post-annealing heating rate directly affect the phase transformation trend, film morphology, crystallographic orientation and ferroelectric properties of the PZT films. Development of a thin secondary phase/layer enriched with Fe and lean in Pb and oxygen at the PZT/Pt interface has been confirmed. Processing of films at a working pressure of ∼0.7Pa with an argon/oxygen gas composition of 90:10 followed by a fast and short duration air-annealing at a temperature of ∼650°C is found to be the most suitable conditions for growing (111)-oriented perovskite PZT films on platinized stainless steel substrates for which about ∼35μCcm−2 remanent polarization and ∼125kVcm−1 coercive field have been realized under an applied field of ∼300kVcm−1. Structural changes as a function of film processing conditions have been correlated with ferroelectric characteristics of the PZT films.

Growth of ZnO nanorod forests and characterization of ZnO-coated nylon fibers

ZnO nanorod forests were grown wrapping nylon fibers using a two-step process. In the first step, the formation of ZnO seeds at nylon fiber surfaces was induced by the dip coating of ZnO nanosols; in the second step, the growth of the ZnO seeds into nanorod forests was carried out via a wet chemical route in a bath containing an equimolar solution of zinc nitrate hexahydrate and hexamethylenetetramine. The as-obtained ZnO-coated nylon fibers were characterized by scanning electron microscopy, Energy dispersive X-ray spectrum imaging, and X-ray diffraction, respectively. Thermal gravimetric analysis of the pristine and the ZnO-coated nylon fibers was also conducted.

Microstructure and Oxidation of a Cast Nickel Aluminide Alloy

ABSTRACTSpecimens of the cast Ni3Al alloy IC221M were annealed in air at 900°C to examine the effects of oxidation and thermal aging on the microstructure. The alloy is comprised of a dendritically solidified γ-γ′ matrix containing γ+Ni5Zr eutectic colonies in the interdendritic regions. Microstructures of aged specimens were examined by optical microscopy and energy dispersive X-ray (EDX) spectrum imaging in the scanning electron microscope (SEM). Two primary changes in the microstructures were observed: (1) there is considerable homogenization of the cast microstructures with aging, and (2) the volume fraction of the γ+Ni5Zr eutectic decreases. Oxidation products were identified using x-ray diffraction and EDX spectrum imaging with multivariate statistical analysis (MSA). During the initial stages of oxidation, the first surface oxide to form is mostly NiO with small amounts of Cr2O3, ZrO2, NiCr2O4, and θ-Al2O3. Initially, oxidation occurs primarily in the interdendritic regions due to microsegregation of alloying elements during casting. With further aging, a continuous film of α-Al2O3forms immediately beneath the surface that eventually evolves into a double layer of α-Al2O3and NiAl2O4. Although these oxides are constrained to the near surface region, others penetrate to greater depths facilitated by oxidation of the γ+Ni5Zr eutectic colonies. These oxides appear in the microstructure as long, thin spikes of ZrO2surrounded by a thin sheath of Al2O3.

Edx Spectrum Imaging of Bulk Specimens: Its Role in Quantitative X-Ray Microanalysis

Energy-dispersive X-ray (EDX) spectrum imaging, where a full spectrum is acquired at each pixel in a rastered image, combines the advantages of imaging and analysis for quantitative compositional mapping. This method has great advantages for the analysis of compositional variations, because the contrast inherent in EDX spectrum images arises from the distinctiveness of the characteristic X-ray spectra in various regions of the surveyed microstructure. EDX spectrum imaging provides for simultaneous spatial, spectral and temporal resolution of the X-rays emitted from the specimen. Many EDX manufacturers have incorporated a spectrum imaging capability within their acquisition and analysis software, and ongoing improvements in computing power will enhance the practicality of spectrum imaging methods, in particular the acquisition, manipulation and analysis of the large raw data files that are generated with this method. This paper surveys the potential role of spectrum imaging in tasks that support true quantitative X-ray microanalysis of bulk specimens: robust qualitative analysis, the construction of representative spectra that describe the specimen, and the extraction of elemental concentrations from the representative spectra.

Correlation of contact resistance with microstructure for Au/Ni/Al/Ti/AlGaN/GaN ohmic contacts using transmission electron microscopy

Ohmic contacts to AlGaN/GaN heterostructures which have low contact resistance and good surface morphology are required for the development of commercial high power, high frequency transistors in the GaN system. The development of such contacts would be helped by a better understanding of the effect of microstructure on electrical behavior, which is studied here. Au/Ni/Al/Ti/AlGaN/GaN ohmic contact structures were rapid thermal annealed in argon for 60 s at temperatures in the range 550–900 °C. The variation of contact resistance with anneal temperature was correlated with the phase distribution observed by transmission electron microscopy (TEM). A combination of TEM techniques was required to determine the resulting microstructure, including energy filtered TEM, high resolution electron microscopy and energy dispersive x-ray spectrum imaging. Contacts with the lowest resistance were formed after 700 °C annealing. Very little consumption of the 30 nm AlGaN layer was observed. An unidentified phase containing Al, Ti and Au is present at the interface in the samples with low specific contact resistance. The identification of the observed thin interfacial phases (including TiN and AlN) is discussed, along with the effects of oxidation and possible mechanisms of ohmic contact formation.