Methane oxidation activity and nanoscale characterization of Pd/CeO2 catalysts prepared by dry milling Pd acetate and ceria
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99 GENERAL AND MISCELLANEOUS↗
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High-speed nanoscale characterization of dewetting via dynamic transmission electron microscopy
The dewetting of thin films can occur in either the solid or the liquid state for which different mass transport mechanisms are expected to control morphological changes. Traditionally, dewetting dynamics have been examined on time scales between several seconds to hours, and length scales ranging between nanometers and millimeters. The determination of mass transport mechanisms on the nanoscale, however, requires nanoscale spatial resolution and much shorter time scales. This study reports the high-speed observation of dewetting phenomena for kinetically constrained Ni thin films on crystalline SrTiO{sub 3} substrates. Movie-mode Dynamic Transmission Electron Microscopy (DTEM) was used for high-speed image acquisition during thin film dewetting at different temperatures. DTEM imaging confirmed that the initial stages of film agglomeration include edge retraction, hole formation, and growth. Finite element modeling was used to simulate temperature distributions within the DTEM samples after laser irradiation with different energies. For pulsed laser irradiation at 18 μJ, experimentally observed hole growth suggests that Marangoni flow dominates hole formation in the liquid nickel film. After irradiation with 13.8 μJ, however, the observations suggest that dewetting was initiated by nucleation of voids followed by hole growth through solid-state surface diffusion.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Direct Nanoscale Characterization of Deep Levels in AgCuInGaSe 2 Using Electron Energy–Loss Spectroscopy in the Scanning Transmission Electron Microscope
A new experimental framework for the characterization of defects in semiconductors is demonstrated. Through the direct, energy-resolved correlation of three analytical techniques spanning six orders of magnitude in spatial resolution, a critical mid-bandgap electronic trap level (E V + 0.56 eV) within Ag 0.2 Cu 0.8 In 1–x Ga x Se 2 is traced to its nanoscale physical location and chemical source. This is achieved through a stepwise, site-specific correlated characterization workflow consisting of device-scale (≈1 mm 2 ) deep level transient spectroscopy (DLTS) to survey the traps present, scanning probe–based DLTS (scanning-DLTS) for mesoscale-resolved (hundreds of nanometers) mapping of the target trap state’s spatial distribution, and scanning transmission electron microscope based electron energy-loss spectroscopy (STEM-EELS) and X-ray energy-dispersive spectroscopy for nanoscale energy-, structure, and chemical-resolved investigation of the defect source. Furthermore, this first demonstration of the direct observation of sub-bandgap defect levels via STEM-EELS, combined with the DLTS methods, provides strong evidence that the longsuspected Cu In/Ga substitutional defects are indeed the most likely source of the E V + 0.56 eV trap state and serves as a key example of this approach for the fundamental identification of defects within semiconductors, in general.
14 SOLAR ENERGY↗
Probing Novel Microstructural Evolution Mechanisms in Aluminum Alloys Using 4D Nanoscale Characterization
Dispersions of nanoscale precipitates in metallic alloys have been known to play a key role in strengthening, by increasing their strain hardenability and providing resistance to deformation. Although these phenomena have been extensively investigated in the last century, the traditional approaches employed in the past have not rendered an authoritative microstructural understanding in such materials. The effect of the precipitates’ inherent complex morphology and their 3D spatial distribution on evolution and deformation behavior have often been precluded. This study reports, for the first time, implementation of synchrotron-based hard X-ray nanotomography in Al–Cu alloys to measure kinetics of different nanoscale phases in 3D, and reveals insights behind some of the observed novel phase transformation reactions. The experimental results of the present study reconcile with coarsening models from the Lifshitz–Slyozov–Wagner theory to an unprecedented extent, thereby establishing a new paradigm for thermodynamic analysis of precipitate assemblies. Lastly, this study sheds light on the possibilities for establishing new theories for dislocation–particle interactions, based on the limitations of using the Orowan equation in estimating precipitation strengthening.
36 MATERIALS SCIENCE↗
Nanoscale building blocks in a novel lithium arsenotungsten bronze: Synthesis and characterization
We report on a novel compound Li{sub 3}AsW{sub 7}O{sub 25} obtained by solid-state reaction and characterized by diffraction and spectroscopic methods. The bronze-type compound crystallizes in the orthorhombic space group Pbca with a=724.38(3) pm, b=1008.15(4) pm, c=4906.16(17) pm and Z=8. The structure is built up by chains of WO{sub 6} octahedra interconnected by AsO{sub 4} tetrahedra and WO{sub 6} octahedra forming a polyhedral arrangement as seen in intergrowth tungsten bronzes. The X-ray single crystal structure refinement allows solving the complex arsenotungstate framework. The powder neutron diffraction data analysis locates the lithium atoms. Thermal analysis showed that Li{sub 3}AsW{sub 7}O{sub 25} is stable up to its melting at 1135(3) K followed by a decomposition at 1182(5) K. The Kubelka–Munk treatment of the UV–vis spectrum revealed a wide band gap in the range of 2.84–3.40 eV depending on the presumed electron transition type. - Graphical abstract: Crystal structure of Li{sub 3}AsW{sub 7}O{sub 25} showing different schematic components. - Highlights: • A report on a novel compound Li{sub 3}AsW{sub 7}O{sub 25} obtained by solid-state reaction. • Chains and nano-blocks of WO{sub 6} octahedra and AsO{sub 4} tetrahedra formed a structure like intergrowth tungsten bronzes. • X-ray diffraction allowed solving the complex arsenotungstate framework. • Powder neutron diffraction data analysis locates the lithium atoms. • UV–vis spectrum revealed the band-gap.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Cryogenic specimens for nanoscale characterization of solid–liquid interfaces
We report new cryogenic characterization techniques for exploring the nanoscale structure and chemistry of intact solid–liquid interfaces have recently been developed. These techniques provide high-resolution information about buried interfaces from large samples or devices that cannot be obtained by other means. These advancements were enabled by the development of instrumentation for cryogenic focused ion beam liftout, which allows intact solid–liquid interfaces to be extracted from large samples and thinned to electron-transparent thicknesses for characterization by cryogenic scanning transmission electron microscopy or atom probe tomography. Future implementation of these techniques will complement current strides in imaging of materials in fluid environments by in situ liquid-phase electron microscopy, providing a more complete understanding of the morphology, surface chemistry, and dynamic processes that occur at solid–liquid interfaces.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
In Situ Nanoscale Characterization of Water Penetration through Plasma Polymerized Coatings
The search continues for means of making quick determinations of the efficacy of a coating for protecting a metal surface against corrosion. One means of reducing the time scale needed to differentiate the performance of different coatings is to draw from nanoscale measurements inferences about macroscopic behavior. Here we connect observations of the penetration of water into plasma polymerized (PP) protective coatings and the character of the interface between the coating and an oxide-coated aluminum substrate or model oxide-coated silicon substrate to the macroscopically observable corrosion for those systems. A plasma polymerized film from hexamethyldisiloxane (HMDSO) monomer is taken as illustrative of a hydrophobic coating, while a PP film from maleic anhydride (MA) is used as a characteristically hydrophilic coating. The neutron reflectivity (NR) of films on silicon oxide coated substrates shows that water moves more readily through the hydrophilic PPMA film. Off-specular X-ray scattering indicates the PPMA film on aluminum is less conformal with the substrate than is the PPHMDSO film. Measurements with infraredvisible sum frequency generation spectroscopy (SFG), which probes the chemical nature of the interface, make clear that the chemical interactions between coating and aluminum oxide are disrupted by interfacial water. With this water penetration and interface disruption, macroscopic corrosion can occur much more rapidly. An Al panel coated with PP-MA corrodes after 1 day in salt spray, while a similarly thin (similar to 30 nm) PP-HMDSO coating protects an Al panel for a period on the order of one month.
36 MATERIALS SCIENCE↗
Advanced nanoscale characterization of aluminum nanoparticles with modified surface morphology via atmospheric helium and carbon monoxide plasmas
Aluminum nanoparticles (nAl) have the potential as energetic additives in explosive/propellant formulations. Scalable methodologies must be pursued to mitigate the inactive amorphous alumina shell surrounding the active aluminum (Al) core with modified surface morphology and chemistry for increased combustion effects. This work explores the feasibility of making reactive core/shell nAl with thinned oxide shells and modified surface coatings via a two-step atmospheric plasma surface treatment process in a custom dielectric barrier discharge plasma reactor. The commercial nAl of nominal average size similar to 40-60nm was first treated with helium (He) followed by He/carbon monoxide (CO) plasmas for different durations. The resultant samples were characterized via high-resolution transmission electron microscopy (HRTEM) and Fourier transform IR (FTIR) spectra. HRTEM images revealed sporadic patchy gamma -alumina deposits on particle surfaces and in gaps among particles for all samples, suggesting the non-uniform plasma effects of the He/CO glow. Nanoscale chemical analyses via scanning transmission electron microscopy elemental mapping and x-ray energy dispersive spectroscopy were further performed. Although no carbon-associated structure appeared in electron energy loss spectroscopy (EELS) spectra, the presence of carbonaceous materials was confirmed as a thin dispersive layer evenly distributed on the nAl surface suggesting either its amorphous nature or is present at a level insufficient to generate satisfactory EELS spectra. The trend of intensity profiles for key elements acquired by drawing lines across a single particle on the elemental maps confirmed that carbonaceous materials only existed on the surface and they were most likely carboxylates that increased with increased He/CO treatment duration, as evident by FTIR results. Finally, this work demonstrated the success of atmospheric plasma-treated reactive nAl with comprehensively characterized surface features via advanced microscopy and spectroscopy.
36 MATERIALS SCIENCE↗
Site-specific nanoscale characterization of zirconium hydrides in the hydride rim structure of hydrogen-charged zircaloy-4 cladding
Zircaloy-4 cladding tubes were hydrogen-charged using a static pressure hydrogen charging method to experimentally produce a zirconium-hydride rim structure similar to that observed in Zircaloy-4 cladding tubes after operation in commercial light-water nuclear reactors. Detailed characterization was performed using electron energy loss spectroscopy (EELS) and four-dimensional scanning transmission electron microscopy (4D-STEM). By mapping the position of the plasmon peak in the low-loss EELS spectrum, it was determined that the zirconium hydrides formed were predominantly solid δ-phase zirconium hydrides. 4D-STEM was used to generate phase and strain maps at nanoscale. The interactions between two zirconium hydride platelets less than 200 nm apart leads to the localized lattice rotations and possible phase change, revealing a potential hydride growth mechanism.
4D-STEM↗
Characterizing nanoscale scanning probes using electron microscopy: A novel fixture and a practical guide
The nanoscale geometry of probe tips used for atomic force microscopy (AFM) measurements determines the lateral resolution, contributes to the strength of the tip-surface interaction, and can be a significant source of uncertainty in the quantitative analysis of results. While inverse imaging of the probe tip has been used successfully to determine probe tip geometry, direct observation of the tip profile using electron microscopy (EM) confers several advantages: it provides direct (rather than indirect) imaging, requires fewer algorithmic parameters, and does not require bringing the tip into contact with a sample. In the past, EM-based observation of the probe tip has been achieved using ad hoc mounting methods that are constrained by low throughput, the risk of contamination, and repeatability issues. We report on a probe fixture designed for use in a commercial transmission electron microscope that enables repeatable mounting of multiple AFM probes as well as a reference grid for beam alignment. This communication describes the design, fabrication, and advantages of this probe fixture, including full technical drawings for machining. Further, best practices are discussed for repeatable, non-destructive probe imaging. Finally, examples of the fixture’s use are described, including characterization of common commercial AFM probes in their out-of-the-box condition.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Atom Probe Tomography and Correlative Microscopy: 3D Nanoscale Characterization of Metals, Minerals and Materials
Invited editorial commentary article on Atom Probe Tomography.
Devaraj, Arun (ORCID:0000000313146212)↗
Characterizing nanoscale precipitation in a titanium alloy by laser-assisted atom probe tomography
Highlights: • Atom-probe tomography was performed on Ti-5Al-5Mo-5V-3Cr wt% after quenching and 300 °C aging. • Isothermal ω phase was identified as Ti-rich and solute depleted after 1 h of aging. • The ω precipitate/matrix interface is O enriched. This may facilitate α formation. • High laser-pulse energies increase the probability of complex ion formation, complicating analysis. • Discrepancies between data from the LEAP 5000 XS and LEAP 4000X Si are discussed. - Abstract: Atom-probe tomography was performed on the metastable β-Ti alloy, Ti-5Al-5Mo-5V-3Cr wt% (Ti-5553), aged at 300 °C for 0 to 8 h, to precipitate the embrittling isothermal ω phase. Accurate precipitate quantification requires monitoring and controlling suitable charge-state ratios in the mass spectrum, which in turn are closely related to the laser pulse energy used. High ultraviolet laser pulse energies result in significant complex molecular ion formation during field-evaporation, causing mass spectral peak overlaps that inherently complicate data analyses. Observations and accurate quantification of the ω-phase under such conditions are difficult. The effect is minimized or eliminated by using smaller laser pulse energies. With a small laser pulse energy, Ti-rich and solute depleted precipitates of the isothermal ω phase with an oxygen enriched interface are observed as early as after 1 h aging time utilizing the LEAP 5000X S (77% detection efficiency). We note that these precipitates were not detected below a 2 h aging time with the LEAP 4000X Si (58% detection efficiency). The results are compared to the archival literature. The Al concentration in the matrix/precipitate interfacial region increases during aging. Nucleation of the α-phase at longer aging times may be facilitated by the O and Al enrichment at the matrix/precipitate interface (both strong α-stabilisers). The kinetics and compositional trajectory of the ω-phase with aging time are quantified, facilitating direct correlation of the APT data to previously published mechanical testing.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Nanoscale Characterization of Back Surfaces and Interfaces in Thin-Film Kesterite Solar Cells
Not provided.
Materials Science↗
Nanoscale characterization of the biomechanical properties of collagen fibrils in the sclera
We apply the PeakForce Quantitative Nanomechanical Property Mapping (PFQNM) atomic force microscopy mode for the investigation of regional variations in the nanomechanical properties of porcine sclera. We examine variations in the collagen fibril diameter, adhesion, elastic modulus and dissipation in the posterior, equatorial and anterior regions of the sclera. The mean fibril diameter, elastic modulus and dissipation increased from the posterior to the anterior region. Collagen fibril diameter correlated linearly with elastic modulus. Our data matches the known macroscopic mechanical behavior of the sclera. We propose that PFQNM has significant potential in ocular biomechanics and biophysics research.
60 APPLIED LIFE SCIENCES↗
Nanoscale characterization of β-phase H{sub x}Li{sub 1−x}NbO{sub 3} layers by piezoresponse force microscopy
We investigate a non-destructive approach for the characterization of proton exchanged layers in LiNbO{sub 3} with sub-micrometric resolution by means of piezoresponse force microscopy (PFM). Through systematic analyses, we identify a clear correlation between optical measurements on the extraordinary refractive index and PFM measurements on the piezoelectric d{sub 33} coefficient. Furthermore, we quantify the reduction of the latter induced by proton exchange as 83 ± 2% and 68 ± 3% of the LiNbO{sub 3} value, for undoped and 5 mol. % MgO-doped substrates, respectively.
36 MATERIALS SCIENCE↗
Nanoscale Characterization of Electrochemical-Mechanical Mechanisms with Electron Microscopy.
Abstract not provided.
Jungjohann, Katherine↗